Technological method for prolonging fatigue life of spring steel

Abstract

The invention discloses a process method for prolonging the fatigue life of spring steel, and belongs to the technical field of steel smelting. Molten iron enters KR pretreatment for deep desulfurization and slagging-off, silicon-manganese deoxidation is selected according to steel grade characteristics, thermodynamic calculation is adopted, the control range of all components of refining slag is determined, VD controls vacuum keeping time, soft blowing time and soft blowing effect, and technological parameters such as the continuous casting pulling speed, secondary cooling water distribution and casting powder are optimized. The number of inclusions in the steel billet is 4.0 / mm < 2 >, the size of the inclusions is within 10 microns, and the surface quality of the steel billet is good.

Description

Technical Field

[0001] The invention belongs to the technical field of steel smelting and relates to a process for improving the fatigue life of spring steel. Background Art

[0002] With the rapid economic development of recent years, the penetration rate of new energy vehicles has greatly increased. Spring steel, as an indispensable steel for automotive parts, is required to have an extremely long fatigue life. The level of non-metallic inclusion control in the steel and the surface quality of the steel billet are the main factors affecting the ultra-long fatigue life of spring steel. Given the high fatigue life requirements of spring steel, research on the refining operations of the main raw and auxiliary materials of spring steel, the control of inclusions, and the continuous casting process operation to meet the fatigue life requirements of spring steel has important practical significance for technological advancement. Summary of the Invention

[0003] The present invention aims to provide a process for improving the fatigue life of spring steel, which can significantly improve the fatigue life of spring steel and obtain an inclusion of 4.0 / mm 2 , steel billets with inclusions within 10μm in size and good surface quality.

[0004] The technical solution of the present invention: A process for improving the fatigue life of spring steel comprises the following process steps: (1) The molten iron enters the KR for deep desulfurization and slag removal. After slag removal, the sulfur content of the molten iron [S] is controlled to be ≤0.006%, and the slag thickness is ≤20mm; (2) The converter smelting is carried out according to the normal smelting process. During the tapping process, low-titanium, low-aluminum ferrosilicon, metallic manganese and low-carbon ferrochrome are added to deoxidize and alloy the molten steel. After tapping, 1000-1100 kg of fast-melting low-aluminum, low-basicity refining slag is added. (3) The molten steel is transferred to the LF refining station, and the temperature is raised to 1560℃ by electricity. 1000kg of fast-melting low-aluminum and low-basicity refining slag and 200-300kg of lime are added to the ladle to make slag. The basicity of the slag is controlled at 0.8-0.95. SiC is used to diffuse and deoxidize the refining slag during the refining process. (4) VD is vacuumed to below 67Pa, the vacuum time is 15~20min, and the soft blowing time is 25~30min. During the soft blowing process, the argon gas is controlled so that the slag surface is not broken; (5) The casting speed of the continuous casting process is controlled at 0.48~0.55m / min, the secondary cooling water ratio is 0.17~0.19L / kg, the protective slag is low-aluminum high-carbon steel protective slag, and the thickness of the protective slag in the crystallizer liquid slag layer is 7~10 mm, and the number of inclusions is 4.0 / mm 2 , steel billets with inclusions within 10μm in size and good surface quality.

[0005] The beneficial effects of the present invention are as follows: by passing the molten iron into the KR pretreatment for deep desulfurization and slag removal, silicon and manganese series deoxidation are selected according to the characteristics of the steel grade, and thermodynamic calculations are used to determine the control range of each component of the refined slag, and the continuous casting process parameters are optimized. During the test production, the molten iron is sent to the KR pretreatment for deep desulfurization and slag removal. The converter steel-making process uses low-aluminum, low-titanium ferrosilicon, metallic manganese and low-carbon ferrochrome for deoxidation and alloying. After steel-making, fast-melting low-aluminum, low-alkalinity refined slag is added. After the temperature is increased in the LF station, lime and fast-melting low-aluminum, low-alkalinity refined slag are added for slag making. The refining process uses SiC diffusion deoxidation, and VD controls the vacuum holding time, soft blowing time and soft blowing effect. The continuous casting pouring process uses low pulling speed and weak cooling control, and at the same time, the protective slag is changed from the original protective slag to low-aluminum, high-carbon protective slag, to obtain a steel billet with a small number, small size, low melting point inclusions and good surface quality. The number of inclusions in spring steel can be controlled at 4.0 / mm 2 The size is controlled within 10μm, and the surface quality of the ingot is good without obvious defects. By controlling the level of non-metallic inclusions in the steel and the surface quality of the ingot, the fatigue life of the spring steel is greatly improved. DETAILED DESCRIPTION Example

[0006] A process for improving the fatigue life of spring steel was developed. A pilot production process for improving inclusions and surface quality in a 430×350 rectangular X55SiCrA-R steel mill with five machines and five streams was conducted on a five-meter thick plate mainframe. The pilot process was conducted on the second and third heats of the casting sequence. The process steps included: (1) The molten iron enters the KR for deep desulfurization and slag removal. After slag removal, the sulfur content of the molten iron [S] is 0.004%. The slag thickness after slag removal is measured to be 18 mm.

