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]
　Further, the boiler realizing such extreme high temperature and high pressure environment, or in any of the reactor, the overall structure is not exposed all high temperature. Steam when the boiler water, then the supercritical water, a than is gradually heated and ultra-supercritical water, low alloy ferritic heat-resistant steel of high strength is used at a relatively low temperature region before reaching the hot . They contain 1-7% Cr, it is used in a temperature range of approximately 450 ~ 580 ° C.. In addition to site and low portions high temperatures in the reactor is present in a single reaction vessel, since the temperature of the refined oil before desulfurization reactor entrance is not so high temperature, similarly to the site low alloy ferritic heat-resistant steel used.
[0008]
　Differences of high Cr ferritic heat-resistant steel and low alloy ferritic heat-resistant steel and the difference between the high-temperature corrosion due to the Cr content, a gamma → alpha transformation phenomenon also Cr is involved. The former is mainly composed mainly of martensite, but some bainite is mixed, majority is a starting organization the martensitic structure. That is, the minimum configuration dislocation structure is lath structure, block structures are present so as to include this. In low-alloy ferritic heat resistant steel structure has as ferrite those principals and bainite is mainly a bainite structure with a transformation of shearing, since transformation point is not as low as martensite, internal dislocations mobility is high, lath structure itself is not that most occur. That is, almost no lath structure in the low alloy ferritic heat-resistant steel, the minimum configuration unit or block structure, or a ferrite grain itself. This high-temperature strength of both with each other to greatly affect the turn creep strength.
[0009]
　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.
[0010]
　Ferritic heat resistant steels, if the BCC structure starting tissue (ferrite, bainite, or martensite), having a phase transformation temperature, the so-called transformation point during stable γ phase in a stable α phase and hot at room temperature. Upon cooling the ferritic steel from hot, the 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.
[0011]
　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.
[0012]
　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.
[0013]
　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.
[0014]
　Traditionally, the same phenomenon has been observed in low-alloy ferritic heat-resistant steels, until 50 years ago, has been described, such as in the grain boundary sliding phenomenon due to the effects, or fine particles of the impurity elements. But the research and development in recent years, the site to be heated briefly to the transformation point or higher, incomplete dissolution of carbides at the site to be heated to just above particular transformation point - heat history due to cause reprecipitation carbide coarsening of cause It came to be considered the main cause. Because whether the tissue is fines little effect on the creep strength of ferritic heat-resistant steel, categorizing sites tissue type, tissue structure itself is not the cause of strength reduction, to enhance the tissue over a long period of time It precipitates is by being lost its effect coarsened from the initial.
[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]
　This phenomenon itself is never changed in amount of Cr content, the temperature range in which the phenomenon occurs, the form and the strengthening mechanism of precipitates coarsened there is a difference. This difference is one Type also affects the suppression techniques IV damage, the present invention is to achieve the focused valid Type IV damage prevention to the low-alloy ferritic heat resistant steels in this respect.
[0017]
　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. Also occur in low-alloy heat-resistant steel containing 1 to 7% of Cr was used as a primary purpose use at low temperatures. The application temperature is of course the thermal power plants, petroleum desulfurization reactor comprising conditions having a high temperature above 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.
[0018]
　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.
[0019]
　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.
[0020]
　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.
[0021]
　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.
[0022]
　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.
[0023]
　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.
[0024]
　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.
[0025]
　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.
[0026]
　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.
[0027]
　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 ferritic heat resistant steel B contains only 50ppm or less, low alloy ferritic heat resistant steel containing in particular from 1 to 7% Cr It has not been proposed to.
Disclosure of the Invention
[0028]
　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.
[0029]
　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: 0.08 ~ 0.15% , Si: 0.02 ~ 0.45%, Mn: 0.40 ~ 0.80%, Cr: 1.0 ~ 7.0%, N: 0.003 ~ 0.020%, Mo: 0.20 ~ 1.10%, Nb: 0.005 ~ 0.08%, V: 0.005 ~ 0.40%, W: 0% to 1.5 % less, Ti: 0 ~ 0.12%, Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and La : 0 to 0.0500%, containing, B: less than 0.005% Al: less than 0.025% P: less than 0.020% S: 0.01 % Less, and O: less than 0.010%, limited to, the remainder comprising the steps of preparing the base material is Fe and impurities, forming a groove in said base material, and a surface of said groove the area between the surface position apart pre-weld heat treatment depth of 10 ~ 50 mm from the groove, heated to a temperature of 950 ~ 1050 ° C., before the heat treatment step welding of holding 10 to 30 minutes at that temperature When, 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 pre-weld heat treatment depth from the surface of the groove above a region between 100mm apart following distance position, and heated to a temperature of 680 ~ 750 ° C., and a post-weld heat treatment step of holding time meet the temperature more than 30 minutes and equation (1).
