A medium-chromium heat-resistant ferritic stainless steel, a cold plate preparation method and application thereof

Abstract

The application discloses a medium-chromium heat-resistant ferritic stainless steel and a cold plate preparation method and application thereof. The chemical components of the medium-chromium heat-resistant ferritic stainless steel are as follows: C is less than or equal to 0.020%, N is less than or equal to 0.020%, Si is 0.30% to 0.50%, Mn is 0.20% to 0.50%, Cr is 17.0% to 19.0%, Al is 2.0% to 4.0%, Ni is 0.05% to 0.30%, Mo is 0.10% to 0.30%, Ti is 0.10% to 0.30%, and the balance is Fe and inevitable impurities, and 60 <= (w Al +w Si ) * w Cr <= 70, 1.0 <= 4w Ni + 8w Mo -w Mn <= 2.0. The cold plate preparation method of the medium-chromium heat-resistant ferritic stainless steel comprises the steps of smelting, continuous casting, hot rolling and cold rolling. The cold plate of the medium-chromium heat-resistant ferritic stainless steel has excellent high-temperature oxidation resistance and resistance performance, good processing performance and corrosion resistance, and effectively expands the application field of the medium-chromium heat-resistant ferritic stainless steel product.

Description

Technical Field

[0001] This invention belongs to the field of stainless steel production technology, specifically relating to a medium-chromium heat-resistant ferritic stainless steel with oxidation resistance, high electrical resistance, processability and corrosion resistance, as well as its cold-rolled plate preparation method and application. Background Technology

[0002] Medium-chromium ferritic stainless steels contain 16% to 19% chromium (Cr). These stainless steels are widely used due to their excellent corrosion resistance, machinability, and economic efficiency. The most basic type of medium-chromium ferritic stainless steel is 430 stainless steel. By further reducing the C and N content and adding stabilizing elements such as Nb and Ti, ultra-pure ferritic stainless steels, such as 439 and 441, have been developed. To further improve corrosion resistance, Mo or Cu elements are added, resulting in varieties such as 436, 444, and SUS430J1L.

[0003] For heat-resistant ferritic stainless steel, a Cr2O3, Al2O3, or SiO2 oxide film needs to be formed on the surface, with the Al2O3 oxide film being the densest. Increasing the Al and Si content will, on the one hand, increase the material's resistivity, and on the other hand, reduce its machinability. Furthermore, Al will also weaken the material's corrosion resistance.

[0004] Therefore, a new composition system and preparation process need to be designed for medium-chromium heat-resistant ferritic stainless steel, which can generate a dense Al2O3 oxide film on the surface to improve the material's high-temperature oxidation resistance, ensure the material's electrical resistance and processing performance, and also have certain corrosion resistance. Summary of the Invention

[0005] To solve the above-mentioned technical problems, the present invention provides a medium-chromium heat-resistant ferritic stainless steel, a medium-chromium heat-resistant ferritic stainless steel cold plate, and a method for preparing the same.

[0006] The chemical composition of the medium-chromium type heat-resistant ferritic stainless steel provided by this invention, by mass percentage, is as follows: 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%, with the balance being Fe and unavoidable impurity elements. Furthermore, the content of Al, Si, and Cr elements satisfies 60 ≤ (w / w) Al +w Si )×w Cr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where wAl w Si w Cr w Mn w Ni w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively.

[0007] Preferably, the C and N contents in the medium-chromium type heat-resistant ferritic stainless steel are controlled to be C≤0.012% and N≤0.012%.

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

[0009] The method for preparing medium-chromium type heat-resistant ferritic stainless steel cold-rolled plate provided by the present invention includes the following steps:

[0010] (1) Smelting: Using molten iron as raw material, smelting is carried out through molten iron pretreatment, K-OBM-S, VOD, and LF processes to achieve decarburization, reduction, and alloying. The chemical composition of the molten steel obtained by smelting is controlled by mass percentage as follows: 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%, with the balance being Fe and unavoidable impurity elements. Furthermore, the content of Al, Si, and Cr elements must satisfy 60≤(w Al +w Si )×w Cr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al w Si w Cr w Mn w Ni w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively.

