CN109440014B - Low-chromium low-nickel duplex stainless steel and preparation method thereof - Google Patents
Low-chromium low-nickel duplex stainless steel and preparation method thereof Download PDFInfo
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Abstract
The invention relates to a low-chromium low-nickel duplex stainless steel and a preparation method thereof, belonging to the technical field of steel materials, wherein the steel comprises the following components in percentage by mass: 0.01-0.2% of C, 0.3-0.8% of Si, 8-15% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, less than or equal to 0.5% of Ni, 0.5-2% of Al, 12-19% of Cr, 0.001-0.01% of B, and the balance of Fe and inevitable impurities. The preparation process comprises the following steps: selecting raw materials according to the proportion, smelting and casting into steel ingots; the method comprises the steps of hot forging the steel into a forging blank at 1050-1150 ℃, cooling to room temperature, homogenizing the forging blank at 1200-1250 ℃ for 6-8 hours, hot rolling the homogenized forging blank at 1150-1200 ℃, cooling the hot rolled plate to room temperature at 950-1050 ℃, annealing at 780-1000 ℃ for 5-10 minutes, acid washing the annealed hot rolled plate, and cold rolling to obtain the low-chromium and low-nickel duplex stainless steel. The stainless steel has simple components, low cost and excellent performance, the yield strength is more than or equal to 520MPa, the tensile strength is more than or equal to 850MPa, the elongation is more than or equal to 60 percent, and the weldability and the corrosion resistance of the stainless steel meet the service requirements.
Description
The technical field is as follows:
the invention belongs to the technical field of steel materials, and particularly relates to low-chromium low-nickel duplex stainless steel and a preparation method thereof.
Background art:
the duplex stainless steel has a two-phase organization structure of ferrite and austenite, so that the performance of the duplex stainless steel has the characteristics of both the austenite stainless steel and the ferrite stainless steel, and the duplex stainless steel has excellent comprehensive performance. The duplex stainless steel is successfully and widely applied in the fields of petroleum, chemical industry, shipbuilding, papermaking, seawater desalination, transportation, nuclear power, bridges, building curtain walls and the like. However, since the duplex stainless steel has poor thermoplasticity, hot forming is a key factor that limits successful production, and the problem of expensive manufacturing cost of the duplex stainless steel due to shortage of nickel resources also directly limits the development of the industry.
The softening mechanism of ferrite during deformation is dynamic recovery, and the ferrite can also be generated under the condition of very low strain; whereas austenite is dynamically recrystallized after strain is above a certain critical value. Because the ferrite phase is more "soft," stresses and strains tend to concentrate in the ferrite phase, and the uneven distribution of these two phases tends to cause crack nucleation and propagation at the phase boundary. Therefore, how to approach the softening tendency of the two phases and make the stress and the strain more uniformly distributed is a technical problem to be solved urgently in the field of the preparation of the duplex stainless steel.
The invention content is as follows:
the invention aims to overcome the defects of the prior art and provide the low-chromium low-nickel duplex stainless steel and the preparation method thereof, the design idea that Mn replaces Ni and Al to replace Cr is adopted, and a proper preparation process is adopted, so that on the premise that the corrosion resistance index of the duplex stainless steel meets the use requirement, the alloy element Cr which is not beneficial to thermoplasticity is reduced, the content of trace element B is controlled, and the duplex stainless steel has higher ferrite content through hot rolling at the temperature of more than 1000 ℃, so that the hardness of two phases in the duplex stainless steel is approximate, and the stress and the strain are more uniformly distributed, thereby improving the thermoplasticity of the duplex stainless steel. The duplex stainless steel has the advantages of remarkably reduced hot rolling edge crack tendency and good corrosion resistance. Solves the problem of poor thermoplasticity of the duplex stainless steel.
In order to achieve the purpose, the invention adopts the following technical scheme:
a low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.01-0.2% of C, 0.3-0.8% of Si, 8-15% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, less than or equal to 0.5% of Ni, 0.5-2% of Al, 12-19% of Cr, 0.001-0.01% of B, and the balance of Fe and inevitable impurities.
