Medium-chromium heat-resistant ferritic stainless steel, and preparation method for medium-chromium heat-resistant ferritic stainless steel cold plate and use thereof

Abstract

Disclosed in the present invention are a medium-chromium heat-resistant ferritic stainless steel, and a preparation method for a medium-chromium heat-resistant ferritic stainless steel cold plate and a use thereof. The medium-chromium heat-resistant ferritic stainless steel comprises the chemical compositions: C: ≤0.020%, N: ≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30％, and the balance being Fe and inevitable impurity elements, wherein 60≤(wAl+wSi)×wCr≤70 and 1.0≤4wNi+8wMo-wMn≤2.0. The preparation method for the medium-chromium heat-resistant ferritic stainless steel cold plate comprises smelting, continuous casting, hot rolling, and cold rolling steps. The medium-chromium heat-resistant ferritic stainless steel cold plate of the present invention has both excellent high-temperature oxidation resistance and electrical resistance properties, and good processability and corrosion resistance, thereby effectively expanding the application field of medium-chromium heat-resistant ferritic stainless steel products.

Description

Medium-chromium heat-resistant ferritic stainless steel, cold plate preparation method and application thereof TECHNICAL FIELD

[0001] The present application belongs to the technical field of stainless steel production, and particularly relates to a medium-chromium heat-resistant ferritic stainless steel with oxidation resistance, high resistance, processability and corrosion resistance, and a cold plate preparation method and application thereof. BACKGROUND

[0002] The Cr content of the medium-chromium ferritic stainless steel is between 16-19%, and the stainless steel has been widely applied due to its good corrosion resistance, processability and economy. The most original medium-chromium ferritic stainless steel is 430 stainless steel, and through further reduction of the C and N element contents and addition of Nb, Ti and other stabilizing elements, super-pure ferritic stainless steel such as 439, 441 and the like is derived; in order to further improve the corrosion resistance, Mo or Cu elements are added, such as 436, 444, SUS430J1L and the like.

[0003] For heat-resistant ferritic stainless steel, a Cr2O3, Al2O3 or SiO2 oxide film needs to be generated on the surface, and the Al2O3 oxide film is the most dense. The increase of the Al and Si element contents will increase the resistivity of the material, and on the other hand, will reduce the processability of the material, and the Al element will also weaken the corrosion resistance of the material.

[0004] Therefore, a new component system and preparation process need to be designed for the medium-chromium heat-resistant ferritic stainless steel, which can generate a dense Al2O3 oxide film on the surface to improve the high-temperature oxidation resistance of the material, and can also ensure the resistance and processability of the material, and has certain corrosion resistance. SUMMARY

[0005] To solve the above technical problems, the present application provides a medium-chromium heat-resistant ferritic stainless steel, a medium-chromium heat-resistant ferritic stainless steel cold plate and a preparation method thereof.

[0006] The chemical components of the medium-chromium heat-resistant ferritic stainless steel provided by the present application are as follows in terms of mass percentage: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and inevitable impurity elements, and the Al, Si and Cr element contents satisfy 60≤(w Al +w Si )×w Cr ≤70, and the Mn, Ni and Mo element contents satisfy 1.0≤4w Ni+8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, Mo.

[0007] Preferably, the content of C and N in the medium-chromium type heat-resistant ferritic stainless steel is controlled as C≤0.012% and N≤0.012%.

[0008] Further, the total oxygen content in the medium-chromium type heat-resistant ferritic stainless steel is T[O]≤10ppm.

[0009] The preparation method of the medium-chromium type heat-resistant ferritic stainless steel cold plate provided by the application comprises the following steps:

[0010] (1) Smelting: taking molten iron as raw material, smelting is carried out through molten iron pretreatment, K-OBM-S, VOD and LF processes to realize decarburization, reduction and alloying, and the chemical composition of the molten steel prepared by smelting is controlled as follows in terms of mass percentage: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and inevitable impurity elements, and the content of Al, Si and Cr elements satisfies 60≤(w Al +w Si )×w Cr ≤70, and the content of Mn, Ni and Mo elements satisfies 1.0≤4w Ni +8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, Mo.

