Ferritic stainless steel welded structure, manufacturing method thereof, welding material, and exhaust heat recovery device

Abstract

To provide a ferritic stainless steel welded structure which is excellent in corrosion resistance and heat resistance, especially, corrosion resistance and heat resistance of a weld metal part.SOLUTION: A ferritic stainless steel welded structure includes a base material and a weld metal part. The base material has a composition which consists of, by mass, 0.100% or less C, 1.00% or less Mn, 1.00% or less Ni, 0.100% or less P, 0.050% or less S, 15.00-24.00% Cr, 0.100% or less N, 1.00% or less Cu, 1.00% or less Mo, 3.00% or less Si, 0.80-5.00% Al, 0.50% or less Nb, and 0.50% or less Ti, wherein the total content of Nb and Ti is 6(C+N) or more (C and N each represent contents of C and N), with the balance consisting of Fe and impurities. The weld metal part contains, by mass, 0.10-1.00% Al, and 15.00-24.00% Cr, wherein the total solid solution amount of C and N is 0.015 mass% or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a ferritic stainless steel welded structure, a method for manufacturing the same, a welding material, and an exhaust heat recovery device.

Background Art

[0002] In recent years, in response to global efforts to suppress CO 2 emissions, efforts to effectively utilize exhaust heat have been expanding. For example, as a technology for recovering thermal energy from exhaust gas, many heat exchangers are used in automotive exhaust system components, plants, household energy equipment, etc., and its use is expected to expand in the future.

[0003] The exhaust gas used in the heat exchanger is, for example, combustion exhaust gas of gasoline or LPG (liquefied petroleum gas), which is an oxidizing gas at a high temperature (about 400°C to about 750°C) and contains a lot of water vapor. Therefore, since the heat exchanger is required to have resistance (heat resistance and corrosion resistance) to such an environment, stainless steel materials are used as the material. In addition, the heat exchanger is also exposed to a temperature difference from low temperature (room temperature to about 90°C) to high temperature (about 400°C to about 750°C). In particular, when the heat exchanger becomes large, the thermal stress due to the temperature difference becomes large and it is likely to deform. Therefore, ferritic stainless steel materials with low thermal expansion are often used as the material for the heat exchanger.

[0004] Stainless steel materials have excellent corrosion resistance by forming a Cr oxide film on the surface. However, in an oxidizing environment with high temperature and a lot of water vapor, the growth of Cr oxide is fast, and Cr evaporation also occurs in which the Cr oxide becomes hexavalent Cr and scatters. Therefore, for stainless steel materials used in an oxidizing environment with high temperature and a lot of water vapor, ferritic stainless steel materials capable of forming Al oxide (Al 2 O 3 ) on the surface are used.

[0005] For example, Patent Document 1 proposes a ferritic stainless steel material having a composition containing Cr: 11 to 22% by mass, C: 0.03% by mass or less, N: 0.03% by mass or less, Mn: 1.5% by mass or less, S: 0.008% by mass or less, Si: 2% by mass or less, Al: 1.0 to 6.0% by mass, with the balance being Fe and unavoidable impurities. Also, Patent Document 2 proposes a ferritic stainless steel material having a composition containing, in mass%, C: 0.03% or less, Si: 3% or less, Mn: 1.0% or less, P: 0.04% or less, S: 0.01% or less, Ni: 0.5% or less, Cr: 11 to 21%, Al: 6% or less, Cu: 0.01 to 0.5%, Mo: 0.01 to 0.5%, Nb: 0.1% or less, Ti: 0.005 to 0.50%, Sn: 0.001 to 0.1%, N: 0.03% or less, O: 0.002% or less, H: 0.00005% or less, Pb: 0.01% or less, with the balance being Fe and unavoidable impurities. Furthermore, Patent Document 3 proposes a ferritic stainless steel material having a composition containing C: 0.03% by mass or less, Si: 0.5% by mass or less, Mn: 1.0% by mass or less, P: 0.04% by mass or less, S: 0.01% by mass or less, Ni: 0.6% by mass or less, Cr: 15 to 20% by mass, N: 0.03% by mass or less, Ti: 0.5% by mass or less, B: 0.0005 to 0.003% by mass, Al: 1.5% by mass or more and less than 4.0% by mass, with the balance being Fe and unavoidable impurities.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] The corrosion resistance and heat resistance of ferritic stainless steel materials are related to the amounts of C and N dissolved in the ferritic stainless steel materials. The dissolved C and N combine with Cr to form carbides and nitrides of Cr (hereinafter referred to as "carbonitrides"), which preferentially precipitate at grain boundaries. The area where the carbonitrides of Cr precipitate becomes a state called sensitization where Cr is lacking. When exposed to a highly oxidizing environment with high temperature and a large amount of water vapor, corrosion progresses significantly. Also, Cr oxides and Al oxides are not formed in the part lacking Cr, and Fe is continuously oxidized, so heat resistance cannot be ensured. Therefore, it is effective to reduce the contents of C and N in the ferritic stainless steel materials as much as possible and add elements such as Ti and Nb that preferentially combine with C and N to form carbonitrides to reduce the dissolved amounts of C and N.