The low-chromium low-nickel duplex stainless steel has the yield strength of 520-650 MPa, the tensile strength of 850-950 MPa and the elongation of 60-75%, and the weldability and the corrosion resistance meet the service requirements.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
(1) selecting raw materials according to set components, smelting, and casting into steel ingots;
(2) and (3) hot forging the steel ingot into a forging blank at 1050-1150 ℃, and cooling to room temperature, wherein: the thickness of the forging stock is 40-60 mm;
(3) homogenizing the forging stock at 1200-1250 ℃ for 6-8 h;
(4) hot rolling the homogenized forging stock at the initial rolling temperature of 1150-1200 ℃ and the final rolling temperature of 950-1050 ℃ to form a hot rolled plate, wherein the thickness of the hot rolled plate is 3-5 mm;
(5) cooling the hot rolled plate to room temperature, and annealing at 780-1000 ℃ for 5-10 min;
(6) and (3) washing the annealed hot rolled plate with acid, and cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 0.7-1.6 mm.
In the step (2), the cooling mode after hot forging is water cooling.
In the step (4), the hot rolling single-pass reduction rate is not more than 30%.
In the step (5), the residence in the sigma forming temperature interval is avoided, the temperature of the hot rolled plate is kept at 800-1000 ℃, and then the hot rolled plate is cooled to room temperature by adopting an ultra-fast cooling mode, wherein the ultra-fast cooling speed is more than or equal to 100 ℃/s.
The design principle of the component control of the invention is as follows:
the effect of the chromium element is as follows: chromium is a major alloying element of stainless steels and plays a decisive role in corrosion resistance. However, in strong oxidizing acid and some reducing media, the passivation effect of chromium element is not enough to maintain the corrosion resistance of the material, and it is necessary to add some elements for inhibiting anodic dissolution, such as nickel, aluminum, silicon, etc., to cooperate with the chromium element to play a good corrosion resistance role. In addition, the chromium element can also improve the oxidation resistance of the steel. With the increase of the content of the chromium element, the oxidation resistance can be obviously improved. Meanwhile, chromium can stabilize the ferrite phase and reduce the austenite phase region. Due to the solid solution strengthening effect, the yield strength of the duplex stainless steel is obviously improved along with the increase of the chromium content. However, an excessively high chromium content not only increases the tendency of intermetallic phases, nitrides, carbides to precipitate, but also increases the cost, and above all reduces the thermoplasticity of the duplex stainless steel, since the chromium element reduces the high temperature deformation resistance of the ferrite.
The nickel element acts as follows: nickel, as an element strongly forming austenite and enlarging the austenite phase region, mainly plays a role in controlling the two-phase balance in duplex stainless steel. Under the condition that the contents of elements such as chromium, aluminum and the like are not changed, the content of nickel elements is adjusted to obtain structures of which the ferrite and the austenite respectively account for 50 percent, so that the duplex stainless steel can obtain the optimal pitting corrosion resistance. It is considered that the main role of the nickel element is to control the texture rather than to improve the corrosion resistance. If the nickel element in the duplex stainless steel is too high, the volume fraction of austenite in the steel is too large, and elements such as chromium, molybdenum and the like are enriched in a ferrite phase, so that a brittle sigma phase is easily generated when the material is subjected to heat treatment at 700-950 ℃, and the ductility, toughness and corrosion resistance of the steel are reduced; on the contrary, if the content of nickel element is less than the optimum value, the ferrite content in the material is excessively high, which also deteriorates the toughness of the material, and the delta phase generated upon solid state crystallization deteriorates the weldability of the duplex stainless steel.
The manganese element acts: mn is an element that expands an austenite phase region and stabilizes an austenite structure, and has a half of the action of Ni. Mn is mainly used for replacing part of Ni in the duplex stainless steel, thereby saving the cost. The expansion of lattice caused by solid solution of manganese element can effectively increase the lattice constant of matrix, resulting in the enlargement of octahedral gap, thereby making the interstitial solid solution atom more easily ascending in the octahedral gap. However, too high Mn content may degrade the corrosion resistance of the steel.
