0001]The present invention relates to a manufacturing method and a heat resistant ferritic steel welded structure ferritic heat-resistant steel welded structure. In particular, a structure having a site that binds by welding, a structure is stress over time at elevated temperature is added, for example, power plants, to the heat resistant ferritic steel welded structure and a manufacturing method thereof, for use in chemical plants .
BACKGROUND
[0002]
　Demand for energy resources follows the ever increase, the development of various techniques to create or purifying power or fuel is an essential energy in all industries is needed. In particular, a is in Japan is scarce country in resources, early completion of the art has been strongly desired. However, it is difficult to mass and stable supply of renewable energy in commercial basis, cost reduction techniques or energy storage technologies must be accompanied in its general dissemination. Therefore, the state of the energy conversion technologies, in particular power plants for converting fossil fuels and nuclear fuel into electrical energy, specifically coal-fired power plants, natural gas direct-fired thermal power plant, to rely most nuclear power plant obtained not. On the other hand the subject of such conventional power generation technology, from the resource life based is that environmental load is large, especially CO 2 and it is necessary to solve the problem of emissions at the same time, a pressing issue. Moreover, hazardous substances contained in fossil fuels as a power source of a vehicle, especially SO x reduction of sulfur oxides represented by is seen to proceed strengthening increasingly restricting future, are possible solutions the refinery reactor, in situations where high temperature and high pressure operation unprecedented is desired.
[0003]
　Currently, for example, the efficiency of thermal power generation has stagnated at about 40-50%, and the future, in order to suppress the increased emissions of carbon dioxide, higher efficiency is required. Is not limited to the power plant, thermal efficiency in energy conversion is substantially determined by the temperature and pressure, in the power plant, as the temperature of the steam to drive a generator turbine is high, the energy conversion efficiency is increased.
[0004]
　Currently, steam temperature of coal-fired power plants is the highest at 620 ° C., about 5% is raised 100 ° C. The temperature can be expected about 10% of efficiency is raised 200 ° C.. In other words, efficiency of the power plant as an energy conversion technologies at high pressure is immediately effective, it can be a useful technique that can simultaneously solve the above-mentioned environmental and resource issues. However, to increase the temperature of the steam to drive a generator turbine, as well as members of the turbine, must be improved the performance of the heat-resisting steel used in heat exchangers and pipes.
[0005]
　Further, in the refinery reactor, and it improves the high temperature corrosion resistance requirements become stricter, has led to the acquisition of high-temperature strength is a pressure vessel because sought is presented as a future challenge for the material. In such a background, in particular becoming increasingly great interest in the performance of heat-resisting steel is used at high temperatures.
[0006]
　Among the performance required of the heat-resistant steel, the creep characteristics are particularly important, for decades, so it is possible to operate the plant, it is necessary not to creep rupture over a long period. So far, as the upper limit of the use temperature 600 ℃, 9% research and development of Cr ferritic heat-resistant steels is performed, high-temperature ferritic, such as fire STBA28 and fire STBA29-technical interpretation of thermal power plants to the provisions of the Nuclear Safety Institute heat resistant steels have been developed and put into practical use. These ferritic heat-resistant steels have low thermal expansion coefficient, there is a resistance to deformation due to thermal stress creep fatigue fracture and piping members. Moreover the weldability workability, that no different from ordinary steel material is characterized. Further, the alloy content of such expensive Ni is less as compared with austenitic heat-resistant steels are more used at high temperatures, are the advantages in that amount economics are attractive from an industrial point of view. However, the atomic structure of the iron BCC larger lattice constant for a (body-centered cubic lattice), fast diffusion of a substance in correspondingly high temperature. Therefore from the viewpoint of long durability, unavoidable as physicochemical events that the inferior compared to the austenitic heat-resistant steels. Therefore, expectations for strengthening the high creep rupture strength ferritic heat-resistant steel is always high, the development of ferritic heat-resistant steel to replace austenitic heat-resistant steels have been developed.
[0007]
　Challenge in using the ferritic heat resistant steel at a high temperature for a long time in addition to the creep strength is lower than the austenitic heat-resistant steel, local creep strength reduction sites found in the weld heat affected zone of welded joint generation of is that hard to extremely avoid.
[0008]
　Ferritic heat-resistant steel, when using a low-temperature transformation structure (mainly bainite or martensite) in the starting tissue, having a phase transformation temperature, the so-called transformation point during stable γ phase in a stable α phase and the high temperature at room temperature . This transformation point contributes to low-temperature transformation structure production of high strength containing the high density of dislocations. However, on the other hand, transformation itself since it involves a large change in the steel tissue (Sort of atoms forming the crystal lattice), of the heat-resisting steel is subjected to thermal histories spanning the transformation organization, originally high creep strength It will differ greatly from the the initial thermally refined structure introduced to give.
[0009]
　Heat-affected zone of the most strongly receive the welded joints of the impact of this phenomenon (hereinafter referred to as "HAZ".) Which is the organization. HAZ and fusion of the weld metal is high temperature of at least 1500 ° C., when the thermal influence is exerted toward Here the base material, the change in the maximum temperature of each region according to the distance from the weld metal (maximum heating temperature) a continuous body of the organization. That HAZ is the maximum heating temperature has an organizational structure such as a metal structure that occurs when changing to 1500 ° C. from room temperature is continuous with the distance from the weld metal. However, the tissue is characteristic for retention time by the maximum heating temperature is as short as a few seconds, "coarse-grained HAZ" from the side closer to the weld metal, "fine HAZ", the "two-phase zone HAZ" It is largely classified.
[0010]
　1, each site containing the HAZ of the welded joint, showing the tissue structure according to this classification. As shown in FIG. 1, HAZ6 between the weld metal 1 and the base material 5 is formed, this HAZ6 is composed, in order from the weld metal 1 side, coarse HAZ2, granules HAZ3, in that order of the two-phase region HAZ4 It is.
[0011]
　Among the sites of HAZ, creep damage is caused by "fine HAZ", a phenomenon of destroying the welded joint is referred to as "Type IV damage". The Type IV damage have not yet been resolved in the welding structure consisting of ferritic heat-resistant steel, its resolution is a recent problem. That, Type IV damage preform In the creep environment, the time can be soundly used, despite the temperature condition, only the welded joint leads to selective destruction by creep deformation, welded joint specific it is a destructive phenomenon.
[0012]
　Recently, it has been found that the empirically that this phenomenon occurs in the conventional material (already material allowable stress registered in the standard is determined) is inevitable. From the fact that, which is up to the situation where the safety factor of which is said to be "welded joint creep strength reduction factor", creep strength for safe operation, including until the welded joint is proposed to the world standard.
[0013]
　The Type IV damage occurs on all ferritic heat-resistant steel in practical use has been inevitable, its generating mechanism have been made various discussions.
[0014]
　Region to be a fine grain HAZ before welding is a ferritic heat-resistant steel which originally has the same structure as the base material, this region is welded, HAZ heat exposed for several seconds to a temperature just above the transformation point undergo a cycle. The heat of welding also matrix itself produce alpha → gamma transformation, from the difference between the C solid solubility limit of the alpha phase and gamma-phase, mainly in the originally carbides was coarsely precipitated (ferritic heat-resistant steel M 23 C 6 type carbide) other than the carbides is dissolved again immediately in γ phase. However, especially in fine HAZ, several tens of percent of the carbide which has been coarsely precipitated and remains remains undissolved those reduced to. This is believed to be the most common cause, Type IV injury.
[0015]
　Normally, the joint after welding, heat treatment after welding (stress relief annealing, with SR process called.) Is applied. If the heat treatment temperature is higher that differ only tempering temperature and several tens of degrees is, carbides remaining remained above the non-solid solution with a solid solution with carbon, a new precipitation nuclei of carbide forming elements. Carbides remaining remained undissolved at the same time when coarsened by heat cycle as a result, reduces the precipitation opportunities fine carbides. In other words, coarse carbides are precipitated before welding the remaining left undissolved, that result in loss of "precipitation strengthening ability" by the so-called carbides, the present inventors have results findings of the study.
[0016]
　Therefore, having a transformation point as described above, in the heat-resisting steel to enhance the creep rupture strength by precipitating carbides contain a carbon, it is understood that Type IV damage is inevitable. That, Type IV damage, which can occur at any of steels if heat-resistant steel to achieve creep reinforcing utilizing carbides, notably in high-Cr steels which is designed on the assumption that in particular prolonged use at high temperatures it is. Is a phenomenon occurring even low Cr heat resistant steel with the use of low temperature main purpose (steel species containing less than 1% Cr) but is not a problem unless used at high temperatures. However, of course in the thermal power plant having a condition where the application temperature is a temperature higher than 500 ° C., Type IV damage will be remains a problem unavoidable. Ferritic heat-resistant steels have not applied the precipitation strengthening ability of carbide creep strengthening may say nothing that, since that may occur at all similar behavior even when replacing the carbon nitrogen ferritic heat the Type IV damage can be prevented in the steel can be said is extremely difficult.
[0017]
　Conventional causes, Type IV damage, since the Type IV damage occurs in fine grained region, there is a period that is described as "softening of magnitude in fine HAZ", "hardenability caused by a small grain size there was also the concept that the loss of dislocation strengthening by lowering "of. However, "fine HAZ", rather than "two-phase region HAZ" and the "two-phase region HAZ" near the base material (not the creep strength, short tensile test results) at room temperature and high temperature strength is high, it is detailed It has become a do the results of the study clearly, these hypotheses are not currently supported. Also although confirm the presence or absence of "reduced hardenability" is not obtained, the current understanding of the reinforcing factors governing the long creep strength is mainly precipitates has become common, this is a fine tissue not shown evidence of creep strength reduction mechanism because the concept. That is, not able to determine the direct cause serving grounds, Type IV damage these hypotheses.