[0011] (2) Continuous casting: slab continuous casting is carried out via a tundish, electromagnetic stirring is put into the whole process of continuous casting, and the equiaxed crystal ratio of the cast blank is controlled to be >55%;

[0012] (3) Hot rolling: The heating temperature is controlled at 1150~1200℃, the hot rolling passes are 7, the final rolling temperature is controlled at ≤880℃, and after hot rolling, the coiling temperature is controlled at ≤500℃.

[0013] (4) Cold rolling: First, hot rolling is annealed and pickled. The hot rolling annealing temperature is controlled at 940-1000℃ and the hot rolling annealing time is controlled at 1.4-1.8 min / mm. Then, multiple cold rolling passes are performed. The total cold rolling deformation rate is controlled at 55%-85%. The cold rolling annealing furnace temperature is controlled at 880-940℃ and the cold rolling annealing time is controlled at 1.0-1.4 min / mm. Finally, the surface of the cold plate is ground to obtain a medium-chromium type heat-resistant ferritic stainless steel cold plate.

[0014] Furthermore, in the above-mentioned method for preparing medium-chromium type heat-resistant ferritic stainless steel cold plates, Cr is alloyed in K-OBM-S, aluminum shot is used for reduction in VOD and then Al, Si, Mn and Ti are alloyed, and Ni and Mo are alloyed in LF furnace.

[0015] Furthermore, in the above-mentioned method for preparing medium-chromium type heat-resistant ferritic stainless steel cold-rolled sheet, in the hot rolling step, the final rolling temperature is controlled to be ≤850℃ and the coiling temperature is controlled to be ≤400℃.

[0016] Furthermore, in the above-mentioned method for preparing medium-chromium type heat-resistant ferritic stainless steel cold-rolled sheet, in the cold rolling step, the hot rolling annealing temperature is controlled at 940-980℃, the total cold rolling deformation rate is controlled at 60%-85%, the cold rolling annealing furnace temperature is controlled at 880-920℃, and the surface of the cold-rolled sheet is ground with 230# sandpaper.

[0017] The medium-chromium heat-resistant ferritic stainless steel cold plate provided by the present invention is prepared by the above-mentioned preparation method of medium-chromium heat-resistant ferritic stainless steel cold plate. The medium-chromium heat-resistant ferritic stainless steel cold plate has a width of 1000-1300mm and a thickness of 0.4-2.0mm. The surface type of the medium-chromium heat-resistant ferritic stainless steel cold plate is HL surface, with a roughness of <0.40μm and a total oxygen content T[O] ≤10ppm.

[0018] Furthermore, the medium-chromium type heat-resistant ferritic stainless steel cold-rolled plate has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r of 1.20-1.40, and a room temperature resistivity of 1.15-1.20 μΩ·cm; after continuous high-temperature oxidation at 900℃ for 200 hours in an atmospheric atmosphere, the oxidation weight gain is 0.10-0.15 mg / cm³. 2 No rust spots were observed within 48 hours after a salt spray test at 35℃ and 5% NaCl.

[0019] In addition, the application further provides application of the above-mentioned medium-chromium type heat-resistant ferritic stainless steel cold plate in household appliances, industrial combustion furnaces, automobile exhaust systems and electric heating equipment of new energy vehicles, wherein the medium-chromium type heat-resistant ferritic stainless steel cold plate is used to manufacture high-temperature-resistant parts or electric heating components in household appliances, industrial combustion furnaces, automobile exhaust systems and new energy vehicles.

[0020] The application designs a component system for the medium-chromium type heat-resistant ferritic stainless steel and optimizes a cold plate preparation process, and provides the medium-chromium type heat-resistant ferritic stainless steel, the medium-chromium type heat-resistant ferritic stainless steel cold plate, a preparation method and application thereof, which have good processing performance and certain corrosion resistance on the premise of excellent high-temperature oxidation resistance and resistance performance, and effectively expand the application field of the medium-chromium type heat-resistant ferritic stainless steel product. Compared with the prior art, the technical scheme of the application has the following advantages and beneficial effects:

[0021] (1) The medium-chromium type heat-resistant ferritic stainless steel and the product obtained by reasonably matching Cr, Al and Si main elements and micro-alloying Mn, Ni, Mo and Ti elements can obtain good processing performance and better corrosion resistance on the premise of generating a compact Al2O3 oxide film;

