Ferritic stainless steel materials, martensitic stainless steel materials, ferritic-martensitic duplex stainless steel materials, methods for producing the same, and corrosion-resistant members

Abstract

To provide a stainless steel material which has smooth and glossy surface and has excellent corrosion resistance and fatigue characteristics.SOLUTION: A stainless steel material 10 has a composition comprising, by mass, 0.001 to 0.150% C, 1.00% or less Si, 2.00% or less Mn, 0.050% or less P, 0.0300% or less S, less than 2.00% Ni, 11.00 to 30.00% Cr, 6.00% or less Mo, 0.60% or less Cu, 0.050% or less N, and 0.400% or less Al, wherein Si+2Al is less than 1.20%, and the balance Fe and inevitable impurities. The stainless steel material 10 has a ratio D2 / D1 of a number density D2 of an inclusion 13 on a surface B to a number density D1 of the inclusion 13 in a parent phase 11 at a position C where a depth from the surface B is 1 / 4 of the thickness of 0.50 or less.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to ferritic stainless steel materials, martensitic stainless steel materials, ferritic-martensitic duplex stainless steel materials, methods for producing them, and corrosion-resistant members.

Background Art

[0002] Since stainless steel materials are excellent in various properties such as corrosion resistance, they are used in a wide range of applications such as automotive parts, building parts, and kitchen utensils. Stainless steel materials are classified into steel sheets, bars, steel strips, bars, steel pipes, etc. according to their shapes. A stainless steel sheet, which is a general stainless steel material, is manufactured by the following steps. For example, a hot-rolled steel sheet (thick plate) is produced by continuously casting molten iron obtained by melting raw materials of stainless steel into a slab, hot-rolling the slab, and then annealing and pickling. Also, a cold-rolled steel sheet (thin plate) is produced by cold-rolling a hot-rolled steel sheet and then annealing and pickling. In such a manufacturing process of stainless steel materials, pickling is performed to remove the oxide scale formed on the surface of the stainless steel material. Hereinafter, removing the oxide scale formed on the surface of the stainless steel material is referred to as "descaling".

[0003] However, the oxide scale may not be sufficiently removed only by pickling. Therefore, in a general descaling process, a method is adopted in which mechanical pretreatment such as a scale breaker or shot blasting is performed to crack the oxide scale, and then pickling is performed to make it easier to remove the oxide scale (for example, Patent Documents 1 and 2). Also, a method of immersing a stainless steel material in a salt bath as a chemical pretreatment is known.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] However, in the conventional descaling process using pickling, due to the surface irregularities formed in the pretreatment and the roughening of the surface by pickling, the surface of the stainless steel material becomes white and loses its luster, resulting in a decrease in design quality. In particular, cold-rolled steel materials require a higher level of design quality (smoothness and glossiness) compared to hot-rolled steel materials. Therefore, it is difficult to obtain the desired design quality in the conventional descaling process using pickling. In addition, ferritic stainless steel materials have a thick oxide scale formed on the surface, making it difficult to crack them by mechanical pretreatment and prone to pickling unevenness. Furthermore, when the oxide scale is removed, inclusions are exposed on the surface of the stainless steel material, and these inclusions become a factor in reducing the corrosion resistance and fatigue characteristics of the stainless steel material. Therefore, in order to solve these problems, it is conceivable to polish the surface after the descaling process. However, if the surface is polished until it becomes smooth, the grinding amount increases, resulting in a decrease in yield, and the corrosion resistance and design quality decrease due to polishing burn and entrainment of polishing debris. In addition, since inclusions also exist inside the stainless steel material, even if the surface is polished after the descaling process, new inclusions will be exposed on the surface of the stainless steel material. Therefore, this means is not effective.

[0006] Moreover, martensitic stainless steel materials have a composition system similar to that of ferritic stainless steel materials. However, at high temperatures, an austenite phase is formed, resulting in a two-phase structure of ferrite and austenite or a single austenite phase. By rapidly cooling thereafter, the austenite phase undergoes a diffusionless transformation into a quenched martensite phase. Since this heat treatment and rapid cooling at high temperatures are generally carried out in an air atmosphere, in the manufacturing process of martensitic stainless steel materials and ferrite-martensite duplex stainless steel materials, oxide scale is formed in the same manner as in ferritic stainless steel materials. In the descaling process of these stainless steel materials, there are the same problems as in the conventional descaling process of ferritic stainless steel materials.

[0007] The present invention has been made to solve the above problems, and an object thereof is to provide a ferritic stainless steel material, a martensitic stainless steel material, a ferrite-martensite duplex stainless steel material having a smooth and glossy surface, excellent corrosion resistance and fatigue characteristics, a manufacturing method thereof, and a corrosion-resistant member using these.

Means for Solving the Problems

[0008] As a result of intensive research to solve the above problems, the present inventors have found that by controlling the compositions of ferritic stainless steel materials, martensitic stainless steel materials, and ferritic-martensitic duplex stainless steel materials and irradiating them with laser light under specific conditions, descaling can be achieved while ensuring surface smoothness and glossiness, and the corrosion resistance and fatigue characteristics can be improved by dissolving inclusions on the surface. Based on this finding, various ferritic stainless steel materials, martensitic stainless steel materials, and ferritic-martensitic duplex stainless steel materials were produced and examined. As a result, it was found that ferritic stainless steel materials, martensitic stainless steel materials, and ferritic-martensitic duplex stainless steel materials having a predetermined composition and a ratio D2 / D1 of the number density D2 of inclusions on the surface to the number density D1 of predetermined inclusions in the matrix phase at a position where the depth from the surface is 1 / 4 of the thickness within a specific range can solve the above problems, and the present invention has been completed.

[0009] That is, the present invention contains, on a mass basis, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being Fe and impurities, and the ratio D2 / D1 of the number density D2 of inclusions on the surface to the number density D1 of inclusions having a circle equivalent diameter of 0.5 to 10 μm in the matrix phase at a position where the depth from the surface is 1 / 4 of the thickness is 0.50 or less and the number density D2 of the inclusions on the surface is 75 pieces / mm 2 or less, is a ferritic stainless steel material.

