Smelting method of low-cost reinforced moldability iron and horse dual-phase steel

Abstract

The invention discloses a smelting method of low-cost reinforced formability iron and horse dual-phase steel, and belongs to the technical field of steel smelting. The smelting method comprises a decarburization converter, an LF refining furnace and a slab continuous casting process. Compared with a traditional technological process of BOF + LF + RH + CC, the method has the advantages that the RH refining procedure is omitted, the nitrogen content of molten steel is controlled within 0.0040%, and the production cost is effectively reduced. By increasing the aluminum content of a finished product, the reinforced iron-metal dual-phase steel is obtained, the cracking problem of a common dual-phase steel product during deep drawing at the bulging tail end is solved, and the problem puzzling a user for a long time is solved.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting, and in particular relates to a smelting method of low-cost enhanced formability iron horse dual-phase steel. Background Art

[0002] Nowadays, the trend of lightweight automobiles is becoming more and more obvious. With the increasing environmental protection requirements and the pursuit of energy efficiency, automobile manufacturers are constantly exploring various ways to reduce vehicle weight without sacrificing safety and performance. In this process, automobile companies' requirements for the complex formability of high-strength steel are also continuously increasing.

[0003] As an important automotive material, high-strength steel has high strength and good toughness, which can reduce weight while ensuring the structural strength of the vehicle. However, ordinary duplex steel products have certain limitations in some complex forming processes. For example, cracking is prone to occur during deep drawing at the end of bulging, which brings great trouble to automobile manufacturing. In order to solve this problem, scientific researchers have successfully developed enhanced dual-phase steel after unremitting efforts. This new type of steel significantly improves its forming performance by increasing the aluminum content of the finished product. In the complex forming process, it can better withstand stress and avoid cracking. The emergence of enhanced dual-phase steel is of great significance. It not only solves the problems that have long plagued users, but also greatly expands the application range of ultra-high-strength steel in automotive parts. Automakers can use this steel more confidently to manufacture various parts of complex shapes, such as body structural parts, chassis parts, etc. This will help to further improve the safety and performance of the car, while reducing the overall weight of the vehicle and improving fuel economy. In addition, the successful research and development of enhanced dual-phase steel also provides a new direction for the development of the steel industry. Steel companies can continue to increase their investment in the research and development of high-strength steel, and continuously improve and innovate the performance of steel to meet the growing needs of the automotive industry. At the same time, the cooperation between automakers and steel companies will become closer, jointly promoting the development of automotive lightweight technology.

[0004] The emergence of enhanced dual-phase steel is an important breakthrough in the development of lightweight automobiles. It provides automakers with better material choices, solves long-standing problems, and also brings new opportunities for the development of the steel industry. I believe that in the future, with the continuous advancement of technology, the application of high-strength steel in the automotive field will be more extensive, making greater contributions to the sustainable development of the automotive industry. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a low-cost smelting method for enhancing the formability of dual-phase steel, which overcomes the cracking problem of ordinary dual-phase steel products during deep drawing at the end of bulging by increasing the aluminum content of the finished product.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a low-cost smelting method of enhanced formability iron horse dual-phase steel, the smelting method comprising the following steps: (1) Decarburization converter: The mass percentage of the components of the molten steel at the end of smelting is: C: 0.04-0.06%, S≤0.008%, P≤0.020%; aluminum particles are added after tapping, the oxygen content of the molten steel is 350-500ppm, and the nitrogen content is ≤25ppm; the converter uses high carbon and low oxygen level for tapping; argon is blown from the bottom of the ladle in advance to protect the tapping and avoid severe nitrogen absorption during the tapping process; (2) LF furnace refining: Aluminum particles and aluminum wire are added 8 minutes before refining for double deoxidation to achieve rapid white slag production, and the outgoing slag FeO+MnO≤1%; (3) Slab continuous casting: The thickness of the continuous casting slab is 230 mm. A carbon-free and low-silicon covering agent is added to ensure that the molten steel is not exposed. The continuous casting constant speed is controlled at 1.3-1.4 m / min. The superheat of the molten steel in the tundish is 15-25°C.

[0007] In step (1) of the present invention, the final slag basicity is 3.2-3.6; the terminal temperature is 1630-1660°C; argon is blown from the bottom throughout the whole process, steel is tapped without falling down, argon is blown from the bottom of the ladle before tapping, the steel flow is rounded during the tapping process, and the tapping time is ≥3min.

