Process for improving water-jet uniformity of controlled rolling and controlled cooling of GCr15 bearing steel

Abstract

The application belongs to the technical field of alloy steel rolling, and particularly discloses a process method for improving water-penetration uniformity of controlled rolling and controlled cooling of GCr15 bearing steel, which comprises the following steps: uniformly heating a square continuous casting blank of the GCr15 bearing steel at high temperature with high precision, and rolling the blank by using 18 continuous rolling units; after the 18 continuous rolling units, performing 7-stage 2.5mm ring-slit water tank water-penetration cooling and controlled rolling; after the steel penetrates through the 1# water tank, ensuring that the inlet temperature of the reducing sizing machine is 820-840 DEG C to perform rolling; after the steel comes out of the reducing sizing machine, penetrating through the 3# water tank to perform controlled cooling; after the steel is controlled to be rolled and cooled, performing finishing, packaging and slow cooling on the cooling bed. The application develops a new process by adjusting the water tank pressure, selecting the number of open-close valves at different stages, controlling the opening degree of the open-close valves, and appropriately selecting the water-penetration guide pipe hole diameter according to the incoming material specifications, so that the water-penetration uniformity of the steel can be improved, the steel bending problem can be solved, the subsequent annealing, shot blasting and straightening are not needed, and the economic and time costs are saved.

Description

Technical Field

[0001] This invention belongs to the field of alloy steel rolling technology, and relates to a controlled rolling and controlled cooling process for GCr15 bearing steel, particularly a process for improving the uniformity of water penetration during controlled rolling and controlled cooling of GCr15 bearing steel. Background Technology

[0002] With the rapid development of my country's national economy, the market for high-carbon chromium bearing steel, represented by GCr15, has grown rapidly, and the requirements for product quality are constantly increasing, especially the control of the network carbide level in bearing steel. Due to its composition, GCr15 bearing steel exhibits secondary carbides precipitating in a network pattern along the austenite grain boundaries during the post-rolling cooling process. The presence of network carbides in high-carbon chromium bearing steel increases its brittleness and reduces the lifespan of bearing components. Therefore, most large steel mills in China currently use controlled rolling and controlled cooling to reduce the precipitation of network carbides. Practice has proven that controlled rolling and controlled cooling can effectively reduce the network precipitation of carbides in high-carbon chromium GCr15 bearing steel. However, currently, almost all bearing steel manufacturers suffer from uneven water penetration during controlled rolling and controlled cooling, leading to severe bending of the steel. Because GCr15 bearing steel has high strength, the hardness of the rolled steel increases significantly after controlled rolling and controlled cooling water piercing. Therefore, annealing is necessary before straightening; otherwise, end-point breakage is likely to occur during straightening. Furthermore, straightening without annealing does not significantly improve the curvature of the steel. While annealing and straightening can improve curvature in large batches of steel, it undoubtedly increases the costs of annealing, shot blasting, and straightening for steel mills. Additionally, the time required for subsequent finishing also extends the product delivery cycle, increasing time costs. Therefore, developing a new controlled rolling and controlled cooling water piercing process for GCr15 bearing steel that does not require annealing, shot blasting, or straightening is urgently needed. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a process method for improving the uniformity of water piercing in controlled rolling and cooling of GCr15 bearing steel. This invention develops a new process using existing equipment by adjusting the water tank pressure, selecting the number of on / off valves at different stages, controlling the valve opening size, and appropriately selecting the piercing guide diameter based on the incoming material specifications. This improves the uniformity of steel piercing, solves the problem of steel bending, eliminates the need for subsequent annealing, shot blasting, and straightening, significantly saves costs, and shortens process time.

[0004] This invention is achieved through the following technical solution: A process for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel includes the following steps: 1) 18-stand two-roll rolling mill: The square continuous casting billet of GCr15 bearing steel is heated at ultra-precise high temperature and uniformly, and then rolled by two rolls using an 18-stand continuous rolling mill. 2) Water cooling control in No. 1 water tank: After the 18-stand continuous rolling zone is completed, water cooling control is carried out in a 7-section 2.5mm circumferential seam water tank; 3) Three-roll sizing mill controlled rolling: After the steel passes through the No. 1 water tank, the inlet temperature of the sizing mill is guaranteed to be 820-840℃ for rolling; 4) Controlled cooling water flow through No. 3 water tank: After exiting the reducing and sizing mill, the water flows through No. 3 water tank for controlled cooling operation; 5) After the steel is rolled and cooled, it is placed on a cooling bed for finishing, packaging, and slow cooling.

