Method for eliminating bearing steel wrinkle defects and improving iron oxide scale distribution uniformity

Abstract

The application provides a method for eliminating the wrinkle defect of bearing steel and improving the uniformity of oxide scale distribution, the R angle diameter of the copper tube of the crystallizer used in the continuous casting process is φ33mm, the slow cooling cooling process of the casting blank preheats the slow cooling pit to 300 DEG C, and then the casting blank enters the slow cooling pit again; in the high pressure water phosphorus removal process, the phosphorus removal ring nozzle is arranged in a rectangular shape, the phosphorus removal pressure of the nozzle near the corner is 25Mpa, the flow is 3m 3 / h, the phosphorus removal pressure of the other nozzles is 18Mpa, and the flow is 5m 3 / h; the corner flame heating device is added before and after the first three rolling mills and between the rolling mills in the rough rolling process, so that the corner temperature compensation is realized. The wire rod produced by the method has clean iron scale, uniform deformation, eliminated wrinkle defect and improved wire rod oxide scale uniformity.

Description

Technical Field

[0001] This invention relates to the field of iron and steel smelting technology, and in particular to a method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution. Background Technology

[0002] With the rapid development of domestic hot-rolled wire rod production technology, downstream users of steel mills are placing more stringent requirements on the surface quality of wire rods. For high-quality bearing steel hot-rolled wire rods, wire drawing plants need to perform spheroidizing annealing, pickling or shot blasting to remove iron oxide scale, and then drawing to achieve roundness. This requires not only surface defects ≤30μm, but also uniform iron oxide scale thickness to ensure thorough removal. Steel mills are prone to wrinkling defects during the production of bearing steel hot-rolled wire rods, and due to the high chromium content of bearing steel, the iron oxide scale has high viscosity, making it difficult to control the uniformity of surface iron oxide scale thickness.

[0003] During the rolling process of rectangular continuous casting billets into wire rods, due to the rapid heat dissipation and poor plasticity at the four corners, improper control can easily lead to the formation of four wrinkle defect areas of varying depths parallel to the rolling direction, and the iron oxide scale in the wrinkled areas is relatively thick.

[0004] Chinese Patent CN 114951276 A: A method for eliminating surface wrinkles in bar stock. This patent relates to a method for eliminating surface wrinkles in bar stock. The method achieves wrinkle removal by targeted grinding of the cast billet and optimization of the roll pass and control of the reduction amount in the first four rolling passes. This patent addresses wrinkle defect control in bar stock production, but the targeted grinding of the cast billet increases production costs.

[0005] Chinese Patent CN 115846425 A: A Method for Controlling Wrinkle Defects in High-Carbon Chromium Bearing Steel Bars. This patent relates to a method for controlling wrinkle defects in high-carbon chromium bearing steel bars. The patent controls wrinkle defects through the following six measures: 1. Ensuring a high initial rolling temperature; 2. Controlling the descaling effect of the high-pressure water descaling machine; 3. Adding compressed air descaling facilities to the roughing mill; 4. Optimizing the design of the roughing mill pass; 5. Adding drainage channels to the exit guides of the roughing mill; 6. Establishing limits on the amount of steel passed through the rolls. This patent focuses on controlling wrinkle defects in bar production but does not specifically address the corner defects of the cast billets. Summary of the Invention

[0006] This invention provides a method for eliminating wrinkle defects in bearing steel and improving the uniformity of iron oxide scale distribution, in order to solve the problem that wrinkle defect areas are easily formed at the four corners of rectangular continuous casting billets during the rolling process of wire rod, and the iron oxide scale thickness is relatively thick in the wrinkled areas.

[0007] To achieve the above objectives, this invention provides a method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution. The method flow is as follows: molten iron KR desulfurization → converter smelting → LF refining → RH refining → continuous casting → billet slow cooling → furnace heating → high-pressure water descaling → rough rolling → pre-finish rolling → finish rolling → sizing → wire drawing → Stellmore air cooling → coiling → packaging. In the continuous casting process, the R-angle diameter of the crystallizer copper tube is φ33mm. In the billet slow cooling process, the slow cooling pit is preheated to 300℃ before the billet is placed into the slow cooling pit. In the high-pressure water descaling process, the descaling ring nozzles are arranged in a rectangular pattern, with the descaling pressure near the corner nozzles being 25MPa and the flow rate 3m³ / h. 3 / h, other nozzles have a dephosphorization pressure of 18 MPa and a flow rate of 5 m³ / h. 3 / h; The roughing process adds corner flame heating devices to the front and back of the first three stands and between the stands to achieve corner heating.