[0018]
　Furthermore, the relationship between the grain size and creep strength, but that only grain boundaries inversely proportional to the austenitic heat-resistant steel capable of deformation is also experimentally known, the correlation in the ferritic heat-resistant steel which tissue can be uniformly deformed it is known that there is no. Thus the creation of the HAZ does not produce a "fine HAZ", or even "fine HAZ" could tentatively come hard heat resistant ferritic steel occurs, if it can prevent coarsening due HAZ thermal cycles of carbides, Type possible to completely prevent the IV damage was concluded that it is difficult.
[0019]
　JP 2008-214753, JP 2008-248385, JP 2008-266785, JP 2008-266786 and JP JP-A 2008-291363 discloses the production of such fine-grained HAZ for the purpose of preventing the conventional ferritic heat-resistant steel, for the entire steel pipe containing B 50 ppm or less, and conducted a heat treatment (normalizing processing in a short period of time) prior to welding, allowing Type IV damage prevention techniques have been disclosed. These documents, by this heat treatment, the average particle diameter of the low-temperature transformation before the austenite crystal grains is not less than 100 [mu] m, it is described that it is possible to suppress the grain refining of low temperature transformation structure.
[0020]
　The technique, by brief sintered semi treated before welding, normally dare to remain in the martensite lath or bainite boundaries residual γ is a tissue of eliminating, encourage these growth and coalescence in reheating in welding, in the base material before the welding is a technique that utilizes the "tissue memory effect" to reproduce the old γ grains were produced at a high temperature.
[0021]
　In this technique, since a furnace for performing high-temperature heat treatment to the entire member including a groove before welding (in most cases the length 10m than the steel pipe) is required, it is difficult to construction on site. Furthermore, the time for the risk of deformation of the steel pipe as a product occurs, further reheated by heating the whole steel pipe, it becomes a challenge process load is large, becomes practical solution in view of the field-installed not.
[0022]
　On the other hand, the same "organization memory effect (hereinafter, simply" memory effect "and referred)" is proposed of the steel pipe using the steel components that do not require the growth and coalescence of the residual γ as a technique to utilize JP 2009-293063 and it is disclosed in JP-a-2010-007094.
[0023]
　These were aimed effect of exerting a shearing alpha → gamma transformation type memory effect caused by the addition of more than 100ppm high concentration of B. Since the point to reproduce the old γ grains of the base metal at high temperatures is the same as the technique described in the above-mentioned JP 2008-214753 discloses such a let no technique resulting fine grained region, does not cause Type IV damage It is believed that.
[0024]
　However, although in the case of high B containing steel, such as described in JP-A-2009-293063 and JP 2010-007094 "generation prevention fine grained region" it is achieved, in fine grained region corresponding site, carbides a short period of time re-solid solution through a partial solid solution and re-precipitation due to the "coarsening of carbides" in the is not be avoided in enough. JP 2009-293063 and JP 2010-007094 Patent Publication described technique, crystal structure what is equivalent matrix, and remains precipitation position of the carbide of high-angle grain boundaries by memory effect. For that reason, to produce a fine grained region completely recrystallized, further precipitation position of carbide coarsening compared with the conventional ferritic heat resistant steel which is independent of position from the grain boundaries to produce a new, Type IV the occurrence of damage effect is reduced (delay) is permitted. That is, although the coarsening of precipitates can not completely prevent, certain tissue stabilization by precipitates on the grain boundaries is achieved. Therefore, Type IV damage occurs in the case of high B content steel is delayed, the strength reduction is effective in use a long time, which is limited, e.g. 100,000 hours, Type IV damage itself can be said to have been alleviated . However, still a long time under a creep environment, minutes coarsening of carbides is leading a decrease in the HAZ creep strength can not be avoided. This long creep test results revealed in particular 30,000 hours of creep test results.
[0025]
　Incidentally, a new reinforcement hypothesis stabilization of tissue have been proposed in recent years by deposit on the grain boundary, the conventional has been considered not effective for strengthening. Large angle in coarse precipitates on grain boundaries, in the creep deformation of the large angle grain boundaries after a long period of time can move, since the rows of coarse carbides is left after the grain boundary migration can become a moving barrier of dislocation, particularly 10 in the very long-term creep deformation of more than a million hours is the idea that responsible for strengthening. Type IV injuries are those to completely eliminate the strengthening effect of coarse precipitates column that narrowing the distance between particles by aligned in the row. Accordingly, one concept that can explain why the strength reduction due to Type IV damage as long becomes remarkable.
[0026]
　In addition to these methods, the welded steel pipe, re-heat treatment of the whole welded structure - a technique for equivalent tissue and the base metal by (and Shojun tempering) is described in JP-A-2001-003120. This method is aimed to be solved unevenness in strength of the joint by heat treatment, including the weld metal. However, it is required larger furnace than the heat treatment furnace according to JP 2008-214753 Patent Publication, workability in the field is low. Further weld metal originally Yes determine the alloy composition so that the creep strength can be highest exhibited when subjected to heat treatment after cold weld than it tempering temperature welded cast structure, and normalizing the matrix equivalent - it is usual strength refining processes such as tempering is not designed to be exhibited. In other words, adding the heat treatment applied to the back base material including up weld metal again, detrimental to the creep properties of the welded joint. Therefore, consequently the joint is different from the Type IV damage, it will be broken from the weld metal by "reduced creep strength of the weld metal", creep strength after all welding joints can not be exhibited. That is, techniques such as described in JP 2001-003120 is forced to said incomplete as a technique, Type IV injury measures.
[0027]
　JP-A-2016-14178 and JP-2016-130339 discloses, in steel containing B, respectively 100ppm and 80ppm or more, a technique for preventing Type IV damage has been disclosed by the local heat treatment. These techniques are of using the tissue memory effect using the residual γ present in significant lath boundaries in B-added steel, the portion subjected to the base material or welding before the heat treatment in the opposite residual γ is small Ie there may remain, toughness tends to easily lowered.
[0028]
　As described above, excellent local workability, completely not causing the Type IV damage, ferritic heat-resistant steel structure having a low temperature transformed structure is undeveloped. The so far prevention technology, Type IV damage of considering economy and local workability is, B has not been proposed in the ferritic heat-resistant steel containing only 50ppm or less.
Disclosure of the Invention
[0029]
　An object of the present invention, Type IV can prevent damage and to provide a method for manufacturing a field-installed excellent in heat resistant ferritic steel welded structure, and Type IV intact without adding a high concentration of B to provide a heat resistant ferritic steel welded structure.
[0030]
　Method for producing a ferritic heat-resistant steel welded structure according to an embodiment of the present invention, the base material, heat affected zone, and a method for producing a ferritic heat-resistant steel welded structure comprising a weld metal, chemical composition, by mass%, C: 0.05 ~ 0.12% , Si: 0.02 ~ 0.45%, Mn: 0.40 ~ 0.80%, Cr: 8.0 ~ 12.0%, N: 0.003 ~ 0.080%, Mo: 0.30 ~ 1.30%, Nb: 0.005 ~ 0.10%, V: 0.005 ~ 0.50%, W: 0 ~ 2.0% , Re: 0 ~ 3.5%, Ti: 0 ~ 0.15%, Zr: 0 ~ 0.15%, Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500 %, and La: 0 ~ 0.0500% containing, Ni: less than 0.20%, Cu: less than 0.20%, : Less than 0.005% Al: less than 0.025% P: less than 0.020% S: less than 0.010%, and O: less than 0.010%, limited to, the balance of Fe and impurities there are a step of preparing the base material, and forming a groove in said base material, and the surface of the groove, the pre-weld heat treatment depth position apart of 30 ~ 100 mm from the surface of the groove the area between, heated to a temperature of 1050 ~ 1200 ° C., to form a pre-weld heat treatment step of holding 2-30 minutes at that temperature, after the pre-weld heat treatment step, the weld metal by welding the groove a welding step, after the welding step, the surface of the groove, the area between the position apart a distance from the surface below 100mm the pre-weld heat treatment over a depth of the groove, the temperature of 720 ~ 780 ° C. It was heated to, meet the temperature to 30 minutes or more and formula (1) And a post-weld heat treatment step of holding time.
　　(Log (t) +12) · (T + 273) <13810 (1)
　where, t is the retention time, T is the temperature. unit of t is the time, the unit of T is ℃. Log is the common logarithm.
[0031]
　Ferritic heat resistant steel welded structure according to an embodiment of the present invention, the base material, heat affected zone, and a heat resistant ferritic steel welded structure comprising a weld metal, the chemical composition of the base material,% by weight in, C: 0.05 ~ 0.12%, Si: 0.02 ~ 0.45%, Mn: 0.40 ~ 0.80%, Cr: 8.0 ~ 12.0%, N: 0. 003 ~ 0.080%, Mo: 0.30 ~ 1.30%, Nb: 0.005 ~ 0.10%, V: 0.005 ~ 0.50%, W: 0 ~ 2.0%, Re : 0 ~ 3.5%, Ti: 0 ~ 0.15%, Zr: 0 ~ 0.15%, Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, Y: 0 ~ 0. 0500%, Ce: 0 ~ 0.0500 %, and La: 0 ~ 0.0500%, contain, Ni: less than 0.20%, Cu: less than 0.20%, B: 0.0 Less than 5% Al: less than 0.025% P: less than 0.020% S: less than 0.010%, and O: less than 0.010%, limited to, balance being Fe and impurities, wherein M is deposited on the high-angle grain boundaries of the weld heat affected zone 23 C 6 average particle diameter of type carbides is not more 300nm or less, wherein M on the high-angle grain boundaries 23 C 6 mean particle surface distance of type carbide is 200nm or less , and the said M of the high-angle grain boundaries 23 C 6 coverage by type carbides is 40% or more. However, the M 23 C 6M type carbides are Cr, Fe, Mo and W 1, two or more 70 atomic% or more in total of.
