Production method for controlling internal quality of cold heading steel casting blank

Abstract

The invention provides a production method for controlling the internal quality of a cold heading steel casting blank, which comprises the steps of converter smelting, LF refining, RH vacuum treatment and continuous casting to obtain the cold heading steel casting blank. In the continuous casting process, a crystallizer electromagnetic stirring technology, a solidification tail end electromagnetic stirring technology and a solidification tail end soft reduction technology are adopted, and molten steel in a tundish is heated through electromagnetic induction to control the superheat degree of the molten steel in the tundish to be 18-25 DEG C; the cold forging steel casting blank comprises the following components in percentage by mass: 0.20-0.50% of C, 0.015-0.035% of Al, more than or equal to 0.65% of Mn and less than or equal to 0.004% of S. According to the production method, induction heating is adopted in the continuous casting process, the superheat degree of the tundish is stably controlled, then the pulling speed is stably controlled, and the situation that due to the fact that the superheat degree is unstable, the pulling speed fluctuation is large, and casting blank quality fluctuation and site accidents are caused is avoided.

Description

Technical Field

[0001] This invention relates to the field of iron and steel metallurgy technology, specifically to a production method for controlling the internal quality of cold-headed steel billets. Background Technology

[0002] Cold heading steel products are precision metal parts manufactured using cold heading forming technology (high-speed stamping deformation at room temperature). With standard and special-shaped parts such as bolts, screws, nuts, pins, and electrical connectors as the core, they have three major advantages: high efficiency and energy saving, high precision, and high strength. They are widely used in automobile manufacturing, machinery and equipment, electronics and electrical appliances, construction engineering and other fields, and are key basic components supporting modern industry.

[0003] Cold heading steel has extremely stringent requirements for the internal quality of the cast billet, with the core objective of ensuring zero defects and cracking during subsequent intense cold deformation. Specifically, this requires ultra-high purity, a dense and homogeneous structure, and stable low-magnification microstructure. It also ensures process safety under high-speed deformation. As the demands of the application market for raw materials continue to increase, strengthening the internal microstructure control of cold heading steel and reducing or eliminating internal defects such as central porosity and shrinkage cavities is imperative, especially for the manufacture of high-end standard parts, which requires cold heading steel raw materials to be free of internal defects. Therefore, improving the internal quality of cold heading steel cast billets and eliminating or reducing internal defects such as central porosity and shrinkage cavities has become one of the key issues restricting the widespread application of cold heading steel in the manufacturing of high-end automotive and electronic components.

[0004] Currently, cold heading steel still suffers from problems with inclusions and unstable internal quality control of the billet, leading to unstable product quality control.

[0005] To address the above issues, Chinese invention patent application CN201610171891.6 discloses a method for controlling the central porosity of 30CrMo round steel billets with a cross-section of φ280mm. The key technology lies in the combination of electromagnetic stirring in the crystallizer and electromagnetic stirring at the end of solidification during the continuous casting stage, which reduces the area of ​​the porosity region in the center of the billet and improves its density. Chinese invention patent application CN201310536572.7 discloses a process for controlling the central porosity of 500mm large round billets produced by continuous casting. Using this invention to produce large round billets facilitates the melting of the mold flux, reduces the temperature gradient from the billet shell to the core of the billet, lowers the superheat of the central molten steel, increases the proportion of equiaxed crystals in the billet, and increases the structural density of the billet, thus helping to control the level of central porosity in continuously cast large round billets. Chinese invention patent application number CN201210503475.3 discloses a method for improving center segregation and center porosity of extra-thick slabs by heavy reduction. This patent improves the quality of extra-thick slabs by optimizing continuous casting process parameters and combining light and heavy reduction processes. It can replace ingot casting to produce extra-thick steel plates with a thickness of more than 100mm, with high production efficiency and environmental friendliness.

[0006] Most of the existing technologies mentioned above focus on addressing the central porosity of large-section slab billets (carbon content greater than 0.6%) using end-effector electromagnetic stirring or end-effector compression, and on addressing the central porosity of round billets using end-effector electromagnetic stirring. However, research on improving the production of cold heading steel from small-section cast billets with a carbon content less than 0.6% is limited. With increasingly stringent requirements in automotive and electronic component manufacturing, improving the internal quality of cold heading steel raw material cast billets and eliminating or mitigating internal defects such as central porosity and shrinkage is urgently needed.

