Spheroidizing annealing process of medium-carbon alloy steel for precise guide part

Abstract

The invention discloses a spheroidizing annealing process of medium-carbon alloy steel for a precise guide part in the field of material heat treatment, and aims to solve the problem that overheating phase change or insufficient spheroidizing is easily caused by a traditional annealing process, precise spheroidizing is realized through a five-stage process: firstly, round steel is preheated for 1-2 hours at 500-600 DEG C at the speed of less than or equal to 30 DEG C / h, and slow diffusion and segregation of carbides are promoted; and heating at 800-850 DEG C, and preserving heat for 1.5-2.5 hours, so that the cementite is uniformly austenitized. And carrying out two-stage isothermal treatment at 700-750 DEG C and 650-660 DEG C to control spheroidizing precipitation of carbides. And finally, spray cooling is conducted at the speed of 1000-1500 r / min till the temperature is below 600 DEG C, slow cooling is conducted, and a spheroidized structure is frozen. The process is suitable for medium carbon alloy steel containing 0.45-0.50% of C and the like, the spheroidization rate of 81-86%, the hardness smaller than or equal to 180 HB and the cross section uniformity difference smaller than or equal to 7 HB are achieved in round steel with the diameter being 30-65 mm, the production cost can be reduced by 15%-20%, import dependence is broken through, and the strict requirements of precise guiding parts for structure uniformity and mechanical performance are met.

Description

Technical Field

[0001] The invention belongs to the field of material heat treatment, and in particular relates to a spheroidizing annealing process of medium-carbon alloy steel for precision guide parts. Background Art

[0002] As an important component of high-precision mechanical transmission systems, guide parts place strict requirements on spheroidized annealed materials. First, the material must have a uniform and highly spheroidized microstructure, which can not only reduce the friction coefficient and ensure smooth movement between sliding parts, but also significantly improve wear resistance and fatigue resistance. Secondly, the material after spheroidizing annealing should have good dimensional stability and low residual stress to ensure that it does not deform during precision machining and long-term service and meet strict tolerance requirements. In addition, the material is also required to have excellent machinability and high surface finish, which is of great significance for improving part machining accuracy, reducing machining costs and extending service life. In summary, the requirements of guide parts for spheroidized annealed materials are mainly reflected in microstructural uniformity, mechanical property stability, machining accuracy, wear resistance and fatigue resistance, etc., in order to meet the stringent requirements of high-end mechanical equipment for guiding accuracy and service life.

[0003] Therefore, the annealing process plays a vital role and directly affects the microstructure and mechanical properties of the material. For the spheroidizing annealing process, parameters such as temperature, holding time and cooling rate need to be precisely controlled to ensure that the carbides can be fully spheroidized and form a uniform microstructure. The temperature must be set within a reasonable range that can promote the spheroidization of carbides while preventing overheating and unnecessary phase changes. Too short a holding time may lead to insufficient spheroidization, while too long a holding time may trigger other side reactions. Therefore, repeated experiments and process optimization are required to determine the optimal time. A faster cooling rate may cause a rapid release of thermal stress, resulting in insufficient carbide spheroidization reaction. A slower cooling rate can provide sufficient time for carbides to uniformly form a small, regular spherical structure in the matrix, while effectively reducing residual stress. However, if the temperature is lowered too slowly, it may cause grain coarsening.

[0004] Currently, the majority of high-performance spheroidizing annealing materials still rely on imports. Mature foreign processes and technologies have formed a certain blockade barrier, restricting domestic development in this field. To break this situation, it is urgent to develop spheroidizing annealing technology with independent intellectual property rights. Through systematic research and detailed optimization of key process parameters such as temperature control, holding time, and cooling rate, combined with the application of modern computer control systems and new heat treatment equipment, it is possible to achieve precise control of the carbide spheroidizing process, thereby improving the microstructure and mechanical properties of the material. This not only helps to improve the product's service life and working precision, but also lays a solid technical foundation for enterprises to reduce manufacturing costs and achieve domestic substitution, reflecting the innovativeness and application prospects of process optimization. Summary of the Invention

[0005] To solve the problem of phase change caused by overheating and insufficient spheroidization caused by overcooling in current annealing technology.

