Smelting method for improving purity of tire cord steel

Abstract

The invention discloses a smelting method for improving the purity of tire cord steel. The method specifically comprises the following steps: (1) electric furnace smelting: controlling the phosphorus content Plt in steel; the tapping temperature is 1650-1680 DEG C, and a deoxidizing agent and refining slag are added in the tapping process; (2) primary LF refining: carrying out diffusion deoxidation by adopting high-purity silicon carbide, and controlling the temperature of refined molten steel to be 1600-1650 DEG C and the sulfur content in the steel to be Slt; 0.005% of the total amount of the raw materials; (3) slagging-off treatment is conducted, specifically, a slag layer obtained after primary LF refining is removed; (4) secondary LF refining: controlling the ratio of CaO to SiO in refining slag to be 0.8-1.2 and the ratio of Al2O3 to be 1t; the temperature of the molten steel is 1550-1600 DEG C; (5) VD vacuum treatment is conducted, specifically, the vacuum degree ranges from 300 KPa to 500 KPa, the holding time ranges from 20 min to 30 min, and the argon flow ranges from 80 NL / min to 120 NL / min; (6) argon stirring is conducted after vacuum breaking, wherein the stirring time is 20-30 min, and the argon flow is 40-60 NL / min; according to the method, the purity of the molten steel can be remarkably improved, and the content of Al2O3 in inclusions in the steel can be effectively reduced.

Description

Technical Field

[0001] The invention relates to a smelting method for improving the purity of cord steel, and belongs to the field of purity control in molten steel smelting process. Background Art

[0002] Cord steel is a special steel wire material made of high carbon steel. Its core use is concentrated in the field of reinforcing rubber products, especially playing a key role in tire manufacturing. In recent years, driven by favorable factors such as engineering machinery, automobile industry, and highways, my country's tire industry has achieved rapid development, and the consumption of steel cord has continued to increase, while promoting the rapid development of the steel cord wire rod industry. At the same time as China has become the world's largest automobile market, the cord industry has also developed by leaps and bounds, with basic output accounting for more than half of the global market.

[0003] Cord steel is generally made by drawing Φ5.5-8mm wire rods into Φ0.15-0.38mm filaments, which are then twisted into wires. Since cord steel needs to be drawn into filaments, there are high requirements for the overall quality control of cord steel. In particular, the requirements for the cleanliness of cord steel are the most stringent. The number of inclusions in the steel must be controlled as little as possible. At the same time, there are strict requirements for the type, size and shape of inclusions in the steel. All of these make the production of cord steel more difficult. The deformation ability of inclusions can be characterized by plastic deformation. The main factor affecting the plastic deformation of non-metallic inclusions is their melting point, and the melting point has a certain relationship with the composition of the inclusions, especially Al in the inclusions. 2 O 3 The content of Al in inclusions 2 O 3 The less the content, the more conducive it is to the later processing of the cord steel. Traditional inclusion control methods often focus on the control of the number and size of inclusions, and largely ignore the control of the composition of inclusions. This limitation makes it difficult to effectively reduce the content of Al2O3 in cord steel inclusions in actual production, which in turn affects the processing performance of cord steel. Due to the working conditions and safety performance requirements of ultra-high strength cord steel, its purity is very high. Inclusions larger than 15μm are not allowed to exist, and inclusions are required to be plastic. The main problem in the current domestic production of ultra-high strength cord steel is that the number of inclusions and the stability of inclusion control are poor, which seriously affects the quality level of cord steel. Therefore, it is necessary to develop a stable production method for high-purity cord steel and Al2O3 in inclusions. 2 O 3 The control method of low content is of great significance. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a smelting method for improving the purity of cord steel in view of the shortcomings of the above prior art, which can significantly improve the purity of molten steel and effectively reduce the Al content in the inclusions in the steel.2 O 3 content.

[0005] The technical solution of the present invention to solve the above technical problems is: a smelting method for improving the purity of cord steel, the method specifically comprising the following steps: (1) Electric furnace smelting: Control the phosphorus content in the steel to be less than 0.010%, the tapping temperature to be 1650-1680°C, and add deoxidizer and refined slag during the tapping process; (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1600-1650℃, and the sulfur content in the steel is S<0.005%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: Controlling CaO / SiO in the refining slag 2 =0.8-1.2,Al 2 O 3 <3%, molten steel temperature 1550-1600℃; (5) VD vacuum treatment: vacuum degree 300-500KPa, holding time 20-30 minutes, argon flow rate 80-120NL / min; (6) Argon stirring after vacuum breaking: stirring time 20-30 minutes, argon flow rate 40-60NL / min.

