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

Abstract

The medium-chromium type heat-resistant ferritic stainless steel comprises the following chemical components: less than or equal to 0.020% of C, less than or equal to 0.020% of N, 0.30%-0.50% of Si, 0.20%-0.50% of Mn, 17.0%-19.0% of Cr, 2.0%-4.0% of Al, 0.05%-0.30% of Ni, 0.10%-0.30% of Mo, 0.10%-0.30% of Ti and the balance of Fe and inevitable impurity elements, (wAl + wSi) * wCr is more than or equal to 60 and less than or equal to 70, and 4wNi + 8wMo-wMn is more than or equal to 1.0 and less than or equal to 2.0. The preparation method of the medium-chromium type heat-resistant ferritic stainless steel cold plate comprises the steps of smelting, continuous casting, hot rolling and cold rolling. The medium-chromium type heat-resistant ferritic stainless steel cold plate has excellent high-temperature oxidation resistance and resistance and good processability and corrosion resistance, and the application field of medium-chromium type heat-resistant ferritic stainless steel products is effectively expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of stainless steel production, and specifically relates to a medium-chromium heat-resistant ferritic stainless steel having oxidation resistance, high electrical resistance, processability and corrosion resistance, and a cold plate preparation method and application thereof. Background Art

[0002] The Cr content of medium chromium ferritic stainless steel is between 16% and 19%. This type of stainless steel has been widely used for its good corrosion resistance, processability and economy. The most prototype medium chromium ferritic stainless steel is 430 stainless steel. By further reducing the content of C and N elements and adding stabilizing elements such as Nb and Ti, ultra-pure ferritic stainless steels such as 439 and 441 have been developed. In order to further improve the corrosion resistance, Mo or Cu elements are added, such as 436, 444, SUS430J1L and other varieties.

[0003] For heat-resistant ferritic stainless steel, the surface needs to form Cr2O3, Al2O3 or SiO2 oxide film, among which Al2O3 oxide film is the most dense. The increase of Al and Si content will increase the resistivity of the material on the one hand, and reduce the processing performance of the material on the other hand, and Al element will also weaken the corrosion resistance of the material.

[0004] Therefore, it is necessary to design a new composition system and preparation process for medium chromium heat-resistant ferritic stainless steel, which can not only generate a dense Al2O3 oxide film on the surface to improve the material's high-temperature oxidation resistance, but also ensure the material's resistance and processing performance, and also have certain corrosion resistance. Summary of the invention

[0005] In order to solve the above 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 preparation method thereof.

[0006] The chemical composition of the medium chromium heat-resistant ferrite stainless steel provided by the present invention 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%, the balance is 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 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where wAl 、w Si 、w Cr 、w Mn 、w Ni 、w Mo They represent the mass percentage contents of elements Al, Si, Cr, Mn, Ni and Mo respectively.

[0007] Preferably, the C and N contents in the medium chromium 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 heat-resistant ferritic stainless steel is T[O]≤10ppm.

[0009] The method for preparing the medium chromium heat-resistant ferrite stainless steel cold plate provided by the present invention comprises 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% to 0.50%, Mn: 0.20% to 0.50%, Cr: 17.0% to 19.0%, Al: 2.0% to 4.0%, Ni: 0.05% to 0.30%, Mo: 0.10% to 0.30%, Ti: 0.10% to 0.30%, and the balance is Fe and unavoidable impurity elements, and the content of Al, Si, and Cr elements meets 60 ≤ (w Al +w Si )×w Cr ≤70, the content of Mn, Ni and Mo elements meets 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where 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, and Mo;

[0011] (2) Continuous casting: Slab continuous casting is carried out through a tundish, and electromagnetic stirring is used throughout the continuous casting process to control the equiaxed crystal ratio of the slab to be greater than 55%;

[0012] (3) Hot rolling: the heating temperature is controlled at 1150-1200°C, the hot rolling passes are 7 passes, the final rolling temperature is controlled at ≤880°C, the steel is put into layer cooling after hot rolling, and the coiling temperature is controlled at ≤500°C;

[0013] (4) Cold rolling: first, the hot coil is annealed and pickled, the hot coil annealing temperature is controlled at 940-1000°C, and the hot coil annealing time is controlled at 1.4-1.8 min / mm, then multiple cold rolling is performed, the total cold rolling deformation rate is controlled at 55%-85%, the cold coil annealing furnace temperature is controlled at 880-940°C, and the cold coil annealing time is controlled at 1.0-1.4 min / mm, and finally the cold plate surface is ground to obtain medium chromium type heat-resistant ferritic stainless steel cold plate.