[0008] In step (2) of the present invention, a thick slag layer of 15-20 mm is used to ensure the arc submergence effect and isolate the air. The foaming agent CaC2 is continuously added during the smelting process to make the slag expand and foam to isolate the air, and the foaming of the molten steel plays a double protection role, reducing the nitrogen increase in the LF process, and ensuring that the nitrogen content at the LF end point is ≤30ppm, which is the same as the nitrogen content in the RH path of the traditional process. The LF furnace uses a thick slag layer of 15-20 mm and adds a foaming agent CaC2 to foam the molten steel to play a double protection role, avoiding serious nitrogen absorption in the LF process, and replacing the RH process in the traditional process "BOF+LF+RH+CC".

[0009] In step (3) of the present invention, the T[O] content in the continuous casting slab is ≤30ppm, the N content is ≤40ppm, the acid-soluble aluminum content ranges from 0.500% to 0.700%, and the acid-soluble aluminum content is more than 10 times that of ordinary dual-phase steel.

[0010] The high-formability dual-phase steel obtained by the smelting method of the present invention has an n value of 0.22-0.24. The high-formability dual-phase steel obtained by rolling the continuous casting billet obtained by the smelting method has an n value of 29.4%-60.0% higher than that of ordinary dual-phase steel (n value 0.15-0.17).

[0011] In step (3) of the present invention, a ladle slag detection system is used, and argon gas is blown between the ladle casing, stopper rod, water outlet, and plates for protective pouring, and an immersed water outlet is used, and an automatic control system for liquid level fluctuation is used.

[0012] The chemical composition and mass percentage of the dual-phase steel of the present invention are: C: 0.13-0.18%, Mn: 1.50-1.80%, S≤0.005%, P≤0.025%, Si: 0.30-0.50%, Als: 0.500-0.700%, N≤0.0040%, and the balance is iron and unavoidable impurities.

[0013] In step (3) of the present invention, the chemical composition of the carbon-free and low-silicon covering agent is as follows: CaO: 40-50%, SiO2: 5-10%, Al2O3: 30-35%, MgO≤5.0%, F≤5.0%, Fe2O3≤3.0%.

[0014] The low-cost enhanced formability iron horse dual-phase steel ingot obtained by the smelting method of the present invention can be hot-rolled to produce hot-rolled coils, and cold-rolled to produce high-quality continuous annealing or galvanized products. Compared with the traditional process BOF+LF+RH+CC, the smelting method of the present invention has a process of BOF+LF+CC, omitting the RH refining process, and controlling the nitrogen content of molten steel within 0.0040% by strictly controlling the process parameters of each process, which fully meets the product requirements and effectively reduces the production cost.

[0015] The beneficial effects of the above technical solution are as follows: 1. Compared with the traditional process BOF+LF+RH+CC, the present invention omits the RH refining process, and by strictly controlling the process parameters of each process, the nitrogen content of molten steel is controlled within 0.0040%, which fully meets the requirements of hot stamping and effectively reduces the production cost. 2. The present invention achieves the effect of refining grains and improving elongation by increasing the aluminum content of the finished product, improving the performance of the finished product while also improving the formability, overcoming the cracking problem that ordinary dual-phase steel products are prone to when deep drawing at the end of bulging, and solving the problem that has long troubled users. DETAILED DESCRIPTION

[0016] The present invention will be further described in detail below in conjunction with specific embodiments.

[0017] The converter in each embodiment is 250t, the LF refining is 260t, and the thickness of the conventional slab continuous casting machine is 230mm. Example 1

[0018] A low-cost smelting method for enhancing the formability of dual-phase steel comprises the following steps: (1) Decarbonization converter smelting: automatic steelmaking model is adopted, the final slag basicity is 3.2; the mass percentage of the components at the smelting end point is: C: 0.04%, S: 0.008%, P: 0.020%; the end point temperature is 1660℃; the whole process is argon blowing at the bottom, the steel is tapped without inverting the furnace, the ladle is protected by bottom blowing argon before tapping, the steel flow is rounded during the tapping process, the tapping time is 3 minutes, aluminum particles are added after tapping, the oxygen content of the molten steel is 500ppm, and the nitrogen content is 25ppm.

[0019] (2) LF furnace refining: Aluminum particles and aluminum wires are added 8 minutes before refining for double deoxidation to achieve rapid white slag production. The outgoing slag has a content of FeO+MnO=1%; the slag layer thickness is 20 mm. During the smelting process, the foaming agent CaC2 is continuously added to expand and foam the slag to isolate the air, thus playing a dual role in protecting the slag and reducing the amount of nitrogen added during the LF process. The nitrogen content at the LF endpoint is 30 ppm.

