Annealing method of round steel for 60Si2CrVAT polishing material

Abstract

The invention provides an annealing method of round steel for 60Si2CrVAT polishing material, which comprises the following steps: S1, heating the round steel for 60Si2CrVAT polishing material to 775-785 DEG C at the speed of 10-20 DEG C / s in an electromagnetic field and a protective atmosphere; s2, closing the electromagnetic field and the protective atmosphere, and carrying out resistance heating at 780-790 DEG C and carrying out heat preservation for 2-4 hours; and S3, gradient cooling is conducted according to the high-temperature area of 780-650 DEG C, the medium-temperature area of 650-500 DEG C and the low-temperature area of 500-100 DEG C. Under the specific temperature and atmosphere conditions, the electromagnetic field and resistance heating are combined, the organization structure of the round steel for the 60Si2CrVAT polishing material is effectively improved, the hardness of the material is improved, and meanwhile the oxidation and decarburization phenomena in the annealing process are avoided.

Description

Technical Field

[0001] The present application relates to the technical field of heat treatment of metal materials, and in particular to a method for annealing round steel for 60Si2CrVAT polished material. Background Art

[0002] The chemical composition of 60Si2CrVAT round steel for polishing materials includes: The chemical composition of 60Si2CrVA round steel includes: Carbon (C): 0.56~0.64%, Silicon (Si): 1.40~1.80%, Manganese (Mn): 0.40~0.70%, Sulfur (S): ≤0.030%, Phosphorus (P): ≤0.030%, Chromium (Cr): 0.90~1.20%. It has excellent mechanical properties, tensile strength ≥1862MPa, yield strength ≥1666 MPa, and hardness ≤321 HB (cold drawn + heat treated state).

[0003] 60Si2CrVAT round steel for polishing requires annealing after cold drawing or hot rolling to reduce its hardness to 229HB or less. This improves cutting and cold forming performance, eliminates internal stress, and prevents deformation and cracking during subsequent polishing or cold working. It also prepares uniform spherical carbides for quenching, improving ultimate strength and toughness.

[0004] Patent application number 202211009030.X discloses a method for spheroidizing annealing of 60Cr3 steel, in which 60Cr3 round steel is placed in a continuous furnace for spheroidizing annealing. The continuous furnace is configured as a heating zone, a holding zone, a rapid cooling zone, an isothermal zone, and a slow cooling zone in the direction from feed to discharge. The present invention adopts a continuous furnace for spheroidizing annealing, and configures the spheroidizing annealing as a heating zone, a holding zone, a rapid cooling zone, an isothermal zone, and a slow cooling zone. By designing a reasonable annealing temperature for each zone, controlling the annealing speed, and a reasonable charging thickness, the formation of spheroidized structure is controlled and the spheroidization rate is improved. However, the spheroidization rate of the 60Cr3 steel balls in this patent is only 82-92%. The commonly used annealing process is conventional box furnace annealing, which takes up to 6-8 hours, consumes more than 220kWh / t of energy, has a carbide spheroidization rate of less than 90%, has an uneven size distribution, and the depth of the decarburized layer is generally ≥0.03mm.

[0005] Therefore, it is necessary to provide a better annealing method for 60Si2CrVAT round steel for polished material, so that the spheroidization rate of the structure after spheroidizing annealing is ≥95% and the hardness is ≤190HBW. Summary of the Invention

[0006] The present application is made in view of the above-mentioned problems, and its purpose is to provide a method for annealing round steel for 60Si2CrVAT polished material.

[0007] Specifically, a first aspect of the present application provides a method for annealing round steel for 60Si2CrVAT polished material, comprising the following steps: S1: In an electromagnetic field and protective atmosphere, heat the 60Si2CrVAT polished steel bar to 775-785°C at a rate of 10-20°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 780-790℃ for 2-4h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C.

[0008] Furthermore, the electromagnetic power of the electromagnetic field in step S1 is 20-50 kHz.

[0009] Furthermore, in step S1, the protective atmosphere is nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is 15-20:1.

[0010] Furthermore, in step S1, a temperature difference of 150-200° C. is formed between the surface and the core of the 60Si2CrVAT polished round steel.

[0011] Furthermore, in step S1, the electromagnetic induction coil is synchronized with the roller at a speed of 0.5-2 m / min.

[0012] Furthermore, in step S3, gradient cooling is used to divide the cooling zone into a high temperature zone, a medium temperature zone and a low temperature zone. The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 13-18℃ / s; The medium temperature zone adopts air mist mixed cooling with a cooling rate of 6-10°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 2-5°C / s.