[0006] In order to solve the above problems, the present invention provides the following technical solutions:

[0007] A spheroidizing annealing process for medium carbon alloy steel for precision guide parts comprises the following steps:

[0008] S1: Preheat the round steel. Place the round steel into the continuous annealing furnace 1-2 zone for preheating. Set the measured temperature of the furnace to 500-600°C, with a temperature rise rate of ≤30°C / h, and then keep it warm for 1-2 hours.

[0009] S2: Transfer the round steel from zone 2 to the heating zone, set the temperature of the heating zone to 800-850℃, and then keep it warm for 1.5-2.5 hours;

[0010] S3: The heated and insulated round steel enters the first stage of isothermal treatment, controlling the furnace temperature at 700-750°C and then keeping it warm for 180-240 minutes;

[0011] S4: After the round steel has been isothermal treated in the first stage, it enters the second stage of isothermal treatment, where the furnace temperature is controlled at 650-660°C and then kept warm for 270-305 minutes;

[0012] S5: After the second stage of isothermal treatment, the speed of the cooling fan is set to 1000-1500 rpm, and then the round steel enters the slow cooling section for natural cooling.

[0013] Preferably, the composition of the round steel in S1 is C: 0.45-0.50%, Si: 0.30-0.40%, Mn: 0.90-1.80%, P: ≤0.008%, S: ≤0.003%, Cr: 0.25-0.35%, and Al: 0.020-0.060% by mass percentage.

[0014] Preferably, the round steel material described in S2 is usually distributed in the matrix in an irregular or flaky form, and the furnace temperature rise rate in the preheating stage is set to ≤30°C / h. The preheating stage can allow the carbides to slowly diffuse in a high temperature environment, promote their segregation near the grain boundaries or in specific areas, and the segregation also reduces the carbon content in the matrix, making the subsequent austenitization process more uniform and reducing the phenomenon of uneven structure.

[0015] Preferably, a slow austenitization process occurs inside the material in S2, causing the original flaky or network-like cementite to gradually disappear, which is conducive to the formation of more uniform spherical carbides, avoiding excessively rapid phase change, reducing uneven organizational transformation, and improving spheroidization uniformity.

[0016] Preferably, in S3, slow cooling or isothermal treatment is used to control the stable decomposition process of austenite, so that carbides are slowly precipitated and spheroidized, thereby obtaining more uniform and fine spherical carbides.

[0017] Preferably, after the first isothermal treatment in S4, in order to avoid coarsening of formed carbide particles and precipitation of flaky carbides, the round steel is cooled to 650-660°C at a rate of ≤50°C / h for a second isothermal treatment with a holding time of 270-305 minutes.

[0018] Preferably, the austenite in S4 has been completely transformed, and still contains some trace carbon dissolved in the matrix. Keeping it warm in this temperature range can give the remaining carbides sufficient time to be evenly distributed in the matrix and transform into a more uniform and fine spherical form.

[0019] Preferably, the process in S4 optimizes the distribution and morphology of carbides, avoids coarsening and uneven distribution, and further improves the mechanical properties, wear resistance and processing properties of the material.

[0020] Preferably, the round steel subjected to the second isothermal treatment in S5 is rapidly cooled to below 600° C. by a cold spray blower and then enters the slow cooling section for natural cooling.

[0021] Preferably, the spheroidized structure of the carbides is effectively frozen in S5 to prevent excessive expansion or coarsening at higher temperatures, prevent the structure from returning to a non-ideal state, and help strengthen the comprehensive mechanical properties of the material.

