Economical method for producing fine-grain and high-plasticity SWRH82B series green steel through electric furnace small square billet

Abstract

The invention discloses an economical method for producing fine-grain and high-plasticity SWRH82B series green steel through electric furnace small square billets, the electric furnace small square billets are adopted for production, on the premise that the scrap steel ratio is 50% or above, non-carbon equivalent is used for influencing the original Nb and Ti composite microalloying process, the Mn content and the Si content are controlled according to the lower limit of the standard requirement, the Si content of the steel grade is completely brought in by silicon-manganese alloy, and the yield is high. According to the scheme, small square billet continuous casting cracks are effectively avoided, abnormal structures such as net carbon and martensite in the structure are reduced by reducing carbon equivalent influencing elements, the component of a Jialing device and the component of fans of all sections are effectively adjusted through the STELMOR air cooling process, and the production efficiency is improved. The purpose of improving the plasticity index of microalloy refined grains is achieved, the downstream requirement for high pulling speed and large deformation is met, the same components cover the specification of 5-15 mm, high rolling production efficiency is ensured, and the requirement for low-cost green steel is met.

Description

Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to a method for producing fine-grained, high-plasticity SWRH82B series green steel by using economical electric furnace billets. Background Art

[0002] Microalloying and controlled rolling and cooling of steel are very beneficial to improving the performance of steel and reducing manufacturing costs. In recent years, the price of V alloys has continued to rise. Taking VN alloy as an example, the peak price has risen to 480,000 yuan / ton, resulting in a sharp increase in the manufacturing cost of the SWRH82B series with V microalloying. Shougang took the lead in developing the SWRH82B series with Nb instead of V microalloying to reduce manufacturing costs; existing studies have shown that the SWRH82B series of high-carbon wire containing Nb is very prone to continuous casting billet cracks, and metallographic structure analysis shows that there is a certain amount of acicular ferrite / Widmanstatten or bainite structure, which brings great obstacles to the promotion and application of the next drawing. Some steel companies have taken a compromise route in their research, using Nb and V composite addition, and the cost has decreased. However, the high price of V series alloys has failed to truly achieve the goal of cost reduction. Therefore, it is urgent to develop new production methods to solve the above problems. Summary of the invention

[0003] Technical problems to be solved: In view of the above technical problems, the present invention provides an economical method for producing fine-grained, high-plasticity SWRH82B series green steel from small square billets in an electric furnace, which can effectively solve the shortcomings of high manufacturing cost of SWRH82B series with V microalloying due to the V alloy price, and high-carbon wire SWRH82B series containing Nb is very prone to continuous casting billet cracks.

[0004] Technical solution: A method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets, comprising the following steps: S1. Converter smelting: Add more than 50% scrap steel into the electric furnace and then add it into the blast furnace molten iron. Scrap steel is added in the smelting process. Slag is added. After smelting, the tapping temperature of the electric furnace is ≥1650℃; when 1 / 3 to 2 / 3 of the steel is tapped, add silicon-manganese alloy, ferroniobium, ferrotitanium and carburizer in sequence, and control C: 0.80-0.85 wt.%, Mn: 0.60-0.65 wt.%, Nb: 0.010-0.050 wt.%, Ti: 0.010-0.050 wt.%, S<0.015 wt.%, P<0.015 wt.%; S2. Continuous casting: The cross section of the continuous casting billet is 150 mm × 150 mm or 140 mm × 140 mm; S3. Rolling: Rolling is performed using a rolling mill and cooling is performed using a water tank.

[0005] Preferably, inert gas bottom blowing and stirring is used throughout the entire process from steel tapping to continuous casting.

[0006] Preferably, the superheat of the continuous casting ladle is 25-35°C, the continuous casting is subjected to enhanced water cooling, and the casting speed is ≤5.0 m / min.

[0007] Preferably, the heating temperature is 950-1200° C., the soaking temperature is 1060-1200° C., and the total heating and soaking time is 60-100 min.

[0008] Preferably, the starting rolling temperature is 980-1100° C., and a continuous wire rolling production line is used to roll the steel into a high-carbon SWRH82B series with a specification of 5.5-15 mm, and the final rolling speed is greater than 36 m / s.

[0009] Preferably, after rolling, the wire is cooled in a water tank, the spinning temperature is controlled at 800-950°C, and then cooled in a stelmor cooling line. Different specifications are adjusted by adjusting the opening degree of the Jialing device and the graded air volume to achieve the purpose of refining the grains and improving the plasticity, and then bundled and stacked on the PF line.

