Production method of low-cost high-quality high-carbon bearing steel GCr15 wire rod

Abstract

The invention relates to the field of metallurgy, in particular to a production method of a low-cost high-quality high-carbon bearing steel GCr15 wire rod, the process route comprises the steps of steelmaking, continuous casting, heating in a heating furnace and rolling, crystallizer electromagnetic stirring and tail end electromagnetic stirring are used for continuous casting, and a continuous casting billet dynamic soft reduction process is used. The compression ratio of the cross section area of a casting blank to a final wire rod is larger than or equal to 160, and a high-temperature decarburization prevention coating is sprayed before the casting blank enters a furnace. Through the high compression ratio and severe plastic deformation, coarse carbides are crushed into fine dispersed particles, original as-cast dendritic crystals are crushed, and macrosegregation is relieved; through continuous casting crystallizer electromagnetic stirring, tail end electromagnetic stirring and large continuous casting blank rolling reduction, casting blank element segregation is improved, and the core compactness is improved; through casting blank shot blasting and anti-decarburization coating spraying, the high-temperature diffusion and anti-decarburization requirements of the heating furnace are balanced; and by controlling the rolling temperature and the cooling rate, precipitation of network carbides is inhibited, and the control level of the bearing steel wire rod carbides is further improved.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, and in particular to a method for producing low-cost, high-quality, high-carbon bearing steel GCr15 wire rod. Background Technology

[0002] Bearings operate under high loads, high speeds, and complex conditions for extended periods, and fatigue failure is one of their main modes of damage. GCr15 is one of the most widely used high-carbon bearing steels. Decarburization and carbides are two important factors affecting bearing fatigue life. Decarburization reduces the surface hardness and wear resistance of the bearing; carbides, as hard and brittle phases in steel, easily cause stress concentration and crack initiation during bearing use. Bearing steel wire rods are commonly used for the production of rolling elements. Due to their small size, the requirements for decarburization and carbide control are more stringent than those for bars used in the production of bearing rings. Decarburization occurs because the carbon on the steel surface reacts with components such as O2, H2O, and CO2 in the furnace atmosphere during the heating process of the steel billet, resulting in a lower carbon content on the billet surface compared to the base material. The formation of carbides originates from the segregation of carbon and chromium during continuous casting solidification and the phase transformation during rolling cooling. Increasing the heating temperature and extending the heating time of the billet in the furnace promotes the diffusion and homogenization of elements in bearing steel, which can reduce the carbide rating, but it will exacerbate decarburization on the steel surface. To resolve these two quality control contradictions caused by furnace heating, high-quality bearing steel wire rods are usually produced using a two-heat process. The billet is heated twice in the furnace. The first heating uses a high diffusion temperature and long heating time to ensure sufficient diffusion of elements such as carbon and chromium. After heating, the billet is ground to remove the decarburized layer on the surface. The second heating uses a low-temperature, rapid heating process to reduce the re-generation and deepening of the decarburized layer while meeting rolling requirements.

[0003] The two-heating process can produce high-quality bearing steel that simultaneously meets the requirements for decarburization and carbide formation, but the production cost is high due to the two heating processes and billet grinding. To solve this problem, there is an urgent need for a low-cost production method for high-quality bearing steel GCr15 wire rod. Summary of the Invention

[0004] In view of this, the purpose of this invention is to propose a low-cost, high-quality, high-carbon bearing steel GCr15 wire rod production method to solve the problem of high cost when producing high-quality bearing steel using the two-stage firing process.

[0005] A method for producing low-cost, high-quality, high-carbon bearing steel GCr15 wire rod, comprising the following process: steelmaking → continuous casting → furnace heating → rolling, wherein:

[0006] Steelmaking process: The process of converter → LF refining → RH furnace vacuum treatment is adopted to produce molten steel that meets the standard requirements of GCr15;

[0007] Continuous casting process: The continuous casting process uses electromagnetic stirring in the crystallizer and electromagnetic stirring at the end, and uses dynamic light reduction process for the continuous casting billet. After reduction, the cross-section of the billet is 215mm*245mm, the specification of the rolled wire rod is ≤Φ20mm, the compression ratio of the cross-sectional area of ​​the billet to the final wire rod is ≥160, and the continuous casting billet is shot blasted.

