A method of smelting a wheel steel

Abstract

This application discloses a method for smelting wheel steel, relating to the field of iron and steel smelting technology. This method achieves deep purification of molten steel by reducing the introduction of harmful elements and foreign inclusions. Through the modification treatment of inclusions, fatigue cracks can be effectively eliminated; simultaneously, combined with weak cooling and long-term slow cooling processes, the billet microstructure can be homogenized and internal stress released, thereby significantly improving the cleanliness, density, and mechanical property stability of the wheel steel. Wheel steel prepared using this method has low inclusion content, uniform morphology, low gas content, no obvious segregation in the microstructure, high product flaw detection pass rate, and significantly improved fatigue life and service safety, meeting the stringent requirements for high-end railway wheel steel.

Description

Technical Field

[0001] This application belongs to the field of iron and steel smelting technology, and particularly relates to a method for smelting wheel steel. Background Technology

[0002] As a key material in railway transportation systems, the cleanliness of wheel steel directly affects the performance and service life of wheels. In the traditional wheel steel manufacturing process, due to limitations in smelting and continuous casting processes, various inclusions often exist in the steel, such as oxides, sulfides, and nitrides. These inclusions significantly reduce the fatigue life and mechanical properties of wheel steel. Therefore, improving the cleanliness of wheel steel and reducing the inclusion content is an urgent problem to be solved in the current iron and steel metallurgy field. Summary of the Invention

[0003] To address some or all of the technical problems existing in the prior art, this application provides a method for smelting wheel steel.

[0004] This application provides a method for smelting wheel steel, which includes, in sequence, electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, and slow cooling of the billet, comprising the following steps: Step S1, Electric furnace smelting: Use raw materials with an iron content of ≥85% for smelting, control the carbon content at the end of the electric furnace to be 0.12%~0.40%, phosphorus content ≤0.008%, sulfur content ≤0.05%, and tapping temperature to be 1640℃~1685℃, to avoid over-oxidation of molten steel, and carry out post-furnace slag formation during the tapping process of the electric furnace. Step S2, LF refining: Refining is carried out using lime-saturated slag system. Lime and calcium carbide are added according to the composition of the first sample taken in the LF process to control the composition of the reducing slag. Only aluminum alloys are added in the middle and later stages of refining to control the amount of aluminum added per furnace and the aluminum content in the steel when the LF leaves the station. Step S3, VD vacuum treatment: Under high vacuum conditions, heat and pressure are maintained for 10 to 30 minutes to remove gas from the steel; after breaking the vacuum, silicon-calcium wire, sulfur-cored wire and rare earth wire are fed in sequence to modify the inclusions in the steel and purify the molten steel. Step S4, Continuous Casting and Slow Cooling of Billet: The continuous casting process adopts full-process protective pouring, and the water flow rate of the crystallizer and the water volume of the secondary cooling are controlled; after the billet is removed from the line, it is moved into the slow cooling pit for heat preservation and slow cooling, and the slow cooling time and the billet exiting the pit temperature are controlled.

[0005] Preferably, in step S1, during the slag-making process after the electric furnace, the amount of lime added is 600kg to 800kg, the amount of synthetic slag added is 200kg to 300kg, the amount of fluorite added is 200kg to 250kg, and the amount of aluminum shot added is 30kg to 50kg.

[0006] Preferably, in step S2, based on the carbon and silicon content of the first LF sample, 200kg-600kg of lime and 200kg-250kg of calcium carbide are added; the composition of the reduction slag is controlled as follows: binary basicity R2=(CaO):(SiO2)≥4.0, slag system matching index MI=R2:Al2O3>0.35, and FeO content in the slag<0.5%.

[0007] Preferably, in step S2, the total amount of aluminum added in a single furnace is ≤80kg, and the aluminum content in the steel when the LF leaves the station is controlled to be 0.010%~0.030%.

[0008] Preferably, in step S3, the amount of silicon-calcium wire fed is 0.2m / ton to 1m / ton.

[0009] Preferably, in step S4, the crystallizer water flow rate is controlled at 3000L / min / flow to 3200L / min / flow, and the secondary cooling water flow rate is controlled at 0.28L / kg.

[0010] Preferably, in step S4, the slow cooling time of the billet is ≥36h, and the surface temperature of the billet when it leaves the slow cooling pit is ≤200℃.

