Method for refining low-carbon low-sulfur steel through vacuum carbon deoxidation

Abstract

The invention discloses a method for refining low-carbon low-sulfur steel through vacuum carbon deoxidation, and relates to the technical field of molten steel external refining. The process method comprises the following steps: carrying out pre-deoxidation by adopting a carbon source alloy material without using a metal deoxidation material; vacuum carbon deoxidation treatment is carried out under the condition that the vacuum degree is smaller than or equal to 100 Pa; the flow of the stirring gas is controlled to be 0.2-1.0 NL / (t.min); controlling the vacuum holding time to be not more than 5 minutes and the vacuum period to be not more than 15 minutes; the method comprises the following steps: controlling the tapping temperature of a primary smelting furnace to be 1620-1680 DEG C; in the LF station refining process, the binary alkalinity of refining slag is controlled to be 5.0-8.0, and diffusion deoxidation and white slag making are conducted in cooperation with a metal deoxidizing agent; the low-carbon and low-sulfur steel is produced through organic combination of vacuum carbon deoxidation and LF refining on the premise that a metal deoxidation material is not used for pre-deoxidation, the total oxygen content in the steel can be controlled to be 15 ppm or below, and the sulfur content can be controlled to be 0.005% or below.

Description

Technical Field

[0001] This invention belongs to the field of ladle refining technology for molten steel, and relates to a method for controlling inclusions in steel through a vacuum carbon deoxidation process. Background Technology

[0002] Traditional methods of deoxidizing molten steel using metal deoxidizers generate solid deoxidation products during the process. These products tend to remain in the molten steel, forming inclusions and reducing the purity of the steel, making it difficult to meet the production requirements of low-carbon and low-sulfur steel. At the same time, the use of metal deoxidizers increases the content of impurity elements in the steel, affecting its mechanical and processing properties. Furthermore, in existing vacuum deoxidation processes, the efficiency of gas escape and inclusion flotation is not high, resulting in limited deoxidation effects. Moreover, improper control of process parameters can easily lead to secondary oxidation of the molten steel or incomplete deoxidation.

[0003] Industrial testing has verified (referencing GB / T 24234) that the current technical challenges in this field mainly lie in the difficulty of consistently controlling the total oxygen content below 15 ppm when the carbon content of the final molten steel is ≤0.03%, and the number density of Al2O3 inclusions exceeds 12 per mm². 2 In existing technologies, patent solutions under classification C21C7 / 10 employ a silicon-manganese pre-deoxidation combined with vacuum circulation degassing process, as described in the abstract "Controlling non-metallic inclusions through the synergistic effect of composite deoxidizer and vacuum...". However, under conditions of treating high-oxygen molten steel with an initial oxygen content >400ppm, this solution suffers from drawbacks: desulfurization efficiency fluctuates by more than 18% (measured data range 62%-80%), and the carbon increase in molten steel exceeds 0.015% during carbon injection and heating in vacuum treatment (deviating from the YB / T 4266 standard limit). Therefore, there is an urgent need to develop new carbon-oxygen control technologies to solve the aforementioned technical problems. Summary of the Invention

[0004] The present invention aims to provide a method for refining low-carbon and low-sulfur steel using vacuum carbon deoxidation. Without using metal deoxidizing materials for pre-deoxidation, low-carbon and low-sulfur steel is produced by organically combining vacuum carbon deoxidation and LF refining. The total oxygen content in the steel can be controlled below 15ppm and the sulfur content can be controlled below 0.005%.

[0005] The technical solution of the present invention: A method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation includes the following process steps: 1) When tapping steel from the primary refining furnace, carbon source alloy materials are used for pre-deoxidation and alloying. During the tapping process, 1.0-1.5 kg / t steel of carbon source alloy materials, 2.5-4.0 kg / t steel of lime, and 1.0-3.0 kg / t steel of refining slag are added. 2) After tapping the steel, the ladle is hoisted into the VD vacuum deoxidation station, where carbon and oxygen are reacted under vacuum conditions to generate gaseous deoxidation products; the vacuum carbon deoxidation treatment is carried out under vacuum conditions ≤100Pa, and the vacuum holding time does not exceed 5min. 3) During vacuum carbon deoxidation, control the flow rate of stirring gas to promote stirring of molten steel, accelerate gas escape and the floating of inclusions. After breaking the vacuum, hoist the ladle into the LF station for refining.

[0006] Furthermore, in step 2), the flow rate of the stirring gas is controlled to be 0.2–1.0 NL / (t·min) during the vacuum carbon deoxidation process.