[0011] (2) Continuous casting: Slabs are continuously cast via tundish. Electromagnetic stirring is used throughout the continuous casting process to control the equiaxed crystal ratio of the slab 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] Furthermore, the present invention also provides the application of the above-mentioned medium-chromium heat-resistant ferritic stainless steel cold plate in household appliances, industrial combustion furnaces, automotive exhaust systems and new energy vehicle 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, automotive exhaust systems and new energy vehicles.

[0020] This invention designs the composition system and optimizes the cold-rolled sheet preparation process for medium-chromium heat-resistant ferritic stainless steel. It provides medium-chromium heat-resistant ferritic stainless steel, medium-chromium heat-resistant ferritic stainless steel cold-rolled sheets, their preparation methods, and applications. While ensuring excellent high-temperature oxidation resistance and electrical resistance, the material also exhibits good processing performance and a certain degree of corrosion resistance, effectively expanding the application fields of medium-chromium heat-resistant ferritic stainless steel products. Compared with existing technologies, the technical solution of this invention has the following advantages and beneficial effects:

[0021] (1) The present invention obtains medium-chromium heat-resistant ferritic stainless steel and its products by rationally matching the main elements Cr, Al and Si and micro-alloying the elements Mn, Ni, Mo and Ti. Under the premise of ensuring the formation of a dense Al2O3 oxide film, it can also obtain good processing performance and good corrosion resistance.

[0022] (2) The chromium-type heat-resistant ferritic stainless steel cold-rolled plate of the present invention has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r of 1.20-1.40, a room temperature resistivity of 1.15-1.20 μΩ·cm, and an oxidation weight gain of 0.10-0.15 mg / cm after a high-temperature oxidation test at 900℃ / 200h. 2 Furthermore, there is no oxide film peeling. After surface grinding, a salt spray test was conducted at 35℃ with 5% NaCl. No rust spots were observed within 48 hours. Medium-chromium heat-resistant ferritic stainless steel and its cold-rolled plates have excellent high-temperature oxidation resistance and electrical resistance, as well as good processing performance and certain corrosion resistance. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:

[0024] Figure 1 The image shows the metallographic structure of the medium-chromium heat-resistant ferritic stainless steel cold plate prepared using Example 1 of the present invention.

[0025] Figure 2This is a cross-sectional compositional scanning image of the oxide layer of the medium-chromium heat-resistant ferritic stainless steel cold plate prepared using Example 2 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0027] This invention aims to provide a medium-chromium heat-resistant ferritic stainless steel and a method for preparing its cold-rolled sheet. While ensuring excellent high-temperature oxidation resistance and electrical properties, the material also exhibits good processability and a certain degree of corrosion resistance. Therefore, this invention focuses on designing the composition system and optimizing the cold-rolled sheet preparation process for medium-chromium heat-resistant ferritic stainless steel.

[0028] In a first aspect of the invention, a medium-chromium heat-resistant ferritic stainless steel is provided, wherein the chemical composition of the medium-chromium heat-resistant ferritic stainless steel, by mass percentage, is: 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%, with the balance being Fe and unavoidable impurity elements, and the content of Al, Si, and Cr elements satisfies 60 ≤ (w / w) Al +w Si )×w Cr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al w Si w Cr w Mn w Ni w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively.

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

[0030] In this invention, the compositional design for medium-chromium heat-resistant ferritic stainless steel mainly includes: promoting the formation of a dense Al2O3 oxide film through the composite addition of Cr, Al, and Si elements; significantly improving the anti-scraping ability of the oxide film by adding trace amounts of Ti element; enhancing the corrosion resistance of the material by adding Ni and Mo elements and controlling Mn element content; and improving the resistivity of the material while ensuring its cold workability by controlling the content of Al and Si elements. The resulting medium-chromium heat-resistant ferritic stainless steel not only possesses excellent high-temperature oxidation resistance and electrical resistance but also good corrosion resistance and processing performance, thus broadening the application fields of medium-chromium heat-resistant ferritic stainless steel. The roles and content requirements of each element in the medium-chromium heat-resistant ferritic stainless steel of this invention are described below:

[0031] C and N: Carbon and nitrogen have extremely low solubility in ferritic stainless steel and diffuse rapidly. During the cooling process after high-temperature heating, chromium carbides and nitrides precipitate, which is the root cause of high-temperature brittleness and high-temperature sensitization in ferritic stainless steel. Furthermore, chromium carbides readily generate CO bubbles at high temperatures, escaping from under the oxide film and compromising its density. Therefore, it is necessary to strictly control the C and N content. In this invention, the C and N content are both controlled to ≤0.020%, preferably ≤0.012%.

