Method for eliminating wrinkle defect of bearing steel and improving distribution uniformity of oxide scale

Abstract

The invention provides a method for eliminating the wrinkle defect of bearing steel and improving the distribution uniformity of oxide scale, which comprises the following steps: in the continuous casting process, the R angle diameter of a crystallizer copper pipe is phi 33 mm, in the casting blank slow cooling process, a slow cooling pit is heated to 300 DEG C in advance for preheating, and then the casting blank enters the slow cooling pit; in the high-pressure water phosphorus removal process, phosphorus removal ring nozzles are arranged in a rectangular shape, the phosphorus removal pressure of the nozzles close to the corners is 25 Mpa, the flow is 3 m < 3 > / h, and the phosphorus removal pressure of other nozzles is 18 Mpa, and the flow is 5 m < 3 > / h; in the rough rolling process, corner flame heating devices are additionally arranged in front of and behind the front three rolling mills and among racks, and corner temperature compensation is achieved. The steel wire rod iron sheet produced through the method is completely removed, deformation is uniform, the wrinkle defect is eliminated, and the uniformity of the steel wire rod iron sheet is improved.

Description

Technical Field

[0001] The invention relates to the technical field of steel smelting, and in particular to a method for eliminating wrinkle defects of bearing steel and improving the uniformity of iron oxide scale distribution. Background Art

[0002] With the rapid development of domestic hot-rolled wire production technology, downstream users of steel mills have put forward more stringent requirements on the surface quality of wires. For high-quality wire bearing steel hot-rolled wire rods, wire drawing plants need to perform spheroidizing annealing → pickling or shot blasting to remove the iron oxide scale → drawing and rounding. Not only does it require surface defects to be ≤30μm, but also the thickness of the hot-rolled wire rod oxide scale is required to be uniform in order to remove the wire rod oxide scale cleanly. Steel mills are prone to wrinkle defects when producing hot-rolled bearing steel wire rods, and due to the high chromium content of bearing steel, the viscosity of the iron oxide scale is high, and the uniformity of the surface oxide scale thickness is difficult to control.

[0003] During the process of rolling the rectangular continuous casting billet into wire rod, 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 with different depths and parallel to the rolling direction, and the thickness of the iron oxide scale in the wrinkled area is relatively thick.

[0004] Chinese Patent CN 114951276 A: A method for eliminating wrinkles on the surface of a bar. This patent is about a method for eliminating wrinkles on the surface of a bar. The purpose of removing wrinkles is achieved by performing targeted grinding on the ingot and optimizing the pass profile and controlling the reduction amount for the first four rolling passes. This patent controls wrinkle defects in bar production, and targeted grinding of the ingot increases production costs.

[0005] Chinese Patent CN 115846425 A: A method for controlling wrinkle defects in high-carbon chromium bearing steel for small bars. This patent relates to a method for controlling wrinkle defects in high-carbon chromium bearing steel for small bars. This patent controls wrinkle defects through the following 6 measures: 1. Ensure a high rolling temperature; 2. Control the descaling effect of the high-pressure water descaling machine; 3. Add compressed air to remove iron oxide scale facilities in the rough rolling mill; 4. Optimize the design of the rough rolling pass; 5. Add drainage grooves to the exit guide of the rough rolling; 6. Formulate the limit requirements for the amount of steel overload of the roll. This patent controls wrinkle defects in bar production, and does not carry out targeted control of the corners of the ingot. Summary of the invention

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

[0007] In order to achieve the above-mentioned object, the present invention provides a method for eliminating wrinkle defects of bearing steel and improving the uniformity of distribution of oxidized iron scale. The method process is as follows: molten iron KR desulfurization → converter smelting → LF refining → RH refining → continuous casting → slow cooling of ingot → heating in heating furnace → high-pressure water dephosphorization → rough rolling → pre-finishing rolling → finishing rolling → sizing reduction → spinning → Stelmor air cooling → coiling → packaging. The R angle diameter of the crystallizer copper tube used in the continuous casting process is φ33mm. The slow cooling process of the ingot preheats the slow cooling pit to 300°C for preheating, and then the ingot enters the slow cooling pit again. In the high-pressure water dephosphorization process, the dephosphorization ring nozzles are arranged in a rectangular shape, the dephosphorization pressure of the nozzles near the corners is 25Mpa, and the flow rate is 3m 3 / h, the other nozzles’ dephosphorization pressure is 18Mpa, flow rate is 5m 3 / h; in the rough rolling process, corner flame heating devices are added before and after the first three rolling mills and between the racks to achieve corner temperature compensation.

