Production process for improving segregation of bearing steel rectangular continuous casting billet

Abstract

The invention discloses a production process for improving segregation of a rectangular continuous casting billet of bearing steel. The production process comprises the steps of converter smelting, LF refining, VD vacuum degassing, continuous casting, square billet heating furnace heating and round steel rolling. By optimizing electromagnetic stirring parameters and controlling the cooling strength, segregation frames approach to a square from a rectangle, the proportion of the segregation frames in the section is reduced, and the component uniformity of the steel billet is improved; the enrichment of segregation elements in the center is reduced, the mechanical property stability, including hardness, toughness and fatigue life, of the steel is improved, and the use requirements of high-end bearings are met; by optimizing the cooling strength and the soft reduction process, the occurrence rate of center shrinkage cavities and crack defects is reduced, and the yield and the rolling qualification rate of continuous casting billets are remarkably increased; according to the face recognition rolling technology, the influence range of a segregation frame is effectively reduced, quality fluctuation caused by segregation in the rolling process is reduced, and the follow-up machining difficulty and production cost are reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of smelting and rolling, and in particular relates to a production process for improving the segregation of rectangular continuous casting billets of bearing steel. Background Art

[0002] Bearing steel is widely used in the fields of automobiles, machinery manufacturing, wind power generation, high-speed railways, etc., and the market demand is stable and continues to grow. With the development of high-end equipment manufacturing, especially the rise of new energy vehicles, intelligent manufacturing and green energy, the market demand for high-performance bearing steel will further expand. By developing high-quality bearing steel, steel mills can not only enter the high-end market, but also take the initiative in domestic substitution of imported materials, effectively increasing market share and brand value.

[0003] Improving the segregation of rectangular continuous casting billets of bearing steel is crucial to meeting the stringent requirements of high-performance bearing applications. Segregation is the phenomenon of uneven distribution of alloying elements and impurities in steel during solidification, which will lead to inhomogeneity in the internal structure of the material, thereby affecting the mechanical properties and service life of the bearing steel. Segregation will also have an adverse effect on subsequent heat treatment and processing performance, increasing the risk of quenching cracks and processing deformation. Especially for high-end bearing steel, segregation may cause cracks, reduce fatigue performance, and increase the defect rate during processing, thereby affecting the stability and reliability of downstream products. By improving continuous casting process parameters, optimizing electromagnetic stirring and controlling cooling intensity, and performing face rolling during rolling, the segregation of bearing steel can be effectively reduced, and the purity and uniformity of bearing steel can be improved, thereby meeting the strict material requirements of high-performance bearings, while reducing production costs and scrap rates, and enhancing corporate competitiveness. Summary of the invention

[0004] The purpose of the present invention is to provide a production process for improving the segregation of rectangular continuous casting billets of bearing steel, improving the continuous casting process parameters, optimizing electromagnetic stirring and controlling the cooling intensity, and performing surface rolling during rolling, which can effectively reduce the segregation of bearing steel and improve the purity and uniformity of bearing steel, thereby meeting the strict requirements of high-performance bearings for materials, while reducing production costs and scrap rates.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention discloses a production process for improving the segregation of rectangular continuous casting billets of bearing steel, comprising converter smelting, LF refining, VD vacuum degassing, continuous casting, billet heating furnace heating, and round steel rolling; wherein:

[0007] Continuous casting process;

[0008] (1) The pouring temperature is controlled at 1520±20℃. Too high temperature will lead to excessive fluidity of molten steel and aggravate segregation. Too low temperature will easily cause premature solidification of molten steel and form cracks during casting. The high carbon content of GCr15 makes the temperature difference between its liquidus and solidus smaller. The lower casting speed helps to reduce turbulence and control the stability of molten steel flow in the crystallizer. Therefore, the casting speed is controlled at 0.6-0.9m / min. In the area of ​​70%-90% solid phase ratio, light pressing operation is carried out with a pressing amount of 1.5-2mm to reduce the formation of central shrinkage cavity and segregation frame and improve the uniformity of internal composition of the billet.