[0011] The smelting method for wheel steel in this application has the following advantages and positive effects: By reducing the introduction of harmful elements and foreign inclusions into the steel, deep purification of molten steel is achieved. Modification treatment of inclusions effectively eliminates fatigue cracks; simultaneously, combined with weak cooling and prolonged slow cooling processes, the billet microstructure is homogenized and internal stress is released, thereby significantly improving the cleanliness, density, and mechanical property stability of wheel steel. Wheel steel prepared using the method described in this application has low inclusion content, uniform morphology, low gas content, no obvious segregation in the microstructure, high product flaw detection pass rate, and significantly improved fatigue life and service safety, meeting the stringent requirements for high-end railway wheel steel. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0013] This application provides a method for smelting wheel steel, comprising the following steps: Step S1, Electric Furnace Smelting: Raw materials with an iron content of ≥85% are used for smelting. The carbon content at the end of the electric furnace is controlled at 0.12%~0.40% to maintain a reasonable carbon content and avoid over-oxidation of the molten steel; the phosphorus content is ≤0.008% and the sulfur content is ≤0.05% to control the content of harmful elements and inhibit segregation and precipitation of brittle phases; the tapping temperature is 1640℃~1685℃ to ensure the fluidity of the molten steel and the stability of the subsequent refining temperature window to avoid over-oxidation of the molten steel. Slag formation is carried out after the furnace during the tapping process of the electric furnace.

[0014] During the slag-making process after the electric furnace, the amount of lime added is 600kg to 800kg, the amount of synthetic slag added is 200kg to 300kg, the amount of fluorite added is 200kg to 250kg, and the amount of aluminum shot added is 30kg to 50kg.

[0015] Step S2, LF Refining: Refining is carried out using a lime-saturated slag system to form a high-basicity, strongly reducing refining slag, achieving deep deoxidation and desulfurization. Based on the composition of the initial LF process sample, lime and calcium carbide are added (200kg-600kg lime and 200kg-250kg calcium carbide are added based on the carbon and silicon content of the initial LF sample). The reducing slag composition is controlled as follows: binary basicity R2 = (CaO):(SiO2) ≥ 4.0, enhancing desulfurization capacity and inhibiting the reversion of sulfur and phosphorus in the molten steel; slag system matching index MI = R2:Al2O3 > 0.35; FeO content in the slag < 0.5%, significantly reducing the formation of brittle oxides and improving the plasticity and cleanliness of the molten steel. In the later stages of refining, only aluminum alloys are added to stabilize deoxidation and avoid over-deoxidation. Control the amount of aluminum added per furnace (total amount of aluminum added per furnace ≤ 80 kg) and the aluminum content in the steel when the LF leaves the station. The aluminum content in the steel when the LF leaves the station should be controlled at 0.010% to 0.030% to maintain sufficient deoxidation strength.

[0016] Step S3, VD vacuum treatment: Under high vacuum conditions, maintain temperature and pressure for 10 min to 30 min to remove gas from the steel; after breaking the vacuum, feed in silicon-calcium wire, sulfur-cored wire and rare earth wire in sequence to modify the inclusions in the steel and purify the molten steel; the amount of silicon-calcium wire fed in is 0.2 m / ton to 1 m / ton.

[0017] Step S4, Continuous Casting and Slow Cooling of the Billet: The continuous casting process employs full-process protective pouring to isolate the steel from air and prevent secondary oxidation. The flow rate of the crystallizer water and the secondary cooling water ratio are controlled. The crystallizer water flow rate is controlled at 3000 L / min / flow to 3200 L / min / flow to ensure uniform billet shell growth, reduce surface cracks, depressions, and internal porosity, and improve the surface quality of the billet. The secondary cooling water ratio is controlled at 0.28 L / kg to reduce cooling intensity, decrease the temperature gradient and internal stress within the billet, suppress center segregation, shrinkage cavities, and cracks, resulting in a more uniform billet microstructure. After the billet leaves the casting line, it is moved to a slow cooling pit for heat preservation and slow cooling. The slow cooling time and the billet's exit temperature are controlled, with a slow cooling time ≥36 hours and a billet surface temperature ≤200℃ upon exiting the pit. This slowly releases internal stress and promotes a uniform microstructure.

[0018] This application provides a specific embodiment.

[0019] The steel grade used in this embodiment is ER7 high-speed railway wheel steel, with a steel output of 80 tons, and the process is carried out according to the following steps: Step S1, Electric Furnace Smelting: The raw materials with an iron content of 88.0% are used for smelting, and a small amount of high-quality scrap steel without harmful elements is added; the carbon content at the end of the electric furnace is controlled at 0.3342%, the phosphorus content at 0.0079%, the sulfur content at 0.0205%, and the tapping temperature at 1640℃~1685℃; slag making is carried out simultaneously during the tapping process of the electric furnace, with 781kg of lime, 262kg of synthetic slag, 226kg of fluorite, and 64kg of aluminum shot added.

[0020] Step S2, LF Refining: Refining is carried out using a lime-saturated slag system; the first sampling is conducted in the LF process, and lime and calcium carbide are added according to the carbon and silicon content obtained from the sampling; the composition of the reducing slag is controlled as follows: CaO content is 62%, SiO2 content is 6.1%, Al2O3 content is 23.1%, FeO content is 0.81%, binary basicity R2=(CaO):(SiO2)=10.16, slag system matching index MI=R2:Al2O3=0.43; only aluminum alloys are added in the later stages of refining, and the aluminum content in the steel is controlled to be 0.0275% when leaving the LF station.

