Austenitic stainless steel material and welded structure

Abstract

To provide an inexpensive austenitic stainless steel that has excellent corrosion resistance and can be welded to form a weld having excellent corrosion resistance.SOLUTION: An austenitic stainless steel contains, by mass, C: 0.010-0.060%, Si: 2.00% or less, Mn: 3.00% or less, P: 0.035% or less, S: 0.0300% or less, Ni: 6.00-14.00%, Cr: 20.0-26.0%, Cu: 0.01-3.00%, Al: 0.200% or less, Ti: 0.090-2.000%, N: 0.100-0.250%, O: 0.0070% or less with the balance being Fe and impurities.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to austenitic stainless steel materials and welded structures.

Background Art

[0002] Austenitic stainless steel materials typified by SUS304 are used in various applications such as building members and automobile parts because of their good corrosion resistance and strength. However, SUS304 may not have sufficient corrosion resistance depending on the application. Therefore, for applications where higher corrosion resistance is required, austenitic stainless steel materials (SUS316, SUS316L) with an increased amount of Ni and added Mo are used.

[0003] On the other hand, when austenitic stainless steel materials are used in various applications, they are often welded. However, the welded part, particularly the HAZ (Heat Affected Zone), may be sensitized and the corrosion resistance may decrease. In the HAZ, when held at the precipitation temperature of Cr carbides, Cr carbides precipitate at the grain boundaries, and a Cr-depleted layer is formed around them, causing sensitization. Note that the HAZ means a portion where the temperature rises due to the influence of welding. Regarding the sensitization of the HAZ, it is known that the formation of Cr carbides can be suppressed by reducing the C content or adding Ti. Since SUS316L has a reduced C content, it is considered to have good corrosion resistance in the HAZ. However, since SUS316L contains a large amount of expensive elements such as Mo and Ni, the product price is high.

[0004] As an austenitic stainless steel material excellent in the corrosion resistance of the HAZ, for example, in mass%, C: 0.04 to 0.15%, Si: 1.50% or less, Mn: 2.0 to 6.0%, P: 0.06% or less, S: 0.005% or less, Ni: 1.0 to 4.9%, Cr: 15.0 to 19.0%, Cu: 1.0 to 3.5%, N: 0.04 to 0.20%, Sn: 0.02% or less, B: 0.001 to 0.010%, with the balance being substantially composed of Fe and inevitable impurities, when the welded HAZ part is etched in a 10% oxalic acid solution at a current of 1 A per 1 cm 2 of area for 90 seconds, a low Ni austenitic stainless steel sheet has been proposed which is characterized by having no sensitized structure (Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Since the amount of Cr in the austenitic stainless steel sheet of Patent Document 1 is small, the corrosion resistance may not be sufficient depending on the application. The present invention has been made to solve the above problems, and an object thereof is to provide an inexpensive austenitic stainless steel material excellent in corrosion resistance and capable of forming a welded part excellent in corrosion resistance when welded. Another object of the present invention is to provide an inexpensive welded structure excellent in the corrosion resistance of the base material and the welded part.

Means for Solving the Problems

[0007] As a result of studying the composition of the austenitic stainless steel material based on the composition of SUS316L, the present inventors have found that the above problems can be solved by setting a specific composition, and have completed the present invention.

[0008] That is, the present invention is an austenitic stainless steel material containing, by mass, C: 0.010 to 0.060%, Si: 2.00% or less, Mn: 3.00% or less, P: 0.035% or less, S: 0.0300% or less, Ni: 6.00 to 14.00%, Cr: 20.0 to 26.0%, Cu: 0.01 to 3.00%, Al: 0.200% or less, Ti: 0.090 to 2.000%, N: 0.100 to 0.250%, O: 0.0070% or less, with the balance being Fe and impurities.

[0009] In addition, the present invention is a welded structure in which metal materials are welded to each other, and at least one of the metal materials is the welded structure of the austenitic stainless steel material.

Advantages of the Invention

[0010] According to the present invention, it is possible to provide an inexpensive austenitic stainless steel material that is excellent in corrosion resistance and can form a welded portion excellent in corrosion resistance when welded. In addition, according to the present invention, it is possible to provide an inexpensive welded structure excellent in corrosion resistance of the base material and the welded portion.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements can be appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention, and such modified and improved embodiments also fall within the scope of the present invention. In addition, in this specification, the “%” display regarding components means “mass %” unless otherwise specified.

