Method for reducing banded structure of bearing steel wire rod

Abstract

The invention discloses a method for reducing a bearing steel wire rod banded structure, and belongs to the technical field of bearing steel metallurgy. The method specifically comprises the following steps that 1.5%-2.5% soft reduction deformation is carried out in the continuous casting process, the high-temperature diffusion temperature is controlled to be 1280 DEG C, the diffusion time is 11 hours, and then the steel wire rod with the diameter phi being 14 mm is rolled through a controlled rolling and controlled cooling technology. The test result shows that compared with the process without soft reduction or shortening the diffusion time, the method has the advantages that the banded level of the carbide can be obviously reduced to be lower than 1.5 level, carbide particles are refined to be 2.5 microns on average, and the structure uniformity and the comprehensive performance of the material are improved. The method is simple in process, high in production efficiency and suitable for industrial production, and has important popularization value.

Description

Technical Field

[0001] The present invention belongs to the technical field of bearing steel metallurgy, and particularly relates to a method for reducing the banded structure of bearing steel wire rods. Background Art

[0002] GCr15 bearing steel is widely used in various rolling elements, such as steel balls, rollers, and needles, due to its high wear resistance, high contact fatigue strength, and excellent comprehensive properties. However, during the production and use processes, the carbide banded structure is an important issue affecting the material properties. The formation of the banded structure is mainly related to the segregation of chemical elements during solidification. Especially in high-carbon hypereutectoid steels like GCr15, due to the large interval between the liquidus and solidus lines, obvious solidification segregation occurs, resulting in a large amount of carbide precipitation in high-concentration regions, forming a large banded structure. The existence of the carbide banded structure causes material anisotropy, makes the segregation band become the fatigue crack source, greatly shortens the fatigue life of the rolling elements, and affects the product performance and reliability. Currently, the commonly used improvement measures include controlling the original segregation of the continuous casting billet and implementing high-temperature diffusion treatment, but these technologies still have deficiencies in reducing the banded level and refining the particle size, and cannot fully meet the application requirements of high-performance bearing steel. Therefore, there is an urgent need for a more efficient and economical improvement method. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for reducing the banded structure of bearing steel wire rods, which significantly reduces the banded level and refines the carbide particles by optimizing the combination of continuous casting soft reduction process and high-temperature diffusion treatment, thereby improving the comprehensive properties of bearing steel.

[0004] To solve the above technical problems, the present invention adopts the following technical solutions:

[0005] A method for reducing the banded structure of bearing steel wire rods according to the present invention performs a soft reduction deformation of 1.5% - 2.5% during continuous casting, controls the high-temperature diffusion temperature at 1180 - 1300 °C, the diffusion time at 10 - 12 hours, and then rolls it into wire rods through a controlled rolling and controlled cooling process.

[0006] Further, the size of the wire rod is Φ14mm.

[0007] Further, the steel grade is GCr15.

[0008] Further, control the high-temperature diffusion temperature at 1280 °C and the diffusion time at 11 hours.

[0009] Further, this method promotes the dissolution and refinement of carbide particles, reduces the average size of carbide particles to 2.5 μm, and simultaneously reduces the banded level to below 1.5 levels.

[0010] Furthermore, the mass percentage of its chemical components includes: C 0.95% - 1.05%, Si 0.15% - 0.35%, Mn 0.20% - 0.40%, P ≤ 0.015%, S ≤ 0.010%, Cr 1.40% - 1.60%, and the rest is Fe and inevitable trace impurities, with the total mass fraction being 100%.

[0011] Furthermore, converter BOF smelting is adopted, followed by LF refining and RH vacuum degassing treatment to ensure the purity and chemical composition stability of the molten steel; during continuous casting, the superheat of the billet is controlled at 20 - 30°C.

[0012] Furthermore, the wire - laying temperature is controlled at 780 ± 15°C, and the temperature entering the heat - preservation hood is 600 ± 15°C.

[0013] Furthermore, the controlled rolling and controlled cooling process is specifically as follows: an 18 - stand continuous rolling mill is adopted, the starting rolling temperature is 1050 - 1100°C, the final rolling temperature is 900 - 950°C, and Φ14mm wire rods are rolled; immediately after wire - laying, it enters the water - mist cooling zone with a length of 8 - 10m and a cooling rate of 15 - 20°C / s, enabling the wire rods to quickly pass through the austenite unstable zone (750 - 650°C); it enters the heat - preservation hood with a length of 25 - 30m, an inlet temperature of 600 ± 15°C, an outlet temperature of 450 ± 15°C, and a cooling rate of 5 - 8°C / s to control the pearlite transformation; after the outlet of the heat - preservation hood, it is air - cooled to room temperature with a cooling rate of 3 - 5°C / s.