[0010] Furthermore, the present invention has a composition comprising, by mass, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being Fe and impurities. The ratio D2 / D1 of the number density D2 of the inclusions on the surface to the number density D1 of the inclusions in the matrix at a position where the depth from the surface is 1 / 4 of the thickness and having an equivalent circle diameter of 0.5 to 10 μm is 0.50 or less. and the number density D2 of the inclusions on the surface is 75 pieces / mm 2 or less, It is a martensitic stainless steel material.

[0011] Furthermore, the present invention has a composition comprising, by mass, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being Fe and impurities. The ratio D2 / D1 of the number density D2 of the inclusions on the surface to the number density D1 of the inclusions in the matrix at a position where the depth from the surface is 1 / 4 of the thickness and having an equivalent circle diameter of 0.5 to 10 μm is 0.50 or less. and the number density D2 of the inclusions on the surface is 75 pieces / mm 2 or less, It is a ferritic-martensitic duplex stainless steel material.

[0012] Furthermore, the present invention is a method for manufacturing the ferritic stainless steel material, the martensitic stainless steel material, or the ferritic-martensitic duplex stainless steel material, comprising: a descaling step of irradiating a laser beam onto the surface of the cold-rolled steel material to remove the oxide scale formed on the surface of the cold-rolled steel material. The irradiation of the laser light is carried out under conditions capable of melting a region with a depth of 0.50 to 10.00 μm from the interface between the matrix phase and the oxide scale in the cold-rolled steel material.

[0013] Furthermore, the present invention is a corrosion-resistant member including the ferritic stainless steel material, the martensitic stainless steel material, or the ferritic-martensitic duplex stainless steel material.

Effects of the Invention

[0014] According to the present invention, it is possible to provide a ferritic stainless steel material, a martensitic stainless steel material, a ferritic-martensitic duplex stainless steel material, a manufacturing method thereof, and a corrosion-resistant member using these, which have a smooth and shiny surface and are excellent in corrosion resistance and fatigue characteristics.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0016] 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 may 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 “%” indication regarding components means “mass %” unless otherwise specified.

[0017] The ferritic stainless steel material, martensitic stainless steel material, and ferritic-martensitic duplex stainless steel material (hereinafter collectively referred to as "stainless steel material") according to the embodiment of the present invention contain C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being composed 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" means 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 allowed within a range that does not adversely affect the present invention. For example, the stainless steel material may contain О as an impurity at 0.02% or less. Note that "martensitic stainless steel material" and "ferritic-martensitic duplex stainless steel material" correspond to those obtained by performing quenching heat treatment on the stainless steel material, and are classified into either one according to the volume fraction of the martensite phase. Also, "ferritic stainless steel material" corresponds to that which has not been subjected to quenching heat treatment.

[0018] In addition, the stainless steel material according to the embodiment of the present invention can further contain one or more selected from Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W: 0.001 to 1.000%, Zr: 0.001 to 1.000%, Co: 0.001 to 1.200%. Furthermore, the stainless steel material according to the embodiment of the present invention can further contain one or more selected from Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, Sn: 0.001 to 0.500%, REM: 0.200% or less. The following will explain each component in detail.

[0019] <C: 0.001~0.150%> If the content of C is too high, in addition to becoming hard and reducing workability, sensitization occurs when affected by heat such as welding, and the corrosion resistance of the stainless steel material decreases. Therefore, the upper limit value of the content of C is controlled to 0.150%, preferably 0.100%, more preferably 0.060%, and even more preferably 0.040%. On the other hand, if the content of C is too low, it will lead to deterioration of workability and an increase in refining cost. Therefore, the lower limit value of the content of C is controlled to 0.001%, preferably 0.002%, more preferably 0.005%, and even more preferably 0.010%.

[0020] <Si: 1.00% or less> If the content of Si is too high, it will harden and the workability of the stainless steel material will decrease. Therefore, the upper limit value of the content of Si is controlled to 1.00%, preferably 0.80%, more preferably 0.70%, and even more preferably 0.60%. On the other hand, the lower limit value of the content of Si is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0021] <Mn: 2.00% or less> Mn is an element that improves the heat resistance of the stainless steel material. However, if the content of Mn is too high, the corrosion resistance of the stainless steel material will decrease. Also, since Mn is an austenite phase (γ-phase) forming element, it generates the γ-phase at high temperature (martensite phase at room temperature), and the workability of the stainless steel material also decreases. Therefore, the upper limit value of the content of Mn is controlled to 2.00%, preferably 1.50%, more preferably 1.20%, and even more preferably 1.00%. On the other hand, the lower limit value of the content of Mn is not particularly limited, but is preferably 0.01%, more preferably 0.05%, and even more preferably 0.10%.

[0022] <P: 0.050% or less> If the content of P is too high, the corrosion resistance and workability of the stainless steel material will deteriorate. Therefore, the upper limit value of the content of P is controlled to be 0.050%, preferably 0.035%, more preferably 0.030%, and even more preferably 0.020%. On the other hand, the lower limit value of the content of P is not particularly limited, but is preferably 0.001%, more preferably 0.005%, and even more preferably 0.010%.

[0023] <S: 0.0300% or less> If the content of S is too high, the hot workability will decrease, the manufacturability of the stainless steel material will deteriorate, and it will also have an adverse effect on the corrosion resistance. Therefore, the upper limit value of the content of S is controlled to be 0.0300%, preferably 0.0100%, more preferably 0.0050%, and even more preferably 0.0010%. On the other hand, the lower limit value of the content of S is not particularly limited, but is preferably 0.0001%, more preferably 0.0002%, and even more preferably 0.0003%.

[0024] <Ni: less than 2.00%> Ni is an element that improves the corrosion resistance of the stainless steel material. However, since Ni is an austenite phase (γ-phase) forming element like Mn, if its content is too high, a γ-phase (martensite phase at room temperature) will be generated at high temperatures, and the workability of the stainless steel material will deteriorate. Also, since Ni is an expensive element, it will also lead to an increase in manufacturing costs. Therefore, the content of Ni is controlled to be less than 2.00%, preferably 1.00% or less, more preferably 0.50% or less, and even more preferably 0.35% or less. On the other hand, the lower limit value of the content of Ni is not particularly limited, but is preferably 0.01%, more preferably 0.03%, and even more preferably 0.05%.