[0007] Therefore, it is of great significance to explore a process method for controlling the internal quality of cold heading steel billets in response to the above-mentioned problems. Summary of the Invention

[0008] To overcome the shortcomings of the above-mentioned technologies, the purpose of this invention is to provide a production method for controlling the internal quality of cold-headed steel billets, thereby solving the problem of unstable internal quality control of cold-headed steel billets.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A production method for controlling the internal quality of cold-heading steel billets includes converter smelting, LF refining, RH vacuum treatment and continuous casting to obtain cold-heading steel billets; its special feature is that: in the continuous casting process, electromagnetic stirring technology in the crystallizer, electromagnetic stirring at the end of solidification and light reduction process at the end of solidification are adopted, and electromagnetic induction heating is used to control the superheat of the molten steel in the tundish to 18℃~25℃. The cold heading steel billet comprises the following components by mass percentage: C: 0.20~0.50%, Al: 0.015~0.035%, Mn≥0.65%, S≤0.004%.

[0010] As a preferred embodiment, during the continuous casting process, the billet pulling speed is maintained at 2.1~2.4m / min after the tundish is opened.

[0011] Furthermore, during the electromagnetic stirring process in the crystallizer, the current is 200~300A / m, the frequency is 2~4HZ, the liquid level fluctuation in the crystallizer is ±5mm, the total cooling water flow is 230~310L / min, and the specific water flow is 0.58~0.63L / kg; the crystallizer vibration parameters are: amplitude 7.6~8.0mm, vibration frequency 169~181; the current for the electromagnetic stirring at the solidification end is 300~500A / m, the frequency is 4~6HZ, and the total reduction is 22~25mm.

[0012] As a preferred embodiment, during the converter smelting process, the mass percentage of carbon at the time of steel tapping is C≥0.06%.

[0013] As a preferred embodiment, the mass percentage of sulfur in the molten steel after the LF refining treatment is S≤0.003%.

[0014] As a preferred embodiment, during the RH vacuum treatment, soft argon blowing is maintained for 15-20 minutes, and the outlet temperature of the molten steel after the RH vacuum treatment is completed is 1560-1570℃.

[0015] As a preferred embodiment, the light pressing process employs a light pressing device, which uses 4 to 7 tension rollers.

[0016] As a preferred embodiment, the billet obtained after continuous casting is a square billet with a cross-section of 160mm × 160mm.

[0017] As a preferred embodiment, the production method includes the following steps: 1) Converter smelting: Molten steel undergoes decarburization and dephosphorization treatment, aluminum deoxidation treatment, and alloy addition in a top-and-bottom blown converter. The carbon content is ≥0.06% when the steel is tapped from the converter. The molten steel from the converter is then treated with argon blowing at an argon station. 2) LF refining: After LF furnace treatment, the sulfur content in the molten steel is ≤0.003%; 3) RH vacuum treatment: Maintain soft argon blowing for 15-20 minutes; after RH vacuum treatment, the outlet temperature should be strictly controlled at 1560-1570℃. 4) Obtaining billets through continuous casting: The billet pulling speed is controlled at 2.1~2.4m / min; the billet is fed into an induction heating tundish for induction heating, and the superheat of the molten steel in the tundish is controlled to be stable at 18~25℃, the liquid level fluctuation in the crystallizer is ±5mm, the total cooling water volume is 230~310L / min, the specific water volume is 0.58~0.63L / kg, the crystallizer amplitude is 7.6~8.0mm, and the vibration frequency is 169~181; the crystallizer is equipped with electromagnetic stirring, and the electromagnetic stirring current is controlled at 200~300A / m, and the frequency is controlled at 2~4HZ; electromagnetic stirring is equipped at the end of solidification, and the current is controlled at 300~500A / m, and the frequency is controlled at 4~6HZ; a light reduction device is equipped for light reduction at the end of solidification, and the total reduction is controlled at 22~25mm; 4~7 straightening rolls are used. 5) Slow cooling: The billet is slowly cooled in the pit for ≥48 hours and the temperature after exiting the pit is ≤200℃.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses a production method for controlling the internal quality of cold-headed steel billets. Induction heating is used during continuous casting to stably control the superheat of the tundish, thereby stably controlling the casting speed. This avoids large fluctuations in casting speed due to unstable superheat, which could lead to billet quality fluctuations and on-site accidents. This invention further stabilizes the solidification end position by maintaining a stable tundish superheat and a stable casting speed, maximizing the effects of the electric stirring at the solidification end and the light and heavy pressing technology at the solidification end. This invention significantly improves the internal quality of cold heading steel billets by combining induction heating tundish with continuous casting process parameters, light and heavy pressure reduction technology, and solidification end electric stirring technology.