[0009] (2) The crystallizer electromagnetic stirring frequency is 2-3 Hz, and the current intensity is 300-400A. Through low-frequency stirring, the horizontal flow of the molten steel in the crystallizer is enhanced and the component distribution is homogenized; the electromagnetic stirring frequency of the secondary cooling zone is 3-5 Hz, and the current intensity is 200-300A, which further promotes the homogenization of the composition of the molten steel at the solid-liquid interface and improves segregation;

[0010] (3) Cooling water flow in the secondary cooling zone: first zone: 0.25-0.30 L / kg steel, second zone: 0.20-0.25 L / kg steel, third zone: 0.15-0.20 L / kg steel, to achieve segmented cooling to reduce the temperature difference between the surface and the center of the billet; add a water mist cooling device to ensure uniform cooling of the cross section of the billet and reduce component segregation caused by the temperature difference in the center;

[0011] Rolling process: face rolling, with the long side as the thickness direction of the rolling direction, so that the plastic deformation is concentrated on the segregation frame, changing its shape and size; the heating temperature range is 1180℃±20℃, too high temperature will easily cause the austenite grains to grow, which is not conducive to the refinement of the segregation area; too low temperature will lead to reduced rolling plasticity and affect the deformation effect; the first rolling reduction is 20-30%, and the total compression ratio is 70%-80%. High pressure reduction helps to eliminate central segregation and make the segregation frame gradually approach square from rectangular; the cooling rate after rolling is controlled to 20-30℃ / s, and air cooling or weak water spray cooling is used to avoid excessive temperature difference between the surface and the inside of the steel, which leads to secondary segregation.

[0012] Furthermore, the finished rolled product has a specification of 165 mm;

[0013] Furthermore, the size of the continuous casting rectangular billet is 320 mm×415 mm.

[0014] Further, continuous casting process:

[0015] (1) Casting temperature 1520℃;

[0016] (2) Pulling speed: 0.78 m / min;

[0017] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.6 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet;

[0018] (4) The crystallizer electromagnetic stirring frequency is 2.5 Hz and the current intensity is 380 A;

[0019] (5) The electromagnetic stirring frequency in the second cooling zone is 3.5 Hz and the current intensity is 270 A;

[0020] (6) Cooling water flow in the second cooling zone: first zone: 0.27 L / kg steel, second zone: 0.22 L / kg steel, third zone: 0.18 L / kg steel, achieving segmented cooling;

[0021] Rolling process:

[0022] (1) Heating temperature: 1180°C;

[0023] (2) The first rolling reduction is 24%, and the total reduction ratio is 76%;

[0024] (3) The cooling rate after rolling is 25℃ / s;

[0025] (4) The finished rolled product specification is 165 mm.

[0026] Further, continuous casting process:

[0027] (1) Casting temperature 1510℃;

[0028] (2) Pulling speed: 0.75 m / min;

[0029] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.65 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet;

[0030] The crystallizer electromagnetic stirring frequency is 2.2 Hz, and the current intensity is 370 A;

[0031] The electromagnetic stirring frequency of the second cooling zone is 3.8 Hz, and the current intensity is 240 A;

[0032] Cooling water flow in the second cooling zone: first zone: 0.26L / kg steel, second zone: 0.24L / kg steel, third zone: 0.17L / kg steel, achieving segmented cooling;

[0033] Rolling process:

[0034] Heating temperature: 1170°C;

[0035] The first rolling reduction is 25%, and the total reduction ratio is 76%;

[0036] The cooling rate after rolling is 24℃ / s;

[0037] The finished rolled product specification is 165mm.

[0038] Further, continuous casting process:

[0039] (1) Casting temperature 1530℃;

[0040] (2) Pulling speed: 0.73 m / min;

[0041] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.55 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet;

[0042] The crystallizer electromagnetic stirring frequency is 2.6 Hz, and the current intensity is 390 A;

[0043] The electromagnetic stirring frequency of the second cooling zone is 3.3 Hz, and the current intensity is 260 A;

[0044] Cooling water flow in the second cooling zone: first zone: 0.25L / kg steel, second zone: 0.23L / kg steel, third zone: 0.16L / kg steel, achieving segmented cooling;

[0045] Rolling process:

[0046] Heating temperature: 1190°C;

[0047] The first rolling reduction is 26%, and the total reduction ratio is 76%;

[0048] The cooling rate after rolling is 23℃ / s;

[0049] The finished rolled product specification is 165mm.

[0050] Furthermore, the aspect ratio of the finished frame is close to 1.02-1.03.