[0025] <Cr: 11.00 - 30.00%> If the Cr content is too high, it will not only lead to an increase in refining costs, but also harden due to solid solution strengthening, resulting in a decrease in the workability of stainless steel. Therefore, the upper limit of the Cr content is controlled to 30.00%, preferably 24.00%, more preferably 22.00%, and still more preferably 18.00%. On the other hand, if the Cr content is too low, sufficient corrosion resistance cannot be obtained. Therefore, the lower limit of the Cr content is controlled to 11.00%, preferably 13.00%, more preferably 14.00%, and still more preferably 15.00%.

[0026] <Mo: 6.00% or less> Mo is an element that improves the corrosion resistance of stainless steel. Since Mo is expensive, if the Mo content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit of the Mo content is controlled to 6.00%, preferably 5.00%, more preferably 3.00%, and still more preferably 2.00%. On the other hand, the lower limit of the Mo content is not particularly limited, but is preferably 0.10%, more preferably 0.50%, and still more preferably 1.00%.

[0027] <Cu: 0.60% or less> Cu is an element that improves the workability of stainless steel. If the Cu content is too high, the corrosion resistance of the stainless steel will decrease, and a low melting point phase will be formed during casting, leading to a decrease in hot workability. Therefore, the upper limit of the Cu content is controlled to 0.60%, preferably 0.40%, and more preferably 0.20%. On the other hand, the lower limit of the Cu content is not particularly limited, but is preferably 0.02%, and more preferably 0.04%.

[0028] <N: 0.050% or less> N is an element that improves corrosion resistance. If the N content is too high, it will harden and the workability of the stainless steel will decrease. Therefore, the upper limit of the N content is controlled to 0.050%, preferably 0.040%, more preferably 0.030%, and still more preferably 0.020%. On the other hand, the lower limit of the N content is not particularly limited, but is preferably 0.001%, preferably 0.005%, and more preferably 0.010%.

[0029] <Al: less than 0.400%> Al is an element added as needed for deoxidation in the refining process to improve corrosion resistance and heat resistance. If the Al content is too high, the amount of inclusions generated will increase and the quality will deteriorate. Therefore, the upper limit value of the Al content is controlled at 0.400%, preferably 0.100%, more preferably 0.050%. On the other hand, the lower limit value of the Al content is not particularly limited, but is preferably 0.001%, more preferably 0.005%.

[0030] <Si + 2Al: less than 1.20%> The stainless steel material according to the embodiment of the present invention targets those with low Si and Al contents. Specifically, Si + 2Al (each element symbol represents the content of each element) is less than 1.20%, preferably 1.10% or less, more preferably 1.00% or less, still more preferably 0.90% or less. The lower limit value of Si + 2Al is not particularly limited, but is preferably 0.01%, more preferably 0.05%, still more preferably 0.10%.

[0031] <Ti: 0.001 - 0.500%> Ti is an element that combines with C and N to improve corrosion resistance and intergranular corrosion resistance and is added as needed. From the perspective of obtaining the effect of Ti, the lower limit value of the Ti content is controlled at 0.001%, preferably 0.005%. On the other hand, if the Ti content is too high, it will cause surface defects, leading to quality deterioration, and the workability of the stainless steel material will also deteriorate. Therefore, the upper limit value of the Ti content is controlled at 0.500%, preferably 0.300%, more preferably 0.100%.

[0032] <Nb: 0.001 - 1.000%> Like Ti, Nb is an element that combines with C and N to improve corrosion resistance and intergranular corrosion resistance, and is added as necessary. From the perspective of obtaining the effect of Nb, the lower limit of the Nb content is controlled to be 0.001%, preferably 0.004%, more preferably 0.010%. On the other hand, if the Nb content is too high, the workability of the stainless steel material will deteriorate. Therefore, the upper limit of the Nb content is controlled to be 1.000%, preferably 0.600%, more preferably 0.060%.

[0033] <V: 0.001~1.000%> V is an element that improves corrosion resistance and is added as necessary. From the perspective of obtaining the effect of V, the lower limit of the V content is controlled to be 0.001%, preferably 0.010%. On the other hand, if the V content is too high, the workability of the stainless steel material will deteriorate. Therefore, the upper limit of the V content is controlled to be 1.000%, preferably 0.200%.

[0034] <W: 0.001~1.000%> W is an element that improves high-temperature strength and corrosion resistance and is added as necessary. From the perspective of obtaining the effect of W, the lower limit of the W content is controlled to be 0.001%, preferably 0.010%. On the other hand, if the W content is too high, it will become hardened and the workability will deteriorate, and at the same time, surface defects will increase and the surface quality of the stainless steel material will deteriorate. Therefore, the upper limit of the W content is controlled to be 1.000%, preferably 0.300%.

[0035] <Zr: 0.001~1.000%> Zr is an element that combines with C and N to improve oxidation resistance and intergranular corrosion resistance and is added as necessary. From the perspective of obtaining the effect of Zr, the lower limit of the Zr content is controlled to be 0.001%, preferably 0.010%. On the other hand, if the Zr content is too high, the workability of the stainless steel material will deteriorate. Therefore, the upper limit of the Zr content is controlled to be 1.000%, preferably 0.200%, more preferably 0.050%.

[0036] <Co: 0.001~1.200%> Co is an element that improves heat resistance and is added as required. From the perspective of obtaining the effect of Co, the lower limit value of the Co content is controlled to 0.001%, preferably 0.010%. On the other hand, since Co is expensive, if the Co content is too high, it will lead to an increase in manufacturing cost. Therefore, the upper limit value of the Co content is controlled to 1.200%, preferably 0.400%.

[0037] <Ca: 0.0001~0.0100%> Ca is an element that improves the hot workability of stainless steel materials and is added as required. Also, Ca is an element that improves intergranular oxidation resistance by forming sulfides and suppressing the grain boundary segregation of S. From the perspective of obtaining the effect of Ca, the lower limit value of the Ca content is controlled to 0.0001%, preferably 0.0003%. On the other hand, if the Ca content is too high, the number of inclusions increases, leading to a decrease in workability. Therefore, the upper limit value of the Ca content is controlled to 0.0100%, preferably 0.0050%.