[0022] (2) The medium-chromium type heat-resistant ferritic stainless steel cold plate has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r value of 1.20-1.40, a room temperature resistivity of 1.15-1.20 mu Omega*cm, an oxidation weight gain rate of 0.10-0.15 mg / cm 2 after a high-temperature oxidation test at 900 DEG C for 200 hours, and no oxide film peeling phenomenon, and no rust spot is observed within 48 hours after a salt spray test in a 5% NaCl spray at 35 DEG C after surface grinding, so that the medium-chromium type heat-resistant ferritic stainless steel and the cold plate have excellent high-temperature oxidation resistance and resistance performance, and also have good processing performance and certain corrosion resistance. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical schemes in the embodiments of the application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings. In the drawings:

[0024] FIG. 1 is a metallographic structure diagram of the medium-chromium type heat-resistant ferritic stainless steel cold plate prepared by the embodiment 1 of the application;

[0025] Fig. 2 is a cross-section composition surface scanning diagram of the oxide layer of the cold plate of the medium-chromium heat-resistant ferrite stainless steel prepared by using the embodiment 2 of the present application. DETAILED DESCRIPTION

[0026] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in combination with the specific embodiments of the present application and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments of the present application, all the other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present application.

[0027] The present application aims to provide a medium-chromium heat-resistant ferrite stainless steel and a cold plate preparation method thereof, which has excellent high-temperature oxidation resistance and electrical resistance performance, and also has good processing performance and certain corrosion resistance. To this end, the present application designs the component system and optimizes the cold plate preparation process for the medium-chromium heat-resistant ferrite stainless steel.

[0028] In the first aspect of the present application, a medium-chromium heat-resistant ferrite stainless steel is provided, the chemical components of which are as follows in terms of mass percentage: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and inevitable impurity elements, and the Al, Si and Cr element content satisfies 60≤(w Al +w Si )×w Cr ≤70, the Mn, Ni and Mo element content satisfies 1.0≤4w Ni +8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of the elements Al, Si, Cr, Mn, Ni and Mo.

[0029] Further, the total oxygen content in the above-mentioned medium-chromium heat-resistant ferrite stainless steel is controlled to be T[O]≤10ppm.

[0030] In the present application, the composition system design of the medium-chromium heat-resistant ferritic stainless steel mainly includes: promoting the generation of dense Al2O3 oxide film by complex addition of Cr, Al and Si elements, significantly improving the spalling resistance of the oxide film by adding trace Ti element, improving the corrosion resistance of the material by adding Ni and Mo elements and controlling the Mn element, and improving the resistivity of the material while ensuring the cold working formability of the material by controlling the content of Al and Si elements, so that the obtained medium-chromium heat-resistant ferritic stainless steel not only has excellent high-temperature oxidation resistance and resistivity, but also has good corrosion resistance and processing performance, thereby widening the application field of the medium-chromium heat-resistant ferritic stainless steel material. The role of each element in the medium-chromium heat-resistant ferritic stainless steel of the present application and the content requirements thereof are introduced as follows:

[0031] C and N: The solubility of carbon and nitrogen in ferritic stainless steel is extremely low, and the diffusion speed is relatively fast. During the cooling process after high-temperature heating, chromium carbide and nitride will be precipitated, which is the root cause of the high-temperature brittleness and high-temperature sensitization of ferritic stainless steel. In addition, chromium carbide is easy to generate CO bubbles at high temperature, which escapes from under the oxide film and destroys the density of the oxide film. Therefore, the content of C and N needs to be strictly controlled. In the present application, the content of C and N is controlled to be ≤0.020%, and preferably ≤0.012%.

[0032] Si: Silicon is a high-temperature oxidation-resistant element. In the high-temperature oxidation of stainless steel, SiO2 is generated, which is distributed at the interface between the oxide film and the metal substrate, can prevent the penetration of oxygen, and reduce the oxidation rate of the alloy. Silicon can also moderately increase the resistivity of the material. However, excessive silicon is not only not conducive to the oxidation resistance of stainless steel, but also reduces the plasticity of the alloy and worsens the cold working performance. Therefore, in the present application, the content of Si is controlled to be 0.30% to 0.50%.

