[0001]The present invention relates to a welded structure members.
BACKGROUND
[0002]Thermal power, the boiler, such as industrial, petroleum, fossil fuels such as coal used as a fuel. Fossil fuels, because it contains sulfur (S), sulfur oxides (SOx) are produced in the exhaust gas when burned. When the temperature of the exhaust gas is decreased, SOx is sulfuric acid reacts with the moisture in the gas. Thus, condensation with the component surface in below the dew point temperature, corrosion (sulfate dew-point corrosion) occurs. Similarly, in the flue gas desulfurization equipment used in various industries, if the exhaust gas containing SOx flows, sulfuric dew-point corrosion occurs when the temperature decreases. Conventionally, to prevent sulfuric acid dew point corrosion, it retained exhaust gas temperature above 0.99 ° C..
[0003]
　However, from the viewpoint of increasing the effective use of energy in recent years demand for energy in order to as effectively as possible collecting the thermal energy, for example, the exhaust gas temperature from the heat exchanger there is a movement to reduce to below the dew point of sulfuric acid, relative to sulfuric acid material having resistance has become necessary.
[0004]
　With WO 99/009231 (Patent Document 1), excellent corrosion resistance in an environment (50 ~ 100 ℃ 40 ~ 70% at a temperature of concentrations of the environment in which sulfuric acid is condensation) high concentrations of sulfuric acid condenses as austenitic stainless steel having good hot workability, by mass%, C: 0.05% or less, Si: 1.0% or less, Mn: 2.0% or less, P: 0.04% or less, S: 0.01% or less, Ni: 12 ~ 27%, Cr: 15 ~ 26%, Cu: 8.0% exceeds 3.0% or less, Mo: 2.0% to beyond 5.0% hereinafter, Nb: 1.0% or less, Ti: 0.5% or less, W: 5.0% or less, Zr: 1.0% or less, Al: 0.5% or less, N: less than 0.05%, Ca: 0.01% or less, B: 0.01% or less, rare earth elements: total includes 0.01% or less, the balance being Fe and not Austenitic stainless steels have been disclosed which consists avoid impurities.
[0005]
　The JP-A 4-346638 (Patent Document 2), a hot workability excellent sulfidation acid dew-point corrosion of stainless steel, by mass, C: 0.050% or less, Si: 1.00% or less, Mn : 2.00% or less, P: 0.050% or less, S: 0.0050% or less, Ni: 8.0 ~ 30%, Cr: 15 ~ 28%, Mo: 3% to 7% greater than or less, Cu : 5% more than 2% or less, N: 0.05 ~ 0.35%, B: containing 0.0015% of 0.010% than or less, O is at 60ppm or less, moreover, Cu in the alloy, Mo, stainless steel in which the content of B and O have the relation 10000 × B / (Mo + Cu + 1000 × O) = 1.5 ~ 10.0 are disclosed.
[0006]
　In JP-2001-107196 (Patent Document 3), as an excellent austenitic steel welded joint resistance to weld cracking exhibit good corrosion resistance under acid environment, in mass%, C: 0.08% or less, Mn: 3%, P: 0.02% or less, Ni: 4 ~ 75%, Cr: 15 ~ 30%, Al: 0.5% or less, N: 0.1% or less, O (oxygen): 0.1 % or less, Nb, Ta, 0.1 ~ 5% in total of at least one or more of Ti and Zr, 0 ~ 20% in total of either or both of Mo or W, Co: 0 ~ 5% , V: 0 ~ 0.25%, B: 0 ~ 0.01%, Ca: 0 ~ 0.01%, Mg: 0 ~ 0.01%, REM: 0 ~ comprises 0.01%, further wherein in "Si ≦ 0.15 (Nb + Ta + Ti + Zr) +0.25" satisfies the Si, 0 ~ 8% or less, and the expression " u ≦ 1.5 (Nb + Ta + Ti + Zr) +4.0 Cu satisfying ", contains the S satisfying the formula" S ≦ 0.0015 (Nb + Ta + Ti + Zr) +0.003 ", balance being substantially Fe, Ni, Co and the total content of Cu austenitic steel welded joint is disclosed having a weld metal portion made of a chemical composition satisfying the formula "Ni + Co + 2Cu ≧ 25".
CITATION
Patent Document
[0007]
Patent Document 1: WO 99/009231
Patent Document 2: JP-A 4-346638 Patent Publication
Patent Document 3: JP 2001-107196 JP
Summary of the Invention
Problems that the Invention is to Solve
[0008]
　In austenitic stainless steel itself having a chemical composition described in Patent Documents 1 and 2 exhibit good corrosion resistance under acid environment. However, in the case of the welding structural members using such austenitic stainless steel, the corrosion at the interface between the base metal and the weld metal proceeds, sometimes dissimilar metal corrosion occurs.