[0032]
　According to the present invention, it is possible to prevent Type IV damage without adding a high concentration of B, and a method of manufacturing a field-installed excellent in heat resistant ferritic steel welded structure, and Type IV undamaged ferritic heat-resistant steel welded structure is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033]
[1] Figure 1 each site containing the heat-affected zone of the welded joint is a schematic cross-sectional schematic view of a joint for explaining the respective tissue.
FIG. 2 is for explaining the concept and method of measuring coverage by precipitates organizational model and grain boundaries of the weld heat affected zone is a schematic diagram of a high-angle grain boundaries covering state.
FIG. 3 is a graph showing the relationship between the existing forms of conditions and carbide pre-weld heat treatment.
[4] FIG. 4 is a diagram showing status and Nomenclature butt before welding of the welded joint, and the pre-weld heat treatment applied range.
FIG. 5 is the old γ grain coarsening tendency and the holding temperature of the subject steel of the present invention, is a graph showing the time relationship.
FIG. 6 is a diagram showing the relationship between the old γ grain size and Charpy impact absorption energy of the target steel of the present invention.
[7] FIG. 7 is a graph showing post-weld heat treatment conditions.
FIG. 8 is a heat treatment time and 600 ° C. after welding is a diagram showing the 100,000 hours estimated creep rupture strength relationship.
[9] FIG. 9 is a graph showing the relationship between the retention time of the heat treatment after welding and the welding joint toughness.
[10] FIG 10 is welded heat treatment temperature and the M 23 C 6 is a graph showing the relationship between the average particle diameter of type carbide.
[11] Figure 11, M 23 C 6Is a graph showing the relationship between the average particle size and 600 ° C. estimated creep rupture strength of the mold carbide.
[12] FIG 12 is welded after the heat treatment temperature and high angle grain boundaries on the M 23 C 6 is a graph showing the relationship between the type carbide coverage.
FIG. 13 is large angle M on the grain boundaries 23 C 6 coverage and 600 ° C. by type carbide is a graph showing the relationship between 100,000 hours estimated creep rupture strength.
[14] FIG 14 is a schematic diagram of a 30mm thickness Temperature propagation state measuring steel plate test piece (3-view drawing).
FIG. 15 is the time of heating the weld GMA surface 1050 ° C., is a graph showing the elapsed time related to the temperature in the depth direction 30mm position.
FIG. 16 is the time of heating the weld GMA surface 1050 ° C., is a graph showing the time variation of the temperature distribution in the depth direction.
[17] FIG. 17 is an electron micrograph of a tissue having a lath structure.
[18] FIG. 18 is an electron micrograph of the tissue lath structure has been lost.
DESCRIPTION OF THE INVENTION
[0034]
　The object of the present invention as previously described, in the HAZ of the welded joint of a steel material that satisfies the predetermined main chemical components and regulatory values, without Type IV damage occurring, a substantial difference in creep strength of the welded joint and the base metal to provide a no welded structure. Cr content of the steel in question is 8.0% or more. From the viewpoint of corrosion resistance application temperature range 500 ° C. or higher, the creep rupture strength of 100,000 hours considered as a function of temperature, breaking strength of 600 ° C. as the representative value is targeted to be at least 75 MPa. At the same time the groove of processability, Charpy impact toughness at 0 ℃ as a measure of toughness difficult to weld cracking to occur considering the workability of welding is targeted to be at least 27 J.
[0035]
　An object of the present invention to completely prevent the coarsening due HAZ thermal cycle through the portion dissolution of carbides is a root cause, Type IV injury. In the present invention Therefore, to Type IV damage to the structure itself is hard to chemical components occur, with the utmost take measures on component design, to vicinity of the GMA weld joint, a heat treatment prior to welding applied by limiting the conditions of the process with applying.
[0036]
　The heat resistant ferritic steel welded structure of the present invention, the base material, be those HAZ, is composed of the weld metal, the shape is not particularly limited, but may be tubular or plate-like. Moreover, those lengths when the shape of the structure is a tubular is more than 100mm, when a plate-like, is suitable for those length or width is 100mm or more. Further, the present invention is the fact that the high temperature of the pressure vessel such as a suitable subject, (thickness in the case of steel) that thickness is preferably at least 4 mm.
[0037]
　For techniques underlying the present invention will be described below with experimental results.
[0038]
　Experimental results shown below, were obtained using the following as the test piece and various experiments produced.
[0039]
　In the laboratory, it was melted and cast to the steel chemical components (mass%) shown in Table 1 in an induction heating vacuum melting furnace with a steel capacity of 300kg, and a 300kg weight of the steel ingot. Thereafter, the steel ingot was held for 60 minutes oven was reheated to 1180 ° C. in an electric furnace of air atmosphere, and hot rolled steel sheet test piece then 30mm thickness by hot rolling experimental apparatus. Hot rolling ends at a temperature above 900 ° C., then allowed to cool. The resulting steel sheet specimens were then returned 2 hours baked at 770 ° C.. Have a lath martensite structure at this stage, M 23 C 6 that carbides mainly composed of type carbide is mainly precipitated, optical microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) , it was confirmed by the electrolytic extraction residue渣定weight analysis method. Type precipitates were collated by the energy value of the reflection peak by X-ray diffraction came with energy dispersive X-ray analysis (EDX), and electrowinning residue TEM (qualitative analysis).
[0040]
[Table 1]

[0041]
　Here, "M 23 C 6 M of type carbide" is one is Cr, Fe, Mo, or a total of 70 atomic% or more of W.
[0042]
　Incidentally, M 23 C 6 intergranular coverage by type carbide is the magnification of 10,000 times of the SEM image and the thin TEM observation image was determined by the length occupancy of deposits on the large angle grain boundaries. Further, (angular difference of the normal orientation of the adjacent crystal orientation) grain boundary character was measured using an electron backscatter analyzer (EBSD), "large angle when the angle between the adjacent crystal grains of 15 ° or more particle It was judged to be the field ". Here, the large-angle grain boundaries are crystallographic designation martensite or bainite "old γ grain boundaries" means "packet boundaries", or "most of the block boundaries", as precipitation nuclei of precipitates is an effective crystal grain boundaries. Occupancy of precipitates on the high angle grain boundary, two-dimensional observations, assuming approximately equal to the area occupancy on the three-dimensional grain boundaries (boundary) plane was used as the measurement value. This value can be converted to a simple 3-dimensional value in equation obtained by calculation analysis, it is determined that there is no need to seek a scientifically accurate value, giving priority to the convenience due to accept the observations.
[0043]
　2, for explaining a method for measuring coverage by HAZ organization model and the grain boundary precipitates, (in the figure there two.) High angle grain boundary 9 grain boundary coating by carbides tissues including it is a conceptual diagram of. Incidentally, L in FIG. 2 1 ~ L 10 is M 23 C 6 occupation length 7 on the grain boundaries of the type carbide each separately shown, La and Lb, respectively showing a high angle grain boundary length 8.
[0044]
　"Grain boundary coverage" as shown in FIG. 2, (in FIG. 2, L large angle precipitates length sum of the grain boundary 9 1 ~ L 10 sum up) the sum of the large angle grain boundary lengths a value obtained by dividing the (La + Lb), if it is completely covered becomes 100%, is a parameter to determine if it has not been completely covered 0%. In this case, the length covering the upper grain boundary carbides is occupied length, size and the precipitate, not necessarily the major axis itself of oval precipitates on the grain boundaries.
[0045]
　"Grain boundary coverage" is the first 10,000 times the electron microscope observation, large angle grain EDX or also 10,000 fold particles deposited on field M by transmission electron diffraction pattern analysis in TEM analysis of 23 C 6 type carbide to be identified. It is also effective to increase the rapidity measured using a reflection electron image of EDX. A length followed by the particles to cover the large angle grain boundaries measured by the electron microscopic field. The measurement was carried out by taking at least one sample per five fields, five or more test strips per steel, it can be determined by a total of 25 or more visual fields in situ observation or analysis of the electron micrograph. The actual calculation is carried out by (the total sum of high-angle grain boundaries occupied length by particles) / (the sum of the large angle grain boundary length).
[0046]
　Moreover, the the average particle surface distance of high-angle grain boundaries on the precipitates, the coverage of the resulting precipitate by the microscopic observation over a high angle grain boundary length minus 1, further precipitation of this as divided by the number, it can be obtained similarly in the manner of FIG.
[0047]
　However, this interval is not an accurate value, precipitates in assuming taking a square distribution on the grain boundary is obtained by approximating by the following formula (2). It is actually the average value is different from the actually measured data of the particle size depending which position was cut surface is observed with an electron microscope of a positive ellipsoid (precipitate density is particularly pronounced when low.) That corrects, an approximation formula by calculating the analysis, there are several types depending distribution assumptions. The present invention was correlated clear understanding of the most creep strength, using a model assuming a "square distribution on the grain interface." This is also the present invention own empirical formula plus correction to match experimentally.
[0048]
　λａｖｅ＝１．３［ｌｓ］ａｖｅ－［ｄｓ］ａｖｅ　　　（２）
[0049]
　Here, [ls] ave is average interparticle center distance (nm), virtual it believes [ds] ave is the average diameter of the particles (nm) (however, a portion of the size of the particles occupying grain boundaries a Do not mean diameter). λave is the distance between the average particle surface (nm). The average particle center distance measures precipitates number of the grain boundaries, which can be determined by dividing the grain boundary length.
[0050]
　For the production of welded joints, the width of the steel sheet test pieces of the prepared the 30mm thick and 200 mm, one of the width direction of the steel sheet test piece, included angle side 22.5 °, of 45 ° as GMA pairs the weld groove to form a V groove to produce a machined test piece. The test piece was welded two butt. Route butt is a 1 mm, the heat input of about 1 kJ / mm, at a welding speed of about 10 cm / min, to form a welded joint enliven 30-35 pass. The welded joint of the full-length 400mm and more prepared, to evaluate its joint properties, was also observed and analyzed structure of the HAZ. Creep test was evaluated by the parallel portion diameter 6 mm, parallel part length 30 mm, total length 70 ~ 86 mm creep test piece. Specimens were taken and processed approximately weld line from the welded joint test specimens as center HAZ is positioned perpendicular and thickness direction perpendicular to the direction in between marks distance. Note that the weld metal is applied to Alloy 625 Ni-based alloy according to Table 2 is a commercially available Ni-base alloy, and over-matched joint so as not to cause breakage from the weld metal, HAZ characteristic evaluation reliably It was devised so that it can be implemented.