[0033] Mn: Manganese is an unavoidable element in the raw materials for smelting stainless steel. As a solid solution strengthening element, it can improve the toughness of ferritic stainless steel. However, excessive manganese can reduce the corrosion resistance of the steel plate. Therefore, in the present application, the content of Mn is controlled to be 0.20% to 0.50%.

[0034] Cr: Chromium is the most important alloying element in stainless steel and is also a strong ferrite-forming element. It is one of the main alloying elements for oxidation resistance and corrosion resistance in stainless steel. At the same time, as a third element, chromium strongly promotes the formation of Al2O3 oxide film, which can reduce the content of Al element in the corresponding metal substrate for the formation of single Al2O3 oxide film. For medium-chromium ferritic stainless steel, the content of Cr in the present application is controlled to be 17.0% to 19.0%.

[0035] Al: Aluminum is a key element to improve the oxidation resistance of heat-resistant stainless steel, because the Al2O3 oxide film is more dense and stable than Cr2O3 and SiO2. In addition, aluminum is an excellent deoxidizer that can achieve ideal deoxidation and provide a prerequisite for obtaining a high yield of stabilized Ti elements. Aluminum can significantly increase the resistivity of the material. However, aluminum can cause strong embrittlement of ferritic stainless steel, sharply reducing the toughness of the material. Therefore, the Al content in the present application is controlled to be 2.0-4.0%.

[0036] Ni: In ferritic stainless steel, nickel can increase the strength of the steel, reduce the room temperature toughness of the steel, and improve the corrosion resistance of the steel in reducing media, including uniform corrosion, pitting corrosion and crevice corrosion performance. Therefore, the Ni content in the present application is controlled to be 0.05%-0.30%.

[0037] Mo: The addition of molybdenum gives the ferritic stainless steel more excellent corrosion resistance, improves the passivation ability of the ferritic stainless steel and the stability of the passivation film, and especially improves the Cl- corrosion resistance. In addition, molybdenum also plays a solid solution strengthening effect, which improves the high temperature strength and creep strength of the stainless steel. Therefore, the Mo content in the present application is controlled to be 0.10%-0.30%.

[0038] Ti: Titanium has a strong affinity with carbon and nitrogen, and will preferentially form titanium carbide and titanium nitride in the steel, avoiding the precipitation of chromium carbide and chromium nitride. In addition, Ti as an active element, can improve the density and anti-peeling performance of the oxide film. Therefore, the Ti content in the present application is controlled to be 0.10%-0.30%.

[0039] In the second aspect of the present application, a preparation method of a medium chromium type heat-resistant ferritic stainless steel cold plate is provided, and the process route is smelting→continuous casting→hot rolling→cold rolling. The medium chromium type heat-resistant ferritic stainless steel cold plate is prepared by adopting the optimized process of slab continuous casting, low temperature hot rolling, low temperature annealing and multi-pass large deformation cold rolling, and specifically comprising the following steps:

[0040] (1) Smelting: Taking molten iron as raw material, smelting is carried out through molten iron pretreatment, K-OBM-S, VOD and LF processes to realize decarburization, reduction and alloying. The chemical composition of the molten steel prepared by smelting is controlled as follows in terms of mass percentage: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and unavoidable impurity elements, and the Al, Si and Cr element contents satisfy 60≤(w Al +w Si )×wCr ≤70, the element content of Mn, Ni, Mo satisfies 1.0≤4w Ni +8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, Mo.

[0041] (2) Continuous casting: slab continuous casting is performed via a tundish, which can be single casting, 2 continuous casting or 3 continuous casting, electromagnetic stirring is put into the whole continuous casting process, and the equiaxed crystal ratio of the casting blank is controlled to be >55%.

[0042] (3) Hot rolling: hot rolling needs to ensure multi-pass rolling, low-temperature rolling and low-temperature coiling, so as to ensure grain refinement of the hot-rolled plate and increase deformation energy storage, wherein the heating temperature is controlled to be 1150-1200℃, the hot rolling pass is 7 passes, the finish rolling temperature is controlled to be ≤880℃, and after hot rolling, layer cooling is put into, and the coiling temperature is controlled to be ≤500℃.