[0009]
　Further, if the austenitic steel welded joint having a weld metal having a chemical composition described in Patent Document 3 is excellent in resistance to weld cracking exhibit good corrosion resistance under acid environment. However, even in austenitic steel welded joint having a weld metal that is proposed in this document, the chemical composition of the base material may be dissimilar metal corrosion occurs.
[0010]
　Thus, conventionally, by the example it does not consider the dissimilar metal corrosion occurring between the base metal and the weld metal.
[0011]
　The present invention aims at providing a welding structural member comprising an austenitic stainless steel joint capable of suppressing the dissimilar metal corrosion occurring between the base metal and the weld metal.
Means for Solving the Problems
[0012]
　The present inventors have made intensive studies in order to achieve the above object, we found the following findings.
[0013]
　(A) in an environment where a high concentration of sulfuric acid condenses, in order to impart good corrosion resistance to austenitic stainless steels, be contained Cu more than 3.0%, it is contained Mo exceeding 2.0% it, be contained from 15.0 to 20.0% of Cr, by managing the content of N to less than 0.05%, important to adjust the composition of the passive film formed on the steel surface it is.
[0014]
　To (b) generally, Mo is to form a dense passivation film at the steel surface with Cr, it is known to provide good corrosion resistance to the steel. However, as described above, the welding structural members when exposed to a corrosive environment, the dissimilar metal contact corrosion problems. Here, in the welding structural members, the oxidation film is formed on the weld metal surface, the oxide film may be a dense passivation film, but 0.10 percent Mo content of the weld metal exceeds 6. to be in the range of less than 0%, passivation film formed on the surface of the welded metal portion will contain an oxide film unstable Mo, also inhibit thickening of Ni and Cu to the film, corrosion resistance in the dissimilar metal contact corrosion environments where high concentrations of sulfuric acid condenses to deteriorate. In contrast, when the Mo content of the weld metal is less than 0.10% is the weld metal surface enriched is Ni or Cu in the passive film of Cr entities that form, it exhibits excellent corrosion resistance It is. Therefore, Mo content in the base metal as well as management to 5.0% or less exceed 2.0%, Mo content of the weld metal is important to limit below 0.10%.
[0015]
　(C) the dissimilar metal contact corrosion, unlike conventional corrosion (low potential) less noble the potential of the metal is high, the dissolution of Fe and Cr are accelerated. When the base material of austenitic stainless steel contains a predetermined amount of Co and / or Sn, in such bimetallic corrosion environment, it can reduce the dissolution rate of Fe and Cr, bimetallic corrosion it can be dramatically improved corrosion resistance in the environment.
[0016]
　The present invention has been made based on the above findings, and the gist of the invention described below.
[0017]
　A welded structure member comprising an austenitic stainless steel fittings,
the chemical composition of the base material, in
mass%, C: 0.05% or
less, Si: 1.0% or
less, Mn: 2.0% or
less, P 0.04% or
less, S: 0.01% or
less, Ni: 12.0
~ 27.0%, Cr: less than 15.0% or more
20.0%, Cu: more than 3.0% 8. 0% or less,
Mo: 5.0% exceeds 2.0% or
less,
Nb: 0 ~ 1.0%,
Ti: 0 ~ 0.5%, Co: 0 ~
0.5%, Sn: 0 ~
% 0.1,
W: 0 ~
5.0%, Zr: 0 ~ 1.0%, Al: 0
~ 0.5%, N: less than%
0.05, Ca: 0 ~
0.01%, B : 0 to 0.01% or
a rare earth element: 0 to 0.01% in total,
the balance is Fe and inevitable impurities,
the chemical composition of the weld metal, in
mass% C: 0.10% or less,
Si: 0.50% or
less, Mn: 3.5% or
less, P: 0.03% or
less, S: 0.03% or
less, Cu: 0.50% or
less, Ni: 51.0% or more 80.0 % or
less, Cr: 14.5
~ 23.0%, Mo: 0.10% or
less, Al: 0.40% or
less, Nb, 1 or more selected from Ta and Ti: less 4.90% in total ,
Co: 2.5% or
less, V: 0.35% or
less, W: 4.5% or less,
the balance being Fe and unavoidable impurities, the welding structural members.
Effect of the invention
[0018]
　According to the present invention, the austenitic stainless steel fittings, it is possible to suppress the dissimilar metal corrosion occurring between the base metal and weld metal, at a temperature of the environment (50 ~ 100 ° C. to a high concentration of sulfuric acid condenses It is 40 to 70% strength sulfuric acid is excellent in corrosion resistance in an environment) to condensation. Therefore, it is suitable as welding structural members used in such environments. The austenitic stainless steel fittings, for example, an austenitic stainless steel tube fittings.
DESCRIPTION OF THE INVENTION
[0019]
　It will be described below in detail welded structure members of the present invention. In the following description, "%" for the content means "mass%".