　　(Log (t) +10) · (T + 273) <10539 (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.
[0030]
　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, the chemical composition but, by mass%, C: 0.08 ~ 0.15% , Si: 0.02 ~ 0.45%, Mn: 0.40 ~ 0.80%, Cr: 1.0 ~ 7.0%, N: 0.003 ~ 0.020%, Mo : 0.20 ~ 1.10%, Nb: 0.005 ~ 0.08%, V: 0.005 ~ 0.40%, W: 0% or more 1 less than .5%, Ti: 0 ~ 0.12 %, Ca: 0 ~ 0.0050%, Mg: 0 ~ 0.0050%, Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and La: 0 ~ 0.0500%, contain, B: less than 0.005%, Al: less than 0.025%, P: less than 0.020%, S: 0.0 Less than 0%, and O: less than 0.010%, limited to the balance is the base material is Fe and impurities, M deposited on high-angle grain boundaries of the HAZ 23 C 6 of type carbide average particle size is at 200nm or less, wherein M on high-angle grain boundaries 23 C 6 mean particle surface distance of type carbides is not more 150nm or less, the M of the high-angle grain boundaries 23 C 6 coverage by type carbide is it is equal to or greater than 50%. 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.
[0031]
　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
[0032]
[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.
FIG. 7 is, M in HAZ 23 C 6 is a diagram showing the relationship between Charpy impact absorption energy at an average particle diameter and 0 ℃ the type carbide.
FIG. 8 is, HAZ of M 23 C 6 550 ° C. of inter-particle distance and welded joint is a graph showing the relationship between 100,000 hours estimated creep rupture strength.
[9] FIG. 9 is a graph showing post-weld heat treatment conditions.
FIG. 10 is a heat treatment time and 550 ° C. after welding is a diagram showing the 100,000 hours estimated creep rupture strength relationship.
[11] FIG 11 is a graph showing the relationship between the retention time of the heat treatment after welding and the welding joint toughness.
[12] FIG 12 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.
[13] 13, M 23 C 6 average particle size and 550 ° C. of type carbide is a graph showing the relationship between 100,000 hours estimated creep rupture strength.
FIG. 14 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. 15 is large angle M on the grain boundaries 23 C 6 coverage and 550 ° C. by type carbide is a graph showing the relationship between 100,000 hours estimated creep rupture strength.
[16] FIG 16 is a schematic diagram of a 30mm thickness Temperature propagation state measuring steel plate test piece (3-view drawing).
FIG. 17 is the time of heating the weld GMA surface 950 ° C., which is a graph showing the elapsed time related to the temperature in the depth direction 30mm position.
FIG. 18 is the time of heating the weld GMA surface 950 ° C., which is a graph showing the time variation of the temperature distribution in the depth direction.
[19] FIG. 19 is an electron micrograph of a tissue having a lath structure.
FIG. 20 is an electron micrograph of the tissue lath structure has been lost.
DESCRIPTION OF THE INVENTION
[0033]
　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 product of interest and from 1.0 to 7.0%. From the viewpoint of corrosion resistance application temperature range 450 ° C. or higher, the creep rupture strength of 100,000 hours considered as a function of temperature, breaking strength of 550 ° C. as the representative value is targeted to be at least 100 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.
[0034]
　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.
[0035]
　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.
[0036]
　For techniques underlying the present invention will be described below with experimental results.
[0037]
　Experimental results shown below, were obtained using the following as the test piece and various experiments produced.
[0038]
　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 30 minutes oven was reheated to 1150 ° 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. Hot rolled specimens, in an electric resistance heating furnace of 980 ° C. and heating maintained for 90 minutes or more, then allowed to cool to room temperature, addition then returned 2 hours baked at 740 ° C.. The bainite structure structure at this stage is present in the tissue, M 23 C 6 that carbides mainly of type carbides and Mo are mainly precipitated, optical microscopy, transmission electron microscopy (TEM), scanning electron microscope (SEM), and 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).
[0039]
[Table 1]

[0040]
　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. Furthermore, precipitates Mo mainly of Mo 2 was C-type carbides. The former (the tiny ones cubic) lump in on large angle grain boundaries, the latter was confirmed to have precipitated the needle in the grains.
