Rolling process method for improving hardness of steel for motor shaft

Abstract

The invention discloses a rolling process method for improving the hardness of steel for a motor shaft, and relates to the field of steel rolling, and the method comprises the following components: S1, optimizing a heating process, S2, carrying out through water cooling before controlled rolling, S3, carrying out forced through water cooling after rolling, and S4, carrying out cooling bed self-tempering treatment. According to the method, parameters in the rolling process are optimized, the hardness of the position 2 mm of the bar is improved to 20-25 HRC, self-tempering is conducted through a cooling bed heat preservation cover structure, the hardening and tempering effect is achieved, the mechanical property requirement of the steel for the motor shaft is met, the production process procedures are saved, the production cost and carbon emission are reduced, and great benefits are achieved for environment protection.

Description

Technical Field

[0001] The invention relates to the technical field of steel rolling, in particular to a high-speed rolling process method for improving the hardness of steel for motor shafts. Background Art

[0002] With the rapid development of modern industry, the performance requirements of motor shafts, as key components in mechanical equipment, are increasing. Motor shafts not only need to withstand complex mechanical loads, but also need to have good wear resistance, fatigue resistance and high hardness to ensure long-term and stable operation of the equipment.

[0003] Traditional rolling process methods have certain limitations in improving the hardness of steel for motor shafts. On the one hand, traditional processes often find it difficult to accurately control temperature parameters during the rolling process, such as heating temperature, rolling temperature, and cooling temperature, resulting in uneven internal structure of the steel and limited hardness improvement effect. On the other hand, traditional processes lack an effective self-tempering mechanism in post-rolling treatment. Steel is prone to generate large internal stress and structural stress during the cooling process, affecting its comprehensive mechanical properties. In addition, traditional processes also have shortcomings in energy utilization and environmental protection. For example, the energy consumption during the heating process is high and carbon emissions are high, which does not meet the requirements of green manufacturing.

[0004] In summary, the traditional rolling process method has many shortcomings in improving the hardness of motor shaft steel, and it is difficult to meet the high standards of material performance required by modern industry. Therefore, it is particularly important to develop a rolling process method to improve the hardness of motor shaft steel. Summary of the Invention

[0005] The purpose of the present invention is to make up for the shortcomings of the existing technology and provide a high-speed rolling process method for improving the hardness of motor shaft steel. It can achieve a significant improvement in the hardness of motor shaft steel by optimizing the parameter control of key links such as heating, rolling and cooling, while taking into account the requirements of energy saving and consumption reduction and green manufacturing.

[0006] In order to solve the above technical problems, the present invention provides the following technical solutions: a rolling process method for improving the hardness of steel for motor shafts, the specific steps of the method are:

[0007] Optimize the heating process and increase the soaking temperature to 1200℃;

[0008] Before controlled rolling, water tanks are used for intermittent water flow to reduce the core temperature of the round steel, so that the Kocks temperature is controlled at 790-830℃, with a target of 805℃.

[0009] After rolling, a water tank is used for strong water penetration to control the final rolling temperature between 640-670℃ to achieve a weak quenching effect;

[0010] The cooling bed is put into use of an insulation cover in advance, and the steel moves on the cooling bed at a speed of 15-20 seconds per step. The steel is slowly cooled on the cooling bed and undergoes self-tempering.

[0011] Furthermore, in the optimized heating process, a regenerative heating furnace is used to heat the billet, and the billet size is 250mm×300mm×10500mm. During the heating process, the temperature of each section of the heating furnace is strictly controlled to ensure that the billet is evenly heated, avoiding local overheating or insufficient heating, so as to ensure the structural uniformity and performance stability of the steel in the subsequent rolling process. The regenerative heating furnace can effectively recover the waste heat of the flue gas, improve energy utilization, reduce energy consumption and carbon emissions during the heating process, and meet the requirements of green manufacturing. During the heating process, the heating time of the billet must also be precisely controlled. The heating cycle is determined according to the size and material properties of the billet. The billet reaches an even heating temperature of 1200°C, so that the alloy elements in the steel are fully dissolved, preparing for subsequent rolling and performance regulation.

[0012] Furthermore, when the water tank is used for intermittent water penetration before the controlled rolling, the valve opening degree, flow rate and pressure of the water tank need to be set according to the specifications of the round steel and the rolling speed. For round steel of different specifications, the washing machine shaft adopts Φ25-32mm steel bar. By adjusting the parameters of the water tank, the core temperature of the round steel is reduced to an appropriate range, thereby controlling the temperature entering Kocks at 790-830℃, with a target of 805℃. The intermittent water penetration method can avoid surface crack defects caused by the surface temperature of the round steel being too low, and at the same time reduce the core temperature so that the round steel has a suitable temperature gradient when entering the Kocks rolling mill, which is beneficial to improving the deformation uniformity and mechanical properties of the steel during the rolling process. During the water penetration process, the temperature changes of the round steel need to be monitored in real time, and the parameters of the water tank are adjusted in time according to the actual temperature conditions to ensure that the temperature entering Kocks is stable within the target range.