[0007] Furthermore, the tapping temperature of the primary smelting furnace mentioned in step 1) is 1620–1680°C.

[0008] Furthermore, in step 3), during the LF station refining process, the binary basicity of the LF slag is controlled between 5.0 and 8.0.

[0009] Furthermore, in the LF station refining process, a metal deoxidizer is used for diffusion deoxidation and white slag formation.

[0010] Furthermore, the metal deoxidizer is at least one of aluminum wire, aluminum block, or aluminum shavings.

[0011] Technical principle of the invention: In metallurgical processes, the application of vacuum technology only allows for a shift in reaction equilibrium when a gaseous phase is involved and the number of molars of gaseous products exceeds the number of molars of gaseous reactants. Vacuum oxygen decarburization is a decarburization process derived from the principle of vacuum carbon deoxidation. During VD vacuum decarburization, [C] and [O] react to produce CO gas. Lowering the partial pressure of CO in the vacuum promotes the reaction of [C] and [O] to produce CO gas. It follows the following metallurgical thermodynamic laws: (1) (2) In the formula: The activity of carbon in molten steel, % The activity of oxygen in molten steel, % ρ is the partial pressure of CO in a vacuum, Pa; K is the equilibrium constant of the C and O reaction in molten steel; is the activity coefficient of carbon in molten steel; is the activity coefficient of oxygen in molten steel; T is the absolute temperature of molten steel, in K.

[0012] This shows that the reactivity of [C] and [O] under vacuum increases with the increase of vacuum level. Therefore, as the partial pressure of CO decreases, the reaction between oxygen and C in steel is reactivated, thereby achieving the purpose of reducing C.

[0013] The main innovations and beneficial effects of this invention are as follows: By using carbon source alloy materials for pre-deoxidation instead of metallic deoxidizing materials, the generation of solid deoxidation products is avoided, reducing the source of inclusions in the steel from the outset; by performing vacuum carbon deoxidation under a vacuum degree ≤100Pa, thermodynamic conditions favorable to the carbon-oxygen reaction are created, allowing the carbon monoxide gas generated by the carbon-oxygen reaction to be effectively discharged, achieving deep deoxidation; by controlling the stirring gas flow rate to 0.2~1.0NL / (t·min), both sufficient stirring of the molten steel to promote gas escape and inclusion flotation are ensured, while avoiding secondary oxidation and slag entrapment caused by excessive stirring; the vacuum holding time is controlled to no more than 5 minutes and the vacuum cycle is... Within 15 minutes, production efficiency was improved while ensuring deoxidation effect. By controlling the tapping temperature of the primary refining furnace at 1620-1680℃, suitable temperature conditions were provided for subsequent vacuum carbon deoxidation. During the refining process at the LF station, the binary basicity of the refining slag was controlled at 5.0-8.0. Combined with the use of metal deoxidizers for diffusion deoxidation and white slag formation, the sulfur and oxygen content in the steel was further reduced, and the purity of the molten steel was improved. The synergistic coordination of various process parameters enabled the production of low-carbon and low-sulfur steel through the organic combination of vacuum carbon deoxidation and LF refining without the use of metal deoxidizers for pre-deoxidation. The total oxygen content in the steel can be controlled below 15ppm, and the sulfur content can be controlled below 0.005%. Detailed Implementation Example 1

[0014] A method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation includes the following steps: The tapping temperature of the primary furnace is 1650℃. No metallic deoxidizing materials are used during tapping. High-carbon ferromanganese with a carbon content of 8% is used as the carbon source alloy material for pre-deoxidation and alloying, with an addition rate of 1.2 kg / t steel. Simultaneously, 3.2 kg / t steel of lime and 2.0 kg / t steel of refining slag are added. After tapping, the ladle is hoisted into the VD vacuum deoxidation station for vacuum carbon deoxidation treatment at a vacuum degree of 80 Pa. The vacuum holding time is 4 min, and the vacuum cycle is 12 min. During the vacuum carbon deoxidation treatment, the bottom-blown argon stirring gas flow rate is controlled at 0.6 NL / (t·min) to promote steel stirring, accelerate gas escape, and facilitate the flotation of inclusions. After the ladle is lifted into the LF (Refining and Refining) station, the binary basicity of the LF slag is controlled at 6.5. Aluminum wire is used as a metallic deoxidizer for diffusion deoxidation and white slag formation, with an addition rate of 0.8 kg / t of steel. The resulting molten steel has a total oxygen content of 12 ppm and a non-metallic inclusion count of 15 per mm. 2The steel achieved a yield strength of 350 MPa, a tensile strength of 480 MPa, and an elongation of 28%. This embodiment effectively reduced residual deoxidation products and significantly decreased the inclusion content in the steel through a vacuum carbon deoxidation process. Example 2