Role of silicon and aluminum: silicon is a ferrite forming element, and when the stainless steel contains silicon element under the oxidation condition, dense SiO can be produced on the surface of the stainless steel2The oxidation film can obviously improve the high-temperature oxidation resistance of the material. The stainless steel containing silicon has good fluidity and can be cast into high-quality heat-resistant stainless steel castings. The addition of Si to stainless steel improves the pitting corrosion resistance in chlorine-containing media. Further, it can be seen from the results of auger analysis that Si is concentrated in the surface layer, and the distributions of Si and Cr in the passivation film are almost synchronized. This synergistic effect enhances stainless steelPassivation capability of steel surface film. But the silicon element promotes the sigma phase formation. Also, an increase in the amount of silicon may decrease the weldability of the steel. Aluminum is an element for stabilizing ferrite, can improve the high-temperature oxidation resistance of steel and improve the welding performance, has obvious precipitation hardening effect when the aluminum content reaches about 1 percent, and in Fe-high manganese steel, Al and Cr in stainless steel play the same role, thereby improving the corrosion resistance. But aluminum can reduce the nitric acid corrosion resistance of the steel.
The function of carbon: the carbon content in the steel increases, the yield point and tensile strength increase, but the plasticity and impact toughness decrease, and when the carbon content exceeds 0.23%, the weldability of the steel deteriorates, so that low alloy structural steels for welding generally have a carbon content of not more than 0.2%. High carbon content also reduces the atmospheric corrosion resistance of the steel. In addition, carbon can increase the cold brittleness and age sensitivity of the steel. The carbide formed by C in steel is a great harm to the corrosion resistance of austenite. Because of the strong affinity of C atom, it combines with nearby Cr element to form carbide rich in C, Cr, whose main carbide is M23C6The carbides are mainly precipitated and precipitated in grain boundaries and crystal interior, so that the Cr element in the nearby area is reduced, and the Cr element is locally enriched due to the slow diffusion speed of the Cr element, so that a chromium-poor area and a chromium-rich area appear in a solid solution matrix, and the capability of resisting intergranular corrosion of the material is greatly reduced. The continuity and stability of the material matrix are damaged by the massive precipitation of the carbide, when the material is stressed by the outside, different deformation resistance behaviors appear at each part in the stainless steel material, the mechanical property of the stainless steel material shows inconsistent plastic property, and then microcracks, namely local fracture damage of the material, preferentially appear at the parts with weaker resistance.
The function of boron: boron can be enriched in grain boundaries to fill in grain boundary vacancies, thereby inhibiting crack propagation, so that the addition of trace amount of B can improve the thermoplasticity of the duplex stainless steel. However, the content of B cannot be too high, and too high B forms B compounds in the duplex stainless steel, so that the plasticity and toughness of the material are seriously reduced, and therefore, the content of B should be strictly controlled below 0.01 percent.
The duplex stainless steel of the application adopts Mn to replace Ni and Al to replace Cr, prepares a novel stainless steel with high performance and low cost, can greatly relieve the current shortage of nickel resources in China, has yield strength about 2 times that of the common austenitic stainless steel although the cost is reduced, and has a microstructure consisting of ferrite and austenite (the volume ratio is close to 1: 1) in a use state. The duplex stainless steel has higher ductility and toughness, intercrystalline corrosion resistance and welding performance than ferrite stainless steel, and simultaneously has higher strength and chloride stress corrosion resistance than austenite stainless steel, and has better thermoplasticity.
The invention has the beneficial effects that:
(1) the low-chromium low-nickel duplex stainless steel has simple components and low cost, and particularly, when the low-chromium low-nickel duplex stainless steel is applied to structural steel manufacture to replace the traditional duplex stainless steel, the cost is greatly reduced.