[0022] Effects and advantages of the spheroidizing annealing process of medium carbon alloy steel for precision guide parts of the present invention:

[0023] 1. This patent proposes a spheroidizing annealing process for medium-carbon alloy steel used for precision guide parts. By adjusting the parameters such as preheating, heating, isothermal and cooling rate during the annealing process, the spheroidizing rate and processing performance of the material are significantly improved.

[0024] 2. This patent controls the heating temperature and cooling rate by adding a preheating section, especially after cooling to 650-660℃ and holding it for a certain period of time, and then quickly cooling it to below 600℃, which promotes the uniform precipitation and spheroidization of carbides, and ultimately achieves a spheroidization rate of up to 80% and a Brinell hardness of ≤180HBW.

[0025] 3. This patent effectively refines the carbide structure, improves the cold forming performance of the material, reduces tool wear and energy consumption, reduces possible deformation or dimensional deviation during processing, and ensures the dimensional consistency of parts under high precision requirements.

[0026] 4. This patent can reduce production costs by about 15-20% and reduce dependence on imported materials, thereby enhancing the competitiveness of domestic enterprises in the field of high-end machinery manufacturing. In addition, this process also improves the environmental friendliness of the production process and promotes independent innovation and sustainable development of the domestic steel industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a micrograph of the superheated structure of a medium carbon alloy steel for precision guide parts in the spheroidizing annealing process of the present invention;

[0028] Figure 2 This is a micrograph of the underheated structure of a medium-carbon alloy steel for precision guide parts in the spheroidizing annealing process according to the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention 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, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0030] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus. In the absence of further restrictions, the elements defined by the sentence "include..." do not exclude the presence of other identical elements in the process, method, article or apparatus that includes the elements.

[0031] Example 1

[0032] This embodiment provides a spheroidizing annealing process for medium carbon alloy steel for precision guide parts, which is applicable to the following implementation contents:

[0033] Purpose of the experiment:

[0034] Provided is a spheroidizing annealing process for medium carbon alloy steel for precision guide parts.

[0035] Experimental materials:

[0036] The composition of round steel is calculated by mass percentage: C: 0.47%, Si: 0.35%, Mn: 1.80%, P: 0.005%, S: 0.001%, Cr: 0.31%, Al: 0.037%. The diameter of the round steel is Φ30mm.

[0037] Experimental steps:

[0038] S1: Preheat the round steel. Place the round steel into the continuous annealing furnace in zone 1-2 for preheating. Set the furnace temperature to 695-702°C and keep it warm for 105 minutes.

[0039] S2: Transfer the round steel from zone 2 to the heating zone and set the temperature of the heating zone to 727-733℃ and keep it warm for 115 minutes;

[0040] S3: After heating and holding, the round steel enters the first stage of isothermal treatment after 50 minutes, with a cooling rate of 36°C / h and a furnace temperature of 705-710°C. The heat preservation in this stage is 135 minutes.

[0041] S4: After the round steel has been isothermal treated in the first stage, it enters the second stage of isothermal treatment after 50 minutes. The cooling rate is 48℃ / h, the furnace temperature is measured to be 660-665℃, and the heat preservation in this stage is 270 minutes.

[0042] S5: After the second stage of isothermal treatment, the speed of the cooling fan is set to 50 rpm. After the material is cooled to 596℃, it enters the slow cooling section for natural cooling.

[0043] Experimental results: See Table 1 for details.

[0044] Table 1: Test results of Example 1

[0045]

[0046] This embodiment provides a spheroidizing annealing process for medium-carbon alloy steel for precision guide parts, which undergoes preheating, heating, and two-stage isothermal treatment followed by cooling. Test results show that the spheroidization rate of Φ30mm round steel reaches 82%-85%, and the hardness HB near the surface, 1 / 2 radius, and center are 175.0-181.0, 177.0-180.0, and 177.0-182.0, respectively, with good hardness uniformity at each location. This process achieves ideal spheroidization effect and hardness distribution by controlling the heating temperature, holding time, and cooling rate, providing a feasible process solution for the preparation of medium-carbon alloy steel for precision guide parts.