[0012] (Austenitic Stainless Steel Material) The austenitic stainless steel material according to an embodiment of the present invention contains C: 0.010 to 0.060%, Si: 2.00% or less, Mn: 3.00% or less, P: 0.035% or less, S: 0.0300% or less, Ni: 6.00 to 14.00%, Cr: 20.0 to 26.0%, Cu: 0.01 to 3.00%, Al: 0.200% or less, Ti: 0.090 to 2.000%, N: 0.100 to 0.250%, O: 0.0070% or less, and the balance consists of Fe and impurities. Here, in this specification, "stainless steel material" means a material formed from stainless steel, and its material form is not particularly limited. Examples of the material form include plate shape (including strip shape), rod shape, tubular shape, etc. Also, various shaped steels such as T-shaped and I-shaped cross-sectional shapes may be used. Further, "impurities" mean components that are mixed in due to raw materials such as ores and scraps and various factors in the manufacturing process when industrially manufacturing the austenitic stainless steel material, and are permitted within a range that does not adversely affect the present invention.

[0013] Moreover, the austenitic stainless steel material according to an embodiment of the present invention may further contain one or more selected from Mo: 3.00% or less, B: 0.0001 to 0.0100%. Furthermore, the austenitic stainless steel material according to an embodiment of the present invention may further contain one or more selected from Mg: 0.0001 to 0.1000%, REM: 0.0001 to 0.1000%, Ca: 0.0001 to 0.1000%. Furthermore, the austenitic stainless steel material according to an embodiment of the present invention may further contain one or more selected from Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, Zr: 0.001 to 1.000%, W: 0.001 to 1.000%, Co: 0.001 to 1.000%, Hf: 0.001 to 1.000%, Ta: 0.001 to 1.000%, Sn: 0.001 to 0.100%. Hereinafter, each component will be described in detail.

[0014] <C: 0.010~0.060%> If the content of C is too high, the corrosion resistance of the austenitic stainless steel itself will decrease. Also, when the austenitic stainless steel is welded, sensitization of the HAZ occurs, resulting in a decrease in the corrosion resistance of the welded part. Therefore, the upper limit value of the C content is controlled to 0.060%, preferably 0.059%, more preferably 0.058%. On the other hand, if the C content is too low, it will lead to an increase in refining cost. Therefore, the lower limit value of the C content is controlled to 0.010%, preferably 0.015%, more preferably 0.020%. In this specification, "corrosion resistance" means corrosion resistance in a corrosive environment containing NaCl such as seawater or salt water.

[0015] <Si: 2.00% or less> If the content of Si is too high, the workability of the austenitic stainless steel will decrease. Therefore, the upper limit value of the Si content is controlled to 2.00%, preferably 1.80%, more preferably 1.60%. On the other hand, the lower limit value of the Si content is not particularly limited, but is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%.

[0016] <Mn: 3.00% or less> Mn is an austenite phase (γ-phase) forming element. If the content of Mn is too high, the corrosion resistance of the austenitic stainless steel will decrease. Therefore, the upper limit value of the Mn content is controlled to 3.00%, preferably 2.80%, more preferably 2.50%. 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%, still more preferably 0.10%.

[0017] <P: 0.035% or less> If the content of P is too high, the workability of the austenitic stainless steel will decrease. Therefore, the upper limit value of the P content is controlled to 0.035%, preferably 0.034%, more preferably 0.033%. On the other hand, the lower limit value of the P content is not particularly limited, but is preferably 0.001%, more preferably 0.005%, still more preferably 0.010%.

[0018] <S: below 0.0300%> If the content of S is too high, the manufacturability of austenitic stainless steel materials will deteriorate. Therefore, the upper limit value of the content of S is controlled to be 0.0300%, preferably 0.0250%, more preferably 0.0200%. On the other hand, the lower limit value of the content of S is not particularly limited, but is preferably 0.0001%, more preferably 0.0003%, still more preferably 0.0005%.

[0019] <Ni: 6.00 - 14.00%> Ni, like Mn, is an austenite phase (γ-phase) forming element. Since Ni is expensive, if the content is too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the content of Ni is controlled to be 14.00%, preferably 11.00%, more preferably 10.00%. On the other hand, if the content of Ni is too low, the corrosion resistance and workability of austenitic stainless steel materials will deteriorate. Therefore, the lower limit value of the content of Ni is controlled to be 6.00%, preferably 6.50%, more preferably 7.00%.