[0014] Furthermore, in the method for preparing the above-mentioned medium chromium heat-resistant ferritic stainless steel cold plate, Cr is alloyed in K-OBM-S, aluminum shots are 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 method for preparing the above medium chromium heat-resistant ferritic stainless steel cold plate, in the hot rolling step, the final rolling temperature is controlled to be ≤850°C, and the coiling temperature is controlled to be ≤400°C.

[0016] Furthermore, in the preparation method of the above-mentioned 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°C, the total cold rolling deformation rate is controlled to be 60%-85%, the cold coil annealing furnace temperature is controlled to be 880-920°C, and a 230# sand belt is used to grind the cold plate surface.

[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 the medium chromium heat-resistant ferritic stainless steel cold plate. The width of the medium chromium heat-resistant ferritic stainless steel cold plate is 1000-1300 mm, the thickness is 0.4-2.0 mm, the surface type of the medium chromium heat-resistant ferritic stainless steel cold plate is HL surface, the roughness is less than 0.40 μm, and the total oxygen content T[O] is ≤10 ppm.

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

[0019] In addition, 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, automobile 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, automobile exhaust systems and new energy vehicles.

[0020] The present invention designs the component system and optimizes the cold plate preparation process for medium-chromium heat-resistant ferritic stainless steel, provides medium-chromium heat-resistant ferritic stainless steel, medium-chromium heat-resistant ferritic stainless steel cold plate and its preparation method and application, which ensures that the material has excellent high-temperature oxidation resistance and electrical resistance, and also has good processing performance and certain corrosion resistance, effectively expanding the application field of medium-chromium heat-resistant ferritic stainless steel products. Compared with the prior art, the technical solution of the present 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 reasonable matching of the main elements of Cr, Al, and Si and microalloying of the elements of Mn, Ni, Mo, and Ti, which can obtain good processing performance and good corrosion resistance under the premise of ensuring the formation of a dense Al2O3 oxide film;

[0022] (2) The medium chromium heat-resistant ferrite stainless steel cold plate of the present invention has a grain size of 7 to 8, an elongation after fracture of 30% to 33%, a plastic strain ratio r value of 1.20 to 1.40, a room temperature resistivity of 1.15 to 1.20 μΩ·cm, and an oxidation weight gain rate of 0.10 to 0.15 mg / cm after a 900°C / 200h high temperature oxidation resistance test. 2 , and there is no oxide film falling off; after surface grinding, a salt spray test was carried out in a 35°C, 5% NaCl spray, and no rust spots were observed within 48 hours. The medium chromium heat-resistant ferritic stainless steel and its cold plate have excellent high-temperature oxidation resistance and electrical resistance, and have good processing performance and certain corrosion resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0024] Figure 1 The metallographic structure diagram of the medium chromium heat-resistant ferrite stainless steel cold plate prepared by Example 1 of the present invention;

[0025] Figure 2This is a scanning diagram of the cross-sectional composition of the oxide layer of the medium chromium heat-resistant ferritic stainless steel cold plate prepared by Example 2 of the present invention. DETAILED DESCRIPTION

[0026] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the specific embodiments of the present invention and the corresponding drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0027] The present invention aims to provide a medium chromium heat-resistant ferritic stainless steel and a cold plate preparation method thereof, which not only ensures that the material has excellent high-temperature oxidation resistance and electrical resistance, but also has good processing performance and certain corrosion resistance. To this end, the present invention designs the component system and optimizes the cold plate preparation process for the medium chromium heat-resistant ferritic stainless steel.