[0005] A further improvement to the present invention is as follows: In step 1), the size of the square continuous casting billet is 210*210mm, and the temperature of ultra-precise temperature control and high-temperature uniform heating is 1220±5℃.

[0006] Furthermore, in step 2), during the water cooling controlled rolling process of the 7-segment 2.5mm circumferential seam water tank: (1) When the incoming material specification is 28.8mm≤Φ<50mm, select the Φ64mm conduit of the No.1 water tank, open the 1, 2, 3, and 4 positive-flush valves, and set the opening degree to 90%, 60%, 50%, and 40% respectively, and adjust the pressure to 1.2Mpa; (2) When the incoming material specification is 50mm≤Φ<65mm, select the Φ90mm conduit of the No.1 water tank, open the 1, 2, 3, and 4 positive-flush valves, and set the opening degree to 100%, 70%, 50%, and 40% respectively, and adjust the pressure to 1.3Mpa.

[0007] Furthermore, in step 4), (1) when the incoming material specification is 20mm≤Φ<30mm, select the Φ40mm conduit of the No.3 water tank, open the 1 and 2 positive flush valves, set the opening degree to 70% and 50% respectively, and adjust the pressure to 0.94Mpa; (2) when the incoming material specification is 30mm≤Φ<45mm, select the Φ64mm conduit of the No.3 water tank, open the 1, 2 and 3 positive flush valves, set the opening degree to 100%, 60% and 50% respectively, and adjust the pressure to 1.05Mpa; (3) when the incoming material specification is 45mm≤Φ≤60mm, select the Φ90mm conduit of the No.3 water tank, open the 1, 3 and 4 positive flush valves, set the opening degree to 100%, 90% and 80% respectively, and adjust the pressure to 1.30Mpa.

[0008] The beneficial effects of this invention are as follows: (1) The present invention provides a process method for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel. The method uses a 1220±5℃ ultra-precise temperature control heating furnace to heat the original continuous casting billet on all four sides, thereby improving the homogenization effect of the continuous casting billet. During the controlled rolling and controlled cooling water quenching process, the surface temperature drop rate is consistent and the edge structure transformation is uniform, thereby improving the hardness uniformity.

[0009] (2) The present invention provides a process method for improving the uniformity of water flow in controlled rolling and controlled cooling of GCr15 bearing steel. The water tank guide pipe diameter has a wide selection range. Based on the incoming material size, the guide pipe diameter is matched as small as possible while ensuring smooth steel passage, so that the water flow is more concentrated in the guide pipe and the uniformity of water flow in the steel is improved.

[0010] (3) The present invention provides a process method for improving the uniformity of water quenching in controlled rolling and cooling of GCr15 bearing steel. The method matches the required opening and closing valve positions of the water tank according to different incoming material specifications, so as to compensate for the uneven cooling of the steel and further improve the uniformity of water quenching.

[0011] (4) The present invention provides a process method for improving the uniformity of controlled rolling and controlled cooling water penetration of GCr15 bearing steel. Different processes are selected according to different incoming material specifications. Under the condition of a certain opening, the water tank pressure is appropriately increased so that the water tank circumferential gap can be uniformly drained, which can further improve the uniformity of steel cooling.

[0012] (5) The present invention provides a process method for improving the uniformity of water quenching in controlled rolling and cooling of GCr15 bearing steel, which reduces the number of production steps. The old process required quenching 3 water tanks, while the new process only requires quenching 2 water tanks, thus saving production costs to a certain extent.

[0013] (6) The present invention provides a process method for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel. New processes can be selected according to different water quenching specifications of steel, and the process is highly operable on site.