(2) According to the invention, Mn replaces Ni, Cr content is reduced, Al content is increased, and trace B is added, so that the thermoplasticity of the obtained hot rolled steel plate is obviously improved, and the problems of serious edge crack and low yield in the conventional hot rolling process are avoided.
(3) In the duplex stainless steel of the present invention, since the Cr content is reduced and the Mo content is reduced, the amount of precipitation of a brittle phase (σ) mainly composed of elements such as Fe — Cr — Mo in the obtained steel sheet is reduced, and the impact toughness is remarkably improved.
(4) The steel plate obtained by the invention has excellent mechanical properties, and also has good weldability and corrosion resistance.
The invention develops a new duplex stainless steel, replaces Ni and Al with Mn to replace Cr, further reduces the cost, improves the ferrite hardness at high temperature by Al, and reduces the high-temperature deformation resistance of ferrite by Cr, so that the invention can try to replace Cr with Al, relieves the deformation incompatibility of two phases in the thermal deformation process and solves the problem of poor thermoplasticity in the hot rolling process of the duplex stainless steel.
Description of the drawings:
FIG. 1 is a calculated equilibrium phase diagram for Thermo-Calc software for a low chromium, low nickel duplex stainless steel of example 1 of the present invention;
FIG. 2 is a calculated equilibrium phase diagram for Thermo-Calc software for a low chromium, low nickel duplex stainless steel of example 2 of the present invention;
FIG. 3 is a calculated equilibrium phase diagram for Thermo-Calc software for a low chromium, low nickel duplex stainless steel of example 3 of the present invention;
FIG. 4 is a calculated equilibrium phase diagram for Thermo-Calc software for a low chromium, low nickel duplex stainless steel of example 4 of the present invention.
FIG. 5 is a calculated equilibrium phase diagram for Thermo-Calc software for a low chromium, low nickel duplex stainless steel of example 5 of the present invention.
The specific implementation mode is as follows:
the present invention will be described in further detail with reference to examples.
Example 1
The low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.01 percent of C, 0.3 percent of Si, 10 percent of Mn, less than or equal to 0.01 percent of P, less than or equal to 0.01 percent of S, 0.5 percent of Al, 15 percent of Cr, 0.4 percent of Ni, 0.01 percent of B, and the balance of Fe and inevitable impurities, and the equilibrium phase diagram of the duplex stainless steel is obtained by calculation of Thermo-Calc software and is shown in figure 1.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
after comprehensive metering calculation and ingredient dissolution, casting into steel ingots; hot forging the steel ingot into a forging stock with the thickness of 40mm at 1120 ℃, and cooling the forging stock to room temperature by water; homogenizing the forged blank at 1250 ℃ for 6 h; hot rolling the homogenized forging stock at 1200 ℃, wherein the final rolling temperature is 1050 ℃, the single-pass reduction rate of hot rolling is not more than 30%, and a hot rolled plate with the thickness of 3mm is formed; after the temperature of the hot rolled plate is kept to 1000 ℃, ultra-fast cooling is adopted, the cooling speed is 110 ℃/s, and the hot rolled plate is cooled to room temperature; annealing the hot rolled plate at 1000 ℃ for 8 min; and (3) washing the annealed hot rolled plate with acid, and performing cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 0.7 mm. The material has yield strength of 556-570 MPa, tensile strength of 840-855 MPa and elongation of 62-65%, and the weldability and corrosion resistance of the material meet the service requirements.
