Stainless steel material, method for manufacturing the same, and processed products

Abstract

To provide a stainless steel material excellent in corrosion resistance even when partially exposing a base during processing.SOLUTION: A stainless steel material includes an oxide film on the surface of a base. The oxide film including a Cr2O3 inner layer having a thickness of 50 nm or more has a total thickness of 300-1000 nm, a carrier density of 2.00×1020 pieces / cm3, a lightness index L* of 50.0 or less in a L*a*b* color system and a chromatic index a* and b* of ±5.00 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to stainless steel materials, methods for manufacturing the same, and processed products thereof. [Background technology]

[0002] Stainless steel is a material with excellent corrosion resistance, and its lustrous silvery-white surface makes it suitable for use in various parts such as interior and exterior building materials and exhaust system components. Furthermore, to enhance the aesthetic appeal of stainless steel, it is often given various colors, such as black, using methods such as chemical coloring, painting, and oxidation treatment. For example, Patent Document 1 describes a black stainless steel material in which a black coating (oxide film) has been formed on the surface of the stainless steel material by an oxidation treatment method. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2019-178392 [Overview of the project] [Problems that the invention aims to solve]

[0004] When manufacturing various products using stainless steel, various processes such as bending, welding, and polishing are performed. Depending on the processing conditions (for example, bending with a large bending radius), the oxide film formed on the surface of the stainless steel may crack, partially exposing the base material. In such areas of stainless steel where the base material is exposed, the absence of an oxide film on the surface reduces corrosion resistance and can lead to corrosion.

[0005] This invention was made to solve the above-mentioned problems, and aims to provide a stainless steel material and a method for manufacturing the same that have good corrosion resistance even when the base material is partially exposed during processing. Furthermore, the present invention aims to provide processed products with good corrosion resistance.

Means for Solving the Problem

[0006] As a result of intensive research to solve the above problems, the present inventors have found that by forming an oxide film having predetermined characteristics on the surface of a stainless steel material, even if the base material is partially exposed during processing, it is difficult for the corrosion resistance to deteriorate, and thus the present invention has been completed.

[0007] That is, the present invention is a stainless steel material having an oxide film on the surface of the base material, The aforementioned substrate contains, by mass, Mn: 0.05~1.00%, Cr: 16.00~25.00%, Ti: 0.08~0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 0.005~1.00%, Mo: 2.00% or less, and N: 0.100% or less. the oxide film has a Cr2O3 inner layer with a thickness of 50 nm or more, the overall thickness is 300 to 1000 nm, and the carrier density is 2.00×10 20 per cm 3 or less, L * a * b * the lightness index L in the colorimetric system * is 50.0 or less, and the chromaticity indices a * and b * are within ±5.00.

[0008] Further, the present invention is a method for manufacturing the above stainless steel material, By mass, it contains Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 0.005-1.00%, Mo: 2.00% or less, and N: 0.100% or less. a stainless steel rolled material is subjected to heat treatment at a temperature of 900 °C or higher for 30 seconds or more in an atmosphere where the O2 concentration is 1 to 10 vol% and the water vapor concentration is 5 to 20 vol%, and the value represented by the following formula (1): 2×O2 concentration + water vapor concentration ···(1) is 15 to 30.

[0009] Furthermore, the present invention is The substrate surface has an oxide film a processed product of a stainless steel material, having a portion where the base material is exposed in a part of the processed portion death, The aforementioned oxide film is made of Cr with a thickness of 50 nm or more. 2 O 3 It has an inner layer, an overall thickness of 300-1000 nm, and a carrier density of 2.00 × 10⁻¹⁶ 20 pieces / cm 3 Below, L* a * b * Lightness index L in a color system * If the index is 50.0 or less, the Chromanetics index a * and b * It is within ±5.00. It is a processed product. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a stainless steel material that exhibits good corrosion resistance even when the base material is partially exposed during processing, and a method for manufacturing the same. Furthermore, according to the present invention, it is possible to provide processed products with good corrosion resistance. [Brief explanation of the drawing]

[0011] [Figure 1] This is a top view illustrating the location of partial polishing in the embodiment. [Modes for carrying out the invention]

[0012] The embodiments of the present invention, completed based on the above perspective, will be described in detail below. The present invention is not limited to the following embodiments, and it should be understood that modifications, improvements, etc., to the following embodiments, based on the ordinary knowledge of those skilled in the art, without departing from the spirit of the invention, also fall within the scope of the present invention. In this specification, unless otherwise specified, any "%" indication for ingredients refers to "mass%".

