Sulfur-containing steel manganese sulfide inclusion control method

Abstract

The invention discloses a sulfur-containing steel manganese sulfide inclusion control method, and relates to the technical field of steel production, and the method comprises the following steps: controlling the tapping steel remaining amount of an electric furnace to be 10t-20t, carrying out deoxidation, alloying and slagging operation in the tapping process, and moving a buggy ladle to a ladle hoisting station for argon stirring after the tapping is finished; the method comprises the following steps: lifting a molten steel ladle to a VD station, vacuumizing until the vacuum degree reaches 0-1 bar, carrying out bottom nitrogen blowing and vacuum breaking in the whole vacuum process, taking a nitrogen sample and analyzing a steel sample, adding a 40m calcium line to carry out calcium treatment, statically stirring for 10-15 minutes, adding an aluminum line to adjust the aluminum content after sampling analysis, increasing 0.015-0.020 sulfur per 100kg of 100 tons of molten steel on a VD sulfur line, and controlling the sulfur content to be an internal control lower limit + 0.005%. According to the method, the steel rating of the medium-low-sulfur steel is achieved, the A fine system is smaller than or equal to 2.0 grade, the coarse system is smaller than or equal to 1.5 grade, and the manganese sulfide rating of the high-sulfur steel is 2.2-2.3 grade.

Description

Technical Field

[0001] The invention relates to the technical field of steel production, and in particular to a method for controlling manganese sulfide inclusions in sulfur-containing steel. Background Art

[0002] The main technical difficulties in controlling MnS inclusions in sulfur-containing steel are as follows: (1) The most significant factor affecting the morphology of sulfides is the oxygen content in steel. When the oxygen activity in steel is high, the sulfides are Class I; as the oxygen activity decreases, the sulfides gradually change from Class II to Class III. As the oxygen content increases, the average diameter and area fraction of MnS inclusions increase, the number decreases, and the aspect ratio decreases. However, the optimal range of oxygen content in sulfur-containing steels has rarely been reported.

[0003] (2) MnS inclusions are also affected by S in steel. When the S content is low, Fe (S) dendrites are first precipitated during solidification, and MnS is enriched in the liquid phase in the liquid phase. After reaching the eutectic point composition, Fe (S) and MnS (S) are precipitated, forming type II MnS inclusions at the grain boundary; when the S content is high, the precipitation temperature of MnS inclusions is high, and MnS inclusions precipitate from the liquidus in the form of divorced eutectic at an early stage, evenly distributed in the dendrite gaps, and forming angular type III MnS inclusions inside the austenite grains. Most domestic manufacturers add sulfur based on experience in the sulfur addition process, which makes the final sulfur control less accurate and scientific.

[0004] (3) The basicity of refined slag has a great influence on the deoxidation of molten steel and the sulfur recovery rate. As the basicity increases, the deoxidation capacity of the refined slag also increases. However, a high-basicity slag system is conducive to the desulfurization reaction, resulting in a low sulfur recovery rate in high-S steel. Therefore, the design of the refined slag system must meet the requirements of both deoxidation and sulfur retention, and the composition design is difficult. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for controlling manganese sulfide inclusions in sulfur-containing steel.

[0006] In order to solve the above technical problems, the technical solution of the present invention is as follows: A method for controlling manganese sulfide inclusions in sulfur-containing steel, comprising: The steel volume retained in the electric furnace is controlled to be 10t-20t. Deoxidation, alloying and slag making operations are performed during the steel tapping process. After the steel tapping is completed, the ladle car is moved to the ladle hanging station for argon stirring. The argon flow rate is 300 L / min and the stirring time is 2min. After the molten steel ladle is hoisted to the VD station, vacuum is evacuated until the vacuum degree reaches 0-1bar. Nitrogen is blown from the bottom throughout the vacuum process. Nitrogen and steel samples are taken for analysis after breaking the air. 40m calcium wire is added for calcium treatment and static stirring is performed for 10-15min. After sampling and analysis, aluminum wire is added to adjust the aluminum content. The VD sulfur line adds 0.015-0.020 sulfur per 100kg of 100 tons of molten steel, and the sulfur content is controlled to be the internal control lower limit + 0.005%.