[0019] The cold heading steel billet manufactured using this invention has significantly improved central porosity, with central porosity ≤ 1.0 grade, central shrinkage cavity ≤ 1.0 grade, and central crack ≤ 1.0 grade. Attached Figure Description

[0020] Figure 1 This is a low-magnification photograph of the cast billet in Example 1 of this invention; Figure 2 This is a longitudinal photograph of the billet in Example 1 of this invention; Figure 3 This is a low-magnification photograph of the cast billet in Example 2 of this invention; Figure 4 This is a longitudinal sample photograph of the billet in Example 2 of this invention; Figure 5 This is a low-magnification photograph of the casting billet in the comparative example of this invention; Figure 6 This is a longitudinal photograph of the cast billet in the comparative example of this invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 In this embodiment, the carbon content of the steel is between 0.20% and 0.50%, the aluminum content is between 0.015% and 0.035%, the manganese content is ≥0.65%, and the sulfur content is ≤0.004%. Specific component contents are shown in Table 1, expressed as a percentage by mass. The process route is converter-argon blowing-LF-RH-CC, producing a 160mm × 160mm square billet. The production method for controlling the internal quality of cold-headed steel billets according to this invention includes the following steps: 1) Converter smelting: Molten steel undergoes decarburization and dephosphorization treatment, aluminum deoxidation treatment, and the addition of necessary alloys in a top-and-bottom blown converter. The carbon content of the molten steel when tapped from the converter is 0.06 wt%. The molten steel from the converter is then treated with argon blowing at the argon station. 2) LF refining: The target S content of the molten steel after LF furnace treatment is 0.003 wt%; 3) RH vacuum treatment: RH refining is carried out by soft blowing argon for 20 minutes; the temperature at the outlet after refining is strictly controlled at 1560~1570℃. 4) Continuous casting to obtain billet: put it into the induction heating tundish for induction heating, and control the superheat at 23℃; put it into the crystallizer for electromagnetic stirring, electromagnetic stirring at the end of solidification and light reduction process; The pulling speed is controlled at 2.2 m / min; Liquid level fluctuation in the crystallizer is ±5mm; Total cooling water flow: 275L / min, specific water flow: 0.6L / kg; Vibration parameters: Amplitude 7.8mm, Frequency: 176; The electromagnetic stirring current of the crystallizer is controlled at 200A / m, and the frequency is controlled at 3HZ; The solidification end current is controlled at 300A / m, and the frequency is controlled at 5HZ; The light pressing device is activated, and the total pressing amount is controlled at 22mm; five tension rollers are activated, with pressing amounts of 2mm, 3mm, 6mm, 6mm, and 5mm respectively. 5) Slow cooling: The billet is slowly cooled in the pit for 48 hours, and the temperature when it comes out of the pit is 200℃.

[0023] Example 2 This embodiment describes a production method for controlling the internal quality of cold-headed steel billets. The difference from Embodiment 1 is that: the superheat is controlled at 18°C, the casting speed is controlled at 2.3 m / min, the electromagnetic stirring current in the crystallizer is controlled at 300 A / m, and the frequency is controlled at 3 Hz; the current at the solidification end is controlled at 350 A / m, and the frequency is controlled at 6 Hz; a pressing device is used, with a total pressing amount controlled at 24 mm; five straightening rollers are used, with pressing amounts of 2 mm, 3 mm, 7 mm, 7 mm, and 5 mm respectively.

[0024] Comparative Example A production method for controlling the internal quality of cold-headed steel billets. The difference from Example 1 is that: no induction heating tundish is used, no solidification end-pressing process is employed, and the tundish superheat reaches 35°C.

[0025] The obtained slabs were subjected to low-magnification inspection and rating, and the rating was carried out with reference to the "YBT153-2015 Low-Magnification Microstructure Defect Rating Chart for High-Quality Structural Steel Continuous Casting Slabs". The rating results are shown in Table 2, and the low-magnification photograph of the slab in Example 1 is shown in Table 2. Figure 1 and Figure 2 See the low-magnification photograph in Example 2. Figure 3 and Figure 4 See the low-magnification photos for comparison. Figure 5 and Figure 6 .