[0013] Furthermore, when a water tank is used for strong water penetration after rolling, it is necessary to ensure that the cooling capacity of the water tank is sufficient, and the round steel is quickly cooled so that the final rolling temperature is controlled between 640-670°C to achieve weak quenching. During the strong water penetration process, the water flow, pressure and spray angle must be accurately controlled to ensure that the surface of the round steel is evenly cooled to avoid tissue stress and deformation problems caused by uneven cooling. The weak quenching effect can form a certain thickness of martensitic structure on the surface of the round steel, improve the surface hardness, and maintain a certain toughness inside, laying the foundation for subsequent self-tempering treatment. In addition, the time and intensity of the strong water penetration need to be adjusted according to the specifications and rolling speed of the round steel to ensure that the final rolling temperature is stable within the target range and that the hardness and mechanical properties of the steel meet the requirements.

[0014] Furthermore, the cooling bed is put into use with an insulation cover in advance, and the structural design of the insulation cover must meet the insulation performance requirements, which can effectively reduce the heat loss of the steel on the cooling bed and provide a suitable temperature environment for the slow cooling and self-tempering of the steel. The steel moves on the cooling bed at a speed of 15-20 seconds / step. The setting of this movement speed is determined comprehensively based on factors such as the specifications and thickness of the steel and the length of the cooling bed. The steel has enough time to self-temper on the cooling bed, so that the residual stress inside the steel is released, and the martensite structure undergoes tempering transformation to form a tempered bainite structure, thereby improving the comprehensive mechanical properties of the steel. During the cooling process of the cooling bed, the temperature changes of the steel need to be monitored in real time, and the use status of the insulation cover and the movement speed of the steel are adjusted according to the temperature conditions to ensure that the self-tempering process is fully carried out.

[0015] Furthermore, before optimizing the heating process, the billet needs to be pretreated, including checking the surface quality of the billet and removing surface oxide scale and crack defects to prevent these defects from expanding during the subsequent rolling process and affecting the quality of the steel. At the same time, the chemical composition of the billet needs to be rechecked to ensure that the chemical composition of the billet meets the requirements of 40Cr steel, C: 0.32%~0.45%, Si: 0.18%~0.33%, Mn: 0.56%~0.78%, Ni+Cu≤0.06%, P+S≤0.025%, and the balance is Fe, which lays the foundation for the subsequent production of qualified motor shaft steel. During the pretreatment process, appropriate detection methods and equipment need to be used to ensure that the quality of the billet meets the requirements.

[0016] Furthermore, during the controlled water cooling before rolling and the strong water cooling after rolling, the water temperature needs to be controlled to ensure that the water used in the water cooling process has an appropriate temperature to achieve an ideal cooling effect. If the water temperature is too high, the cooling efficiency will be reduced and the temperature of the round steel cannot be effectively controlled. If the water temperature is too low, the surface of the round steel may cool too quickly, resulting in large internal stress and even crack defects. Therefore, a special water treatment system needs to be set up to monitor and adjust the water temperature in the water cooling process in real time to keep the water temperature within an appropriate range to ensure the stability and reliability of the cooling process.

[0017] Furthermore, during the rolling process, the rolling speed and rolling pressure of the rolling mill need to be adjusted according to the specifications of the round steel and the rolling process requirements to ensure the stability of the rolling process and the dimensional accuracy of the steel. For steel bars for washing machine shafts with a diameter of Φ25-32mm, a reduced speed rolling method needs to be adopted during the rolling process to ensure that the steel is evenly cooled in the water tank to avoid uneven cooling due to excessively fast rolling speed, which affects the hardness and mechanical properties of the steel. At the same time, the rolling mill rolls need to be regularly inspected and maintained to ensure the surface quality and dimensional accuracy of the rolls, so as to ensure that the rolled round steel has good surface quality and dimensional tolerance.

[0018] Furthermore, during the self-tempering treatment process on the cooling bed, it is also necessary to control the stacking method of the steel on the cooling bed to avoid mutual squeezing or over-stacked steels, which will affect the cooling and self-tempering effect of the steel. The steel should be evenly distributed on the cooling bed and maintain a certain distance to ensure air circulation so that the steel can be evenly cooled and self-tempered. In addition, the residence time of the steel on the cooling bed needs to be arranged according to the production rhythm and the cooling condition of the steel to ensure that the self-tempering process is fully completed and the hardness of the steel reaches 20-25HRC, which meets the mechanical properties requirements of the motor shaft steel.

[0019] Furthermore, during the entire rolling process, a complete online monitoring system needs to be set up to monitor and record the key process parameters such as heating temperature, rolling speed, water penetration temperature, final rolling temperature, and cooling bed cooling temperature in real time, and automatically adjust the process parameters through the control system to ensure the stability and consistency of the process parameters. The online monitoring system must also have a fault alarm function. When the process parameters are abnormal or the equipment fails, it can send an alarm signal in time so that the operator can deal with it in time to ensure the safety and stable operation of the rolling process, thereby ensuring the quality of the steel and production efficiency.