[0051] Compared with the prior art, the beneficial technical effects of the present invention are:

[0052] The present invention optimizes electromagnetic stirring parameters and controls cooling intensity, so that the segregation frame approaches a square from a rectangle, reduces the proportion of the segregation frame in the cross section, and improves the composition uniformity of the steel billet; reduces the enrichment of segregation elements in the center, improves the stability of the mechanical properties of the steel, including hardness, toughness and fatigue life, and meets the use requirements of high-end bearings; reduces the occurrence rate of central shrinkage holes and crack defects by optimizing cooling intensity and light reduction process, and significantly improves the yield rate and rolling qualification rate of continuous casting billets; the surface rolling process effectively reduces the influence range of the segregation frame, reduces the quality fluctuation caused by segregation during the rolling process, and reduces the difficulty of subsequent processing and production costs. DETAILED DESCRIPTION

[0053] Example 1: A production process for improving the segregation of rectangular continuous casting billets of bearing steel according to the present invention is carried out in the following steps:

[0054] The size of the continuous casting rectangular billet is 320mm×415mm;

[0055] 1. Continuous casting process:

[0056] (1) Casting temperature 1520℃;

[0057] (2) Pulling speed: 0.78 m / min;

[0058] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.6 mm to reduce the formation of central shrinkage holes and segregation frames and improve the uniformity of the internal composition of the steel billet.

[0059] (4) The crystallizer electromagnetic stirring frequency is 2.5 Hz and the current intensity is 380 A;

[0060] (5) The electromagnetic stirring frequency in the second cooling zone is 3.5 Hz and the current intensity is 270 A;

[0061] (6) Cooling water flow in the second cooling zone: first zone: 0.27 L / kg steel, second zone: 0.22 L / kg steel, third zone: 0.18 L / kg steel, achieving segmented cooling;

[0062] 2. Rolling process:

[0063] (1) Heating temperature: 1180°C;

[0064] (2) The first rolling reduction is 24%, and the total reduction ratio is 76%;

[0065] (3) The cooling rate after rolling is 25℃ / s.

[0066] (4) The finished rolled product specification is 165 mm.

[0067] Embodiment 2: A production process for improving the segregation of rectangular continuous casting billets of bearing steel according to the present invention is carried out in the following steps:

[0068] The size of the continuous casting rectangular billet is 320mm×415mm;

[0069] 1. Continuous casting process:

[0070] (1) Casting temperature 1510℃;

[0071] (2) Pulling speed: 0.75 m / min;

[0072] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.65 mm to reduce the formation of central shrinkage holes and segregation frames and improve the uniformity of the internal composition of the billet.

[0073] The crystallizer electromagnetic stirring frequency is 2.2 Hz, and the current intensity is 370 A;

[0074] The electromagnetic stirring frequency of the second cooling zone is 3.8 Hz, and the current intensity is 240 A;

[0075] Cooling water flow in the second cooling zone: first zone: 0.26L / kg steel, second zone: 0.24L / kg steel, third zone: 0.17L / kg steel, achieving segmented cooling;

[0076] 2. Rolling process:

[0077] Heating temperature: 1170°C;

[0078] The first rolling reduction is 25%, and the total reduction ratio is 76%;

[0079] The cooling rate after rolling is 24℃ / s.

[0080] The finished rolled product specification is 165mm.

[0081] Embodiment 3: A production process for improving the segregation of rectangular continuous casting billets of bearing steel according to the present invention is carried out in the following steps:

[0082] The size of the continuous casting rectangular billet is 320mm×415mm;

[0083] 1. Continuous casting process:

[0084] (1) Casting temperature 1530℃;

[0085] (2) Pulling speed: 0.73 m / min;

[0086] (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.55 mm to reduce the formation of central shrinkage holes and segregation frames and improve the uniformity of the internal composition of the steel billet.

[0087] The crystallizer electromagnetic stirring frequency is 2.6 Hz, and the current intensity is 390 A;

[0088] The electromagnetic stirring frequency of the second cooling zone is 3.3 Hz, and the current intensity is 260 A;

[0089] Cooling water flow in the second cooling zone: first zone: 0.25L / kg steel, second zone: 0.23L / kg steel, third zone: 0.16L / kg steel, achieving segmented cooling;

[0090] 2. Rolling process:

[0091] Heating temperature: 1190°C;

[0092] The first rolling reduction is 26%, and the total reduction ratio is 76%;

[0093] The cooling rate after rolling is 23℃ / s.

[0094] The finished rolled product specification is 165mm.

[0095] Comparative Example 1:

[0096] In Comparative Example 1, except that the casting temperature during the continuous casting process is different from that in Example 1, the rest is exactly the same as in Example 1. In this comparative example, the casting temperature is 1580°C.

[0097] Comparative Example 2:

[0098] In Comparative Example 2, except for the pulling speed which is different from that in Example 1, the rest is exactly the same as that in Example 1. In this comparative example, the pulling speed is 1.3 m / min.