Example 2
The low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.02% of C, 0.3% of Si, 10% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 0.8% of Al, 19% of Cr, 0.4% of Ni, 0.01% of B and the balance of Fe and inevitable impurities, and an equilibrium phase diagram of the duplex stainless steel is obtained by calculation through Thermo-Calc software and is shown in figure 2.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
after comprehensive metering calculation and ingredient dissolution, casting into steel ingots; hot forging the steel ingot into a forging stock with the thickness of 60mm at 1050 ℃, and cooling the forging stock to room temperature by water; carrying out homogenization treatment on the forged blank for 8 hours at 1200 ℃; hot rolling the homogenized forging stock at 1150 ℃, wherein the final rolling temperature is 950 ℃, and the single-pass reduction rate of hot rolling is not more than 30% to form a hot rolled plate with the thickness of 5 mm; after the temperature of the hot rolled plate is kept to 800 ℃, ultra-fast cooling is adopted, the cooling speed is 130 ℃/s, and the hot rolled plate is cooled to room temperature; annealing the hot rolled plate at 780 ℃ for 5 min; and (3) washing the annealed hot rolled plate with acid, and performing cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 1.6 mm. The material has yield strength of 600-615 MPa, tensile strength of 860-875 MPa and elongation of 55-58%, and the weldability and corrosion resistance of the material meet the service requirements.
Example 3
The low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.03% of C, 0.3% of Si, 8% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 1.1% of Al, 16% of Cr, 0.5% of Ni, 0.01% of B and the balance of Fe and inevitable impurities, and an equilibrium phase diagram of the duplex stainless steel is obtained by calculation through Thermo-Calc software and is shown in figure 3.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
after comprehensive metering calculation and ingredient dissolution, casting into steel ingots; hot forging the steel ingot into a forging stock with the thickness of 55mm at 1070 ℃, and cooling the forging stock to room temperature by water; carrying out homogenization treatment on the forged blank at 1220 ℃ for 7 h; hot rolling the homogenized forging stock at 1180 ℃, wherein the finishing temperature is 1000 ℃, and the hot rolling single-pass reduction rate is not more than 30% to form a hot rolled plate with the thickness of 4.2 mm; after the temperature of the hot rolled plate is kept to 900 ℃, ultra-fast cooling is adopted, the cooling speed is 120 ℃/s, and the hot rolled plate is cooled to room temperature; annealing the hot rolled plate at 850 ℃ for 7 min; and (3) washing the annealed hot rolled plate with acid, and performing cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 1.2 mm. The material has yield strength of 550-570 MPa, tensile strength of 840-855 MPa and elongation of 60-63%, and the weldability and corrosion resistance of the material meet the service requirements.
Example 4
The low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.04% of C, 0.3% of Si, 10% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 1.4% of Al, 15% of Cr, 0.4% of Ni, 0.01% of B and the balance of Fe and inevitable impurities, and an equilibrium phase diagram of the duplex stainless steel is obtained by calculation of Thermo-Calc software and is shown in figure 4.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
after comprehensive metering calculation and ingredient dissolution, casting into steel ingots; hot forging the steel ingot into a forging stock with the thickness of 50mm at 1090 ℃, and cooling the steel ingot to room temperature; homogenizing the forged blank at 1250 ℃ for 7 h; hot rolling the homogenized forging stock at 1200 ℃, wherein the final rolling temperature is 1030 ℃, the single-pass reduction rate of hot rolling is not more than 30 percent, and a hot rolled plate with the thickness of 3.8mm is formed; after the temperature of the hot rolled plate is preserved to 990 ℃, ultra-fast cooling is adopted, the cooling speed is 110 ℃/s, and the hot rolled plate is cooled to the room temperature; annealing the hot rolled plate at 920 ℃ for 7 min; and (3) washing the annealed hot rolled plate with acid, and performing cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 1.0 mm. The material has yield strength of 565-580 MPa, tensile strength of 840-855 MPa and elongation of 60-63%, and the weldability and corrosion resistance of the material meet the service requirements.
Example 5
The low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.03% of C, 0.3% of Si, 12% of Mn, less than or equal to 0.01% of P, less than or equal to 0.01% of S, 2% of Al, 12% of Cr, 0.3% of Ni, 0.01% of B, and the balance of Fe and inevitable impurities, and an equilibrium phase diagram of the duplex stainless steel is obtained by calculation of Thermo-Calc software and is shown in FIG. 5.