[0008] In addition, an exhaust heat recovery device including a heat exchanger or the like is manufactured by performing processing such as welding on a ferritic stainless steel material. When welding is performed, in the weld metal part, the carbonitrides of Ti and Nb are dissolved and the dissolved amounts of C and N increase. In the ferritic stainless steel material in which the contents of C and N are controlled to an extremely low level as described above, since the carbonitrides of Ti and Nb are re-formed by natural cooling after welding, the dissolved amounts of C and N remain at a low level, and it is possible to suppress the decrease in corrosion resistance and heat resistance due to sensitization. However, in the ferritic stainless steel materials described in Patent Documents 1 to 3 containing Al, since the diffusion of Ti and Nb is slow, it is difficult for the carbonitrides of Ti and Nb to be re-formed by natural cooling after welding, and the dissolved amounts of C and N increase. Since this is greatly affected by the diffusion rate, it cannot be solved by excessive addition of Ti and Nb. On the contrary, when Ti and Nb are excessively added, inclusions such as TiO 2 increase, leading to a decrease in surface quality and toughness. Thus, Patent Documents 1 to 3 do not recognize at all the problem of the decrease in the corrosion resistance and heat resistance of the weld metal part in a ferritic stainless steel welded structure obtained by welding a ferritic stainless steel material.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, corrosion resistance and heat resistance of a weld metal part), a method for manufacturing the same, and a waste heat recovery device. Another object of the present invention is to provide a welding material suitable for manufacturing a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, corrosion resistance and heat resistance of a weld metal part).

Means for Solving the Problems

[0010] As a result of intensive studies on a ferritic stainless steel welded structure including a base material and a weld metal part, the present inventors have found that the above problems can be solved by controlling the composition of the base material, and the contents of Al and Cr and the total solid solution amount of C and N in the weld metal part, and have completed the present invention. Further, the present inventors have found that the above ferritic stainless steel welded structure can be manufactured by performing arc welding using a ferritic stainless steel material having a specific composition as a base material and a welding material having a specific composition, and have completed the present invention.

[0011] That is, the present invention is a ferritic stainless steel welded structure including a base material and a weld metal part, wherein the base material contains, on a mass basis, C: 0.001~0.050% , Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001~0.050% , Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C + N) or more (C and N represent the contents of C and N, respectively), and the balance consists of Fe and impurities, and the weld metal part contains, on a mass basis, Al: 0.10 to 1.00% and Cr: 15.00 to 24.00%, and the total solid solution amount of C and N is 0.015 mass% or less, and is a ferritic stainless steel welded structure.

[0012] The present invention also relates to a method for manufacturing a ferritic stainless steel welded structure, which uses a ferritic stainless steel material as a base material and performs arc welding using a welding material, wherein the ferritic stainless steel material contains, by mass, C: 0.001~0.050% , Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001~0.050% , Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti is 6(C+N) or more (where C and N represent the contents of C and N, respectively), and the balance consists of Fe and impurities, and the welding material contains, by mass, C: 0.010~0.017% , Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.009~0.015% , Cu: 1.00% or less, Mo: 1.00% or less, Si: 2.00% or less, Al: 0.02~ 0.50 %、 , Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti is 6(C+N) or more (where C and N represent the contents of C and N, respectively), and the balance consists of Fe and impurities.

[0013] The present invention also relates to a welding material for arc welding that uses, as a base material, a ferritic stainless steel material containing, by mass, C: 0.001~0.050% , Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001~0.050% , Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti is 6(C+N) or more (where C and N represent the contents of C and N, respectively), and the balance consists of Fe and impurities, and contains, by mass, C:0.010~0.017% , Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 - 24.00%, N: 0.009~0.015% , Cu: 1.00% or less, Mo: 1.00% or less, Si: 2.00% or less, Al: 0.02~ 0.50 %、 It contains Nb: 0.50% or less and Ti: 0.50% or less, and the total content of Nb and Ti is 6(C + N) or more (where C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities. It is a welding material having such a composition.

[0014] Furthermore, the present invention is an exhaust heat recovery device including the ferritic stainless steel welded structure.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, the corrosion resistance and heat resistance of the welded metal part), a method for manufacturing the same, and an exhaust heat recovery device. Also, according to the present invention, it is possible to provide a welding material suitable for manufacturing a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, the corrosion resistance and heat resistance of the welded metal part).

Brief Description of the Drawings

[0016]

Figure 1

Embodiments for Carrying Out the Invention

[0017] Hereinafter, embodiments of the present invention completed based on the above viewpoints will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that within the scope not departing from the gist of the present invention, modifications, improvements, etc. appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art also fall within the scope of the present invention. In addition, in this specification, the “%” indication regarding a component means “mass %” unless otherwise specified.

[0018] The ferritic stainless steel welded structure according to an embodiment of the present invention includes a base material and a weld metal part. This ferritic stainless steel welded structure is manufactured by using a ferritic stainless steel material as the base material and performing arc welding using a welding material. Here, in this specification, “ferritic” means that the metal structure is mainly a ferrite phase at normal temperature. Therefore, “ferritic” includes those that slightly contain phases other than the ferrite phase (for example, austenite phase, martensite phase, etc.). Further, “stainless steel material” means a material formed from stainless steel, and its material shape is not particularly limited. Examples of the material shape include plate shape (including strip shape), rod shape, tubular shape, etc. Further, the material may be various shaped steels such as T-shaped and I-shaped in cross-sectional shape. Furthermore, “welding material” means a material (filler material) used to bond the base material during welding. The welding material is typically formed from stainless steel, and its shape is not particularly limited and can be made into a rod shape, wire shape, strip shape, plate shape, etc. The welding material may be appropriately selected according to the welding method, and specific examples thereof include TIG welding rods, solid wires for gas shielded arc welding, strip electrodes, covered arc welding rods with flux coated on the surface, and flux-cored wires for gas shielded arc welding with flux wound around a steel plate.

[0019] FIG. 1 shows a schematic partial enlarged cross-sectional view of a ferritic stainless steel welded structure. As shown in FIG. 1, the ferritic stainless steel welded structure (100) includes a base material (10) and a weld metal part (30). Further, the ferritic stainless steel welded structure (100) further includes a heat affected zone (20) between the base material (10) and the weld metal part (30). Here, the "base material" means the part that is not affected by welding. Also, the "heat affected zone" means the part that is not melted but is affected by the heat of welding (also referred to as HAZ). Further, the "weld metal part" means the part that is melted by the influence of welding and then re-solidifies.