[0020]
　1. Chemical composition of the base material
　is described in detail below the chemical composition of the base metal.
[0021]
　C: 0.05% or less
　C is an element effective for increasing the strength. However, C is combines with Cr to form a Cr carbide in grain boundaries, to lower the intergranular corrosion resistance. Therefore, the content is 0.05% or less. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.002%. If it is necessary to increase the strength, it is preferable to contain more than 0.03%. However, if the securing of corrosion resistance is a priority, the content of C may lower it is desirable to 0.03% or less.
[0022]
　Si: 1.0% or less
　Si may or may not be added, be added, has a deoxidizing effect. However, to facilitate a reduction in hot workability when its content exceeds 1.0%, processing into products on an industrial scale is extremely difficult in the case of containing Cu of more than 3.0%. Therefore, Si content is 1.0% or less. In order to ensure this effect, it is preferable to contain 0.05% or more. Incidentally, when very low Al content for the purpose of improving the hot workability, it is preferable to sufficiently perform the deoxidation by 0.1% or more Si.
[0023]
　Mn: 2.0% or less
　Mn may or may not be added, be added, to increase the hot workability by fixing the S, has the effect of stabilizing the austenitic phase. However, when the content exceeds 2.0%, the effect is saturated, which only costly. Therefore, the content of Mn and 2.0% or less. In order to ensure the above-mentioned effects, Mn is preferably set to content of 0.1% or more.
[0024]
　P: 0.04% or less
　P, so degrades the hot workability and corrosion resistance, its content is preferably as low, in particular, corrosion resistance exceeds 0.04% in the "environment of high concentrations of sulfuric acid condenses" degradation is significantly of. Accordingly, the content of P is set to 0.04% or less. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.003%.
[0025]
　S: 0.01% or less
　S is an element degrading the hot workability, the content is better as low as possible. In particular, leading to hot workability of significant degradation exceeds 0.01%. Therefore, the content of S is 0.01% or less. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.0001%.
[0026]
　Ni: 12.0 ~ 27.0%
　Ni, as well as has the effect of stabilizing the austenite phase and also acts to improve the corrosion resistance of in a "high concentration of sulfuric acid environment condensation". In order to sufficiently secure such effects, it is necessary to contain Ni in an amount of 12.0%. However, when the content exceeds 27.0%, the effect is saturated. Moreover, since Ni is an expensive element, it lacks economical and cost becomes extremely high. Therefore, the content of Ni and 12.0 to 27.0%. In order to ensure sufficient corrosion resistance in a "high concentration of sulfuric acid environment condenses" is preferably contains a Ni in an amount exceeding 15.0%, containing Ni in an amount exceeding 20.0% more preferred if brought into.
[0027]
　Cr: 15.0% or more and less than 20.0%
　Cr is an effective element for ensuring corrosion resistance of austenitic stainless steels. In particular, in the austenitic stainless steel to regulate the N on the content of below 15.0% or more of Cr, and preferably it is contained with the amount of Cu and Mo described below 16.0% or more of Cr, "high concentration it can be sulfuric acid to ensure good corrosion resistance in an environment "to condense. However, the inclusion a large amount of Cr, to lower the N content, even when the Cu and Mo austenitic stainless steel added in combination, the corrosion resistance is degraded rather in the in the environment, also, machining lowering of sex also occur. In particular, Cr content corrosion degradation of austenitic stainless steel is significantly in the environment exceeds 26.0%. Furthermore, to enhance the hot workability of the Cu and Mo austenitic stainless steel added in combination, to facilitate the product processing on an industrial scale, when the content of Cr to less than 20.0% since the preferred, the content of Cr is less than 20.0% 15.0% or more.
[0028]
　Cu: 8.0% or less beyond the Pasento 3.0
　Cu is an essential element to ensure the corrosion resistance in sulfuric acid in the environment. The Cu in excess of 3.0% by the inclusion with Mo and Cr and later to the amount of a predetermined amount in the "environment where a high concentration of sulfuric acid condenses" good austenitic stainless steel in which the N to content below it is possible to impart corrosion resistance. Since the corrosion resistance improving effect higher the content of Cu to be added in combination with Cu and Mo is large, Cu is more be preferably in the content of more than 3.5%, content of more than 4.0% preferably, more preferred if the content of more than 5.0%. Incidentally, corrosion resistance in the environment by increasing the content of Cu is improved but reduces the hot workability, in particular, when the content of Cu exceeds 8.0%, the N to content below produce the hot workability of significant degradation even. Therefore, the Cu content was 8.0% or less than 3.0%.