[0020] <Cr: 20.0 - 26.0%> If the content of Cr is too high, the formation of intermetallic compounds (σ-phase) will be promoted, so the workability of austenitic stainless steel materials will deteriorate. Therefore, the upper limit value of the content of Cr is controlled to be 26.0%, preferably 25.5%, more preferably 25.0%. On the other hand, if the content of Cr is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit value of the content of Cr is controlled to be 20.0%, preferably 20.5%.

[0021] <Cu: 0.01 - 3.00%> If the Cu content is too high, the corrosion resistance of the austenitic stainless steel will decrease. Therefore, the upper limit of the Cu content is controlled to 3.00%, preferably 2.50%, more preferably 2.00%. On the other hand, if the Cu content is too low, the workability of the austenitic stainless steel will decrease. Therefore, the lower limit of the Cu content is controlled to 0.01%, preferably 0.10%, more preferably 0.15%.

[0022] <Al: 0.200% or less> If the Al content is too high, the amount of inclusions generated will increase and the quality will deteriorate. Therefore, the upper limit of the Al content is controlled to 0.200%, preferably 0.100%, more preferably 0.050%. On the other hand, the lower limit of the Al content is not particularly limited, but is preferably 0.0001%, more preferably 0.0002%, still more preferably 0.0003%.

[0023] <Ti: 0.090 - 2.000%> Ti is an element that fixes C and N in the austenitic stainless steel to improve intergranular corrosion resistance. Therefore, by adding Ti, the sensitization of the HAZ is suppressed and the corrosion resistance of the welded part is improved. Also, Ti is an element that disperses and precipitates Ti carbonitrides. Therefore, by adding Ti, the coarsening of crystal grains during welding can be suppressed by the pinning effect of the dispersed and precipitated Ti carbonitrides. From the viewpoint of obtaining such an effect of Ti, the lower limit of the Ti content is controlled to 0.090%, preferably 0.095%, more preferably 0.100%. Also, if the Ti content is too high, the workability of the austenitic stainless steel will decrease. Therefore, the upper limit of the Ti content is controlled to 2.000%, preferably 1.800%, more preferably 1.600%.

[0024] <N: 0.100 - 0.250%> N is an element effective for improving corrosion resistance and stabilizing the austenite phase. From the viewpoint of obtaining such an effect by N, the lower limit value of the N content is controlled to 0.100%, preferably 0.105%. On the other hand, N combines with Cr to form Cr nitride, which causes sensitization and thus reduces the corrosion resistance of the welded part. The formation of this Cr nitride can be suppressed by preferentially forming Ti carbonitride by adding Ti. From the viewpoint of ensuring the effect of suppressing the formation of Cr nitride by Ti and suppressing sensitization, the upper limit value of the N content is controlled to 0.250%, preferably 0.230%, more preferably 0.210%.

[0025] <O: 0.0070% or less> O is a factor for generating alumina (Al2O3)-based inclusions. Since alumina-based inclusions are hard and difficult to be broken by rolling and remain as coarse inclusions (with a diameter of 15 μm or more), the fatigue characteristics of austenitic stainless steel materials are deteriorated. That is, when the content of O is too high, the amount of formation of this alumina-based inclusions increases and the fatigue characteristics of austenitic stainless steel materials are deteriorated. Therefore, the upper limit value of the O content is controlled to 0.0070%, preferably 0.0060%, more preferably 0.0055%. On the other hand, the lower limit value of the O content is not particularly limited, but is preferably 0.0010%, more preferably 0.0020%, still more preferably 0.0030%.

[0026] <Mo: 3.00% or less> Mo is an element added as necessary to improve corrosion resistance. However, since Mo is expensive, if the content of Mo is too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the Mo content is controlled to 3.00%, preferably 2.00%, more preferably 1.00%, still more preferably 0.50%, particularly preferably 0.20%. On the other hand, the lower limit value of the Mo content is not particularly limited, but is preferably 0.001%, more preferably 0.002%, still more preferably 0.003%.

[0027] <B: 0.0001 - 0.0100%> B is an element added as necessary to improve workability (hot workability). From the viewpoint of obtaining the effect of B, the lower limit of the content of B is controlled to 0.0001%, preferably 0.0010%. On the other hand, if the content of B is too high, the corrosion resistance of the austenitic stainless steel material will decrease. Therefore, the upper limit of the content of B is controlled to 0.0100%, preferably 0.0060%, more preferably 0.0040%.

