A method for controlling inclusions in low-basicity slag pure steel

Abstract

The invention discloses an inclusion control method for low-basicity slag pure steel. By optimizing the process links such as steel tapping oxygen content, steel tapping temperature control, ferrosilicon and alloy addition mechanism, LF refining end oxygen content, tundish setting, etc., the formation of large-sized inclusions in the pouring process is reduced, thereby reducing the total oxygen content and fracture inclusion size of the produced rolled material, and the purity of the steel is greatly improved.

Description

Technical Field

[0001] The invention relates to an inclusion control method for low-basicity slag pure steel, in particular to the control of large-size inclusions in spring steel and cord steel. Background Art

[0002] In the context of high-strengthening of spring steel and cord steel to achieve weight reduction and carbon reduction, occasional large-diameter inclusions in steel often seriously reduce the service stress of the steel, which is an important obstacle to the development of high-strengthening materials.

[0003] The mainstream steel industry processes for controlling the plasticization of inclusions in spring steel and cord steel mostly use low-basicity slag systems, silicon-manganese deoxidation, and aluminum-free, low-aluminum alloys, refractory materials, and auxiliary materials for production, which can basically achieve the control of the low melting point area of ​​the main inclusion composition. Due to the weak deoxidation ability of silicon-manganese, the TFe content in the final slag of refining is often high, the oxygen content in the steel is high and fluctuates greatly, and the number of inclusions is large. With the influence of turbulent flow of molten steel in the tundish during the pouring process, inclusions are very easy to collide, accumulate and grow, and large-sized inclusions are produced in the material, resulting in a significant decrease in the service stress of the finished product. Summary of the invention

[0004] In view of the above technical problems, the purpose of the present invention is to provide a novel inclusion control method for low-basicity slag clean steel, so as to reduce the formation of large-sized inclusions during the pouring process of low-basicity slag clean steel.

[0005] In order to achieve the above object, the present invention specifically adopts the following technical solutions:

[0006] A method for controlling inclusions in low-basicity slag clean steel, characterized by comprising:

[0007] BOF or EAF furnace tapping:

[0008] Control the oxygen content of steel tapping below 200ppm and the tapping temperature at 1580℃~1620℃ to ensure low oxygen tapping and prevent slag.

[0009] When 20 tons of steel is tapped, 40% of the total required amount of ferrosilicon and carburizer are added in sequence, and acidic slag is added before the end of tapping;

[0010] Keep blowing argon gas at the bottom for stirring during the steel tapping process, and continue blowing argon gas at the bottom for more than 5 minutes after the steel tapping is completed to promote alloy melting and deoxidation reaction;

[0011] LF furnace refining:

[0012] The refined slag is heated for 15 minutes. During the heating process, 60kg to 100kg of ferrosilicon powder is added in batches to the slag surface for diffusion deoxidation.

[0013] After slagging, when the refined slag reaches a translucent state, add 40% of the total amount of ferrosilicon and ferromanganese alloy, fully melt and take samples for analysis, and then fine-tune the composition to the target value; during the heating process, add a total of 20kg of ferrosilicon powder in batches to maintain the deoxidation effect and keep the refined slag translucent;

[0014] After refining, the oxygen value is set below 12ppm and the TFe content in the slag is below 3%;

[0015] Continuous Casting:

[0016] The tundish has no dam and adopts an integral nozzle for full protection casting.

[0017] Preferably, slightly acidic slag with a basicity of 0.9-1.0 is added before the end of steel tapping.

[0018] Preferably, a CaO-SiO2 based covering agent is used in the continuous casting process, and the TFe content is controlled below 1%.

[0019] Preferably, the bottom blowing argon gas flow rate is ≥500NL / min.