[0038] <B: 0.0001~0.0080%> B is an element that improves the hot workability of stainless steel materials and is added as required. Also, B is an element that improves the secondary workability of stainless steel materials by grain boundary strengthening. From the perspective of obtaining the effect of B, the lower limit value of the B content is controlled to 0.0001%, preferably 0.0003%, more preferably 0.0005%. On the other hand, if the B content is too high, it will lead to a decrease in weldability and fatigue strength. Therefore, the upper limit value of the B content is controlled to 0.0080%, preferably 0.0040%, more preferably 0.0025%.

[0039] <Sn: 0.001~0.500%> Sn is an element that improves corrosion resistance and high-temperature strength and is added as necessary. From the perspective of obtaining the effect of Sn, the lower limit value of the Sn content is controlled to 0.001%, preferably 0.002%. On the other hand, if the Sn content is too high, a low melting point phase is formed, resulting in a decrease in the hot workability of the stainless steel material. Therefore, the upper limit value of the Sn content is controlled to 0.500%, preferably 0.100%, more preferably 0.050%.

[0040] <REM:0.200% or less> REM (rare earth element) is an element that improves the hot workability of stainless steel materials, similar to B and Ca, and is added as necessary. Also, REM is an element that improves corrosion resistance by forming sulfides that are difficult to elute and suppressing the formation of MnS that serves as a corrosion initiation point. However, if the REM content is too high, it will lead to an increase in manufacturing costs. Therefore, the upper limit value of the REM content is controlled to 0.200%, preferably 0.100%. On the other hand, the lower limit value of the REM content is not particularly limited, but from the perspective of obtaining the effect of REM, it is preferably 0.001%, more preferably 0.010%. 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.

[0041] For the stainless steel material according to the embodiment of the present invention, the ratio D2 / D1 of the number density D2 of inclusions with an equivalent circle diameter of 0.5 to 10 μm on the surface (for example, surface B in FIG. 1) to the number density D1 of inclusions with an equivalent circle diameter of 0.5 to 10 μm in the matrix phase (for example, position C in FIG. 1) at a depth of 1 / 4 of the thickness from the surface (for example, surface B in FIG. 1) is 0.50 or less, preferably 0.49 or less, more preferably 0.48 or less. By controlling the ratio D2 / D1 of the number density of inclusions within such a range, the proportion of inclusions present on the surface can be reduced compared to the inclusions present in the matrix phase, so that the corrosion resistance and fatigue characteristics of the stainless steel material can be improved. Incidentally, the lower limit of the ratio D2 / D1 of the inclusion number density is not particularly limited because the smaller it is, the higher the improvement effect on corrosion resistance and fatigue characteristics. For example, it is 0.01.

[0042] The number density D1 of inclusions with an equivalent circle diameter of 0.5 to 10 μm in the matrix phase at a position where the depth from the surface of the stainless steel material is 1 / 4 of the thickness (hereinafter referred to as "the number density D1 of inclusions in the matrix phase") can be calculated as follows. First, an arbitrary location (10 or more fields of view) at a position where the depth from the surface of the stainless steel material is 1 / 4 of the thickness (matrix phase) is photographed with an electron microscope. Next, the photographed image is binarized and divided into inclusions (black) with an equivalent circle diameter of 0.5 to 10 μm and the matrix phase (white), the number of inclusions is obtained by counting the black regions, and the number density D1 of inclusions in the matrix phase can be calculated by dividing the obtained number of inclusions by the area of the observation field of view. Similarly, the number density D2 of inclusions with an equivalent circle diameter of 0.5 to 10 μm on the surface of the stainless steel material (hereinafter referred to as "the number density D2 of inclusions on the surface") can be calculated by photographing an arbitrary location (10 or more fields of view) on the surface of the stainless steel material with an electron microscope and dividing the number of inclusions obtained in the same manner as above by the area of the observation field of view. Here, since most of the inclusions are in the range of an equivalent circle diameter of 0.5 to 10 μm, the inclusions with a size in this range are counted as the number, and the number densities D1 and D2 of the inclusions are used. The equivalent circle diameter means the diameter of a circle when the area of each observed black region is converted into a circle having the same area.

[0043] As the electron microscope, the Schottky scanning electron microscope SU5000 manufactured by Hitachi High-Tech Corporation can be used. In addition, the identification of inclusions can be performed with an EDX detector EMAX3.3SP2 manufactured by Oxford Instruments attached to the electron microscope. For image processing, analysis software (AZtecSteel) manufactured by Oxford Instruments can be used.

[0044] The number density D1 of inclusions in the matrix phase is, for example, 80 to 300 pieces / mm2 is the degree.

[0045] The number density D2 of inclusions on the surface is preferably 75 inclusions / mm 2 or less, more preferably 60 inclusions / mm 2 or less. By controlling the number density D2 of inclusions on the surface within this range, the amount of inclusions present on the surface of the stainless steel material can be reduced, so that the corrosion resistance and fatigue strength of the stainless steel material can be stably improved. Note that the lower limit value of the number density D2 of inclusions on the surface is not particularly limited because the smaller it is, the higher the effect of improving corrosion resistance and fatigue characteristics. For example, it is 10 inclusions / mm 2 or the like.

[0046] The inclusions are non-metallic inclusions (particularly, sulfide-based or oxide-based inclusions), and specific examples thereof include MnS, TiN, TiC, NbN, NbC, CaO, SiO 2 , Al 2 O 3 and composite compounds thereof.

[0047] The stainless steel material according to the embodiment of the present invention preferably has a fusion-solidified layer on the surface layer. Here, as an example, a schematic cross-sectional view of the stainless steel material according to the embodiment of the present invention is shown in FIG. 1. As shown in FIG. 1, the stainless steel material 10 includes a matrix phase 11 and a fusion-solidified layer 12 formed on the surface A of the matrix phase 11. The matrix phase 11 contains inclusions 13. The fusion-solidified layer 12 may also contain inclusions 13, but there are few inclusions 13 exposed on the surface B of the fusion-solidified layer 12. This is because the inclusions 13 exposed on the surface B due to descaling by laser light are dissolved.

[0048] The thickness of the melt-solidified layer is not particularly limited, but is preferably 0.50 to 10.00 μm, more preferably 1.00 to 10.00 μm, and still more preferably 2.00 to 10.00 μm. When the thickness of the melt-solidified layer is less than 0.50 μm, inclusions are likely to be insufficiently dissolved. Therefore, the number of inclusions exposed on the surface increases, and the corrosion resistance and fatigue characteristics of the stainless steel material tend to deteriorate. On the other hand, when the thickness of the melt-solidified layer exceeds 10.00 μm, the surface tends to become rough, and it becomes difficult to obtain a smooth and shiny surface.