[0029]
　Mo: 5.0% or less exceed 2.0%
　Mo is an effective element for ensuring corrosion resistance of austenitic stainless steels. Especially to contain an amount of Mo exceeding 2.0% with a predetermined amount of Cr and Cu, in the "environment where a high concentration of sulfuric acid condenses", good corrosion resistance in austenitic stainless steel containing a predetermined amount of N grant can do. However, Mo and the large amount of reduction is the inclusion hot workability, in particular, the content of Mo exceeds 5.0%, N produce the hot workability of significant degradation even when a predetermined amount . Therefore, the content of Mo was set to 5.0% or less than 2.0%. In order to ensure sufficient corrosion resistance in "Environmental high concentration of sulfuric acid condenses" is be contained Mo in an amount exceeding 3.0% preferred.
[0030]
　Nb: 0 ~ 1.0%
　Nb, which may not be added, be added, with corrosion resistance, the effect of enhancing inter alia intergranular corrosion resistance and secure the C. However, if its content exceeds 1.0%, rather it decreases corrosion resistance generates nitrides even when the N to a predetermined amount, also leads also hot workability occurs. Therefore, the content of Nb 0 to 1.0%. In order to ensure the above-mentioned effects, Nb is preferably in the amount of 0.02% or more.
[0031]
　Ti: 0 ~ 0.5% Ti
　may not be added, but if added, the corrosion resistance and fixing C as with Nb, has the effect of enhancing inter alia intergranular corrosion resistance. However, when the content exceeds 0.5%, rather it decreases corrosion resistance generates nitrides even when the N to a predetermined amount, also leads also hot workability occurs. Therefore, the content of Ti was 0 to 0.5%. In order to ensure the above-mentioned effects, Ti is preferably in the amount of 0.01% or more.
[0032]
　Co:
　0 ~ 0.5% Sn: 0 ~ 0.1%
　as described above, dissimilar metal contact corrosion, unlike conventional corrosion (low potential) less noble the potential of the metal is increased, Fe and dissolution of Cr is accelerated. Co and Sn, in such bimetallic corrosion environment, can reduce the dissolution rate of Fe and Cr, is an element which can remarkably improve the corrosion resistance in the dissimilar metal contact corrosion environment. Therefore, it is preferable to contain one or more kinds of these elements. Although the above effect, Co is less than 0.01%, Sn becomes significant at 0.001% or more. However, if the content of these elements is excessive, as it reduces the productivity, the upper limit of Co is 0.5%, the upper limit of Sn is set to 0.1%.
[0033]
　W: 0 ~ 5.0% W
　may or may not be added, be added, it has the effect of increasing the corrosion resistance in the "environment of high concentrations of sulfuric acid condenses". However, also contain W exceeds 5.0%, the effect is saturated, which only costly. Therefore, the content of W is, was 0 to 5.0%. In order to ensure the above-mentioned effects, W is preferably set to content of 0.1% or more.
[0034]
　Zr: 0 ~ 1.0%
　Zr, which may not be added, be added, has an effect of improving the corrosion resistance in the "environment of high concentrations of sulfuric acid condenses". However, also contain Zr exceeds 1.0%, the effect is saturated, which only costly. Therefore, the content of Zr is 0 and ~ 1.0%, in order to ensure the above-mentioned effects, Zr is preferably in the amount of 0.02% or more.
[0035]
　Al: 0 ~
　0.5% Al, which may not be added, be added, has a deoxidizing effect. However, when the content of Al exceeds 0.5%, hot workability even austenitic stainless steel in which the N to a predetermined content is reduced. Therefore, the Al content 0 to 0.5%. The lower limit of the Al content may be in the range of unavoidable impurities. However, Al is because it has a deoxidizing effect, when the content of the above-described Si was extremely low, it is preferable to be contained 0.02% or more by sufficiently perform deoxidation. Even when which contains 0.05% or more Si, in order to realize the best deoxidation effect, the content of Al preferably 0.01% or more.
[0036]
　N: less than 0.05%
　N is conventionally stabilized austenite structure, has been positively added for the purpose of enhancing the resistance to "local corrosion" such as pitting and crevice corrosion. However, in the "environment where a high concentration of sulfuric acid condenses" the present invention is applied, when the content of N is more than 0.05%, Mo and greater than Cu, 2.0% more than 3.0% corrosion resistance of austenitic stainless steel which contains a Cr less 15.0 or 20.0% decreases rather. Further, 8.0% of the upper limit of the content of Cu and Mo, respectively, even when the 5.0%, hot workability if the content of N is 0.05% or more is reduced . Therefore, the corrosion resistance and hot workability in the "environment of high concentrations of sulfuric acid condenses" in order to impart to the austenitic stainless steels, the content of N is set to less than 0.05%. Incidentally, N content, the better the lower the. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.0005%.
[0037]
　Ca: 0 ~ 0.01% Ca
　may or may not be added, be added, has the effect of suppressing a deterioration of hot workability by combining with S. However, it causes the content thereof is reduced cleanliness of the steel exceeds 0.01%, scratches occur during production in hot. Therefore, the content of Ca was 0 to 0.01%. In order to ensure the above-mentioned effects, Ca is preferably set to content of 0.0005% or more. More lower limit of the preferred content of Ca is 0.001%.
