A process for improving the internal quality of large size bars
By using clean steel smelting and optimized continuous casting process parameters, combined with appropriate heating and rolling processes, the internal quality problems of large-diameter bars were solved, enabling the production of high-quality bars and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- HUNAN VALIN XIANGTAN IRON & STEEL CO LTD
- Filing Date
- 2022-11-29
- Publication Date
- 2026-08-04
AI Technical Summary
Existing technologies for producing large-diameter bars with a cross-section of 350×430 have problems such as internal shrinkage cavities, porosity, center segregation, and extremely poor hardness, resulting in substandard product quality, high costs, and severely restricting the development of high-quality large-diameter bars.
Clean steelmaking processes are used to control the impurity content in steel, optimize continuous casting process parameters, and combine light and heavy reduction distribution, appropriate heating processes, and controlled rolling and cooling processes, including converter smelting, ladle refining, continuous casting temperature control, electric stirring parameter design, heating and rolling processes, to ensure the quality of billets and rolled round bars.
These processes improve the internal quality of large-diameter bars, and the low-density quality, carbon difference, and hardness difference of cast billets and rolled round bars meet user requirements, thereby reducing production costs.
Smart Images
Figure CN115889458B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of metallurgical technology and relates to a process method for improving the internal quality of large-diameter bars with a diameter of φ180mm and above. Background Technology
[0002] The rapid development of various industries and continuous technological advancements have led to the rapid growth of the high-end equipment manufacturing industry. The increased demand for high-quality, large-size bar stock has driven the rapid development of large-section continuous casting machine equipment technology and processes. Previously, large-size products were rolled using ingot casting, which resulted in a high ingot compression ratio and good product quality. However, this method also resulted in low yield and high energy consumption, leading to high costs for ingot casting and rolling of large-size products, severely hindering the development of high-quality, large-size products.
[0003] In the production of 350×430 cross-section continuous casting machines, the internal structure of large-diameter bars with diameters of φ180mm~φ220mm is characterized by shrinkage cavities, porosity, severe central segregation, and significant differences in carbon and hardness within the same cross-section, making it impossible to guarantee the internal quality of the large-diameter bars. Summary of the Invention
[0004] This invention aims to provide a process control technology to solve the internal quality problems of rolling φ180mm~φ220mm large-size bars from 350mm×430mm cross-section continuous casting billets. The technology is used to produce 350mm×430mm cross-section continuous casting billets with good low-magnification quality, significantly improved control of carbon segregation and ingot segregation, and qualified flaw detection for φ180mm~φ220mm large-size bars. The low-magnification quality, carbon difference and hardness difference of the same cross section, and square segregation fully meet the requirements.
[0005] The technical solution of the present invention: A process for improving the internal quality of large-diameter bars, the key process steps of which include: (1) Converter smelting and ladle refining: Clean steel smelting process is adopted to control the phosphorus content in the steel to P≤0.015%, the sulfur content to S≤0.005%, and the total oxygen content to TO≤0.0012%; (2) Continuous casting temperature: The continuous casting temperature on the molten steel is the liquidus temperature of the steel grade +50~70℃ for the turnover ladle, and the liquidus temperature of the steel grade +80~100℃ for the new ladle or overhaul ladle. The superheat of the tundish is 15~30℃. (3) Continuous casting speed and cooling: The cross-section of the billet is 350×430, the continuous casting speed is 0.47~0.60m / min, the cooling of the crystallizer is 3200~3800L / min, and the secondary cooling water volume is 0.16~0.26L / kg; (4) Continuous casting electric stirring: The electric stirring current of the crystallizer is 150~300A and the electric stirring frequency is 2.5Hz; the electric stirring current of the end is 200~400A and the electric stirring frequency is 5~8Hz; (5) Distribution of light and heavy reduction in continuous casting: The reduction of alloy structural steel in stands 2, 3, 4, 5, 6 and 7 is 2mm, 3mm, 5mm, 5mm, 5mm and 5mm respectively, with a total reduction of 25mm; The reduction of high-quality carbon structural steel in stands 3, 4, 5, 6 and 7 is 5mm respectively, with a total reduction of 25mm. (6) Heating: Total heating time 180~300min, preheating temperature 680~850℃, preheating time 60~90min, heating temperature 1160~1220℃, heating time 90~180min, soaking temperature 1180~1220℃, soaking time 60~120min; (7) Rolling: The initial rolling temperature is 1050~1150℃, the continuous rolling temperature is 980~1100℃, the final rolling temperature is 960~1010℃, and the upper cooling bed temperature is 780~850℃. Rolling adopts large reduction, and the reduction of the first and second passes is not less than 80mm and 75mm respectively.