[0049] The stainless steel material according to an embodiment of the present invention preferably has an arithmetic mean roughness Ra of the surface of 0.01 to 0.40 μm, more preferably 0.01 to 0.30 μm, and still more preferably 0.01 to 0.20 μm. By controlling the arithmetic mean roughness Ra of the surface within such a range, the smoothness of the stainless steel material can be ensured. Here, in this specification, the "arithmetic mean roughness Ra" means the arithmetic mean roughness Ra measured in accordance with JIS B0601:2013.

[0050] The stainless steel material according to an embodiment of the present invention preferably has a 60-degree specular gloss Gs(60°) of the surface of 200 to 750%, more preferably 300 to 750%, and still more preferably 400 to 750%. By controlling the 60-degree specular gloss Gs(60°) of the surface within such a range, the glossiness of the stainless steel material can be ensured. Here, in this specification, the "60-degree specular gloss Gs(60°)" means the 60-degree specular gloss Gs(60°) measured in accordance with JIS Z8741:1997.

[0051] The stainless steel material according to an embodiment of the present invention is preferably a cold-rolled stainless steel material, and more preferably a cold-rolled stainless steel sheet. In this specification, the cold-rolled steel material and cold-rolled steel sheet after removal of the oxide scale are referred to as "cold-rolled stainless steel material" and "cold-rolled stainless steel sheet", and the cold-rolled steel material and cold-rolled steel sheet before removal of the oxide scale are referred to as "cold-rolled steel material" and "cold-rolled steel sheet". Hereinafter, a case where the stainless steel material according to the embodiment of the present invention is a cold-rolled stainless steel sheet will be described as an example. The thickness (sheet thickness) of the cold-rolled stainless steel sheet according to an embodiment of the present invention is not particularly limited, but is preferably less than 3 mm, more preferably 2.5 mm or less, and still more preferably 2 mm or less. Further, the lower limit thereof is, for example, 0.1 mm, and may be 0.3 mm.

[0052] The cold-rolled stainless steel sheet according to an embodiment of the present invention can be produced by using a method known in the art, except that a descaling step of irradiating the surface of the cold-rolled steel sheet having the above composition with a laser beam to remove the oxide scale formed on the surface is performed.

[0053] The method for producing the cold-rolled steel sheet having the above composition is not particularly limited, but can be produced, for example, as follows. First, the stainless steel having the above composition is melted to obtain a steel slab by forging or casting. Next, the steel slab is hot-rolled, annealed, and then descaled. The descaling method is not particularly limited and can be performed by pickling, polishing, or using a laser beam. Next, the hot-rolled steel sheet that has been descaled is cold-rolled and annealed to obtain a cold-rolled steel sheet. Note that the conditions for each step may be appropriately adjusted according to the composition of the stainless steel and the like and are not particularly limited.

[0054] Irradiation of the cold-rolled steel sheet with a laser beam is performed under conditions that can melt a region from a depth of 0.50 to 10.00 μm, preferably 1.00 to 10.00 μm, more preferably 2.00 to 10.00 μm from the interface between the matrix phase and the oxide scale in the cold-rolled steel sheet. By irradiating the laser beam under such conditions, the oxide scale is removed while ensuring the surface smoothness and glossiness, and the inclusions on the surface are dissolved by the heat influence to form a melt-solidified layer on the surface, thereby improving the corrosion resistance and fatigue characteristics. If the irradiation conditions are such that only a region with a depth of less than 0.50 μm from the surface of the cold-rolled steel sheet can be melted, the inclusions cannot be sufficiently dissolved, so the inclusions exposed on the surface cannot be sufficiently reduced, and the corrosion resistance and fatigue characteristics of the stainless cold-rolled steel sheet deteriorate. Also, if the irradiation conditions are such that a region with a depth exceeding 10.00 μm from the surface of the cold-rolled steel sheet is melted, the surface of the stainless cold-rolled steel sheet becomes rough, and a smooth and glossy surface cannot be obtained.

[0055] Here, FIG. 2 shows a schematic cross-sectional view for explaining the difference between descaling by laser beam irradiation and descaling by a conventional method. As shown in FIG. 2(a), an oxide scale 21 is formed on the surface of the matrix phase 11 of the cold-rolled steel material (cold-rolled steel sheet) 20. Also, inclusions 13 are present at the interface D (the surface of the matrix phase 11) between the matrix phase 11 and the oxide scale 21. When descaling (removing the oxide scale 21) is performed by a conventional method (pickling and / or polishing), as shown in FIG. 2(b), the inclusions 13 present at the interface D between the matrix phase 11 and the oxide scale 21 are exposed on the surface E. Also, even if the surface layer of the matrix phase 11 is removed together with the oxide scale 21 in order to remove the inclusions 13 present at the interface D between the matrix phase 11 and the oxide scale 21, since the inclusions 13 are present inside the matrix phase 11, the inclusions 13 inside the matrix phase 11 are exposed on the surface E. Therefore, it is difficult to reduce the inclusions 13 exposed on the surface E by the conventional method.

[0056] When descaling is performed by irradiating with a laser beam, as shown in Fig. 2(c), in addition to removing the oxide scale 21, the inclusions 13 existing at the interface D between the matrix phase 11 and the oxide scale 21 dissolve. As a result, a fusion-solidified layer 12 is formed on the surface layer of the matrix phase 11, and the number of inclusions 13 exposed on the surface B decreases. The decrease in the number of inclusions 13 occurs because the inclusions 13 near the surface melt during the formation of the fusion-solidified layer 12, become diluted with the matrix phase components, and rapidly solidify before reprecipitation. In addition to this, in the vicinity of the fusion-solidified layer 12, solid solution of the inclusions 13 occurs due to the temperature rise even in the portions that did not directly melt, resulting in a reduction in the size and the number of the inclusions 13. Also, even when the inclusions are not completely melted and rendered harmless, the corrosion resistance and fatigue strength are improved because the inclusions are partially melted and the equivalent circle diameter of the inclusions 13 becomes smaller.