[0043] (4) Cold rolling: the cold rolling process needs to ensure good processability of the material, which needs low-temperature slow annealing and multi-pass large deformation cold rolling, wherein hot coiling annealing and pickling are first performed, the hot coiling annealing temperature is controlled to be 940-1000℃, the hot coiling annealing time is controlled according to 1.4-1.8min / mm, then multi-pass cold rolling is performed, the total deformation rate of cold rolling is controlled to be 55%-85%, the cold coiling annealing furnace temperature is controlled to be 880-940℃, the cold coiling annealing time is controlled according to 1.0-1.4min / mm, and finally the surface of the cold plate is polished to obtain the medium-chromium heat-resistant ferritic stainless steel cold plate.

[0044] Further, in the preparation method of the above-mentioned medium-chromium heat-resistant ferritic stainless steel cold plate, in order to improve the production efficiency and the recovery rate of valuable elements, ensure the purity of the molten steel, the high content of Cr element is alloyed in K-OBM-S, aluminum shots are used for reduction in VOD and then alloying of easily oxidizable elements Al, Si, Mn and Ti is performed, and alloying of valuable elements Ni and Mo is performed in the LF furnace.

[0045] Preferably, in the preparation method of the medium-chromium heat-resistant ferritic stainless steel cold plate, in the hot rolling step, the finish rolling temperature is controlled to be ≤850℃, and the coiling temperature is controlled to be ≤400℃.

[0046] Preferably, in the preparation method of the medium-chromium heat-resistant ferritic stainless steel cold plate, in the cold rolling step, the hot coil annealing temperature is controlled to be 940-980℃, the total cold rolling deformation rate is controlled to be 60%-85%, the cold coil annealing furnace temperature is controlled to be 880-920℃, and the surface of the cold plate is polished by using a 230# abrasive belt.

[0047] In a third aspect of the present application, a medium-chromium heat-resistant ferritic stainless steel cold plate is provided, which is prepared by the above-mentioned preparation method of the medium-chromium heat-resistant ferritic stainless steel cold plate, the cold plate has a width of 1000-1300mm, a thickness of 0.4-2.0mm, and a surface type of HL surface with a roughness of <0.40μm, and the total oxygen content T[O] is ≤10ppm.

[0048] The medium-chromium heat-resistant ferritic stainless steel of the present application, the medium-chromium heat-resistant ferritic stainless steel cold plate prepared after smelting, continuous casting, hot rolling and cold rolling, has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r value of 1.20-1.40, a room temperature resistivity of 1.15-1.20μΩ·cm, an oxidation weight gain rate of 0.10-0.15mg / cm 2 after continuous high-temperature oxidation at 900℃ in an atmospheric atmosphere, and no oxidation film peeling phenomenon; and no rust spot is observed within 48h after a salt spray test in a 5% NaCl spray at 35℃ after surface polishing.

[0049] In a fourth aspect of the present application, the application of a medium-chromium heat-resistant ferritic stainless steel cold plate in household appliances, industrial combustion furnaces, automobile exhaust systems and new energy automobile electric heating equipment is provided, wherein the cold plate is used to manufacture high-temperature resistant parts or electric heating components in household appliances, industrial combustion furnaces, automobile exhaust systems and new energy automobiles.

[0050] The medium-chromium heat-resistant ferritic stainless steel and the preparation method of the cold plate thereof of the present application are described in detail below in combination with the examples of the present application and the comparative examples of the prior art.

[0051] The chemical components of the medium-chromium heat-resistant ferritic stainless steel cold plates prepared by the medium-chromium heat-resistant ferritic stainless steel of examples 1-3 of the present application and the medium-chromium heat-resistant ferritic stainless steel cold plates prepared by the comparative examples 1-3 of the prior art are shown in Table 1 below (the balance is Fe and unavoidable impurity elements):

[0052] Table 1: Components of the ferritic stainless steel cold plates of examples 1-3 and comparative examples 1-3 (wt.%)

[0053] In examples 1-3 of the present application, the contents of the alloying elements Al, Si, Cr, Mn, Ni and Mo satisfy 60≤(w Al +w Si) x w Cr ≤ 70 and 1.0 ≤ 4w Ni + 8w Mo - w Mn ≤ 2.0; in Comparative Example 1, (w Al + w Si ) x w Cr > 70, 4w Ni + 8w Mo - w Mn < 1.0; in Comparative Example 2, (w Al + w Si ) x w Cr < 10, 4w Ni + 8w Mo - w Mn > 2.0; in Comparative Example 3, (w Al + w Si ) x w Cr < 40, 4w Ni + 8w Mo - w Mn < 1.0.