[0038]
　B: 0 ~ 0.01% B
　may or may not be added, be added, has the effect of improving the hot workability. However, addition of a large amount of B promotes the precipitation of Cr-B compound to the grain boundaries, leading to corrosion deterioration. In particular, the content of B is lead to significant corrosion of deterioration exceeds 0.01%. Therefore, the content of B was 0 to 0.01%. In order to ensure the said effects, B is preferably set to content of 0.0005% or more. More lower limit of the preferred content of B is 0.001%.
[0039]
　Rare earth element: 0 to 0.01% total
　rare earth elements, but may not be added, be added, has an effect of improving the hot workability. However, when the content exceeds 0.01% in total reduces the cleanliness of the steel, causing the flaw generated during production in hot. Therefore, to not more than 0.01% the content of the rare earth elements in total. In order to ensure the said effects, it is preferably not less than 0.0005% and the content of the rare earth element in total. Incidentally, Sc, is a generic name for a total of 17 elements Y and lanthanoid.
[0040]
　Chemical composition of the base material is incorporated within a range defined above for each element, respectively, the balance being Fe and unavoidable impurities.
[0041]
　2. Chemical composition of the weld metal
　will now be described in detail the chemical composition of the weld metal.
[0042]
　C: 0.10% or less
　C is an element to stabilize the austenite phase is a matrix. However, to produce a Cr carbonitride by weld heat cycles and excessively added, cause the strength decreases with causing the corrosion resistance deteriorated. Further, C is reacted with Fe in Si and matrix segregated at the grain boundaries to produce a low-melting compound, increases the reheat cracking sensitivity. Therefore, C content is 0.10% or less. Preferable upper limit is 0.03%. Although preferably low as possible C content, the extreme reduction leads to cost increase, the lower limit may be 0.005%.
[0043]
　Si: 0.50% or less
　Si is added as a deoxidizer, segregates at grain boundaries during solidification of the weld metal, reacts with Fe of C and the matrix to produce a low-melting compound, when the multilayer welding cause of reheat cracking. Therefore, Si content is at most 0.50%. Incidentally, Si content is preferably as low as possible, if the deoxidation contains sufficient Al, Mn or the like is not necessarily added. If it is necessary to obtain a deoxidation effect it is preferable to contain 0.02% or more.
[0044]
　Mn: 3.5% or less
　Mn is added as a deoxidizing agent, to stabilize the austenite phase is a matrix. However, to promote the formation of intermetallic compounds excessive addition during high temperature and a long period of use, leading to embrittlement. Therefore, Mn content is at most 3.5%. A preferred upper limit is 2.0%. The lower limit is not particularly necessary to set. Moreover, Mn, if the deoxidation is sufficiently carried out by other elements (Si, Al), the content thereof may be 0%.
[0045]
　P: 0.03% or less
　P is an unavoidable impurity, during welding, segregated in the final solidification portion during solidification of the weld metal lowers the melting point of the residual liquid phase, to generate a solidification cracking. Therefore, P content is at most 0.03%. The preferable upper limit is 0.015%. Incidentally, P content is better as low as possible unless there is a problem in the manufacturing cost. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.003%.
[0046]
　S: 0.03% or less
　S is the same as unavoidable impurities as the above P, during welding, together with generating the formed solidification cracking a low melting point eutectic material during solidification of the weld metal, the grain boundaries segregation to decrease the fixing strength of the grain boundaries, causing reheat cracking. Therefore, S content is at most 0.03%. The preferable upper limit is 0.015%. Incidentally, S content is preferably as low as possible unless there is a problem in the manufacturing cost. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.0001%.
[0047]
　Cu: 0.50% or less
　Cu is an element effective for improving the corrosion resistance of a high concentration of sulfuric acid environment. However, when the content exceeds 0.50%, it lowers the melting point of the final solidification to liquid phase, to generate a solidification cracking. Further, Cu is segregated at grain boundaries during solidification reduces the fixing strength of the grain boundaries, leading to reheat cracking during multilayer welding. Therefore, Cu content is 0.50% or less. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.01%.
[0048]
　Ni: 51.0% or more 80.0% or less
　Ni, along with stabilizing the austenite phase as a matrix, an essential element for ensuring the corrosion resistance in inclusive environment of high concentrations of sulfuric acid. However, excessive addition, to increase the weld crack susceptibility, Ni leads to cost increase because of an expensive element. Therefore, Ni content is 80.0% or less than 51.0%.