The preparation method of the low-chromium low-nickel duplex stainless steel comprises the following steps:
after comprehensive metering calculation and ingredient dissolution, casting into a steel ingot, hot forging the steel ingot into a forging stock with the thickness of 45mm at 1060 ℃, and cooling to room temperature by water; homogenizing the forged blank at 1250 ℃ for 6 h; hot rolling the homogenized forging stock at 1200 ℃, wherein the finishing temperature is 1040 ℃, and the hot rolling single-pass reduction rate is not more than 30% to form a hot rolled plate with the thickness of 3.2 mm; after the temperature of the hot rolled plate is kept to 1000 ℃, ultra-fast cooling is adopted, the cooling speed is 120 ℃/s, and the hot rolled plate is cooled to room temperature; annealing the hot rolled plate at 990 ℃ for 8 min; and (3) washing the annealed hot rolled plate with acid, and performing cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 0.9 mm. The material has yield strength of 520-550 MPa, tensile strength of 830-840 MPa and elongation of 65-68%, and the weldability and corrosion resistance of the material meet the service requirements.
Claims (2)
1. The preparation method of the low-chromium low-nickel duplex stainless steel is characterized in that the low-chromium low-nickel duplex stainless steel comprises the following components in percentage by mass: 0.01-0.2% of C, 0.3-0.8% of Si, 8-15% of Mn, less than or equal to 0.02% of P, less than or equal to 0.01% of S, less than or equal to 0.5% of Ni, 0.5-2% of Al, 12-19% of Cr, 0.001-0.01% of B, and the balance of Fe and inevitable impurities;
the preparation method comprises the following steps:
(1) selecting raw materials according to set components, smelting, and casting into steel ingots;
(2) and (3) hot forging the steel ingot into a forging blank at 1050-1150 ℃, and cooling to room temperature, wherein: the thickness of the forging stock is 40-60 mm;
(3) homogenizing the forging stock at 1200-1250 ℃ for 6-8 h;
(4) carrying out hot rolling on the homogenized forging stock, wherein the initial rolling temperature is 1150-1200 ℃, the final rolling temperature is 950-1050 ℃ to form a hot rolled plate, the thickness of the hot rolled plate is 3-5 mm, and the single-pass reduction rate of the hot rolling is not more than 30%;
(5) after the hot rolled plate is kept at the temperature of 800-1000 ℃, an ultra-fast cooling mode with the cooling speed of more than or equal to 100 ℃/s is adopted, and annealing is carried out for 5-10 min at the temperature of 780-1000 ℃ after the hot rolled plate is cooled to the room temperature;
(6) and (3) washing the annealed hot rolled plate with acid, and cold rolling to obtain the low-chromium and low-nickel duplex stainless steel, wherein the thickness of the low-chromium and low-nickel duplex stainless steel is 0.7-1.6 mm.
2. The method for preparing the low-chromium low-nickel duplex stainless steel as claimed in claim 1, wherein in the step (6), the prepared low-chromium low-nickel duplex stainless steel has the yield strength of 520-650 MPa, the tensile strength of 850-950 MPa and the elongation of 60-75%, and the weldability and the corrosion resistance of the stainless steel meet the service requirements.
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| CN115110011A (en) * | 2021-03-22 | 2022-09-27 | 江苏润晨新材料科技有限公司 | Preparation method of low-carbon high-toughness high-speed steel |
| CN114574781B (en) * | 2022-03-04 | 2022-12-13 | 江苏铭展特钢制造有限公司 | Wear-resistant stainless steel bar for rail transit and preparation method thereof |
| CN114774805A (en) * | 2022-05-11 | 2022-07-22 | 沈阳大学 | Memory type duplex stainless steel and preparation thereof |
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| WO2012102330A1 (en) * | 2011-01-27 | 2012-08-02 | 新日鐵住金ステンレス株式会社 | Alloying element-saving hot rolled duplex stainless steel material, clad steel sheet having duplex stainless steel as mating material therefor, and production method for same |
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