[0026] Table 1: Composition content of cold heading steel in the examples and comparative examples, % Table 2: Low-magnification quality rating of cast billets under different process conditions As shown in Table 2 and Figures 1-6 As shown, compared with the comparative examples, the billets produced by the method of the present invention in Examples 1 and 2 have significantly improved central porosity and shrinkage cavities, with central porosity ≤ 1.0 grade, central shrinkage cavities ≤ 1.0 grade, and central cracks ≤ 1.0 grade. The internal quality of the billets is stable. In particular, in Example 2, the central porosity, central shrinkage cavities, and central cracks of each sample are all rated less than 0.5.

[0027] Therefore, it can be seen that the present invention significantly improves the internal quality of cold heading steel billets by combining induction heating tundish with continuous casting process parameters, light and heavy pressure reduction technology, and solidification end electric stirring technology.

[0028] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. All equivalent transformations made using the contents of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A production method for controlling the internal quality of cold-heading steel billets, comprising converter smelting, LF refining, RH vacuum treatment, and continuous casting to obtain cold-heading steel billets; characterized in that: During the continuous casting process, electromagnetic stirring technology in the crystallizer, electromagnetic stirring at the end of solidification, and light reduction at the end of solidification are adopted. Electromagnetic induction heating is used to control the superheat of the molten steel in the tundish to 18°C~25°C. The cold heading steel billet comprises the following components by mass percentage: C: 0.20~0.50%, Al: 0.015~0.035%, Mn≥0.65%, S≤0.004%.

2. The production method according to claim 1, characterized in that, During the continuous casting process, the billet pulling speed is maintained at 2.1~2.4m / min after the tundish is opened.

3. The production method according to claim 1, characterized in that, During the electromagnetic stirring process of the crystallizer, the current is 200~300A / m, the frequency is 2~4HZ, the liquid level fluctuation in the crystallizer is ±5mm, the total cooling water volume is 230~310L / min, and the specific water volume is 0.58~0.63L / kg; the crystallizer vibration parameters are: amplitude 7.6~8.0mm, vibration frequency 169~181.

4. The production method according to claim 1, characterized in that, The current of the electromagnetic stirring at the solidification end is 300~500A / m, and the frequency is 4~6HZ.

5. The production method according to claim 1, characterized in that, During the continuous casting process, the total reduction is 22~25mm.

6. The production method according to claim 1, characterized in that, During the converter smelting process, the mass percentage of carbon when tapping steel from the converter is C≥0.06%; the mass percentage of sulfur in the molten steel after the LF refining treatment is S≤0.003%.

7. The production method according to claim 1, characterized in that, During the RH vacuum treatment, soft argon blowing is maintained for 15-20 minutes. After the RH vacuum treatment is completed, the outlet temperature of the molten steel is 1560-1570℃.

8. The production method according to claim 1, characterized in that, The light pressing process employs a light pressing device, which uses 4 to 7 tension rollers.

9. The production method according to claim 1, characterized in that, The billet obtained after continuous casting is a square billet with a cross-section of 160mm × 160mm.

10. The production method according to any one of claims 1 to 9, characterized in that, The production method includes the following steps: 1) Converter smelting: Molten steel undergoes decarburization and dephosphorization treatment, aluminum deoxidation treatment, and alloy addition in a top-and-bottom blown converter. The carbon content is ≥0.06% when the steel is tapped from the converter. The molten steel from the converter is then treated with argon blowing at an argon station. 2) LF refining: After LF furnace treatment, the sulfur content in the molten steel is ≤0.003%; 3) RH vacuum treatment: Maintain soft argon blowing for 15-20 minutes; after RH vacuum treatment, the outlet temperature should be strictly controlled at 1560-1570℃. 4) Obtaining the billet through continuous casting: The billet pulling speed is controlled at 2.1~2.4m / min; the billet is fed into an induction heating tundish for induction heating, and the superheat of the molten steel in the tundish is controlled to be stable at 18~25℃, the liquid level fluctuation in the crystallizer is ±5mm, the total cooling water volume is 230~310L / min, the specific water volume is 0.58~0.63L / kg, the crystallizer amplitude is 7.6~8.0mm, and the vibration frequency is 169~181; the crystallizer is equipped with electromagnetic stirring, and the electromagnetic stirring current is controlled at 200~300A / m, and the frequency is controlled at 2~4HZ; electromagnetic stirring is equipped at the solidification end, and the current is controlled at 300~500A / m, and the frequency is controlled at 4~6HZ; a light reduction device is equipped, and the total reduction is controlled at 22~25mm; 4~7 straightening rolls are equipped. 5) Slow cooling: The billet is slowly cooled in the pit for ≥48 hours and the temperature after exiting the pit is ≤200℃.

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