Stainless steel material and method for manufacturing the same

Abstract

To provide a stainless steel material excellent in hydrogen embrittlement resistance and temper color resistance.SOLUTION: The stainless steel material has a desorption amount of 0.50 ppm or less in a temperature range of 25 to 300°C, and a desorption peak temperature of higher than 100°C, when hydrogen to be desorbed is measured with the use of a temperature-programmed desorption method. In the stainless steel material, in the entire depth region from a surface up to 5 nm, an Al concentration is 5 to 60 mass% and an O concentration is 5 mass% or higher, and in the entire depth region from 5 nm below the surface up to 15 nm, a total concentration of Ti and Nb is 3 to 35 mass%, when the concentrations of the elements in a depth direction are measured with the use of glow discharge emission spectrometry and the total amount of cation elements excluding C and N is defined as 100 mass%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to stainless steel materials and methods for producing the same. [Background technology]

[0002] Stainless steel is commonly used in cooking appliances such as ranges, kettles, and rice cookers, as well as in heating appliances such as stoves and heaters. However, exposure to high-temperature environments during use can cause discoloration due to tempering, which significantly impairs the aesthetic appeal. Tempering is a phenomenon where the surface of stainless steel becomes discolored due to the oxidation of Fe and Cr, and the thickness of the oxide film changes the reflected light, resulting in various colors (yellow, red, blue). Therefore, stainless steel used in these applications requires resistance to tempering, i.e., resistance to tempering. One technique known to improve temper color resistance is to perform bright annealing (also called "BA") to form an oxide film enriched with elements such as Si and Al on the surface of stainless steel (for example, Patent Documents 1-5). Bright annealing refers to a heat treatment in which annealing is performed in a non-oxidizing atmosphere.

[0003] However, bright annealing in a hydrogen-based, non-oxidizing atmosphere (hereinafter referred to as "hydrogen gas atmosphere") is prone to hydrogen embrittlement. In particular, in a hydrogen gas atmosphere with a low dew point (dew point temperature of -50°C or lower), brightly annealed stainless steel materials tend to absorb hydrogen easily, making them susceptible to hydrogen embrittlement. Hydrogen embrittlement can cause problems such as increased cracking during processing of stainless steel materials, so it must be suppressed. As a technology to suppress hydrogen embrittlement, stainless steel materials with controlled composition, precipitate size, and number have been proposed (Patent Document 6). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-open No. 62-156254 [Patent Document 2] Japanese Patent Application Publication No. 8-295999 [Patent Document 3] Patent No. 3939557 [Patent Document 4] Japanese Patent Application Publication No. 9-202945 [Patent Document 5] Patent No. 6106450 [Patent Document 6] International Publication No. 2020 / 194484 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, although the stainless steel material disclosed in Patent Document 6 has good resistance to hydrogen embrittlement, it does not undergo bright annealing, and therefore does not have sufficient resistance to temper color. Thus, conventional technologies have presented the challenge of achieving both hydrogen embrittlement resistance and temper color resistance simultaneously.

[0006] This invention was made to solve the above-mentioned problems, and aims to provide a stainless steel material with excellent resistance to hydrogen embrittlement and temper color, and a method for manufacturing the same. [Means for solving the problem]

[0007] The inventors attempted to increase the Al concentration in the oxide film and the total concentration of Ti and Nb near the interface between the oxide film and the base material in order to suppress the oxidation of Fe and Cr, which are the causes of discoloration due to tempering. Furthermore, the inventors attempted to appropriately control the state of hydrogen present in the stainless steel material in order to suppress hydrogen embrittlement. As a result of fabricating and analyzing various stainless steel materials, the inventors found that stainless steel materials with specific properties can achieve both resistance to hydrogen embrittlement and resistance to tempering. The inventors also found that stainless steel materials with these properties can be easily manufactured by a specific method. This invention was completed based on these findings.

[0008] In other words, the present invention relates to a stainless steel material in which, when hydrogen is desorbed using a temperature-increasing desorption method, the amount of desorption in the temperature range of 25 to 300°C is 0.50 ppm or less and the desorption peak temperature is higher than 100°C, and when the elemental concentration in the depth direction is measured using glow discharge emission spectrometry, and the total amount of cationic elements excluding C and N is set to 100 mass%, the Al concentration in the entire depth region from the surface to 5 nm is 5 to 60 mass%, the O concentration is 5 mass% or more, and the total concentration of Ti and Nb in the entire depth region from 5 nm to 15 nm is 3 to 35 mass%.