[0020] (3) Slab continuous casting: Slab continuous casting machine with a thickness of 230mm is used. The ladle slag detection system is used to avoid slag. The continuous casting tundish adopts slag retaining wall and slag retaining weir. The tundish uses carbon-free magnesium refractory, aluminum-carbon argon blowing upper water inlet, carbon-free low-silicon covering agent, and the tundish is based on not exposing the molten steel. The ladle water inlet is argon-sealed for protection pouring, and an immersed water inlet is used to ensure that the slag does not enter the tundish. The ladle casing, stopper rod, water inlet, and plate space are argon-blown for protection pouring; the immersed water inlet is used to prevent slag rolling; the continuous casting constant pulling speed is controlled at 1.3m / min; the liquid level fluctuation automatic control system is used; the molten steel superheat is 15℃; the continuous casting slab T[O]: 17ppm, N content 40ppm. The high formability iron horse duplex steel n value obtained after rolling the continuous casting slab is 0.22. Example 2

[0021] A low-cost smelting method for enhancing the formability of dual-phase steel comprises the following steps: (1) Decarbonization converter smelting: automatic steelmaking model is adopted, the final slag basicity is 3.6; the mass percentage of the components at the end of smelting is: C: 0.06%, S: 0.006%, P: 0.018%; the end temperature is 1630℃; the whole process is argon-blown smelting, the steel is tapped without inverting the furnace, the ladle is bottom-blown with argon protection before tapping, the steel flow is rounded during the tapping process, the tapping time is 3.2 minutes, aluminum particles are added after tapping, the oxygen content of the molten steel is 350ppm, and the nitrogen content is 24ppm.

[0022] (2) LF furnace refining: Aluminum particles and aluminum wires are added 8 minutes before refining for double deoxidation to achieve rapid white slag production. The outgoing slag has a content of FeO+MnO=0.9%; the slag layer thickness is 15 mm. During the smelting process, the foaming agent CaC2 is continuously added to expand and foam the slag to isolate the air, thus playing a dual role in protecting the slag and reducing the amount of nitrogen added during the LF process. The nitrogen content at the LF endpoint is 25 ppm.

[0023] (3) Slab continuous casting: Slab continuous casting machine with a thickness of 230mm is used. The ladle slag detection system is used to avoid slag. The continuous casting tundish adopts slag retaining wall and slag retaining weir. The tundish uses carbon-free magnesium refractory, aluminum-carbon argon blowing upper water inlet, carbon-free low-silicon covering agent, and the tundish is based on not exposing the molten steel. The ladle water inlet is argon-sealed for protection pouring, and an immersed water inlet is used to ensure that the slag does not enter the tundish. The ladle casing, stopper rod, water inlet, and plate space are argon-blown for protection pouring; the immersed water inlet is used to prevent slag rolling; the continuous casting constant pulling speed is controlled at 1.4m / min; the liquid level fluctuation automatic control system is used; the molten steel superheat is 25℃; the continuous casting slab T[O]: 30ppm, N content 35ppm. The high formability iron horse duplex steel n value obtained after rolling the continuous casting slab is 0.24. Example 3

[0024] A low-cost smelting method for enhancing the formability of iron-horse dual-phase steel comprises the following steps: (1) Decarbonization converter smelting: automatic steelmaking model was adopted, and the final slag basicity was 3.4; the mass percentage of the components at the end of smelting was: C: 0.05%, S: 0.007%, P: 0.019%; the end temperature was 1640℃; argon was blown from the bottom of the smelting process, and the steel was tapped without inverting the furnace. The ladle was bottom-blown with argon before tapping, and the steel flow was rounded during the tapping process. The tapping time was 3.1 min. Aluminum particles were added after tapping. The oxygen content of the molten steel was 450ppm, and the nitrogen content was 22ppm.

[0025] (2) LF furnace refining: Aluminum particles and aluminum wires are added 8 minutes before refining for double deoxidation to achieve rapid white slag production. The outgoing slag has FeO+MnO=0.6%; the slag layer thickness is 16 mm. During the smelting process, the foaming agent CaC2 is continuously added to expand and foam the slag to isolate the air, which plays a dual role in protection and reduces the amount of nitrogen added during the LF process. The nitrogen content at the LF endpoint is 27 ppm.

