Control process for improving shrinkage cavity defect of bearing steel hot-rolled billet
Through the two-stage heating + homogenization process, the heating process of the bearing steel hot-rolled billet is controlled, the problem of shrinkage is solved, product quality and safety is improved, and the production efficiency is improved without equipment is achieved.
Patent Information
- Application Number
- CN202510137321.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-07
- Publication Date
- 2025-04-22
AI Technical Summary
The hot-rolled billet of bearing steel is prone to shrinkage during heating, resulting in risk of breakage during rolling and lifting of steel billets, affecting product quality and safety.
The two-stage heating + homogenization process is adopted to control the furnace temperature, heating temperature, heating time and slow cooling time of the cast billet to ensure the temperature uniformity of the billet during the heating process and avoid local overburning.
By precisely controlling the heating parameters, the problem of hot-rolled blank shrinkage is effectively eliminated, product quality is improved, production risks are reduced, and equipment and investment is not required.
Smart Images
Figure CN119859742A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the technical field of steel rolling, in particular to a control process for improving shrinkage defects of hot-rolled billets of bearing steel. Background Art
[0002] GCr15 is one of the commonly used steel grades for producing bearing rolling elements and rings. The product has the advantages of stable composition, low harmful elements, high steel purity, uniform carbides, and few surface defects. It has a wide plastic processing range, stable heat treatment quality, high and uniform hardness, good wear resistance, and high contact fatigue strength. Compared with other steel grades, the probability of shrinkage holes in hot-rolled billets of bearing steel during heating is significantly higher. After shrinkage holes appear, there will be a risk of fracture during the rolling and lifting process of the billet. If not discovered in time, it will cause subsequent production accidents and quality problems of the final product. Summary of the invention
[0003] The technical problem to be solved by the present invention is to provide a control process for improving the shrinkage defects of hot-rolled billets of bearing steel.
[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: comprising a heating step; the heating step: adopts a two-stage heating + soaking process; When the temperature of the casting billet is ≥500℃, the temperature of the first stage of heating is controlled at 800~1000℃, the total heating time is controlled at 5~6 hours, and the casting billet has no idle steps in the heating furnace; When the ingot temperature is less than 500℃, first slowly cool the ingot to room temperature, control the temperature of one stage heating at 500-800℃, and control the total heating time at 6-7 hours. Add additional rolling ingots in the furnace and there should be no empty steps between all ingots.
[0005] Furthermore, in the heating step, the temperature of the second stage heating is 1000-1200°C.
[0006] Furthermore, in the heating step, the soaking temperature is 1200°C.
[0007] Furthermore, the bearing steel grade is GCr15.
[0008] The beneficial effect of adopting the above technical solution is that the present invention improves the quality of hot-rolled steel billets by accurately controlling the steel billet entry temperature, heating temperature, heating time and steel billet slow cooling time. The present invention does not require additional equipment and investment, makes full use of existing equipment and processes, adopts reasonable steel billet entry temperature, heating furnace segmented heating parameter control, special steel loading method, and heating time control, effectively solves the shrinkage of hot-rolled steel billets of bearing steel, solves subsequent quality risks, and reduces quality losses. BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.
[0010] Figure 1 This is a surface quality diagram of the hot rolled billet rolled in Example 1 of the present invention; Figure 2 This is a surface quality diagram of the hot rolled billet rolled in Example 2 of the present invention; Figure 3 This is a surface quality diagram of the hot rolled billet rolled in Comparative Example 1; Figure 4 This is a surface quality diagram of the hot rolled billet rolled in Example 3 of the present invention; Figure 5 This is a diagram of the surface quality of the hot-rolled slab produced in Comparative Example 2. DETAILED DESCRIPTION
[0011] The shrinkage problem of hot-rolled billet bearing steel has been analyzed and believed to be related to the continuous casting process of bearing steel in the early stage. However, the subsequent analysis of the number and regularity of shrinkage holes in hot-rolled billets using tools showed that there was no obvious relationship with the continuous casting process. Therefore, the inventors analyzed and believed that it was related to the transportation method of bearing steel and the heating process before hot-rolled billets. This method mainly improves the uniformity of temperature during the heating process to avoid shrinkage holes in the billet caused by local overburning in the furnace. Bearing steel has a high carbon content and contains a certain amount of chromium, so its thermal conductivity is worse than that of ordinary carbon steel. Currently, there are two distribution modes for bearing steel billets, one is hot loading and the other is cold loading. During hot loading, the center temperature is about 700°C and the surface temperature is about 600°C. At this time, during the heating process of the heating furnace, there will be no large temperature difference between the inside and outside and no local excessive temperature. When cold-charged into the furnace, the temperature inside and outside the ingot is room temperature. Due to poor thermal conductivity, the temperature inside and outside the reheating furnace will be higher than the temperature in the core. When the heating rate is too fast and there is a significant difference between the internal and external temperatures, stress will form inside the ingot, causing cracks in the core, aggravating the shrinkage problem of the billet. The empty steps between the billets will also cause an increase in the local heating rate. Therefore, other steel grades need to be used for cold charging to eliminate the empty steps of the bearing steel in the furnace, and at the same time reduce the heating rate to improve the uniformity of the internal and external temperatures during the billet heating process. The above principle eliminates the shrinkage problem of the billet after billet opening.