[0008] Heating process in the heating furnace: Before the billet enters the furnace, it is sprayed with anti-high temperature decarburization coating. The high temperature diffusion temperature in the furnace is 1200℃~1250℃, the high temperature diffusion time is 150min~200min, the total heating time is 280min~380min, and the residual oxygen content in the flue gas is 1%~2%.

[0009] Rolling process: initial rolling temperature 1090℃~1120℃, final rolling temperature 870℃~930℃, wire drawing temperature 800℃~860℃, cooling rate after wire drawing 2℃ / S~5℃ / S, final cooling temperature 550℃~650℃.

[0010] Furthermore, the high-temperature decarburization resistant coating is an Al2O3-SiO2 composite decarburization resistant coating, with an Al2O3 content of 65%~68%, a SiO2 content of 28%~32%, and 5%~8% sodium silicate added as a binder; after the coating is heated at a high temperature of 1200℃~1250℃, the density is ≥97% and the porosity is ≤3%.

[0011] Furthermore, the coating thickness after spraying the high-temperature decarburization resistant coating is 0.1mm~0.3mm, and the coating coverage is ≥99%.

[0012] Furthermore, in the continuous casting process, the cross-section of the billet before pressing down is 240mm*240mm, the pressing down is 215mm*245mm, the total pressing down is 25mm, the electromagnetic stirring current of the crystallizer is 550A, the frequency is 2HZ, the electromagnetic stirring current at the end is 600A, the frequency is 10HZ, and the carbon segregation index at the center of the continuous casting billet is 0.95-1.05.

[0013] Furthermore, the prepared GCr15 wire rods exhibited the following characteristics: carbide liquid precipitation grade 0, carbide banding grade ≤ 1.5, carbide network grade ≤ 2.0, and decarburized layer ≤ 0.5%D.

[0014] The beneficial effects of this invention are as follows: This invention uses a high compression ratio and intense plastic deformation to break coarse carbides into fine, dispersed particles, thus breaking down the original cast dendrites, reducing macroscopic segregation, and consequently lowering the carbide rating. Electromagnetic stirring in the continuous casting crystallizer, end-stage electromagnetic stirring, and a large reduction in the continuous casting billet reduce elemental segregation and increase core density. Shot blasting of the billet followed by spraying with an anti-decarburization coating balances the high-temperature diffusion and decarburization prevention requirements of the heating furnace. Controlling the rolling temperature and cooling rate suppresses the precipitation of network carbides, further improving the carbide control level of bearing steel wire rod. This invention uses a lower-cost process than two-stage processes, producing bearing steel wire rods with carbide and decarburization layer control levels comparable to those of two-stage processes. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0016] Example 1

[0017] A low-cost, high-quality bearing steel GCr15 wire rod production method, the specific process is as follows:

[0018] 1. Steelmaking process: 170t converter is used for smelting, LF refining time is 60min, RH furnace vacuum treatment ultimate vacuum degree is 45Pa, treatment time is 28min; composition conforms to GB / T18254-2019 "High carbon chromium bearing steel" standard.

[0019] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 215mm × 245mm, the final wire rod diameter is 6.5mm, and the compression ratio is approximately (215 × 245) / (π × (10 / 2)²) ≈ 670. Before the continuous casting machine reduces the billet cross-section, it is 240mm * 240mm. A dynamic light reduction process is used, reducing the billet to 215mm * 245mm, with a total reduction of 25mm. The electromagnetic stirring current in the crystallizer is 550A at a frequency of 2Hz, and the final electromagnetic stirring current is 600A at a frequency of 10Hz. The carbon segregation index at the center of the billet is 1.05. Shot blasting removes loose iron oxide scale from the billet surface.

[0020] 3. Heating process in the heating furnace: Spraying Al2O3-SiO2 composite coating (Al2O3 66%, SiO2 30%, sodium silicate 4%), coating thickness 0.2mm; segmented temperature control of the heating furnace: preheating section 900℃, heating section 1200℃, soaking section 1250℃, high temperature diffusion time 150min, total heating time 280min, residual oxygen content in flue gas 1%; high temperature density of the coating = 97.5%, porosity = 2.5%.