[0020] Since the base material is not affected by welding, it has the same composition and metal structure as the ferritic stainless steel material, which is the material of the ferritic stainless steel welded structure. The base material (ferritic stainless steel material) contains C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 - 24.00%, N: 0.100% or less, Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 - 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, and the total content of Nb and Ti is 6(C + N) or more (where C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities. Here, in this specification, "impurities" mean the components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when industrially manufacturing stainless steel materials, and are those that are allowed within the range that does not adversely affect the present invention. For example, impurities include inevitable impurities.

[0021] Also, the base material (ferritic stainless steel material) can further contain at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, and W: 1.00% or less, as required. Also, the base material (ferritic stainless steel material) can further contain at least one selected from REM: 0.10% or less and Ca: 0.10% or less, as required. Furthermore, the base material (ferritic stainless steel material) can further contain at least one selected from Sn: 0.10% or less and B: 0.0100% or less, as required. In the description of each of the following elements, the term "base material" includes not only the base material of the ferritic stainless steel welded structure but also the ferritic stainless steel material used in the manufacture of the ferritic stainless steel welded structure.

[0022] (C: 0.100% or less) C is an element that affects properties such as the intergranular corrosion resistance (sensitization suppression effect) of the base material and the workability of the ferritic stainless steel material. If the C content is too high, the intergranular corrosion resistance of the base material and the workability of the ferritic stainless steel material will deteriorate. Therefore, the upper limit value of the C content is 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit value of the C content is not particularly limited, but reducing the C content will lead to an increase in refining cost. Therefore, the lower limit value of the C content is preferably 0.0005%, more preferably 0.001%.

[0023] (Mn: 1.00% or less) Mn is an element useful as a deoxidizing element. If the Mn content is too high, it is likely to generate MnS which serves as a corrosion initiation point and destabilizes the ferrite phase. Therefore, the upper limit value of the Mn content is 1.00%, preferably 0.90%, more preferably 0.80%. On the other hand, the lower limit value of the Mn content is not particularly limited, but is preferably 0.01%, more preferably 0.05%.

[0024] (Ni: 1.00% or less) Ni is an element effective in improving the corrosion resistance of the base material and the toughness of the weld metal part. If the Ni content is too high, the ferrite phase will be destabilized and the manufacturing cost will also increase. Therefore, the upper limit value of the Ni content is 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit value of the Ni content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0025] (P: 0.100% or less) P is an element that affects properties such as the weldability and workability of ferritic stainless steel materials. If the P content is too high, the above properties may deteriorate. Therefore, the upper limit value of the P content is 0.100%, preferably 0.080%, more preferably 0.050%. On the other hand, the lower limit value of the P content is not particularly limited, but reducing the P content leads to an increase in refining costs. Therefore, the lower limit value of the P content is preferably 0.001%, more preferably 0.010%.

[0026] (S: 0.050% or less) S is an element that generates MnS, which serves as a corrosion initiation point, and affects the toughness of the weld metal part. If the S content is too high, the toughness of the weld metal part may deteriorate. Therefore, the upper limit value of the S content is 0.050%, preferably 0.040%, more preferably 0.030%. On the other hand, the lower limit value of the S content is not particularly limited, but reducing the S content leads to an increase in refining costs. Therefore, the lower limit value of the S content is preferably 0.0001%, more preferably 0.0005%.

[0027] (Cr: 15.00 - 24.00%) Cr is an element effective in improving the corrosion resistance and oxidation resistance of the base material. If the Cr content is too high, the toughness of the base material decreases and the manufacturing cost increases. Therefore, the upper limit value of the Cr content is 24.00%, preferably 23.50%, more preferably 23.00%. On the other hand, if the Cr content is too low, the above effects may not be fully obtained. Therefore, the lower limit value of the Cr content is 15.00%, preferably 15.50%, more preferably 16.00%.

[0028] (N: 0.100% or less) N is an element that affects properties such as the intergranular corrosion resistance (sensitization inhibition effect) of the base material and the workability of ferritic stainless steel. If the N content is too high, the intergranular corrosion resistance of the base material and the workability of ferritic stainless steel will decrease. Therefore, the upper limit value of the N content is 0.100%, preferably 0.050%, more preferably 0.030%. On the other hand, the lower limit value of the N content is not particularly limited, but reducing the N content will lead to an increase in refining costs. Therefore, the lower limit value of the N content is preferably 0.0005%, more preferably 0.001%.

[0029] (Cu: 1.00% or less) Cu is an element effective in improving the corrosion resistance of the base material. If the Cu content is too high, the ferrite phase will become unstable and the manufacturing cost will also increase. Therefore, the upper limit value of the Cu content is 1.00%, preferably 0.70%, more preferably 0.30%. On the other hand, the lower limit value of the Cu content is not particularly limited, but it is preferably 0.001%, more preferably 0.01%.

[0030] (Mo: 1.00% or less) Mo is an element effective in improving the corrosion resistance and oxidation resistance of the base material. If the Mo content is too high, the workability of ferritic stainless steel will decrease and the manufacturing cost will increase. Therefore, the upper limit value of the Mo content is 1.00%, preferably 0.80%, more preferably 0.50%. On the other hand, the lower limit value of the Mo content is not particularly limited, but it is preferably 0.001%, more preferably 0.005%.

[0031] (Si: 3.00% or less) Si is an element effective in improving the corrosion resistance of the base metal. If the Si content is too high, the workability of the ferritic stainless steel material and the toughness of the weld metal part will decrease. Therefore, the upper limit value of the Si content is 3.00%, preferably 2.50%, more preferably 2.00%. On the other hand, the lower limit value of the Si content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%.