[0021] Step S3, VD vacuum treatment: Under vacuum conditions ≤67Pa, heat and pressure are maintained for 17 minutes to remove hydrogen and nitrogen gases from the steel; after breaking the vacuum, 60m of silicon-calcium wire (80 tons of molten steel) is fed in, followed by rare earth wire to modify inclusions in the steel and purify the molten steel.

[0022] Step S4, Continuous Casting and Slow Cooling of Billet: The continuous casting process adopts full-process protective pouring; the water flow rate of the three-strand crystallizer is controlled at 3047L / min~3088L / min, and the secondary cooling water flow rate is 0.28L / kg; after the billet leaves the line, it is immediately moved into the slow cooling pit for heat preservation and slow cooling for 36 hours. When the billet leaves the slow cooling pit, the surface temperature is 192℃. Flame cleaning is not used after slow cooling.

[0023] The wheel steel smelted according to the method of this embodiment has low inclusion content, uniform morphology, high steel cleanliness, significantly improved mechanical properties and fatigue life, and a φ1mm flaw detection pass rate of 99%.

[0024] This application achieves deep purification of molten steel by reducing the introduction of harmful elements and foreign inclusions. Through the modification treatment of inclusions, fatigue cracks can be effectively eliminated. Simultaneously, combined with weak cooling and prolonged slow cooling processes, the billet microstructure can be homogenized and internal stress released, thereby significantly improving the cleanliness, density, and mechanical property stability of the wheel steel. Wheel steel prepared using the method of this application has low inclusion content, uniform morphology, low gas content, no obvious segregation in the microstructure, high product flaw detection pass rate, and significantly improved fatigue life and service safety, meeting the stringent requirements for high-end railway wheel steel.

[0025] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method for smelting wheel steel, comprising, in sequence, electric furnace smelting, LF refining, VD vacuum treatment, continuous casting, and slow cooling of the cast billet, characterized in that, Includes the following steps: Step S1, Electric furnace smelting: Use raw materials with an iron content of ≥85% for smelting, control the carbon content at the end of the electric furnace to be 0.12%~0.40%, phosphorus content ≤0.008%, sulfur content ≤0.05%, and tapping temperature to be 1640℃~1685℃, to avoid over-oxidation of molten steel, and carry out post-furnace slag formation during the tapping process of the electric furnace. Step S2, LF refining: Refining is carried out using lime-saturated slag system. Lime and calcium carbide are added according to the composition of the first sample taken in the LF process to control the composition of the reducing slag. Only aluminum alloys are added in the middle and later stages of refining to control the amount of aluminum added per furnace and the aluminum content in the steel when the LF leaves the station. Step S3, VD vacuum treatment: Under high vacuum conditions, heat and pressure are maintained for 10 to 30 minutes to remove gas from the steel; after breaking the vacuum, silicon-calcium wire, sulfur-cored wire and rare earth wire are fed in sequence to modify the inclusions in the steel and purify the molten steel. Step S4, Continuous Casting and Slow Cooling of Billet: The continuous casting process adopts full-process protective pouring, and the water flow rate of the crystallizer and the water volume of the secondary cooling are controlled; after the billet is removed from the line, it is moved into the slow cooling pit for heat preservation and slow cooling, and the slow cooling time and the billet exiting the pit temperature are controlled.

2. The method for smelting wheel steel according to claim 1, characterized in that, In step S1, during the slag-making process after the electric furnace, the amount of lime added is 600kg to 800kg, the amount of synthetic slag added is 200kg to 300kg, the amount of fluorite added is 200kg to 250kg, and the amount of aluminum shot added is 30kg to 50kg.

3. The method for smelting wheel steel according to claim 1, characterized in that, In step S2, based on the carbon and silicon content of the first LF sample, 200kg-600kg of lime and 200kg-250kg of calcium carbide are added; the composition of the reduction slag is controlled as follows: binary basicity R2=(CaO):(SiO2)≥4.0, slag system matching index MI=R2:Al2O3>0.35, and FeO content in the slag<0.5%.

4. The method for smelting wheel steel according to claim 1, characterized in that, In step S2, the total amount of aluminum added in a single furnace is ≤80kg, and the aluminum content in the steel when the LF leaves the station is controlled at 0.010%~0.030%.

5. The method for smelting wheel steel according to claim 1, characterized in that, In step S3, the amount of silicon-calcium wire fed in is 0.2m / ton to 1m / ton.

6. The method for smelting wheel steel according to claim 1, characterized in that, In step S4, the crystallizer water flow rate is controlled at 3000L / min / flow to 3200L / min / flow, and the secondary cooling water flow rate is controlled at 0.28L / kg.

7. The method for smelting wheel steel according to claim 1, characterized in that, In step S4, the slow cooling time of the billet is ≥36h, and the surface temperature of the billet is ≤200℃ when it leaves the slow cooling pit.