[0009] Furthermore, the present invention is A method for manufacturing the aforementioned stainless steel material, A bright annealing step in which cold-rolled stainless steel is brightly annealed in a hydrogen gas atmosphere, and a heating step in which the cold-rolled stainless steel is heated in an air atmosphere or an inert gas atmosphere at a temperature range of 50°C or more and less than 100°C. Between the bright annealing step and the heating treatment step, there is a skin pass rolling step in which the cold-rolled stainless steel material is skin-pass rolled. Includes The It is the law. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a stainless steel material with excellent resistance to hydrogen embrittlement and temper color, and a method for manufacturing the same. [Brief explanation of the drawing]

[0011] [Figure 1] It is a graph showing the relationship between the hydrogen release rate and temperature of the stainless steel plates in Tests No. 1 to 4. [Figure 2] It is the elemental concentration profile in the depth direction in Test No. 4.

Embodiments for Carrying out the Invention

[0012] Hereinafter, embodiments of the present invention will be specifically described. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements can be appropriately added to the following embodiments based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention, and such modified and improved embodiments also fall within the scope of the present invention. In this specification, the “%” indication regarding components means “mass %” unless otherwise specified.

[0013] The stainless steel material of the present invention controls the state of hydrogen in the stainless steel material from the viewpoint of improving hydrogen embrittlement resistance. As an index for evaluating this state of hydrogen, a method of evaluating desorbed hydrogen by the temperature-programmed desorption method was used. Here, the temperature-programmed desorption method is a technique in which the stainless steel material is heated at a constant heating rate, and the released hydrogen is detected by a gas chromatograph or a quadrupole mass spectrometer. Hydrogen is trapped in many defects such as lattice defects such as atomic vacancies, dislocations, and grain boundaries, interfaces of precipitates and inclusions, and voids. By using the temperature-programmed desorption method, hydrogen with different states of existence can be measured.

[0014] The stainless steel material of the present invention exhibits a desorption amount of 0.50 ppm or less in the temperature range of 25 to 300°C when measured using the temperature rise desorption method. A desorption amount within this range indicates a sufficiently low hydrogen content in the stainless steel material, thereby improving its resistance to hydrogen embrittlement. The measurement temperature range (25 to 300°C) for the temperature rise desorption method is assumed to be the temperature range in which the stainless steel material of the present invention is used. From the viewpoint of stably obtaining the above effects, a desorption amount of 0.45 ppm or less is preferable, and 0.40 ppm or less is more preferable. Furthermore, since a lower hydrogen content enhances the effect of improving hydrogen embrittlement resistance, the lower limit of the desorption amount is not particularly limited, but for example, it is 0.01 ppm.

[0015] Furthermore, when measuring the hydrogen desorbed by the stainless steel material of the present invention using the temperature-increasing desorption method, the desorption peak temperature is higher than 100°C. When the desorption peak temperature is high, hydrogen is strongly trapped in the carbonitrides and lattice defects of the stainless steel material, making it difficult for hydrogen to move within the stainless steel material. On the other hand, when the desorption peak temperature is low, hydrogen is weakly trapped in the carbonitrides and lattice defects of the stainless steel material, making it easier for hydrogen to move within the stainless steel material. When hydrogen trapping is weak, hydrogen in the stainless steel material moves as diffusible hydrogen during bending and other processes, concentrating in the processed area and increasing the risk of inducing cracking due to hydrogen embrittlement. Diffusible hydrogen refers to hydrogen that diffuses and moves through grain boundaries and between lattice spaces. By controlling the desorption peak temperature to be higher than 100°C, it is possible to suppress such cracking due to hydrogen embrittlement. Moreover, from the viewpoint of stably obtaining this effect, a desorption peak temperature of 105°C or higher is preferable, and 110°C or higher is more preferable. Furthermore, since a higher desorption peak temperature reduces the risk of hydrogen embrittlement, there is no particular upper limit to the desorption peak temperature, although it is, for example, 200°C.

[0016] The stainless steel material of the present invention controls the concentration of predetermined elements on and near the surface (oxide film) from the viewpoint of improving temper color resistance. As an index for evaluating the concentration of predetermined elements on and near the surface, a method of evaluating elemental concentration in the depth direction by glow discharge emission spectrometry was used. Here, glow discharge emission spectrometry is a technique for measuring elemental concentrations by sputtering Ar ions onto the surface of stainless steel, atomizing and exciting them in a plasma, and then focusing the light emitted from these excited atoms with a focusing lens and converting it into photoelectric light. Since the light emitted from the excited atoms has a wavelength specific to each element, the concentration of each element can be measured.

[0017] The stainless steel material of the present invention has an elemental concentration in the depth direction measured by glow discharge emission spectrometry. When the total amount of cationic elements excluding C and N is set to 100% by mass, the Al concentration in the entire depth region from the surface to 5 nm is 5 to 60% and the O concentration is 5% or more. With Al and O concentrations within this range, it can be said that an Al-enriched oxide film is formed on the surface of the stainless steel material, thereby improving temper color resistance. The depth region from the surface to 5 nm corresponds to the thickness of the oxide film. From the viewpoint of stably obtaining the above effect, the Al concentration is preferably 8 to 40%, and more preferably 10 to 35%. The O concentration is preferably 10% or more, and more preferably 15% or more. The upper limit of the O concentration is not particularly limited, but for example, it is 90%.