[0014] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0015] The present invention adopts the continuous casting soft reduction technology, reducing the central segregation index of the billet from 1.26 to 1.05 during continuous casting, significantly improving the billet segregation, and providing a basis for the subsequent dissolution and uniform distribution of carbides. By controlling the high - temperature diffusion process parameters, including the diffusion temperature (1180 - 1300°C) and diffusion time (11 hours), it promotes the dissolution and refinement of carbide particles, reducing the average size of carbide particles to 2.5μm, and at the same time reducing the banding level to below 1.5 levels.

[0016] Compared with the traditional process, the present invention can significantly reduce carbide segregation and reticular structure, improving the isotropy of the material. By precisely adjusting the soft reduction and diffusion parameters, the distribution and size of carbide particles can be flexibly adjusted according to product requirements. It avoids too long high - temperature diffusion time, while achieving higher production efficiency and product quality improvement.

[0017] Through comparative tests with the prior art, it is verified that the process flow of the present invention has significant advantages in improving carbide particle refinement and reducing banding level. Especially after the optimization of the matching of soft reduction and high - temperature diffusion time, bearing steel wire rods with higher uniformity and better performance can be obtained.

[0018] (1) By combining the continuous casting soft reduction technology with optimized high-temperature diffusion treatment, the present invention can reduce the carbide banding grade of bearing steel wire rods to below 1.5 levels, effectively reducing the anisotropy of the material and improving the fatigue life and overall reliability of rolling elements. (2) The high-temperature diffusion treatment significantly refines carbide particles, with the average size controlled within 2.5 μm, avoiding the formation of large particles or network structures, thereby improving the tissue uniformity and fatigue resistance of the material and meeting the requirements of high-precision application fields. (3) The present invention optimizes the process based on existing continuous casting and high-temperature diffusion equipment, without the need to add complex equipment, and has strong process controllability. At the same time, it avoids excessive diffusion time, improves production efficiency, reduces energy consumption and costs, and has significant economic benefits and industrial promotion value. Detailed implementation mode

[0019] Example 1: A method for reducing the banded structure of bearing steel wire rods according to the present invention is carried out according to the following steps:

[0020] The test material is GCr15 bearing steel, which is smelted in a converter (BOF), refined by LF and degassed in a RH vacuum to ensure the purity of the molten steel and the stability of chemical components. The chemical composition control range is C 1.00%, Si 0.25%, Mn 0.30%, P 0.012%, S 0.008%, Cr 1.50%, and the rest is Fe and impurities;

[0021] The superheat of the continuous casting billet is controlled at 20 - 30 °C, the billet cross-section is 390 mm × 510 mm, the drawing speed is constant, and the soft reduction deformation amount is controlled at 1.5% - 2.5%;

[0022] The high-temperature diffusion temperature is 1280 °C, and the diffusion time is 11 hours;

[0023] After blooming, it is rolled into Φ14 mm wire rods, the spinning temperature is 780 °C, and the temperature entering the heat preservation cover is 600 °C; the rolling start temperature is 1070 °C, the final rolling temperature is 930 °C, and it is rolled into Φ14 mm wire rods; immediately after spinning, it enters the water mist cooling zone, and the cooling rate is 15 °C / s; it enters the heat preservation cover, the inlet temperature is 6005 °C, the outlet temperature is 450 °C, and the cooling rate is 8 °C / s; after exiting the heat preservation cover, it is air-cooled to room temperature, and the cooling rate is 5 °C / s.

[0024] The average carbide banding grade is 1.5 levels, and the average carbide particle size is 2.5 μm.

[0025] Comparative example 1:

[0026] In Comparative Example 1, except that the soft reduction technology was not adopted, which was different from Example 1, the rest was exactly the same as Example 1. The test results showed that the average carbide banding level was 3.5; the average carbide particle size was 6.92 μm, and some particles were distributed in a network pattern.

[0027] Comparative Example 2:

[0028] In Comparative Example 2, except that the high-temperature diffusion time was shortened to 8 hours, which was different from Example 1, the rest was exactly the same as Example 1. The test results showed that the average carbide banding level was 2.5; the average carbide particle size was 5.23 μm.

[0029] Comparative Example 3:

[0030] In Comparative Example 3, except that the high-temperature diffusion time was extended to 14 hours, which was different from Example 1, the rest was exactly the same as Example 1. The carbide banding level was close to that of Example 1, but the production efficiency was significantly reduced; the equipment energy consumption increased, and it was not economical.