[0028] <Mg: 0.0001~0.1000%> Mg is an element added as necessary to improve hot workability. From the viewpoint of obtaining the effect of Mg, the lower limit of the content of Mg is controlled to 0.0001%, preferably 0.0005%, more preferably 0.0010%. Also, if the content of Mg is too high, the amount of inclusions generated will increase and the quality will deteriorate. Therefore, the upper limit of the content of Mg is controlled to 0.1000%, preferably 0.0500%, more preferably 0.0100%.

[0029] <REM: 0.0001~0.1000%> REM (rare earth element) is an element added as necessary to improve hot workability. From the viewpoint of obtaining the effect of REM, the lower limit of the content of REM is controlled to 0.0001%, preferably 0.0005%, more preferably 0.0010%. Also, since REM is expensive, if the content of REM is too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit of the content of REM is controlled to 0.1000%, preferably 0.0500%, more preferably 0.0100%. Note that REM refers to the general term of two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu). These may be used alone or as a mixture.

[0030] <Ca: 0.0001~0.1000%> Ca is an element added as necessary to improve hot workability. From the perspective of obtaining the effect of Ca, the lower limit of the Ca content is controlled to 0.0001%, preferably 0.0005%, more preferably 0.0010%. Also, if the Ca content is too high, the amount of inclusions generated will increase and the quality will deteriorate. Therefore, the upper limit of the Ca content is controlled to 0.1000%, preferably 0.0500%, more preferably 0.0100%.

[0031] <Nb: 0.001~1.000%> Nb is an element added as necessary to fix C in austenitic stainless steel materials and improve intergranular corrosion resistance. From the perspective of obtaining the effect of Nb, the lower limit of the Nb content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Nb content is too high, the workability of austenitic stainless steel materials will deteriorate. Therefore, the upper limit of the Nb content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0032] <V: 0.001~1.000%> V is an element added as necessary to fix C in austenitic stainless steel materials and improve intergranular corrosion resistance. From the perspective of obtaining the effect of V, the lower limit of the V content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the V content is too high, the workability of austenitic stainless steel materials will deteriorate. Therefore, the upper limit of the V content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0033] <Zr: 0.001~1.000%> Zr is an element that is added as necessary to fix C in austenitic stainless steel materials and improve intergranular corrosion resistance. From the viewpoint of obtaining the effect of Zr, the lower limit value of the Zr content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Zr content is too high, the workability of the austenitic stainless steel material will deteriorate. Therefore, the upper limit value of the Zr content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0034] <W:0.001~1.000%> W is an element that is added as necessary to improve high-temperature strength and corrosion resistance. From the viewpoint of obtaining the effect of W, the lower limit value of the W content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the W content is too high, the workability of the austenitic stainless steel material will deteriorate and the manufacturing cost will increase. Therefore, the upper limit value of the W content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0035] <Co:0.001~1.000%> Co is an element that is added as necessary to improve corrosion resistance. From the viewpoint of obtaining the effect of Co, the lower limit value of the Co content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Co content is too high, the workability of the austenitic stainless steel material will deteriorate and the manufacturing cost will increase. Therefore, the upper limit value of the Co content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0036] <Hf:0.001~1.000%> Hf is an element added as needed to fix C in austenitic stainless steel materials to improve intergranular corrosion resistance. From the viewpoint of obtaining the effect of Hf, the lower limit value of the Hf content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Hf content is too high, the workability of the austenitic stainless steel material will deteriorate. Therefore, the upper limit value of the Hf content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0037] <Ta: 0.001~1.000%> Ta is an element added as needed to fix C in austenitic stainless steel materials to improve intergranular corrosion resistance. From the viewpoint of obtaining the effect of Ta, the lower limit value of the Ta content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Ta content is too high, the workability of the austenitic stainless steel material will deteriorate. Therefore, the upper limit value of the Ta content is controlled to 1.000%, preferably 0.800%, more preferably 0.500%.

[0038] <Sn: 0.001~0.100%> Sn is an element added as needed to improve corrosion resistance. From the viewpoint of obtaining the effect of Sn, the lower limit value of the Sn content is controlled to 0.001%, preferably 0.005%, more preferably 0.010%. Also, if the Sn content is too high, the manufacturability of the austenitic stainless steel material will deteriorate. Therefore, the upper limit value of the Sn content is controlled to 0.100%, preferably 0.050%, more preferably 0.030%.