[0032] (Al: 0.80 - 5.00%) Al is an element effective in improving the corrosion resistance of the base metal, similar to Si. If the Al content is too high, the toughness of the base metal will decrease. Therefore, the upper limit value of the Al content is 5.00%, preferably 4.50%, more preferably 4.00%. On the other hand, the lower limit value of the Al content is 0.80%, preferably 1.00%, more preferably 1.20% from the viewpoint of obtaining the above effects.

[0033] (Nb: 0.50% or less, Ti: 0.50% or less, total content of Nb and Ti: 6(C + N) or more) Nb and Ti are elements that affect properties such as the intergranular corrosion resistance (sensitization suppression effect) of the base metal. If the Nb content is too high, the workability of the ferritic stainless steel material and the toughness of the base metal will decrease. Therefore, the upper limit value of the Nb content is 0.50%, preferably 0.48%, more preferably 0.45%. Also, if the Ti content is too high, the workability and surface quality of the ferritic stainless steel material will decrease. Therefore, the upper limit value of the Ti content is 0.50%, preferably 0.48%, more preferably 0.45%. On the other hand, the lower limit value of the total content of Nb and Ti is controlled in relation to the contents of C and N that reduce the intergranular corrosion resistance. Specifically, the lower limit value of the total content of Nb and Ti is 6(C + N), preferably 7(C + N). Here, C and N represent the contents of C and N respectively.

[0034] (Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less) Zr, Co, V, and W are elements effective in improving the oxidation resistance of the base material. If the contents of Zr, Co, V, and W are too high, the workability of the ferritic stainless steel material and the toughness of the base material will decrease, and the manufacturing cost will increase. Therefore, the upper limit values of the contents of Zr, Co, V, and W are all 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit values of the contents of Zr, Co, V, and W are not particularly limited, but are preferably 0.001%, more preferably 0.01%.

[0035] (REM: 0.10% or less, Ca: 0.10% or less) REM (rare earth elements) and Ca are elements effective in improving the oxidation resistance of the base material. If the contents of REM and Ca are too high, it will lead to an increase in the manufacturing cost of the ferritic stainless steel material. Therefore, the upper limit values of the contents of REM and Ca are all 0.10%, preferably 0.08%, more preferably 0.05%. On the other hand, the lower limit values of the contents of REM and Ca are not particularly limited, but are preferably 0.0001%, more preferably 0.003%. Note that REM refers to the general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements from lanthanum (La) to lutetium (Lu) (lanthanoids). These may be used alone or as a mixture.

[0036] (Sn: 0.10% or less) Sn is an element effective in improving the corrosion resistance of the base material. If the content of Sn is too high, Sn will segregate and the manufacturability will decrease. Therefore, the upper limit value of the content of Sn is 0.10%, preferably 0.08%, more preferably 0.05%. On the other hand, the lower limit value of the content of Sn is not particularly limited, but is preferably 0.001%, more preferably 0.005%.

[0037] (B: 0.0100% or less) B is an element effective in improving the secondary workability of ferritic stainless steel materials. If the content of B is too high, the fatigue strength of ferritic stainless steel materials will decrease. Therefore, the upper limit value of the content of B is 0.0100%, preferably 0.0080%, more preferably 0.0050%. On the other hand, the lower limit value of the content of B is not particularly limited, but is preferably 0.0001%, more preferably 0.0005%.

[0038] The weld metal part contains 0.10 - 1.00% of Al and 15.00 - 24.00% of Cr. If the content of Al in the weld metal part is too high, it becomes difficult to form titanium and niobium carbonitrides. As a result, since the amount of C and N in solid solution increases during cooling after welding, sensitization occurs. Therefore, from the viewpoint of improving the formation rate of titanium and niobium carbonitrides and reducing the amount of C and N in solid solution during cooling after welding, the upper limit value of the content of Al in the weld metal part is 1.00%, preferably 0.90%, more preferably 0.80%. By setting such an upper limit value, sensitization in the weld metal part can be suppressed, and it becomes possible to improve the corrosion resistance and heat resistance of the weld metal part. On the other hand, if the content of Al in the weld metal part is too low, the heat resistance of the weld metal part will decrease. Therefore, the lower limit value of the content of Al in the weld metal part is 0.10%, preferably 0.15%, more preferably 0.20%. By setting such a lower limit value, the heat resistance in the weld metal part can be ensured.

[0039] If the Cr content in the weld metal part is too low, the heat resistance will decrease. Therefore, the lower limit of the Cr content in the weld metal part is 15.00%, preferably 15.5%, more preferably 16.0%. By setting such a lower limit, the heat resistance in the weld metal part can be ensured. On the other hand, if the Cr content in the weld metal part is too high, the toughness of the weld metal part will decrease and the manufacturing cost will increase. Therefore, the upper limit of the Cr content in the weld metal part is 24.00%, preferably 23.50%, more preferably 23.00%. By setting such an upper limit, the toughness in the weld metal part can be ensured while suppressing the increase in manufacturing cost.

[0040] The total amount of C and N in solid solution in the weld metal part is 0.015% or less, preferably 0.014% or less. By setting the total amount of C and N in solid solution to 0.015% or less, it is possible to suppress the precipitation of Cr carbonitrides due to the combination of C and N in solid solution with Cr under high-temperature environments. Therefore, the toughness of the weld metal part under high-temperature environments can be improved and sensitization can be suppressed. In addition, the lower limit of the total amount of C and N in solid solution is not particularly limited, but is typically 0.0001%, preferably 0.0005%, more preferably 0.001%. In this specification, the total amount of C and N in solid solution means the amount calculated by the method described in the examples below. Also, since it is difficult to calculate the amount of C and N in solid solution individually, it should be noted that in the present invention, the total amount of C and N in solid solution is calculated for convenience.