[0049]
　Cr: 14.5 ~ 23.0% Cr
　is an element effective for securing oxidation resistance and corrosion resistance at high temperatures, in order to ensure corrosion resistance in inclusive environment of high concentrations of sulfuric acid it is an essential element. In order to ensure sufficient oxidation resistance and corrosion resistance, it is necessary more than 14.5%. However, excessive addition causes the rather deteriorates the corrosion resistance significantly deteriorates the workability. Therefore, Cr content is 14.5 to 23.0%.
[0050]
　Mo: 0.10% or less
　Mo is conventionally be added the high concentration of been considered to be an element effective for improving the corrosion resistance in a sulfuric acid environment, use a base material having the chemical composition for have joints and includes Mo in the range of less than 6.0% greater than the 0.10% in the weld metal, passive film is formed on the weld metal surface passivation film formed on the surface of the base material a potential difference occurs between the, dissimilar metal corrosion is likely to progress. Therefore, the Mo content was set to 0.10% or less. Mo is often as small as possible, it may be 0%. However, excessive reduction so causes an increase in manufacturing cost, a practical lower limit is 0.01%.
[0051]
　Al: 0.40% or less
　Al is added as a deoxidizing agent, degrade the fluidity and uniformity of the weld bead of the weld metal to produce a slag during welding and contains a large amount, weldability significantly reduced. Also, narrowing the welding conditions region for forming the back wave. Therefore, Al content is required to be 0.40% or less. A preferred upper limit is 0.30%, and more preferable upper limit is 0.20%. Al is often as small as possible, it may be 0%. However, excessive reduction so causes an increase in manufacturing cost, a practical lower limit is 0.001%.
[0052]
　Nb, 1 or more selected from Ta and Ti: 4.90% or less in total
　Ti, Nb and Ta, the C in the weld metal was fixed as a carbide, also crystals to form an oxide containing S in addition to improving the fixing force of the grain boundaries, the carbide crystallized out complicates the grain boundaries of the shape, S, to disperse the grain boundary segregation of Cu to prevent reheat cracking during multi-layer welding by. However, Nb, if the total content of one or more selected from Ta and Ti exceeds 4.90% can lead to coarsening of carbides, with deteriorating the toughness deteriorates the workability. Therefore, Nb, 1 or more of the total content is selected from Ta and Ti, or less 4.90%. The lower limit of this total content is preferably adjusted to 2.0%.
[0053]
　Co: 2.5% or less
　Co may or may not be added, it is added, along with stabilizing the austenitic phase similar to the Ni, effective to improve the corrosion resistance in a high concentration of sulfuric acid environment elements it is. However, Co is a very expensive element than in Ni, addition of a large amount leads to cost increase. Therefore, Co content is 2.5% or less. A preferred upper limit is 2.0%, a more preferred upper limit is 1.5%. Although the above effect becomes significant at 0.5% or more.
[0054]
　V: 0.35% or less
　V may or may not be added, be added, is an element effective for improving the high temperature strength. However, excessive addition causes the precipitation of a large amount of carbonitrides, deteriorating the toughness. Therefore, V content is preferably set to 0.35% or less. The above effect is remarkable in 0.05% or more.
[0055]
　W: 4.5% or less
　W may or may not be added, be added is an effective element for improving corrosion resistance of a high concentration of sulfuric acid environment. However, when the content exceeds 4.5%, not only the effect is saturated, rather lead to formation of carbides and intermetallic compounds during use, causing corrosion resistance and toughness degradation. W content is 4.5% or less. The above effect becomes noticeable at 1.0% or more.
[0056]
　The chemical composition of the weld metal, and contained within a range defined above for each element, respectively, the balance being Fe and unavoidable impurities.
[0057]
　3. Chemical composition of the weld material
[0058]
　Welding the base material having the above chemical composition, as a welding material for obtaining the weld metal having the above chemical composition, it is preferable to use those having the following chemical composition.
[0059]
　That is, the welding
material, C: 0.08% or
less, Si: 2.0% or
less, Mn: 3.1% or
less, P: 0.02% or
less, S: 0.02% or
less, Ni: 4
~ 80.0% .0, Cr: 15.0 ~
30.0%, Al: 0.5% or
less, Nb, 1 or more selected from Ta and Ti: 4.90% in total less,
Mo: 0.10% W:
0 ~ 4.5% Co: 0 ~ 5.0%, Cu: 0 ~ 8.0%, V: 0 ~ 0.25%, B: 0 ~ 0.01%, Ca : 0 to 0.01%, Mg: 0 to 0.01%, rare earth element: 0 to 0.01% in total, the balance is preferably used one having a chemical composition of Fe and unavoidable impurities.

[0060]
　Reasons for limiting each element is as follows.
[0061]
　C: 0.08% or less
　C content, in order to provide satisfactory performance in the weld metal is preferably not more than 0.08%. The lower limit is may be 0%, and the preferable lower limit for obtaining the above effects is 0.002%.