[0010] Beneficial effects: Conventional SWRH82B is generally produced by long-process converter steel in order to meet the requirements of molten steel cleanliness and reduce structural abnormalities. The long-process production results in high overall carbon emissions, and it is difficult to meet the high-carbon steel and green steel production standards. The overall carbon footprint of the method of the present invention is reduced by 45% compared with the converter long process, and can meet the green steel production standards; The present invention adopts Nb and Ti composite microalloying with a low Mn and low Si component system without adding any alloying elements. Compared with conventional Mn, Cr, V and multi-element composite systems, the carbon equivalent influencing elements of the present invention are free of any carbon equivalent influencing elements except C and Mn, and the isothermal transformation CCT curve moves to the left, resulting in a smaller net carbon generation interval causing downstream drawing fracture and substandard plasticity under the same cooling rate conditions, making it less likely to generate net carbon, and the Mn element is offline controlled according to standard requirements, and no alloying elements are added except Nb and Ti, resulting in a smaller net carbon generation interval causing downstream drawing fracture and substandard plasticity caused by Mn and Cr segregation in the core of the billet under the same cooling rate conditions, meeting the requirements of achieving high drawing speed and large deformation in the downstream; The present invention improves the plasticity index by refining the grains with Nb and Ti, thereby solving the brittle fracture caused by plasticity problems from the source, and the same components cover the specifications of 5-15 mm, ensuring the high efficiency of rolling production, further compressing the aging time, and meeting the needs of fast production and fast sales. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the metallographic structure diagram of SWRH82B series green steel obtained in Example 1 of the present invention; Figure 2 It is the metallographic structure diagram of the product obtained in Comparative Example 1; Figure 3 It is the metallographic structure diagram of the product obtained in Example 2. DETAILED DESCRIPTION

[0012] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments: Example 1

[0013] After adding more than 50% scrap steel into the electric furnace, molten iron from the blast furnace is added. Slag is added during the scrap steel ratio process. After smelting, the tapping temperature of the electric furnace is ≥1650℃; when 1 / 3 to 2 / 3 of the steel is tapped, silicon-manganese alloy, ferroniobium, ferrotitanium and common carburizer are added in sequence to control Si: 0.16 wt.%, C: 0.83 wt.%, Mn: 0.62 wt.%, Nb: 0.019 wt.%, Ti: 0.018 wt.%, S: 0.010wt.%, P: 0.015 wt.%; inert gas bottom blowing and stirring are used throughout the process from tapping to continuous casting, the superheat of the continuous casting tundish is controlled at 30℃, the continuous casting is strengthened with water cooling, the pulling speed is ≤5.0 m / min, and the billet section is a square billet of 150mm×150mm; the heating temperature is controlled at 955℃, the soaking temperature is controlled at 1065℃, and the total heating and soaking time is 70 min, the rolling temperature is controlled at 985 ℃, and the continuous wire rolling production line is used to roll into 5.5-15 mm high carbon SWRH82B series. The final rolling speed is greater than 36 m / s. After rolling, it is cooled in a water tank and the wire drawing temperature is controlled at 805 ℃. It is then cooled in the Stelmor cooling line and bundled and stacked in the PF line. The metallographic structure of the obtained SWRH82B series green steel is as follows: Figure 1 As shown: there is neither martensite structure nor reticular carbon structure.

[0014] Comparative Example 1 After adding more than 50% scrap steel into the electric furnace, blast furnace molten iron is added, and slag is added during the scrap steel ratio process. After smelting, the tapping temperature of the electric furnace is ≥1650℃; when 1 / 3 to 2 / 3 of the steel is tapped, silicon-manganese alloy, ferroniobium, ferrotitanium and ordinary carburizer are added in sequence, and C: 0.82 wt.%, Si: 0.17 wt.%, Mn: 0.89 wt.%, Nb: 0.015 wt.%, Ti: 0.018 wt.%, S: 0.015wt.%, P: 0.017 wt.%; inert gas bottom blowing and stirring are used throughout the process from tapping to continuous casting, the superheat of the continuous casting tundish is controlled at 30℃, the continuous casting is strengthened by water cooling, the pulling speed is ≤5.0 m / min, and the billet section is a square billet of 150mm×150mm; the heating temperature is controlled at 955℃, the soaking temperature is controlled at 1065℃, and the total heating and soaking time is 70 min, the rolling temperature is controlled at 985 ℃, and the continuous wire rolling production line is used to roll into 5.5-15 mm high carbon SWRH82B series, the final rolling speed is greater than 36 m / s, and the wire is cooled in a water tank after rolling. The wire laying temperature is controlled at 805 ℃, and then cooled in the Stelmor cooling line, bundled and stacked on the PF line. The metallographic structure of the product is as follows Figure 2 Shown: There is a three-level carbon network structure.