[0054] The main process parameters of the preparation method of the medium-chromium heat-resistant ferritic stainless steel cold plate of Examples 1-3 of the present application are shown in Table 2 as follows:

[0055] Table 2 Main process parameters of Examples 1-3

[0056] The chromium ferritic stainless steel cold plate prepared by the embodiment 1-3 of the present application and the chromium ferritic stainless steel cold plate prepared by the prior art comparative example 1-3 are analyzed and tested for performance. The metallographic structure of the chromium ferritic stainless steel cold plate prepared by the embodiment 1 of the present application is shown in Fig. 1, the cross-section component surface scanning of the oxidation layer of the chromium ferritic stainless steel cold plate prepared by the embodiment 2 of the present application is shown in Fig. 2, and the performance test results are shown in Table 3. The performance parameters are determined according to the following standards and methods: the grain size is determined according to GBT 6394 “Metal Average Grain Size Determination Method”; the mechanical tensile test is performed according to GBT 228.1 “Metal Material Tensile Test Part 1: Room Temperature Test Method”; the plastic strain ratio is determined according to GB / T 5027 “Metal Material Thin Plate and Thin Strip Plastic Strain Ratio (r value) Determination”; the room temperature resistivity is determined according to GB / T 6146 “Precise Resistance Alloy Resistivity Test Method”; the high temperature oxidation experiment is performed according to GB / T 13303 “Steel Oxidation Resistance Performance Test Method”; and the salt spray corrosion test is performed according to GB / T 10125 “Artificial Atmosphere Corrosion Test Salt Spray Test”. Moreover, when the performance parameters are tested, three samples are taken for each embodiment and comparative example, and the average value of the three samples is the final result. In addition, after the sample is mechanically ground and polished perpendicular to the sample thickness direction, the metallographic structure of the material is observed by optical microscope, the cross-section of the oxidation layer is observed by scanning electron microscope, and the composition structure of the oxidation layer is given.

[0057] Table 3 Performance summary of the chromium ferritic stainless steel cold plate of the embodiment 1-3 and the comparative example 1-3

[0058] From the actual test and experiment results, it can be seen that, in terms of the grain size of the ferritic stainless steel cold plate, the embodiments 1-3 are grade 7-8, which is equivalent to the comparative example 2 and better than the comparative examples 1 and 3; in terms of the elongation after fracture, the embodiments 1-3 are 30%-33%, which is equivalent to the comparative example 2 but better than the comparative examples 1 and 3; in terms of the plastic strain ratio r value, the embodiments 1-3 are 1.20-1.40, which is slightly worse than the comparative example 2 but better than the comparative examples 1 and 3; in terms of the room temperature resistivity, the embodiments 1-3 are 1.15-1.20 μΩ·cm, which is slightly lower than the comparative example 1 but far better than the comparative examples 2 and 3; in terms of the high temperature oxidation weight gain, the embodiments 1-3 are 0.10-0.15 mg / cm 2Comparative Example 1 is equivalent to, but much better than Comparative Examples 2 and 3, and the cold plate surface of Examples 1-3 forms a single dense Al2O3 film; in terms of salt spray corrosion resistance, no rust spots are observed within 48 h for Examples 1-3, which are worse than Comparative Example 2, but much better than Comparative Examples 1 and 3. The above comparative test results show that the medium-chromium heat-resistant ferritic stainless steel and the cold plate thereof according to the present application have excellent high-temperature oxidation resistance and electrical resistance, and also have good processability and certain corrosion resistance.