[0008] Preferably, the dephosphorization 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 before and after and between the frames of the first three rolling mills in the rough rolling process is to add one set of corner flame heating devices in front of the 1# frame and after the 3# frame, and add two sets of corner flame heating devices between the 1# and 2# frames and between the 2# and 3# frames.

[0010] Compared with the prior art, the advantages and positive effects of the present invention are that, in order to eliminate the wrinkle defects of wire bearing steel and improve the uniformity of the distribution of oxidized iron scale, this patent increases the R angle of the copper tube of the crystallizer in the smelting and continuous casting link, optimizes the cooling process of the continuous casting billet, improves the flow rate and pressure of the nozzle at the corner of the one-time dephosphorization in the rolling link, and performs multiple flame heating on the corner in the middle of the rough rolling unit during the rough rolling stage, so as to achieve a small temperature drop at the corner of the casting billet during the rolling process, clean removal of the iron scale, uniform deformation, elimination of wrinkle defects, and improvement of the uniformity of the oxidized iron scale of the wire rod. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The wrinkle diagram of the ingot of comparative example 1;

[0012] Figure 2 This is a wrinkle defect diagram of the wire rod of comparative example 1;

[0013] Figure 3 This is the distribution diagram of the wire rod oxide scale of Comparative Example 1;

[0014] Figure 4 This is the thickness diagram of the wire rod iron sheet of Comparative Example 1;

[0015] Figure 5 This is the distribution diagram of the wire rod scale in Example 1;

[0016] Figure 6 This is the distribution diagram of wire rod oxide scale in Example 2. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0018] Example 1

[0019] This embodiment provides a method for eliminating the wrinkle defect of bearing steel and improving the uniformity of the distribution of iron oxide scale. The method is used in a steel plant to produce 180mm*240mm cross-section GCr15 and roll φ23mm specification wire rods. The practical process is as follows:

[0020] (1) The production process is as follows: smelting process: hot metal KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → slow cooling of ingots; rolling process: heating in a heating furnace → high-pressure water dephosphorization → rough rolling → pre-finishing rolling → finishing rolling → sizing → spinning → Stelmor air cooling → coiling → packaging.

[0021] (2) In the above production process, in the continuous casting link of the smelting process, a new crystallizer copper tube with an R angle diameter of φ33mm is used. In the cooling link of the smelting process, the ingot is put into the slow cooling pit for slow cooling. The slow cooling pit is preheated to 300°C. The ingot is cooled in a "one"-shaped close-packed pile. The slow cooling pit is covered with an asbestos mesh. In the high-pressure water dephosphorization link of the rolling process, the dephosphorization ring nozzles are arranged in a rectangular shape, with 4 nozzles on the top and bottom and 3 nozzles on the left and right. The water supply of the nozzles near the corners of the rectangle is controlled by a separate valve station. The dephosphorization pressure of the 8 nozzles near the corners is 25Mpa and the flow rate is 3m 3 / h, the other 6 nozzles have a dephosphorization pressure of 18Mpa and a flow rate of 5m 3 / h. In the rough rolling process, corner flame heating devices are added before and after the first three rolling mills and between the stands. One set of corner heating devices is added before the 1# stand and after the 3# stand, and two sets of corner heating devices are added between the 1# and 2# stands and between the 2# and 3# stands to achieve corner temperature compensation.

[0022] The method of this embodiment is used to roll the GCr15 bearing steel wire rod with a diameter of 23 mm. Figure 5 As shown in the figure, the wire rod was pickled online for multiple times at the head and tail, and no wrinkle defects were found. Metallographic examination of the wire rod showed that the iron oxide scale was evenly distributed with a thickness of about 13-15μm.

[0023] Example 2

[0024] This embodiment provides a method for eliminating wrinkle defects in bearing steel and improving the uniformity of iron oxide scale distribution. The method is used in a steel plant to produce 180mm*240mm cross-section GCr15 and roll φ10mm specification wire rods in practice as follows:

[0025] (1) The production process is as follows: smelting process: hot metal KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → slow cooling of ingots; rolling process: heating in a heating furnace → high-pressure water dephosphorization → rough rolling → pre-finishing rolling → finishing rolling → sizing → spinning → Stelmor air cooling → coiling → packaging.