[0039] It is preferable that the ratio of Cr equivalent to Ni equivalent (Cr equivalent / Ni equivalent) in the austenitic stainless steel material according to the embodiment of the present invention is 1.48~1.95. Here, the Ni equivalent is represented by the following formula (1). Ni equivalent = Ni + 0.5Mn + 30C + 30(N - 0.06) ···(1) Further, the Cr equivalent is represented by the following formula (2). Cr equivalent = Cr + 1.5Si + Mo + 0.5Nb + 2Ti ···(2) In formulas (1) and (2), each element symbol represents the content (% by mass) of each element. When a predetermined element is not contained, the value of that element is taken as 0. If the ratio of the Cr equivalent to the Ni equivalent is within the above range, FA mode solidification can be achieved during welding, so that hot cracking can be suppressed.

[0040] In the austenitic stainless steel material according to the embodiment of the present invention, the content of Ti carbonitride is preferably 0.01% or more, more preferably 0.02% or more. By controlling the content of Ti carbonitride within such a range, the coarsening of crystal grains during welding can be suppressed by the pinning effect of Ti carbonitride. The upper limit value of the content of Ti carbonitride is not particularly limited, but is preferably 1.00%, more preferably 0.80%, and still more preferably 0.60%. The content of Ti carbonitride can be measured by the method described later.

[0041] The type of the austenitic stainless steel material according to the embodiment of the present invention is not particularly limited as long as it has the above characteristics. For example, the austenitic stainless steel material according to the embodiment of the present invention can be various steel materials such as hot-rolled steel materials, hot-rolled annealed steel materials, cold-rolled steel materials, and cold-rolled annealed steel materials.

[0042] The austenitic stainless steel material according to the embodiment of the present invention can be manufactured by using methods known in the art except for melting the stainless steel having the above composition. Specifically, when the austenitic stainless steel material is a cold-rolled annealed steel material, it can be manufactured as follows. First, the stainless steel having the above composition is melted and forged or cast, and then hot rolling is performed to obtain a hot-rolled steel material. Next, annealing, pickling, and cold rolling are appropriately performed on the hot-rolled steel material to obtain a cold-rolled steel material. Next, annealing and pickling are appropriately performed on the cold-rolled steel material to obtain a cold-rolled annealed steel material. Regarding the conditions in each process, they may be appropriately adjusted according to the composition of the austenitic stainless steel material, and are not particularly limited.

[0043] The austenitic stainless steel material according to the embodiment of the present invention is excellent in corrosion resistance, can form a welded part excellent in corrosion resistance when welded, and is inexpensive, so it can be used in various applications such as building members and automobile parts.

[0044] (Welded structure) In the welded structure according to the embodiment of the present invention, metal materials are welded to each other, and at least one of the metal materials is the above-mentioned austenitic stainless steel material. Since the above-mentioned austenitic stainless steel material is excellent in corrosion resistance, can form a welded part excellent in corrosion resistance when welded, and is inexpensive, it is possible to obtain an inexpensive welded structure excellent in corrosion resistance of the base material and the welded part.

[0045] The other metal material may be a metal material different from the above-mentioned austenitic stainless steel material, but it is preferable that both are the above-mentioned austenitic stainless steel materials. By using the above-mentioned austenitic stainless steel materials for both of the metal materials to be welded, the corrosion resistance of the base material and the welded part can be further improved.

[0046] In the welded structure according to the embodiment of the present invention, the content of the δ-ferrite phase in the weld metal part is preferably 1.0 to 10.0%, more preferably 2.0 to 9.0%. By controlling the δ-ferrite phase in the weld metal part within the above range, since the weld metal part solidifies in the FA mode, high-temperature cracking can be suppressed. Here, in this specification, the "weld metal part" means a part that melts and re-solidifies due to the influence of welding.

[0047] In the welded structure according to an embodiment of the present invention, the pitting potential of the welded portion is preferably 0.50 V or more. If the pitting potential is within such a range, it can be said that the corrosion resistance of the welded portion is good. Note that the upper limit value of the pitting potential is not particularly limited, but is, for example, 2.00 V, preferably 1.50 V. Here, in this specification, the "welded portion" means a portion including both the welded metal portion and the HAZ. That is, the "welded portion" includes both a portion that melts and re-solidifies and a portion that is not melted but is affected by heat due to the influence of welding. Further, the pitting potential of the welded portion can be measured by the method described later. Also, the potential is based on Ag / AgCl.