[0047] Example 2

[0048] This embodiment provides a spheroidizing annealing process for medium carbon alloy steel for precision guide parts, which is characterized by round steel with different mass percentages and different process parameters. The following implementation content:

[0049] Purpose of the experiment:

[0050] Provided is a spheroidizing annealing process for medium carbon alloy steel for precision guide parts.

[0051] Experimental materials:

[0052] The composition of the round steel is calculated by mass percentage: C: 0.47%, Si: 0.35%, Mn: 1.80%, P: 0.005%, S: 0.001%, Cr: 0.31%, Al: 0.037%. The diameter of the round steel is Φ55mm.

[0053] Experimental steps:

[0054] S1: Preheat the round steel. Place the round steel into the continuous annealing furnace in zone 1-2 for preheating. Set the furnace temperature to 700-705°C and keep it warm for 105 minutes.

[0055] S2: Transfer the round steel from zone 2 to the heating zone and set the temperature of the heating zone to 729-735℃ for 122 minutes;

[0056] S3: After heating and holding, the round steel enters the first stage of isothermal treatment after 45 minutes, with a cooling rate of 40℃ / h and a furnace temperature of 703-708℃. The heat preservation in this stage is 150 minutes.

[0057] S4: After the round steel has been isothermal treated in the first stage, it enters the second stage of isothermal treatment after 50 minutes. The cooling rate is 48℃ / h, the furnace temperature is measured to be 655-660℃, and the heat preservation in this stage is 283 minutes.

[0058] S5: After the second stage of isothermal treatment, the speed of the cooling fan is set to 55 rpm. After the material is cooled to 590℃, it enters the slow cooling section for natural cooling.

[0059] Experimental results: See Table 2 for details.

[0060] Table 2: Test results of Example 2

[0061]

[0062] This embodiment targets medium-carbon alloy steel round bars with a diameter of Φ55mm, and prepares materials for precision guide parts by optimizing process parameters. Based on the continuation of the core process ideas of Example 1, the experiment adjusted the preheating temperature, heating zone holding time, isothermal treatment cooling rate and spray cooling parameters according to the characteristics of larger diameter steel. The test results show that the spheroidization rate of Φ55mm round steel reaches 81%-83%, the near-surface hardness HB is 177.0-180.0, 179.0-182.0 at the 1 / 2 radius, and 176.0-183.0 at the center. The hardness difference in each area is less than 6 HB, and the uniformity is good. The experiment shows that after adjusting the process parameters for steels of different diameters, the material spheroidization effect is ideal, and the hardness distribution meets the requirements of precision guide parts for uniformity of organization. The applicability of the spheroidizing annealing process in the preparation of Φ55mm medium-carbon alloy steel is verified, and a differentiated process reference is provided for the production of steels for precision guide parts of different specifications.

[0063] Example 3

[0064] This embodiment provides a spheroidizing annealing process for medium carbon alloy steel for precision guide parts, which is characterized by round steel with different mass percentages and different process parameters. The following implementation content:

[0065] Experimental materials:

[0066] The composition of the round steel is calculated by mass percentage: C: 0.50%, Si: 0.36%, Mn: 1.80%, P: 0.003%, S: 0.001%, Cr: 0.33%, Al: 0.035%. The diameter of the round steel is Φ65mm.

[0067] Purpose of the experiment:

[0068] Provided is a spheroidizing annealing process for medium carbon alloy steel for precision guide parts.

[0069] Experimental steps:

[0070] S1: Preheat the round steel. Place the round steel into the continuous annealing furnace in zone 1-2 for preheating. Set the furnace temperature to 702-707°C and keep it warm for 151 minutes.