[0013] <Stainless steel material> The stainless steel material according to an embodiment of the present invention comprises a base material and an oxide film formed on the surface of the base material. In this specification, "stainless steel material" means a material formed from stainless steel, and its shape is not particularly limited. Examples of shapes include plates (including strips), rods, and tubes. Furthermore, it may be various types of shaped steel, such as T-shaped and I-shaped cross-sections. The oxide film has the function of imparting corrosion resistance and a black color to stainless steel materials. First, let's explain the characteristics of oxide films.

[0014] (Thickness of the Cr2O3 inner layer: 50 nm or more) The oxide film has a Cr2O3 inner layer with a thickness of 50 nm or more. The Cr2O3 inner layer is a layer formed on the substrate side of the oxide film and has the function of ensuring the barrier properties (substrate protection ability) of the oxide film. From the viewpoint of ensuring this function, the lower limit of the thickness of the Cr2O3 inner layer is 50 nm, preferably 60 nm, and more preferably 70 nm. On the other hand, the upper limit of the thickness of the Cr2O3 inner layer is not particularly limited, but is preferably 900 nm, more preferably 800 nm.

[0015] (Overall thickness: 300-1000nm) The overall thickness of the oxide film affects the color tone. From the viewpoint of imparting a desired black color tone, the lower limit of the overall thickness is 300 nm, preferably 310 nm, and more preferably 320 nm. On the other hand, if the overall thickness is large, cracking and peeling of the oxide film are more likely to occur during processing of the stainless steel material. Therefore, the upper limit of the overall thickness is 1000 nm, preferably 950 nm, and more preferably 900 nm.

[0016] In this specification, the total thickness of the oxide film is defined as the depth from the surface to the point where the oxygen (O) concentration is 1 / 4 of its maximum value, as shown in the depth-direction component concentration profile obtained using glow discharge emission spectroscopy (GD-OES). The thickness of the Cr2O3 inner layer is defined as the portion of the oxide film where the Cr concentration / (Fe concentration + Cr concentration + Mn concentration + Ti concentration) × 100 is 70% or more. The concentration of each element can be determined by glow discharge emission spectroscopy (GD-OES).

[0017] (Carrier density: 2.00 × 10) 20 pieces / cm 3 below) Metal corrosion progresses through a paired process of metal dissolution (anodic reaction) and oxygen reduction around the dissolved area (cathode reaction). This is because electrical neutrality is maintained by consuming the electrons generated in the anodic reaction in the cathode reaction. Therefore, if the cathode reaction in stainless steel can be suppressed, the anodic reaction (metal dissolution) can also be suppressed. The cathode reaction occurs in the presence of water when electrons generated in the anode reaction move within the metal and react with dissolved oxygen in the water at the surface. Therefore, the cathode reaction can be suppressed by coating the metal surface with an insulating material that hinders electron movement. However, oxide films mainly composed of Cr2O3 do not provide sufficient insulation because structural defects (e.g., oxygen vacancies or metals with different valencies than Cr) act as carriers for electron movement, and thus cannot adequately suppress the cathode reaction. Consequently, controlling the carrier density of the oxide film is crucial to adequately suppress the cathode reaction in stainless steel materials.

[0018] For the reasons mentioned above, the upper limit of the carrier density of the oxide film is 2.00 × 10⁻⁶. 20 pieces / cm 3 Preferably 1.00 × 10 20 pieces / cm 3 Furthermore, by setting the upper limit of the carrier density of the oxide film as described above, corrosion becomes less likely to occur even if the base material is partially exposed during processing. On the other hand, the lower limit of the carrier density of the oxide film is not particularly limited, as a smaller value increases the effect of suppressing the cathode reaction, but it is generally 1.00 × 10⁻⁶. 14 pieces / cm 3 Preferably 1.00 × 10 15 pieces / cm 3 That is the case. In this specification, the carrier density of the oxide film can be measured by electrochemical impedance measurement.

[0019] (Lightness index L * : Below 50.0, Chromanetics Index a * and b * (Within ±5.00) The oxide film is L * a * b * Lightness index L in a color system * If the index is 50.0 or less, the Chromanetics index a * and b * The value is within ±5.00. Brightness index L * , Chromanetics Index a * and b * If the value falls within the above range, it can be said that the desired shade of black has been obtained. Here, in this specification, "lightness index L * " and "Chromanetics Index a * and b * This can be measured in accordance with JIS Z8722:2009.