[0020] The beneficial effects of the present invention are:

[0021] Compared with the common process, the inclusion control method of low-basicity slag pure steel of the present invention reduces the TFe content of the final slag of the refined slag from about 5% to less than 3%, the oxygen value at the end of LF refining from about 15ppm to less than 12ppm, and the total oxygen content of the produced rolled product from about 15ppm to less than 10ppm. In the rotary bending fatigue test, the size of the fracture inclusions was reduced from an average of about 60μm to less than 40μm, and the purity of the steel was greatly improved. DETAILED DESCRIPTION Example 1

[0022] This embodiment provides a method for controlling inclusions in low-basicity slag pure steel. Taking 55SiCrA spring steel as an example, the method includes the following steps:

[0023] (1) BOF furnace steel production

[0024] The oxygen content of steel produced from a 100-ton BOF furnace is 180ppm and the steel producing temperature is 1604℃.

[0025] During the steel-tapping process, argon blowing and stirring at a speed of 500NL / min are maintained. When 20 tons of steel is tapped, 1000kg of ferrosilicon and 300kg of carbon powder are added. At the end of steel-tapping, 1000kg of slightly acidic refined slag with a basicity of 0.9-1.0 is added. After the steel-tapping is completed, argon blowing and stirring are continued for 6 minutes to promote alloy melting and deoxidation reaction.

[0026] (2) LF refining

[0027] Refining slag heating for 15 minutes, during the heating process, add ferrosilicon powder in three batches, a total of 80kg, to the slag surface. After slag melting, add 1000kg ferrosilicon, 1000kg ferromanganese, and 1000kg ferrochrome when the refined slag reaches translucent state. Continue heating for 5 minutes, take samples for analysis after full melting. Then continue to add alloy to fine-tune the composition to the target value. During the heating process, add about 20kg ferrosilicon powder in two batches to maintain the deoxidation effect and keep the refined slag translucent.

[0028] At the end of LF refining, the oxygen content was 10.5ppm. The final slag was analyzed and the TFe content was 2.4%.

[0029] (3) Continuous casting

[0030] The tundish has no dam, uses an integral nozzle, and fully protected casting. A CaO-SiO2 covering agent with a TFe content of 0.4% is used.

[0031] (4) Finished product analysis

[0032] The rolled material was sampled and analyzed, and the total oxygen content was 8.3ppm.

[0033] After heat treatment, the spring steel wire was subjected to a rotary bending fatigue test, and the maximum inclusion diameter at the fracture was 35 μm. Example 2

[0034] This embodiment provides a method for controlling inclusions in low-basicity slag pure steel. Taking 55SiCrV spring steel as an example, the method includes the following steps:

[0035] (1) EAF furnace tapping

[0036] The oxygen content of steel tapped from a 100-ton EAF furnace is 160ppm and the tapping temperature is 1587℃.

[0037] During the steel-tapping process, argon blowing and stirring at a rate of 550NL / min are maintained. When 20 tons of steel is tapped, 1000kg of ferrosilicon and 300kg of carbon powder are added. At the end of steel-tapping, 1000kg of slightly acidic refined slag with a basicity of 0.9-1.0 is added. After the steel-tapping is completed, argon blowing and stirring are continued for 6 minutes to promote alloy melting and deoxidation reaction.

[0038] (2) LF refining

[0039] Refining slag heating for 15 minutes, during the heating process, add 100kg of ferrosilicon powder in three batches to the slag surface, after slag melting, add 1000kg of ferrosilicon, 1000kg of ferromanganese, 1000kg of ferrochrome, and 250kg of ferrovanadium when the refined slag reaches translucent state. Continue heating for 5 minutes, take samples for analysis after full melting. Then continue to add alloy to fine-tune the composition to the target value, and add about 20kg of ferrosilicon powder in two batches during the heating process to maintain the deoxidation effect, and keep the refined slag translucent.

[0040] At the end of LF refining, the oxygen content was 10.2ppm. The final slag was analyzed and the TFe content was 1.9%.

[0041] (3) Continuous casting

[0042] The tundish has no dam, uses an integral nozzle, and fully protected casting. A CaO-SiO2 covering agent with a TFe content of 0.4% is used.

[0043] (4) Finished product analysis

[0044] The rolled material was sampled and analyzed, and the total oxygen content was 7.7ppm.

[0045] After heat treatment, the spring steel wire was subjected to a rotary bending fatigue test, and the maximum inclusion diameter at the fracture was 31 μm.