[0071] S2: Transfer the round steel from zone 2 to the heating zone and set the temperature of the heating zone to 730-735℃ for 130 minutes;

[0072] S3: After heating and holding, the round steel enters the first stage of isothermal treatment after 55 minutes, with a cooling rate of 33°C / h and a furnace temperature of 700-705°C. The heat preservation in this stage is 155 minutes.

[0073] S4: The round steel at the end of the first stage isothermal treatment, after 50 minutes, enters the second stage isothermal treatment, the cooling rate is 50℃ / h, the actual measured furnace temperature is 650-655℃, the holding time is 305 minutes in this stage;

[0074] S5: The round steel at the end of the second stage isothermal treatment, the spray cooling fan speed is set to 50 revolutions / minute, the material is cooled to 580℃ and then enters the slow cooling stage for natural cooling.

[0075] Experimental results: Details are shown in Table 3.

[0076] Table 3: Test results of Example 3

[0077]

[0078] In this example, medium-carbon alloy steel round steel with a carbon content of 0.50% and a diameter of Φ65mm is used as raw material, and the material for precision guide is prepared by adjusting the process parameters. For higher carbon content and larger diameter characteristics, the preheating temperature, holding time, isothermal cooling rate and cooling parameters are optimized. Tests show that the spheroidization rate of Φ65mm round steel is 83%-86%, the near-surface hardness HB is 175.0-180.0, 1 / 2 radius is 173.0-178.0, center is 176.0-178.0, the hardness difference of each region is less than 7 HB, and the uniformity is good. Experiments show that through the synergistic optimization of composition and parameters, the ideal spheroidization effect and hardness distribution are realized, and the applicability of higher carbon content and larger diameter steel is verified, which provides process support for the preparation of differential specification precision guide steel.

[0079] Comparative Example 1

[0080] This example provides a spheroidizing annealing process for carbon alloy steel, and provides a traditional preparation process for carbon alloy steel, and the following implementation content:

[0081] Experimental raw materials:

[0082] Medium-high carbon alloy steel: 45 steel, T8 steel, T10 steel

[0083] Experimental purpose:

[0084] Through high-temperature overheating treatment, the carbon alloy steel grain is severely coarse, and the Widmanstatten structure or overburning structure is formed, which greatly reduces the strength and toughness of the material, and realizes the performance spheroidizing annealing.

[0085] Experimental steps:

[0086] S1: Heat the material to 100-200℃ higher than the quenching temperature;

[0087] S2: According to the size of the workpiece, usually 2-3 times of the normal quenching holding time, long time holding intensifies grain coarsening;

[0088] S3: Ensure that the austenite is transformed into coarse pearlite plus ferrite or coarse martensite plus retained austenite during cooling. Regardless of the structure, the grains are significantly coarse.

[0089] Experimental results:

[0090] After high-temperature spheroidizing annealing of 45, T8, and T10 steels, the microstructure and mechanical properties of the materials showed significant degradation. Microstructurally, the austenite grains of all three steels were significantly coarsened due to the combined effects of the ultra-high quenching temperature and 2-3 times the normal holding temperature. The grain size of 45 steel grew rapidly from -10μm in normal quenching to 50-80μm. Upon cooling, coarse pearlite and ferrite formed, with localized acicular Widmanstätten precipitation. The grains of T8 / T10 steels coarsened to 30-60μm, and coarse martensite laths formed during air cooling, with the proportion of retained austenite soaring to 15%-20%. Mechanical properties have seen a simultaneous collapse in strength and toughness. The tensile strength of 45 steel has plummeted from 650 MPa to 480-520 MPa, and the impact energy has plummeted from 25 J to less than 8 J. The tensile strength of T8 / T10 steel has dropped from over 800 MPa to 600-650 MPa, and the impact energy has been halved from 15 J to less than 5 J, with fracture surfaces exhibiting cleavage brittleness. Hardness also exhibits divergent characteristics. The HB value of 45 steel has dropped from 200 to 160-170 due to the coarsening of the pearlite lamellae. While T8 / T10 steel maintains a high hardness of 50-55 HRC, its practical value has been completely eliminated due to the collapse of toughness.