[0021] 4. Rolling process: A 20-stand high-speed wire rod mill is used, with a finishing mill speed of 52m / s and a roll gap adjustment accuracy of ±0.005mm; the initial rolling temperature is 1120℃, the final rolling temperature is 930℃, and the wire drawing temperature is 860℃; the Steyrmore controlled cooling line has a fan pressure of 0.4MPa, a cooling rate of 5℃ / s, and a final cooling temperature of 650℃.

[0022] 5. Product performance: Carbide liquid precipitation grade 0, carbide banding grade 1.5, carbide network grade 2.0, decarburization layer depth 0.5%D (D=10mm), production cost is reduced by 120 yuan / t compared with the second-fired product.

[0023] Example 2

[0024] A low-cost, high-quality bearing steel GCr15 wire rod production method, the specific process is as follows:

[0025] 1. Steelmaking process: 60t converter smelting, LF refining time 60min, RH furnace vacuum treatment ultimate vacuum degree 48Pa, treatment time 26min; composition conforms to GB / T18254-2019 standard.

[0026] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 215mm×245mm, the final wire rod diameter is 20mm, and the compression ratio is (215×245) / (π×(20 / 2)²)≈167; the cross-section of the billet before pressing down in the continuous casting machine is 240mm*240mm, the pressing down is 215mm*245mm, the total pressing down is 25mm, the electromagnetic stirring current of the crystallizer is 550A, the frequency is 2HZ, the electromagnetic stirring current at the end is 600A, the frequency is 10HZ, and the carbon segregation index at the center of the continuously cast billet is 0.95; shot blasting treatment.

[0027] 3. Heating process in the heating furnace: Spraying Al2O3-SiO2 composite coating (Al2O3 65%, SiO2 32%, sodium silicate 3%), coating thickness 0.18mm, coverage 99.9%; segmented temperature control of the heating furnace: preheating section 880℃, heating section 1180℃, soaking section 1200℃, high temperature diffusion time 180min, total heating time 360min, residual oxygen content in flue gas 2%; high temperature coating density 98%, porosity 2%.

[0028] 4. Rolling process: 18-stand high-speed wire rod mill is used, with a finishing mill speed of 16m / s and a roll gap adjustment accuracy of ±0.005mm; the initial rolling temperature is 1100℃, the final rolling temperature is 870℃, and the wire drawing temperature is 800℃; the Steyrmore controlled cooling line has a fan pressure of 0.35MPa, a cooling rate of 2℃ / s, and a final cooling temperature of 550℃.

[0029] 5. Product performance: Carbide liquid precipitation grade 0, carbide banding grade 1.5, carbide network grade 1.5, decarburization layer depth 0.4%D (D=20mm), production cost is reduced by 120 yuan / t compared with the second-fired product.

[0030] Example 3

[0031] A low-cost, high-quality bearing steel GCr15 wire rod production method, the specific process is as follows:

[0032] 1. Steelmaking process: 50t converter smelting, LF refining time 48min, RH furnace vacuum treatment ultimate vacuum degree 42Pa, treatment time 30min; composition conforms to GB / T18254-2019 standard.

[0033] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 215mm × 245mm, the final wire rod diameter is 5mm, and the compression ratio is approximately (215 × 245) / (π × (5 / 2)²) ≈ 2683. Before the continuous casting machine reduces the billet cross-section to 240mm * 240mm, and after reduction to 215mm * 245mm, the total reduction is 25mm. The electromagnetic stirring current in the crystallizer is 550A at a frequency of 2Hz, and the final electromagnetic stirring current is 600A at a frequency of 10Hz. The carbon segregation index at the center of the continuously cast billet is 1.0. Shot blasting treatment is also performed.

[0034] 3. Heating process in the heating furnace: Spraying Al2O3-SiO2 composite coating (Al2O3 68%, SiO2 28%, sodium silicate 4%), coating thickness 0.22mm, coverage 99.9%; segmented temperature control of the heating furnace: preheating section 920℃, heating section 1190℃, soaking section 1220℃, high temperature diffusion time 200min, total heating time 380min, residual oxygen content in flue gas 1.5%; high temperature coating density 97.8%, porosity 2.2%.