[0028] In a first aspect of the present invention, a medium chromium heat-resistant ferritic stainless steel is provided, wherein the chemical composition of the medium chromium heat-resistant ferritic stainless steel is as follows by 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 remainder is 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 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al 、w Si 、w Cr 、w Mn 、w Ni 、w Mo They represent the mass percentage contents of elements Al, Si, Cr, Mn, Ni and Mo respectively.

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

[0030] In the present invention, the composition system design for medium-chromium heat-resistant ferritic stainless steel mainly includes: promoting the formation of dense Al2O3 oxide film by composite addition of Cr, Al, and Si elements, significantly improving the anti-stripping ability of the oxide film by adding trace Ti elements, improving the corrosion resistance of the material by adding Ni and Mo elements and controlling the Mn element, and controlling the content of Al and Si elements to improve the resistivity of the material and ensure the cold processing formability of the material. The obtained medium-chromium heat-resistant ferritic stainless steel not only has excellent high-temperature oxidation resistance and resistance performance, but also has good corrosion resistance and processing performance, which broadens the application field of medium-chromium heat-resistant ferritic stainless steel materials. Among them, the role of each element in the medium-chromium heat-resistant ferritic stainless steel of the present invention and its content requirements are introduced as follows:

[0031] C and N: The solubility of carbon and nitrogen in ferritic stainless steel is extremely low, and the diffusion rate is relatively fast. During the cooling process after high-temperature heating, chromium carbides and nitrides will precipitate, which is the root cause of high-temperature brittleness and high-temperature sensitization of ferritic stainless steel. In addition, chromium carbides are prone to generate CO bubbles at high temperatures, which escape from under the oxide film and destroy the compactness of the oxide film. Therefore, it is necessary to strictly control the content of C and N elements. In the present invention, the content of C and N is controlled to ≤0.020%, preferably ≤0.012%.

[0032] Si: Silicon is a high-temperature antioxidant element. During the high-temperature oxidation of stainless steel, SiO2 is generated and distributed at the interface between the oxide film and the metal matrix, which can prevent oxygen from penetrating and reduce the oxidation rate of the alloy. Silicon can also moderately increase the resistivity of the material. However, too much silicon is not only detrimental to the oxidation resistance of stainless steel, but also reduces the plasticity of the alloy and deteriorates the cold working performance. Therefore, in the present invention, the Si content is controlled to 0.30% to 0.50%.

[0033] Mn: Manganese is an inevitable element in the raw materials for 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 the present invention, the Mn content is controlled to 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 in stainless steel for oxidation resistance and corrosion resistance. At the same time, as the third element, chromium strongly promotes the formation of Al2O3 oxide film, and can reduce the content of Al element 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 to 17.0% to 19.0% in the present invention.

[0035] Al: Aluminum is a key element to improve the oxidation resistance of heat-resistant stainless steel because the Al2O3 oxide film is denser and more stable than Cr2O3 and SiO2. In addition, aluminum is an excellent deoxidizer, which can achieve an ideal deoxidation effect 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 and sharply reduce the toughness of the material. Therefore, in the present invention, the Al content is controlled to 2.0-4.0%.

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

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

[0038] Ti: Titanium has a strong affinity with carbon and nitrogen. It will preferentially form titanium carbides and titanium nitrides in steel, avoiding the precipitation of chromium carbides and chromium nitrides. In addition, as an active element, Ti will improve the compactness and anti-stripping performance of the oxide film. Therefore, in the present invention, the Ti content is controlled to 0.10% to 0.30%.

[0039] In the second aspect of the present invention, a method for preparing a medium chromium heat-resistant ferritic stainless steel cold plate is provided, wherein the process route is smelting → continuous casting → hot rolling → cold rolling, and the medium chromium heat-resistant ferritic stainless steel cold plate is prepared by an optimized process of slab continuous casting, low temperature hot rolling, low temperature annealing and multi-pass large deformation cold rolling, and specifically comprises 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% to 0.50%, Mn: 0.20% to 0.50%, Cr: 17.0% to 19.0%, Al: 2.0% to 4.0%, Ni: 0.05% to 0.30%, Mo: 0.10% to 0.30%, Ti: 0.10% to 0.30%, and the balance is Fe and unavoidable impurity elements, and the content of Al, Si, and Cr elements meets 60 ≤ (w Al +w Si )×wCr ≤70, the content of Mn, Ni and Mo elements meets 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al 、w Si 、w Cr 、w Mn 、w Ni 、w Mo They represent the mass percentage contents of elements Al, Si, Cr, Mn, Ni and Mo respectively.