[0020] The oxide film preferably has a composite oxide of Mn and Cr (Mn-Cr spinel oxide) on its surface. By providing such a composite oxide of Mn and Cr on the surface, it becomes easier to control the carrier density of the oxide film within the above range.

[0021] The stainless steel substrate is not particularly limited, but from the viewpoint of facilitating the formation of an oxide film having the above-mentioned characteristics, it is preferable that it contains Mn: 0.05 to 1.00%, Cr: 16.00 to 25.00%, and Ti: 0.08 to 0.50%. Furthermore, the stainless steel base material may further include at least one selected from C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, and N: 0.100% or less. Furthermore, the stainless steel base material may further include at least one selected from Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

[0022] In one embodiment, the stainless steel base material may have a composition containing Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, and N: 0.100% or less, with the remainder being Fe and impurities. In another embodiment, the stainless steel base material may have a composition consisting of Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, N: 0.100% or less, Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less, with the remainder being Fe and impurities. Herein, in this specification, "impurities" means components that are mixed in during the industrial production of stainless steel materials due to various factors in the raw materials such as ore and scrap, and the manufacturing process, and which are acceptable as long as they do not adversely affect the present invention. For example, impurities include unavoidable impurities. Examples of impurities include oxygen (O). The reasons for limiting the content of each of the above elements are explained below.

[0023] (Mn: 0.05~1.00%) Mn is an effective element for ensuring the color tone of the oxide film (blackened film after blackening heat treatment). In particular, Mn provides a black color tone by forming a complex oxide with Cr. However, if the Mn content is too high, it becomes easier to generate MnS, which acts as a corrosion initiation site, and also destabilizes the ferrite phase. Therefore, the upper limit of the Mn content is 1.00%, preferably 0.95%, and more preferably 0.90%. On the other hand, if the Mn content is too low, the above effects may not be sufficiently obtained. Therefore, the lower limit of the Mn content is 0.05%, preferably 0.055%, and more preferably 0.06%.

[0024] (Cr: 16.00~25.00%) Cr is an effective element for improving the corrosion resistance and oxidation resistance of stainless steel materials. Furthermore, Cr is also an effective element for ensuring the color tone of the oxide film (the blackened film after blackening heat treatment). However, if the Cr content is too high, the toughness of the stainless steel material decreases, and the growth of the oxide film is inhibited, preventing the formation of an oxide film with a black color tone. Therefore, the upper limit of the Cr content is 25.00%, preferably 24.50%, and more preferably 24.00%. On the other hand, if the Cr content is too low, the above effects cannot be fully obtained. Therefore, the lower limit of the Cr content is 16.00%, preferably 16.25%, and more preferably 16.50%.

[0025] (Ti: 0.08~0.50%) Ti is an element that affects resistance to intergranular corrosion (sensitization suppression). Furthermore, Ti is an effective element for ensuring the color tone of the oxide film (blackened film after blackening heat treatment). In particular, Ti forms a complex oxide with Cr, giving it a black color, and also suppresses the peeling of the oxide film by forming Ti oxide (TiO2) on the surface. However, if the Ti content is too high, the workability and surface quality of the stainless steel material will deteriorate. Therefore, the upper limit of the Ti content is 0.50%, preferably 0.45%, and more preferably 0.40%. Conversely, if the Ti content is too low, the above effects cannot be fully obtained. Therefore, the lower limit of the Ti content is 0.08%, preferably 0.085%, and more preferably 0.09%.

[0026] (C: 0.100% or less) Carbon (C) is an element that affects properties of stainless steel, such as resistance to intergranular corrosion (sensitization inhibition) and workability. However, if the C content is too high, the workability and resistance to intergranular corrosion of the stainless steel will decrease. Therefore, the upper limit of the C content is 0.100%, preferably 0.080%, and more preferably 0.060%. On the other hand, there is no particular lower limit for the C content, but excessively low C content leads to increased refining costs. Therefore, the lower limit of the C content is preferably 0.0001%, and more preferably 0.0003%.

[0027] (Si:1.00% or less) Si is an element that improves the oxidation resistance of stainless steel materials. However, if the Si content is too high, the workability and toughness of the welded joint will decrease. Therefore, the upper limit of the Si content is 1.00%, preferably 0.90%, and more preferably 0.80%. On the other hand, the lower limit of the Si content is not particularly limited, but from the viewpoint of obtaining the effects of Si, it is preferably 0.005%, more preferably 0.01%, and even more preferably 0.015%.