[0048] The welded structure according to an embodiment of the present invention can be manufactured by using a method known in the art, except that the above-described austenitic stainless steel material is used for at least one of the metal materials. The method of welding metal materials is not particularly limited, and known methods in the art such as arc welding (TIG welding, etc.), electron beam welding, laser welding, plasma arc welding, and spot welding can be used. For welding, a filler metal may be appropriately used to adjust the content of the δ-ferrite phase in the welded metal portion. Note that the welding conditions may be appropriately adjusted according to the type of welding and the composition of the austenitic stainless steel material, and are not particularly limited.

Examples

[0049] 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.

[0050] (Examples 1 to 9 and Comparative Examples 1 to 4) 30 kg of stainless steel having the composition shown in Table 1 was melted by vacuum melting, forged into a plate with a thickness of 30 mm, heated at 1230 °C for 2 hours, and hot-rolled to a thickness of 4.0 mm to obtain a hot-rolled steel sheet. Next, the hot-rolled steel sheet was annealed and pickled to obtain a hot-rolled annealed steel sheet, and then the hot-rolled annealed steel sheet was cold-rolled to a thickness of 1.0 mm to obtain a cold-rolled steel sheet. Next, after annealing the cold-rolled steel sheet, it was water-cooled and pickled to obtain a cold-rolled annealed steel sheet.

[0051]

Table 1

[0052] The following evaluations were performed on the cold-rolled annealed steel sheet obtained above.

[0053] <Content of Ti carbonitride> A square test piece with a side length of 20 mm was cut out from the cold-rolled annealed steel sheet by cutting, and the entire surface was wet-polished with a #600 abrasive, and then electrolytic etching by the SPEED method was performed. The SPEED method uses a 10 mass% acetylacetone solution, performs constant potential electrolysis at 400 mV until 5 k coulombs of electrolysis is reached, and filters the solution after electrolysis with a filter having a grid diameter of 0.05 μm to collect inclusions (Ti carbonitride). The amount of collected inclusions and the amount of weight loss of the square test piece were determined by mass measurement. Then, the content of inclusions (Ti carbonitride) was determined by the following formula. Content of inclusions (Ti carbonitride) = Amount of collected inclusions / Amount of weight loss of square test piece × 100

[0054] <Content of δ-ferrite phase in the weld metal part> For the cold-rolled annealed steel sheet, pseudo-welding processing was carried out in the same manner as TIG welding (without filler metal) of bead-on-plate (however, welding was not performed). In TIG welding, the welding heat input was adjusted so that the back bead width was 3 mm. Then, in the pseudo-welded part, the content of the δ-ferrite phase was measured using a ferrite scope (FERITESCOPE (registered trademark) FMP30 manufactured by Fischer). The measurement was carried out at three arbitrary locations in the pseudo-welded part, and the average value was taken as the result. In this evaluation, if the content of the δ-ferrite phase is 1.0 to 10%, it can be considered that the weld metal part solidifies in the FA mode.

[0055] <Corrosion resistance of the welded part: Pitting potential> The corrosion resistance of the welded part was evaluated by measuring the pitting potential in accordance with JIS G0577:2014. Specifically, the pitting potential was measured as follows. Pseudo-welding processing was carried out on the cold-rolled annealed steel sheet in the same manner as above, and the corrosion resistance of the pseudo-welded part was evaluated in accordance with JIS G0577:2014. After cutting out a 15 mm × 20 mm test piece with the pseudo-welded part in the center, wet polishing with #600 was performed. Next, except for the electrode surface, the other parts were insulated and coated with silicone resin so that the electrode surface (exposed part) of this test piece was 10 mm × 10 mm to obtain a test piece for pitting potential measurement. Next, the test piece for pitting potential measurement was immersed in a 3.5% NaCl solution at 30°C that had been sufficiently degassed with Ar, and potentiodynamic anodic polarization was carried out at 20 mV / min from the natural potential to measure the pitting potential. The pitting potential was the potential when the current flowed at 100 μA / cm 2 This evaluation considered those with a pitting potential of 0.50 V vs. Ag / AgCl (hereinafter, all potentials are based on Ag / AgCl) or higher to be qualified.