[0091] Example 1: Through innovative research on the spheroidizing annealing process of medium-carbon alloy steel for precision guide parts, the spheroidization rate has been significantly improved to a high level of 80%, greatly improving the internal structure and processing performance of the material, thereby providing a reliable technical guarantee for the manufacture of precision machinery parts, and providing key technical support for the research and development and production of CNC machine tools, automated production lines and high-end precision machinery equipment. This breakthrough process not only fills the domestic technological gap in the field of high-performance slide rail manufacturing, but also can effectively reduce energy consumption and operating costs. Compared with imported materials, the domestic alternative it provides can reduce manufacturing costs by about 15%-20%. With the continuous development of intelligent manufacturing, digital factories and high-precision machinery industries, this invention will not only be widely promoted in the domestic market, but also meet the market's growing demand for high-precision and high-reliability parts, and help enhance my country's competitiveness in the global high-end equipment manufacturing field.

[0092] This example uses medium-carbon alloy steel round bars with a carbon content of 0.47% and a diameter of 30 mm as raw material. By controlling the preheating temperature, the holding time in the heating zone, and the cooling rate and holding time during the two-stage isothermal treatment, material for precision guide components is produced. Tests show that the round bar achieves a spheroidization rate of 82%-85%, with hardnesses (HB) of 175.0-181.0 near the surface, 1 / 2 radius, and 177.0-180.0, and 177.0-182.0 at the center, respectively. Hardness uniformity across these regions is excellent. This process provides a standardized solution for spheroidizing annealing of small-diameter medium-carbon alloy steel, meeting the material microstructure uniformity requirements of precision guide components.

[0093] In Example 2, spheroidizing annealing of medium-carbon alloy steel round bars with a diameter of 55 mm was achieved by increasing the preheating temperature, extending the holding time in the heating zone, and adjusting the isothermal cooling rate. The experimental results showed that the round steel had a spheroidization rate of 81%-83%, with hardness values ​​of HB 177.0-180.0 near the surface, 179.0-182.0 at the half radius, and 176.0-183.0 at the center. The hardness difference was less than 6 HB, indicating excellent uniformity. This process demonstrates the feasibility of adapting parameter optimization to medium-diameter steel and provides a process reference for the production of differentiated specifications.

[0094] Example 3 uses high-carbon, large-diameter round steel with a carbon content of 0.50% and a diameter of 65 mm as raw material. By increasing the preheating temperature, extending the holding time, and optimizing the isothermal cooling rate, spheroidizing annealing of high-carbon, large-size steel was achieved. Tests showed that the round steel had a spheroidization rate of 83%-86%, with a uniform hardness distribution of HB 175.0-180.0 near the surface, 173.0-178.0 at the 1 / 2 radius, and 176.0-178.0 at the center. This process, through the coordinated optimization of composition and parameters, solves the spheroidization problem of high-carbon, large-diameter steel and expands the application range of the spheroidizing annealing process.

[0095] All three examples focus on controlling heating temperature, holding time, and cooling rate as the core process strategy. Targeting the differences in round steel diameter from Φ30mm to Φ65mm and carbon content from 0.47% to 0.50%, process parameters are gradually optimized. As the diameter increases, the preheating temperature is slightly increased from 695-702°C to 702-707°C, and the holding time is extended from 105 minutes to 151 minutes to ensure uniform heat penetration. As the carbon content increases, the isothermal cooling rate in the first stage is adjusted from 36°C / h to 33°C / h to provide more time for spheroidization of high-carbon microstructures. Experimental results show that the spheroidization rate of round steel of different specifications remains stable at 81%-86%, and the hardness difference between regions is controlled within 7HB. This demonstrates that through differentiated parameter adaptation, this process effectively achieves spheroidizing annealing of medium-carbon alloy steels of varying diameters and carbon contents. The spheroidization effect and hardness uniformity meet the requirements for precision guide steel, providing a replicable and reliable process system for serial production.