[0051]
[Table 2]

[0052]
(Before heat treatment welding)
　As described above, Type IV damage, Ac by heat transfer of the welding 3 together with carbides that are briefly heated to just above points are dissolved only partially around the carbides, fine (particle diameter size substantially to 100nm or less) is supplied carbon in the matrix by complete dissolution of carbides, by the subsequent heat treatment after welding, on undissolved carbides remaining, and these carbon, reprecipitation carbide steel transition element caused by carbides become coarse and. The present invention, in order to prevent this, prior to welding, and heat treatment is performed for, Type IV damage prevention. Specifically, a carbide is precipitated at the site to be welded heat affected zone of welded joint (HAZ portion corresponding site) immediately before welding, Ac 3 by heating to a temperature above points, more than 2 minutes to the temperature holding leave completely dissolved again by suppressing the coarsening itself by weld heat affected carbide through undissolved carbides.
[0053]
　Heat treatment prior to welding heats the groove to a temperature of 1050 ~ 1200 ° C., the site to be HAZ after welding is 2 minutes or more regardless of the thickness position is held such that the temperature of interest it is a feature. The holding time is a function of the original plate thickness Metropolitan case of implementing the heating from the outer surface, the weld is not necessarily be joined flat plates to each other, it is difficult to formulate them. Therefore, pre-embedded thermocouple HAZ outer corresponding sites in the steel plate of the same shape (the range of chemical composition the present invention), by heating the entire member, the site more than 2 minutes, such that the temperature of interest the temperature pattern of the heating device it is sufficient to determine.
[0054]
　Later, carried out immediately before the welding, a heat treatment for, Type IV damage prevention as "pre-weld heat treatment".
[0055]
　Figure 3 is a diagram showing the effect of the maximum heating temperature retention time and the carbide forms on the temperature in the pre-weld heat treatment. The test is 50mm square, a portion of the steel plate test piece of 10mm thick cut products Make several, various temperatures, heat treated for a time, the precipitation presence of carbides in the subsequent section of the cutting to transmission electron microscopic structure observation confirmed. After heat treatment of the "●" In the figure, M remaining remained undissolved in the middle decompose during specimen after cooling 23 C 6 examples showed a type carbides, "○" is completely dissolved all carbides it is an example that was not observed. Once you have residual undissolved carbides at all, since the creep strength of the amount corresponding weld heat affected zone decreases, the preferred range that includes only the results of ○ in FIG.
[0056]
　3, if the holding time is less than 2 minutes, undissolved carbides regardless of the heating temperature is partially or remain all in the tissue, the possibility of coarsened by heat treatment after welding of the post is suggested It was. On the other hand, if it is reheated to a temperature of 1050 ~ 1200 ° C., always undissolved carbides regardless of the heating temperature if the holding time is not less than 2 minutes does not remain at all, had completely dissolved.
[0057]
　On the other hand, when the heating temperature is less than 1050 ° C., undissolved carbides remaining in the partially or all tissues. Table 1 The steel for increasing the transformation point to be observed in the case of the HAZ of such rapid heating (50 ° C. / sec or more), Ac 3 point is sometimes reaches a maximum at 1000 ° C.. This uses the thermal expansion coefficient measurement test device reproduces the rapid heating was confirmed in a separate thermal cycle reproduction test. Therefore, substantially becomes a two-phase region heated state by heating at 1000 ° C. or less, carbides form at a site that does not exceed the transformation temperature without decomposition solid solution which is slightly coarsened as compared with the room temperature. On the other hand, in the region partially transformed into γ phase, the temperature of Ac 3 becomes a temperature at which slightly exceeds point, carbides are believed to remain without forming a solid solution. That is, in the case of thus partially γ phase transformation to such rapid heating at a high temperature, unless heated above 1050 ° C., or tissue results in leaving an incomplete solid solution (undissolved) carbides these incomplete solid solution carbides readily coarsened by heat treatment after welding of the post.
[0058]
　Accordingly, the temperature of the pre-weld heat treatment required to fully prevent Type IV damage in the present invention is 1050 ° C. or more, it can be seen that the retention time is more than 2 minutes. Incidentally, the heat treatment prior to welding at 1200 ° C. or higher, since the toughness of the steel material may be deteriorated though gamma particle size after alpha → gamma transformation a short time becomes coarse, the maximum heating It is the temperature to 1200 ℃.
[0059]
　In the present invention, subjected to a welding pre-heat treatment of the above in the vicinity of the groove only. Specifically, the region between the surface of the groove (hereinafter referred to as "groove surface".), A predetermined depth from the groove surface (hereinafter referred to as "pre-weld heat treatment depth".) And a position apart but, to be in 1050 ~ 1200 ℃.
[0060]
　In determining the pre-weld heat treatment depth, the narrowing dissolved in the base material by welding, it is necessary to consider the width of the HAZ spread depending on the welding heat input. Figure 4 is a schematic view showing a weld groove of abutted steel sheets each other as V groove, at the same time, the groove surface 10 subjected to a pre-weld heat treatment length in the depth direction of the steel plate, the weld cross-section It illustrates in schematic diagram. Type IV damage generated on the outer edge portion of the HAZ. Therefore, it is necessary to hold appropriate 1050 ° C. or more than 2 minutes as heat treatment before the welding deeper than sites HAZ outer edge is assumed to be located.
[0061]
　Here it should be noted, in the welding is to be sure there is a portion Komu dissolving the base material. Original GMA surface is retracted into the base material side to form a Fusion Line separating the weld metal (a mixture of the weld metal or weld metal and the base metal has solidified from the molten state) and a HAZ. The boundary is also called a bond, HAZ is generated toward the interior base material from the bond. High temperature pressure vessels and power generation plumbing to which the present invention is directed, high strength, thus also high residual stresses remain in the joint portion, since the like reheat cracking during post-weld heat treatment cracking and welding is concerned , it is most often relatively Hoyle heat welding is employed. In this case also be higher compared to the transformation point of the base material is originally carbon steel, HAZ width is not very wide. Width when HAZ of about 50mm thick plate are at 5mm or less, high heat-input welding HAZ width is in excess of 10mm in 100mm than extra-thick material is not usually applied. Substantial heat input is 5 kJ / mm, no more high heat input welding is not applicable. That this maximum HAZ width of case is 5 mm, it was confirmed by prototype testing of welded joint 10 body. That is, the Type IV damage if holds only requires time, pre-weld heat treatment over at least 5 mm 1050 ° C. to a depth of can be prevented.
[0062]
　On the other hand, amount with dissolved by the weld metal of the aforementioned base material, the results measured at the welded joint trial test was found to be up to 5mm similarly. Amount with the dissolved varies depending steel type, the result value is specific to the subject grades of the present invention.
[0063]
　From the above, so that the pre-weld heat treatment to a depth of up to 10mm in total from groove surface may be performed more than 2 minutes at 1050 ~ 1200 ° C..
[0064]
　However, further attention as a point necessary to place welding the final pass, i.e. after the weld pass has reached the surface of the steel material, the shallow weld metal at the site for the shape defect eliminating the weld metal toe portion, a so-called "cosmetic there is a case in which Mori "is. Cosmetic prime is also called from a cross-sectional shape as that of the "umbrella". Umbrella example, the boundary between the small groove or raised weld metal and the base metal surface by incomplete fusion or welding metal supply shortage of bond positions generated by narrowing dissolved base metal of the weld metal, stress fracture concentrated It is arranged in order to avoid that as a starting point. In particular it is common to avoid stress concentration by forming a large umbrella in subject grades of the present invention mainly composed of martensite. Weld metal width of the surface layer portion Considering to weld final pass for such defects prevent or preventing stress concentration, there are cases where HAZ spans from the tangent of the opening crest and a steel outer layer surface before welding to 30 mm.
[0065]
　Considering all of these, the weld before the heat treatment depth is required to be 30mm or more. To implement such a deep heat treatment, especially when carrying out the heat from the outer surface, it is necessary to devise the following. For example, when to realize this by the high frequency induction heating, 3 kHz frequency to deepen the depth of penetration induced current or less, it is effective to reduce as much as possible. Directly in the case of electrical heating, it is effective to optimize experimentally the electrode contact position for the electric heating. In the case of furnace heating, it is effective to increase the energy density for the temperature rise of 30mm depth position and heated by increasing the volume of the furnace from any direction of GMA. It may be applied as appropriate determining technique of the 30mm pre heat treatment depth welding in any way.
[0066]
　That is, the groove surface, it is always up to the position of the boundary lines 13 and 14 to be 30mm or more positions that are prerequisite to hold more than 2 minutes to 1050 ~ 1200 ° C..
[0067]
　However, groove-welding surface is vertical is rare, is substantially V groove, X groove, such as K groove is used. Therefore, in order to be covered by the HAZ is heat treated before always weld region, most of groove position with possibility of departing from the groove center base material surface (front and back both) of 30mm depth position 13 * 14 If * it is preferable to heat treatment prior to welding the to the site of the line. In this way, the welding path at the center of plate thickness, even deep penetration sites were generated by gouging the like, are possible infallible Type IV damage prevention process. At least 13 * and 14 * in sandwiched by all regions more than two minutes, it is preferable to hold the 1050 ~ 1200 ° C..
[0068]
　That is, the surface of the groove, the area between the position apart more pre-weld heat treatment depth from the farthest from the tip of the groove of the surface of the groove, more than 2 minutes to a temperature of 1050 ~ 1200 ° C. it is preferably maintained.