[0035] 4. Rolling process: A 22-stand high-speed wire rod mill is used, with a finishing mill speed of 98m / s and a roll gap adjustment accuracy of ±0.005mm; the initial rolling temperature is 1090℃, the final rolling temperature is 860℃, and the wire drawing temperature is 820℃; the Steyrmore controlled cooling line has a fan pressure of 0.5MPa, a cooling rate of 3℃ / s, and a final cooling temperature of 600℃.

[0036] 5. Product performance: Carbide liquid precipitation grade 0, carbide banding grade 1.5, carbide network grade 2.0, decarburization layer depth 0.3%D (D=5mm), production cost is reduced by 120 yuan / t compared with the second-fired product.

[0037] Comparative Example 1

[0038] 1. Steelmaking process: Same as in Example 2.

[0039] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 160mm×160mm, the final wire rod diameter is 5.5mm, and the compression ratio is ≈1000; no shot blasting treatment is performed, the surface Ra of the cast billet is 15μm, and the iron oxide scale removal rate is 60%.

[0040] 3. Heating process in the heating furnace: No anti-decarburization coating was applied; the heating furnace parameters were the same as in Example 2 (soaking zone 1200℃, diffusion 180min, total heating 360min, residual oxygen 2%).

[0041] 4. Rolling process: Same as in Example 2.

[0042] 5. Product performance: carbide liquid precipitation grade 0, carbide banding grade 1.5, carbide network grade 2.0, decarburized layer depth 1.2%D (D=5.5mm).

[0043] Comparative Example 2

[0044] 1. Steelmaking process: Same as in Example 1.

[0045] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 150mm×150mm, the final wire rod diameter is 8mm, and the compression ratio is ≈1200; no shot blasting treatment was performed.

[0046] 3. Heating process of heating furnace: No anti-decarburization coating was sprayed; heating furnace soaking zone 1180℃, high temperature diffusion time 150min, total heating time 250min, residual oxygen 2%.

[0047] 4. Rolling process: initial rolling temperature 1080℃, final rolling temperature 870℃, wire drawing temperature 800℃, cooling rate 2℃ / s, final cooling temperature 550℃.

[0048] 5. Product performance: carbide liquid precipitation grade 1.0, carbide banding grade 2.0, carbide network grade 2.5, decarburized layer depth 0.8%D (D=8mm).

[0049] Comparative Example 3

[0050] 1. Steelmaking process: Same as in Example 1.

[0051] 2. Continuous casting process: The cross-sectional dimensions of the continuously cast billet are 100mm×100mm, the final wire rod diameter is 6mm, and the compression ratio is ≈80; shot blasting is performed, and anti-decarburization coating is sprayed (same as in Example 1).

[0052] 3. Heating process of heating furnace: soaking zone 1200℃, high temperature diffusion time 170min, total heating time 290min, residual oxygen 2%.

[0053] 4. Rolling process: initial rolling temperature 1080℃, final rolling temperature 900℃, wire drawing temperature 850℃, cooling rate 4℃ / s, final cooling temperature 600℃.

[0054] 5. Product performance: carbide liquid precipitation grade 0.5, carbide banding grade 2.0, carbide network grade 2.0, decarburized layer depth 0.4%D (D=6mm).

[0055] Comparative Analysis of Examples and Comparative Cases

[0056] Synergistic effect of shot blasting and coating: Examples 1-3 all used shot blasting and composite coating, and the decarburization layer depth was ≤0.5%D. However, Comparative Example 1 did not use this combination, and the decarburization layer reached 1.2%D. This proves that the combination can effectively isolate oxygen and solve the decarburization problem caused by high temperature diffusion.

[0057] The key role of high compression ratio: In Examples 1-3, the compression ratio was ≥160, and the carbide liquid precipitation was grade 0, while in Comparative Example 3, the compression ratio was 80, and the carbide liquid precipitation was grade 0.5. This shows that a compression ratio of ≥160 can completely break down coarse carbides and improve segregation.