[0041] Generally, for a ferritic stainless steel welded structure manufactured using a ferritic stainless steel material containing Al, in order to suppress sensitization in the weld metal part, it is necessary to perform heat treatment after welding to precipitate carbonitrides of Ti or Nb and reduce the amount of C and N in solid solution. However, heat treatment requires detailed control of the furnace temperature and cooling rate, so the manufacturing cost increases. Also, deformation may occur during heat treatment, and it is difficult to perform heat treatment itself when the size is large. In contrast, the ferritic stainless steel welded structure according to the embodiment of the present invention can suppress sensitization in the weld metal part without performing heat treatment after welding. The ferritic stainless steel welded structure according to the embodiment of the present invention that does not undergo heat treatment after welding has an oxide film containing less than 30% Al on the surface (the surfaces of the base metal, heat affected zone, and weld metal part). The content of Al in this oxide film is preferably 20% or less. Here, in this specification, the content of Al in the oxide film means the one measured by the method described in the examples below.

[0042] However, the ferritic stainless steel welded structure according to the embodiment of the invention may be heat treated after welding. The ferritic stainless steel welded structure according to the embodiment of the present invention that undergoes heat treatment after welding has an oxide film containing 30 mass% or more of Al on the surface. By providing such an oxide film on the surface, the high-temperature oxidation resistance can be improved. From the viewpoint of stably enhancing the high-temperature oxidation resistance, the content of Al in this oxide film is preferably 32% or more, more preferably 35% or more. On the other hand, the upper limit value of the Al content is not particularly limited, but for example, it is 90%, preferably 80%.

[0043] The ferritic stainless steel welded structure according to the embodiment of the present invention can be manufactured by using a ferritic stainless steel material having the above composition as the base metal and performing arc welding using a welding material.

[0044] The ferritic stainless steel material having the above composition can be manufactured by a conventional method. Specifically, first, the ferritic stainless steel having the above composition is melted and then forged or cast, and then hot-rolled to obtain a hot-rolled material. Next, annealing, pickling, and cold rolling are sequentially performed on the hot-rolled material to obtain a cold-rolled material. Next, annealing and pickling are sequentially performed on the cold-rolled material to obtain a cold-rolled annealed material. Note that the conditions in each step may be appropriately adjusted according to the composition of the stainless steel and the like, and are not particularly limited. The hot-rolled material, cold-rolled material, or cold-rolled annealed material produced in such a manner can be used as the ferritic stainless steel material. Among these, the ferritic stainless steel material is preferably a cold-rolled annealed material. Further, the hot-rolled material, cold-rolled material, or cold-rolled annealed material may be subjected to a forming process into a predetermined member shape. Examples of the forming process include various press processes using a mold and machining such as bending. Note that the conditions in each step may be appropriately adjusted according to the composition of the ferritic stainless steel material and are not particularly limited.

[0045] The welding material for arc welding contains C: 0.100% or less, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 - 24.00%, N: 0.100% or less, Cu: 1.00% or less, Mo: 1.00% or less, Si: 2.00% or less, Al: 0.50% or less, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C + N) or more (where C and N represent the contents of C and N respectively), and the balance consists of Fe and impurities. Further, the welding material for arc welding may further contain at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Ca: 0.10% or less, Sn: 0.10% or less, B: 0.0100% or less as required.

[0046] The welding material for arc welding has a composition similar to that of the ferritic stainless steel material used as the base material as described above. Generally, when arc welding is performed using a ferritic stainless steel material containing Al as a base material, in order to suppress a decrease in the heat resistance of the welded metal part, a welding material having a composition in which the Al content is equal to or more than that of the base material is used. On the other hand, the welding material for arc welding used in the embodiment of the present invention has a composition with a lower Al content than the base material in order to reduce the Al content in the welded metal part. That is, considering the Al content (0.10 to 1.00%) in the welded metal part, the welding material for arc welding is controlled so that the Al content is 0.50% or less. Furthermore, if the Cr content in the welded metal part is too low, the heat resistance will decrease. Therefore, considering the Cr content (15.00 to 24.00%) in the welded metal part, the welding material for arc welding is controlled so that the Cr content is 15.00 to 24.00%.

[0047] The welding material for arc welding can be manufactured by a conventional method. For example, when the welding material is rod-shaped (wire-shaped), stainless steel having the above composition is melted and hot-rolled to obtain a hot-rolled bar (hot-rolled wire). Next, after annealing and pickling the hot-rolled bar, wire drawing is performed, and then annealing and pickling are performed to obtain the welding material.

[0048] Arc welding is performed using the welding material having the above composition. Arc welding may be performed by welding a plurality of ferritic stainless steel materials to each other, or by welding a ferritic stainless steel material to a metal material of another material. The type of arc welding is not particularly limited, and examples include TIG welding and plasma arc welding. The conditions for arc welding may be appropriately adjusted according to the type of arc welding, the composition of the ferritic stainless steel material, etc., and are not particularly limited.

[0049] The ferritic stainless steel welded structure according to the embodiment of the present invention can suppress sensitization in the welded metal part without performing heat treatment after arc welding. Therefore, heat treatment does not have to be performed after arc welding. However, in order to improve the high-temperature oxidation resistance of the ferritic stainless steel welded structure according to the embodiment of the present invention, heat treatment may be performed after arc welding. The conditions of the heat treatment are not particularly limited, but it is preferable to heat the ferritic stainless steel welded structure for 1 minute or more in an oxygen partial pressure of 2×10 -5 Pa or more and a temperature range of 1000 °C or higher. Note that the gas other than oxygen in the heat treatment atmosphere is not particularly limited, and hydrogen, argon, etc. can be used. Further, the heat treatment can be performed using, for example, a heating furnace. The form of the heating furnace may be a batch type or a continuous type. Further, after the heat treatment, it is preferable to cool while holding in a temperature range of 900 to 750 °C for 5 minutes or more. In order to hold in a temperature range of 900 to 750 °C for 5 minutes or more, for example, the cooling rate in the temperature range of 900 to 750 °C may be 30 °C / min or less. Further, after holding at an arbitrary constant temperature in the temperature range of 900 to 750 °C for 5 minutes or more, it may be cooled to a temperature range below 750 °C at a cooling rate exceeding 30 °C / min.