[0069]
　On the other hand, the steel becomes γ phase at temperature, coarse particle size γ Holding certain period of time occurs. Coarsening of the particle size by improving the hardenability, there is no problem in the high temperature properties since increasing the creep strength. However, the results of which were actually construction, the heating of greater than 30 minutes coarsened crystal grain size greater than about 200 [mu] m, the toughness of the joint is lowered revealed results of the experiment.
[0070]
　Figure 5 is a diagram showing the time of holding and heating the invention steel 1050 ~ 1200 ° C., the retention time and the old γ grain size relationship. Grain growth rate of up to 30 minutes is not seen is a big difference. However, if the retention time exceeds 30 minutes, clearly it can be seen that the old γ grain size is equal to or greater than 200 [mu] m. This high temperature stability particles having the function to prevent the grain growth in the temperature range, for example NbC, TiN, Al 2 O 3 exists precipitate particles or the like at a constant density, the pinning effect is effectively works determine particle size substantially in particle spacing in the time range, the time the pinning effect thermal activation process becomes active starts out is a phenomenon that can be explained by considering that the 30 minutes.
[0071]
　Figure 6 is a diagram similarly showing the old γ particle size and 2mmV notch Charpy impact test results related to the present invention steel. The former γ grain size is 200μm or more, which are generally required for processing or welding of the pressure vessel, it can be seen that below the Charpy impact absorption energy value 27J of 0 ° C.. That is, FIGS. 5 and 6, in order to the toughness of the present invention is a target obtained even in joint, retention time of welding before the heat treatment it can be seen that shall not exceed 30 minutes.
[0072]
　In the present invention, and 100mm the maximum value before the heat treatment depth welding. The reason will be described later in detail "partial pre-weld heat treatment characteristics."
[0073]
　As described above, pre-weld heat treatment of the present invention, the surface of the groove, the area between the position apart pre-weld heat treatment depth of 30 ~ 100 mm from the surface of the groove, to a temperature of 1050 ~ 1200 ° C. heated, held for 2 to 30 minutes at that temperature. Welding before the heat treatment is carried out in two or more times, using the first of the remaining heat, it may be set to be 2 to 30 minutes in total. The cooling after the heat treatment, for example, cooling.
[0074]
(Presence state of post-weld heat treatment conditions and precipitates)
　Subsequently, forms part of a method for manufacturing a heat resistant ferritic steel welded structure according to the present invention, a post-weld heat treatment, the precipitate morphology of tissue that resulting Description to.
[0075]
　The heat treatment after welding of the present invention, after welding the groove, the groove surface, the temperature of the site within 100mm pre-weld heat treatment over a depth toward the base material 720 ~ 780 ° C. (hereinafter "post-weld heat treatment temperature "and referred.) was heated to, temperature to 30 minutes or more, and a process of holding time satisfying formula (1).
[0076]
　Post-weld heat treatment is usually at (transformation point -20 of the base material) ° C. below the temperature, it is common to impart an amount of time corresponding to the plate thickness. However, in order to exhibit the same creep rupture strength as the base material M 23 C 6 is necessary to control the precipitation state of type carbide equivalent to the base metal. At the same time, the post-weld heat treatment, there is substantially shrink back effect of high hardness martensitic structure weld metal occurs been hardened, brittle fracture of the weld metal, or in preventing brittle fracture of the bond It is valid.
[0077]
　In the present invention, once the base material as a pre-weld heat treatment from heating to γ ​​region, a martensitic structure which remains even quenched similarly preform if the heating area, high hardness. Therefore, it is necessary to prevent quenching cracks and brittle fracture, the toughness decreases. After welding heat treatment is heat treatment required to achieve this. That is, usually tempered after welding heat treatment be carried out, in the present invention, including the base material heated to the γ region in the heat treatment prior to welding in order to soften the weld metal and the bond of the welded joint, sometimes a high hardness tissue HAZ carried out in order. Therefore, (hereinafter referred to as "heat treatment after welding depth".) Depth direction of the heating range of the temperature heating by heat treatment after welding, it is necessary to pre-heat treatment depth or welding.
[0078]
　Kyokin based weld metal such as commonly present invention is directed, in a possible premise an alloy designed for the temperature of the heat treatment after welding (tempering temperature -20 ° C. of the base metal) below the temperature there. That is, the alloy of the weld metal, is designed to the high temperature strength and creep strength equal to or larger than that of the base material can be exhibited when it is tempered at a temperature lower than the base metal. When Conversely tempered at high temperatures, to soften proceeds tissue recovery, reduced high-temperature strength, creep strength tends to decrease. Thus, after welding heat treatment, while ensuring the high-temperature strength, creep strength so that the above base material equivalent, it is necessary to strictly control the state of existence of precipitates has a creep reinforcer. That is, even by coarsening the precipitates heat treatment temperature becomes too high after welding also creep strength of the joint without sufficient precipitation to obtain too low conversely does not become more than the base metal equivalent.
[0079]
　Therefore, in the present invention precipitates, by controlling the state of presence of grain boundary precipitates supporting the creep strength of ferritic heat-resistant steel to the end with inter alia long, to solve this problem. Type IV lesions precipitation density of grain boundary precipitates as described above, i.e., caused by a reduction in grain boundary occupancy. That is, the creep strength at the grain boundary occupancy Similarly, in another cause the even or the weld metal in the base material decreases suggests that lowered. The present inventors have found that in order to improve the creep rupture strength of the weld joint, M in HAZ 23 C 6 were investigated precipitated form of type carbide. As a result, M 23 C 6 average particle size equal M be at 300nm following type carbide 23 C 6 high-angle grain boundaries of the coverage by type carbide (hereinafter referred to as "grain boundary coverage".) There are at least 40% and large angle M precipitated at the grain boundaries on the 23 C 6 found that the average particle surface distance of type carbide (hereinafter referred to as "interparticle distance") is required to be a 200nm or less in the HAZ after heat treatment after welding It was.
[0080]
　In the present invention, as an essential condition that the addition of post-weld heat treatment of holding for 30 minutes or more at a temperature range of 720 ~ 790 ° C.. Thus it is possible to the site of the precipitates containing HAZ and fittings and the desired form of the foregoing.
[0081]
　However, growth of precipitates is a function of temperature and time, the precipitate size is higher temperatures as long as the deposition temperature range, also precipitation and growth as long promptly produces. Therefore, the introduction of parameters viewed as equivalent to the temperature and time in terms of diffusion, further limiting the post-weld heat treatment conditions of the steel according to the present invention. Based on experimental results, it is effective for preventing excessive coarsening of the following formula (1) precipitates in the heat treatment after welding the scope of the present invention. (1) In the equation, T is temperature (° C.), t is the holding time (time), Log is the common logarithm.
　(Log (t) +12) · (T + 273) <13810 (1)
[0082]
　7, the heat treatment condition range after welding, described in drawing relationships temperature and time of the heat treatment after welding (1), showed an effective temperature, time range in the present invention. It is necessary to post-weld heat treatment over 30 minutes, the heat treatment after the pole prolonged welding to attract coarsening of precipitates, substantially it is necessary to perform in a finite time. Incidentally, (1) assumes a body diffusion-limited growth law of precipitates, the invention-specific precipitates obtained by modifying the formula of Larson-Miller viewed as constant permeability of time and temperature in the diffusion of substances growth prediction equation it is. (1) various constants in the formula may form various temperatures of the precipitates was observed by transmission electron microscopy in the steel which had been held by the time conditions were determined by statistical analysis of the results.
[0083]
　Outside range hatched in FIG. 7, the average particle or size exceeds 300nm precipitates, or if the inter-particle distance of precipitates becomes 200nm, or greater than the creep of the welded joint portion occurs both at the same time that strength decreases was confirmed by creep test up to 600 ° C., and 650 ° C. of 10,000 hours.
[0084]
　Figure 8 is welded after the heat treatment temperature and 600 ° C., 10 thousand hours estimated creep rupture strength (600 ℃, 650 ℃, implemented 10,000 hours of creep rupture test at each temperature of 700 ° C., a temperature from its results - Time organized by the parameter method, show the estimated creep rupture strength) of the relationship.
[0085]
　The post-weld heat treatment temperature is 720 ° C. or below 780 ° C. greater than the creep rupture strength is lowered, 600 ° C., which is the target value of the present invention, it can be seen that does not exceed 75 MPa. Further, the relationship Charpy impact absorption energy at 720 to post weld heat treatment time and 0 ℃ when heat treated after welding at various temperatures ranging from 780 ° C. in FIG. After welding heat treatment regardless of the temperature, if not carried out for more than 30 minutes, it can be seen that it is impossible to obtain the necessary toughness. Note that sites of greatest toughness tends to decrease in the welded joint, since the crystal grain size is large and tends bond, the toughness of the welded joint in the subsequent behalf impact test was processed by cutting out 2mm notch the bond position representing in Charpy absorbed energy was measured using the strip. If separately describe toughness of each part is not limited thereto.
[0086]
　10 M in HAZ 23 C 6 is a graph showing the mean particle diameter (circle average equivalent particle diameter) and the relationship of the heat treatment after welding temperature type carbide. The holding time in the post-weld heat treatment temperature was studied as up to 10 hours. During this time, M due to the change in retention time regardless of the temperature 23 C 6 little effect on the average particle diameter of type carbide, particle size was substantially a function of temperature.
[0087]
　As apparent from FIG. 10, when the post-weld heat treatment temperature exceeds 780 ° C., M 23 C 6 average particle diameter of type carbide is seen that coarse beyond 300 nm.
[0088]
　11 M 23 C 6 shows the average particle size and 600 ° C., of 100,000 hours estimated creep rupture strength relationship type carbide. When the average particle diameter exceeds 300 nm, it can be seen that the estimated creep rupture strength Type IV damage occurs does not reach the 75MPa target value. Incidentally, the results in FIG ● became a normal creep rupture a ductile, ○ is the shape of a Type IV injury, an example of low ductile fracture, the electron microscopic observation of the organization, clearly the damage patterns It is distinguished that can be identified.