[0014] (7) The present invention provides a process method for improving the uniformity of controlled rolling and controlled cooling water piercing of GCr15 bearing steel. Under the condition that the existing water tank remains unchanged, the new process developed can improve the uniformity of steel piercing, solve the problem of steel bending, and eliminate the need for subsequent annealing, shot blasting and straightening. It has certain advantages in terms of energy saving and cost reduction. Attached Figure Description

[0015] Figure 1 The GCr15 bearing steel treated in Comparative Example 1; Figure 2 This is a diagram showing the depth of the rapid cooling layer of GCr15 bearing steel after processing in Comparative Example 1. Figure 3 This is a diagram of the rapid cooling layer of GCr15 bearing steel obtained in Example 1; Figure 4This is a comparison diagram of the bending degree of GCr15 bearing steel obtained in Comparative Example 1 and Example 1. Detailed Implementation

[0016] The present invention will now be described in detail with reference to specific embodiments.

[0017] Comparative Example 1: Existing GCr15 bearing steel specification Φ40mm controlled rolling and controlled cooling water quenching process (1) The 210*210mm square continuous casting billet of GCr15 bearing steel is heated at 1200±20℃ and rolled by two rolls using an 18-stand continuous rolling mill.

[0018] (2) A 7-section 3.5mm circumferential seam water tank is used for water cooling and controlled rolling.

[0019] (3) For incoming material with a specification of Φ45.7mm, select the Φ120mm conduit of water tank #1, open valves 1, 2, and 3, and set the opening degree to 80%, 100%, and 100% respectively. Adjust the pressure to 0.82Mpa.

[0020] (4) The rolling temperature of the three-roll sizing mill is 800℃.

[0021] (5) After the three-roll sizing mill rolls the finished product with a specification of Φ40mm, it is inserted into the No. 3 water tank and a Φ90mm diameter guide pipe is selected. Open the positive punch valves 1, 2, 3 and 4, and set the opening degree to 95%, 90%, 90% and 80% respectively. Adjust the pressure to 0.78Mpa.

[0022] (6) After exiting the No. 3 water tank, continue to the No. 4 water tank by selecting a Φ90mm diameter guide pipe, open the No. 1 and No. 2 positive flush valves, set the opening degree to 95% and 90% respectively, and adjust the pressure to 0.75Mpa.

[0023] Example 1: The controlled rolling and controlled cooling water-quenching process for GCr15 bearing steel with a specification of Φ40mm according to the present invention (1) The 210*210mm square continuous casting billet of GCr15 bearing steel is heated at 1220±5℃ with ultra-precise high temperature and uniform heating, and then rolled by two rolls using an 18-stand continuous rolling mill.

[0024] (2) A 7-section 2.5mm circumferential seam water tank is used for water cooling and controlled rolling.

[0025] (3) For incoming material with a specification of Φ45.7mm, select the Φ64mm conduit of water tank #1, open the positive flush valves 1, 2, 3, and 4, and set the opening degree to 90%, 60%, 50%, and 40% respectively, and adjust the pressure to 1.2Mpa.

[0026] (4) The rolling temperature of the three-roll sizing mill is 830℃.

[0027] (5) After the three-roll sizing mill rolls the finished product with a specification of Φ40mm, it passes through the No. 3 water tank, selects the Φ64mm guide pipe, opens the 1, 2 and 3 positive punch valves, and sets the opening degree to 100%, 60% and 50% respectively, and adjusts the pressure to 1.05Mpa.

[0028] Example 2: Controlled rolling and controlled cooling water-quenching process for GCr15 bearing steel with a specification of Φ45mm according to the present invention (1) The 210*210mm square continuous casting billet of GCr15 bearing steel is heated at 1220±5℃ with ultra-precise high temperature and uniform heating, and then rolled by two rolls using an 18-stand continuous rolling mill.

[0029] (2) A 7-section 2.5mm circumferential seam water tank is used for water cooling and controlled rolling.

[0030] (3) For incoming material with a specification of Φ57.8mm, select the Φ90mm conduit of water tank #1, open the positive flush valves 1, 2, 3, and 4, and set the opening degree to 100%, 70%, 50%, and 40% respectively, and adjust the pressure to 1.30Mpa.

[0031] (4) The rolling temperature of the three-roll sizing mill is 830℃.

[0032] (5) After the three-roll sizing mill rolls the finished product with a specification of Φ45mm, pass it through the No. 3 water tank, select the Φ90mm guide pipe, open the 1, 3 and 4 positive punch valves, set the opening degree to 100%, 90% and 80% respectively, and adjust the pressure to 1.30Mpa.