[0015] Comparative Example 2 After adding more than 50% scrap steel into the electric furnace, blast furnace molten iron is added, and slag is added during the scrap steel ratio process. After smelting, the tapping temperature of the electric furnace is ≥1650℃; when 1 / 3 to 2 / 3 of the steel is tapped, silicon-manganese alloy, ferroniobium, ferrotitanium and ordinary carburizer are added in sequence, and C: 0.83 wt.%, Si: 0.18 wt.%, Mn: 0.63 wt.%, Nb: 0.027 wt.%, Ti: 0.030 wt.%, S: 0.018wt.%, P: 0.019 wt.%; inert gas bottom blowing and stirring are used throughout the process from tapping to continuous casting, the superheat of the continuous casting tundish is controlled at 30℃, the continuous casting is strengthened by water cooling, the pulling speed is ≤5.0 m / min, and the billet section is a square billet of 150mm×150mm; the heating temperature is controlled at 955℃, the soaking temperature is controlled at 1065℃, and the total heating and soaking time is 70 min, the rolling temperature is controlled at 985 ℃, and the continuous wire rolling production line is used to roll into 5.5-15 mm high carbon SWRH82B series, the final rolling speed is greater than 36 m / s, and the wire is cooled in a water tank after rolling. The wire laying temperature is controlled at 805 ℃, and then cooled in the Stelmor cooling line, bundled and stacked on the PF line. The metallographic structure of the product is as follows Figure 3 As shown: there is a three-level martensitic structure.

[0016] Table 1 Performance results of the products obtained from Example 1 and Comparative Examples 1-2 , It can be seen from Table 1 that the SWRH82B series green steel prepared by the method of the present invention has a tensile strength of 1150-1190 and a plasticity of more than 30, which further indicates that the SWRH82B series green steel prepared by the method of the present invention has good strength stability and good plasticity index.

[0017] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets, characterized in that: The following steps are involved: S1. Converter smelting: Add more than 50% scrap steel into the electric furnace and then add it into the blast furnace molten iron. Scrap steel is added in the smelting process. Slag is added. After smelting, the tapping temperature of the electric furnace is ≥1650℃; when 1 / 3 to 2 / 3 of the steel is tapped, add silicon-manganese alloy, ferroniobium, ferrotitanium and carburizer in sequence, and control C: 0.80-0.85 wt.%, Mn: 0.60-0.65 wt.%, Nb: 0.010-0.050 wt.%, Ti: 0.010-0.050 wt.%, S<0.015 wt.%, P<0.015 wt.%; S2. Continuous casting: The cross section of the continuous casting billet is 150 mm × 150 mm or 140 mm × 140 mm; S3. Rolling: Rolling is performed using a rolling mill and cooling is performed using a water tank.

2. The method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets according to claim 1, characterized in that: Inert gas bottom blowing and stirring is used throughout the entire process from steel tapping to continuous casting.

3. The method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets according to claim 1, characterized in that: The superheat of the continuous casting tundish is 25-35°C, the continuous casting is enhanced by water cooling, and the casting speed is ≤5.0 m / min.

4. The method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets according to claim 1, characterized in that: The heating temperature is 950-1200 °C, the soaking temperature is 1060-1200 °C, and the total heating and soaking time is 60-100 min.

5. The method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets according to claim 1, characterized in that: The starting rolling temperature is 980-1100 °C, and the continuous wire rolling production line is used to roll the high-carbon SWRH82B series with a specification of 5.5-15 mm, and the final rolling speed is greater than 36 m / s.

6. The method for producing fine-grained, high-plasticity SWRH82B series green steel from economical electric furnace billets according to claim 1, characterized in that: After rolling, the wire is cooled in a water tank and the wire drawing temperature is controlled at 800-950℃. Then it is cooled in the stelmor cooling line. The opening degree of the Jialing device and the graded air volume are adjusted for different specifications to achieve the purpose of refining the grains and improving the plasticity. The wire is then bundled and stacked on the PF line.

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