[0032] Si: Silicon is a high-temperature antioxidant element. During the high-temperature oxidation of stainless steel, it generates SiO2, which is distributed at the interface between the oxide film and the metal substrate. This prevents oxygen penetration and reduces the oxidation rate of the alloy. Silicon can also moderately increase the resistivity of the material. However, excessive silicon not only negatively impacts the oxidation resistance of stainless steel but also reduces the alloy's plasticity, deteriorating its cold working properties. Therefore, in this invention, the Si content is controlled at 0.30%–0.50%.

[0033] Mn: Manganese is an unavoidable element in the raw materials used in stainless steel smelting. 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 this invention, the Mn content is controlled at 0.20% to 0.50%.

[0034] Cr: Chromium is the most important alloying element in stainless steel and a strong ferrite-forming element. It is one of the main alloying elements for oxidation resistance and corrosion resistance in stainless steel. Simultaneously, as a third element, chromium strongly promotes the formation of Al2O3 oxide film, reducing the Al content in the corresponding metal matrix in the formation of a single Al2O3 oxide film. For medium-chromium ferritic stainless steel, the Cr content is controlled at 17.0%–19.0% in this invention.

[0035] Al: Aluminum is a key element in improving the oxidation resistance of heat-resistant stainless steel because the Al2O3 oxide film is denser and more stable than Cr2O3 and SiO2. Furthermore, aluminum is an excellent deoxidizer, achieving ideal deoxidation effects and providing a prerequisite for obtaining a high yield of stabilized Ti. Aluminum can significantly increase the resistivity of materials. However, aluminum causes severe embrittlement of ferritic stainless steel, drastically reducing the material's toughness. Therefore, in this invention, the Al content is controlled at 2.0–4.0%.

[0036] Ni: In ferritic stainless steel, nickel can increase the steel's strength, decrease its room temperature toughness, and improve its corrosion resistance in reducing media, including resistance to uniform corrosion, pitting corrosion, and crevice corrosion. Therefore, in this invention, the Ni content is controlled at 0.05% to 0.30%.

[0037] Mo: The addition of molybdenum endows ferritic stainless steel with superior corrosion resistance, improves its passivation ability and the stability of the passivation film, and particularly enhances its resistance to Cl- corrosion. In addition, molybdenum also plays a solid solution strengthening role, improving the high-temperature strength and creep strength of stainless steel. Therefore, in this invention, the Mo content is controlled at 0.10%–0.30%.

[0038] Ti: Titanium has a strong affinity for carbon and nitrogen, preferentially forming titanium carbides and titanium nitrides in steel, thus preventing the precipitation of chromium carbides and chromium nitrides. Furthermore, as an active element, Ti improves the density and anti-scraping properties of the oxide film. Therefore, in this invention, the Ti content is controlled at 0.10%–0.30%.

[0039] In a second aspect of the present invention, a method for preparing medium-chromium heat-resistant ferritic stainless steel cold-rolled sheet is provided. The process route is smelting → continuous casting → hot rolling → cold rolling. An optimized process of slab continuous casting, low-temperature hot rolling, low-temperature annealing, and multi-pass large deformation cold rolling is used to prepare the medium-chromium heat-resistant ferritic stainless steel cold-rolled sheet. Specifically, it includes the following steps:

[0040] (1) Smelting: Using molten iron as raw material, smelting is carried out through molten iron pretreatment, K-OBM-S, VOD, and LF processes to achieve decarburization, reduction, and alloying. The chemical composition of the molten steel obtained by smelting is controlled by mass percentage as follows: 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%, with the balance being Fe and unavoidable impurity elements. Furthermore, the content of Al, Si, and Cr elements must satisfy 60≤(w Al +w Si )×wCr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al w Si w Cr w Mn w Ni w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively.

[0041] (2) Continuous casting: Slabs are continuously cast via tundish, and can be cast in single, double or triple order. Electromagnetic stirring is used throughout the continuous casting process to control the equiaxed crystal ratio of the slab to >55%.