[0012] Based on the above theory, the control process for improving the shrinkage defect of hot-rolled bearing steel billet includes the following steps: (1) Heating step: adopt two-stage heating + soaking process; When the temperature of the billet is ≥500℃, the temperature of the first stage heating is controlled at 800-1000℃, the temperature of the second stage heating is 1000-1200℃, and the soaking temperature is 1200℃; the heating temperature in the furnace gradually rises from the initial stage of the first stage to the end of the second stage, and the soaking temperature is 1200℃ as a whole; from the billet entering the furnace to the billet leaving the furnace, it is transported at a uniform speed, and the total heating time is controlled at 5-6 hours, and the billet has no idle steps in the heating furnace; When the temperature of the ingot is less than 500℃, first put the ingot into the insulation pit for slow cooling for 72 hours or more to slowly cool the ingot to room temperature; the temperature of the first heating stage is controlled at 500-800℃, the temperature of the second heating stage is 800-1200℃, and the soaking temperature is 1200℃; the heating temperature in the furnace gradually rises from the initial stage of the first stage to the end of the second stage, and the soaking stage is 1200℃ as a whole; from the time the billet enters the furnace to the time it leaves the furnace, it is transported back at a uniform speed, and the total heating time is controlled at 6-7 hours; a batch of other steel grades of rolled ingots are added before and after the entire batch of bearing steel ingots in the furnace, and there is no empty step between all ingots, that is, there is no empty step between the rolled ingots and the batch of bearing steel ingots, and there is no empty step between the bearing steel ingots.
[0013] (2) Rolling steps: The ingot with a cross-sectional size of 280 × 325 mm (raw material billet size) is rolled into a billet with a cross-sectional size of 160 × 160 mm (finished billet size) by 9 rolling passes.
[0014] (3) After adopting the above process, the GCr15 steel 280×325mm ingot will not have the problem of overburning in the furnace, and the shrinkage cavity of the hot-rolled ingot can be effectively eliminated, thereby improving product quality and reducing production risks.
[0015] Example 1: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0016] (1) Heating steps: The temperature of the ingot entering the furnace is 570°C. There is no empty step between the ingots after entering the furnace, and there is an empty step at the beginning and end of the batch. A regenerative heating furnace is used, with a first-stage heating temperature of 800°C, a second-stage heating temperature of 1100°C, and an even heating temperature of 1200°C. The total heating time is controlled within 5 hours. The frequency of steel tapping is controlled during production. The ingots need to be transported continuously and cannot stay in the same position.
[0017] (2) Rolling step: using 9 rolling passes to roll the ingot from 280×325 mm to 160×160 mm; (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0018] Example 2: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0019] (1) Heating steps: The temperature of the billet entering the furnace should be 570℃, and there should be no empty steps between the billets after entering the furnace; a regenerative heating furnace is used, with a first-stage heating temperature of 900℃, a second-stage heating temperature of 1200℃, and an average heating temperature of 1200℃; the total heating time is controlled within 6 hours, and the steel tapping frequency is controlled during production. The billets need to be transported continuously and cannot stay in the same position.
[0020] (2) Rolling steps: The ingot is rolled from 280×325 mm to 160×160 mm in 9 passes.
[0021] (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0022] Example 3: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0023] (1) Heating steps: The temperature of the ingot entering the furnace is 500°C, and there is no empty step between the ingots after entering the furnace; a regenerative heating furnace is used, with a first-stage heating temperature of 950°C, a second-stage heating temperature of 1000°C, and an average heating temperature of 1200°C; the total heating time is controlled within 5.5 hours, and the steel tapping frequency is controlled during production. The ingots need to be transported continuously and cannot stay in the same position.
[0024] (2) Rolling step: using 9 rolling passes to roll the ingot from 280×325 mm to 160×160 mm; (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0025] Comparative Example 1: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0026] (1) Heating step: The temperature of the ingot entering the furnace is room temperature. After entering the furnace, there are empty steps before and after the ingots in the batch, and there are no empty steps between the ingots in the batch. A regenerative heating furnace is used, with a first-stage heating temperature of 600°C, a second-stage heating temperature of 1150°C, and an average heating temperature of 1200°C. The total heating time is controlled within 6 hours. The frequency of steel tapping is controlled during production. The ingots need to be transported continuously and cannot stay in the same position.
[0027] (2) Rolling steps: The ingot is rolled from 280×325 mm to 160×160 mm in 9 passes.
[0028] (3) Shrinkage holes appear at the first and last billets of the finished product.