[0028] (P:0.100% or less) P is an element that affects properties such as weldability and workability of stainless steel materials. If the P content is too high, the above properties may deteriorate. Therefore, the upper limit of the P content is 0.100%, preferably 0.080%, and more preferably 0.060%. On the other hand, there is no particular lower limit for the P content, but excessively low P content leads to an increase in refining costs. Therefore, the lower limit of the P content is preferably 0.001%, and more preferably 0.005%.

[0029] (S:0.100% or less) S is an element that generates MnS, which acts as a corrosion initiation site, and affects properties such as the toughness of welded joints in stainless steel materials. If the S content is too high, the above properties may deteriorate. Therefore, the upper limit of the S content is 0.100%, preferably 0.080%, and more preferably 0.060%. On the other hand, there is no particular lower limit for the S content, but excessively low S content leads to an increase in refining costs. Therefore, the lower limit of the S content is preferably 0.0001%, and more preferably 0.0002%.

[0030] (Ni: 1.00% or less) Ni is an effective element for improving the corrosion resistance and weld toughness of stainless steel materials. However, if the Ni content is too high, the ferrite phase becomes unstable and manufacturing costs increase. Therefore, the upper limit of the Ni content is 1.00%, preferably 0.90%, and more preferably 0.80%. On the other hand, the lower limit of the Ni content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.005%, and more preferably 0.01%.

[0031] (Cu:1.00% or less) Cu is an effective element for improving the corrosion resistance of stainless steel materials. However, if the Cu content is too high, the ferrite phase becomes unstable and manufacturing costs increase. Therefore, the upper limit of the Cu content is 1.00%, preferably 0.90%, and more preferably 0.80%. On the other hand, the lower limit of the Cu content is not particularly limited, but is preferably 0.005%, and more preferably 0.01%.

[0032] (Mo: 2.00% or less) Mo is an effective element for improving the corrosion resistance and oxidation resistance of stainless steel materials. However, if the Mo content is too high, it leads to a decrease in the workability of the stainless steel material and an increase in manufacturing costs. Therefore, the upper limit of the Mo content is 2.00%, preferably 1.95%, and more preferably 1.90%. On the other hand, the lower limit of the Mo content is not particularly limited, but is preferably 0.001%, and more preferably 0.005%.

[0033] (N:0.100% or less) Nitrogen (N) is an element that affects properties such as resistance to intergranular corrosion (sensitization inhibition) and workability. However, if the N content is too high, the intergranular corrosion resistance and workability of stainless steel materials will decrease. In addition, if the N content is high, TiN will precipitate more easily, reducing the amount of solid-solution Ti in the steel, and inhibiting the formation of a black coating after blackening heat treatment. Furthermore, the formed nitrides are prone to becoming the starting point for corrosion, reducing corrosion resistance. For this reason, the upper limit of the N content is 0.100%, preferably 0.095%, and more preferably 0.090%. On the other hand, there is no particular lower limit for the N content, but excessively low N content leads to an increase in refining costs. For this reason, the lower limit of the N content is preferably 0.001%, and more preferably 0.003%.

[0034] (Nb:0.50% or less) Nb is an element that affects properties such as resistance to intergranular corrosion (sensitization suppression). However, if the Nb content is too high, the workability and toughness of the stainless steel material will decrease. Therefore, the upper limit of the Nb content is 0.50%, preferably 0.45%, and more preferably 0.40%. On the other hand, the lower limit of the Nb content is not particularly limited, but is preferably 0.005%, and more preferably 0.01%.

[0035] (Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less) Al, Zr, Co, V, and W are effective elements for improving the oxidation resistance of stainless steel materials. However, if the content of Al, Zr, Co, V, and W is too high, the workability and toughness of the stainless steel material will decrease, and the manufacturing cost will increase. Therefore, the upper limit for the content of Al, Zr, Co, V, and W is 1.00%, preferably 0.95%, and more preferably 0.90%. On the other hand, the lower limit for the content of Al, Zr, Co, V, and W is not particularly limited, but is preferably 0.0001%, and more preferably 0.0005%.