[0013] Furthermore, the electromagnetic field is an alternating magnetic field of 4-6 kHz.

[0014] Furthermore, the cooling pressure of the atomized water in the spray cooling is 0.3-0.5 MPa; and / or The flow rate of atomized water cooling is 0.7-0.9L / min·m 2 .

[0015] Furthermore, the ratio of compressed air to water in the mist mixing cooling is 2-4:1; and / or The fan speed in the aerosol mixing cooling is 1000-1200rpm.

[0016] Furthermore, the dew point temperature of nitrogen in the nitrogen cooling is ≤-40°C.

[0017] The present invention has the following beneficial effects: (1) The annealing method of the present invention is carried out under an electromagnetic field and a protective atmosphere, which not only improves the heating efficiency but also effectively prevents the oxidation and decarburization of the round steel during the heating process. By precisely controlling the heating rate and the holding temperature, the uniformity of the internal structure of the round steel and the spheroidization effect of the carbides are ensured. Especially in the gradient cooling stage, the present invention adopts a variety of cooling methods and parameter optimization to achieve precise control of the cooling rate of the round steel, further improving the annealing effect.

[0018] (2) The gradient cooling process of the present invention achieves rapid and uniform cooling through cooling in the high temperature zone, effectively avoiding the problems of overheating and grain growth in the high temperature stage; the medium temperature zone further refines the structure and improves the hardness and strength of the material; and the low temperature zone ensures the stability and toughness of the material.

[0019] In addition, by precisely controlling parameters such as the frequency of the electromagnetic field, the pressure and flow of spray cooling, the ratio of compressed air to water in the mist mixing cooling, and the fan speed, the annealing effect is further improved, so that the final 60Si2CrVAT round steel for polishing has excellent comprehensive performance, meeting the high material requirements of the high-end manufacturing field. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is described and illustrated below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are merely used to explain this application and are not intended to limit this application. Based on the embodiments provided in this application, all other embodiments obtained by those of ordinary skill in the art without making any creative work are within the scope of protection of this application.

[0021] Obviously, the following descriptions are merely some examples or embodiments of the present application. Those skilled in the art can apply the present application to other similar scenarios without inventive effort. Furthermore, it is also understood that, although the effort involved in such a development process may be complex and lengthy, for those skilled in the art related to the content disclosed in the present application, changes in design, manufacturing, or production based on the technical content disclosed in the present application are merely conventional technical means and should not be construed as an insufficiency of the content disclosed in the present application.

[0022] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0023] A method for annealing round steel for 60Si2CrVAT polished material comprises the following steps: S1: In an electromagnetic field and protective atmosphere, heat the 60Si2CrVAT polished steel bar to 775-785°C at a rate of 10-20°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 780-790℃ for 2-4h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C.

[0024] The composition of the 60Si2CrVAT round steel for polished materials in the present invention includes: carbon: 0.58%-0.62%, silicon: 1.50%-1.90%, manganese: 0.40%-0.90%, phosphorus: ≤0.020%, sulfur: ≤0.020%, chromium: 0.90%-1.20%, nickel: ≤0.35%, copper: ≤0.25%, vanadium: 0.10%-0.20%, and the remainder is iron and unavoidable impurities. The addition of chromium and vanadium can improve hardenability and resistance to temper softening, allowing it to maintain excellent elasticity in high-temperature environments.

[0025] In step S1, the 60Si2CrVAT polished round steel is heated to 775-785°C at a rate of 10-20°C / s, where the heating rate can be any value among 10°C / s, 11°C / s, 12°C / s, 13°C / s, 14°C / s, 15°C / s, 16°C / s, 17°C / s, 18°C / s, 19°C / s, and 20°C / s; and the temperature can be any value among 775°C, 776°C, 778°C, 780°C, 782°C, 783°C, and 785°C.

[0026] Step S1 is carried out under an electromagnetic field and a protective atmosphere, which not only improves the heating efficiency but also effectively prevents oxidation and decarburization of the round steel during the heating process. By precisely controlling the heating rate and the holding temperature, the uniformity of the internal structure of the round steel and the spheroidization effect of the carbides are ensured.