[0042] (3) Hot rolling: Hot rolling requires multiple rolling passes, low temperature rolling and low temperature coiling to ensure the grain refinement of hot-rolled plate and increase deformation energy storage. The heating temperature is controlled at 1150~1200℃, the hot rolling passes are 7, the final rolling temperature is controlled at ≤880℃, and the plate is put into a cooling layer after hot rolling. The coiling temperature is controlled at ≤500℃.

[0043] (4) Cold rolling: To ensure good processing performance of the material, the cold rolling process requires low-temperature slow annealing and multi-pass large deformation cold rolling. First, hot rolling annealing and pickling are carried out. 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, multi-pass cold rolling is carried out. 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 medium-chromium heat-resistant ferritic stainless steel cold plate.

[0044] Furthermore, in the above-mentioned method for preparing medium-chromium type heat-resistant ferritic stainless steel cold plates, in order to improve production efficiency and the yield of precious elements and ensure the purity of molten steel, high-content Cr elements are alloyed in K-OBM-S, reduced in VOD using aluminum shot and then alloyed with easily oxidized elements Al, Si, Mn and Ti, and alloyed with precious elements Ni and Mo in LF furnace.

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

[0046] Preferably, in the preparation method of medium-chromium heat-resistant ferritic stainless steel cold plate, 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 plate is ground with 230# sandpaper.

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

[0048] The medium-chromium heat-resistant ferritic stainless steel of this invention is a medium-chromium heat-resistant ferritic stainless steel cold-rolled sheet prepared by smelting, continuous casting, hot rolling, and cold rolling. It has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r of 1.20-1.40, a room temperature resistivity of 1.15-1.20 μΩ·cm, and an oxidation weight gain of 0.10-0.15 mg / cm² after continuous high-temperature oxidation at 900℃ for 200 hours in an atmospheric atmosphere. 2 Furthermore, there was no oxide film peeling; after surface grinding, a salt spray test was conducted at 35°C with 5% NaCl, and no rust spots were observed within 48 hours.

[0049] In a fourth aspect of the invention, a medium-chromium heat-resistant ferritic stainless steel cold-rolled sheet is provided for use in household appliances, industrial furnaces, automotive exhaust systems, and electric heating equipment for new energy vehicles, wherein the cold-rolled sheet is used to manufacture high-temperature resistant parts or electric heating components in household appliances, industrial furnaces, automotive exhaust systems, and new energy vehicles.

[0050] The following describes in detail the preparation method of the medium-chromium type heat-resistant ferritic stainless steel and its cold-rolled plate, in conjunction with embodiments of the present invention and prior art.

[0051] The chemical compositions of the medium-chromium heat-resistant ferritic stainless steel cold plates prepared using Examples 1-3 of the present invention and the medium-chromium heat-resistant ferritic stainless steel cold plates prepared using the prior art in Comparative Examples 1-3 are shown in Table 1 below (the balance is Fe and unavoidable impurity elements):

[0052] Table 1. Composition (wt.%) of ferritic stainless steel cold-rolled sheets from Examples 1-3 and Comparative Examples 1-3

[0053]

[0054] In embodiments 1-3 of this invention, the contents of alloying elements Al, Si, Cr, Mn, Ni, and Mo satisfy 60 ≤ (wAl +w Si )×w Cr ≤70 and 1.0≤4w Ni +8w Mo -w Mn ≤2.0; In Comparative Example 1, (w Al +w Si )×w Cr >70, 4w Ni +8w Mo -w Mn <1.0; in Comparative Example 2, (w Al +w Si )×w Cr <10,4w Ni +8w Mo -w Mn >2.0; In Comparative Example 3, (w Al +w Si )×w Cr <40, 4w Ni +8w Mo -w Mn <1.0.

[0055] The main process parameters for the preparation methods of the medium-chromium type heat-resistant ferritic stainless steel cold plates in Examples 1-3 of this invention are shown in Table 2 below:

[0056] Table 2 Main process parameters of Examples 1-3

[0057]