[0006] The present invention further defines the scheme: Preferably, the CaO / SiO of the refined slag in step (1) is 2 =3-5,Al 2 O 3 <3%.

[0007] Preferably, the deoxidizer in step (1) includes at least one of ferrosilicon, aluminum or silicon carbide.

[0008] Preferably, the temperature of the molten steel in the secondary LF refining in step (4) is 1570-1600°C, and the CaO / SiO 2 =1.0-1.2.

[0009] Preferably, the oxygen content of the final molten steel is O≤15ppm, the number of 1-5μm inclusions is ≤15 / mm², and the Al content of the inclusions is 2 O 3 Content ≤15%.

[0010] The beneficial effects of the present invention are as follows: the present invention adopts electric furnace smelting - primary LF refining - slag removal - secondary LF refining - VD vacuum, the electric furnace smelting controls the P content in the steel and the temperature of the molten steel, the primary LF refining controls the CaO / SiO content in the refined slag 2、Al 2 O 3 content and molten steel temperature and S content in steel; the molten steel is subjected to secondary LF refining after slag treatment, and the CaO / SiO ratio of the refined slag is controlled 2 、Al 2 O 3 content and temperature of molten steel; the molten steel is subjected to VD vacuum treatment, and the type of inclusions is adjusted by vacuum degree, vacuum holding time and argon flow rate; after vacuum breaking, argon is used for stirring, and inclusions are removed by controlling stirring time and argon flow rate; The present invention controls the CaO / SiO ratio of the slag in stages. 2 and Al 2 O 3 content; two LF refining combined with slag removal to remove harmful inclusions; VD vacuum treatment and argon stirring work together to accurately control the composition of inclusions, which can significantly improve the purity of molten steel and effectively reduce Al in inclusions in steel. 2 O 3 Content, so that the number of 1-5μm inclusions ≤ 15 / mm², Al in the inclusions 2 O 3 Content ≤15%. DETAILED DESCRIPTION Example

[0011] This embodiment provides a smelting method for improving the purity of cord steel, and the method specifically comprises the following steps: (1) Electric furnace smelting: The phosphorus content in the steel is controlled to be 0.008%, the tapping temperature is 1680℃, deoxidizer and refined slag are added during the tapping process, and the CaO / SiO 2 =5,Al 2 O 3 The deoxidizer is a mixture of ferrosilicon and silicon carbide. (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1650°C, and the sulfur content S in the steel is 0.004%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: Controlling CaO / SiO in the refining slag 2 =0.8,Al 2 O 3 2%, molten steel temperature 1600℃; (5) VD vacuum treatment: vacuum degree 300 KPa, holding time 30 minutes, argon flow rate 120 NL / min; (6) Argon stirring after vacuum breaking: stirring time 30 min, argon flow rate 60NL / min.

[0012] The smelting method can significantly improve the purity of molten steel, corresponding to the rolled product [O] of 10ppm and the number of 1-5μm inclusions of 6 / mm 2 , Al in inclusions 2 O 3 Content 10%. Example

[0013] This embodiment provides a smelting method for improving the purity of cord steel, and the method specifically comprises the following steps: (1) Electric furnace smelting: Control the phosphorus content in the steel to be less than 0.006%, the tapping temperature to 1650°C, add deoxidizer and refined slag during the tapping process, and the CaO / SiO 2 =3,Al 2 O 3 The content of ferrosilicon and silicon carbide is 2.5%, and the deoxidizer is a mixture of ferrosilicon and silicon carbide; (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1600°C, and the sulfur content S in the steel is 0.004%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: Controlling CaO / SiO in the refining slag 2 =1.2,Al 2 O 3 2.5%, molten steel temperature 1550℃; (5) VD vacuum treatment: vacuum degree 500 KPa, holding time 20 minutes, argon flow rate 80 NL / min; (6) Argon stirring after vacuum breaking: stirring time 20 min, argon flow rate 40NL / min.

