Low-chromium stainless steel formula and preparation method thereof

Abstract

The invention relates to the field of stainless steel, and discloses a low-chromium stainless steel formula and a preparation method thereof. Comprising the following raw materials in percentage by weight: 0.05%-0.07% of carbon, 0.2%-0.3% of silicon, 10%-12% of manganese, less than or equal to 0.025% of phosphorus, less than or equal to 0.015% of sulfur, 4%-5% of nickel, 14%-15% of chromium, 0.8%-1% of copper, 0.25%-0.3% of nitrogen, 0.1%-0.3% of aluminum, 0.8%-1.2% of molybdenum, 0.15%-0.2% of niobium, 0.05%-0.08% of titanium, 0.05%-0.1% of vanadium, 0.05%-0.1% of cobalt and the balance of iron. Through cooperation of chromium, nickel, molybdenum and the like, the nickel stabilizes a matrix to facilitate chromium film formation, the molybdenum enhances the corrosion resistance of the film in a severe environment, nitrogen and manganese promote enrichment of the chromium surface, the manganese reduces sulfur damage, titanium and niobium fix carbon to avoid poor chromium in the grain boundary, and aluminum forms a protective film to be matched with the chromium film.

Description

Technical Field

[0001] The present invention relates to the technical field of stainless steel, and specifically to a low-chromium stainless steel formula and a preparation method thereof. Background Art

[0002] In the modern industrial field, stainless steel, as an important metal material, is widely used in multiple industries such as construction, machinery manufacturing, chemical industry, and food processing. With its excellent corrosion resistance, high strength, and good processing performance, it meets the strict requirements for material properties in different scenarios. With the continuous progress of industrial technology and the increasing diversification of market demands, the requirements for the performance of stainless steel are becoming more and more stringent. It not only needs to maintain stable performance in conventional environments but also demonstrate excellent adaptability under complex and harsh working conditions.

[0003] In traditional low-chromium stainless steel formulas, due to the low chromium content, the stability and integrity of the surface passivation film are poor, and it is easily eroded by corrosive media, resulting in poor corrosion resistance. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides a low-chromium stainless steel formula and a preparation method thereof, which solve the problem that in traditional low-chromium stainless steel formulas, due to the low chromium content, the stability and integrity of the surface passivation film are poor, and it is easily eroded by corrosive media, resulting in poor corrosion resistance.

[0005] To achieve the above objectives, the present invention is realized through the following technical solutions: A low-chromium stainless steel formula includes the following raw materials in percentages: carbon 0.05%-0.07%, silicon 0.2%-0.3%, manganese 10%-12%, phosphorus ≤0.025%, sulfur ≤0.015%, nickel 4%-5%, chromium 14%-15%, copper 0.8%-1%, nitrogen 0.25%-0.3%, aluminum 0.1%-0.3%, molybdenum 0.8%-1.2%, niobium 0.15%-0.2%, titanium 0.05%-0.08%, vanadium 0.05%-0.1%, cobalt 0.05%-0.1%, and the balance is iron.

[0006] Preferably, the mass ratio of manganese to nitrogen is 33.3:1 - 48:1.

[0007] A method for preparing low-chromium stainless steel includes the following steps:

[0008] S1. Raw material preparation: Take the raw materials according to the percentages and conduct pretreatment;

[0009] S2. Melting: Sequentially add the pretreated raw materials into an electric arc furnace for melting to obtain a raw material solution;

[0010] S3. Refining: Refine the raw material solution by the argon oxygen decarburization process to obtain molten steel;

[0011] S4. Casting: Pour the molten steel into the continuous caster, and control the solidification process of the billet by adjusting the cooling water volume and drawing speed to obtain a steel billet;

[0012] S5. Hot rolling: Gradually heat the steel billet in zones, perform rough rolling and finish rolling after high-pressure descaling, and coiling after laminar cooling to obtain a hot-rolled black skin coil;

[0013] S6. Solution pickling: Perform solution treatment on the hot-rolled black skin coil, enter the pickling treatment after shot blasting and scale breaking treatment to obtain a hot-rolled white skin coil;

[0014] S7. Cold rolling: After the hot-rolled white skin coil is rolled by a continuous rolling mill / 20-high single rolling mill, a cold-hardened coil is obtained. After surface degreasing and solution treatment, it enters electrolysis and pickling treatment, and after online skin pass rolling and tension leveling treatment, a cold-rolled 2B surface steel coil is obtained.