[0029] Example 4: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0030] (1) Heating steps: The temperature of the ingot entering the furnace is room temperature, and the ingot is rolled. There is no empty step between the 5 rows of ingots and the bearing steel, and there is no empty step between the bearing steel ingots. A regenerative heating furnace is used, with a first-stage heating temperature of 600°C, a second-stage heating temperature of 1150°C, and an even heating temperature of 1200°C. The total heating time is controlled within 6 hours, and the steel tapping frequency is controlled during production. The ingots need to be continuously transported and cannot stay in the same position.
[0031] (2) Rolling steps: The ingot is rolled from 280×325 mm to 160×160 mm in 9 passes.
[0032] (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0033] Example 5: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0034] (1) Heating steps: The temperature of the ingot entering the furnace is room temperature, and the ingot is rolled. There is no empty step between the 5 rows of ingots and the bearing steel, and there is no empty step between the bearing steel ingots. A regenerative heating furnace is used, with a first-stage heating temperature of 500°C, a second-stage heating temperature of 800°C, and an even heating temperature of 1200°C. The total heating time is controlled within 7 hours, and the steel tapping frequency is controlled during production. The ingots need to be continuously transported and cannot stay in the same position.
[0035] (2) Rolling steps: The ingot is rolled from 280×325 mm to 160×160 mm in 9 passes.
[0036] (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0037] Example 6: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0038] (1) Heating steps: The temperature of the ingot entering the furnace is room temperature, and the ingot is rolled. There is no empty step between the 5 rows of ingots and the bearing steel, and there is no empty step between the bearing steel ingots. A regenerative heating furnace is used, with a first-stage heating temperature of 800°C, a second-stage heating temperature of 1200°C, and an even heating temperature of 1200°C. The total heating time is controlled within 6.5 hours. The frequency of steel tapping is controlled during production. The ingots need to be continuously transported and cannot stay in the same position.
[0039] (2) Rolling steps: The ingot is rolled from 280×325 mm to 160×160 mm in 9 passes.
[0040] (3) The surface quality of the finished product is normal and there are no shrinkage holes.
[0041] Comparative Example 2: The control process for improving shrinkage defects in hot-rolled bearing steel billets is specifically described as follows.
[0042] (1) Heating steps: The temperature of the ingot entering the furnace is room temperature, and the matching steel grades are used. There is no empty step between the bearing steel ingots. A regenerative heating furnace is used, with a first-stage heating temperature of 700°C, a second-stage heating temperature of 1150°C, and an average heating temperature of 1200°C. The total heating time is controlled within 5 hours, and the steel tapping frequency is controlled during production. The ingots need to be transported continuously and cannot stay in the same position.
[0043] (2) Rolling step: using 9 rolling passes to roll the ingot from 280×325 mm to 160×160 mm; (3) Shrinkage holes appear on the surface of some steel billets of the finished product.
[0044] The surface quality results of the hot rolled billets produced in the embodiments and comparative examples are shown in Table 1: Table 1: Test results
[0045] Comparing Examples 1 and 2, when the billet enters the furnace at a temperature greater than 500°C, uniform heating can be achieved within 5 hours, and shrinkage problems will not occur if the heating time is slightly extended (the heating time is extended but the billet does not stay in the same position for a long time).
[0046] Comparison between Example 1 and Comparative Example 2 shows that when the same heating process is used, shrinkage holes will occur in the cold billet when it is put into the furnace. The comparison shows that after the cold billet is put into the furnace, the heating rate is too fast and the temperature difference between the inside and outside of the billet is too high, resulting in strong stress inside, which will cause shrinkage holes in the hot-rolled billet of bearing steel.
[0047] Compared with Example 3 and Comparative Example 1, when the cold billet is put into the furnace, due to the empty step at the head and tail of the billet, the heating rate of the billet at the head and tail will be too high, forming internal stress and causing shrinkage problems in the hot-rolled billet of bearing steel.
Claims
1. A control process for improving shrinkage defects of hot-rolled bearing steel billets, characterized in that: The method comprises a heating step; the heating step adopts a two-stage heating + soaking process; When the temperature of the casting billet is ≥500℃, the temperature of the first stage of heating is controlled at 800~1000℃, the total heating time is controlled at 5~6 hours, and the casting billet has no idle steps in the heating furnace; When the ingot temperature is less than 500℃, first slowly cool the ingot to room temperature, control the temperature of one stage heating at 500-800℃, and control the total heating time at 6-7 hours. Add additional rolling ingots in the furnace and there should be no empty steps between all ingots.
2. A control process for improving shrinkage defects of hot-rolled bearing steel billets according to claim 1, characterized in that: In the heating step, the temperature of the second stage heating is 1000-1200°C.
3. The control process for improving shrinkage defects of hot-rolled bearing steel billets according to claim 1, characterized in that: In the heating step, the soaking temperature is 1200°C.
4. A control process for improving shrinkage defects of hot-rolled bearing steel billets according to claim 1, 2 or 3, characterized in that: The bearing steel grade is GCr15.