[0008] Preferably, the phosphorus removal ring nozzles are provided with four on each of the upper and lower sides, and three on each of the left and right sides.

[0009] Preferably, the method for adding corner flame heating devices to the front and back of the first three stands and between the stands in the roughing process is to add one set of corner flame heating devices in front of the No. 1 stand and after the No. 3 stand, and add two sets of corner flame heating devices between the No. 1 and No. 2 stands and between the No. 2 and No. 3 stands.

[0010] Compared with the prior art, the advantages and positive effects of the present invention are as follows: In order to eliminate the wrinkle defects of wire rod bearing steel and improve the uniformity of iron oxide scale distribution, this patent increases the R angle of the copper tube of the crystallizer in the continuous casting process, optimizes the continuous casting billet cooling process, improves the flow rate and pressure of the nozzle at the corner of the primary descaling stage in the rolling process, and performs multiple flame heatings at the corner of the middle of the roughing mill during the roughing stage. This achieves the purpose of small temperature drop at the corner of the billet during the rolling process, clean removal of iron scale, uniform deformation, elimination of wrinkle defects, and improvement of the uniformity of iron oxide scale in wire rod. Attached Figure Description

[0011] Figure 1 The image shows the wrinkles on the billet in Comparative Example 1.

[0012] Figure 2 The diagram shows the wrinkle defects of the wire rod in Comparative Example 1.

[0013] Figure 3 This is a diagram showing the distribution of iron oxide scale on wire rods in Comparative Example 1.

[0014] Figure 4 This is a diagram showing the sheet metal thickness of wire rod in Comparative Example 1;

[0015] Figure 5 This is a diagram showing the distribution of iron oxide scale on the wire rod in Example 1;

[0016] Figure 6 This is a diagram showing the distribution of iron oxide scale on the wire rod in Example 2. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1

[0019] This embodiment provides a method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution. The practical process of this method in a steel plant producing 180mm*240mm cross-section GCr15 wire rod with a diameter of φ23mm is as follows:

[0020] (1) The production process is as follows: Smelting process: hot iron KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → billet slow cooling; Rolling process: heating furnace heating → high pressure water dephosphorization → rough rolling → pre-finish rolling → finish rolling → sizing → wire drawing → Steyrmo air cooling → coiling → packaging.

[0021] (2) In the above production process, in the continuous casting stage of the smelting process, a new crystallizer copper tube is used, with a copper tube R-angle diameter of φ33mm. In the billet cooling stage of the smelting process: the billet is slowly cooled in a slow cooling pit, which is preheated to 300℃. The billet is stacked in a close-packed "I" shape for cooling, and the slow cooling pit is covered with an asbestos mesh. In the high-pressure water descaling stage of the rolling process: the descaling ring nozzles are arranged in a rectangular pattern, with 4 nozzles at the top and bottom, and 3 nozzles on the left and right. The nozzles near the corners of the rectangle are controlled by separate valves. The descaling pressure of the 8 nozzles near the corners is 25MPa, and the flow rate is 3m³ / h. 3 / h, the other 6 nozzles have a dephosphorization pressure of 18 MPa and a flow rate of 5 m³ / h. 3 / h. In the roughing stage of the rolling process, corner flame heating devices are added to the front and back of the first three stands and between the stands. Specifically, one set of corner heating devices is added before the No. 1 stand and after the No. 3 stand, and two sets of corner heating devices are added between the No. 1 and No. 2 stands and between the No. 2 and No. 3 stands to achieve corner heating.

[0022] The method described in this embodiment is used to roll φ23mm GCr15 bearing steel wire rod as follows: Figure 5 As shown, the wire rod underwent multiple pickling cycles at both ends online, and no wrinkles or defects were observed. Metallographic examination of the wire rod revealed a uniform distribution of iron oxide scale, with a thickness of approximately 13-15 μm.

[0023] Example 2

[0024] This embodiment provides a method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution. The practical process of this method in a steel plant producing 180mm*240mm cross-section GCr15 wire rod with a diameter of φ10mm is as follows:

[0025] (1) The production process is as follows: Smelting process: hot iron KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → billet slow cooling; Rolling process: heating furnace heating → high pressure water dephosphorization → rough rolling → pre-finish rolling → finish rolling → sizing → wire drawing → Steyrmo air cooling → coiling → packaging.