[0036] (REM: 0.100% or less, Ca: 0.100% or less) REM and Ca are effective elements for improving the oxidation resistance of stainless steel materials. However, if the content of REM and Ca is too high, it will lead to an increase in the manufacturing cost of the stainless steel material. Therefore, the upper limit for the content of REM and Ca is 0.100%, preferably 0.090%, and more preferably 0.080%. On the other hand, the lower limit for REM and Ca is not particularly limited, but is preferably 0.0001%, and more preferably 0.0003%. REM is a collective term for 17 elements including Sc, Y, and lanthanides, and refers to rare earth metals. Specifically, examples include La, Ce, and Nd, and one of these can be included individually or in combination of two or more. If two or more rare earth elements are included, the above REM content refers to the total content of these rare earth elements.

[0037] (Sn:0.100% or less) Sn is an effective element for improving the corrosion resistance of stainless steel materials. However, if the Sn content is too high, Sn segregates, reducing manufacturability. Therefore, the upper limit of the Sn content is 0.100%, preferably 0.090%, and more preferably 0.080%. On the other hand, the lower limit of the Sn content is not particularly limited, but is preferably 0.001%, and more preferably 0.002%.

[0038] (B:0.0100% or less) B is an effective element for improving the secondary workability of stainless steel materials. However, if the B content is too high, the fatigue strength of the stainless steel material will decrease. Therefore, the upper limit of the B content is 0.0100%, preferably 0.0090%, and more preferably 0.0080%. On the other hand, the lower limit of the B content is not particularly limited, but is preferably 0.0001%, and more preferably 0.0003%.

[0039] The base metal structure is ferritic. Hereinafter, "ferritic" means a metal whose structure at room temperature is mainly the ferrite phase.

[0040] The stainless steel material according to the embodiment of the present invention has an oxide film having the above-described characteristics, and therefore exhibits good corrosion resistance even when the base material is partially exposed during processing. Accordingly, the stainless steel material according to the embodiment of the present invention is suitable for use in the manufacture of various processed products.

[0041] <Manufacturing method for stainless steel materials> The method for manufacturing stainless steel material according to the embodiment of the present invention is not particularly limited as long as it is a method capable of manufacturing stainless steel material having the above-described characteristics. The stainless steel material according to the embodiment of the present invention can be manufactured, for example, by heat-treating a rolled stainless steel material at a temperature of 900°C or higher for 30 seconds or more in an atmosphere in which the O2 concentration is 1 to 10 volume%, the water vapor concentration is 5 to 20 volume%, and the value represented by the following formula (1) is 15 to 30. 2 × O2 concentration + water vapor concentration ... (1)

[0042] If the atmosphere during heat treatment is not under the above conditions, it is not possible to control the carrier density of the oxide film within the above range. For example, if the O2 concentration exceeds 10% by volume, the amount of Mn and Fe oxides in the oxide film increases, and the carrier density becomes high. On the other hand, if the O2 concentration is less than 1% by volume, it becomes difficult to form an oxide film of a predetermined thickness. From the viewpoint of stably controlling the carrier density of the oxide film within the above range, the O2 concentration is preferably 1.5 to 9.5% by volume, and more preferably 2 to 9%. If the water vapor concentration is outside the range of 5-20 volume%, lattice defects in the oxide film increase, and the carrier density becomes higher. From the viewpoint of stably controlling the carrier density of the oxide film within the above range, the water vapor concentration is preferably 6-19 volume%, more preferably 7-18%. If the value represented by equation (1) is outside the range of 15 to 30, the number of lattice defects in the oxide film increases, and the carrier density becomes higher. From the viewpoint of stably controlling the carrier density of the oxide film within the above range, the value represented by equation (1) is preferably 15.5 to 29, more preferably 16 to 28.

[0043] If the heat treatment temperature is less than 900°C and the duration is less than 30 seconds, the oxide film will not grow sufficiently, and it will not be possible to form an oxide film of the desired thickness. The heat treatment temperature is preferably 900 to 1200°C, more preferably 910 to 1180°C, from the viewpoint of stably forming an oxide film of the desired thickness. Furthermore, the heat treatment time is preferably 30 to 300 seconds, more preferably 35 to 280 seconds, from the viewpoint of stably forming an oxide film of the desired thickness.

[0044] The rolled stainless steel material is not particularly limited, and hot-rolled materials, cold-rolled materials, etc., can be used. The rolled material can be manufactured according to methods known in the art. For example, cold-rolled material can be manufactured by melting stainless steel having a predetermined composition, hot-rolling, annealing, and pickling, and then cold-rolling.