[0058] Analysis and performance tests were conducted on the medium-chromium heat-resistant ferritic stainless steel cold plates prepared using Examples 1-3 of the present invention and those prepared using existing technologies in Comparative Examples 1-3. The metallographic structure of the medium-chromium heat-resistant ferritic stainless steel cold plate prepared using Example 1 of the present invention is shown below. Figure 1 The cross-sectional compositional scanning electron microscope (SEM) image of the oxide layer of the medium-chromium type heat-resistant ferritic stainless steel cold plate prepared using Example 2 of this invention is shown below. Figure 2The performance test results are summarized in Table 3 below. The standards and methods for determining the performance parameters are as follows: grain size was determined according to GB / T 6394 "Method for Determination of Average Grain Size of Metals"; tensile testing was conducted according to GB / T 228.1 "Metallic Materials - Tensile Testing - Part 1: Room Temperature Test Method"; plastic strain ratio was determined according to GB / T 5027 "Determination of Plastic Strain Ratio (r Value) of Thin Plates and Strips of Metallic Materials"; room temperature resistivity was determined according to GB / T 6146 "Method for Testing Resistivity of Precision Resistance Alloys"; high-temperature oxidation testing was conducted according to GB / T 13303 "Test Method for Oxidation Resistance of Steel"; and salt spray corrosion testing was conducted according to GB / T 10125 "Artificial Atmosphere Corrosion Test - Salt Spray Test". Furthermore, for each example and comparative example, three samples were taken, and the average value of the three samples was the final result. In addition, after mechanical grinding and polishing of the samples perpendicular to the sample thickness direction, the metallographic structure of the material was observed using an optical microscope, and the cross-section of the oxide layer was observed using a scanning electron microscope, providing the composition and structure of the oxide layer.

[0059] Table 3 Summary of the properties of heat-resistant ferritic stainless steel cold-rolled plates in Examples 1-3 and Comparative Examples 1-3

[0060]

[0061] The actual testing and experimental results show that, in terms of grain size, Examples 1-3 have a grain size of 7-8, comparable to Comparative Example 2, and superior to Comparative Examples 1 and 3; in terms of elongation after fracture, Examples 1-3 have an elongation of 30%-33%, comparable to Comparative Example 2, but superior to Comparative Examples 1 and 3; in terms of plastic strain ratio r, Examples 1-3 have an elongation of 1.20-1.40, slightly worse than Comparative Example 2, but better than Comparative Examples 1 and 3; in terms of room temperature resistivity, Examples 1-3 have an elongation of 1.15-1.20 μΩ·cm, slightly lower than Comparative Example 1, but far superior to Comparative Examples 2 and 3; and in terms of high-temperature oxidation resistance and weight gain, Examples 1-3 have a weight gain of 0.10-0.15 mg / cm. 2 The performance was comparable to Comparative Example 1, but far superior to Comparative Examples 2 and 3. Furthermore, a uniform and dense Al2O3 film formed on the surface of the cold-rolled plates in Examples 1-3. Regarding salt spray corrosion resistance, no rust spots were observed in Examples 1-3 within 48 hours, which was inferior to Comparative Example 2, but far superior to Comparative Examples 1 and 3. The above comparative test results demonstrate that the medium-chromium type heat-resistant ferritic stainless steel and its cold-rolled plates of the present invention possess excellent high-temperature oxidation resistance and electrical resistance, while also exhibiting good processing performance and a certain degree of corrosion resistance.

[0062] In summary, this invention designs the compositional system and optimizes the cold-rolled sheet preparation process for medium-chromium heat-resistant ferritic stainless steel, providing medium-chromium heat-resistant ferritic stainless steel, medium-chromium heat-resistant ferritic stainless steel cold-rolled sheets, their preparation methods, and applications. While ensuring excellent high-temperature oxidation resistance and electrical resistance, the material also exhibits good processing performance and a certain degree of corrosion resistance, effectively expanding the application fields of chromium heat-resistant ferritic stainless steel products. Compared with existing technologies, the technical solution of this invention has the following advantages and beneficial effects:

[0063] (1) The present invention obtains medium-chromium heat-resistant ferritic stainless steel and its products by rationally matching the main elements Cr, Al and Si and micro-alloying the elements Mn, Ni, Mo and Ti. Under the premise of ensuring the formation of a dense Al2O3 oxide film, it can also obtain good processing performance and good corrosion resistance.

[0064] (2) The chromium-type heat-resistant ferritic stainless steel cold-rolled plate of the present invention has a grain size of 7-8, an elongation after fracture of 30%-33%, a plastic strain ratio r of 1.20-1.40, a room temperature resistivity of 1.15-1.20 μΩ·cm, and an oxidation weight gain of 0.10-0.15 mg / cm after a high-temperature oxidation test at 900℃ / 200h. 2 Furthermore, no oxide film peeling was observed; after surface grinding, a salt spray test was conducted at 35℃ with 5% NaCl spray, and no rust spots were observed within 48 hours. Medium-chromium heat-resistant ferritic stainless steel and its cold-rolled plates possess excellent high-temperature oxidation resistance and electrical resistance, while also exhibiting good machinability and certain corrosion resistance.