[0015] Preferably, the pretreatment in S1 includes crushing the massive raw materials to make their particle size 5 - 30 mm.

[0016] Preferably, the melting temperature in S2 is 1550 - 1650 °C and the time is 40 - 90 minutes.

[0017] Preferably, the refining temperature in S3 is 1600 - 1650 °C, the refining time is 20 - 30 minutes, and the argon flow rate is 20 - 30 L / min.

[0018] Preferably, the casting speed for pouring the molten steel into the continuous caster in S4 is 1 - 1.5 m / min, the cooling water volume is 80 - 120 m 3 / h, and the drawing speed is 0.8 - 1.2 m / min.

[0019] Preferably, the heating temperature for heating in S5 is 1150 - 1250 °C, the heating time is 40 - 65 minutes, the number of passes of the hot rolling reduction is 7 - 13 passes, the reduction per pass is 7 - 9.5%, and the rolling force of the finish rolling is not more than 1500 tons.

[0020] Preferably, the solution treatment in S6 is to heat up to the solution temperature of 1050 - 1150 °C at a speed of 10 - 20 °C / s, the holding time is 0.2 - 2 minutes / mm thickness, and then cool by air cooling, fog cooling, and water cooling in sequence, and the cooling speed is 95 - 120 °C / s.

[0021] Preferably, the total cold rolling deformation amount in S7 is 60 - 80%, the surface degreasing uses a professional degreasing agent, the conductivity of the degreasing solution is controlled at 30 - 50 ms / cm, the temperature is controlled at 40 - 60 °C, the heating rate of the solution treatment is 15 - 25 °C / s, and the current density of the electrolysis is 1000 - 1500 A / m 2 , the elongation of the skin pass is not less than 0.5%, and the elongation of the tension leveling is not less than 0.3%.

[0022] The present invention provides a low-chromium stainless steel formulation and its preparation method. It has the following beneficial effects:

[0023] 1. In the present invention, chromium cooperates with nickel, molybdenum, etc. Nickel stabilizes the matrix to facilitate the formation of a chromium film, molybdenum enhances the corrosion resistance of the film in harsh environments, nitrogen and manganese promote the enrichment of chromium on the surface, and manganese reduces the damage of sulfur. Titanium and niobium fix carbon to avoid chromium depletion at grain boundaries, aluminum forms a protective film to cooperate with the chromium film, and copper changes the electronic structure of the film, thereby forming a stable, dense and self-healing passivation film. Even if it is locally damaged, it can be quickly repaired, thus solving the problem in the traditional low-chromium stainless steel formulation that due to the relatively low chromium content, the stability and integrity of the surface passivation film are poor, and it is easily eroded by corrosive media, resulting in poor corrosion resistance.

[0024] 2. In the present invention, carbon, silicon, and nitrogen are used for solid solution strengthening of the matrix to improve strength and hardness. Vanadium, niobium, and titanium form fine carbides and nitrides for precipitation strengthening and grain refinement, enhancing strength, toughness, and wear resistance. Cobalt improves thermal strength and high-temperature hardness, enabling the stainless steel to maintain good mechanical properties under different temperature conditions and meeting the requirements of various working conditions for material properties.

[0025] 3. In the present invention, by controlling the chromium content at a relatively low level and using elements such as manganese and nitrogen to partially replace nickel, the dependence on expensive and scarce chromium and nickel resources is reduced, the production cost is effectively reduced, the resource utilization efficiency is improved, and the competitiveness of the product in the market is enhanced.