[0015] Based on Example 1, the optimized process parameters are as follows: the tapping temperature of the primary refining furnace is 1640℃. During the tapping process, high-carbon ferrochrome with a carbon content of 10% is added as a carbon source alloy material at a rate of 1.0 kg / t steel, along with 3.5 kg / t steel of lime and 2.5 kg / t steel of refining slag. Vacuum deoxidation (VD) is performed under a vacuum of 60 Pa for 3 minutes, with a vacuum cycle of 10 minutes. During vacuum carbon deoxidation, the bottom-blown argon stirring gas flow rate is controlled at 0.3 NL / (t·min). During LF refining, the binary basicity of the LF slag is controlled at 7.0. Aluminum blocks are used as a metallic deoxidizer for diffusion deoxidation and white slag formation, with an aluminum block addition rate of 0.6 kg / t steel. The steel obtained through this optimized process has a total oxygen content of 10 ppm and a non-metallic inclusion count of 12 inclusions / mm. 2 The steel achieved a yield strength of 355 MPa, a tensile strength of 485 MPa, and an elongation of 30%. Compared to Example 1, this optimized scheme further reduced the oxygen content and the number of inclusions in the steel, thereby improving the mechanical properties of the steel. Example 3

[0016] Using the implementation method with the boundary parameters of the claims, the tapping temperature of the primary refining furnace is 1620℃. High-carbon ferromanganese is added as a carbon source alloy material during the tapping process at a rate of 1.5 kg / t steel, along with 2.5 kg / t steel of lime and 3.0 kg / t steel of refining slag. Vacuum deoxidation (VD) is performed under a vacuum of 100 Pa for 5 minutes, with a vacuum cycle of 15 minutes. During vacuum carbon deoxidation, the bottom-blown argon stirring gas flow rate is controlled at 1.0 NL / (t·min). In the LF refining process, the binary basicity of the refining slag is controlled at 8.0. Aluminum scrap is used as a metallic deoxidizer for diffusion deoxidation and white slag formation, with an addition rate of 1.0 kg / t steel. The steel obtained using this boundary parameter process has a total oxygen content of 15 ppm and a non-metallic inclusion count of 18 inclusions / mm². 2 The steel exhibits a yield strength of 345 MPa, a tensile strength of 475 MPa, and an elongation of 26%. This embodiment demonstrates that even under the boundary conditions of the claims, vacuum carbon deoxidation can still be effectively achieved, significantly reducing inclusions in the steel and achieving the purpose of the invention.

Claims

1. A method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation, characterized in that... The key process steps include the following: 1) When tapping steel from the primary refining furnace, carbon source alloy materials are used for pre-deoxidation and alloying. During the tapping process, 1.0-1.5 kg / t steel of carbon source alloy materials, 2.5-4.0 kg / t steel of lime, and 1.0-3.0 kg / t steel of refining slag are added. 2) After tapping the steel, the ladle is hoisted into the VD vacuum deoxidation station, where carbon and oxygen are reacted under vacuum conditions to generate gaseous deoxidation products; the vacuum carbon deoxidation treatment is carried out under vacuum conditions ≤100Pa, and the vacuum holding time does not exceed 5min. 3) During vacuum carbon deoxidation, the flow rate of the stirring gas is controlled to promote stirring of the molten steel, accelerate the escape of gas and the floating of inclusions. After breaking the vacuum, the ladle is hoisted into the LF station for refining; low carbon and low sulfur steel is obtained, with a total oxygen content of less than 15 ppm and a sulfur content of less than 0.005%.

2. The method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation according to claim 1, characterized in that: In step 2), the flow rate of the stirring gas is controlled to be 0.2–1.0 NL / (t·min) during the vacuum carbon deoxidation process.

3. The method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation according to claim 1, characterized in that: The tapping temperature of the primary smelting furnace mentioned in step 1) is 1620-1680℃.

4. The method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation according to claim 1, characterized in that: In step 3), during the refining process at the LF station, the binary basicity of the LF slag is controlled between 5.0 and 8.

0.

5. The method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation according to claim 1, characterized in that: In the refining process at the LF station, a metal deoxidizer is used for diffusion deoxidation and white slag formation.

6. The method for refining low-carbon, low-sulfur steel using vacuum carbon deoxidation according to claim 5, characterized in that: The metal deoxidizer is at least one of aluminum wire, aluminum block, or aluminum shavings.