[0045] The composition of the rolled stainless steel is not particularly limited, but from the viewpoint of facilitating the formation of an oxide film having the above-mentioned characteristics, it is preferable that it contains Mn: 0.05 to 1.00%, Cr: 16.00 to 25.00%, and Ti: 0.08 to 0.50%. Furthermore, the rolled stainless steel material may further contain at least one selected from C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, and N: 0.100% or less. Furthermore, the rolled stainless steel material may further contain at least one selected from Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

[0046] In one embodiment, the stainless steel rolled material may have a composition containing Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, and N: 0.100% or less, with the remainder being Fe and impurities. In another embodiment, the rolled stainless steel material may have a composition consisting of Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, N: 0.100% or less, Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less, with the remainder being Fe and impurities.

[0047] <Processed products> The processed product according to the embodiment of the present invention is a processed product of the above-mentioned stainless steel material. In this specification, "stainless steel processed product" means a product obtained by processing stainless steel material by various known methods. The processing method is not particularly limited, but examples include pressing, polishing, and roll forming.

[0048] A processed product according to an embodiment of the present invention has a portion of the processed area in which the base material is exposed. Even with such an exposed portion of the base material, corrosion of that portion is less likely to occur, thus improving the corrosion resistance of the processed product.

[0049] The processed products according to the embodiments of the present invention have good corrosion resistance and can therefore be used in various products that require corrosion resistance. Examples of processed products are not limited to exhaust system parts such as mufflers and exterior building material panels that are joined to mounting jigs. [Examples]

[0050] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0051] Stainless steel having the composition shown in Table 1 (the remainder being Fe and impurities) was melted and hot-rolled to obtain a hot-rolled sheet with a thickness of 3.0 mm. The hot-rolled sheet was then annealed at 1050°C and pickled to obtain a hot-rolled annealed sheet. Next, the hot-rolled annealed sheet was cold-rolled to obtain a cold-rolled sheet with a thickness of 1.0 mm. Next, the cold-rolled sheet was heat-treated under the conditions shown in Table 2 to obtain a stainless steel sheet. During the heat treatment, the predetermined O2 and water vapor concentrations were controlled by adjusting the introduction ratio of O2 gas, N2 gas, and water vapor in the atmosphere furnace. A test piece measuring 300 mm (rolling direction) × 100 mm (width direction) was cut from the obtained stainless steel sheet.

[0052] [Table 1]

[0053] [Table 2]

[0054] The following evaluations were performed on the above test specimens.

[0055] (Overall thickness of the oxide film and thickness of the Cr2O3 inner layer) A 50mm square test piece was cut from the test specimen, and its surface was degreased with acetone. Next, the pre-treated coating was analyzed using glow discharge emission spectroscopy (GD-OES) in accordance with JIS K0144:2018. In GD-OES, the thickness of the oxide film was defined as the depth from the surface to the point where the oxygen (O) concentration was 1 / 4 of its maximum value, based on the obtained depth-direction component concentration profile. Furthermore, the thickness of the Cr2O3 inner layer was defined as the portion of the oxide film where the Cr concentration / (Fe concentration + Cr concentration + Mn concentration + Ti concentration) × 100 was 70% or higher. The concentrations of each element were calculated from the depth-direction component concentration profile obtained by GD-OES.

[0056] (Carrier density of oxide film) A 20mm x 15mm test piece was cut from the specimen, a wire was spot-welded to one end, and the portion other than the 10mm x 10mm test surface was coated with silicone resin (one-component condensation type RTV rubber KE44 manufactured by Shin-Etsu Chemical Co., Ltd.). Next, an electrochemical impedance measurement was performed at 30°C under an Ar degassing atmosphere using a 0.1 mol / L Na2SO4 aqueous solution as the test solution. The electrochemical impedance measurement was performed using the HZ-7000 electrochemical measurement system manufactured by Hokuto Denko Co., Ltd., by measuring the impedance change by applying a sine wave at a predetermined potential, and the capacitance C of the oxide film was measured. The measurement potential was -0.2~0.5V vs. SSE (SSE indicates a saturated KCl silver-silver chloride electrode type reference electrode), the sine wave was 1Hz~100kHz, and the amplitude was 10mV. Based on the obtained C, a 1 / C plot called a Mott-Schottky plot was created. 2 -In the V-curve graph, the slope A of the graph from 0 to -0.4V was derived using the least squares method. The relationship between slope A and carrier density N q Since the relationship can be expressed by the following equation, the carrier density of the oxide film was derived from the slope A based on this equation.