[0027] In step S2, the electromagnetic field and protective atmosphere are turned off, and resistance heating is used to maintain the temperature at 780-790°C for 2-4 hours. This maintains a relatively stable environment during the insulation process, allowing the carbides within the round steel to fully spheroidize, improving the hardness and strength of the material while ensuring uniformity of the structure. The insulation temperature can be any value from 780°C, 781°C, 783°C, 785°C, 787°C, 788°C, and 790°C, and the insulation time can be any length from 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours to ensure that the carbides within the round steel achieve the desired spheroidization effect.

[0028] In step S3, gradient cooling is used, which is divided into a high-temperature zone, a medium-temperature zone, and a low-temperature zone. This not only achieves precise control of the cooling rate of the round steel, but also avoids structural defects caused by improper cooling rate. Among them, 650℃≤high-temperature zone<780℃, 500℃≤medium-temperature zone<650℃, and 100℃≤low-temperature zone500℃ correspond to the rapid cooling, structural refinement, and stability improvement stages of the round steel, respectively. Rapid cooling in the high-temperature zone can effectively avoid overheating of the round steel in the high-temperature stage, prevent grain growth, and ensure the hardness and strength of the material; the medium-temperature zone further refines the structure and improves the comprehensive mechanical properties of the material through an appropriate cooling rate; the low-temperature zone ensures the stability and toughness of the material and avoids structural defects caused by too fast cooling. Through these three stages of gradient cooling, precise control of the cooling rate of the round steel is achieved, further improving the annealing effect.

[0029] In this embodiment, the electromagnetic power of the electromagnetic field in step S1 is 20-50 kHz. Furthermore, the electromagnetic power of the electromagnetic field in step S1 is preferably 30-40 kHz. Electromagnetic power within this range can more effectively promote the heating process of the round steel while maintaining low energy consumption. Furthermore, the power density of the electromagnetic field is 15 W / mm³. A uniform distribution of the electromagnetic field is also crucial to ensure uniform heating of the round steel during the heating process, avoiding structural defects caused by local overheating or uneven cooling.

[0030] In this embodiment, the protective atmosphere in step S1 is nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is 15-20:1. Preferably, the volume ratio of nitrogen to hydrogen is 18:1. The nitrogen in the protective atmosphere can effectively prevent oxidation of the round steel during the heating process, while the hydrogen helps to reduce the oxidized surface, further reducing decarburization. By precisely controlling the ratio of nitrogen and hydrogen, the round steel can be ensured to be in an optimal chemical environment during the heating process, thereby improving the annealing effect.

[0031] In this embodiment, in step S1, a temperature difference of 150-200° C. is formed between the surface and the core of the 60Si2CrVAT polished round steel. This temperature difference helps to promote the thermal stress distribution inside the round steel, thereby facilitating the uniform spheroidization of carbides.

[0032] In this embodiment, in step S1, the electromagnetic induction coil is synchronized with the roller at a speed of 0.5-2 m / min. By precisely controlling the synchronization speed of the electromagnetic induction coil and the roller, the round steel can be evenly heated during the heating process, avoiding local overheating or uneven cooling.

[0033] Furthermore, in step S3, gradient cooling is used to divide the cooling zone into a high temperature zone, a medium temperature zone and a low temperature zone. The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 13-18℃ / s; The medium temperature zone adopts air mist mixed cooling with a cooling rate of 6-10°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 2-5°C / s.

[0034] In the high-temperature zone, the combination of electromagnetic fields and spray cooling accelerates the cooling rate, ensuring rapid cooling of the round steel surface, effectively inhibiting grain growth, and improving the material's hardness and strength. Furthermore, precise control of the atomized water cooling pressure and flow rate during spray cooling further enhances the cooling effect and ensures cooling uniformity. In the medium-temperature zone, the use of air-mist mixed cooling further optimizes the round steel's cooling rate by adjusting the ratio of compressed air to water and the fan speed, refining the microstructure and improving the material's overall performance. In the low-temperature zone, the use of nitrogen cooling ensures the round steel's stability and toughness during cooling to room temperature. Furthermore, strict control of the nitrogen dew point effectively prevents oxidation and corrosion of the round steel.

[0035] Furthermore, the cooling rate in the high temperature zone is any value among 13°C / s, 14°C / s, 15°C / s, 16°C / s, 17°C / s, and 18°C / s, the cooling rate in the medium temperature zone is any value among 6°C / s, 7°C / s, 8°C / s, 9°C / s, and 10°C / s, and the cooling rate in the low temperature zone is any value among 2°C / s, 3°C / s, 4°C / s, and 5°C / s. By precisely controlling the cooling rate in each cooling zone, the present invention achieves refined management of the round steel cooling process, further improves the annealing effect, and ensures the excellent performance of the final product.