[0089]
　12, the heat treatment after welding temperature and HAZ of high angle grain boundaries on M 23 C 6 shows a relationship between the occupancy of the type carbide (grain boundary coverage). Again was conducted tested as retention time 30 minutes to 10 hours, the time of precipitates size dependence is not observed significantly, resulting in a large difference in grain boundary coverage was observed from, not shown in the diagram distinction of data by time. Temperature significantly affect the grain boundary coverage.
[0090]
　That after welding heat treatment temperature is coarsened precipitates exceeds 780 ° C. is as shown in FIG. 10. On the other hand, the heat treatment after 30 minutes of welding, already M at the same temperature 23 C 6 since the amount nearly thermodynamic equilibrium value type carbides (amounts in particular determined by the C concentration) is precipitated completed, post-weld heat treatment temperature with the high temperature of increasing the average particle diameter, the number decreased to (small particles of particles caused the Ostward maturation solid solution, stabilized tissue by interfacial energy is decreased resulting larger particles grow .). That is, increase in size of the particles, in order to eliminate small particles, M 23 C 6 reducing intergranular coverage by type carbide. On the other hand, at temperatures below 720 ° C. M 23 C 6 can not be deposited to the extent type carbide precipitation to reach thermodynamic equilibrium amount, even though the particle size is small, distance between particles becomes rather large, in this case not 40% is sufficient grain boundary coverage is obtained. That is, only by properly implement pre-weld heat treatment also be realized complete solid-solution of carbide, will not be obtained only precipitates state can not be achieved the creep strength of the material stably.
[0091]
　Thus, by appropriate pre-weld heat treatment and after proper weld heat treatment, M 23 C 6 intergranular coverage by type carbides can be more than 40% was found experimentally. Further, as shown in FIG. 13, M 23 C 6 in HAZ grain boundary coverage by type carbides is 40% or more, the estimated 100,000 hours creep rupture strength of the base metal equivalent is obtained, there is no strength reduction. Since tissue factor causing Type IV damage is gone, it become possible to prevent the complete same phenomenon.
[0092]
　The average particle size (equivalent circle diameter) of the above experimental results high angle grain boundaries on the precipitate in was determined by as follows. First, the cross-sectional structure of the test piece was subjected to post weld heat treatment was observed by SEM, and then observed by EBSD grain boundary structure constituting the ferrite structure in more detail. Among them, the crystal misorientation adjacent 15 ° or more, yet the common rotation axis of the angle between adjacent crystal orientation, is selected when the martensitic transformation, block grain boundary characteristic diffraction angles, i.e. 54 ° and 60 °, and those of 16 ° to draw on EBSD incidental SEM, it is to as "block boundaries (high angle grain boundaries)." Its large angle (M is a heat treatment completed form in this invention steels carbide precipitated at grain boundaries on 23 C 6 in no type carbide only precipitation.) 10,000 times based on an electron micrograph of the precipitate, the particles on the section to determine the diameter on the photograph.
[0093]
　10,000 times image photo observes the above five fields in the heat affected zone of one of the joint, the cross-sectional area of ​​the precipitate was measured for all the particles, assuming that this is all yen, and backward from the area It was a circle equivalent diameter.
[0094]
　The maximum value of the heat treatment after welding depth is limited to 100 mm. Which is identical to the maximum value before the heat treatment depth welding. Heat treatment after welding depth must not be smaller than before the heat treatment depth welding. The reason is of course that in order to realize the "softening quenching was dense dislocation structure" as post weld heat treatment is intended to impart to the above prior heat treatment depth welding. Meanwhile, the tempering the base material beyond 100mm, especially since the dislocation structure of the martensite structure is responsible for the initial resistance of the creep deformation, be synonymous with performing a long tempering in the base material , high-temperature strength of the base material, thereby causing the thus lowering the initial creep strength. If the heat treatment after welding the range within 100mm in the target steel of the present invention, extreme softening of the joint does not occur, since there is no effect on the high-temperature strength and initial creep strength, and its depth upper limit and 100mm .
[0095]
(Partial pre-weld heat treatment characteristics of)
　one of the features of the present invention, by welding before the heat treatment is to prevent the incomplete solid solution of carbides in HAZ.
[0096]
　Be heat-treated before welding to the whole material can be obtained the same effect as the present invention, a heat treatment prior to welding the entire pressure vessel large capacity furnaces, impractical in terms of heating capacity, very requires a high cost, it will not be a practical solution.
[0097]
　On the other hand, if the partial heat treatment to allow partially complete dissolution of carbides as in the present invention, depending on the heating method of the heat treatment apparatus, for example, conveniently the use of high-frequency heating apparatus or electrical heating device and short time processing is terminated, it can become a realistic measure technology can significantly suppress the cost.
[0098]
　However, even the heat treatment any case of "local heating", has a common problem of "intermediate temperature heating". That is, the temperature of the target, heating only site of interest, in a portion adjacent to its scope, the intermediate temperature range that is heated to a lower temperature zone than the target temperature is produced. Therefore, it is necessary to consider the possibility that the sites that are not revealing tissue and the desired effect occurs and can result in a special tissue changes at low temperature sites always. However, in the case of the present invention it was verified that this problem does not occur experimentally.
[0099]
　When carrying out the pre-weld heat treatment at 1050 ~ 1200 ° C., the adjacent site is reheated to a temperature range of 1050 ° C. or less, Ac to generate a Type IV damage 3 to be the site to be heated to a temperature just above points exist Become. The site is likely to coarsen due to incomplete dissolution of carbides occurs also contemplated.
[0100]
　However, originally Type IV damage, such alpha → gamma briefly exposed just above the temperature of the transformation point, partly dissolves in the matrix phase in the carbide because has been transformed into gamma phase is short, complete solid it is responsible for the cooling insoluble carbides are generated in less soluble. Undissolved carbides are coarsened by subsequent heat treatment after welding. At that time recrystallized γ grains of the grain boundary positions occurring is, since it produces a different site from the old γ grain boundary position, coarsening of incomplete solid solution carbides, and the former γ grain boundaries newly generated completely resulting in a different site. Therefore, decreases the precipitation density of the grain boundaries can not be realized rows carbide precipitation in a long time, becomes a relatively random coarse carbides, mobility of dislocations is increased relatively.
[0101]
　Retention time of the site to be heated just above the transformation point of this time alone even when heated multiple times heated once even if there are at most about 10 seconds or a total of,. Therefore, the undissolved carbides (incomplete solid solution) occurs, such as, with leads to coarsening during redeposition, the carbides were precipitated in the grain boundary on the first former gamma, weld heat-affected can no longer be precipitated into the resulting nascent old γ grain boundaries by transformation again in parts, it is the result being left on the grains.
[0102]
　Upon consideration of the phenomenon described above, if provided with sufficient retention time in reverse, even at a temperature just above the transformation point, generation of undissolved carbides causing TYPE IV damage, i.e. incomplete solid solution of carbides It will not occur. The present inventors have this thing was confirmed experimentally. The time required to carbide solid solution in the transformation point just above temperature, was heated to just above the transformation point by changing the retention time in the various specimens, M in the field of view in the structural photograph by TEM 23 C 6 type carbide is almost disappeared assuming time, I have found that about 2 minutes experimentally. That is, if the pre-weld heat treatment for incomplete solid solution prevention of carbides in the weld heat affected zone, Ac 3 as long as it is heated over 2 minutes immediately above point, since the carbides at the site is completely dissolved, the Type IV damage will not occur.
[0103]
　Meanwhile, more than to heat the steel material from the groove surface, the heat-affected width will expand from the open crest with time into steel interior, sites exposed to just above the transformation point will move to successive steel interior, always short heating become sites likely would remain occur.
[0104]
　Therefore, when performing simple partial heating the groove surface, it should be noted phenomenon such movement of the heat-affected zone. If if HAZ moves constantly toward the steel inner surface, so that would create a generation organization of new Type IV damage to the heating tip section by welding before the heat treatment.
[0105]
　Therefore, the movement behavior of the position of the portion which becomes the transformation temperature of the alpha → gamma transformation was investigated using steel sheets of 30mm thickness. Figure 14 shows a schematic diagram of a temperature propagation conditions for measuring specimen. First, a hole of 0.5mm extending from 1mm pitch surface of the steel sheet from the heating end face 17 of the steel sheet to a thickness of the center position of the steel sheet, bonding the thermocouple to the hole bottom. Then a hole for temperature measurement having an opening, Al 2 O 3 closing filled with powder, to prevent escape of the measuring hole of the heat. On top of that, heated by high-frequency induction heating device from the end, and heating continued as surface layer is always 1050 ° C., it was investigated Propagation temperature at each thermocouple.
[0106]
　Specimens 16 shown in FIG. 14, holes 18 reaching the thickness center 21 for installing the temperature measuring thermocouple 19 from the heating end face 17, along the length of the plate direction 20, located just wide central portion They are arranged in 22. Of these, shown from the heating face 17 changes with time of the temperature in the position of 30mm in Figure 15. The horizontal axis "heating time" in FIG. 15, i.e., the elapsed time from the temperature increase start time, different from the "hold time" (the time elapsed after reaching the target region setting temperature). When heated to 1050 ° C., the temperature of the 30mm position by heating with heat transfer from the heating end face is substantially constant is after about 60 seconds, Ac subsequent Table 1 Steel 3 beyond the transformation point 920 ° C. gradual in the temperature rises, it can be seen that are not found only a small increase of about not nearly change was observed.