[0026] (3) Slab continuous casting: Slab continuous casting machine with a thickness of 230mm is used. The ladle slag detection system is used to avoid slag. The continuous casting tundish adopts slag retaining wall and slag retaining weir. The tundish uses carbon-free magnesium refractory, aluminum-carbon argon blowing upper water inlet, carbon-free low-silicon covering agent, and the tundish is based on not exposing the molten steel. The ladle water inlet is argon-sealed for protection pouring, and an immersed water inlet is used to ensure that the slag does not enter the tundish. The ladle casing, stopper rod, water inlet, and plate space are argon-blown for protection pouring; the immersed water inlet is used to prevent slag rolling; the continuous casting constant pulling speed is controlled at 1.35m / min; the liquid level fluctuation automatic control system is used; the molten steel superheat is 20℃; the continuous casting slab T[O]: 27ppm, N content 33ppm. The high formability iron horse duplex steel n value obtained after rolling the continuous casting slab is 0.23. Example 4

[0027] A low-cost smelting method for enhancing the formability of iron-horse dual-phase steel comprises the following steps: (1) Decarbonization converter smelting: automatic steelmaking model is adopted, the final slag basicity is 3.5; the mass percentage of the components at the end of smelting is: C: 0.05%, S: 0.006%, P: 0.018%; the end temperature is 1650℃; the whole process is argon-blown smelting, the steel is tapped without inverting the furnace, the ladle is protected by bottom blowing argon before tapping, the steel flow is rounded during the tapping process, the tapping time is 3.4 minutes, aluminum particles are added after tapping, the oxygen content of the molten steel is 430ppm, and the nitrogen content is 23ppm.

[0028] (2) LF furnace refining: Aluminum particles and aluminum wires are added 8 minutes before refining for double deoxidation to achieve rapid white slag production. The outgoing slag has a FeO+MnO content of 0.7%; the slag layer thickness is 19 mm. During the smelting process, the foaming agent CaC2 is continuously added to expand and foam the slag to isolate the air, which plays a dual role in protecting the slag and reducing the amount of nitrogen added during the LF process. The nitrogen content at the LF endpoint is 27 ppm.

[0029] (3) Slab continuous casting: Slab continuous casting machine with a thickness of 230mm is used. The ladle slag detection system is used to avoid slag. The continuous casting tundish adopts slag retaining wall and slag retaining weir. The tundish uses carbon-free magnesium refractory, aluminum-carbon argon blowing upper water inlet, carbon-free low-silicon covering agent, and the tundish is based on not exposing the molten steel. The ladle water inlet is argon-sealed for protection pouring, and an immersed water inlet is used to ensure that the slag does not enter the tundish. The ladle casing, stopper rod, water inlet, and plate space are argon-blown for protection pouring; the immersed water inlet is used to prevent slag rolling; the continuous casting constant pulling speed is controlled at 1.4m / min; the liquid level fluctuation automatic control system is used; the molten steel superheat is 22℃; the continuous casting slab T[O]: 25ppm, N content 34ppm. The high formability iron horse duplex steel n value obtained after rolling the continuous casting slab is 0.22. Example 5

[0030] A low-cost smelting method for enhancing the formability of iron-horse dual-phase steel comprises the following steps: (1) Decarbonization converter smelting: automatic steelmaking model is adopted, the final slag basicity is 3.3; the mass percentage of the components at the end of smelting is: C: 0.06%, S: 0.007%, P: 0.019%; the end temperature is 1645℃; the whole process is argon-blown smelting, the steel is tapped without inverting the furnace, the ladle is bottom-blown with argon before tapping, the steel flow is rounded during the tapping process, the tapping time is 3.5 minutes, aluminum particles are added after tapping, the oxygen content of the molten steel is 370ppm, and the nitrogen content is 21ppm.

[0031] (2) LF furnace refining: Aluminum particles and aluminum wires are added 8 minutes before refining for double deoxidation to achieve rapid white slag production. The outgoing slag has a FeO+MnO content of 0.8%; the slag layer thickness is 17 mm. During the smelting process, the foaming agent CaC2 is continuously added to expand and foam the slag to isolate the air, which plays a dual role in protecting the slag and reducing the amount of nitrogen added during the LF process. The nitrogen content at the LF endpoint is 24 ppm.

[0032] (3) Slab continuous casting: Slab continuous casting machine with a thickness of 230mm is used. The ladle slag detection system is used to avoid slag. The continuous casting tundish adopts slag retaining wall and slag retaining weir. The tundish uses carbon-free magnesium refractory, aluminum-carbon argon blowing upper water inlet, carbon-free low-silicon covering agent, and the tundish is based on not exposing the molten steel. The ladle water inlet is argon-sealed for protection pouring, and an immersed water inlet is used to ensure that the slag does not enter the tundish. The ladle casing, stopper rod, water inlet, and plate space are argon-blown for protection pouring; the immersed water inlet is used to prevent slag rolling; the continuous casting constant pulling speed is controlled at 1.35m / min; the liquid level fluctuation automatic control system is used; the molten steel superheat is 17℃; the continuous casting slab T[O]: 22ppm, N content 32ppm. The high formability iron horse duplex steel n value obtained after rolling the continuous casting slab is 0.24.