[0018] Furthermore, in the stainless steel material of the present invention, the elemental concentration in the depth direction is measured using glow discharge emission spectrometry, and when the total amount of cationic elements excluding C and N is set to 100% by mass, the total concentration of Ti and Nb in the entire depth region from 5 nm to 15 nm from the surface is 3 to 35%. Since Ti and Nb suppress the oxidation of Fe and Cr and inhibit the growth of oxide films, the temper color resistance can be improved by controlling the total concentration of Ti and Nb within the above range. The depth region from 5 nm to 15 nm from the surface corresponds to the vicinity of the oxide film (near the interface between the oxide film and the base material). From the viewpoint of stably obtaining the above effect, the total concentration of Ti and Nb is preferably 3 to 25%, and more preferably 10 to 20%.

[0019] The composition of the stainless steel material of the present invention is not particularly limited as long as it has the above-mentioned properties, but it is preferable to have a composition that includes C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.050% or less, S: 0.0030% or less, Cr: 19.0~30.0%, Mo: 2.50% or less, N: 0.030% or less, Al: 0.30% or less, Nb: 0.40% or less, Ti: 0.40% or less, Ni: 1.00% or less, Cu: 1.00% or less, with the remainder being Fe and impurities. Furthermore, the composition of the stainless steel material of the present invention may further include, in addition to the elements of the above composition, one or more elements selected from B: 0.0050% or less, V: 0.50% or less, W: 0.50% or less, Sn: 0.30% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, Zr: 0.50% or less, Co: 0.50% or less, Ga: 0.01% or less, Hf: 0.10% or less, and REM: 0.10% or less.

[0020] Here, "impurities" refers to components (e.g., unavoidable impurities) 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 in the manufacturing process, and which are acceptable as long as they do not adversely affect the present invention. Furthermore, "stainless steel material" is a concept that includes various shapes such as stainless steel strips, stainless steel sheets, stainless steel foils, stainless steel wires, and stainless steel shapes.

[0021] <C: Below 0.030%> C is an element that affects the corrosion resistance and temper color resistance of stainless steel materials. Stainless steel materials used in household appliances are often required to have temper color resistance. However, if the C content is too high, the temper color resistance will decrease. Therefore, the upper limit value of the C content is 0.030%, preferably 0.020%, more preferably 0.015%. On the other hand, the lower limit value of the C content is not particularly limited. However, the lower the C content, the more time is required for the refining process, and the manufacturing cost may increase. Therefore, the lower limit value of the C content is preferably 0.0002%, more preferably 0.0005%.

[0022] <Si: 1.00% or less> Si enhances the temper color resistance of stainless steel materials and is an effective element as a deoxidizing element. However, if the Si content is too high, there is a risk that the toughness and bending workability will decrease due to hardening and the desired hydrogen embrittlement resistance cannot be obtained. Therefore, the upper limit value of the Si content is 1.00%, preferably 0.80%, more preferably 0.60%. On the other hand, the lower limit value of the Si content is not particularly limited. However, from the perspective of obtaining the above effects, it is preferably 0.05%, more preferably 0.08%.

[0023] <Mn: 1.00% or less> Mn is an element effective in improving the toughness, bending workability and hydrogen embrittlement resistance of stainless steel materials. However, if the Mn content is too high, there is a risk that the temper color resistance and bending workability will decrease. Therefore, the upper limit value of the Mn content is 1.00%, preferably 0.50%. On the other hand, the lower limit value of the Mn content is not particularly limited. However, from the perspective of obtaining the above effects, it is preferably 0.05%, more preferably 0.08%.

[0024] <P: 0.050% or less> P is an element that may reduce the toughness of stainless steel materials. Therefore, the upper limit value of the P content is 0.050%, preferably 0.040%. On the other hand, the lower limit value of the P content is not particularly limited, but the lower the P content, the more time is required for the refining process, and the manufacturing cost may increase. Therefore, the lower limit value of the P content is preferably 0.001%, more preferably 0.010%.

[0025] <S: 0.0030% or less> S is an element that may generate sulfide-based inclusions and reduce the temper color resistance and hot workability of stainless steel materials. Therefore, the upper limit value of the S content is 0.0030%, preferably 0.0025%. On the other hand, the lower limit value of the S content is not particularly limited, but the lower the S content, the more time is required for the refining process, and the manufacturing cost may increase. Therefore, the lower limit value of the S content is preferably 0.0001%, more preferably 0.0002%.