[0041] (2) Continuous casting: Slab continuous casting is carried out through a tundish, which can be single casting, double casting or triple casting. Electromagnetic stirring is used throughout the continuous casting process to control the equiaxed crystal ratio of the slab to be >55%.

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

[0043] (4) Cold rolling: The cold rolling process must ensure good processing properties of the material, and requires low-temperature slow annealing and multiple passes of large deformation cold rolling. First, the hot coil is annealed and pickled. The hot coil annealing temperature is controlled at 940-1000°C, and the hot coil annealing time is controlled at 1.4-1.8 min / mm. Then, multiple passes of cold rolling are performed, and the total cold rolling deformation rate is controlled at 55%-85%. The cold coil annealing furnace temperature is controlled at 880-940°C, and the cold coil annealing time is controlled at 1.0-1.4 min / mm. Finally, the cold plate surface is ground to obtain medium chromium heat-resistant ferritic stainless steel cold plate.

[0044] Furthermore, in the preparation method of the above-mentioned medium chromium heat-resistant ferritic stainless steel cold plate, in order to improve production efficiency and the recovery rate of precious elements and ensure the purity of molten steel, high-content Cr elements are 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 precious elements Ni and Mo are alloyed in LF furnace.

[0045] Preferably, in the method for preparing the medium chromium heat-resistant ferritic stainless steel cold plate, in the hot rolling step, the final rolling temperature is controlled to be ≤850°C, and the coiling temperature is controlled to be ≤400°C.

[0046] Preferably, in the preparation method of 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°C, the total cold rolling deformation rate is controlled to be 60%-85%, the cold coil annealing furnace temperature is controlled to be 880-920°C, and a 230# sand belt is used to grind the cold plate surface.

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

[0048] The medium chromium heat-resistant ferrite stainless steel of the present invention is a medium chromium heat-resistant ferrite stainless steel cold plate prepared by smelting, continuous casting, hot rolling and cold rolling, and 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 μΩ·cm, and an oxidation weight gain rate of 0.10-0.15 mg / cm after continuous high-temperature oxidation at 900°C for 200 hours in an atmospheric atmosphere. 2 , and there is no oxide film falling off; after surface grinding, and then a salt spray test was carried out in a 35°C, 5% NaCl spray, no rust spots were observed within 48 hours.

[0049] In the fourth aspect of the present invention, a medium chromium heat-resistant ferritic stainless steel cold plate is provided for use in household appliances, industrial combustion furnaces, automobile exhaust systems and electric heating equipment for new energy vehicles, 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 vehicles.

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

[0051] The chemical compositions of the medium chromium heat-resistant ferritic stainless steel cold plates prepared by using Examples 1-3 of the present invention and the medium chromium heat-resistant ferritic stainless steel cold plates prepared by using 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 Composition of ferritic stainless steel cold plates of Examples 1-3 and Comparative Examples 1-3 (wt.%)

[0053]

[0054] In Examples 1-3 of the present invention, the contents of the 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 of the method for preparing the medium chromium heat-resistant ferrite stainless steel cold plate of Examples 1-3 of the present invention are shown in Table 2 below:

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

[0057]