[0026] 4. In the present invention, the melting efficiency and the uniformity of the molten steel are improved through raw material preparation. During melting, the dissolution of elements and the composition uniformity are ensured, and chromium loss is reduced. The AOD process is used for refining to deeply remove impurities and improve the purity of the molten steel. During casting, high-quality billets are obtained by matching the speed and the cooling water volume. During hot rolling, the grains are refined and the strength is improved through zone heating, multi-pass rolling, and reasonable cooling. Solution pickling enables the alloying elements to be fully dissolved, enhancing corrosion resistance and surface quality. Cold rolling and post-treatment further improve the dimensional accuracy, surface finish, and mechanical properties, meeting the requirements of high-precision applications, and preparing a low-chromium stainless steel with excellent comprehensive performance. Description of the Drawings

[0027] Figure 1 is a process flow chart of a method for preparing a low-chromium stainless steel proposed by the present invention. Specific Embodiments

[0028] The technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative work fall within the scope of protection of the present invention.

[0029] The embodiment of the present invention provides a low-chromium stainless steel formula, including the following raw materials in percentage: carbon 0.05%-0.07%, silicon 0.2%-0.3%, manganese 10%-12%, phosphorus ≤0.025%, sulfur ≤0.015%, nickel 4%-5%, chromium 14%-15%, copper 0.8%-1%, nitrogen 0.25%-0.3%, aluminum 0.1%-0.3%, molybdenum 0.8%-1.2%, niobium 0.15%-0.2%, titanium 0.05%-0.08%, vanadium 0.05%-0.1%, cobalt 0.05%-0.1%, and the balance is iron; the mass ratio of manganese to nitrogen is 33.33:1 - 48:1.

[0030] Specifically, by adding carbon, the strength and hardness of the stainless steel can be improved to a certain extent. Carbon is an effective solid solution strengthening element. It can form an interstitial solid solution with iron, increase lattice distortion, and hinder dislocation movement, thereby enhancing the strength of the steel. However, too high carbon content will reduce the corrosion resistance of the stainless steel. Therefore, it is controlled within a relatively low range of 0.05%-0.07% to minimize the adverse impact on corrosion resistance while ensuring a certain strength.

[0031] By adding silicon, it plays a role in deoxidation and improves the purity of the steel. Silicon is a commonly used deoxidizer. During the melting process, it can combine with oxygen to form silicon dioxide, thereby removing oxygen impurities in the molten steel. In addition, silicon can also solid solution strengthen ferrite, improve the strength, hardness and elastic modulus of the steel, and enhance the mechanical properties of the stainless steel.

[0032] By adding manganese, the austenite region is expanded and the austenite structure is stabilized. Manganese can partially replace nickel, reduce costs, and at the same time improve the strength and toughness of the steel. Manganese combines with sulfur to form manganese sulfide, reducing the harmful effects of sulfur and improving the hot working performance of the steel. And in this formula, the mass ratio of manganese to nitrogen is controlled to be 33.33:1 - 48:1, enabling manganese and nitrogen to act synergistically to further improve the strength and corrosion resistance of the steel.

[0033] By adding phosphorus, although phosphorus is a harmful element, its content is strictly controlled ≤0.025% in this formula. To a certain extent, an appropriate amount of phosphorus can improve the strength and hardness of steel, especially improve the cutting performance of steel in low-temperature environments. However, too high a phosphorus content will exacerbate the cold brittleness phenomenon of steel. Therefore, it is necessary to strictly control its content to ensure the quality of steel.

[0034] By adding sulfur, sulfur is also a harmful element. Its content is strictly controlled ≤0.015% in this formula. A small amount of sulfur will reduce the hot working performance and toughness of steel, making it easy to generate cracks during the processing of steel. Strictly controlling the sulfur content can improve the purity and comprehensive performance of steel and reduce the occurrence of hot brittleness phenomenon.

[0035] By adding nickel, the corrosion resistance and toughness of stainless steel are significantly improved. Nickel is an important austenite-forming element. It can expand the austenite region, make the steel form a stable austenite structure at room temperature, improve the corrosion resistance, plasticity and toughness of steel, and help maintain good corrosion resistance and processing performance even in the case of low chromium.

[0036] By adding chromium, a dense chromium oxide protective film is formed on the surface of stainless steel, improving the corrosion resistance of steel. Chromium is the key element determining the corrosion resistance of stainless steel. Although the chromium content in this formula is relatively low (14%-15%), it can still endow stainless steel with good corrosion resistance in cooperation with other alloying elements.