[0041]
　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.
[0042]
　2, for explaining a method for measuring coverage by HAZ organization model and the grain boundary precipitates (present three in the figure, the most thick solid line.) Grain boundary 9 high-angle carbide tissues including it is a conceptual diagram of the grain boundary covered by. Incidentally, L in FIG. 2 1 ~ L 11 is M 23 C 6 type of occupation length 7 of the grain boundary carbide large angle grain boundaries every shown separately in the in the field of view, La, Lb, Lc, respectively high-angle grain boundaries indicating the length of 8.
[0043]
　"Grain boundary coverage" as shown in FIG. 2, (in FIG. 2, L large angle precipitates length sum of the grain boundary 9 1 ~ L 11 sum up) the sum of the large angle grain boundary lengths a value obtained by dividing the (La + Lb + Lc), 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.
[0044]
　"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).
[0045]
　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.
[0046]
　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.
[0047]
　λａｖｅ＝１．５［ｌｓ］ａｖｅ－１．１［ｄｓ］ａｖｅ　　　（２）
[0048]
　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. Further, (2) is to vary depending on the steel type and the heat treatment conditions, the thus for example, a high Cr ferritic heat-resistant steel and austenitic heat-resistant steels can not be applied.
[0049]
　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.
[0050]
[Table 2]

[0051]
(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 10 minutes at that temperature holding leave completely dissolved again by suppressing the coarsening itself by weld heat affected carbide through undissolved carbides.
[0052]
　Heat treatment prior to welding heats the groove to a temperature of 950 ~ 1050 ° C., the site to be HAZ after welding is 10 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 10 minutes or more, such that the temperature of interest the temperature pattern of the heating device it is sufficient to determine.
[0053]
　Later, carried out immediately before the welding, a heat treatment for, Type IV damage prevention as "pre-weld heat treatment".
[0054]
　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 30mm 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.
[0055]
　3, if the holding time is less than 10 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 above 950 ° C., always undissolved carbides regardless of the heating temperature if the holding time is more than 10 minutes does not remain at all, had completely dissolved.
[0056]
　On the other hand, if the heating temperature is lower than 950 ° C., the steel Table 1 essentially becomes a two-phase region a heated state, carbides form at a site that does not exceed the transformation temperature decomposition solid solution which is slightly coarsened as compared with the room temperature there is no. 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 two-phase zone heating, indeed even the area where there is no incomplete solid solution of carbides, any 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.
[0057]
　Accordingly, the temperature of the pre-weld heat treatment required to fully prevent Type IV damage in the present invention is 950 ° C. or more, the retention time is found to be at least 10 minutes. Incidentally, the heat treatment prior to welding at 1050 ° C. or higher temperatures, 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 in 1050 ℃ temperature. In the case of high Cr ferritic heat-resistant steel (Cr amount is more than 8%) is, M 23 C 6 type carbide is stable relatively to a high temperature, the maximum temperature is acceptable even higher. However, in low alloy Cr ferritic heat-resistant steel, since the carbides are relatively unstable, upper-limit temperature is set lower inevitably.
[0058]
　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 the 950 ~ 1050 ℃.
[0059]
　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 welding field destination 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 950 ° C. or higher than 10 minutes as heat treatment before the welding deeper than sites HAZ outer edge is assumed to be located.
[0060]
　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 about thickness 30mm is less than 3mm, HAZ width, such as the HAZ width exceeding 10mm in heavy gauge material of 100mm than there can be no normal. Substantial heat input is 5 kJ / mm, no more high heat input welding is not applicable. Maximum HAZ width in this case is that in the subject grades of the present invention is 5 mm, 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.
[0061]
　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 3mm as well. Amount with the dissolved varies depending steel type, the result value is specific to the subject grades of the present invention.
[0062]
　From the above, so that the pre-weld heat treatment at a depth from the groove surface to 8mm in total may be performed 950 ~ 1050 ° C. at 10 minutes or more.
[0063]
　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. 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 10 mm.
[0064]
　Considering all of these, the weld before the heat treatment depth is required to be 10mm 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 10mm 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 10mm pre heat treatment depth welding in any way.
[0065]
　That is, the groove surface, it always becomes a necessary condition to hold up to the position of the boundary lines 13 and 14 to be 10mm or more positions 1050 ~ 1200 ° C. over 10 minutes.