[0058] The medium chromium heat-resistant ferritic stainless steel cold plates prepared by using Examples 1-3 of the present invention and the medium chromium heat-resistant ferritic stainless steel cold plates prepared by using Comparative Examples 1-3 of the prior art were analyzed, tested and tested for performance. The metallographic structure diagram of the medium chromium heat-resistant ferritic stainless steel cold plate prepared by using Example 1 of the present invention is shown in Figure 1 The cross-sectional composition scanning diagram of the oxide layer of the medium chromium heat-resistant ferrite stainless steel cold plate prepared by Example 2 of the present invention is shown in FIG. Figure 2, the performance test results are summarized in Table 3. Among them, the performance parameter determination standards and methods are as follows: grain size is carried out according to GBT 6394 "Method for determination of average grain size of metals"; mechanical tensile test is carried out according to GBT 228.1 "Metallic material tensile test Part 1: Room temperature test method"; plastic strain ratio is carried out according to GB / T 5027 "Determination of plastic strain ratio (r value) of metal sheets and strips"; room temperature resistivity is carried out according to GB / T 6146 "Precision resistance alloy resistivity test method"; high temperature oxidation experiment is carried out according to GB / T 13303 "Steel oxidation resistance test method"; salt spray corrosion test is carried out according to GB / T 10125 "Artificial atmosphere corrosion test salt spray test". Moreover, when testing the performance parameters, 3 samples are taken for each embodiment and comparative example, and the average value of the 3 samples is the final result. In addition, after mechanical grinding and polishing of the sample perpendicular to the thickness direction of the sample, the metallographic structure of the material is observed by an optical microscope, and the oxide layer section is observed by a scanning electron microscope to give the composition structure of the oxide layer.

[0059] Table 3 Summary of heat-resistant ferritic stainless steel cold plate properties of Examples 1-3 and Comparative Examples 1-3

[0060]

[0061] It can be seen from the actual detection and test results that the grain size of the ferritic stainless steel cold plate in Examples 1-3 is 7-8, which is equivalent to Comparative Example 2 and better than Comparative Examples 1 and 3; in terms of elongation after fracture, Examples 1-3 are 30%-33%, which is equivalent to Comparative Example 2, but better than Comparative Examples 1 and 3; in terms of plastic strain ratio r value, Examples 1-3 are 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 are 1.15-1.20 μΩ·cm, slightly lower than Comparative Example 1, but far better than Comparative Examples 2 and 3; in terms of high temperature oxidation resistance weight gain, Examples 1-3 are 0.10-0.15 mg / cm 2 , which is equivalent to Comparative Example 1, but much better than Comparative Examples 2 and 3, and a single and dense Al2O3 film is formed on the surface of the cold plate of Examples 1-3; in terms of salt spray corrosion resistance, no rust spots are observed in Examples 1-3 within 48 hours, which is 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 of the present invention have excellent high-temperature oxidation resistance and electrical resistance, and have good processing performance and certain corrosion resistance.

[0062] In summary, the present invention designs the component system and optimizes the cold plate preparation process for medium chromium heat-resistant ferritic stainless steel, provides medium chromium heat-resistant ferritic stainless steel, medium chromium heat-resistant ferritic stainless steel cold plate and its preparation method and application, while ensuring that the material has excellent high-temperature oxidation resistance and electrical resistance, it also has good processing performance and certain corrosion resistance, effectively expanding the application field of chromium heat-resistant ferritic stainless steel products. Compared with the prior art, the technical solution of the present 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 reasonable matching of the main elements of Cr, Al, and Si and microalloying of the elements of Mn, Ni, Mo, and Ti, which can obtain good processing performance and good corrosion resistance under the premise of ensuring the formation of a dense Al2O3 oxide film;

[0064] (2) The medium chromium heat-resistant ferrite stainless steel cold plate of the present invention has a grain size of 7 to 8, an elongation after fracture of 30% to 33%, a plastic strain ratio r value of 1.20 to 1.40, a room temperature resistivity of 1.15 to 1.20 μΩ·cm, and an oxidation weight gain rate of 0.10 to 0.15 mg / cm after a 900°C / 200h high temperature oxidation resistance test. 2 , and there is no oxide film falling off; after surface grinding, a salt spray test was carried out in 35℃, 5% NaCl spray, and no rust spots were observed within 48 hours. Medium chromium heat-resistant ferritic stainless steel and its cold plate have excellent high-temperature oxidation resistance and electrical resistance, as well as good processing performance and certain corrosion resistance.