[0037] By adding copper, the corrosion resistance of stainless steel in certain media is improved, especially in the atmospheric environment and some reducing media. Copper can also improve the cutting performance and cold working performance of steel, making the steel easier to process and form. Adding 0.8%-1% of copper in this formula can further enhance the comprehensive performance of stainless steel.

[0038] By adding nitrogen, it plays a role in solution strengthening and stabilizing the austenite structure. Nitrogen is a strong austenite-forming element. It can replace part of nickel, reducing costs. At the same time, nitrogen can improve the strength, hardness and pitting corrosion resistance of steel, and enhance the comprehensive performance of steel in cooperation with elements such as manganese.

[0039] By adding aluminum, an aluminum oxide protective film is formed on the surface of stainless steel, improving the oxidation resistance and high-temperature resistance of steel. Aluminum can also refine the grains, improve the strength and toughness of steel, and can improve the performance of stainless steel in high-temperature environments.

[0040] By adding molybdenum, the pitting corrosion and crevice corrosion resistance of stainless steel in harsh environments containing chloride ions and other substances are enhanced. Molybdenum can improve the stability of the passivation film of steel, prevent the destruction of the passivation film by erosive ions such as chloride ions, thereby improving the corrosion resistance of steel and significantly enhancing the performance of stainless steel in specific corrosion environments.

[0041] By adding niobium, it combines with elements such as carbon and nitrogen to form stable carbides and nitrides, refine the grain size, improve the strength and toughness of the steel. Niobium can also fix the carbon in the steel, reduce the precipitation of carbides at the grain boundaries, improve the intergranular corrosion resistance of the steel, and improve the comprehensive mechanical properties and corrosion resistance of stainless steel.

[0042] By adding titanium, it forms stable titanium carbide with carbon, avoiding the combination of carbon and chromium to form chromium carbide, reducing the phenomenon of chromium depletion at the grain boundaries, improving the intergranular corrosion resistance of the steel. Titanium can also refine the grain size, improve the strength and toughness of the steel, and effectively enhance the corrosion resistance and mechanical properties of stainless steel.

[0043] By adding vanadium, it forms fine and dispersed carbides and nitrides with carbon, nitrogen, etc., playing the role of precipitation strengthening and grain refinement, improving the strength, hardness and wear resistance of the steel. Vanadium can also improve the high-temperature performance of the steel, enabling the steel to maintain good mechanical properties at high temperatures, and further enhancing the comprehensive performance of stainless steel.

[0044] By adding cobalt, it improves the thermal strength and high-temperature hardness of stainless steel. Cobalt can increase the interatomic binding force of the steel, improve the strength and hardness of the steel at high temperatures, and improve the high-temperature stability of the steel, enabling stainless steel to have better performance in high-temperature environments.

[0045] By adding iron, as the matrix of stainless steel, it provides a bearing basis for other alloying elements and determines the basic physical and mechanical properties of stainless steel. Iron is the main component element of stainless steel, and other alloying elements are dissolved in the iron lattice and exert their respective performance advantages through interaction with iron.

[0046] Through the mutual cooperation of each raw material, a complex and stable alloy system is formed. Chromium forms a Cr-Mo-N composite passivation film with molybdenum and nitrogen, and copper releases Cu + ions to inhibit Cl - erosion, manganese and nitrogen synergistically stabilize the austenite phase, niobium and titanium form Nb(C,N) / Ti N particles to pin the grain boundaries, eliminate the precipitation of Cr23C6, and aluminum generates Al 2 O 3 secondary film to block Cl -Diffusion, vanadium refines corrosion products, cobalt inhibits hydrogen-induced cracking, and the cost is reduced by decreasing the nickel content. Each component gives full play to its own advantages and makes up for the shortcomings of others, thus constructing a more stable corrosion-resistant mechanism, achieving a good balance between the mechanical properties and corrosion resistance of low-chromium stainless steel. It not only has high strength and hardness and can withstand large external forces, but also has excellent corrosion resistance and can adapt to a variety of complex use environments, thus solving the problem in the traditional low-chromium stainless steel formula that due to the low chromium content, the stability and integrity of the surface passivation film are poor and it is easily eroded by corrosive media, resulting in poor corrosion resistance.