[0006] The beneficial effects of this invention are as follows: Addressing the problems associated with rolling large-diameter bars from 350×430 cross-section continuous casting billets, this invention employs clean steel smelting control technology, optimizes continuous casting process parameters, and distributes light and heavy reduction amounts. Combined with appropriate heating and controlled rolling / cooling processes, it enables the production of round bars with diameters of φ180mm and above. The billets exhibit excellent low-magnification quality, with the carbon difference across the same cross-section of medium carbon steel not exceeding 0.03%, the hardness difference (HBW value) not exceeding 10, and passing ultrasonic testing. The low-magnification quality, carbon difference and hardness difference across the same cross-section, and square segregation fully meet the user's requirements for large-diameter bars. Attached Figure Description
[0007] Figure 1 This is a low-magnification image of a continuously cast billet with a cross-section of 350mm × 430mm, as shown in Example 1.
[0008] Figure 2 A low-magnification transverse view of the rolled round steel bar of Example 1 with a diameter of φ220mm.
[0009] Figure 3 Longitudinal low-magnification view of rolled round steel in Example 1 with a specification of φ220mm.
[0010] Figure 4 This is a low-magnification image of a continuously cast billet with a cross-section of 350mm × 430mm, as shown in Example 2.
[0011] Figure 5 A low-magnification transverse view of the rolled round steel in Example 2, with a diameter of φ220mm.
[0012] Figure 6Longitudinal low-magnification view of rolled round steel in Example 2 with a specification of φ220mm.
[0013] Figure 7 This diagram shows the locations of sampling points for carbon segregation and hardness in rolled round steel. Detailed Implementation
[0014] Example 1: A process for improving the internal quality of large-diameter bars involves controlling the S=0.043%, P=0.123%, Si=0.46% in the molten iron fed into the converter at a temperature of 1318℃, without pretreatment, to smelt alloy structural steel 42CrMoA. Key process steps include: (1) Converter smelting and ladle refining: Clean steel smelting process is adopted, and P=0.012%, S=0.004%, TO=0.0008% in steel are controlled; (2) Continuous casting temperature of molten steel: This furnace is a normal turnover ladle, the continuous casting temperature of the upper ladle is 1556℃, and the superheat of the tundish is 20~30℃; (3) The cross-section of the billet is 350×430, the continuous casting speed is 0.48m / min, the cooling rate of the crystallizer is 3200L / min, and the secondary cooling water volume is 0.17L / Kg; (4) Electric stirring parameter design: The electric stirring current of the crystallizer is 160A and the electric stirring frequency is 2.5Hz. The electric stirring current at the end is 200A and the electric stirring frequency is 8Hz. (5) Distribution of light and heavy compression: The compression amounts of alloy structural steel frames 4, 5, 6, 7, 8 and 9 are 2mm, 3mm, 4mm, 5mm, 5.5mm and 5.5mm respectively, with a total compression amount of 25mm; (6) Heating: Preheating section temperature 700℃, preheating section time 90min, heating section temperature 1180℃, heating section time 120min, soaking section temperature 1190℃, soaking section time 90min; (7) Rolling: The initial rolling temperature is 1050℃, the continuous rolling temperature is 980℃, the final rolling temperature is 960℃, the upper cooling bed temperature is 800℃, and the rolling adopts a large reduction. The reduction of the first and second passes is 80mm and 75mm respectively.
[0015] See the low magnification images of cast billets and rolled round bars. Figure 1 , Figure 2 , Figure 3 .
[0016] Carbon and hardness ranges of the round steel rolled in this batch: Sampling points for carbon segregation and hardness of the rolled round steel are as follows: Figure 7 As shown, the carbon content and hardness at each sampling point are shown in Table 1 and Table 2, respectively.
[0017] Table 1 Carbon Difference of Rolled Round Steel in Example 1 .
[0018] Table 2. Extremely poor hardness of rolled round steel in Example 1 .