[0026] <Cr: 19.0 - 30.0%> Cr is a major element for forming an oxide film (passive film) on the surface of stainless steel materials, and properties such as corrosion resistance and temper color resistance can be improved by the passive film. From the perspective of forming an oxide film enriched with Al, the lower limit value of the Cr content is 19.0%, preferably 19.2%. On the other hand, if the Cr content is too high, the toughness and bending workability will decrease. Therefore, the upper limit value of the Cr content is 30.0%, preferably 29.6%.

[0027] <Mo: 2.50% or less> Mo is a major element for strengthening the oxide film (passive film) of stainless steel materials, and properties such as corrosion resistance and temper color resistance can be improved by the passive film. However, if the Mo content is too high, toughness and bendability may decrease due to hardening, and the desired hydrogen embrittlement resistance may not be obtained. Therefore, the upper limit value of the Mo content is 2.50%, preferably 2.00%, more preferably 1.50%. On the other hand, the lower limit value of the Mo content is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0028] <N: 0.030% or less> N is an element that may combine with Al to form AlN, which serves as a starting point for bend cracking and may reduce the hydrogen embrittlement resistance of stainless steel materials. Therefore, the upper limit value of the N content is 0.030%, preferably 0.025%. On the other hand, the lower limit value of the N content is not particularly limited, but the lower the N content, the more time is required in the refining process, and the manufacturing cost may increase. Therefore, the lower limit value of the N content is preferably 0.001%, more preferably 0.010%.

[0029] <Al: 0.30% or less> Al is an element effective for improving temper color resistance by forming an oxide film enriched with Al on the surface of stainless steel materials. However, if the Al content is too high, it is likely to generate AlN, which serves as a starting point for bend cracking, and the hydrogen embrittlement resistance of stainless steel materials may decrease. Therefore, the upper limit value of the Al content is 0.30%, preferably 0.25%. On the other hand, the lower limit value of the Al content is not particularly limited, but from the perspective of obtaining the above effects, it is preferably 0.01%, more preferably 0.02%.

[0030] <Nb: 0.40% or less> Nb preferentially combines with C and N to form Nb carbonitrides, and suppresses the oxidation of Fe and Cr to inhibit the growth of the oxide film, thereby improving the temper color resistance of the stainless steel material. However, if the Nb content is too high, the amount of dissolved Nb not consumed in the formation of Nb carbonitrides increases. As a result, the bending workability may decrease due to hardening. Therefore, the upper limit value of the Nb content is 0.40%, preferably 0.35%. On the other hand, the lower limit value of the Nb content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0031] <Ti: 0.40% or less> Similar to Nb, Ti preferentially combines with C and N to form Ti carbonitrides, and suppresses the oxidation of Fe and Cr to inhibit the growth of the oxide film, thereby improving the temper color resistance of the stainless steel material. Also, Ti is an element that suppresses the decrease in corrosion resistance due to the formation of Cr carbonitrides. However, if the Ti content is too high, the Ti carbonitrides become coarsened, and starting from that, the bending workability decreases. Therefore, the upper limit value of the Ti content is 0.40%, preferably 0.35%. On the other hand, the lower limit value of the Ti content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0032] <Ni: 1.00% or less> Ni is an element that improves the corrosion resistance of the stainless steel material and suppresses the decrease in bending workability. However, since Ni is an austenite phase stabilizing element, if the Ni content is too high, the ferrite phase becomes unstable and the temper color resistance decreases. Therefore, the upper limit value of the Ni content is 1.00%, preferably 0.80%. On the other hand, the lower limit value of the Ni content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0033] <Cu: 1.00% or less> Cu is an element that improves the corrosion resistance and bending workability of stainless steel materials. However, since Cu is an austenite phase stabilizing element, if the Cu content is too high, the ferrite phase becomes unstable and the temper color resistance decreases. Therefore, the upper limit value of the Cu content is 1.00%, preferably 0.80%. On the other hand, the lower limit value of the Cu content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.03%.

[0034] <B: 0.0050% or less> B is an element effective for improving the secondary workability of stainless steel materials by increasing the grain boundary strength by preferentially concentrating at grain boundaries. However, if the B content becomes excessive, the boride (Cr2B) at grain boundaries coarsens, resulting in a decrease in bending workability. Therefore, the upper limit value of the B content is 0.0050%, preferably 0.0030%. On the other hand, the lower limit value of the B content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.0002%, more preferably 0.0005%.