[0065] It should be noted that, except for those explicitly described herein, the process methods of the present invention can be implemented using conventional methods or apparatus in the art. Unless otherwise specified, the terms used herein have the meanings commonly understood by those skilled in the art. Furthermore, when a numerical range is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Further, when the range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Moreover, when multiple range descriptive features are provided, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0066] It should also be noted that, in this document, the term "comprising" or any other variation thereof is intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device.

[0067] Furthermore, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the present invention.

Claims

1. A medium-chromium heat-resistant ferritic stainless steel, characterized by, The chemical composition of the medium-chromium type heat-resistant ferritic stainless steel, by mass percentage, is: 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%, with the balance being Fe and unavoidable impurity elements, and the content of Al, Si, and Cr elements satisfies 60≤( w Al + w Si )× w Cr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4 w Ni +8 w Mo - w Mn ≤2.0, where w Al , w Si , w Cr , w Mn , w Ni , w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively. By adding Ni and Mo elements and controlling the content of Mn element, the corrosion resistance of the material is improved, and by controlling the content of Al and Si elements, the resistivity of the material is improved and the cold working formability of the material is ensured. The medium-chromium heat-resistant ferritic stainless steel 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; and the oxidation weight gain rate is 0.10-0.15 mg / cm after continuous high-temperature oxidation at 900 DEG C for 200 h in an atmospheric atmosphere, and no oxidation film peeling phenomenon occurs 2 . After surface grinding, salt spray test is carried out in 5% NaCl spray at 35℃, and no rust spot is observed within 48h.

2. The medium-chromium heat-resistant ferritic stainless steel according to claim 1, characterized in that, The content of C and N 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 medium-chromium heat-resistant ferritic stainless steel cold plate, characterized by, The method comprises the following steps: (1) Smelting: Using molten iron as raw material, smelting is carried out through molten iron pretreatment, K-OBM-S, VOD, and LF processes to achieve decarburization, reduction, and alloying. The chemical composition of the molten steel obtained by smelting is controlled by mass percentage as follows: 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%, with the balance being Fe and unavoidable impurity elements. The content of Al, Si, and Cr elements must meet 60≤( w Al + w Si )× w Cr ≤70, the content of Mn, Ni and Mo elements meets the requirement of 1.0≤4 w Ni +8 w Mo - w Mn ≤2.0, where w Al , w Si , w Cr , w Mn , w Ni , w Mo These represent the mass percentage content of elements Al, Si, Cr, Mn, Ni, and Mo, respectively. (2) Continuous casting: slab continuous casting is carried out through a tundish, electromagnetic stirring is applied throughout the continuous casting process, and the equiaxed crystal ratio of the cast slab is controlled to be greater than 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 less than or equal to 880℃, and after hot rolling, the material is subjected to layer cooling, and the coiling temperature is controlled to be less than or equal to 500℃; (4) Cold rolling: firstly, hot coiling annealing and pickling are carried out, 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 carried out, 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; The grain size of the medium-chromium heat-resistant ferrite stainless steel cold plate prepared by smelting, continuous casting, hot rolling and cold rolling is 7-8, the elongation after fracture is 30-33%, the plastic strain ratio r is 1.20-1.40, the room temperature resistivity is 1.15-1.20 mu Omega*cm; after continuous high-temperature oxidation at 900 DEG C for 200h in air atmosphere, the oxidation weight gain rate is 0.10-0.15 mg / cm 2 , and there is no phenomenon of oxidation film peeling. After surface grinding, salt spray test is carried out in 5% NaCl spray at 35℃, and no rust spot is observed within 48h.

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 carried out using aluminum pellets and then Al, Si, Mn, Ti are alloyed, in the LF furnace, Ni, 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 less than or equal to 850℃, and the coiling temperature is controlled to be less than or equal to 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 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 less than 0.40μm, and the total oxygen content T[O] is less than or equal to 10ppm.

9. Application of the medium-chromium heat-resistant ferritic stainless steel cold plate according to claim 8 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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