[0096] Those skilled in the art will appreciate that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented with electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0097] In addition, each functional module in each embodiment of the present application may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0098] The above is only a specific implementation method of the present application, but the scope of protection of the present application is not limited to this. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed in this application, which should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

[0099] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection of the present invention.

Claims

1. A spheroidizing annealing process for medium carbon alloy steel for precision guide parts, characterized in that: The following steps are involved: S1: Preheat the round steel. Place the round steel into the continuous annealing furnace 1-2 zone for preheating. Set the measured temperature of the furnace to 500-600°C, with a temperature rise rate of ≤30°C / h, and then keep it warm for 1-2 hours. S2: Transfer the round steel from zone 2 to the heating zone, set the temperature of the heating zone to 800-850℃, and then keep it warm for 1.5-2.5 hours; S3: The heated and insulated round steel enters the first stage of isothermal treatment, controlling the furnace temperature at 700-750°C and then keeping it warm for 180-240 minutes; S4: After the round steel has been isothermal treated in the first stage, it enters the second stage of isothermal treatment, where the furnace temperature is controlled at 650-660°C and then kept warm for 270-305 minutes; S5: After the second stage of isothermal treatment, the speed of the cooling fan is set to 1000-1500 rpm, and then the round steel enters the slow cooling section for natural cooling.

2. The spheroidizing annealing process of medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: The composition of the round steel in S1 is C: 0.45-0.50%, Si: 0.30-0.40%, Mn: 0.90-1.80%, P: ≤0.008%, S: ≤0.003%, Cr: 0.25-0.35%, and Al: 0.020-0.060% in percentage by mass.

3. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: The round steel material described in S2 is usually distributed in the matrix in an irregular or flaky form. The furnace temperature rise rate in the preheating stage is set to ≤30°C / h. The preheating stage can allow the carbides to slowly diffuse in a high-temperature environment, promoting their segregation near the grain boundaries or in specific areas. Segregation also reduces the carbon content in the matrix, making the subsequent austenitization process more uniform and reducing the phenomenon of structural inhomogeneity.

4. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: A slow austenitization process occurs inside the material in S2, causing the original flake or network cementite to gradually disappear, which is conducive to the formation of more uniform spherical carbides, avoiding excessively rapid phase changes, reducing uneven organizational transformations, and improving spheroidization uniformity.

5. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: In S3, slow cooling or isothermal treatment is used to control the stable decomposition process of austenite, so that carbides are slowly precipitated and spheroidized, thereby obtaining more uniform and fine spherical carbides.

6. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: After the first isothermal treatment described in S4, in order to prevent the coarsening of the formed carbide particles and the precipitation of flake carbides, the round steel is cooled to 650-660°C at a rate of ≤50°C / h for a second isothermal treatment with a holding time of 270-305 minutes.

7. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: The austenite in S4 has been completely transformed, and there is still some trace carbon dissolved in the matrix. Keeping it warm in this temperature range can give the remaining carbides enough time to be evenly distributed in the matrix and transform into a more uniform and fine spherical form.

8. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: The process in S4 optimizes the distribution and morphology of carbides and also avoids coarsening and uneven distribution, further improving the mechanical properties, wear resistance and processing performance of the material.

9. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: The round steel that has been isothermally treated in the second section of S5 is rapidly cooled to below 600°C by a cold spray blower and then enters the slow cooling section for natural cooling.

10. The spheroidizing annealing process for medium carbon alloy steel for precision guide parts according to claim 1, characterized in that: S5 effectively freezes the spheroidized structure of carbides, preventing excessive expansion or coarsening at higher temperatures, preventing the structure from returning to a non-ideal state, and helping to strengthen the comprehensive mechanical properties of the material.

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