[0057] The conditions of the laser to be irradiated may be adjusted in consideration of the following matters according to the apparatus to be used. (Type of laser beam) When using a continuous-wave laser beam, since the energy required for removing the oxide scale becomes large, the required power becomes large, and the range in which the thermal influence occurs is too large, making it difficult to control the thickness of the fusion-solidified layer, a pulsed laser beam that can instantaneously apply heat is preferable. (Wavelength) Generally, the reflectivity of a substance with respect to light has wavelength dependence. When selecting a wavelength with a low reflectivity, the heat input increases and the evaporation of the oxide scale easily occurs. Therefore, by selecting a wavelength with a high reflectivity of the matrix phase and a low reflectivity of the oxide, the oxide scale can be selectively evaporated and removed without melting the matrix phase more than necessary. (Pulse width) The pulse width represents the time during which one pulse is irradiated. The narrower the pulse width, the more instantaneous heating occurs. When the pulse width is narrow, ablation occurs before the heat input by the laser is transferred to the surroundings. As a result, the ablation threshold decreases, and the thermal influence on the matrix phase decreases. When laser irradiation is performed under conditions where melting of the matrix phase occurs, the narrower the pulse width, the more rapid cooling occurs, and the reprecipitation of the melted inclusions is suppressed. However, the pulse width is mainly determined by the performance of the oscillator, and devices capable of oscillating with a short pulse width are expensive. Therefore, it is preferable to select a short pulse width within the specification range of the device. (Oscillation frequency) The shorter the pulse width, the higher the oscillation frequency can be. The higher the oscillation frequency, the more pulses are irradiated per unit time, and the removal rate of the oxide scale improves. Therefore, it is preferable to select a high oscillation frequency within the specification range of the device.

[0058] (Scanning frequency) The scanning frequency represents the moving speed in the plane direction of the pulse irradiation position. The higher the scanning frequency, the faster the removal rate of the oxide scale. However, if it is too high, gaps will occur between the pulse irradiation positions, and the oxide scale will remain, resulting in a decrease in the descaling rate. Therefore, it is preferable to increase the scanning frequency within the range where the descaling rate can be maintained. (Laser beam diameter) The larger it is, the wider the irradiation range, that is, the range that can be descaled with one pulse, and the better the descaling efficiency. However, the energy density (fluence) of one pulse decreases. It is preferable to increase the beam diameter within the range where the fluence capable of evaporating and removing the oxide scale is maintained. (Fluence) By irradiating a laser beam having a fluence exceeding the ablation threshold of the oxide constituting the oxide scale, the oxide scale can be removed by evaporation. The higher the fluence, the greater the thickness of the oxide scale that can be removed. However, if the fluence is too high, not only the oxide scale but also the evaporation removal of the parent phase will occur. In addition, although the pulsed laser has less thermal influence compared to the continuous wave laser, the higher the fluence, the greater the heat input to the parent phase, and the larger the molten part and the heat affected part. Therefore, considering the balance between the characteristics (thickness, structure, composition, etc.) of the oxide scale to be removed and the heat input to the parent phase, the fluence may be adjusted within a range where the parent phase is not melted more than necessary. When the fluence distribution is different within the beam spot, it may be controlled using the average fluence.

[0059] The stainless steel material according to the embodiment of the present invention having the above characteristics is excellent in corrosion resistance and can be used as a corrosion-resistant member. Further, since this stainless steel material is also excellent in fatigue characteristics, it is suitable for use in corrosion-resistant members that require fatigue characteristics. Furthermore, since this stainless steel material has a smooth and shiny surface and is excellent in design, it is suitable for use in corrosion-resistant members that require design.

[0060] The corrosion-resistant member according to the embodiment of the present invention includes the above stainless steel material. The stainless steel material used for this corrosion-resistant member may be processed into various shapes by a method known in the art. The corrosion-resistant member according to the embodiment of the present invention may further include members other than the above stainless steel material. The corrosion-resistant member is not particularly limited, and examples thereof include automotive parts, architectural parts, and kitchen utensils.

Example

[0061] 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.

[0062] 30 kg of stainless steel having the compositions of Steel Grades A to E shown in Table 1 (the balance being Fe and impurities) was melted by vacuum melting, forged into a steel slab with a thickness of 30 mm, heated at 1230 °C for 2 hours, hot-rolled to a thickness of 3 mm, and annealed at 1100 °C for 5 minutes in an air atmosphere to obtain a hot-rolled steel sheet. The hot-rolled steel sheet was cut into 50 mm (rolling direction) × 50 mm (width direction) by processing, and then pickled to remove scale. The pickling to remove scale was carried out by holding an aqueous hydrofluoric and nitric acid solution containing 50 g / L of hydrofluoric acid and 150 g / L of nitric acid at 60 °C in a constant-temperature bath, immersing the hot-rolled steel sheet for 60 to 600 seconds, and then immediately washing it with running water and allowing it to dry naturally. The specific immersion times were 60 seconds for Steel Grade A, 100 seconds for Steel Grade B, 400 seconds for Steel Grade C, 600 seconds for Steel Grade D, and 60 seconds for Steel Grade E. Thereafter, the hot-rolled steel sheet was cold-rolled from a thickness of 3 mm to 1 mm and annealed at 1100 °C for 5 minutes in an air atmosphere to obtain a cold-rolled steel sheet (ferritic stainless steel material). Further, for Steel Grades A and B, the cold-rolled steel sheet was heated at 1000 °C for 3 minutes in an air atmosphere and then water-cooled to perform quenching heat treatment, thereby obtaining cold-rolled steel sheets (martensitic stainless steel material and ferrite-martensite duplex stainless steel material) in which a martensite phase was generated. The obtained cold-rolled steel sheets were used in the following respective examples and comparative examples.

