Method for improving quality of bearing steel core

Abstract

The invention provides a method for improving the core quality of bearing steel, which specifically comprises the following steps of: (1) controlling the number of cogging rolling passes to be 9 when the bearing steel is produced; and (2) in the first five passes of cogging rolling, at least three passes adopt a high-pressure rolling mode with the reduction rate being larger than or equal to 20%. According to the method, the rolling process is optimized, the rolling reduction rate is improved by low times, the bearing super-superior level is achieved, and the bearing steel quality is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of iron and steel metallurgy, and in particular to a method for improving the quality of the core of a bearing steel. Background Art

[0002] Currently, GCr15 bearing steel meets the low-magnification requirements of the GB / 18254 standard, with a central porosity of ≤1.5 for high-quality and premium grades, and ≤1 for premium grades. The low-magnification microstructure of 130mm round steel meets the requirements of high-quality and premium grades, but falls short of premium grades. This compromises the quality and brand image of bearing steel and hinders its development towards higher-end products. Central shrinkage cavities in round steel are caused by the volumetric contraction that occurs during solidification of the ingot as the liquid phase transforms into the solid phase, as well as the inability of the molten steel to compensate for the volumetric contraction caused by continued cooling of the solidified center of the ingot due to heat transfer outward. This is particularly true for large continuous castings, which often exhibit numerous intermittent shrinkage cavities and a concentration of low-melting-point inclusions. The bearing steel has a wide solid-liquid two-phase region, and large continuous castings have large cross-sectional areas and longer mushy regions, making the formation of intermittent shrinkage cavities highly susceptible to shrinkage compensation. If sufficient penetration and compaction are not achieved during the subsequent heating and rolling process, shrinkage cavities are unavoidable in the round steel. Summary of the Invention

[0003] In order to eliminate the low-magnification shrinkage cavity of bearing steel, the present invention provides a method for improving the quality of the core of bearing steel. By optimizing the rolling process and improving the rolling reduction rate, the low-magnification is improved to reach the superior level of bearings and improve the quality of bearing steel.

[0004] The technical means adopted in the present invention are as follows:

[0005] A method for improving the quality of the core of a bearing steel, comprising:

[0006] (1) When producing bearing steel, the number of slab rolling passes is controlled to 9;

[0007] (2) In the first five passes of slab rolling, at least three passes adopt a large-volume rolling method with a reduction rate of ≥20%.

[0008] Furthermore, except for the passes rolled using a high-pressure rolling method, the reduction ratio of other passes is less than 20%.

[0009] Furthermore, a high-pressure rolling method is adopted in the third, fourth and fifth rolling passes.

[0010] Furthermore, the rolling mill used for bloom rolling is a reversible rolling mill.

[0011] Furthermore, during the slab rolling process, the steel slab is turned 90° after every two rolling passes.

[0012] Furthermore, by adjusting the reduction rate of each pass, the aspect ratio of the steel billet after each rolling pass is controlled within 1.45.

[0013] Compared with the prior art, the present invention has the following advantages:

[0014] The method for improving the core quality of bearing steel provided by the present invention reduces the number of rolling passes for the bearing steel blanking from the usual 11 rolling passes to 9 rolling passes, and combines at least three high-pressure rolling passes in the first five rolling passes, so that the steel blank can be quickly compacted, the core of the steel blank is made denser, and the central shrinkage cavity is eliminated, the quality of the bearing steel is improved, and the low-magnification inspection of the produced bearing steel can reach the excellent level. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0016] Figure 1 This is a low-magnification morphology image of the bearing steel in Example 1. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings 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. The following description of at least one exemplary embodiment is actually only illustrative and is in no way intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0018] The present invention provides a method for improving the quality of the core of bearing steel, which specifically includes:

[0019] (1) When producing bearing steel, the number of slab rolling passes is controlled to 9;

[0020] (2) In the first five passes of slab rolling, at least three passes adopt a large-volume rolling method with a reduction rate of ≥20%.

[0021] Furthermore, except for the passes rolled using a high-pressure rolling method, the reduction ratio of other passes is less than 20%.

[0022] Furthermore, a high-pressure rolling method is adopted in the third, fourth and fifth rolling passes.