[0007] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, wherein: before controlling the steel retention amount of the electric furnace to be 10t-20t, performing deoxidation, alloying and slag making operations during the steel tapping process, and moving the ladle car to the ladle hanging station for argon stirring after the steel tapping is completed, the argon flow rate is 300 L / min, and the stirring time is 2min, it also includes: Based on the sulfur content, sulfur-containing steel is divided into high-sulfur steel and medium-low sulfur steel, and the sulfur content of the high-sulfur steel is 0.24%-0.38%, and the sulfur content of the medium-low sulfur steel is 0.015%-0.070%; The carbon content of high-sulfur steel is controlled at 0.06%-0.10%, and the tapping temperature is 1600℃-1680℃; the carbon content of medium- and low-sulfur steel is controlled at 0.35%-0.40%, and the tapping temperature is 1610℃-1680℃.

[0008] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, the deoxidation, alloying and slag making operations during the steel tapping process include: After the high-sulfur steel output reaches 5t, 2kg / t silicon-manganese alloy and 11kg / t low-carbon manganese-iron alloy are added with the steel flow for post-furnace deoxidation and alloying; when the output reaches 2 / 3, 11kg / t-12.5kg / t iron sulfide is added for sulfur alloying; when the output reaches 3 / 4, 1kg / t-1.5kg / t lime is added for slagging; After the output of medium and low sulfur steel reaches 5t, 80kg-100kg aluminum shot, 16kg / t silicon-manganese alloy, 1-2kg / t ferrosilicon alloy and 1-2kg / t ferrovanadium alloy are added with the steel flow for post-furnace deoxidation and alloying; after the output of about 3 / 4 of the steel is reached, 550kg lime and 250kg modified refined slag are added for slagging.

[0009] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, wherein: in the step of controlling the steel retention amount of the electric furnace to be 10t-20t, performing deoxidation, alloying and slag making operations during the steel tapping process, and moving the ladle car to the ladle hanging station for argon stirring after the steel tapping is completed, the argon flow rate is 300 L / min, and the stirring time is 2min, the method further comprises: The high-sulfur steel molten steel is hoisted to the LF refining station, and lime is added through the silo for slag adjustment. The addition amount is 5kg / t. After adding lime, the bottom blowing argon flow rate of the LF refining furnace is adjusted to 20L / min-50L / min, and it lasts for 5min-8min. Then the lower electrode is electrified to slag for 5min-15min, and the temperature measurement and sampling operation is carried out. The online oxygen determination is carried out at a temperature ≥1500℃. If it is lower than 100ppm, no diffusion deoxidation operation is carried out. If it is higher than 100ppm and lower than 130ppm, ferrosilicon powder and silicon carbide are used for diffusion deoxidation. If it is greater than 130ppm, aluminum wire is fed into the wire feeder for precipitation deoxidation operation, and the bottom blowing argon flow rate is adjusted to 300L / min for stirring after feeding the aluminum wire. When the oxygen content reaches 60ppm-100ppm, the LF refining soft blowing stage is entered; The medium and low sulfur steel molten steel is lifted to the LF refining station, the Alt content is sampled, and when Alt is less than 0.030%, aluminum wire is fed to make the Alt content reach 0.030%. 20±5m denaturing wire is added for denaturation treatment, and the remaining elements are alloyed according to the target. After the addition, nitrogen is blown at the bottom of the LF refining furnace for 60-70 minutes, and 350-400kg of iron sulfide is added 5 minutes before entering the VD furnace.