[0047] Please refer to the appendix Figure 1 , a method for preparing low-chromium stainless steel, comprising the following steps:

[0048] S1. Raw material preparation: Take raw materials according to percentages and perform pretreatment; the pretreatment in S1 includes crushing massive raw materials to make their particle size 5 - 30 mm.

[0049] Specifically, by controlling the raw material particle size ≤ 30 mm, the melting efficiency of the electric arc furnace can be improved and the composition segregation caused by local unmelted blocks can be reduced; at the same time, the particle size lower limit ≥ 5 mm avoids excessive oxidation of powder raw materials and ensures the stable recovery rate of alloy elements (such as niobium, molybdenum). By taking raw materials according to precise percentages and performing the above pretreatment, the precise ratio of each element in the subsequent melting process can be ensured, the specific surface area of the raw materials is increased, and the elements are more fully mixed and reacted, laying a foundation for obtaining stainless steel with uniform composition and stable performance.

[0050] S2. Melting: Sequentially add the pretreated raw materials into an electric arc furnace for melting to obtain a raw material solution; the melting temperature in S2 is 1550 - 1650 °C and the time is 40 - 90 minutes.

[0051] Specifically, the melting temperature of 1550 - 1650 °C covers the liquidus of the iron matrix and high-melting-point alloy elements (such as chromium, molybdenum) to ensure complete melting; the melting time of 40 - 90 minutes promotes composition homogenization through dynamic stirring (arc electromagnetic force), and at the same time, a mixed gas of O 2 :Ar = 1:3 is introduced. Oxygen is used for decarburization and argon is used to inhibit chromium oxidation, reducing the chromium loss to ≤ 1.5%. Through this melting process, various raw materials are fully melted and fused with each other, ensuring that alloy elements are evenly distributed in the molten steel and providing high-quality raw material solution for the subsequent refining process.

[0052] S3. Refining: Refine the raw material solution using the argon-oxygen decarburization process to obtain molten steel; the refining temperature in S3 is 1600 - 1650 °C, the refining time is 20 - 30 minutes, and the argon flow rate is 20 - 30 L / min.

[0053] Specifically, in the AOD process, argon dilutes the CO partial pressure to enhance the decarburization reaction (C + O 2 → CO↑), reducing the carbon content from 0.15% to ≤ 0.07%. Meanwhile, argon stirring (flow rate 20 - 30 L / min) accelerates the floating of inclusions, making the purity of the molten steel reach [T.O] ≤ 20 ppm; the refining temperature of 1600 - 1650 °C avoids the decrease in fluidity caused by excessive cooling of the molten steel. Through refining, impurities and gases such as carbon, sulfur, and phosphorus in the molten steel are further removed, the composition and temperature of the molten steel are adjusted, the purity and quality of the molten steel are improved, the performance of the stainless steel is enhanced, and high-quality molten steel is provided for subsequent casting.

[0054] S4. Casting: Pour the molten steel into the continuous caster, and control the solidification process of the billet by adjusting the cooling water volume and drawing speed to obtain a steel billet; the casting speed of pouring the molten steel into the continuous caster in S4 is 1 - 1.5 m / min, the cooling water volume is 80 - 120 m 3 / h, and the drawing speed is 0.8 - 1.2 m / min.

[0055] Specifically, the casting speed of 1 - 1.5 m / min matches the drawing speed of 0.8 - 1.2 m / min to form a stable solidification shell and avoid leakage; the cooling water volume of 80 - 120 m 3 / h is dynamically regulated in the secondary cooling zone to make the temperature difference between the surface and the core of the billet ≤ 200 °C, suppressing internal cracks; finally, a 200 - mm - thick billet without shrinkage cavities is obtained. By precisely controlling the casting and cooling parameters, the molten steel solidifies and forms as expected, obtaining a steel billet with good internal structure and qualified external dimensions, reducing internal defects of the billet.