[0035] <V: 0.50% or less> V is an element that improves the strength without impairing the toughness of stainless steel materials. However, if the V content is too high, there is a risk of decreasing the bending workability and toughness, and the cost increases. Therefore, the upper limit value of the V content is 0.50%, preferably 0.40%. On the other hand, the lower limit value of the V content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0036] <W: 0.50% or less> W is an element that improves the strength without impairing the toughness of stainless steel materials. However, if the W content is too high, there is a risk of decreasing the bending workability and toughness, and the cost increases. Therefore, the upper limit value of the W content is 0.50%, preferably 0.40%. On the other hand, the lower limit value of the W content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0037] <Sn: Below 0.30%> Sn is an element effective in improving the corrosion resistance of stainless steel materials. However, if the Sn content is too high, the bending workability and toughness will decrease. Therefore, the Sn content should be 0.30% or less, preferably 0.20% or less. On the other hand, the lower limit value of the Sn content is not particularly limited, but from the viewpoint of obtaining the effect of Sn, it is preferably 0.01%, more preferably 0.05%.

[0038] <Ca: Below 0.0100%> Ca is an element effective in fixing S and purifying stainless steel materials. However, if the Ca content is too high, the amount of inclusions generated will increase and the bending workability will decrease. Therefore, the upper limit value of the Ca content is 0.0100%, preferably 0.0050%. On the other hand, the lower limit value of the Ca content is not particularly limited, but from the viewpoint of obtaining the above effect, it is preferably 0.0005%, more preferably 0.0010%.

[0039] <Mg: Below 0.0100%> Mg is an element effective in refining stainless steel materials. However, if the Mg content is too high, the amount of inclusions generated will increase and the bending workability will decrease. Therefore, the upper limit value of the Mg content is 0.0100%, preferably 0.0050%. On the other hand, the lower limit value of the Mg content is not particularly limited, but from the viewpoint of obtaining the above effect, it is preferably 0.0001%, more preferably 0.0005%.

[0040] <Zr: Below 0.50%> Zr is an element effective in fixing C and purifying stainless steel materials. However, if the Zr content is too high, the bending workability of the stainless steel material will decrease. Therefore, the upper limit value of the Zr content is 0.50%, preferably 0.40%. On the other hand, the lower limit value of the Zr content is not particularly limited, but from the viewpoint of obtaining the above effect, it is preferably 0.001%, more preferably 0.005%.

[0041] <Co: Below 0.50%> Co is an element that improves the strength of stainless steel materials without impairing their toughness. However, if the Co content is too high, there is a risk that the bending workability and toughness will decrease, and the cost will increase. Therefore, the upper limit value of the Co content is 0.50%, preferably 0.40%. On the other hand, the lower limit value of the Co content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.01%, more preferably 0.05%.

[0042] <Ga: 0.01% or less> Ga is an element that improves the hot workability of stainless steel materials. However, if the Ga content is too high, the manufacturability will decrease. Therefore, the upper limit value of the Ga content is 0.01%, preferably 0.005%. On the other hand, the lower limit value of the Ga content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.0001%, more preferably 0.0005%.

[0043] <Hf: 0.10% or less> Hf is an element effective for fixing C and purifying stainless steel materials. However, if the Hf content is too high, the bending workability of the stainless steel material will decrease. Therefore, the upper limit value of the Hf content is 0.10%, preferably 0.08%. On the other hand, the lower limit value of the Hf content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.001%, more preferably 0.005%.

[0044] <REM: 0.10% or less> REM (rare earth element) preferentially binds to S and P to form compounds, so it can suppress the decrease in the bending workability and temper color resistance of stainless steel materials due to S and P. However, if the REM content is too high, the stainless steel material may harden, and there is a risk that the toughness and bending workability will decrease. Therefore, the upper limit value of the REM content is 0.10%, preferably 0.08%. On the other hand, the lower limit value of the REM content is not particularly limited, but from the viewpoint of obtaining the above effects, it is preferably 0.001%, more preferably 0.005%. REM refers to the collective term for the two elements scandium (Sc) and yttrium (Y), and the 15 elements from lanthanum (La) to lutetium (Lu) (lanthanoids). These may be used individually or as a mixture. Among REM elements, La and Y are preferred.

[0045] The microstructure of the stainless steel material of the present invention is not particularly limited and may be ferritic, austenitic, or ferritic-austenitic duplex, but among these, it is preferably ferritic or ferritic-austenitic duplex, and more preferably ferritic. Here, "ferritic" refers to metals whose microstructure at room temperature is primarily the ferrite phase. Therefore, "ferritic" also includes metals that contain small amounts of other phases (for example, austenite or martensite). Similarly, "austenitic" and "ferrite-austenite duplex" refer to metals whose microstructure at room temperature is primarily the austenite phase and ferrite and austenite phases, respectively.

[0046] The thickness of the stainless steel material of the present invention is not particularly limited, but is preferably 3.2 mm or less, more preferably 0.1 to 3.0 mm, and even more preferably 0.5 to 2.5 mm.