[0010] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, wherein: after the molten steel ladle is hoisted to the VD station, vacuum is drawn until the vacuum degree reaches 0-1 bar, nitrogen is blown at the bottom during the whole vacuum process, nitrogen samples and steel samples are taken for analysis after breaking the air, 40m calcium wire is added for calcium treatment, static stirring is performed for 10-15min, aluminum wire is added after sampling and analysis to adjust the aluminum content, the VD sulfur line increases sulfur by 0.015-0.020 per 100kg of molten steel, and the sulfur content is controlled to be the internal control lower limit + 0.005%, and further comprises: Secondary cooling water distribution control, crystallizer electromagnetic stirring and low-temperature pouring technology are used in the continuous casting process.

[0011] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, the continuous casting superheat is controlled to be 15-30°C.

[0012] As a preferred solution of the method for controlling manganese sulfide inclusions in sulfur-containing steel of the present invention, the parameters of electromagnetic stirring of the crystallizer are: 250A*2HZ.

[0013] The beneficial effects of the present invention are: The present invention realizes the grading of medium and low sulfur steel: A fine series ≤2.0 grade, coarse series ≤1.5 grade; the manganese sulfide distribution reaches the BE level of French standard NF A04-108, and the manganese sulfide morphology of high sulfur free cutting steel is graded according to German standard SEP1572, reaching between 2.2 and 2.3 grades. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other accompanying drawings can be obtained based on these accompanying drawings without paying creative labor.

[0015] Figure 1 This is a schematic diagram of the morphology of manganese sulfide in high-sulfur steel produced by the method for controlling manganese sulfide inclusions in sulfur-containing steel provided in Example 1; Figure 2 This is a schematic diagram of the morphology of manganese sulfide in medium-low sulfur steel produced by the method for controlling manganese sulfide inclusions in sulfur-containing steel provided in Example 2. DETAILED DESCRIPTION

[0016] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific implementation modes and in combination with the accompanying drawings.

[0017] Example 1: This example provides a method for controlling manganese sulfide inclusions in sulfur-containing steel, which is used for high-sulfur steel. It should be noted that the sulfur content in the high-sulfur steel is 0.24% to 0.38%. The control method specifically includes the following steps: Electric furnace process: The carbon content of the steel tapped from the electric furnace is controlled to be 0.06%-0.10%, the target carbon content is 0.07%-0.09%, and the tapping temperature is 1600℃-1680℃. In order to reduce the slag in the tapping process, the steel tapping amount of the electric furnace is 10t-20t, and deoxidation, alloying and slag making operations are performed during the tapping process. After the tapping amount is 5t, 2kg / t silicon-manganese alloy and 11kg / t low-carbon manganese-iron alloy are added with the steel flow for post-furnace deoxidation and alloying; when the tapping amount is about 2 / 3, 11kg / t-12.5kg / t iron sulfide is added for sulfur alloying, and when the tapping amount is about 3 / 4, 1kg / t-1.5kg / t lime is added for slag making. After the tapping is completed, in order to fully melt the alloy and make full use of the good dynamic conditions of steel slag mixing, the inclusions are fully floated. Drive the ladle car to the ladle hanging station for large argon stirring for 2 minutes with an argon flow rate of 300 L / min.

[0018] LF refining process: After the molten steel is hoisted to the LF process, lime is added through the silo for slag adjustment, and the amount of additional lime is 5kg / t. After adding lime, the argon flow rate of the LF refining furnace bottom is adjusted to a smaller flow rate, which is controlled at 20L / min-50 L / min for about 5min-8min. After the lower electrode is electrified for slag formation for about 5min-15min, temperature measurement and sampling operations are carried out. Iron sulfide, silicon manganese alloy, low carbon ferromanganese alloy, high carbon ferromanganese alloy and ferrophosphorus are added according to the composition to adjust the chemical composition. When the temperature is ≥1500℃, online oxygen determination is carried out. The first oxygen setting should be no less than 100ppm; if it is less than 100ppm, diffusion deoxidation operation will not be performed; if it is less than 130ppm, ferrosilicon powder and silicon carbide will be used for diffusion deoxidation, requiring small quantities and multiple batches. During diffusion deoxidation, ferrosilicon powder should be evenly added to the slag surface to avoid adding it to the molten steel; if it is greater than 130ppm, a wire feeder can be used to feed aluminum wire for precipitation deoxidation. The deoxidation degree of Al wire can be reduced by about 20ppm[O] according to the feeding of 20m Al wire per furnace. After feeding Al wire, the bottom blowing argon flow rate is increased to 300L / min for stirring. The LF refining soft blowing stage can be entered only when the oxygen content reaches 60ppm-100ppm.