[0056] S5. Hot rolling: The steel billet is heated in a zoned progressive manner, descaled under high pressure, then rough - rolled and finish - rolled, and coiled after laminar cooling to obtain a hot - rolled black - skin coil; the heating temperature for heating in S5 is 1150 - 1250 °C, the heating time is 40 - 65 minutes, the number of passes of the hot - rolling reduction is 7 - 13 passes, the reduction per pass is 7 - 9.5%, and the rolling force of the finish rolling is not more than 1500 tons.

[0057] Specifically, zoned heating avoids thermal stress cracking; 7 - 13 passes of rolling (total reduction 70 - 85%) refine the austenite grains to ASTM 5 - 6 grades through recrystallization; the finish - rolling temperature ≥ 900 °C inhibits the precipitation of δ - ferrite. Through hot rolling, the as - cast structure of the steel billet is further broken, the grains are refined, the mechanical properties and processing properties of the steel are improved, and certain shape and dimensional accuracy are imparted to the steel.

[0058] S6. Solutionizing and pickling: The hot-rolled black skin coil is solutionized, and after shot blasting and descaling, it enters the pickling process to obtain a hot-rolled white skin coil. In S6, the solutionizing process is to heat up to the solution temperature of 1050 - 1150°C at a rate of 10 - 20°C / s, the holding time is 0.2 - 2 minutes / mm thickness, and then it is cooled successively by air cooling, fog cooling, and water cooling, with a cooling rate of 95 - 120°C / s.

[0059] Specifically, the solution treatment completely dissolves carbides (such as Cr 23 C 6 ), and rapid water cooling (≥95°C / s) locks the supersaturated solid solution to improve corrosion resistance; the pickling solution HNO 3 dissolves the chromium oxide layer and HF dissolves silicate to obtain a smooth surface. Sulfuric acid + mixed acid (nitric acid, hydrofluoric acid) is used for pickling treatment to remove the surface scale and improve the surface quality.

[0060] S7. Cold rolling: After the hot-rolled white skin coil is rolled by a continuous rolling mill / twenty-high single rolling mill, a cold-hardened coil is obtained. After surface degreasing and solutionizing, it enters the electrolysis and pickling processes, and after online leveling and tension leveling, a cold-rolled 2B surface steel coil is obtained. In S7, the total cold rolling deformation is 60 - 80%, professional degreasing agent is used for surface degreasing, the conductivity of the degreasing solution is controlled at 30 - 50 ms / cm, the temperature is controlled at 40 - 60°C, the heating rate of the solutionizing process is 15 - 25°C / s, the current density of electrolysis is 1000 - 1500 A / m 2 , the elongation of leveling is not less than 0.5%, and the elongation of tension leveling is not less than 0.3%.

[0061] Specifically, cold rolling with a deformation of 60 - 80% induces dislocation strengthening, and the yield strength is increased to ≥800 MPa; neutral salt electrolysis can uniformly dissolve the chromium oxide on the surface of stainless steel, and at the same time, the force formed when the generated hydrogen and oxygen escape from the strip surface can strip the surface oxide. In addition, due to the action of electrons and water during the electrolysis process, the purpose of descaling can also be achieved. Through pickling treatment, the oxides and iron scales on the surface of stainless steel can be completely removed, and the current density is 1000 - 1500 A / m 2 balances the corrosion efficiency and uniformity; leveling and tension leveling eliminate residual stress, and through cold rolling and subsequent treatments, the dimensional accuracy and surface finish of the steel are further improved, obtaining good surface quality and mechanical properties to meet the requirements of different application scenarios for stainless steel sheets.

[0062] The following is a further introduction with specific examples:

[0063] Example 1:

[0064] A low chromium stainless steel formula includes the following percentage raw materials: carbon 0.07%, silicon 0.3%, manganese 12%, phosphorus ≤0.025%, sulfur ≤0.015%, nickel 5%, chromium 15%, copper 1%, nitrogen 0.3%, aluminum 0.3%, molybdenum 1.2%, niobium 0.2%, titanium 0.08%, vanadium 0.1%, cobalt 0.1%, and the rest is iron.

[0065] The mass ratio of manganese to nitrogen is 40:1.