[0046] Comparative Example

[0047] This comparative example provides a common inclusion control method for 55SiCrA spring steel of Example 1, comprising the following steps:

[0048] (1) BOF furnace steel production

[0049] The oxygen content of steel produced from a 100-ton BOF furnace is 337ppm and the steel temperature is 1631℃.

[0050] During the steel-making process, argon blowing and stirring are maintained at a large speed of 500NL / min. When 20 tons of steel is tapped, 2000kg of ferrosilicon, 1000kg of ferromanganese, 1000kg of ferrochrome and 300kg of carbon powder are added. At the end of the steel-making process, 2000kg of slightly acidic refined slag is added.

[0051] (2) LF refining

[0052] During the LF refining slag heating process, 80 kg of silicon carbide was added in three batches, and samples were taken for analysis after heating for 20 minutes. Then, alloy was added to fine-tune the composition to the target value, and about 20 kg of silicon carbide was added in two batches during the heating process.

[0053] At the end of LF refining, the oxygen content was 17ppm and the final slag analysis showed that the TFe content was 4.1%.

[0054] (3) Continuous casting

[0055] The tundish is equipped with a dam to extend the residence time of the molten steel in the tundish, and an integral nozzle is used for full protection casting. An MgO-based covering agent with a TFe content of 2.2% is used.

[0056] (4) Finished product analysis

[0057] The rolled material was sampled and analyzed, and the total oxygen content was 14.5ppm.

[0058] After heat treatment, the spring steel wire was subjected to a rotary bending fatigue test, and the maximum inclusion diameter at the fracture was 83 μm.

[0059] By comparing the above Example 1 with the comparative example, it can be seen that the inclusion control method of low-basicity slag pure steel of the present invention reduces the formation of large-sized inclusions during the pouring process by optimizing the process links such as the oxygen content of steel tapping, steel tapping temperature control, ferrosilicon and alloy addition mechanism, the oxygen content at the end of LF refining, and the setting of the tundish, thereby reducing the total oxygen content of the rolled material and the size of the fracture inclusions, and greatly improving the purity of the steel.

[0060] 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 method for controlling inclusions in low-basicity slag pure steel, characterized in that include: BOF or EAF furnace tapping: Control the oxygen content of steel tapping below 200ppm and the tapping temperature at 1580℃~1620℃ to ensure low oxygen level steel tapping and prevent slag. When 20 tons of steel is tapped, 40% of the total required amount of ferrosilicon and carburizer are added in sequence, and acidic slag is added before the end of tapping; Keep blowing argon gas at the bottom for stirring during the steel tapping process, and continue blowing argon gas at the bottom for more than 5 minutes after the steel tapping is completed to promote alloy melting and deoxidation reaction; LF furnace refining: The refined slag is heated for 15 minutes. During the heating process, 60kg to 100kg of ferrosilicon powder is added in batches to the slag surface for diffusion deoxidation. After slagging, when the refined slag reaches a translucent state, add 40% of the total required amount of ferrosilicon and ferromanganese alloy, fully melt and take samples for analysis, and then fine-tune the composition to the target value; During the heating process, 20 kg of ferrosilicon powder was added in batches to maintain the deoxidation effect and keep the refined slag translucent; After refining, the oxygen value is set below 12ppm and the TFe content in the slag is below 3%; Continuous Casting: The tundish has no dam and adopts an integral nozzle for full protection casting.

2. The method for controlling inclusions in low-basicity slag clean steel according to claim 1, characterized in that Before the end of steel tapping, slightly acidic slag with a basicity of 0.9-1.0 is added.

3. The method for controlling inclusions in low-basicity slag clean steel according to claim 1, characterized in that The continuous casting process uses a CaO-SiO2 covering agent, and the TFe content is controlled below 1%.

4. The method for controlling inclusions in low-basicity slag clean steel according to claim 1, characterized in that The total oxygen content of the rolled product is less than 10ppm, and the inclusion size of the fracture surface in the rotary bending fatigue test is less than 40μm.

5. The method for controlling inclusions in low-basicity slag clean steel according to claim 1, characterized in that The maximum bottom blowing argon flow rate is ≥500NL / min.