[0066]
　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 10mm 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 10 minutes or more, it is preferable to retain the 950 ~ 1050 ° C..
[0067]
　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, 950 ~ 1050 ° C. temperature above 10 minutes it is preferably maintained.
[0068]
　Incidentally, when the pre-heat treatment depth welded to 50mm than, be heating the preform extensive enough could not be secured (for this reason the holding time at the temperature range of interest, "Partial detailed in the pre-weld heat treatment of features. "). For this reason, the maximum value of the pre-weld heat treatment depth and 50 mm. This range for the physical constants change such as the heat transfer rate change would steels of interest are invention steels specific values.
[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 over 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 950 ~ 1050 ° 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 is more than 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. M 23 C 6 but type carbide is the expected similar effects when it is stable up to high temperatures, in the present invention is to apply a relatively small target grades of Cr content, the effect can not be expected.
[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]
　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 10 ~ 50 mm from the surface of the groove, to a temperature of 950 ~ 1050 ° C. heated, held for 10 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 10 to 30 minutes in total. The cooling after the heat treatment, for example, cooling.
[0073]
(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.
[0074]
　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 680 ~ 750 ° 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).
[0075]
　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 bainite structure of relatively high hardness weld metal occurs been hardened, brittle fracture of the weld metal, or to prevent brittle fracture of the bond it is effective in.
[0076]
　In the present invention, once the base material as a pre-weld heat treatment from heating to γ ​​region, the base material if the heating area is also similarly quenching the as bainite and high hardness as compared to the ferrite phase. 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.

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: 0.08 ~
　0.15%, Si: 0.
　~
　0.45%

　N:02, 0.003 ~ 0.020%, Mo: 0.20 ~ 1.10% ,
　Nb:
　0.005 ~ 0.08%, V: 0.005 ~ 0.40%,
　W: 0% or more and less than%
　1.5,
　Ti: 0 ~ 0.12%, Ca: 0 ~ 0.0050
　%,
　Mg: 0 ~ 0.0050%,
　Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and
　La: 0 ~ 0.0500%,
　contain,
　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 the steps of preparing said base material is Fe and impurities,
　forming a groove in said base material,
　and the surface of the groove, pre-weld heat treatment depth of 10 ~ 50 mm from the surface of the groove the region between the spaced apart position, 950 heated to ~ 1050 ° C. of temperature, and pre-weld heat treatment step of holding 10 to 30 minutes at that temperature,
　after the pre-weld heat treatment process, and welding the groove wherein the welding step of forming the weld metal,
　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 said groove, 680 heating-to a temperature of 750 ° C., and a post-weld heat treatment step of holding time satisfies more than 30 minutes at that temperature and equation (1), the manufacturing method of the heat resistant ferritic steel welded structure.
　　(Log (t) +10) · (T + 273) <10539 (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 200nm or less,
　the on the high-angle grain boundaries M 23 C 6 mean particle surface distance of type carbides is not more 150nm or less,
　the M of the high-angle grain boundaries 23 C 6 coverage by type carbides is 50% 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 material, in
　mass% W: 0.5% or more and less than 1.5%, and
　Ti: 0.05 ~ 0.12%,
　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%, 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 6]
　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%,
　the chemical composition, by mass%,
　C: 0.08 ~ 0
　% .15,

　Si: 0.02 ~ 0.45%, Mn: 0.40 ~
　0.80%, Cr: 1.0 ~ 7.0%, N: 0.003 ~
　0.020%, Mo:
　~ 1.10 0.20,
　Nb: 0.005 ~ 0.08%, V: 0.005 ~
　0.40%, W: 0% or more and less than%
　1.5, Ti: 0 ~ 0.12%, 　Ca:
　0 ~ 0.0050%, Mg: 0 ~ 0.0050%, 　Y: 0 ~ 0.0500%, Ce: 0 ~ 0.0500%, and 　La: 0 ~ 0.0500%, 　contain, 　B: less than 　0.005% Al: less than 　0.025% P: less than 　0.020% S: less than 0.010%, and 　O: 0.010% Not ,

　Limited to,
　balance being Fe and impurities,
　M deposited on high-angle grain boundaries of the HAZ 23 C 6 average particle diameter of type carbides is not more 200nm or less,
　wherein M on the high-angle grain boundaries 23 C 6 mean particle surface distance of type carbides is not more 150nm or less,
　the M of the high-angle grain boundaries 23 C 6 coverage by type carbides is 50% 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.