[0066] A method for preparing low-chromium stainless steel comprises the following steps:

[0067] S1. Raw material preparation: take the raw materials according to percentage and pre-treat them;

[0068] S2, smelting: adding the pretreated raw materials into an electric arc furnace in sequence for smelting to obtain a raw material solution;

[0069] S3, refining: using argon oxygen decarburization process to refine the raw material solution to obtain molten steel;

[0070] S4, casting: casting the molten steel into the continuous casting machine, and controlling the solidification process of the ingot by adjusting the cooling water volume and the casting speed to obtain a steel ingot;

[0071] S5, hot rolling: the steel billet is heated gradually in different zones, rough rolled and finished rolled after high pressure descaling, and coiled after laminar cooling to obtain hot rolled black coil;

[0072] S6, solution pickling: the hot-rolled black coil is subjected to solution treatment, and then to pickling treatment after shot blasting and descaling to obtain a hot-rolled white coil;

[0073] S7. Cold rolling: The hot-rolled white coil is rolled by a continuous rolling mill / a twenty-high single rolling mill to obtain a cold hard coil. After surface degreasing and solution treatment, it enters electrolysis and pickling treatment, and after online leveling and straightening treatment, a cold-rolled 2B surface steel coil is obtained.

[0074] The pretreatment in S1 includes crushing the bulk raw materials to a particle size of 10 mm.

[0075] The smelting temperature in S2 is 1600°C and the smelting time is 65 minutes.

[0076] The refining temperature in S3 was 1625°C, the refining time was 25 minutes, and the argon gas flow rate was 25 L / min.

[0077] In S4, the casting speed of the molten steel into the continuous casting machine is 1.25m / min, and the cooling water volume is 100m 3 / h, pulling speed is 1m / min.

[0078] The heating temperature during S5 is 1200 °C, the heating time is 50 minutes, the number of passes for hot rolling deformation is 9 passes, the deformation per pass is 8%, and the rolling force during finish rolling is not more than 1500 tons.

[0079] The solution treatment during S6 is to heat up to the solution temperature of 1100 °C at a rate of 15 °C / s, the holding time is 2 minutes / mm thickness, and then air cooling, fog cooling, and water cooling methods are used for cooling in sequence, and the cooling rate is 110 °C / s.

[0080] The total deformation during cold rolling in S7 is 70%, professional degreasing agent is used for surface degreasing, the conductivity of the degreasing solution is controlled at 40 ms / cm, the temperature is controlled at 50 °C, the heating rate of the solution treatment is 20 °C / s, and the current density of electrolysis is 1250 A / m 2 , the elongation during skin pass is not less than 0.5%, and the elongation during tension leveling is not less than 0.3%.

[0081] Example 2:

[0082] The difference between this example and the above Example 1 is as follows:

[0083] A low-chromium stainless steel formulation, characterized by including the following raw materials in percentages: carbon 0.05%, silicon 0.2%, manganese 10%, phosphorus ≤ 0.025%, sulfur ≤ 0.015%, nickel 4%, chromium 14%, copper 0.8%, nitrogen 0.25%, aluminum 0.1%, molybdenum 0.8%, niobium 0.15%, titanium 0.05%, vanadium 0.05%, cobalt 0.05%, and the balance is iron.

[0084] Example 3:

[0085] The difference between this example and the above Example 1 is as follows:

[0086] A low-chromium stainless steel formulation, characterized by including the following raw materials in percentages: carbon 0.06%, silicon 0.25%, manganese 11%, phosphorus ≤ 0.025%, sulfur ≤ 0.015%, nickel 4.5%, chromium 14.5%, copper 0.9%, nitrogen 0.225%, aluminum 0.2%, molybdenum 1%, niobium 0.125%, titanium 0.065%, vanadium 0.075%, cobalt 0.075%, and the balance is iron.

[0087] Table 1:

[0088] Comparison Example 1 Example 2 Example 3 Standard value Yield strength (MPa) 550 480 520 280 Tensile strength (MPa) 780 680 730 500 Hardness (HRB) 98 92 94 85 Pitting potential (mV, SCE) 320 250 290 200

[0089] The comparison in the above table is for the traditional low-chromium stainless steel formula. It can be seen from Table 1 that different amounts of carbon, silicon, manganese, phosphorus, sulfur, nickel, chromium, copper, nitrogen, aluminum, molybdenum, niobium, titanium, vanadium, cobalt, and iron can affect the pitting potential, yield strength, tensile strength, and hardness of stainless steel. By synergistically regulating the composition of the passive film, the stability of austenite, and the distribution of precipitation phases of stainless steel through various elements, a highly dense composite passive film is formed and the grain boundary structure is refined, achieving a breakthrough in corrosion resistance under low-chromium conditions, thus solving the problem of poor corrosion resistance of traditional low-chromium stainless steel due to low chromium content, poor stability and integrity of the surface passive film, and susceptibility to corrosion by corrosive media.