[0023] Furthermore, the rolling mill used for the slab rolling is a reversible rolling mill, such as a 950 slab rolling mill.

[0024] Furthermore, during the slab rolling process, the steel slab is turned 90 degrees after every two rolling passes to ensure that all sides of the steel slab are rolled.

[0025] Furthermore, in order to prevent the square defect caused by large-scale rolling during the slab rolling process, the width-to-height ratio of the steel billet after each rolling pass is controlled within 1.45 by adjusting the reduction rate of each pass.

[0026] The present invention reduces the number of rolling passes for bearing steel slabs from the usual 11 to 9, and combines this with high-pressure rolling in at least three of the first five rolling passes, so that the steel billet can be quickly compacted, the core of the steel billet is made denser, and the central shrinkage cavity is eliminated, thereby improving the quality of the bearing steel and enabling the produced bearing steel to reach an excellent level in low-magnification inspection.

[0027] Example 1

[0028] The method for improving the core quality of bearing steel provided in the embodiment adopts a 950 blanking machine, specifically comprising:

[0029] (1) When producing bearing steel, the number of slab rolling passes is controlled to 9;

[0030] (2) A high-pressure rolling method with a reduction ratio of ≥20% is used in the third, fourth, and fifth passes, and a reduction ratio of <20% is used in the other passes. The specific reduction ratios of the passes in this embodiment are shown in Table 1.

[0031] (3) The billet rolling adopts a reversible rolling mill for reciprocating rolling, and the billet is turned 90° after every two rolling passes;

[0032] (4) By adjusting the reduction rate of each pass, the aspect ratio of the steel billet after each rolling pass is controlled within 1.45.

[0033] Table 1 Rolling parameters of each pass in Example 1

[0034] path Height (mm) Width (mm) Pressing amount (mm) Width (mm) Remark 410 320 Ingot size 1 345 65 2 285 330 60 10 Steel turning 3 265 65 4 210 305 55 10 Steel turning 5 230 75 6 190 235 40 25 Steel turning 7 190 45 12 8 190 202 0 Steel turning 9 175 200 27 10

[0035] Comparative Example

[0036] In the comparative example, when producing bearing steel, the slab rolling passes are conventionally 11 passes, and the rolling parameters of each pass are shown in Table 2.

[0037] Table 2 Rolling parameters of each pass in comparative example

[0038]

[0039]

[0040] The method described in Example 1 was repeated to prepare 4 samples. The low-magnification morphology of the samples was as follows: Figure 1 As shown, the samples were inspected and graded at low magnification, and the results are shown in Table 3. It can be seen that the central porosity level of each sample can reach level 0.5, that is, the excellent level. In the comparative example, the low magnification inspection and grading results of the bearing steel samples obtained by slab rolling without adopting the method described in this embodiment are shown in Table 4, and the low magnification central porosity is level 1.5 or level 1.

[0041] Table 3 Low-magnification inspection and rating results of Example 1

[0042]

[0043] Table 4 Rating results of low-magnification inspection of comparative examples

[0044]

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the quality of the core of bearing steel, characterized in that: Specifically include: (1) When producing bearing steel, the number of slab rolling passes is controlled to 9; (2) In the first five passes of slab rolling, at least three passes adopt a large-volume rolling method with a reduction rate of ≥20%.

2. The method for improving the core quality of bearing steel according to claim 1, characterized in that: Except for the passes rolled using a high-pressure rolling method, the reduction rate of other passes is less than 20%.

3. The method for improving the core quality of bearing steel according to claim 1, characterized in that: The 3rd, 4th and 5th rolling passes are performed using a high-pressure rolling method.

4. The method for improving the core quality of bearing steel according to claim 1, characterized in that: The rolling mill used for slab rolling is a reversible rolling mill.

5. The method for improving the core quality of bearing steel according to claim 1, characterized in that: During the slab rolling process, the steel slab is turned 90° after every two rolling passes.

6. The method for improving the core quality of bearing steel according to claim 1, characterized in that: By adjusting the reduction rate of each pass, the aspect ratio of the steel billet after each rolling pass is controlled within 1.45.

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