[0047] The stainless steel material of the present invention preferably does not crack in a tight bending test measured in accordance with JIS Z2248:2006. If it has such properties, it can be said to have excellent resistance to hydrogen embrittlement. The dimensions of the test specimen used for the close-fitting bending test shall be 40 mm (width direction) x 90 mm (rolling direction).

[0048] The stainless steel material of the present invention is measured in accordance with JIS Z8730:2009 after the stainless steel material has been held in air at 400°C for 24 hours. * a * b * a color system * (hereinafter referred to as “a* The value is called "value". ) and b * (hereinafter referred to as “b * The values ​​are all less than 10. If a material has these characteristics, it can be said to have excellent temper color resistance. The test specimens used in this color difference test shall be 50 mm square. It is preferable to degrease and clean the test specimens with an organic solvent or the like before holding them in the air at 400°C for 24 hours.

[0049] The method for manufacturing the stainless steel material of the present invention is not particularly limited as long as it is a method capable of producing a stainless steel material having the above-described properties. A typical method for manufacturing the stainless steel material of the present invention includes a bright annealing step of bright annealing a cold-rolled stainless steel material in a hydrogen gas atmosphere, and a heating step of heating the cold-rolled stainless steel material in an air atmosphere or an inert gas atmosphere at a temperature range of 50°C or more and less than 100°C.

[0050] The bright annealing process is carried out by bright annealing cold-rolled stainless steel in a hydrogen gas atmosphere. By bright annealing under these conditions, an Al-enriched oxide film can be formed on the surface of the stainless steel, thereby improving its resistance to temper color. Here, a hydrogen gas atmosphere refers to an atmosphere primarily composed of hydrogen gas, and may also contain other inert gases such as nitrogen or argon. A preferred hydrogen gas atmosphere is one in which hydrogen gas is 100%.

[0051] The annealing temperature and annealing time in the bright annealing process are not particularly limited and can be set appropriately according to the composition of the stainless steel material. The annealing temperature is typically 800 to 1100°C, preferably 850 to 1050°C, and the annealing time is typically 10 minutes or less, preferably 10 to 120 seconds.

[0052] The cold-rolled stainless steel material used in the bright annealing process is not particularly limited, but it is preferably a cold-rolled stainless steel material having the composition described above. Specifically, the cold-rolled stainless steel material preferably has a composition containing C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.050% or less, S: 0.0030% or less, Cr: 19.0~30.0%, Mo: 2.50% or less, N: 0.030% or less, Al: 0.30% or less, Nb: 0.40% or less, Ti: 0.40% or less, Ni: 1.00% or less, Cu: 1.00% or less, with the remainder being Fe and impurities. Furthermore, in addition to the elements in the above composition, cold-rolled stainless steel may further contain one or more elements selected from B: 0.0050% or less, V: 0.50% or less, W: 0.50% or less, Sn: 0.30% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, Zr: 0.50% or less, Co: 0.50% or less, Ga: 0.01% or less, Hf: 0.10% or less, and REM: 0.10% or less.

[0053] The heating process involves heating the cold-rolled stainless steel material in an air atmosphere or an inert gas atmosphere at a temperature range of 50°C to less than 100°C. By heating under these conditions, the state of hydrogen presence in the stainless steel material can be appropriately controlled, thereby improving its resistance to hydrogen embrittlement. Here, an inert gas atmosphere refers to an atmosphere primarily composed of an inert gas, and may include various gases other than inert gases such as nitrogen or argon. A preferred inert gas atmosphere is one in which the inert gas is 100%.

[0054] The heating temperature in the heating process is 50°C or higher and less than 100°C, preferably 60 to 95°C, and more preferably 65 to 90°C. Under these temperature conditions, it is possible to reduce the hydrogen concentration in the cold-rolled stainless steel material and obtain a stainless steel material with the desired hydrogen presence. The heating time can be set appropriately according to the heating temperature, but is typically 1 day or more, preferably 2 days or more, and more preferably 3 days or more. There is no particular upper limit to the heating time, but in reality it is 100 days, for example, 50 days.

[0055] The heating process may be carried out in the temperature range of 100 to 250°C instead of the temperature range of 50°C to less than 100°C. In this case, the heating time can be shortened (for example, 1 to 60 minutes). However, it should be noted that depending on the composition of the stainless steel material, heating in the temperature range of 100 to 250°C may not yield stainless steel material with the above-mentioned properties.

[0056] A skin pass rolling step may be further included between the bright annealing step and the heating step, if necessary. Performing a skin pass rolling step makes it easier to reduce the hydrogen concentration in the cold-rolled stainless steel material, making it possible to stably obtain stainless steel material with a desired hydrogen content. The conditions for the skin pass rolling process are not particularly limited and can be adjusted as appropriate according to the composition of the stainless steel material.