[0107]
　Therefore, if the heat is supplied by heat transfer from only one end face of the steel plate, after 60 seconds the temperature gradient is determined that is determined by the heat transfer coefficient of approximately material, if the steel is long enough with respect to heat input It believed to approach the temperature distribution infinity matches the assumed temperature curve and 0 ℃ for. That is, in the site remote than 30 mm, although the maximum heating temperature is gradually lowered from around 920 ° C., also means that the temperature does not rise any more.
[0108]
　Ac 1 The site to be exposed to three or less temperature over 2 minutes under a constant temperature gradient, Ac 1 because there can be heated to a temperature above points, without causing decomposition solute phenomenon brief carbide, Thus residual undissolved carbides, that is, the partial solid solution serving incomplete solid solution of carbides does not occur at all, softening by dislocation density reduction of the matrix phase is no room of occurrence of Type IV damage be caused. Ac 1 point and the Ac 3 sites in the site to be held at an intermediate temperature of points, simply becomes tissue biphasic, this is a state in which by changing the ratio as a function of the maximum heating temperature, which was a γ phase therein in Although degradation dissolution of carbides occurs, if there is no change in the temperature distribution, decomposition dissolution of carbides with γ phase is completely generated, the incomplete solid solution no longer observed. That would not occur incomplete solid solution tissue causes tissue serving carbide, Type IV damage even in a two-phase coexisting temperature range.
[0109]
　The phenomenon described above, by heating the steel sheet test piece shown in FIG. 14 from the open distal end surface, 10 seconds (23), 30 seconds (24), 60 seconds (25), 120 seconds (26), 300 seconds (27 ), 600 seconds (28), a thermocouple indication temperature of each position when only held 7 condition time 1200 seconds (29) records, which can be regarded as the temperature distribution in a depth direction position from the groove surface in, to confirm the state of the temperature change. The results are shown in Figure 16. Position and Ac of 30mm from simultaneously groove surface in FIG. 3 showing the transformation temperature.
[0110]
　Temperature distribution in 120 seconds or more is hardly changed. Heat input from the heat removal and groove surface in the depth direction becomes possible commensurate with substantially per unit area in terms of 120 seconds, it's not fluctuate in this time period.
[0111]
　Accordingly, substantially TYPE IV damage in the steel components shown in the present invention, heating the open distal end surface 1050 ~ 1200 ° C., and if held more than 2 minutes at the same temperature to a range of 30mm depth, welding even taking into account the width change the base material dissolved inclusive and HAZ of the time, it will be has been confirmed does not occur. Even when the temperature of the heating GMA surface was 1200 ° C., although the heating range is widened, the same effect can be obtained, it was more effective.
[0112]
　Note that the steady state of the above such temperature distribution obtained, sufficiently large volume of the steel material, but only if the heating end face regarded diffusion direction of heat long enough. Not only groove surface, a wider range, including other surfaces, or when heating the whole, the temperature distribution of the steel does not become a steady state, moves site constantly become alpha → gamma transformation temperature near because gradually, it is not necessarily guaranteed that a certain place, such as the continues to be heated at the same temperature over 60 seconds. Therefore, in order to achieve this steady state always for the purpose of imparting a temperature distribution in the steady state to the heat sink serving as the base material, the surface area can be heated, is preferably not more than 50% of the total target member. In this case, by heating the position away from the groove, it can be suppressed not be maintained a steady temperature profile.
[0113]
　Furthermore, even when the heat treatment prior to welding only Hirakisakimen, substantially steel to become a finite size, the infinity ideal model environment can not be maintained to 0 ° C., thermal the reflected heat from the end surface opposite the side surface of the steel material, or groove at transfer, the temperature distribution is not a steady state. That 15 can not be reproduced. To achieve the steady state temperature distribution, the length of the base material (dimensions of the heating end face perpendicular direction) is preferably not less than 3 times the pre-weld heat treatment depth.
[0114]
　Also have sufficient space to be a heat sink, or a finite size, Continuing with prolonged heating, there is a possibility that can not be maintained steady state. As the temperature distribution can be reliably steady state, the upper limit of the retention time was 30 minutes. The upper limit of the holding time is more preferably 25 minutes, more preferably from 20 minutes. Retention time is more preferably less than 10 minutes, more preferably not more than 8 minutes.
[0115]
　Incidentally, the steady state of such a heat transfer, assuming the volume of the heat sink can also be calculated three-dimensionally with one-dimensional finite difference method and the FEM analysis. Be effective to ensure entry into force of the present invention, also there is also possible to enhance the effect of the present invention, preferred.
[0116]
　Technology unprecedented to prevent Type IV damage by utilizing the temperature distribution steady state, such as above. Incidentally, the high-B steel since it prevents the Type IV damage due to local heat treatment by utilizing the chemical components do not produce fine grained region, there is no need to confirm the steady state temperature distribution, also take advantage of the state You need not be. Furthermore, in this case it is necessary to add a B 80 ppm or more, but it is to use a tissue memory effect using the residual γ present in significant lath boundaries in B-added steel, subjected to matrix or pre-weld heat treatment reversed the site there may remain although the residual γ is small, toughness tends to easily lowered (JP 2016-14178 and JP 2016-130339 JP). By the present invention has a 50ppm the upper limit of the case of adding B, and on the subject grades are different, the memory effect is not utilized due to residual gamma. Its fine grained region Tissues for to generate the HAZ outer edge, the crystal grain size present inventors that no effect on the creep properties of the ferritic heat-resistant steels are separately verified experimentally. Accordingly, HAZ of organization is different, since the factors that control is only the state of carbide precipitates, and different techniques.
[0117]
　Because it can dispel the concern that residual γ is present, the present invention has the advantage that as compared with the case of adding B 80 ppm or more, toughness is excellent.
[0118]
　Note ferritic heat-resistant steel welded structure according to the present invention, the enforcement width or length of the pre-weld heat treatment, as it is preferable (above 50% or less of the width or length of the structure, the constant temperature distribution When also considering to the state, and more preferably 1/3 or less.). Site which has been subjected to welding before the heat treatment can be distinguished as follows.
[0119]
　If "Enforcement width or length of the post-weld heat treatment" than "before the enforcement width or length of the heat treatment welding" is small, the resulting structure, M 23 C 6 there is a region where type carbide is not precipitated It will be. Therefore, M 23 C 6 If the storage type carbide is not precipitated are present, the area is, it can be determined that whether the boundary pre-weld heat treatment is performed.
[0120]
　On the other hand, be subjected to post weld heat treatment at a site not subjected to welding before the heat treatment, M 23 C 6 can not be improved intergranular coverage by type carbide to 40% or more. Therefore, if than "welding prior to the enforcement width or length of the heat treatment" "Enforcement width or length of the post-weld heat treatment" is large, whether the boundary pre-weld heat treatment has been performed, M 23 C 6 type carbide grain boundary coverage by can be determined by whether at least 40%.
[0121]
　Incidentally, M 23 C 6 whether or M of type carbide 23 C 6 intergranular coverage by type carbide, as described above, can be confirmed by transmission electron diffraction pattern analysis in the electron microscope observation or TEM analysis.
[0122]
　The boundary of the region subjected to post-weld heat treatment may be determined by the presence or absence of lath structure of martensite. That is, in the pre-weld heat treatment site and the vicinity thereof has been subjected, because it is quenched from a temperature lower than the base material, the hardenability is reduced. Therefore, the site and its vicinity pre-weld heat treatment has been performed weak development of Las, Las structure disappears when subjected to post weld heat treatment at the site. Presence of lath structure can be easily determined by TEM or EBSD.
[0123]
　Figure 17 is an electron microscope image of tissue with lath structure. Figure 18 is an electron microscope image of tissue lath structure has been lost. In Figure 17, the tissue is not subjected to the same thermal history as the HAZ, is observed lath boundaries extending in parallel from the upper left of the paper to the bottom right. In Figure 18, results of the post-weld heat treatment of tissue of FIG. 17, lath boundaries disappeared and are changed to the tissue to be referred to as sub-grains to form a substantially isotropic grains.
[0124]
　The ferritic heat-resistant steel welded structure according to the present embodiment, after welding only a portion of the structure heat treatment is performed. Therefore, heat resistant ferritic steel welded structure according to the present embodiment includes a portion having a lath structure, and a portion having no lath structure. According to this embodiment, as compared with the case of performing heat treatment after welding on the overall structure resistance, it is possible to reduce costs, local workability is enhanced. Further, as compared with the case of performing heat treatment after welding on the overall structure resistance, suppressing softening of the tissue, it is possible to improve the high temperature strength and intended creep strength.
[0125]
　Next, we describe the chemical components of the heat-resisting steel of the present invention. Incidentally, "%" for the content of each element means "mass%".
[0126]
　C: 0.05 ~ 0.12%
　C increases the hardenability, carbide M is an important precipitates in the present invention 23 C 6 is an element which forms a. In the present invention, the addition of C 0.05% or more in order to form a martensitic structure required for improving the creep rupture strength. To enhance the precipitation strengthening ability is preferable to add C over 0.07%. On the other hand, when the C content is too high, it precipitates become coarse, to decrease the grain boundary coverage rather, the C amount is 0.12% or less. Also, faster coarsening of carbides generated at the grain boundaries and the amount of C is large, because it can reduce the creep rupture strength, it is most preferable to set the C content to 0.10% or less.
[0127]
　Si: 0.02 ~
　0.45% Si is a deoxidizing element, the addition of 0.02% or more. To enhance the effect of deoxidation, it is preferable to add 0.10% or more Si. Further, Si is effective in improving the oxidation resistance, and more preferably added more than 0.20%. On the other hand, the addition of Si exceeding 0.45%, the toughness is sometimes impaired become oxide containing Si is the starting point of brittle fracture. The addition of excess Si is to replace the Mo or W in solid solution Fe 2 Mo or Fe 2 for promoting the precipitation of W, creep rupture strength may be lowered, Si amount is 0. It is 45% or less. To improve the toughness, Si content is preferably 0.40% or less, more preferably 0.35% or less.