[0050] Since the ferritic stainless steel welded structure according to the embodiment of the present invention is excellent in corrosion resistance and heat resistance, it can be used in various applications where these characteristics are required. Examples of applications include exhaust heat recovery devices including heat exchangers used in automotive exhaust system components, plants, and household energy equipment.

[0051] The welding material for arc welding according to the embodiment of the present invention is used for arc welding using a ferritic stainless steel material having the above composition as a base material, and has the above composition. The welding material for arc welding according to the embodiment of the present invention having such characteristics can suppress sensitization in the weld metal part during arc welding and improve the corrosion resistance and heat resistance of the weld metal part.

[0052] The waste heat recovery device according to an embodiment of the present invention includes the above-described ferritic stainless steel welded structure. Since the waste heat recovery device according to the embodiment of the present invention having such a feature includes a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance of a weld metal part, its performance can be improved.

Example

[0053] Hereinafter, the content of the present invention will be described in detail with reference to examples, but the present invention is not construed as being limited thereto.

[0054] <Fabrication of ferritic stainless steel plate (base material)> A ferritic stainless steel having the composition shown in Table 1 (the balance is Fe and impurities) was melted, hot-rolled to obtain a hot-rolled plate with a thickness of 3.0 mm, and then the hot-rolled plate was annealed at 1050 °C and pickled to obtain a hot-rolled annealed plate. Next, the hot-rolled annealed plate was cold-rolled to obtain a cold-rolled plate with a thickness of 1.5 mm, and then the cold-rolled plate was finish-annealed at 1000 °C and pickled to obtain a cold-rolled annealed plate. Next, a test piece with a width of 50 mm × a rolling direction of 500 mm was cut out from the cold-rolled annealed plate by cutting.

[0055]

Table 1

[0056] <Fabrication of welding material (welding rod)> A ferritic stainless steel having the composition shown in Table 2 was melted, hot-rolled to obtain a hot-rolled wire rod with a diameter of 5.5 mm, and then the hot-rolled wire rod was annealed at 1050 °C and pickled to obtain a hot-rolled annealed wire rod. Next, the hot-rolled annealed wire rod was drawn to a diameter of 1.5 mm, then annealed at 1050 °C and pickled, and cut to a length of 530 mm to obtain a welding material.

[0057]

Table 2

[0058] <Fabrication of Ferritic Stainless Steel Welded Structure> Two pieces of the above-mentioned ferritic stainless steel plates were used. After beveling with a 60° groove on their long side edges, the two plates were butt-jointed, and the above-mentioned welding material was sandwiched between them, followed by TIG welding. The welding conditions were set as follows: welding current was 180 A, welding speed was 50 cm / min, electrode diameter was 2.4 mm, and electrode distance was 1.0 mm. The types of the ferritic stainless steel plates and welding materials used are shown in Table 3. For some of the examples, heat treatment was carried out after TIG welding. The heat treatment was performed by putting the welded structure into a vacuum furnace, heating at a temperature of 1025 °C for 5 minutes, with an oxygen partial pressure of 5×10 -4 Pa, and then cooling at a cooling rate of 5 °C / min in the temperature range of 900 - 750 °C. The oxygen partial pressure was controlled by changing the pressure inside the vacuum furnace. Also, the cooling rate was controlled by the introduction amount of nitrogen gas for cooling into the vacuum furnace. The following evaluations were conducted on the ferritic stainless steel welded structure obtained in this way.

[0059] <Contents of Al and Cr in the Weld Metal Part> A 30 mm square test piece for measurement was cut out from the ferritic stainless steel welded structure so that the weld metal part was located at the center. After wet-polishing the entire surface of the test piece for measurement with #600, it was degreased with acetone. Next, in accordance with JIS K0144:2001, glow discharge optical emission spectrometry (GD-OES) was used to analyze the component concentration in the depth direction. In the component concentration profile in the depth direction obtained from this analysis, the Al and Cr concentrations at the position where the O (oxygen) concentration becomes one-tenth of the maximum value were taken as the contents of Al and Cr in the weld metal part.

[0060] <Total Solid Solubility of C and N in the Weld Metal Part> First, the production amounts of titanium and niobium carbonitrides were measured by the following procedure. A 50 mm square test piece for measurement was cut out from a ferritic stainless steel welded structure so that the welded metal part was located at the center, and then the entire surface of the test piece for measurement was subjected to #600 wet polishing. This test piece for measurement was electrolytically etched using the SPEED method. For the electrolytic etching, potentiostatic electrolysis was performed in a 10% acetylacetone solution at 400 mV until the electric charge reached 5000 coulombs. After electrolysis, the solution was filtered through a filter with a lattice diameter of 0.05 μm to collect carbonitrides. Then, the dissolution amount and the collected carbonitride amount were determined by mass measurement. Next, X-ray diffraction (XRD) analysis was performed on the collected carbonitrides. In the XRD analysis, the sum of the peak intensities of Ti carbonitride and Nb carbonitride was determined from the XRD profile. Hereinafter, the sum of the peak intensities of Ti carbonitride is referred to as "Ti carbonitride peak intensity", and the sum of the peak intensities of Nb carbonitride is referred to as "Nb carbonitride peak intensity". The peak positions (diffraction angle 2θ) of each carbonitride used in the calculation are as follows. Ti carbonitride - TiC: 48.838°, TiN: 49.895° Nb carbonitride - NbC: 40.557°, NbN: 41.307° Next, the consumption amounts of C and N used for the formation of Ti carbonitride and Nb carbonitride (hereinafter referred to as "consumed C+N amount") were calculated by the following formula. Consumed C+N amount [mass%] = Collected carbonitride amount [g] × (0.21 × Ti carbonitride peak intensity + 0.12 × Nb carbonitride peak intensity) / (Ti carbonitride peak intensity + Nb carbonitride peak intensity) / Dissolution amount [g] × 100 Next, the total solid solution amount of C and N [mass%] was calculated by subtracting the consumed C+N amount [mass%] from the total content of C and N [mass%].