[0062]
　Si: 2.0% or less
　Si has its content is 2.0% more than remarkably deteriorates hot workability in welding material production, reheat cracking by increasing the Si content of the weld metal because increases susceptibility is preferably 2.0% or less. The lower limit is may be 0%, and the preferable lower limit for obtaining the above effects is 0.02%.
[0063]
　Mn: 3.1% or less
　Mn, if its content exceeds 3.1%, the deteriorates hot workability in welding material production, since leads to generation of a large amount of fume during welding, 3.1 % by is preferably less. The lower limit is may be 0%, and the preferable lower limit for obtaining the above effects is 0.01%.
[0064]
　P: 0.02% or less
　P is an unavoidable impurity, during welding, segregated in the final solidification portion during solidification of the weld metal lowers the melting point of the residual liquid phase, to generate the solidification cracking, 0.02 % by is preferably less. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.003%.
[0065]
　S: 0.02% or less
　S, as well as its content deteriorates the hot workability in welding material production exceeds 0.02%, to increase the S content of the weld metal solidification cracking susceptibility and since increasing the reheat crack sensitivity, it is preferably not more than 0.02%. The lower limit is may be 0% excess reduction so causes an increase in manufacturing cost, a practical lower limit is 0.0001%.
[0066]
　Ni: 4.0 ~ 80.0%
　Ni, as well as to stabilize the austenitic phase is a matrix, an essential element for ensuring the corrosion resistance in inclusive environment of high concentrations of sulfuric acid. However, excessive addition, to increase the weld crack susceptibility, Ni leads to cost increase because of an expensive element. For this reason, and from 4.0 to 80.0 percent. However, it is preferable that an amount satisfying Ni + Co + 2Cu ≧ 25.
[0067]
　Cr: 15.0 to
　30.0% Cr content is preferably to provide adequate reheat cracking in the weld metal is 15.0 to 30.0%.
[0068]
　Al: 0.5% or less
　Al is added as a deoxidizing agent, degrade the fluidity and uniformity of the weld bead of the weld metal to produce a slag during welding and contains a large amount, weldability significantly reduced. Therefore, Al is preferably 0.5% or less. The lower limit is may be 0%, and the preferable lower limit for obtaining the above effects is 0.01%.
[0069]
　Nb, 1 or more selected from Ta and Ti: 4.90% or less in total
　Ti, Nb and Ta, the C in the weld metal was fixed as a carbide, also crystals to form an oxide containing S in addition to improving the fixing force of the grain boundaries, the carbide crystallized out complicates the grain boundaries of the shape, S, to disperse the grain boundary segregation of Cu to prevent reheat cracking during multi-layer welding by. However, in the weld metal, Nb, when one or more of the total content is selected from Ta and Ti exceeds 4.90% can lead to coarsening of carbides, with deteriorating the toughness, workability degrade. Therefore, the total content of these in the weld material also should be limited, specifically, Nb, 1 or more of the total content is selected from Ta and Ti, to less 4.90% good. The lower limit of this total content is preferably adjusted to 2.0%.
[0070]
　Mo: 0.10% or less
　Mo is conventionally be added the high concentration of been considered to be an element effective for improving the corrosion resistance in a sulfuric acid environment, use a base material having the chemical composition for have joints and includes Mo in the range of less than 6.0% greater than the 0.10% in the weld metal, passive film is formed on the weld metal surface passivation film formed on the surface of the base material a potential difference occurs between the, dissimilar metal corrosion is likely to progress. Therefore, the content of Mo in the weld metal to 0.10% or less, it is necessary to reduce the Mo content in the welding material as much as possible. Therefore, Mo content is better to 0.10% or less. Mo is often as small as possible, it may be 0%.
[0071]
　W: 0 ~ 4.5%
　W, when included in the weld metal, since it is an element effective for improving the corrosion resistance of a high concentration of sulfuric acid environment, it may be contained in the welding material. However, when the content exceeds 4.5%, not only the effect is saturated, rather lead to formation of carbides and intermetallic compounds during use, causing corrosion resistance and toughness degradation. Therefore, W content is preferably set to 0 to 4.5%. The above effect becomes noticeable at 1.0% or more.
[0072]
　Co: 0 ~ 5.0%
　Co, the content of the case may be free, containing, in order to provide the performance required for the weld metal is preferably 5.0% or less.
[0073]
　Cu: 0 ~ 8.0%
　Cu, which may be free, if it contains, since the content is remarkably decreases the hot workability in welding material production and 8.0 percent, when including it is preferable that the content of at most 8.0%.
[0074]
　V: 0 ~ 0.25%
　V, the content of the case may be free, containing, in order to provide the performance required for the weld metal is preferably not more than 0.25%.
[0075]
　B: 0 ~ 0.01% B
　may or may not include, the content of the case, including, it is preferable to provide the performance required for the weld metal is 0.01% or less.