[0099] Comparative Example 3:

[0100] In Comparative Example 3, except that the electromagnetic stirring intensity of the crystallizer is different from that of Example 1, the rest is exactly the same as Example 1. In this comparative example, the electromagnetic stirring frequency of the crystallizer is 1 Hz, and the electromagnetic stirring current is 200A.

[0101] Comparative Example 4:

[0102] In Comparative Example 4, except that the second cooling zone does not adopt zone cooling, which is different from Example 1, the rest is exactly the same as Example 1. In this comparative example, the second cooling zone adopts a uniform cooling intensity of 0.25 L / kg.

[0103] Comparative Example 5:

[0104] In Comparative Example 5, except for the reduction amount of light pressing which is different from that in Example 1, the rest is exactly the same as in Example 1. In this comparative example, the reduction amount of light pressing at 80% of the solid phase region is 0.8 mm.

[0105] Comparative Example 6:

[0106] In Comparative Example 6, except that the surface rolling is not adopted, which is different from Example 1, the rest is exactly the same as Example 1. In this comparative example, random rolling is adopted.

[0107] Table 1 is a further explanation of the effect of improving segregation of the present invention.

[0108] Table 1 Frame proportion and frame aspect ratio of various examples of bearing steel (mass percentage / %)

[0109]

[0110]

[0111] It can be seen from Table 1 that: (1) The proportion of segregation frame in the ingot in the embodiment is significantly lower than that in the comparative example. By optimizing the continuous casting parameters and electromagnetic stirring, the present invention effectively reduces the proportion of segregation frame in the cross section. (2) The aspect ratio of the finished frame in the embodiment is close to 1.02-1.03, while the comparative example exceeds 1.35 (up to 1.42). The present invention successfully improves the shape of the segregation frame through processes such as face rolling and segmented cooling, making it closer to a square from an obvious rectangle, thereby improving the uniformity of material performance. (3) In the embodiment using zoned cooling in the second cooling zone, the proportion of the finished frame is as low as 21.2%-23.1%, which is much lower than the comparative example (24.9%-25.6%). This verifies the key role of the segmented cooling process in reducing the formation of segregation frames. (4) In the area with a solid phase ratio of 70%-90%, a reduction of 1.5-2mm is used, which significantly reduces the formation of central shrinkage cavities and segregation frames. In comparative example 5, the reduction amount is insufficient (0.8 mm), resulting in limited improvement in the segregation problem, and the aspect ratio of the finished frame is still higher than 1.39. (5) The finished frame ratio of the embodiment using face rolling is lower than that of comparative example 5 using random rolling, and the aspect ratio of the frame is closer to 1. This shows that the present invention significantly improves the uniformity of the steel in the optimized design of the rolling direction. The present invention optimizes the entire process from continuous casting to rolling, successfully achieving a reduction in the proportion of segregated frames, an improvement in shape, and uniformity in performance, which is significantly better than traditional processes.

[0112] It can be seen from the above embodiments and comparative examples that: (1) the casting temperature of comparative example 1 is too high, and the pulling speed of comparative example 2 is too fast, which will cause the molten steel to flow too fast, easily leading to the enrichment of the central component and the segregation degree reaching 1.4 or more; (2) the insufficient stirring of comparative example 3 causes the central segregation frame to still be a distinct rectangle. (3) the cooling unevenness of comparative example 4 causes the proportion of the segregation frame to be reduced by only 10%-15%. (4) the light pressing reduction of comparative example 5 is insufficient, the improvement of the segregation problem is limited, and the central shrinkage cavity is still obvious. (5) the random rolling method of comparative example 6 does not significantly improve the shape of the segregation frame.