[0063]

Table 1

[0064] (Examples 1 to 7) For the cold-rolled steel sheets having the compositions of the respective steel grades, a descaling process by irradiation with laser light was carried out. The irradiation with laser light was carried out using a commercially available device (LaserClear50A manufactured by IHI Inspection & Measurement Co., Ltd.). The cold-rolled steel sheet was placed on the movable stage of this device, and while moving it at 0.2 m / min along the rolling direction, it was scanned at a constant speed in the plate width direction from above the cold-rolled steel sheet, and pulsed laser light was irradiated once. The scan width per pass was 25 mm. The irradiation conditions for the pulsed laser light were as follows. Wavelength: 1085 nm Pulse width: 220 ns Oscillation frequency: 60 kHz Scan frequency: 100 Hz Laser beam diameter: 90 μm Average fluence: 8 J / cm 2

[0065] (Comparative Example 1) A descaling process by pickling was performed on the cold-rolled steel sheet having the composition of Steel Grade A. The pickling was carried out as follows. An aqueous hydrofluoric and nitric acid solution containing 30 g / L of hydrofluoric acid and 100 g / L of nitric acid was held at 60 °C in a thermostatic bath, and the cold-rolled steel sheet was immersed for 600 seconds and then immediately washed with running water and air-dried.

[0066] (Comparative Example 2) Belt grinding using SiC abrasive paper (grit #400) and water-soluble grinding oil was performed on the cold-rolled steel sheet after the descaling process obtained in Comparative Example 1. The grinding depth was set to a depth of 20 μm from the surface.

[0067] The following evaluations were performed on the stainless cold-rolled steel sheets after the descaling process obtained in the above examples and comparative examples.

[0068] (Number density D1, D2 of inclusions) Test pieces of 50 mm square were cut out from the center parts in the width direction and the length direction of the stainless cold-rolled steel sheets obtained in the above examples and comparative examples, and an arbitrary portion of the surface was photographed at 200 times magnification using a Schottky scanning electron microscope SU5000 manufactured by Hitachi High-Technologies Corporation. Also, the surface of this test piece was polished to remove 1 / 4 (250 μm) of the thickness, and the matrix phase at a position where the depth from the surface was 1 / 4 of the thickness was exposed, and then an arbitrary portion of this exposed surface was photographed in the same manner as above. The photographing was performed with 0.48 mm × 0.64 mm (0.3072 mm 2 ) as one field of view and for 10 fields of view. Next, using the analysis software (AZtecSteel) manufactured by Oxford Instruments Co., Ltd., the photographed images were binarized and separated into inclusions (black) with an equivalent circle diameter of 0.5 to 10 μm and the matrix phase (white). The conditions for image analysis were as follows. Resolution: 4096 Minimum detectable size: 8 pixels (0.5 μm) Color threshold of inclusions: 47 - 24057 Note that those less than 8 pixels were excluded as noise. Next, in the binarized image, the number of black regions with an equivalent circle diameter of 0.5 - 10 μm was counted to obtain the number of inclusions, and the number density D1 and D2 of inclusions were calculated by dividing the obtained number of inclusions by the area of the observation field of view. The results of the number density D1 and D2 of inclusions were taken as the average value of the results in each field of view. Also, based on the calculated number density D1 and D2 of inclusions, the ratio D2 / D1 of the number density of inclusions was calculated.

[0069] (Thickness of the melt-solidified layer) The stainless steel cold-rolled steel sheet was cut in the thickness direction (the direction perpendicular to the surface) parallel to the rolling direction, and the microstructure image of the cut surface was observed up to 10000 times using an electron microscope. The melt-solidified layer was discriminated from the difference in contrast, and its thickness was measured. The thickness was measured at 10 arbitrary locations, and the average value was taken as the result.

[0070] (Measurement of surface roughness) Regarding the surface of the stainless steel cold-rolled steel sheet, in accordance with JIS B0601:2013, the arithmetic mean roughness Ra was measured using a contact-type surface roughness meter (Surfcom 2800 manufactured by Tokyo Seimitsu Co., Ltd.). The arithmetic mean roughness Ra was measured at 5 locations excluding the range from the end to 5 mm with a reference length of 4 mm, and the average value was taken as the evaluation result. Note that the distance between each measurement position was more than 5 mm.

[0071] (Measurement of gloss) Regarding the surface of the stainless steel cold-rolled steel sheet, in accordance with JIS Z8741:1997, the 60-degree specular gloss Gs(60°) was measured using a gloss meter (PG-1M manufactured by Nippon Denshoku Industries Co., Ltd.). The 60-degree specular gloss Gs(60°) was measured at 5 locations excluding the range from the end to 5 mm, and the average value was taken as the evaluation result. Note that the distance between each measurement position was more than 5 mm.

[0072] (Corrosion resistance test) The corrosion resistance test was carried out according to JASO M609 and M610, and a composite cycle test was performed. Specifically, a salt-dry-wet repeated test was conducted, which repeated salt spray, drying, and wetting. In the salt-dry-wet repeated test, for the cold-rolled stainless steel sheet, spraying with a 5% NaCl aqueous solution (for 2 hours at 35°C), drying (at a relative humidity of 30% and a temperature of 60°C for 4 hours), and wetting (at a relative humidity of 95% and a temperature of 50°C for 2 hours) were taken as one cycle. After each cycle, the sheet was washed with water and dried, and then the surface of the cold-rolled stainless steel sheet was observed to calculate the rusted area ratio. And the number of cycles when the rusted area ratio reached 10% or more was taken as the number of corrosion occurrence cycles. The calculation of the rusted area ratio was carried out in the following procedure. The surface of the cold-rolled stainless steel sheet after the salt-dry-wet repeated test was photographed, and the ratio of the area of the rusted part in the central 25 mm × 25 mm range excluding the end faces was obtained. The area of the rusted part was obtained by binarizing the photograph of the surface of the cold-rolled stainless steel sheet by image analysis, calculating the area per pixel, and then counting the number of pixels of the rusted part. The rusted area ratio was calculated by the following formula. Rusted area ratio (%) = Area of rusted part (mm 2 ) / Total area of the observation part (625 mm 2 ) × 100 In this evaluation, based on the number of corrosion occurrence cycles of the cold-rolled stainless steel sheet in Comparative Example 2, the improvement rate of the number of corrosion occurrence cycles of the cold-rolled stainless steel sheets in Examples 1 to 7 and Comparative Example 1 was calculated. Those with an improvement rate of the calculated number of corrosion occurrence cycles of 20% or more were marked as "〇", those with 10% or more and less than 20% were marked as "△", and those with less than 10% were marked as "×".