[0076]
　Ca:
　0 ~ 0.01% Mg: 0 ~ 0.01%
　rare earth elements: total 0 ~
　0.01% Ca, Mg and rare earth elements, which may or may not include any, of each element in the case of including content is preferably any element to provide the performance required for weld metal also below 0.01%.
[0077]
　4. Method for producing a welded joint
　above welded joint according to the present invention, for example, TIG method, gas-shielded arc welding method typified by MIG method, shielded metal arc welding method, be made by welding method such as submerged arc welding method can. Above all, it is preferable to use the TIG method.
Example 1
[0078]
　Having various chemical compositions shown in Table 1, to produce an ingot of 50 kg, by hot forging and hot rolling from the ingot to obtain a steel plate having a thickness of 11 mm. This steel sheet was subjected to solution heat treatment (1100 ℃ × 30min), was plate material 300mmL × 50mmW × 10mmt.
[0079]
[Table 1]

[0080]
　After grooving one end of the plate material, the TIG welding was performed in a state of butting the two sheets of plate members, to obtain a welded joint. Welding material was used having a chemical composition shown in Table 2. Further, Table 3 shows the results of the chemical composition of the weld metal was analyzed by X-ray fluorescence analysis.
[0081]
[Table 2]

[0082]
[table 3]

[0083]
　From the obtained welded joint, corrosion test pieces containing a weld metal portion in the center of (10mmL × 70mmW × 3mmt) was collected and conducted corrosion test.
[0084]
　Corrosion test, corrosion test pieces, 50% H maintained at 100 ° C. 2 SO 4 and 336h immersed in liquid, was calculated corrosion rate (corrosion rate of the entire test piece) from the mass decrease. It was also measured corrosion thinning at the interface between the base metal and the weld metal portion (the maximum value). On the other hand, test piece was cut out (7mmL × 7mmW × 2mmt) from the base material and溶金portion of the weld joint, 50% H maintained at 100 ° C. 2 SO 4 was measured corrosion potential in solution, the potential difference (soluble corrosion potential of the gold unit - corrosion potential of base material) was calculated. The results are shown in Table 4.
[0085]
[Table 4]

[0086]
　As shown in Table 4, Comparative Examples 1 and 2, the chemical composition of the base material are out of the range defined in the present invention, Comparative Examples 3, 4 and 5, the chemical composition of the weld metal (in particular, Mo content) is out of range defined in the present invention. As a result, in any of Comparative Examples, a large potential difference between the weld metal and the base metal, the corrosion resistance is deteriorated. In contrast, none of Examples 1-9, a small potential difference between the weld metal and base material was provided with a good corrosion resistance. In particular, Examples 6 and 7 contain Co or Sn in the matrix was equipped with better corrosion resistance.
Industrial Applicability
[0087]
　According to the present invention, the austenitic stainless steel fittings, it is possible to suppress the dissimilar metal corrosion occurring between the base metal and weld metal, at a temperature of the environment (50 ~ 100 ° C. to a high concentration of sulfuric acid condenses It is 40 to 70% strength sulfuric acid is excellent in corrosion resistance in an environment) to condensation. Therefore, it is suitable as welding structural members used in such environments.

WE CLAIM

A welded structure member comprising an austenitic stainless steel fittings,
the chemical composition of the base material, in
mass%, C: 0.05% or
less, Si: 1.0% or
less, Mn: 2.0% or
less, P 0.04% or
less, S: 0.01% or
less, Ni: 12.0
~ 27.0%, Cr: less than 15.0% or more
20.0%, Cu: more than 3.0% 8. 0% or less,
Mo: 5.0% exceeds 2.0% or
less,
Nb: 0 ~ 1.0%,
Ti: 0 ~ 0.5%, Co: 0 ~
0.5%, Sn: 0 ~
% 0.1,
W: 0 ~
5.0%, Zr: 0 ~ 1.0%, Al: 0
~ 0.5%, N: less than%
0.05, Ca: 0 ~
0.01%, B : 0 to 0.01% or
a rare earth element: 0 to 0.01% in total,
the balance is Fe and inevitable impurities,
the chemical composition of the weld metal, in
mass% C: 0.10% or less,
Si: 0.50% or
less, Mn: 3.5% or
less, P: 0.03% or
less, S: 0.03% or
less, Cu: 0.50% or
less, Ni: 51.0% or more 80.0 % or
less, Cr: 14.5
~ 23.0%, Mo: 0.10% or
less, Al: 0.40% or
less, Nb, 1 or more selected from Ta and Ti: less 4.90% in total ,
Co: 2.5% or
less, V: 0.35% or
less, W: 4.5% or less,
the balance being Fe and unavoidable impurities, the welding structural members.
[Requested item 2]
　The chemical composition of the base material, in
mass% Co: 0.01 ~ 0.5% and / or
Sn: containing 0.001 to 0.1 percent,
welded structure according to claim 1.