[0061] <Al concentration in the oxide film> A 50-mm square test piece for measurement was cut out from a ferritic stainless steel welded structure, and its surface was degreased with acetone. Next, in accordance with JIS K0144:2001, glow discharge optical emission spectrometry (GD-OES) was used to analyze the component concentrations in the depth direction. In the component concentration profile in the depth direction obtained by this analysis, the Al, Fe, and Cr concentrations at the position where the O (oxygen) concentration becomes 3 / 4 of the maximum value were determined, and the Al concentration in the oxide film was determined by the following formula. Al concentration in oxide film [mass%] = Al concentration / (Fe concentration + Cr concentration + Al concentration) × 100

[0062] <Sensitization of the weld metal part> Considering the actual use environment of the ferritic stainless steel welded structure, a simulated heat treatment of the use environment was carried out on the ferritic stainless steel welded structure using an electric arc furnace under an air atmosphere with a moisture concentration of 25% by volume at 600 °C for 100 hours. Next, a 50-mm square test piece for measurement was cut out from the ferritic stainless steel welded structure that had undergone the simulated heat treatment of the use environment so that the weld metal part was located at the center, and then the entire surface of the test piece for measurement was subjected to #600 wet polishing. Next, for this test piece for measurement, in accordance with the method for corrosion test of stainless steel in sulfuric acid - copper sulfate specified in JIS G0575:2012, after spreading copper grains on the bottom of the flask, 400 mL of a 15.7% sulfuric acid / 5.5% copper sulfate aqueous solution and the test piece for measurement were placed and heated on a hot plate. After maintaining the boiling state for 20 hours, the test piece for measurement was taken out, washed with water, and dried. Next, using a universal testing machine (UH-300kNI manufactured by Shimadzu Corporation), a 1 t bend was applied to the test piece for measurement in a direction perpendicular to the welding direction, and the bend top was observed with an optical microscope. As a result of this observation, those with cracks occurring along the grain boundaries were evaluated as × (sensitization present), and those without crack occurrence were evaluated as ○ (no sensitization).

[0063] <Corrosion resistance of the weld metal part> A simulated heat treatment of the use environment was carried out on the ferritic stainless steel welded structure in the same manner as above. Next, a test piece for measurement with a width of 50 mm × a rolling direction of 100 mm was cut out from a ferritic stainless steel welded structure that had undergone simulated heat treatment of the use environment so that the welded metal part was located at the center. After that, #600 wet polishing was performed on both surfaces of the test piece for measurement. Next, three sides of the test piece for measurement (excluding one side in the width direction) were coated with resin (one-component condensation type RTV rubber KE44 manufactured by Shin-Etsu Silicone Co., Ltd.). Next, two polyethylene tubes with a diameter of 20 mm × a length of 10 mm were adhered onto a 70 mm × 150 mm bakelite plate, and the uncoated side of the test piece for measurement was placed thereon and adhered. A salt dry-wet composite cycle test (CCT) was performed on the sample thus obtained. The sample was placed in a CCT apparatus such that the surface of the test piece for measurement was at 75° with respect to the horizontal plane and the uncoated side of the test piece for measurement was at the bottom, and 5% saline spray (35°C, 2 hours), drying (60°C, 25% RH, 4 hours), and wetting (50°C, 95% RH, 2 hours) were taken as one cycle and 30 cycles were performed. Then, the sample was washed with water and dried, and the rusting area ratio of the welded metal part on the surface of the test piece for measurement was evaluated (in accordance with JIS G0595:2004). In this evaluation, if the rating number (RN) is 5 or more (corresponding to a rusting area ratio of 15% or less), it can be determined that the corrosion resistance is excellent, and if the RN is less than 5, the corrosion resistance is poor.

[0064] <Heat resistance of the welded metal part> A 50 mm square test piece for measurement was cut out from a ferritic stainless steel welded structure so that the welded metal part was located at the center. After the entire surface of the test piece for measurement was polished wet with #600, it was degreased with acetone. Next, the length, width, and thickness of the test piece for measurement were measured with a micrometer to obtain the surface area and the mass was measured. Next, after performing simulated heat treatment of the use environment in the same manner as above, the mass was measured. Then, the oxidation weight gain was determined by the following formula. Oxidation weight gain [mg / cm 2 = (Mass of the test piece for measurement after simulated heat treatment of the use environment [mg] - Mass of the test piece for measurement before simulated heat treatment of the use environment [mg]) / Surface area [cm 2 In this evaluation, when the oxidation weight gain is 1.0 mg / cm​2 If it is below, it has excellent heat resistance, 1.0 mg / cm 2 If it exceeds, it can be judged that the heat resistance is inferior. The above evaluation results are shown in Table 3.