[0014] The smelting method can significantly improve the purity of molten steel, corresponding to the rolled product [O] of 15ppm and the number of 1-5μm inclusions of 15 / mm. 2 , Al in inclusions 2 O 3 The content is 15%. Example

[0015] This embodiment provides a smelting method for improving the purity of cord steel, and the method specifically comprises the following steps: (1) Electric furnace smelting: The phosphorus content in the steel is controlled to be 0.009%, the tapping temperature is 1670℃, deoxidizer and refined slag are added during the tapping process, and the CaO / SiO 2 =4,Al 2 O 3 The content of ferrosilicon and silicon carbide is 2.5%, and the deoxidizer is a mixture of ferrosilicon and silicon carbide; (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1580°C, and the sulfur content S in the steel is 0.004%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: Controlling CaO / SiO in the refining slag 2 =1.0,Al 2 O 3 2.5%, molten steel temperature 1580℃; (5) VD vacuum treatment: vacuum degree 400 KPa, holding time 25 minutes, argon flow rate 100 NL / min; (6) Argon stirring after vacuum breaking: stirring time 25 min, argon flow rate 50 NL / min.

[0016] The smelting method can significantly improve the purity of molten steel, corresponding to the rolled product [O] of 13ppm, and the number of 1~5μm inclusions of 12 / mm 2 , Al in inclusions 2 O 3 The content is 13%. Example

[0017] This embodiment provides a smelting method for improving the purity of cord steel, and the method specifically comprises the following steps: (1) Electric furnace smelting: The phosphorus content in the steel is controlled to be 0.008%, the tapping temperature is 1660℃, deoxidizer and refined slag are added during the tapping process, and the CaO / SiO 2 =3.5,Al 2 O 3 The content of ferrosilicon and silicon carbide is 2.5%, and the deoxidizer is a mixture of ferrosilicon and silicon carbide; (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1640°C, and the sulfur content S in the steel is 0.004%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: Controlling CaO / SiO in the refining slag 2 =0.9,Al 2 O 3 2%, molten steel temperature 1570℃; (5) VD vacuum treatment: vacuum degree 350KPa, holding time 20 minutes, argon flow rate 120NL / min; (6) Argon stirring after vacuum breaking: stirring time 30 min, argon flow rate 40NL / min.

[0018] The smelting method can significantly improve the purity of molten steel, corresponding to the rolled product [O] of 12ppm and the number of 1~5μm inclusions of 10 / mm 2 , Al in inclusions 2 O 3 The content is 12%.

[0019] In addition to the above embodiments, the present invention may also have other implementation modes. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present invention.

Claims

1. A smelting method for improving the purity of cord steel, characterized in that: The method specifically comprises the following steps: (1) Electric furnace smelting: Control the phosphorus content in the steel to be less than 0.010%, the tapping temperature to be 1650-1680°C, and add deoxidizer and refined slag during the tapping process; (2) Primary LF refining: high-purity silicon carbide diffusion deoxidation is used, the refined steel temperature is controlled at 1600-1650℃, and the sulfur content in the steel is S<0.005%; (3) Slag removal: removing the slag layer after primary LF refining; (4) Secondary LF refining: control the CaO / SiO2 of the refining slag to be 0.8-1.2, Al2O3 <3%, and the molten steel temperature to be 1550-1600℃; (5) VD vacuum treatment: vacuum degree 300-500KPa, holding time 20-30 minutes, argon flow rate 80-120NL / min; (6) Argon stirring after vacuum breaking: stirring time 20-30 minutes, argon flow rate 40-60NL / min.

2. A smelting method for improving the purity of cord steel according to claim 1, characterized in that: In the step (1), the CaO / SiO2 of the refined slag is 3-5, and Al2O3 is less than 3%.

3. A smelting method for improving the purity of cord steel according to claim 1, characterized in that: The deoxidizer in step (1) includes at least one of ferrosilicon, aluminum or silicon carbide.

4. A smelting method for improving the purity of cord steel according to claim 1, characterized in that: The temperature of the molten steel in the secondary LF refining in step (4) is 1570-1600°C, and the CaO / SiO2 of the refined slag is 1.0-1.

2.

5. A method for controlling the timing switching of a backup device according to claim 1, characterized in that: The oxygen content of the final molten steel is O≤15ppm, the number of 1-5μm inclusions is ≤15 / mm², and the Al2O3 content in the inclusions is ≤15%.