[0026] (2) In the above production process, in the continuous casting link of the smelting process, a new crystallizer copper tube with an R angle diameter of φ33mm is used. In the cooling link of the smelting process, the ingot is put into the slow cooling pit for slow cooling. The slow cooling pit is preheated to 300°C. The ingot is cooled in a "one"-shaped close-packed pile. The slow cooling pit is covered with an asbestos mesh. In the high-pressure water dephosphorization link of the rolling process, the dephosphorization ring nozzles are arranged in a rectangular shape, with 4 nozzles on the top and bottom and 3 nozzles on the left and right. The water supply of the two nozzles near the corners is controlled by a separate valve station. The dephosphorization pressure of the 8 nozzles near the corners is 25Mpa, and the flow rate is 3m 3 / h. The other 6 nozzles have a dephosphorization pressure of 18Mpa and a flow rate of 5m 3 / h. In the rough rolling process, corner flame heating devices are added before and after the first three rolling mills and between the stands. One set of corner heating devices is added before the 1# stand and after the 3# stand, and two sets of corner heating devices are added between the 1# and 2# stands and between the 2# and 3# stands to achieve corner temperature compensation.

[0027] The method of this embodiment is used to roll the GCr15 bearing steel wire rod with a diameter of 10 mm. Figure 6 As shown in the figure, the wire rod was pickled online for multiple times at the head and tail, and no wrinkle defects were found. The metallographic examination of the wire rod showed that the iron oxide scale was evenly distributed with a thickness of about 11-13μm.

[0028] Comparative case 1:

[0029] In a steel plant, the practical process of producing 180mm*240mm cross-section GCr15 and rolling φ18mm wire rod is as follows:

[0030] (1) The production process is as follows: smelting process: hot metal KR desulfurization → 100-ton converter smelting → LF refining → RH refining → continuous casting → ingot “well” shaped pile cooling; rolling process: heating in a heating furnace → high-pressure water dephosphorization → rough rolling → pre-finishing rolling → finishing rolling → sizing → spinning → Stelmor air cooling → coiling → packaging.

[0031] (2) In the continuous casting process of the smelting process, the R angle diameter of the crystallizer copper tube is φ10 mm, and the R angle radius of 10 mm corresponds to the corner of the ingot with a depth of ≤1 mm (such as Figure 1As shown). In the smelting process, the billet cooling link: the billet raw materials in the factory are naturally cooled, and the billets are arranged in a "well" shape. In the rolling process, the high-pressure water dephosphorization link: the dephosphorization ring nozzles are arranged in a rectangular shape, 4 on the top and 3 on the left and right. Each nozzle uses a set of water supply valves. The nozzle dephosphorization pressure is 18Mpa and the flow rate is 5m 3 / h. There is no flame heating and temperature compensation device in the corners before and after the first three rolling mills and between the stands in the rough rolling process.

[0032] Rolling φ18mm GCr15 bearing steel wire rod, the wire rod is pickled online for multiple turns at the head and tail, and there are wrinkle defects of varying depths (such as Figure 2 As shown). Metallographic examination of the wire rod shows that the thickness of the oxide scale is regularly distributed over the entire circular cross section ( Figure 3 : The thickness of the iron sheet at the four positions ABCD is uneven), and the metallographic morphology of the uneven thickness of the iron sheet can be seen Figure 4 .

[0033] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for eliminating wrinkle defects in bearing steel and improving the uniformity of scale distribution, the method process is: hot metal KR desulfurization → converter smelting → LF refining → RH refining → continuous casting → slow cooling of ingot → heating in heating furnace → high-pressure water dephosphorization → rough rolling → pre-finishing rolling → finishing rolling → sizing → spinning → Stelmor air cooling → coiling → packaging, characterized in that: The R angle diameter of the copper tube of the crystallizer used in the continuous casting process is φ33mm. In the slow cooling process of the ingot, the slow cooling pit is preheated to 300°C, and then the ingot enters the slow cooling pit; in the high-pressure water dephosphorization process, the dephosphorization ring nozzles are arranged in a rectangular shape, and the dephosphorization pressure of the nozzles near the corners is 25Mpa, and the flow rate is 3m 3 / h, the other nozzles’ dephosphorization pressure is 18Mpa, flow rate is 5m 3 / h; in the rough rolling process, corner flame heating devices are added before and after the first three rolling mills and between the racks to achieve corner temperature compensation.

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

3. The method for eliminating wrinkle defects 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 before and after and between the frames of the first three rolling mills in the rough rolling process is to add one set of corner flame heating devices in front of the 1# frame and after the 3# frame, and add two sets of corner flame heating devices between the 1# and 2# frames and between the 2# and 3# frames.

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