[0065]

Table 3

[0066] As shown in Table 3, Examples 1 to 7 in which the composition of the base material and the contents of Al and Cr in the weld metal part and the total solid solution amount of C and N satisfy a predetermined range can suppress the sensitization of the weld metal part and have good corrosion resistance and heat resistance. On the other hand, in Comparative Example 1, since the Al content of the welding material was too high, the Al content of the weld metal part also increased. As a result, since the total solid solution amount of C and N in the weld metal part increased, sensitization occurred and the corrosion resistance decreased. In Comparative Example 2, since the Cr content of the welding material was too low, the Cr content of the weld metal part also decreased. As a result, the heat resistance of the weld metal part decreased. In Comparative Example 3, since the total amount of Nb and Ti in the welding material was too low, the total solid solution amount of C and N in the weld metal part increased. As a result, sensitization occurred and the corrosion resistance decreased. In Comparative Example 4, since the Cr content of the base material was too low, the Cr content of the weld metal part also decreased. As a result, the heat resistance of the weld metal part decreased. In Comparative Example 5, since the Al content of the base material was too low, the Al content of the weld metal part also decreased. As a result, the heat resistance of the weld metal part decreased. In Comparative Example 6, since the Al content of the welding material was too high, the Al content of the weld metal part also increased. Also, Comparative Example 6 does not satisfy the requirement that the total amount of Nb and Ti in the welding material is 6(C + N) or more. Therefore, since the total solid solution amount of C and N in the weld metal part increased, sensitization occurred and both the corrosion resistance and heat resistance decreased.

[0067] As can be seen from the above results, according to the present invention, it is possible to provide a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, corrosion resistance and heat resistance of the weld metal part), a method for manufacturing the same, and a waste heat recovery device. Further, according to the present invention, it is possible to provide a welding material suitable for manufacturing a ferritic stainless steel welded structure excellent in corrosion resistance and heat resistance (particularly, corrosion resistance and heat resistance of the weld metal part).

Claims

1. A ferritic stainless steel welded structure including a base material and a weld metal part, The base material contains, by mass, C: 0.001 to 0.050%, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001 to 0.050%, Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6(C+N) or more (C and N represent the contents of C and N, respectively), and the balance is Fe and impurities, The weld metal portion contains, by mass, 0.10 to 1.00% Al, 15.00 to 24.00% Cr, and a total solid solution amount of C and N of 0.015 mass% or less.

2. The ferritic stainless steel welded structure according to claim 1, wherein the base material further contains, on a mass basis, at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, and W: 1.00% or less.

3. 3. The ferritic stainless steel welded structure according to claim 1, wherein the base metal further contains, on a mass basis, at least one selected from the group consisting of REM: 0.10% or less and Ca: 0.10% or less.

4. The ferritic stainless steel welded structure according to any one of claims 1 to 3, wherein the base material further contains, on a mass basis, at least one selected from Sn: 0.10% or less and B: 0.0100% or less.

5. The ferritic stainless steel welded structure according to any one of claims 1 to 4, wherein the ferritic stainless steel welded structure has an oxide film on a surface thereof containing less than 30 mass% Al.

6. The ferritic stainless steel welded structure according to any one of claims 1 to 4, wherein the ferritic stainless steel welded structure has an oxide film on a surface thereof containing 30 mass% or more of Al.

7. The ferritic stainless steel welded structure according to any one of claims 1 to 6, which is used in an exhaust heat recovery device.

8. A method for manufacturing a ferritic stainless steel welded structure using a ferritic stainless steel material as a base material and arc welding using a welding material, The ferritic stainless steel material contains, by mass, C: 0.001 to 0.050%, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001 to 0.050%, Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti is 6 (C + N) or more (C and N represent the contents of C and N, respectively), and the balance is Fe and impurities, The welding material contains, by mass, C: 0.010 to 0.017%, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.009 to 0.015%, Cu: 1.00% or less, Mo: 1.00% or less, Si: 2.00% or less, Al: 0.02 to 0.50%, Nb: 0.50% or less, and Ti: 0.50% or less, with the total content of Nb and Ti being 6(C+N) or more (C and N represent the contents of C and N, respectively), and the balance being Fe and impurities.

9. The manufacturing method according to claim 8, wherein the ferritic stainless steel material further contains, by mass, at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, and W: 1.00% or less.

10. The method according to claim 8 or 9, wherein the ferritic stainless steel material further contains, on a mass basis, at least one selected from REM: 0.10% or less and Ca: 0.10% or less.

11. The manufacturing method according to any one of claims 8 to 10, wherein the ferritic stainless steel material further contains at least one selected from Sn: 0.10% or less and B: 0.0100% or less, on a mass basis.

12. The method according to any one of claims 8 to 11, wherein no heat treatment is performed after the arc welding.

13. The method according to any one of claims 8 to 11, further comprising the step of: performing a heat treatment after the arc welding.

14. The manufacturing method according to any one of claims 8 to 13, wherein the welding material further contains, by mass, at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Ca: 0.10% or less, Sn: 0.10% or less, and B: 0.0100% or less.

15. A welding material for arc welding using a ferritic stainless steel material as a base metal, the ferritic stainless steel material having a composition, on a mass basis, containing C: 0.001 to 0.050%, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.001 to 0.050%, Cu: 1.00% or less, Mo: 1.00% or less, Si: 3.00% or less, Al: 0.80 to 5.00%, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti being 6(C+N) or more (C and N represent the contents of C and N, respectively), and the balance consisting of Fe and impurities, A welding material having a composition containing, on a mass basis, C: 0.010 to 0.017%, Mn: 1.00% or less, Ni: 1.00% or less, P: 0.100% or less, S: 0.050% or less, Cr: 15.00 to 24.00%, N: 0.009 to 0.015%, Cu: 1.00% or less, Mo: 1.00% or less, Si: 2.00% or less, Al: 0.02 to 0.50%, Nb: 0.50% or less, Ti: 0.50% or less, the total content of Nb and Ti being 6(C+N) or more (C and N represent the contents of C and N, respectively), and the balance consisting of Fe and impurities.

16. The welding material according to claim 15, further comprising, on a mass basis, at least one selected from Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.10% or less, Ca: 0.10% or less, Sn: 0.10% or less, and B: 0.0100% or less.

17. A waste heat recovery device comprising the ferritic stainless steel welded structure according to any one of claims 1 to 7.

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