[0057]

number

[0058] In the above equation, Nq is the carrier density, A is the slope of the Mott-Schottky plot, and e is the elementary charge (1.62 × 10⁻¹⁰). -19 C) is the dielectric constant of the oxide film (12), and ε0 is the dielectric constant of vacuum (8.854 × 10⁻¹⁴). -12 It is F / m.

[0059] (color tone) For five arbitrary locations on the oxide film, color measurements were performed using a spectrophotometer with a measurement diameter of 3 mmφ in accordance with JIS Z8722:2009, and the average value was used to determine the CIELAB (L) color in accordance with JIS Z8781-4:2013. * a * b * Lightness index L (color system) * , Chromanetics Index a * , b* As shown.

[0060] The measurement conditions for the above color tones were as follows: Equipment: Konica Minolta CM-700d Spectrophotometer Light source: Pulsed xenon lamp Photodetector: Dual 36-element silicon photodiode array Target mask: φ3mm Measurement: 10° field of view Auxiliary illuminant: D65 Daylight, Color temperature 6504K Specular reflection processing mode: SCI

[0061] (Corrosion resistance of processed products: CCT test) The test specimens were processed by polishing to obtain processed test products. For polishing, the material was cut into a shape of 50 mm wide x 100 mm long, and then partially or fully polished while cooling to obtain a processed test specimen. Partial polishing was performed at 12 locations on the test specimen so that the base material was exposed in a 5 mm diameter circle. The locations of the partially polished areas on the processed test specimen are shown in Figure 1. Next, the corrosion resistance of the processed test specimens described above was evaluated by a combined cycle (CCT) test. The CCT test was conducted as follows. First, for the processed test specimens obtained by tensile and polishing processes, three sides of the test piece (excluding one side in the width direction) were coated with resin (one-component condensation type RTV rubber KE44 manufactured by Shin-Etsu Chemical Co., Ltd.). For the processed test specimens obtained by TIG welding, a test piece measuring 50 mm wide x 100 mm long was cut out so that the weld was centered, and then three sides of the test piece measuring 50 mm wide x 100 mm long were coated with resin (one-component condensation type RTV rubber KE44 manufactured by Shin-Etsu Chemical Co., Ltd.). Next, two 20 mmφ x 10 mm polyethylene tubes were bonded onto a 70 mm x 150 mm bakelite plate, and the side of the processed test specimen (test piece measuring 50 mm wide x 10 mm long) opposite to the side not coated with resin was placed on top of the tubes and bonded. Next, the samples obtained in this manner were placed in a CCT apparatus with the surface of the processed test specimen (measurement specimen) at a 75° angle to the horizontal plane, and the side of the processed test specimen (measurement specimen) not coated with resin facing downwards. Ten cycles were performed, each consisting of 5% salt spray (35°C, 2 hours), drying (60°C, 25%RH, 4 hours), and wetting (50°C, 95%RH, 2 hours). After that, the samples were washed with water and dried, and the rust area ratio on the surface of the processed test specimen (measurement specimen) was evaluated (in accordance with JIS Z2371:2015). In this evaluation, if the rating number (RN) is 8.0 or higher (corresponding to a rust area ratio of 0.25% or less), the corrosion resistance is judged to be good, and if the RN is less than 8.0, the corrosion resistance is judged to be poor. The results are shown in Table 3.

[0062] [Table 3]

[0063] As shown in Table 3, the stainless steel plates of Test Nos. 1-1 to 1-5 (examples of the present invention) have a Cr2O3 inner layer with a thickness of 50 nm or more, an overall thickness of 300 to 1000 nm, and a carrier density of 2.00 × 10⁻¹⁶ 20 pieces / cm 3 Below, L * a * b * Lightness index L in a color system *If the index is 50.0 or less, the Chromanetics index a * and b * Because it has an oxide film with a tolerance of ±5.00 or less, it exhibited good corrosion resistance even when the base material was partially exposed during processing.