[0057] Because the stainless steel material of the present invention possesses the above-mentioned properties, it exhibits excellent resistance to hydrogen embrittlement and temper color. Therefore, it can be used in various applications where these properties are required. Specifically, the stainless steel material of the present invention can be suitably used in home appliances such as cooking appliances like rice cookers and heating appliances like stoves and heaters. [Examples]

[0058] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0059] Slabs with the compositions shown in Table 1 were melted and hot-rolled to 3.5 mm thick hot-rolled stainless steel sheets, which were then annealed and pickled. Next, the hot-rolled stainless steel sheets were cold-rolled to 0.7 to 2.0 mm thick cold-rolled stainless steel sheets. In Table 1, steel grades A to E are ferritic, and steel grade F is a ferritic-austenite duplex system.

[0060] [Table 1]

[0061] Next, a stainless steel sheet was obtained by bright annealing (hereinafter abbreviated as "BA") in a hydrogen gas atmosphere (100% hydrogen gas) and then heating. In some tests, skin pass rolling (hereinafter abbreviated as "SP rolling") was performed between BA and the heating treatment. Table 2 shows the conditions for BA and heating treatment, and whether or not SP rolling was performed.

[0062] [Table 2]

[0063] Next, the obtained stainless steel sheets were evaluated as follows.

[0064] (Amount of hydrogen desorption and desorption peak temperature) After cutting a 10mm (width direction) x 30mm (rolling direction) test specimen from a stainless steel plate, the specimen was degreased and cleaned with an organic solvent. Next, the hydrogen released from this specimen was evaluated by measuring the amount of hydrogen released using the thermal desorption method (TDA). In TDA, the specimen was heated in an argon atmosphere at a heating rate of 100°C / hour in the temperature range of 25-300°C, and the hydrogen released (desorbed) from the specimen was measured by chromatography. The chromatograph used was capable of detecting hydrogen with an accuracy of 0.01 ppm. From the TDA measurement results, a graph showing the relationship between the hydrogen release (desorption) rate and temperature was created, and the amount of hydrogen desorbed and the desorption peak temperature were determined. The amount of hydrogen desorbed was calculated by integrating the spectrum of the graph. For reference, Figure 1 shows a graph illustrating the relationship between the hydrogen release rate and temperature of stainless steel plates in tests No. 1 to 4.

[0065] (Concentration of each element at a given depth) A test piece of 50 mm (width direction) × 50 mm (rolling direction) was cut out from a stainless steel plate. Next, using this test piece, the Al concentration and O concentration in the entire depth region from the surface to 5 nm, and the total concentration of Ti and Nb in the entire depth region from a depth of 5 nm to 15 nm from the surface were determined by glow discharge optical emission spectroscopy (GDS). These respective concentrations were relative values in the depth-directional elemental concentration profile obtained by this analysis, with the total amount of cationic elements excluding C and N being 100 mass%. GDS was performed using a Marcus-type high-frequency glow discharge optical emission surface analyzer (GD-Profiler2) manufactured by Horiba, Ltd., under the conditions of an Ar gas pressure of 600 Pa, a power of 35 W, a frequency of 100 Hz, and a duty cycle of 0.25. For reference, the depth-directional elemental concentration profile in Test No. 4 is shown in FIG. 2. In the depth-directional elemental concentration profile shown in FIG. 2, the signal intensity is represented in terms of cation fraction conversion.

[0066] (Hydrogen embrittlement resistance: Adhesion bending test) A test piece of 40 mm (width direction) × 90 mm (rolling direction) was cut out from a stainless steel plate. Next, for this test piece, an adhesion bending test was performed using a 100-ton hydraulic press in accordance with JIS Z2248:2006. In this test, those without cracks are represented by ○, and those with cracks are represented by ×. Also, in this test, if there are no cracks, it can be said that the hydrogen embrittlement resistance is excellent.

[0067] (Temper color resistance: Color difference test) A test piece of 50 mm (width direction) × 50 mm (rolling direction) was cut out from a stainless steel plate. Next, after holding this test piece in the atmosphere at 400 °C for 24 hours, in accordance with JIS Z8730:2009, the * a * b * a value in the CIE L * value and b * value were determined. In this test, those with both the a * value and b * value less than 10 were represented by ○, and those with the a * value and b *If at least one of the values ​​is 10 or greater, it is represented as ×. Also, in this test, a * Value and b * If all values ​​are less than 10, it can be said that the paint has excellent temper color resistance. The results of each of the above evaluations are shown in Table 3.