[0026] (2) In the above production process, in the continuous casting stage of the smelting process, a new crystallizer copper tube with a radius of φ33mm is used. In the billet cooling stage of the smelting process: the billet is slowly cooled in a slow cooling pit, which is preheated to 300℃. The billet is stacked in a close-packed "I" shape for cooling, and the slow cooling pit is covered with an asbestos mesh. In the high-pressure water descaling stage of the rolling process: the descaling ring nozzles are arranged in a rectangular pattern, with 4 nozzles at the top and bottom, and 3 nozzles on the left and right. The two nozzles near the corners are controlled by separate valves. The descaling pressure of the 8 nozzles near the corners is 25MPa, and the flow rate is 3m³ / h. 3 / h. The other 6 nozzles have a dephosphorization pressure of 18 MPa and a flow rate of 5 m³ / h. 3 / h. In the roughing stage of the rolling process, corner flame heating devices are added to the front and back of the first three stands and between the stands. Specifically, one set of corner heating devices is added before the No. 1 stand and after the No. 3 stand, and two sets of corner heating devices are added between the No. 1 and No. 2 stands and between the No. 2 and No. 3 stands to achieve corner heating.

[0027] The method described in this embodiment is used to roll φ10mm GCr15 bearing steel wire rod as follows: Figure 6 As shown, the wire rod underwent multiple acid pickling cycles at both ends online, and no wrinkles or defects were observed. Metallographic examination of the wire rod revealed a uniform distribution of iron oxide scale, with a thickness of approximately 11-13 μm.

[0028] Comparison Case 1:

[0029] The following is the practical process of rolling φ18mm wire rod from 180mm*240mm cross-section GCr15 steel in a certain steel plant:

[0030] (1) The production process is as follows: Smelting process: molten iron KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → billet "well" stack cooling; Rolling process: heating furnace heating → high pressure water dephosphorization → rough rolling → pre-finish rolling → finish rolling → sizing → wire drawing → Steyrmo air cooling → coiling → packaging.

[0031] (2) In the continuous casting stage of the smelting process, the diameter of the R-angle of the copper tube in the crystallizer is φ10mm, and the corner of the billet corresponding to the R-angle radius of 10mm has a crack with a depth of ≤1mm (e.g. Figure 1(As shown). Smelting process: Billet cooling stage: The billet raw materials are naturally cooled within the plant, and the billets are arranged in a "well" shaped stack for cooling. Rolling process: High-pressure water descaling stage: The descaling ring nozzles are arranged in a rectangular pattern, with 4 nozzles at the top and bottom, and 3 at the left and right. Each nozzle uses a set of water supply valves. The descaling pressure is 18 MPa, and the flow rate is 5 m³ / s. 3 / h. The roughing stage of the rolling process has no corner flame heating or temperature compensation devices at the front, back, and between the stands of the first three rolling mills.

[0032] The rolled φ18mm GCr15 bearing steel wire rod undergoes multiple pickling cycles at both ends online, resulting in wrinkles of varying depths (e.g., ...). Figure 2 As shown in the figure. Metallographic analysis of the wire rod revealed that the thickness of the iron oxide scale exhibited a regular distribution across the entire circular cross-section. Figure 3 (The sheet metal thickness is unevenly distributed at positions A, B, C, and D). The metallographic morphology of the uneven sheet metal thickness is shown in the figure. Figure 4 .

[0033] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments for application in other fields. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution, the method comprising the following steps: KR desulfurization of molten iron → converter smelting → LF refining → RH refining → continuous casting → slow cooling of billet → heating furnace heating → high-pressure water descaling → rough rolling → pre-finish rolling → finish rolling → sizing → wire drawing → Stellmor air cooling → coiling → packaging, characterized in that... The continuous casting process uses a crystallizer copper tube with a radius of φ33mm. The billet is preheated to 300℃ in the slow cooling pit before being placed into it. In the high-pressure water descaling process, the descaling ring nozzles are arranged in a rectangular pattern, with the nozzles near the corners having a descaling pressure of 25MPa and a flow rate of 3m³ / h. 3 / h, other nozzles have a dephosphorization pressure of 18 MPa and a flow rate of 5 m³ / h. 3 / h; The roughing process adds corner flame heating devices to the front and back of the first three stands and between the stands to achieve corner heating.

2. The method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution according to claim 1, characterized in that, The phosphorus removal ring nozzles are provided with four on each of the upper and lower sides, and three on each of the left and right sides.

3. The method for eliminating wrinkles in bearing steel and improving the uniformity of iron oxide scale distribution according to claim 1, characterized in that: The method for adding corner flame heating devices to the front and back of the first three stands and between the stands in the roughing process is as follows: one set of corner flame heating devices is added in front of stand #1 and behind stand #3, and two sets of corner flame heating devices are added between stands #1 and #2, and between stands #2 and #3.

Images