[0073] (Fatigue property test) The fatigue property test was carried out according to JIS Z2275:1978, and a plane bending fatigue test was performed. Specifically, a test piece was obtained by cutting out a length of 30 mm in the width direction and 90 mm in the rolling direction from the cold-rolled stainless steel sheet and forming R parts with a radius of 30 mm at both ends in the width direction. This test piece was mounted on a plane bending testing machine, and a fatigue test with 10 7 repetitions was carried out. In this fatigue test, the test was performed with two or more test pieces for each stress level, and the time strength was measured. In this evaluation, based on the fatigue strength of the cold-rolled stainless steel sheet of Comparative Example 2, the improvement rates of the time strength of the cold-rolled stainless steel sheets of Examples 1 to 7 and Comparative Example 1 were calculated. Those with an improvement rate of the calculated time strength of 10% or more were marked as "〇", and those less than 10% were marked as "×". The above evaluation results are shown in Table 2.

[0074]

Table 2

[0075] As shown in Table 2, the cold-rolled stainless steel sheets of Examples 1 to 7 with a ratio D2 / D1 of the number density of inclusions of 0.50 or less have an arithmetic mean surface roughness Ra of 0.01 to 0.40 μm and a 60-degree specular gloss Gs(60°) of the surface of 200 to 750%, and it was confirmed that they have a smooth and shiny surface. Also, the cold-rolled stainless steel sheets of Examples 1 to 7 have improved corrosion resistance and fatigue characteristics compared to the cold-rolled stainless steel sheet of Comparative Example 2. On the other hand, for the cold-rolled stainless steel sheet of Comparative Example 1, since descaling was performed by pickling, the ratio D2 / D1 of the number density of inclusions exceeded 0.50. Therefore, the cold-rolled stainless steel sheet of Comparative Example 1 did not sufficiently improve in corrosion resistance and fatigue characteristics compared to the cold-rolled stainless steel sheet of Comparative Example 2.

[0076] As can be seen from the above results, according to the present invention, it is possible to provide a ferritic stainless steel material, a martensitic stainless steel material, a ferritic-martensitic duplex stainless steel material having a smooth and shiny surface, excellent in corrosion resistance and fatigue characteristics, a manufacturing method thereof, and a corrosion-resistant member using these.

Explanation of Signs

[0077] 10 Stainless steel material 11 Parent phase 12 Melt solidification layer 13 Inclusion 20 Cold-rolled steel material 21 Oxide scale

Claims

1. By mass, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being composed of Fe and impurities, The ratio D2 / D1 of the number density D2 of the inclusions on the surface to the number density D1 of the inclusions in the matrix at a position where the depth from the surface is 1 / 4 of the thickness is 0.50 or less, and the number density D2 of the inclusions on the surface is 75 pieces / mm2 or less, a ferritic stainless steel material.

2. By mass, further containing one or more selected from Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W: 0.001 to 1.000%, Zr: 0.001 to 1.000%, Co: 0.001 to 1.200%, the ferritic stainless steel material according to Claim 1.

3. By mass, further containing one or more selected from Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, Sn: 0.001 to 0.500%, REM: 0.200% or less, the ferritic stainless steel material according to Claim 1 or 2.

4. By mass, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, with Si + 2Al being less than 1.20%, and the balance being composed of Fe and impurities, The ratio D2 / D1 of the number density D2 of the inclusions on the surface to the number density D1 of the inclusions in the matrix at a position where the depth from the surface is 1 / 4 of the thickness is 0.50 or less, and the number density D2 of the inclusions on the surface is 75 pieces / mm2 or less, a martensitic stainless steel material.

5. The martensitic stainless steel material according to claim 4, further comprising one or more selected from the group consisting of Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W: 0.001 to 1.000%, Zr: 0.001 to 1.000%, and Co: 0.001 to 1.200% by mass.

6. The martensitic stainless steel material according to claim 4 or 5, further comprising one or more selected from the group consisting of Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, Sn: 0.001 to 0.500%, and REM: 0.200% or less by mass.

7. By mass, C: 0.001 to 0.150%, Si: 1.00% or less, Mn: 2.00% or less, P: 0.050% or less, S: 0.0300% or less, Ni: less than 2.00%, Cr: 11.00 to 30.00%, Mo: 6.00% or less, Cu: 0.60% or less, N: 0.050% or less, Al: 0.400% or less, Si + 2Al is less than 1.20%, and the balance consists of Fe and impurities, A ferritic-martensitic duplex stainless steel material in which the ratio D2 / D1 of the number density D2 of the inclusions on the surface to the number density D1 of the inclusions in the matrix phase at a position where the depth from the surface is 1 / 4 of the thickness is 0.50 or less, and the number density D2 of the inclusions on the surface is 75 pieces / mm 2 or less.

8. The ferritic-martensitic duplex stainless steel material according to claim 7, further comprising one or more selected from the group consisting of Ti: 0.001 to 0.500%, Nb: 0.001 to 1.000%, V: 0.001 to 1.000%, W: 0.001 to 1.000%, Zr: 0.001 to 1.000%, and Co: 0.001 to 1.200% by mass.

9. The ferritic-martensitic duplex stainless steel material according to claim 7 or 8, further comprising one or more selected from the group consisting of Ca: 0.0001 to 0.0100%, B: 0.0001 to 0.0080%, Sn: 0.001 to 0.500%, and REM: 0.200% or less by mass.

10. The stainless steel material according to any one of claims 1 to 9, wherein the arithmetic mean roughness Ra of the surface is 0.01 to 0.40 μm.

11. The stainless steel material according to any one of claims 1 to 10, wherein the 60-degree specular gloss Gs(60°) of the surface is 200 to 750%.

12. The stainless steel material according to any one of claims 1 to 11, having a molten solidified layer on the surface layer.

13. The stainless steel material according to claim 12, wherein the thickness of the molten solidified layer is 0.50 to 10.00 μm.

14. A method for manufacturing the stainless steel material according to any one of claims 1 to 13, comprising a descaling step of irradiating a laser beam onto the surface of a cold-rolled steel material to remove the oxide scale formed on the surface of the cold-rolled steel material, wherein the irradiation of the laser beam is performed under conditions capable of melting a region from the interface between the matrix phase and the oxide scale in the cold-rolled steel material to a depth of 0.50 to 10.00 μm.

15. A corrosion-resistant member including the stainless steel material according to any one of claims 1 to 13.

Images