[0007] (2) The converter smelting is carried out according to the normal smelting process. During the steel-making process, low-titanium, low-aluminum ferrosilicon, metallic manganese and low-carbon ferrochrome are added to deoxidize and alloy the molten steel. After the steel is tapped, 1000 kg of fast-melting low-aluminum, low-basicity refining slag is added.

[0008] (3) The molten steel is transferred to the LF refining station and heated to 1568℃ by electricity. 1000kg of fast-melting low-aluminum and low-basicity refining slag and 200kg of lime are added to the ladle for slagging. The basicity of the refining slag is 0.81. 160kg of SiC is added for diffusion deoxidation during the refining process.

[0009] (4) VD is vacuumed to below 67Pa, the vacuum time is 16min, and the soft blowing time is 25min. During the soft blowing process, the slag surface fluctuates slightly and the molten steel is not exposed.

[0010] (5) The casting speed during the continuous casting process is controlled at 0.49 m / min, the secondary cooling water ratio is controlled at 0.18 L / kg, and the protective slag is low-aluminum high-carbon steel protective slag. The thickness of the protective slag in the crystallizer liquid slag layer is 9 mm.

[0011] (6) The non-metallic inclusions were automatically scanned for the test heat wire rods. The inclusion scanning results are shown in Table 1. Example

[0012] A process for improving the fatigue life of spring steel was developed. A pilot production process for improving inclusions and surface quality in a 430×350 rectangular X55SiCrA-R steel mill with five machines and five streams was conducted on a five-meter thick plate mainframe. The pilot process was conducted on the first and second heats of the casting sequence. The process steps included: (1) The molten iron enters KR for deep desulfurization and slag removal. After slag removal, the sulfur content of the molten iron [S] is 0.005%, and the slag thickness after slag removal is measured to be 11 mm.

[0013] (2) The converter smelting is carried out according to the normal smelting process. During the steel-making process, low-titanium, low-aluminum ferrosilicon, metallic manganese and low-carbon ferrochrome are added to deoxidize and alloy the molten steel. After the steel is tapped, 1090 kg of fast-melting low-aluminum, low-basicity refining slag is added.

[0014] (3) The molten steel is transferred to the LF refining station and heated to 1572℃ by electricity. 1000kg of fast-melting low-aluminum and low-basicity refining slag and 290kg of lime are added to the ladle for slagging. The basicity of the refining slag is 0.93. 200kg of SiC is added for diffusion deoxidation during the refining process.

[0015] (4) VD is vacuumed to below 67Pa, the vacuum time is 20min, and the soft blowing time is 30min. During the soft blowing process, the slag surface fluctuates slightly and the molten steel is not exposed.

[0016] (5) The casting speed during the continuous casting process is controlled at 0.54 m / min, the secondary cooling water ratio is controlled at 0.18 L / kg, and the protective slag is low-aluminum high-carbon steel protective slag. The thickness of the protective slag in the crystallizer liquid slag layer is 10 mm.

[0017] (6) The non-metallic inclusions were automatically scanned on the test heat wire rods. The inclusion scanning results are shown in Table 1. 500 mm of the ingot was taken for surface pickling inspection. The surface pickling results are shown in Table 2.

[0018] Table 1 Scanning results of non-metallic inclusions in the test heat of Example 1 .

[0019] Table 2 Scanning results of non-metallic inclusions in the test heat of Example 2 .

Claims

1. A process for improving the fatigue life of spring steel, characterized in that The process steps include: (1) The molten iron enters the KR for deep desulfurization and slag removal. After slag removal, the sulfur content of the molten iron [S] is controlled to be ≤0.006%, and the slag thickness is ≤20mm; (2) The converter smelting is carried out according to the normal smelting process. During the tapping process, low-titanium, low-aluminum ferrosilicon, metallic manganese and low-carbon ferrochrome are added to deoxidize and alloy the molten steel. After tapping, 1000-1100 kg of fast-melting low-aluminum, low-basicity refining slag is added. (3) The molten steel is transferred to the LF refining station, and the temperature is raised to 1560℃ by electricity. 1000kg of fast-melting low-aluminum and low-basicity refining slag and 200-300kg of lime are added to the ladle to make slag. The basicity of the slag is controlled at 0.8-0.

95. SiC is used to diffuse and deoxidize the refining slag during the refining process. (4) VD is vacuumed to below 67Pa, the vacuum time is 15~20min, and the soft blowing time is 25~30min. During the soft blowing process, the argon gas is controlled so that the slag surface is not broken; (5) The casting speed of the continuous casting process is controlled at 0.48~0.55m / min, the secondary cooling water ratio is 0.17~0.19L / kg, the protective slag is low-aluminum high-carbon steel protective slag, and the thickness of the protective slag in the crystallizer liquid slag layer is 7~10 mm, and the number of inclusions is 4.0 / mm 2 , steel billets with inclusions within 10μm in size and good surface quality.