[0056] The above evaluation results are shown in Table 2.

[0057]

Table 2

[0058] As shown in Table 2, since the cold-rolled annealed steel sheets (austenitic stainless steel materials) of Examples 1 to 9 satisfied a predetermined composition, the weld zone had good corrosion resistance. Although the corrosion resistance of the base material was not measured above, since the corrosion resistance of the base material is higher than that of the weld zone, it can be said that the corrosion resistance of the base material is also good. On the other hand, in the cold-rolled annealed steel sheet (austenitic stainless steel material) of Comparative Example 1, since the Ni content was too high and the N content was too low, the content of the δ-ferrite phase in the weld metal part decreased. Further, since the Cr equivalent / Ni equivalent of this cold-rolled annealed steel sheet was too low, the content of the δ-ferrite phase in the weld metal part decreased, hot cracking was likely to occur, and since it contained a large amount of expensive Ni, the manufacturing cost was also high. In the cold-rolled annealed steel sheet (austenitic stainless steel material) of Comparative Example 2, since the contents of Cr and N were too low, the corrosion resistance of the weld zone was not sufficient. In the cold-rolled annealed steel sheet (austenitic stainless steel material) of Comparative Example 3, since the C content was too high and the Ti content was too low, the corrosion resistance of the weld zone was not sufficient. In the cold-rolled annealed steel sheet (austenitic stainless steel material) of Comparative Example 4, since the Ti content was too low, the corrosion resistance of the weld zone was not sufficient. Further, since the Cr equivalent / Ni equivalent of this cold-rolled annealed steel sheet was too high, the content of the δ-ferrite phase in the weld metal part increased, and hot cracking was likely to occur.

[0059] According to the present invention, it is possible to provide an inexpensive austenitic stainless steel material having excellent corrosion resistance and capable of forming a weld zone having excellent corrosion resistance when welded. Further, according to the present invention, it is possible to provide an inexpensive welded structure having excellent corrosion resistance of the base material and the weld zone.

Claims

1. An austenitic stainless steel material containing, by mass, C: 0.010 to 0.060%, Si: 2.00% or less, Mn: 3.00% or less, P: 0.035% or less, S: 0.0300% or less, Ni: 6.00 to 14.00%, Cr: 20.0 to 26.0%, Cu: 0.01 to 3.00%, Al: 0.200% or less, Ti: 0.090 to 2.000%, N: 0.100 to 0.250%, O: 0.0070% or less, with the balance being Fe and impurities.

2. The austenitic stainless steel material according to Claim 1, further containing one or more selected from Mo: 0.50% or less and B: 0.0001 to 0.0060% by mass.

3. The austenitic stainless steel material according to Claim 1 or 2, further containing one or more selected from Mg: 0.0001 to 0.0100%, REM: 0.0001 to 0.0100%, and Ca: 0.0001 to 0.0100% by mass.

4. The austenitic stainless steel material according to any one of Claims 1 to 3, further containing one or more selected from Nb: 0.001 to 0.500%, V: 0.001 to 0.500%, Zr: 0.001 to 0.500%, W: 0.001 to 0.500%, Co: 0.001 to 0.500%, Hf: 0.001 to 0.500%, Ta: 0.001 to 0.500%, and Sn: 0.001 to 0.050% by mass.

5. The austenitic stainless steel material according to any one of Claims 1 to 4, wherein the ratio (Cr equivalent / Ni equivalent) of the Cr equivalent represented by the following formula (2) to the Ni equivalent represented by the following formula (1) is 1.48 to 1.

95. Ni equivalent = Ni + 0.5Mn + 30C + 30(N - 0.06) ··· (1) Cr equivalent = Cr + 1.5Si + Mo + 0.5Nb + 2Ti ··· (2) In the formulas, each element symbol represents the content (mass%) of each element.

6. The austenitic stainless steel material according to any one of Claims 1 to 5, containing Ti carbonitride of 0.01 mass% or more.

7. A welded structure in which metal materials are welded to each other, wherein at least one of the metal materials is the austenitic stainless steel material according to any one of Claims 1 to 6.

8. The welded structure according to Claim 7, wherein the content of the δ-ferrite phase in the weld metal part is 1.0 to 10.0%.

9. The welded structure according to claim 7 or 8, wherein the pitting potential of the welded portion is 0.50 V or more.

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