[0036] In this embodiment, the electromagnetic field is an alternating magnetic field of 4-6 kHz. This alternating magnetic field, in synergy with the spray cooling in the high-temperature zone, not only enhances the cooling effect but also helps to evenly distribute the internal structure of the round steel, further improving the overall performance of the material. By optimizing the frequency and parameters of the electromagnetic field, the present invention achieves precise control of the heating and cooling processes of the round steel, thereby achieving ideal annealing results.

[0037] In this embodiment, the atomized water cooling pressure of the spray cooling is 0.3-0.5 MPa; the flow rate of the atomized water cooling is 0.7-0.9 L / min·m 2Precise control of the atomized water cooling pressure and flow rate ensures stable and uniform spray cooling, avoiding structural defects caused by uneven cooling. Furthermore, the optimized selection of atomized water cooling pressure and flow rate further improves cooling efficiency, shortens the annealing cycle, and reduces production costs. Furthermore, the spray system utilizes a fan-shaped nozzle array (150mm spacing). This fan-shaped nozzle array ensures that the cooling water evenly covers the surface of the round steel, achieving optimal cooling results.

[0038] In this embodiment, the ratio of compressed air to water in the mist mixing cooling is 2-4:1, and the fan speed during the mist mixing cooling is 1000-1200 rpm. By adjusting the ratio of compressed air to water and the fan speed, the present invention achieves precise control of the cooling rate of round steel in the medium temperature range, further refining the microstructure and improving the hardness and strength of the material. Simultaneously, the uniformity and stability of the mist mixing cooling are effectively guaranteed, avoiding structural defects caused by uneven cooling. Furthermore, the optimized fan speed not only improves cooling efficiency but also reduces energy consumption, making the entire annealing process more environmentally friendly and efficient.

[0039] In this embodiment, the dew point temperature of the nitrogen used in the nitrogen cooling process is ≤ -40°C. The nitrogen is pure. By strictly controlling the dew point temperature of the nitrogen, oxidation and corrosion of the round steel during the cooling process are effectively prevented, ensuring the surface quality and performance stability of the final product. Furthermore, the stability and uniformity of the nitrogen cooling are fully guaranteed, further enhancing the annealing effect.

[0040] The annealing method of the present invention is not only applicable to 60Si2CrVAT round steel for polishing, but can also be extended to annealing treatment of round steel of other similar materials, and has broad application prospects.

[0041] Example 1 A method for annealing round steel for 60Si2CrVAT polished material comprises the following steps: S1: In an electromagnetic field and protective atmosphere, the 60Si2CrVAT polished round steel is heated to 780°C at a rate of 15°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 785℃ for 6 hours; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C; The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 15℃ / s; The medium temperature zone adopts air mist mixing cooling with a cooling rate of 8°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 3°C / s.

[0042] Example 2 A method for annealing round steel for 60Si2CrVAT polished material comprises the following steps: S1: In an electromagnetic field and protective atmosphere, the 60Si2CrVAT polished round steel is heated to 785°C at a rate of 20°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 790℃ for 4h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C; The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 13℃ / s; The medium temperature zone adopts air mist mixing cooling with a cooling rate of 9°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 2°C / s.

[0043] Example 3 A method for annealing round steel for 60Si2CrVAT polished material comprises the following steps: S1: In an electromagnetic field and protective atmosphere, the 60Si2CrVAT polished round steel is heated to 775°C at a rate of 18°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 780℃ for 3h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C; The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 18℃ / s; The medium temperature zone adopts air mist mixing cooling with a cooling rate of 6°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 5°C / s.

[0044] Example 4 A method for annealing round steel for 60Si2CrVAT polished material comprises the following steps: S1: In an electromagnetic field and protective atmosphere, the 60Si2CrVAT polished round steel is heated to 780°C at a rate of 10°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 790℃ for 2h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C; The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 14°C / s; The medium temperature zone adopts air mist mixing cooling with a cooling rate of 9°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 4°C / s.

[0045] Comparative Example 1 This comparative example is basically the same as the embodiment, except that only pure resistance heating is used in step S1.

[0046] Comparative Example 2 This comparative example is basically the same as the embodiment, except that in step S3, only spray cooling is used in the high temperature zone without magnetic field cooling.