[0059] In summary, the present application designs the component system of the medium-chromium heat-resistant ferritic stainless steel and optimizes the cold plate preparation process, and provides the medium-chromium heat-resistant ferritic stainless steel, the cold plate thereof, and the preparation method and application thereof. Under the premise of ensuring excellent high-temperature oxidation resistance and electrical resistance of the material, the material also has good processability and certain corrosion resistance, which effectively expands the application field of chromium heat-resistant ferritic stainless steel products. Compared with the prior art, the technical scheme of the present application has the following advantages and beneficial effects:

[0060] (1) The medium-chromium heat-resistant ferritic stainless steel and the product thereof obtained by the present application through reasonable matching of Cr, Al and Si main elements and micro-alloying of Mn, Ni, Mo and Ti elements can obtain good processability and better corrosion resistance under the premise of forming a dense Al2O3 oxide film;

[0061] (2) The cold plate of the medium-chromium heat-resistant ferritic stainless steel according to the present application has a grain size of 7-8, an elongation of 30%-33%, a plastic strain ratio r value of 1.20-1.40, a room temperature resistivity of 1.15-1.20 μΩ·cm, an oxidation weight gain rate of 0.10-0.15 mg / cm 2 after 900℃ / 200h high-temperature oxidation test, and no oxide film peeling phenomenon; and no rust spots are observed within 48 h after salt spray test at 35℃ and 5% NaCl spray. The medium-chromium heat-resistant ferritic stainless steel and the cold plate thereof have excellent high-temperature oxidation resistance and electrical resistance, and also have good processability and certain corrosion resistance.

[0062] It should be noted that the process of the present application can be implemented by using conventional methods or devices in the art except for those explicitly described herein. The terms and phrases used herein have their ordinary meanings to those skilled in the art unless otherwise defined. Moreover, when a numerical range is disclosed herein, the range is to be construed as continuous along its minimum and maximum values, and to include any and all sub-ranges falling therebetween. Further, when a range is disclosed to include integers, the range is to be construed to include each integer within the range, as well as each sub-range between the minimum and maximum values of the range. In addition, when a plurality of ranges is provided, these ranges can be combined. In other words, unless otherwise indicated, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein.

[0063] It should also be noted that, in the present document, the terms "comprises / comprising" or any other variations thereof are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus.

[0064] It should also be noted that the above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the same. Although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can be modified, or some technical features can be replaced by equivalent features. Such modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the present application.

Claims

1. A medium-chromium heat-resistant ferritic stainless steel, characterized by, The chemical composition of the medium-chromium heat-resistant ferritic stainless steel is as follows in terms of mass percentage: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and inevitable impurity elements, and the Al, Si, Cr element content satisfies 60≤(w Al +w Si )×w Cr ≤70, the Mn, Ni, Mo element content satisfies 1.0≤4w Ni +8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, Mo.

2. The medium-chromium heat-resistant ferritic stainless steel according to claim 1, characterized in that, The C and N content in the medium-chromium heat-resistant ferritic stainless steel is controlled as C≤0.012% and N≤0.012%.

3. The medium-chromium heat-resistant ferritic stainless steel according to claim 1, characterized in that, The total oxygen content in the medium-chromium heat-resistant ferritic stainless steel is T[O]≤10ppm.