[0090] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A low chromium stainless steel formula, characterized in that: The raw materials include the following percentages: carbon 0.05%-0.07%, silicon 0.2%-0.3%, manganese 10%-12%, phosphorus ≤0.025%, sulfur ≤0.015%, nickel 4%-5%, chromium 14%-15%, copper 0.8%-1%, nitrogen 0.25%-0.3%, aluminum 0.1%-0.3%, molybdenum 0.8%-1.2%, niobium 0.15%-0.2%, titanium 0.05%-0.08%, vanadium 0.05%-0.1%, cobalt 0.05%-0.1%, and the rest is iron.

2. A low chromium stainless steel formulation according to claim 1, characterized in that: The mass ratio of manganese to nitrogen is 33.33:1-48:

1.

3. A method for preparing low chromium stainless steel, characterized in that: A low chromium stainless steel formulation as claimed in claim 1 or 2, comprising the following steps: S1. Raw material preparation: take the raw materials according to percentage and pre-treat them; S2, smelting: adding the pretreated raw materials into an electric arc furnace in sequence for smelting to obtain a raw material solution; S3, refining: using argon oxygen decarburization process to refine the raw material solution to obtain molten steel; S4, casting: casting the molten steel into the continuous casting machine, and controlling the solidification process of the ingot by adjusting the cooling water volume and the casting speed to obtain a steel ingot; S5, hot rolling: the steel billet is heated gradually in different zones, rough rolled and finished rolled after high pressure descaling, and coiled after laminar cooling to obtain hot rolled black coil; S6, solution pickling: the hot-rolled black coil is subjected to solution treatment, and then to pickling treatment after shot blasting and descaling to obtain a hot-rolled white coil; S7. Cold rolling: The hot-rolled white coil is rolled by a continuous rolling mill / a twenty-high single rolling mill to obtain a cold hard coil. After surface degreasing and solution treatment, it enters electrolysis and pickling treatment, and after online leveling and straightening treatment, a cold-rolled 2B surface steel coil is obtained.

4. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The pretreatment in S1 includes crushing the bulk raw materials to a particle size of 5-30 mm.

5. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The smelting temperature in S2 is 1550-1650° C. and the smelting time is 40-90 minutes.

6. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The refining temperature in S3 is 1600-1650° C., the refining time is 20-30 minutes, and the argon flow rate is 20-30 L / min.

7. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The casting speed of the molten steel into the continuous casting machine in S4 is 1-1.5 m / min, and the cooling water volume is 80-120 m 3 / h, and the pulling speed is 0.8-1.2m / min.

8. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The heating temperature in S5 is 1150-1250° C., the heating time is 40-65 minutes, the hot rolling deformation is 7-13 passes, the deformation of each pass is 7-9.5%, and the rolling force of the finish rolling is not more than 1500 tons.

9. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The solution treatment in S6 is to heat up to the solution temperature of 1050-1150°C at a rate of 10-20°C / s, keep warm for 0.2-2 minutes / mm thickness, and then cool by air cooling, mist cooling and water cooling in sequence, with a cooling rate of 95-120°C / s.

10. A method for preparing low chromium stainless steel according to claim 3, characterized in that: The total deformation of the cold rolling in S7 is 60-80%, the surface degreasing adopts a professional degreasing agent, the conductivity of the degreasing liquid is controlled at 30-50ms / cm, the temperature is controlled at 40-60°C, the heating rate of the solution treatment is 15-25°C / s, and the current density of the electrolysis is 1000-1500A / m 2 The elongation of the flattening is not less than 0.5%, and the elongation of the straightening is not less than 0.3%.

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