[0047] Comparative Example 3 This comparative example is basically the same as the embodiment, except that in step S3, gradient cooling is not used but single-stage cooling is used.

[0048] Comparative Example 4 This comparative example is basically the same as the embodiment, except that the protective atmosphere is replaced by air.

[0049] Performance testing The annealed 60Si2CrVAT polished materials of Examples 1-4 of the present invention and Comparative Examples 1-4 were subjected to performance tests using round steel. The spheroidization rate was tested in accordance with GB / T 13299 "Methods for evaluating the microstructure of steel" and the hardness test was conducted in accordance with GB / T 231.2 "Brinell hardness test for metallic materials". Three samples were tested in each group and the average value was calculated. The results are shown in the following table:

[0050] As can be seen from the table above, the 60Si2CrVAT round steel used for polished materials in the Examples exhibited significant improvements in both spheroidization and hardness after treatment with the annealing method provided by the present invention. Compared to the comparative example, the round steel in the Examples exhibited a higher spheroidization rate and more uniform and stable hardness. This is attributed to the precise heating rate control, holding temperature selection, and gradient cooling strategy employed in the present invention. In particular, the combination of electromagnetic field and spray cooling in the high-temperature zone effectively increased cooling rate and uniformity, achieving ideal annealing results.

[0051] Furthermore, by comparing the performance of round steel bars of different sizes (e.g., Φ30 and Φ50) after treatment, it can be seen that the annealing method provided by the present invention has good applicability for round steel bars of different sizes. This further broadens the scope of application of the present invention, enabling it to meet more diverse production needs.

[0052] In summary, the present invention provides a method for annealing round steel for 60Si2CrVAT polished material, which significantly improves the performance of round steel through precise process parameter control and innovative cooling strategy, and has broad application prospects and market value.

[0053] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A method for annealing round steel for 60Si2CrVAT polished material, characterized in that: The following steps are involved: S1: In an electromagnetic field and protective atmosphere, heat the 60Si2CrVAT polished steel bar to 775-785°C at a rate of 10-20°C / s; S2: Turn off the electromagnetic field and protective atmosphere, and use resistance heating to keep the temperature at 780-790℃ for 2-4h; S3: Gradient cooling is performed according to the high temperature zone of 780-650°C, the medium temperature zone of 650-500°C, and the low temperature zone of 500-100°C.

2. The round steel annealing method for 60Si2CrVAT polished material according to claim 1, characterized in that: The electromagnetic power of the electromagnetic field in step S1 is 20-50 kHz.

3. The round steel annealing method for 60Si2CrVAT polished material according to claim 1, characterized in that: In step S1, the protective atmosphere is nitrogen and hydrogen, wherein the volume ratio of nitrogen to hydrogen is 15-20:

1.

4. The round steel annealing method for 60Si2CrVAT polished material according to claim 1, characterized in that: In step S1, a temperature difference of 150-200° C. is formed between the surface and the core of the 60Si2CrVAT polished round steel.

5. The round steel annealing method for 60Si2CrVAT polished material according to claim 1, characterized in that: In step S1, the electromagnetic induction coil is synchronized with the roller at a speed of 0.5-2 m / min.

6. The round steel annealing method for 60Si2CrVAT polished material according to claim 1, characterized in that: In step S3, gradient cooling is used to divide the cooling area into high temperature zone, medium temperature zone and low temperature zone. The high temperature zone adopts electromagnetic field + spray cooling, and the cooling rate is 13-18℃ / s; The medium temperature zone adopts air mist mixed cooling with a cooling rate of 6-10°C / s; The low temperature zone is cooled by nitrogen at a cooling rate of 2-5°C / s.

7. The round steel annealing method for 60Si2CrVAT polished material according to claim 6, characterized in that: The electromagnetic field is an alternating magnetic field of 4-6 kHz.

8. The round steel annealing method for 60Si2CrVAT polished material according to claim 6, characterized in that: The atomized water cooling pressure of the spray cooling is 0.3-0.5 MPa; and / or The flow rate of atomized water cooling is 0.7-0.9L / min·m 2 .

9. The round steel annealing method for 60Si2CrVAT polished material according to claim 6, characterized in that: The ratio of compressed air to water in the aerosol mixing cooling is 2-4:1; and / or The fan speed in the aerosol mixing cooling is 1000-1200rpm.

10. The round steel annealing method for 60Si2CrVAT polished material according to claim 6, characterized in that: The dew point temperature of the nitrogen in the nitrogen cooling is ≤-40°C.

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