[0033] Example 3: The controlled rolling and controlled cooling water-quenching process for GCr15 bearing steel with a specification of Φ50mm according to the present invention (1) The 210*210mm square continuous casting billet of GCr15 bearing steel is heated at 1220±5℃ with ultra-precise high temperature and uniform heating, and then rolled by two rolls using an 18-stand continuous rolling mill.

[0034] (2) A 7-section 2.5mm circumferential seam water tank is used for water cooling and controlled rolling.

[0035] (3) For incoming material with a specification of Φ57.8mm, select the Φ90mm conduit of water tank #1, open the positive flush valves 1, 2, 3, and 4, and set the opening degree to 100%, 70%, 50%, and 40% respectively, and adjust the pressure to 1.30Mpa.

[0036] (4) The rolling temperature of the three-roll sizing mill is 833℃.

[0037] (5) After the three-roll sizing mill rolls the finished product with a specification of Φ50mm, pass it through the No. 3 water tank, select the Φ90mm guide pipe, open the 1, 3 and 4 positive punch valves, set the opening degree to 100%, 90% and 80% respectively, and adjust the pressure to 1.30Mpa.

[0038] The following is a comparison of the uniformity of water quenching, curvature, and hardness of GCr15 bearing steel after being treated with different controlled rolling and controlled cooling water quenching processes in the comparative example and the embodiment:

[0039] As can be seen, the present invention significantly improves the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel, while effectively reducing the curvature of the steel and improving the uniformity of hardness. Subsequent processes such as annealing, shot blasting, and straightening are not required, which greatly saves economic and time costs.

[0040] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A process method for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel, characterized in that, Includes the following steps: 1) 18-stand two-roll rolling mill: The square continuous casting billet of GCr15 bearing steel is heated at ultra-precise high temperature and uniformly, and then rolled by two rolls using an 18-stand continuous rolling mill. 2) Water cooling control in No. 1 water tank: After the 18-stand continuous rolling zone is completed, water cooling control is carried out in a 7-section 2.5mm circumferential seam water tank; 3) Three-roll sizing mill controlled rolling: After the steel passes through the No. 1 water tank, the inlet temperature of the sizing mill is guaranteed to be 820-840℃ for rolling; 4) Controlled cooling water flow through No. 3 water tank: After exiting the reducing and sizing mill, the water flows through No. 3 water tank for controlled cooling operation; 5) After controlled rolling and cooling, the steel is placed on a cooling bed for finishing, packaging, and slow cooling; In step 2), during the water cooling controlled rolling process of the 7-section 2.5mm circumferential seam water tank: (1) When the incoming material specification is 28.8mm≤Φ<50mm, select the Φ64mm conduit of the No.1 water tank, open the 1, 2, 3, and 4 positive punch valves, and set the opening degree to 90%, 60%, 50%, and 40% respectively, and adjust the pressure to 1.2Mpa; (2) When the incoming material specification is 50mm≤Φ<65mm, select the Φ90mm conduit of the No.1 water tank, open the 1, 2, 3, and 4 positive punch valves, and set the opening degree to 100%, 70%, 50%, and 40% respectively, and adjust the pressure to 1.3Mpa.

2. The process method for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel according to claim 1, characterized in that: In step 1), the size of the square continuous casting billet is 210*210mm, and the temperature of ultra-precise temperature control and high-temperature uniform heating is 1220±5℃.

3. The process method for improving the uniformity of controlled rolling and controlled cooling water quenching of GCr15 bearing steel according to claim 1, characterized in that: In step 4), (1) when the incoming material specification is 20mm≤Φ<30mm, select the Φ40mm conduit of the No.3 water tank, open the 1 and 2 positive flush valves, set the opening degree to 70% and 50% respectively, and adjust the pressure to 0.94Mpa; (2) when the incoming material specification is 30mm≤Φ<45mm, select the Φ64mm conduit of the No.3 water tank, open the 1, 2 and 3 positive flush valves, set the opening degree to 100%, 60% and 50% respectively, and adjust the pressure to 1.05Mpa; (3) when the incoming material specification is 45mm≤Φ≤60mm, select the Φ90mm conduit of the No.3 water tank, open the 1, 3 and 4 positive flush valves, set the opening degree to 100%, 90% and 80% respectively, and adjust the pressure to 1.30Mpa.

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