[0058] Effect of temperature control synergy: In Examples 1-3, the heating + rolling temperature control synergy resulted in network carbides ≤ 2.0 grade, while in Comparative Example 2, the low temperature short-time diffusion resulted in network carbides reaching 2.5 grade, proving that precise temperature control can suppress the precipitation of network carbides;

[0059] Cost and performance balance: Examples 1-3 achieve the performance level of two-fired products at the low cost of single-fired production (reduced by 120 yuan / t), while the comparative cost is lower but the performance is significantly inferior, demonstrating the core advantage of this invention.

[0060] This invention utilizes a high compression ratio and intense plastic deformation to break coarse carbides into fine, dispersed particles, thereby disintegrating the original cast dendrites, reducing macroscopic segregation, and ultimately lowering the carbide rating. Electromagnetic stirring in the continuous casting mold, end-stage electromagnetic stirring, and a large reduction in the continuous casting billet size improve elemental segregation in the billet and increase core density. Shot blasting of the billet followed by spraying with an anti-decarburization coating balances the high-temperature diffusion and decarburization prevention requirements of the heating furnace. Furthermore, controlling the rolling temperature and cooling rate suppresses the precipitation of network carbides, further enhancing the carbide control level of bearing steel wire rods. This invention employs a lower-cost process than two-stage processes, producing bearing steel wire rods with carbide and decarburization layer control levels comparable to those of two-stage processes.

[0061] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in the details for the sake of brevity.

[0062] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A method for producing low-cost, high-quality, high-carbon bearing steel GCr15 wire rod, characterized in that, The process route is: steelmaking → continuous casting → heating in a heating furnace → rolling, wherein: Steelmaking process: The process of converter → LF refining → RH furnace vacuum treatment is adopted to produce molten steel that meets the standard requirements of GCr15; Continuous casting process: The continuous casting process uses electromagnetic stirring in the crystallizer and electromagnetic stirring at the end, and uses dynamic light reduction process for the continuous casting billet. After reduction, the cross-section of the billet is 215mm*245mm, the specification of the rolled wire rod is ≤Φ20mm, the compression ratio of the cross-sectional area of ​​the billet to the final wire rod is ≥160, and the continuous casting billet is shot blasted. Heating process in the heating furnace: Before the billet enters the furnace, it is sprayed with anti-high temperature decarburization coating. The high temperature diffusion temperature in the furnace is 1200℃~1250℃, the high temperature diffusion time is 150min~200min, the total heating time is 280min~380min, and the residual oxygen content in the flue gas is 1%~2%. Rolling process: initial rolling temperature 1090℃~1120℃, final rolling temperature 870℃~930℃, wire drawing temperature 800℃~860℃, cooling rate after wire drawing 2℃ / S~5℃ / S, final cooling temperature 550℃~650℃.

2. The production method according to claim 1, characterized in that, The high-temperature decarburization resistant coating is an Al2O3-SiO2 composite anti-decarburization coating with an Al2O3 content of 65%~68%, a SiO2 content of 28%~32%, and 5%~8% sodium silicate added as a binder; after the coating is heated at 1200℃~1250℃, the density is ≥97% and the porosity is ≤3%.

3. The production method according to claim 1 or 2, characterized in that, The coating thickness after spraying the high-temperature decarburization resistant coating is 0.1mm~0.3mm, and the coating coverage is ≥99%.

4. The production method according to claim 1, characterized in that, In the continuous casting process, the cross-section of the billet before pressing down is 240mm*240mm, the pressing down is 215mm*245mm, the total pressing down is 25mm, the electromagnetic stirring current of the crystallizer is 550A, the frequency is 2HZ, the electromagnetic stirring current at the end is 600A, the frequency is 10HZ, and the carbon segregation index at the center of the continuous casting billet is 0.95-1.

05.

5. The production method according to claim 1, characterized in that, The prepared GCr15 wire rods had a carbide liquid precipitation grade of 0, a carbide banding grade of ≤1.5, a carbide network grade of ≤2.0, and a decarburized layer of ≤0.5%D.