[0033] The chemical composition of the dual-phase steel of Examples 1-5 is shown in Table 1, and the chemical composition of the carbon-free low-silicon covering agent is shown in Table 2.

[0034] Table 1 Chemical composition and mass percentage of dual-phase steel of Examples 1-5 (%)

[0035] The balance of the components in Table 1 is iron and unavoidable impurities.

[0036] It can be seen from the above embodiments that, compared with the traditional process flow BOF+LF+RH+CC, the present invention omits the RH refining process, and by strictly controlling the process parameters of each process, the nitrogen content of the molten steel is controlled within 0.0040%, which fully meets the hot stamping requirements and effectively reduces the production cost; and the formability is enhanced by adding 0.500-0.700% of acid-soluble aluminum.

[0037] Table 2 Chemical composition and mass percentage of carbon-free and low-silicon covering agent (%)

[0038] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention is described in detail with reference to the above embodiments, those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. Any modification or partial replacement that does not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A low-cost smelting method for enhancing the formability of dual-phase steel, characterized in that: The smelting method comprises the following steps: (1) Decarburization converter: The mass percentage of the components of the molten steel at the end of smelting is: C: 0.04-0.06%, S≤0.008%, P≤0.020%; aluminum particles are added after steel is tapped, the oxygen content of the molten steel is 350-500ppm, and the nitrogen content is ≤25ppm; (2) LF furnace refining: 8 minutes before refining, aluminum particles and aluminum wire are added for double deoxidation to achieve rapid white slag production, and the outgoing slag FeO+MnO≤1%; (3) Slab continuous casting: Add carbon-free and low-silicon covering agent to ensure that the molten steel is not exposed; the continuous casting constant speed is controlled at 1.3-1.4m / min; the superheat of the molten steel in the tundish is 15-25℃.

2. A low-cost smelting method for enhancing formability of dual-phase steel according to claim 1, characterized in that: In the step (1), the final slag basicity is 3.2-3.6; the terminal temperature is 1630-1660°C; argon is blown from the bottom throughout the smelting process, the steel is tapped without inverting the furnace, argon is blown from the bottom of the ladle before tapping, the steel flow is rounded during the tapping process, and the tapping time is ≥3 minutes.

3. A low-cost smelting method for enhancing formability of dual-phase steel according to claim 1, characterized in that: In the step (2), a thick slag layer of 15-20 mm is used, and the foaming agent CaC2 is continuously added during the smelting process to foam the molten steel to provide double protection, ensuring that the nitrogen content at the LF endpoint is ≤30 ppm.

4. A low-cost smelting method for enhancing formability of dual-phase steel according to claim 1, characterized in that: In the step (3), the T[O] content in the continuous casting slab is ≤30ppm, the N content is ≤40ppm, and the acid-soluble aluminum content ranges from 0.500% to 0.700%.

5. The smelting method of a low-cost enhanced formability dual-phase steel according to claim 1, characterized in that: In the step (3), a ladle slag detection system is used, and argon gas is blown between the ladle casing, stopper rod, water outlet, and plates to protect the pouring, and an immersed water outlet is used, and an automatic control system for liquid level fluctuation is used.

6. A smelting method of low-cost enhanced formability dual-phase steel according to any one of claims 1 to 5, characterized in that: The chemical composition and mass percentage of the dual-phase steel are: C: 0.13-0.18%, Mn: 1.50-1.80%, S≤0.005%, P≤0.025%, Si: 0.30-0.50%, Als: 0.500-0.700%, N≤0.0040%, and the balance is iron and unavoidable impurities.

7. A smelting method of low-cost enhanced formability dual-phase steel according to any one of claims 1 to 5, characterized in that: In the step (3), the chemical composition of the carbon-free and low-silicon covering agent is as follows: CaO: 40-50%, SiO2: 5-10%, Al2O3: 30-35%, MgO≤5.0%, F≤5.0%, Fe2O3≤3.0%.

8. A method for smelting low-cost enhanced formability dual-phase steel according to any one of claims 1 to 5, characterized in that: The high-formability dual-phase steel with an n value of 0.22-0.24 is obtained by the smelting method.

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