[0064] In contrast, the stainless steel sheet in Test No. 2-1 (comparative example) had an insufficient heat treatment time and was polished on the entire surface, resulting in a very thin oxide film. Furthermore, the carrier density of the oxide film in this stainless steel sheet became too high. Therefore, this stainless steel sheet did not have sufficient corrosion resistance. In Test No. 2-2 (comparative example), the O2 concentration and the value of formula (1) were too high during heat treatment, resulting in an excessively high carrier density of the oxide film. Consequently, this stainless steel sheet did not exhibit sufficient corrosion resistance. In the stainless steel sheet of Test No. 2-3 (comparative example), the water vapor concentration and the value of formula (1) were too high during heat treatment, resulting in an excessively high carrier density of the oxide film. Therefore, this stainless steel sheet did not have sufficient corrosion resistance. In the stainless steel sheet of test No. 2-4 (comparative example), the value of equation (1) during heat treatment was too high, resulting in an excessively high carrier density of the oxide film. Therefore, this stainless steel sheet did not have sufficient corrosion resistance.

[0065] In Test No. 2-5 (Comparative Example), the heat treatment time was too short, resulting in an excessively small overall thickness of the oxide film and the Cr2O3 inner layer. Consequently, this stainless steel sheet lacked sufficient corrosion resistance. The stainless steel sheet used in test No. 2-6 (comparative example) had too little Mn content and no Ti, so the desired black color could not be obtained. The stainless steel sheet used in test No. 2-7 (comparative example) did not contain Ti, and therefore the desired black color could not be obtained. The stainless steel sheet used in test No. 2-8 (comparative example) had too little chromium content, resulting in an excessively high carrier density. Consequently, this stainless steel sheet lacked sufficient corrosion resistance.

[0066] As can be seen from the above results, the present invention provides a stainless steel material and a method for manufacturing the same that have good corrosion resistance even when the base material is partially exposed during processing. Furthermore, the present invention provides processed products with good corrosion resistance.

Claims

1. A stainless steel material having an oxide film on the surface of the base material, The aforementioned substrate contains, by mass, Mn: 0.05 to 1.00%, Cr: 16.00 to 25.00%, Ti: 0.08 to 0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 0.005 to 1.00%, Mo: 2.00% or less, and N: 0.100% or less. The oxide film has a Cr inner layer with a thickness of 50 nm or more, an overall thickness of 300 to 1000 nm, and a carrier density of 2.00×10 2 O 3 The inner layer has a carrier density of 2.00×10 20 per cm 3 or less, and a stainless steel material having a lightness index L * a * b * in the L*a*b* color system of 50.0 or less, and chromaticity indices a * and b * within ±5.

00. * ​

2. The stainless steel material according to claim 1, wherein the base material further comprises at least one selected by mass from Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

3. A method for manufacturing stainless steel according to claim 1 or 2, For rolled stainless steel containing, by mass, Mn: 0.05-1.00%, Cr: 16.00-25.00%, Ti: 0.08-0.50%, C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 0.005-1.00%, Mo: 2.00% or less, N: 0.100% or less, O 2 The concentration is 1 to 10% by volume, the water vapor concentration is 5 to 20% by volume, and the following formula (1): 2 × 0 2 Concentration + Water vapor concentration ... (1) A method for manufacturing stainless steel material, involving heat treatment at a temperature of 900°C or higher for 30 seconds or more in an atmosphere where the value represented by is between 15 and 30.

4. The method for manufacturing a stainless steel material according to claim 3, wherein the rolled stainless steel material further comprises at least one selected by mass from Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

5. A processed product of stainless steel having an oxide film on the surface of the base material, The processed part has an area where the base material is exposed. The oxide film has a Cr₂O₃ inner layer with a thickness of 50 nm or more, an overall thickness of 300 to 1000 nm, a carrier density of 2.00 × 10²⁰ particles / cm³ or less, a lightness index L* in the L*a*b* color system of 50.0 or less, and Chromanetics indices a* and b* within ±5.00, and is a processed product.

6. The processed article according to claim 5, wherein the base material contains, by mass, Mn: 0.05 to 1.00%, Cr: 16.00 to 25.00%, and Ti: 0.08 to 0.50%.

7. The processed article according to claim 6, wherein the base material further comprises at least one selected by mass from C: 0.100% or less, Si: 1.00% or less, P: 0.100% or less, S: 0.100% or less, Ni: 1.00% or less, Cu: 1.00% or less, Mo: 2.00% or less, and N: 0.100% or less.

8. The processed article according to claim 6 or 7, wherein the base material further comprises at least one selected by mass from Nb: 0.50% or less, Al: 1.00% or less, Zr: 1.00% or less, Co: 1.00% or less, V: 1.00% or less, W: 1.00% or less, REM: 0.100% or less, Ca: 0.100% or less, Sn: 0.100% or less, and B: 0.0100% or less.

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