[0068] [Table 3]

[0069] As shown in Table 3, the stainless steel sheets (examples of the present invention) of Tests No. 2, 4, 5, 7, 8, 10-12, and 14 showed good results in the adhesion bending test (resistance to hydrogen embrittlement) and the color difference test (resistance to temper color) because the amount of hydrogen desorption, desorption peak temperature, Al concentration, O concentration, and total Ti and Nb concentration throughout the predetermined depth region were within the predetermined range. In contrast, the stainless steel plate in Test No. 1 (comparative example) did not yield sufficient results in the adhesion bending test (hydrogen embrittlement resistance) due to a large amount of hydrogen desorption. In the stainless steel sheet of Test No. 3 (comparative example), the hydrogen desorption peak temperature was low, and there were areas with low total concentrations of Ti and Nb throughout the entire specified depth range. As a result, the results of the adhesion bending test (hydrogen embrittlement resistance) and the color difference test (temper color resistance) were insufficient. The stainless steel sheet in Test No. 6 (comparative example) exhibited a large amount of hydrogen desorption, and areas with low Al concentration existed throughout the entire specified depth range. As a result, the results of the adhesion bending test (hydrogen embrittlement resistance) and the color difference test (temper color resistance) were insufficient. The stainless steel sheet in Test No. 9 (comparative example) exhibited a high amount of hydrogen desorption, and also had areas with high total concentrations of Ti and Nb throughout the specified depth range. As a result, the results of the adhesion bending test (hydrogen embrittlement resistance) and the color difference test (temper color resistance) were insufficient. The stainless steel sheet in Test No. 13 (comparative example) exhibited a large amount of hydrogen desorption, and areas with high Al concentration existed throughout the entire specified depth range. As a result, the results of the adhesion bending test (hydrogen embrittlement resistance) and the color difference test (temper color resistance) were insufficient.

[0070] As can be seen from the above results, the present invention provides a stainless steel material with excellent resistance to hydrogen embrittlement and temper color, and a method for manufacturing the same.

Claims

1. When hydrogen is desorbed using the temperature-controlled desorption method, the amount of desorption in the temperature range of 25 to 300°C is 0.50 ppm or less, and the desorption peak temperature is higher than 100°C. A stainless steel material in which, when the elemental concentrations in the depth direction are measured using glow discharge emission spectrometry and the total amount of cationic elements excluding C and N is set to 100 mass%, the Al concentration in the entire depth region from the surface to 5 nm is 5 to 60 mass%, the O concentration is 5 mass% or more, and the total Ti and Nb concentration in the entire depth region from 5 nm to 15 nm is 3 to 35 mass%.

2. The stainless steel material according to claim 1, having a composition on a mass basis comprising C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.050% or less, S: 0.0030% or less, Cr: 19.0 to 30.0%, Mo: 2.50% or less, N: 0.030% or less, Al: 0.30% or less, Nb: 0.40% or less, Ti: 0.40% or less, Ni: 1.00% or less, Cu: 1.00% or less, with the remainder being Fe and impurities.

3. The stainless steel material according to claim 1 or 2, further comprising one or more elements selected by mass from B: 0.0050% or less, V: 0.50% or less, W: 0.50% or less, Sn: 0.30% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, Zr: 0.50% or less, Co: 0.50% or less, Ga: 0.01% or less, Hf: 0.10% or less, and REM: 0.10% or less.

4. A stainless steel material according to any one of claims 1 to 3, which is free from cracks in a tight bending test measured in accordance with JIS Z2248:2006.

5. A method for manufacturing stainless steel material according to Claim 1, A bright annealing process in which cold-rolled stainless steel is brightly annealed in a hydrogen gas atmosphere, A heating treatment step in which the cold-rolled stainless steel material is heated in an air atmosphere or an inert gas atmosphere at a temperature range of 50°C or more and less than 100°C, Between the bright annealing step and the heating step, there is a skin pass rolling step in which the cold-rolled stainless steel material is skin-pass rolled. A method that includes this.

6. The method according to claim 5, wherein the cold-rolled stainless steel material has a composition by mass of C: 0.030% or less, Si: 1.00% or less, Mn: 1.00% or less, P: 0.050% or less, S: 0.0030% or less, Cr: 19.0 to 30.0%, Mo: 2.50% or less, N: 0.030% or less, Al: 0.30% or less, Nb: 0.40% or less, Ti: 0.40% or less, Ni: 1.00% or less, Cu: 1.00% or less, with the remainder being Fe and impurities.

7. The method according to claim 6, wherein the cold-rolled stainless steel further comprises one or more selected by mass from B: 0.0050% or less, V: 0.50% or less, W: 0.50% or less, Sn: 0.30% or less, Ca: 0.0100% or less, Mg: 0.0100% or less, Zr: 0.50% or less, Co: 0.50% or less, Ga: 0.01% or less, Hf: 0.10% or less, and REM: 0.10% or less.

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