[0031] By comparing the unreasonable conditions of the above process parameters, it can be seen that the technical solution of the present invention, through scientific parameter optimization and reasonable process matching, takes into account both performance improvement and economy, realizes a significant improvement in the production process of bearing steel wire rods, and has strong practical application value.

[0032] The present invention has the following advantages: (1) In Comparative Example 1, the soft reduction technology was not adopted, resulting in serious center segregation of the continuous casting billet and a banding level of more than 3.5. Although the soft reduction technology was introduced in Comparative Example 2, the diffusion time was insufficient, and the banding level still reached more than 2.5. The present invention effectively reduces the banding level to less than 1.5 through the soft reduction process combined with an appropriate high-temperature diffusion time (11 hours), meeting the use requirements of high-performance bearing steel. (2) The average carbide particle size in Comparative Example 1 reached 6.92 μm, with significant large particles or network structures; although the particle size in Comparative Example 2 decreased, it was still above 5.23 μm on average, unable to fully meet the fatigue performance requirements of rolling elements. The technical solution of the present invention controls the average carbide particle size within 2.5 μm through optimizing the diffusion parameters, significantly improving the tissue uniformity of the material. (3) Although the diffusion time was extended to 14 hours in Comparative Example 3, the effect of carbide particle refinement was limited, and at the same time, the production efficiency was significantly reduced and the cost increased. The present invention, through reasonable control of the diffusion time (11 hours), not only realizes the refinement of carbide particles and the effective reduction of the banding level, but also avoids the negative impact of over-long diffusion time on production efficiency and cost, reflecting high process economy.

[0033] The embodiments described above are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the spirit of the present invention's design, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for reducing the banded structure of bearing steel wire rods, characterized in that, During continuous casting, a soft reduction deformation of 1.5%-2.5% is implemented, the high-temperature diffusion temperature is controlled at 1180-1300°C, and the diffusion time is 10-12 hours. Subsequently, it is rolled into wire rods through a controlled rolling and controlled cooling process.

2. The method for reducing the banded structure of bearing steel wire rods according to claim 1, characterized in that, The size of the wire rod is Φ14mm.

3. The method for reducing the banded structure of bearing steel wire rod according to claim 1, characterized in that, Its steel grade is GCr15.

4. The method for reducing the banded structure of bearing steel wire rod according to claim 1, characterized in that, The high-temperature diffusion temperature is controlled at 1280°C, and the diffusion time is 11 hours.

5. The method for reducing the banded structure of bearing steel wire rod according to claim 1, characterized in that, This method promotes the dissolution and refinement of carbide particles, reduces the average size of carbide particles to 2.5μm, and simultaneously reduces the banding level to below 1.5 levels.

6. The method for reducing the banded structure of bearing steel wire rods according to claim 1 or 3, characterized in that, The mass percentage content of its chemical composition includes: C 0.95%-1.05%, Si 0.15%-0.35%, Mn 0.20%-0.40%, P≤0.015%, S≤0.010%, Cr 1.40%-1.60%, and the rest are Fe and inevitable trace impurities, with a total mass fraction of 100%.

7. The method for reducing the banded structure of bearing steel wire rods according to claim 1, characterized in that, Converter BOF smelting is adopted, followed by LF refining and RH vacuum degassing treatment to ensure the purity of the molten steel and the stability of the chemical composition; during continuous casting, the superheat of the slab is controlled at 20-30°C.

8. The method for reducing the banded structure of bearing steel wire rod according to claim 1, characterized in that, The spinning temperature is controlled at 780±15°C, and the temperature entering the heat preservation hood is 600±15°C.

9. The method for reducing the banded structure of bearing steel wire rod according to claim 1, characterized in that, The specific controlled rolling and controlled cooling process is as follows: an 18-stand continuous rolling mill is adopted, the starting rolling temperature is 1050-1100°C, the finishing rolling temperature is 900-950°C, and it is rolled into Φ14mm wire rods; immediately after spinning, it enters the water mist cooling zone with a length of 8-10m and a cooling rate of 15-20°C / s, enabling the wire rods to quickly pass through the austenite unstable zone; it enters the heat preservation hood with a length of 25-30m, an inlet temperature of 600±15°C, and an outlet temperature of 450±15°C, and the cooling rate is 5-8°C / s to control the pearlite transformation; after the outlet of the heat preservation hood, it is air-cooled to room temperature with a cooling rate of 3-5°C / s.