4. A method for producing a cold plate of medium-chromium heat-resistant ferritic stainless steel, characterized by, The method comprises the following steps: (1) smelting: taking molten iron as raw material, smelting through molten iron pretreatment, K-OBM-S, VOD, LF processes, realizing decarburization, reduction and alloying, the chemical composition of the molten steel prepared by smelting is controlled as follows in percentage by mass: C≤0.020%, N≤0.020%, Si: 0.30%-0.50%, Mn: 0.20%-0.50%, Cr: 17.0%-19.0%, Al: 2.0%-4.0%, Ni: 0.05%-0.30%, Mo: 0.10%-0.30%, Ti: 0.10%-0.30%, the balance being Fe and inevitable impurity elements, and the Al, Si, Cr element content satisfies 60≤(w Al +w Si )×w Cr ≤70, the Mn, Ni, Mo element content satisfies 1.0≤4w Ni +8w Mo -w Mn ≤2.0, wherein w Al , w Si , w Cr , w Mn , w Ni , w Mo respectively represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, Mo; (2) hot rolling: the molten steel prepared by smelting is subjected to hot rolling to prepare a hot-rolled plate, the hot-rolled plate is cooled to room temperature, and then subjected to a heat treatment to prepare a hot-rolled plate with a thickness of 20-50 mm, a width of 1,000-2,000 mm and a length of 3,000-6,000 mm; (3) cold rolling: the hot-rolled plate is subjected to cold rolling to prepare a cold-rolled plate with a thickness of 0.5-2.0 mm, a width of 1,000-2,000 mm and a length of 3,000-6,000 mm; (4) annealing: the cold-rolled plate is subjected to annealing to prepare an annealed plate; (2) continuous casting: slab continuous casting is performed via a tundish, electromagnetic stirring is applied throughout the continuous casting process, and the equiaxed crystal ratio of the cast slab is controlled to be >55%; (3) hot rolling: the heating temperature is controlled to be 1150-1200℃, the hot rolling pass is 7 passes, the finish rolling temperature is controlled to be ≤880℃, and after the hot rolling, the steel plate is subjected to layer cooling, and the coiling temperature is controlled to be ≤500℃; (4) cold rolling: firstly, hot coiling annealing and pickling are performed, the hot coiling annealing temperature is controlled to be 940-1000℃, the hot coiling annealing time is controlled according to 1.4-1.8min / mm, then multi-pass cold rolling is performed, the total deformation rate of the cold rolling is controlled to be 55%-85%, the cold coiling annealing furnace temperature is controlled to be 880-940℃, the cold coiling annealing time is controlled according to 1.0-1.4min / mm, and finally, the surface of the cold plate is polished to obtain the medium-chromium heat-resistant ferritic stainless steel cold plate.

5. The production method of the medium-chromium heat-resistant ferritic stainless steel cold plate according to claim 4, characterized by, In the K-OBM-S, Cr is alloyed, in the VOD, reduction is performed using aluminum pellets and then Al, Si, Mn and Ti are alloyed, in the LF furnace, Ni and Mo are alloyed.

6. The production method of the medium-chromium heat-resistant ferritic stainless steel cold plate according to claim 4, characterized by, In the hot rolling step, the finish rolling temperature is controlled to be ≤850℃, and the coiling temperature is controlled to be ≤400℃.

7. The production method of the medium-chromium heat-resistant ferritic stainless steel cold plate according to claim 4, characterized by, In the cold rolling step, the hot coiling annealing temperature is controlled to be 940-980℃, the total deformation rate of the cold rolling is controlled to be 60%-85%, the cold coiling annealing furnace temperature is controlled to be 880-920℃, and the surface of the cold plate is polished using a 230# sand belt.

8. A medium-chromium heat-resistant ferritic stainless steel cold plate, characterized by, The medium-chromium heat-resistant ferritic stainless steel cold plate is prepared by the preparation method of the medium-chromium heat-resistant ferritic stainless steel cold plate according to any one of claims 4-7, the width of the medium-chromium heat-resistant ferritic stainless steel cold plate is 1000-1300mm, the thickness is 0.4-2.0mm, the surface type of the medium-chromium heat-resistant ferritic stainless steel cold plate is HL surface, the roughness is <0.40μm, and the total oxygen content T[O] is ≤10ppm.

9. The medium-chromium ferritic stainless steel cold plate according to claim 8, characterized in that, The chromium medium heat-resistant ferrite stainless steel cold plate has a grain size of 7-8, an elongation after fracture of 30-33%, a plastic strain ratio r of 1.20-1.40, and a room temperature resistivity of 1.15-1.20 mu Omega.cm; after continuous high temperature oxidation at 900 DEG C for 200 hours in air, the oxidation weight gain rate is 0.10-0.15 mg / cm 2 ; in a salt spray test at 35 DEG C in 5% NaCl spray, no rust spot is observed within 48 hours.

10. The medium-chromium heat-resistant ferritic stainless steel cold plate according to claim 8 or 9 is applied in household appliances, industrial combustion furnaces, automobile exhaust systems and new energy automobile electric heating equipment, wherein the medium-chromium heat-resistant ferritic stainless steel cold plate is used to manufacture high-temperature-resistant parts or electric heating components in household appliances, industrial combustion furnaces, automobile exhaust systems and new energy automobiles.

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