[0019] VD refining process: After the molten steel is lifted to the VD process, vacuum is drawn until the vacuum degree reaches 0-1bar. Nitrogen is blown from the bottom throughout the vacuum process. After breaking the air, nitrogen and steel samples are taken for analysis. 40m calcium wire is added for calcium treatment and static stirring is performed for 10-15min. After sampling and analysis, aluminum wire is added to adjust the aluminum content to ensure that it meets the requirements. The VD sulfur line adds 0.015-0.020 sulfur per 100kg of 100 tons of molten steel, and the sulfur content is adjusted to the internal control lower limit + 0.005%.

[0020] Continuous casting process: MnS is generally precipitated during solidification. The size of MnS is greatly affected by the center segregation of the ingot. When the ingot has serious center segregation, a high concentration of Mn and S will gather in the center of the ingot. As the temperature decreases, a large number of large-sized MnS inclusions will precipitate. Due to the excellent deformation performance of MnS, the size of MnS will further increase during the subsequent rolling process, which will cause the rating of Class A inclusions in the steel to increase or even exceed the standard. In order to improve the situation of increased rating of Class A inclusions due to center segregation, commonly used methods include secondary cooling water distribution control, crystallizer electromagnetic stirring and low-temperature pouring. Superheat control: 15-30℃, crystallizer electromagnetic stirring: 400A*2HZ, secondary cooling intensity: weak cooling.

[0021] Implementation effect: Manganese sulfide is distributed in spherical or spindle shapes, reaching the ideal level of 2.2~2.3 of German standard SEP1572. The length-to-width ratio of manganese sulfide is 1~3, accounting for 80%, which is equivalent to imported materials.

[0022] Example 2: This example provides a method for controlling manganese sulfide inclusions in sulfur-containing steel, which is used for medium-low sulfur steel. It should be noted that the sulfur content in the medium-low sulfur steel is 0.015%-0.070%. The control method specifically includes the following steps: Electric furnace process: The carbon content of the steel tapped from the electric furnace is controlled to be 0.35%-0.40%, the target carbon content is 0.37%-0.39%, and the tapping temperature is 1610℃-1680℃. In order to reduce the slag in the tapping process, the steel tapping amount of the electric furnace is 10t-20t, and deoxidation, alloying and slag making operations are performed during the tapping process. After the tapping amount is 5t, 80kg-100kg aluminum shot, 16kg / t silicon-manganese alloy, 1-2kg / t ferrosilicon alloy and 1-2kg / t ferrovanadium alloy are added with the steel flow for post-furnace deoxidation and alloying; after the tapping amount is about 3 / 4, 550kg lime and 250kg modified refined slag are added for slag making. After the tapping is completed, in order to fully melt the alloy and make full use of the good dynamic conditions of steel slag mixing, the inclusions are fully floated. The ladle car is driven to the ladle hanging station for large argon stirring for 2min, and the argon flow rate is 300 L / min.

[0023] LF refining process: After the molten steel is lifted to the LF process, according to the sampled Alt content, if Alt < 0.030%, aluminum wire needs to be fed to make the Alt content reach 0.030%, and 20 ± 5m denaturing wire is added for denaturation treatment. Other elements are supplemented with alloys according to the target. After supplementation, nitrogen is blown at the bottom of the LF refining furnace for 60-70 minutes, and 350-400 kg of iron sulfide is added 5 minutes before entering the VD furnace.