[0128]
　Mn: 0.40 ~
　0.80% Mn is a deoxidizing agent, in the present invention the addition of 0.40% or more. Since toughness and deoxidation is insufficient is lowered, it is preferable to add 0.45% or more Mn. Meanwhile, Mn is an austenite forming element, to accelerate local tissue recovery by increasing the mobility of dislocations, excessive creep characteristics deteriorate when added. In the present invention, in order to secure the creep strength, the Mn 0.80% or less. To further enhance the creep rupture strength, preferably it is 0.70% or less Mn content, more preferably less than 0.60%.
[0129]
　Cr: 8.0 ~
　12.0% Cr increases the hardenability of steel is an important element for precipitation strengthening steel as carbide. To increase the creep rupture strength at 500 ° C. or higher temperatures, M mainly of Cr 23 C 6 ensuring the amount of type carbides, early it is necessary to increase the grain boundary coverage, in the present invention, the addition of 8.0% or more. Considering the steam oxidation resistance, it is preferable to add 8.5% or more Cr. On the other hand, the addition in excess of Cr, at a temperature of 650 ° C. M 23 C 6 accelerates the coarsening of type carbides, because the deterioration of the creep characteristic, the Cr content is 12.0% or less. It is preferable that the Cr content 10.5% or less, and more preferable amount is not more than 9.50%.
[0130]
　Mo: 0.30 ~
　1.30% Mo is Fe 2 mainly precipitated in large angle grain boundaries as the intermetallic compound in the form of a Mo. High-angle precipitation of grain boundaries M 23 C 6 since the deposited so as to fill the gap type carbide precipitates spacing (distance between particles) on the grain boundaries becomes even smaller, in the long Creep environment high-angle grain boundaries There is left on columns, even after moving, between this requires a high stress for dislocations to break through, which contributes to creep strength improving. Was added to 0.30% for creep rupture strength increase, because of the grain boundary coverage improvement is preferably added more than 0.80%. On the other hand, an excessive addition of Mo, Fe 2 since coarsening of Mo type intermetallic compound is increased, it is preferably not more than 1.10% of Mo content. If a long time is desired to further improve the creep strength is necessary to strictly control the addition of less than 1.05% is more preferable.
[0131]
　N: 0.003 ~ 0.080%
　N is an element forming a nitride is an effective element for to precipitate VN improve the initial creep strength. To enjoy this effect, to the N as a minimum quantity it contains more than 0.003%. Further, Al is mixed from the refractory, etc. are combined with N, it may not be sufficiently ensured N amount for VN generated. Considering such a case, N amount is preferably added 0.010% or more. However, when the N content exceeds 0.080%, the sometimes either VN Gakaette coarsening, the effect of improving the creep strength for a long time deposition is accelerated not expressed, and 0.080% the upper limit to. Further, N, since an element which embrittle the steel radiates by neutron irradiation, when using heat-resistant steel to the plant or the like of the nuclear power, be a N content below 0.060% preferable.
[0132]
　Nb: 0.005 ~
　0.10% Nb contributes to precipitation strengthening by precipitating as NbC carbides in the grains. If VN composite deposition can be more effectively suppressed the movement of dislocations. Effect is manifested by the addition 0.005%. Utilizing a more stable NbC carbides, for example, to acquire the high-temperature strength is preferably added 0.010% or more. Further preferred additives lower limit is 0.020%. The addition upper limit is set to 0.10% from the viewpoint of the creep strength decreases prevented by early coarsening. In petrochemical plants or the like to emphasize the toughness is preferably limited from the viewpoint of brittle crack propagation promote suppress the addition amount below 0.08% by NbC. It is more preferable that the Nb content below 0.06% in the case of complex deposition effect significantly expectations and said was finely and uniformly dispersed NbC VN.
[0133]
　V: 0.005 ~ 0.50%
　V is an element forming nitrides in combination with N, contributes to precipitation strengthening by precipitating in VN forms in the grains. 0.005% VN precipitation of 600 ° C. In addition, seen from 1000 hours, which contributes to creep strength improving. Preferably the addition of 0.010% or more in order to obtain the composite precipitation strengthening more effectively with NbC, more preferably 0.015% or more. Ferritic heat-resistant steel to which the present invention is applied is a principal strengthening precipitation of large angle grain boundaries, but not large in effect rather long side of intragranular strengthening, enabled when to expect even a little creep strength improving it is a strengthening element. However, under long-term creep environment when added in excess of 0.50% (V, Nb) 2 transforms into an early Z-phase growing such as N, Further, VN is causing a decrease in toughness when coarse. It is therefore desirable to 0.40% or less in the case of adding from the viewpoint of toughness deterioration prevention. More preferred V content is 0.35% or less.
[0134]
　In the present invention, limit cold iron source and such scraps, Ni which is mixed as an impurity from the refractory, Cu, Al, the content of B in the following ranges.

claims

The base material, heat affected zone, and a method for producing a ferritic heat-resistant steel welded structure comprising a weld metal,
　chemical composition, in
　mass%, C: 0.05 ~
　0.12%, Si: 0.
　~
　0.45%

　N:02, 0.003 ~ 0.080%, Mo: 0.30 ~ 1.30% ,
　Nb:
　0.005
　~ 0.10%, V: 0.005
　~ 0.50%, W: 0 ~ 2.0%,
　Re: 0 ~ 3.5%, Ti: 0 ~ 0.15%, 　Zr:
　0 ~ 0.15%, 　Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, 　Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and 　La: 0 ~ 0.0500%, 　contain, 　Ni: less than 　0.20% Cu: less than 　0.20% B: less than 　0.005% Al: less than 0.025%,

　P: less than
　0.020% S: less than 0.010%, and
　O: less than 0.010%,
　limited to,
　the balance comprising the steps of preparing the base material is Fe and impurities,
　open to the base material forming a first,
　a surface of the groove, the area between the position apart pre-weld heat treatment depth of 30 ~ 100 mm from the surface of the groove, heated to a temperature of 1050 ~ 1200 ° C., and before the heat treatment step welding of holding 2-30 minutes at that temperature,
　after the pre-weld heat treatment step, a welding step of forming the weld metal by welding the groove,
　after the welding step, the surface of the groove the region between the position apart a distance from the surface below 100mm the pre-weld heat treatment over a depth of the groove, heated to a temperature of 720 ~ 780 ° C., the temperature more than 30 minutes and formulas (1) and a post-weld heat treatment step of holding time satisfying, full Method for producing a ferrite heat-resistant steel welded structure.
　　(Log (t) +12) · (T + 273) <13810 (1)
　where, t is the retention time, T is the temperature. unit of t is the time, the unit of T is ℃. Log is the common logarithm.
[Requested item 2]
　A method according to claim 1,
　said welding before the heat treatment step, performed in two or more times, the manufacturing method of the heat resistant ferritic steel welded structure.
[Requested item 3]
　A method according to claim 1 or 2,
　M is deposited on the high-angle grain boundaries of the HAZ 23 C 6 average particle diameter of type carbides is not more 300nm or less,
　the on the high-angle grain boundaries M 23 C 6 mean particle surface distance of type carbides is not more 200nm or less,
　the M of the high-angle grain boundaries 23 C 6 coverage by type carbides is 40% or more, a manufacturing method of the heat resistant ferritic steel welded structure .
　However, the M 23 C 6 M of type carbide is Cr, Fe, Mo and W 1, two or more 70 atomic% or more in total of.
[Requested item 4]
　A process according to any one of claims 1 to 3,
　the chemical composition of the base metal, by
　mass%, W: 1.5 ~ 2.0%, and
　Re: 0.5 ~ 3 .5%,
　containing one or two kinds selected from the group consisting of the method of ferritic heat resistant steel welded structure.
[Requested item 5]
　A process according to any one of claims 1 to 4,
　the chemical composition of the base metal, by
　mass%, Ti: 0.005 ~ 0.15%, and
　Zr: 0.005 ~ 0 .15%,
　containing one or two kinds selected from the group consisting of the method of ferritic heat resistant steel welded structure.
[Requested item 6]
　A process according to any one of claims 1 to 5,
　the chemical composition of the base metal, by
　mass%, Ca: 0.0003
　~ 0.0050%, Mg: 0.0003 ~ 0.
　% 0050,
　Y: 0.0100 ~ 0.0500%, Ce: 0.0100 ~ 0.0500%, and
　La: 0.0100 ~ 0.0500%,
　1 or more kinds selected from the group consisting of containing, manufacturing method of ferritic heat resistant steel welded structure.
[Requested item 7]
　The base material, heat affected zone, and a heat resistant ferritic steel welded structure comprising a weld metal,
　the chemical composition of the base material, in
　mass%, C: 0.05 ~
　0.12%, Si: 0.
　~
　0.45%

　N:02, 0.003 ~ 0.080%, Mo: 0.30 ~ 1.30% ,
　Nb:
　0.005
　~ 0.10%, V: 0.005
　~ 0.50%, W: 0 ~ 2.0%,
　Re: 0 ~ 3.5%, Ti: 0 ~ 0.15%, 　Zr:
　0 ~ 0.15%, 　Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, 　Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and 　La: 0 ~ 0.0500%, 　contain, 　Ni: less than 　0.20% Cu: less than 　0.20% B: less than 　0.005% Al: less than 0.025%,

　P: less than
　0.020% S: less than 0.010%, and
　O: less than 0.010%,
　limited to,
　balance being Fe and impurities,
　deposited on high-angle grain boundaries of the weld heat affected zone M 23 C 6 average particle diameter of type carbides is not more 300nm or less,
　wherein M on high-angle grain boundaries 23 C 6 mean particle surface distance of type carbides is not more 200nm or less,
　the M of the high-angle grain boundaries 23 C 6 type carbide by coverage is 40% or more, heat resistant ferritic steel welded structure.
　However, the M 23 C 6 M of type carbide is Cr, Fe, Mo and W 1, two or more 70 atomic% or more in total of.