[0113] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A production process for improving the segregation of rectangular continuous casting billets of bearing steel, characterized in that: Including converter smelting, LF refining, VD vacuum degassing, continuous casting, billet heating furnace heating, round steel rolling; among which: Continuous casting process; (1) The pouring temperature is controlled at 1520±20℃. Too high temperature will lead to excessive fluidity of molten steel and aggravate segregation. Too low temperature will easily cause premature solidification of molten steel and form cracks during casting. The high carbon content of GCr15 makes the temperature difference between its liquidus and solidus smaller. The lower casting speed helps to reduce turbulence and control the stability of molten steel flow in the crystallizer. Therefore, the casting speed is controlled at 0.6-0.9m / min. In the area of ​​70%-90% solid phase ratio, light pressing operation is carried out with a pressing amount of 1.5-2mm to reduce the formation of central shrinkage cavity and segregation frame and improve the uniformity of internal composition of the billet. (2) The crystallizer electromagnetic stirring frequency is 2-3 Hz, and the current intensity is 300-400A. Through low-frequency stirring, the horizontal flow of the molten steel in the crystallizer is enhanced and the component distribution is homogenized; the electromagnetic stirring frequency of the secondary cooling zone is 3-5 Hz, and the current intensity is 200-300A, which further promotes the homogenization of the composition of the molten steel at the solid-liquid interface and improves segregation; (3) Cooling water flow in the secondary cooling zone: first zone: 0.25-0.30 L / kg steel, second zone: 0.20-0.25 L / kg steel, third zone: 0.15-0.20 L / kg steel, to achieve segmented cooling to reduce the temperature difference between the surface and the center of the billet; add a water mist cooling device to ensure uniform cooling of the cross section of the billet and reduce component segregation caused by the temperature difference in the center; Rolling process: face rolling, with the long side as the thickness direction of the rolling direction, so that the plastic deformation is concentrated on the segregation frame, changing its shape and size; the heating temperature range is 1180℃±20℃, too high temperature will easily cause the austenite grains to grow, which is not conducive to the refinement of the segregation area; too low temperature will lead to reduced rolling plasticity and affect the deformation effect; the first rolling reduction is 20-30%, and the total compression ratio is 70%-80%. High pressure reduction helps to eliminate central segregation and make the segregation frame gradually approach square from rectangular; the cooling rate after rolling is controlled to 20-30℃ / s, and air cooling or weak water spray cooling is used to avoid excessive temperature difference between the surface and the inside of the steel, which leads to secondary segregation.

2. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to claim 1 is characterized in that: The finished rolled product specification is 165mm.

3. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to claim 1, characterized in that: The size of the continuous casting rectangular billet is 320mm×415mm.

4. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to claim 1, characterized in that: Continuous casting process: (1) Casting temperature 1520℃; (2) Pulling speed: 0.78 m / min; (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.6 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet; (4) The crystallizer electromagnetic stirring frequency is 2.5 Hz and the current intensity is 380 A; (5) The electromagnetic stirring frequency in the second cooling zone is 3.5 Hz and the current intensity is 270 A; (6) Cooling water flow in the second cooling zone: first zone: 0.27 L / kg steel, second zone: 0.22 L / kg steel, third zone: 0.18 L / kg steel, achieving segmented cooling; Rolling process: (1) Heating temperature: 1180°C; (2) The first rolling reduction is 24%, and the total reduction ratio is 76%; (3) The cooling rate after rolling is 25℃ / s; (4) The finished rolled product specification is 165 mm.

5. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to claim 1, characterized in that: Continuous casting process: (1) Casting temperature 1510℃; (2) Pulling speed: 0.75 m / min; (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.65 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet; The crystallizer electromagnetic stirring frequency is 2.2 Hz, and the current intensity is 370 A; The electromagnetic stirring frequency of the second cooling zone is 3.8 Hz, and the current intensity is 240 A; Cooling water flow in the second cooling zone: first zone: 0.26L / kg steel, second zone: 0.24L / kg steel, third zone: 0.17L / kg steel, achieving segmented cooling; Rolling process: Heating temperature: 1170°C; The first rolling reduction is 25%, and the total reduction ratio is 76%; The cooling rate after rolling is 24℃ / s; The finished rolled product specification is 165mm.

6. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to claim 1, characterized in that: Continuous casting process: (1) Casting temperature 1530℃; (2) Pulling speed: 0.73 m / min; (3) A light reduction operation is performed in the area with a solid phase ratio of 80%, with a reduction of 1.55 mm to reduce the formation of central shrinkage cavities and segregation frames and improve the uniformity of the internal composition of the billet; The crystallizer electromagnetic stirring frequency is 2.6 Hz, and the current intensity is 390 A; The electromagnetic stirring frequency in the second cooling zone is 3.3 Hz, and the current intensity is 260 A; Cooling water flow in the second cooling zone: first zone: 0.25L / kg steel, second zone: 0.23L / kg steel, third zone: 0.16L / kg steel, achieving segmented cooling; Rolling process: Heating temperature: 1190°C; The first rolling reduction is 26%, and the total reduction ratio is 76%; The cooling rate after rolling is 23℃ / s; The finished rolled product specification is 165mm.

7. The production process for improving segregation of rectangular continuous casting billets of bearing steel according to any one of claims 4 to 6, characterized in that: The finished frame has an aspect ratio close to 1.02-1.03.

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