[0024] VD refining process: After the molten steel is lifted to the VD process, vacuum is drawn until the vacuum degree reaches 0-1bar. Nitrogen is blown from the bottom throughout the vacuum process. After breaking the air, nitrogen and steel samples are taken for analysis. 40m calcium wire is added for calcium treatment and static stirring is performed for 10-15min. After sampling and analysis, aluminum wire is added to adjust the aluminum content to ensure that it meets the requirements. The VD sulfur line adds 0.015-0.020 sulfur per 100kg of 100 tons of molten steel, and the sulfur content is adjusted to the internal control lower limit + 0.005%.

[0025] Continuous casting process: MnS is generally precipitated during solidification. The size of MnS is greatly affected by the center segregation of the ingot. When the ingot has serious center segregation, a high concentration of Mn and S will gather in the center of the ingot. As the temperature decreases, a large number of large-sized MnS inclusions will precipitate. Due to the excellent deformation performance of MnS, the size of MnS will further increase during the subsequent rolling process, which will cause the rating of Class A inclusions in the steel to increase or even exceed the standard. In order to improve the situation of increased rating of Class A inclusions caused by center segregation, commonly used methods include secondary cooling water distribution control, crystallizer electromagnetic stirring and low-temperature pouring. Superheat control: 15-30℃, crystallizer electromagnetic stirring: 250A*2HZ, secondary cooling intensity: weak cooling.

[0026] Implementation effect: The original grade is 2.5 for fine and 3.5 for coarse. After modification, the grade of Class A inclusions is 1.5 for fine and 2.0 for coarse. The distribution of manganese sulfide inclusions reaches the BE level of French standard NF A04-108. The control level of manganese sulfide in medium and low sulfur steel of Nangang is equivalent to that of imported materials.

[0027] Therefore, the technical solution of the present application realizes the grading of medium and low sulfur steel: A fine series ≤2.0 grade, coarse series ≤1.5 grade; the manganese sulfide distribution reaches the BE level of French standard NF A04-108, and the manganese sulfide morphology of high sulfur free-cutting steel is rated according to German standard SEP1572, reaching between 2.2 and 2.3 grades.

[0028] In addition to the above embodiments, the present invention may also have other implementation modes; any technical solutions formed by equivalent replacement or equivalent transformation shall fall within the protection scope required by the present invention.

Claims

1. A method for controlling manganese sulfide inclusions in sulfur-containing steel, characterized by: include: The steel volume retained in the electric furnace is controlled to be 10t-20t. Deoxidation, alloying and slag making operations are performed during the steel tapping process. After the steel tapping is completed, the ladle car is moved to the ladle hanging station for argon stirring. The argon flow rate is 300 L / min and the stirring time is 2min. After the molten steel ladle is hoisted to the VD station, vacuum is evacuated until the vacuum degree reaches 0-1bar. Nitrogen is blown from the bottom throughout the vacuum process. Nitrogen and steel samples are taken for analysis after breaking the air. 40m calcium wire is added for calcium treatment and static stirring is performed for 10-15min. After sampling and analysis, aluminum wire is added to adjust the aluminum content. The VD sulfur line adds 0.015-0.020 sulfur per 100kg of 100 tons of molten steel, and the sulfur content is controlled to be the internal control lower limit + 0.005%.

2. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 1, characterized in that: Before the steel quantity retained in the electric furnace is controlled to be 10t-20t, deoxidation, alloying and slag making operations are performed during the steel tapping process, and after the steel tapping is completed, the ladle car is moved to the ladle hanging station for argon stirring, the argon flow rate is 300 L / min, and the stirring time is 2min, the method further includes: Based on the sulfur content, sulfur-containing steel is divided into high-sulfur steel and medium-low sulfur steel, and the sulfur content of the high-sulfur steel is 0.24%-0.38%, and the sulfur content of the medium-low sulfur steel is 0.015%-0.070%; The carbon content of high-sulfur steel is controlled at 0.06%-0.10%, and the tapping temperature is 1600℃-1680℃; the carbon content of medium- and low-sulfur steel is controlled at 0.35%-0.40%, and the tapping temperature is 1610℃-1680℃.

3. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 2, characterized in that: The deoxidation, alloying and slag making operations during the steel tapping process include: After the high-sulfur steel output reaches 5t, 2kg / t silicon-manganese alloy and 11kg / t low-carbon manganese-iron alloy are added with the steel flow for post-furnace deoxidation and alloying; when the output reaches 2 / 3, 11kg / t-12.5kg / t iron sulfide is added for sulfur alloying; when the output reaches 3 / 4, 1kg / t-1.5kg / t lime is added for slagging; After the output of medium and low sulfur steel reaches 5t, 80kg-100kg aluminum shot, 16kg / t silicon-manganese alloy, 1-2kg / t ferrosilicon alloy and 1-2kg / t ferrovanadium alloy are added with the steel flow for post-furnace deoxidation and alloying; after the output of about 3 / 4 of the steel, 550kg lime and 250kg modified refined slag are added for slagging.

4. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 2, characterized in that: After the amount of steel left in the electric furnace is controlled to be 10t-20t, deoxidation, alloying and slag making operations are performed during the steel tapping process, and after the steel tapping is completed, the ladle car is moved to the ladle hanging station for argon stirring, the argon flow rate is 300 L / min, and the stirring time is 2min, the method further includes: The high-sulfur steel molten steel is hoisted to the LF refining station, and lime is added through the silo for slag adjustment. The addition amount is 5kg / t. After adding lime, the bottom blowing argon flow rate of the LF refining furnace is adjusted to 20L / min-50L / min, and it lasts for 5min-8min. Then the lower electrode is electrified to slag for 5min-15min, and the temperature measurement and sampling operation is carried out. The online oxygen determination is carried out at a temperature ≥1500℃. If it is lower than 100ppm, no diffusion deoxidation operation is carried out. If it is higher than 100ppm and lower than 130ppm, ferrosilicon powder and silicon carbide are used for diffusion deoxidation. If it is greater than 130ppm, aluminum wire is fed into the wire feeder for precipitation deoxidation operation, and the bottom blowing argon flow rate is adjusted to 300L / min for stirring after feeding the aluminum wire. When the oxygen content reaches 60ppm-100ppm, the LF refining soft blowing stage is entered; The medium and low sulfur steel molten steel is lifted to the LF refining station, the Alt content is sampled, and when Alt is less than 0.030%, aluminum wire is fed to make the Alt content reach 0.030%. 20±5m denaturing wire is added for denaturation treatment, and the remaining elements are alloyed according to the target. After the addition, nitrogen is blown at the bottom of the LF refining furnace for 60-70 minutes, and 350-400kg of iron sulfide is added 5 minutes before entering the VD furnace.

5. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 2, characterized in that: After the molten steel ladle is lifted to the VD station, vacuum is drawn until the vacuum degree reaches 0-1 bar, nitrogen is blown from the bottom during the whole vacuum process, nitrogen samples and steel samples are taken for analysis after breaking the air, 40m calcium wire is added for calcium treatment, static stirring is performed for 10-15min, aluminum wire is added after sampling and analysis to adjust the aluminum content, the VD sulfur line increases sulfur by 0.015-0.020 per 100kg of molten steel, and the sulfur content is controlled to be the internal control lower limit + 0.005%, and further includes: Secondary cooling water distribution control, crystallizer electromagnetic stirring and low-temperature pouring technology are used in the continuous casting process.

6. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 5, characterized in that: Control the continuous casting superheat to 15-30℃.

7. The method for controlling manganese sulfide inclusions in sulfur-containing steel according to claim 5, characterized in that: The parameters of electromagnetic stirring of the crystallizer are: 250A*2HZ.

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