[0019] Example 2: A process for improving the internal quality of large-diameter bars, wherein the molten iron fed into the converter has a sulfur content of S=0.038%, a phosphorus content of P=0.142%, and a Si content of 0.44%, at a temperature of 1295℃, without pretreatment, and is used to smelt alloy structural steel 42CrMoA. Key process steps include: (1) The converter smelting and ladle refining adopt the clean steel smelting process, and the phosphorus content in the steel is P=0.011%, the sulfur content is S=0.003%, and the total oxygen content is TO=0.0010%; (2) Continuous casting temperature of molten steel: The ladle of this furnace is a major overhaul ladle, the continuous casting temperature of the upper ladle is 1580℃, and the superheat of the middle ladle is 15~25℃; (3) The cross-section of the billet is 350×430, the continuous casting speed is 0.60m / min, the cooling rate of the crystallizer is 3800L / min, and the secondary cooling water volume is 0.26L / kg; (4) Electric stirring parameter design: The electric stirring current of the crystallizer is 300A and the electric stirring frequency is 2.5Hz; the electric stirring current of the end is 400A and the electric stirring frequency is 5Hz. (5) Distribution of light and heavy compression: The compression amounts of the 3rd, 4th, 5th, 6th and 7th frames of high-quality carbon structural steel are 5mm, 5mm, 5mm, 5mm and 5mm respectively, with a total compression amount of 25mm; (6) Heating: Preheating section temperature 830℃, preheating section time 60min, heating section temperature 1210℃, heating section time 120min, soaking section temperature 1220℃, soaking section time 60min; (7) Rolling: The initial rolling temperature is 1150℃, the continuous rolling temperature is 1100℃, the final rolling temperature is 1010℃, the upper cooling bed temperature is 850℃, and the rolling adopts a large reduction. The reduction of the first and second passes is 90mm and 85mm respectively.
[0020] Low magnification of cast billets and low magnification of rolled round bars are shown below. Figure 4 , Figure 5 , Figure 6 .
[0021] Carbon segregation and hardness differences of the rolled round steel in this batch: Sampling points for carbon segregation and hardness of the rolled round steel are as follows: Figure 7 As shown, the carbon content and hardness at each sampling point are shown in Tables 3 and 4, respectively.
[0022] Table 3 Carbon Difference of Rolled Round Steel in Example 2 .
[0023] Table 4. Extremely poor hardness of rolled round steel in Example 2 .
Claims
1. A process for improving the internal quality of large-diameter bars, characterized in that... Key process steps include: (1) Converter smelting and ladle refining: Clean steel smelting process is adopted to control the phosphorus content in the steel to P≤0.015%, the sulfur content to S≤0.005%, and the total oxygen content to TO≤0.0012%; (2) Continuous casting temperature: The continuous casting temperature on the molten steel is the liquidus temperature of the steel grade +50~70℃ for the turnover ladle, and the liquidus temperature of the steel grade +80~100℃ for the new ladle or overhaul ladle. The superheat of the tundish is 15~30℃. (3) Continuous casting speed and cooling: The cross-section of the billet is 350×430, the continuous casting speed is 0.47~0.60m / min, the cooling of the crystallizer is 3200~3800L / min, and the secondary cooling water volume is 0.16~0.26L / kg; (4) Continuous casting electric stirring: The electric stirring current of the crystallizer is 150~300A and the electric stirring frequency is 2.5Hz; the electric stirring current of the end is 200~400A and the electric stirring frequency is 5~8Hz; (5) Distribution of light and heavy reduction in continuous casting: The reduction of alloy structural steel in stands 2, 3, 4, 5, 6 and 7 is 2mm, 3mm, 5mm, 5mm, 5mm and 5mm respectively, with a total reduction of 25mm; The reduction of high-quality carbon structural steel in stands 3, 4, 5, 6 and 7 is 5mm respectively, with a total reduction of 25mm. (6) Heating: Total heating time 180~300min, preheating temperature 680~850℃, preheating time 60~90min, heating temperature 1160~1220℃, heating time 90~180min, soaking temperature 1180~1220℃, soaking time 60~120min; (7) Rolling: The initial rolling temperature is 1050~1150℃, the continuous rolling temperature is 980~1100℃, the final rolling temperature is 960~1010℃, and the upper cooling bed temperature is 780~850℃. Rolling adopts large reduction, and the reduction of the first and second passes is not less than 80mm and 75mm respectively.