[0065] It should be noted that, in addition to the explicit description herein, the process method of the present invention can be implemented by conventional methods or devices in the art, and the noun terms in this article, unless otherwise specified, have the meanings generally understood by those skilled in the art. Moreover, when a numerical range is disclosed herein, the above range is deemed to be continuous and includes the minimum and maximum values ​​of the range, and each value between such minimum and maximum values. Further, when the range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple range description features are provided, the range can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges included therein.

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

[0067] In addition, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the present invention.

Claims

1. A medium chromium heat-resistant ferritic stainless steel, characterized in that: The chemical composition of the medium chromium heat-resistant ferrite stainless steel is as follows by 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 is 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 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where w Al 、w Si 、w Cr 、w Mn 、w Ni 、w Mo They represent the mass percentage contents of elements Al, Si, Cr, Mn, Ni and Mo respectively.

2. The medium chromium heat-resistant ferritic stainless steel according to claim 1, characterized in that: The C and N contents in the medium chromium heat-resistant ferrite stainless steel are controlled to be 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 preparing a medium chromium heat-resistant ferritic stainless steel cold plate, characterized in that: The steps include: (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% to 0.50%, Mn: 0.20% to 0.50%, Cr: 17.0% to 19.0%, Al: 2.0% to 4.0%, Ni: 0.05% to 0.30%, Mo: 0.10% to 0.30%, Ti: 0.10% to 0.30%, and the balance is Fe and unavoidable impurity elements, and the content of Al, Si, and Cr elements meets 60 ≤ (w Al +w Si )×w Cr ≤70, the content of Mn, Ni and Mo elements meets 1.0≤4w Ni +8w Mo -w Mn ≤2.0, where 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, and Mo; (2) Continuous casting: Slab continuous casting is carried out through a tundish, and electromagnetic stirring is used throughout the continuous casting process to control the equiaxed crystal ratio of the slab to be greater than 55%; (3) Hot rolling: the heating temperature is controlled at 1150-1200°C, the hot rolling passes are 7 passes, the final rolling temperature is controlled at ≤880°C, the steel is put into layer cooling after hot rolling, and the coiling temperature is controlled at ≤500°C; (4) Cold rolling: first, the hot coil is annealed and pickled, the hot coil annealing temperature is controlled at 940-1000°C, and the hot coil annealing time is controlled at 1.4-1.8 min / mm, then multiple cold rolling is performed, the total cold rolling deformation rate is controlled at 55%-85%, the cold coil annealing furnace temperature is controlled at 880-940°C, and the cold coil annealing time is controlled at 1.0-1.4 min / mm, and finally the cold plate surface is ground to obtain medium chromium type heat-resistant ferritic stainless steel cold plate.

5. The method for preparing the medium chromium heat-resistant ferritic stainless steel cold plate according to claim 4, characterized in that: Cr alloying was performed in K-OBM-S, reduction using aluminum shot and subsequent alloying of Al, Si, Mn, Ti was performed in VOD, and Ni and Mo alloying was performed in LF furnace.

6. The method for preparing the medium chromium heat-resistant ferrite stainless steel cold plate according to claim 4, characterized in that: In the hot rolling step, the final rolling temperature is controlled to be ≤850°C, and the coiling temperature is controlled to be ≤400°C.

7. The method for preparing the medium chromium heat-resistant ferritic stainless steel cold plate according to claim 4, characterized in that: In the cold rolling step, the hot coil annealing temperature is controlled at 940-980°C, the total cold rolling deformation rate is controlled at 60%-85%, the cold coil annealing furnace temperature is controlled at 880-920°C, and a 230# sand belt is used to grind the cold plate surface.

8. A medium chromium heat-resistant ferritic stainless steel cold plate, characterized in that: 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 to 7, the width of the medium chromium heat-resistant ferritic stainless steel cold plate is 1000-1300 mm, the thickness is 0.4-2.0 mm, the surface type of the medium chromium heat-resistant ferritic stainless steel cold plate is HL surface, the roughness is less than 0.40 μm, and the total oxygen content T[O] is ≤10 ppm.

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

10. Application of the medium chromium heat-resistant ferritic stainless steel cold plate according to claim 8 or 9 in household appliances, industrial combustion furnaces, automobile exhaust systems and electric heating equipment for new energy vehicles, 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 vehicles.

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