[0020] Compared with the existing technology, this high-speed rolling process method for improving the hardness of motor shaft steel has the following beneficial effects:

[0021] 1. This process optimizes the rolling process parameters to increase the hardness of the bar at 2mm to 20-25HRC, and uses the cooling bed insulation cover structure for self-tempering to achieve a tempering effect, meeting the mechanical property requirements of motor shaft steel, saving production process steps, reducing production costs and carbon emissions, and having great benefits for environmental protection.

[0022] 2. This process method effectively improves the hardness of motor shaft steel by optimizing the heating process, controlling intermittent water penetration before rolling, strong water penetration after rolling, and self-tempering on the cooling bed. In particular, by precisely controlling the Kocks temperature and the final rolling temperature, it achieves fine regulation of the internal structure of the steel and forms a tempered bainite structure, thereby significantly improving the hardness and comprehensive mechanical properties of the steel, meeting the requirements of motor shaft steel for high strength and high toughness.

[0023] Other advantages, objects and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art based on an examination of the following or may be learned from the practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive effort.

[0025] Figure 1 The present invention is a process flow chart of a rolling process method for improving the hardness of steel for motor shaft. DETAILED DESCRIPTION

[0026] In order to further illustrate the technical means and effects adopted by the present invention to achieve the predetermined purpose of the invention, the specific implementation methods, structures, features and effects of the present invention are described in detail below in conjunction with the accompanying drawings and preferred embodiments.

[0027] Example 1

[0028] Before production, the surface of each billet must be checked, and defects such as oxide scale and cracks must be thoroughly removed by mechanical grinding or high-pressure water descaling to prevent the defects from expanding during subsequent rolling. At the same time, spectral analysis and other methods are used to re-inspect the chemical composition of the billet to ensure that the content of alloy elements such as carbon, manganese, and silicon meets the material standards for motor shaft steel, laying the foundation for subsequent heat treatment performance.

[0029] A regenerative heating furnace is used to perform gradient heating on the billet. The temperature is first slowly increased through the preheating section to reduce thermal stress, and then the billet enters the high-temperature section to evenly reach the soaking temperature. During the heating process, the heating time is calculated using the heat conduction formula based on the billet diameter and alloy composition to ensure that the alloy elements are fully dissolved in the austenite matrix, providing a uniform organizational foundation for subsequent controlled rolling and controlled cooling.

[0030] Before the round steel enters the Kocks rolling mill, the water tank is started for intermittent water cooling. According to the round steel specifications and rolling speed, the relationship between the water tank valve opening and the flow rate is estimated using fluid mechanics formulas, so that the cooling water is sprayed onto the round steel surface in a pulsed manner. The temperature difference between the core and the surface of the round steel is monitored in real time. By adjusting the water cooling time interval, cracks on the surface caused by rapid cooling are avoided. At the same time, the core temperature is reduced to the ideal range for rolling, forming a temperature gradient that is conducive to rolling deformation.

[0031] In response to the toughness requirements of steel used for washing machine shafts, a reduced-speed rolling process is adopted. The rolling mill pressure parameters are calculated using the rolling force formula, and the motor speed adjustment system is used to match the roller linear speed with the round steel feed speed. At the same time, the roller surface wear is checked regularly, and the roller service status is evaluated using the hardness test formula to ensure uniform metal deformation during the rolling process and avoid defects such as excessive ovality.

[0032] The strong water penetration system is started immediately after the final rolling. By increasing the water pressure and flow, a film boiling cooling state is formed on the surface of the round steel. The relationship between the cooling water volume and the cooling rate is calculated using the heat transfer formula. The final rolling temperature is accurately controlled in the weak quenching range, so that the surface austenite is quickly transformed into martensite, while the core maintains a certain plasticity, forming a gradient structure with surface hardening and internal toughness.

[0033] The cooling bed is equipped with an insulation cover in advance to form a local constant temperature field. When the billet moves in steps at a set speed, its residence time on the cooling bed is calculated by the heat conduction formula to ensure that the martensite structure undergoes tempering transformation during slow cooling to form tempered bainite. At the same time, the spacing between the billets is controlled to avoid mutual blocking and uneven cooling. The self-tempering effect is evaluated by the residual stress detection formula to release the internal stress of the steel and meet the hardness uniformity requirements.

[0034] Monitoring equipment such as infrared thermometers and pressure sensors are deployed throughout the entire process to transmit parameters such as heating temperature and rolling speed to the PLC control system in real time. The system automatically compares the measured values ​​with the target values ​​through preset process control formulas, and immediately adjusts the heating power or water flow rate when deviations occur. If the abnormal parameters exceed the threshold, the fault diagnosis formula triggers an audible and visual alarm, and the production line is forced to shut down urgently to prevent the production of batches of defective products.

[0035] Example 2

[0036] All-round surface flaw detection is carried out on large-sized billets, thick oxide scale is removed by shot blasting machine, local crack defects are gas cut and ground, and the alloy composition is re-checked through chemical analysis formula, with emphasis on controlling the content of elements such as chromium and molybdenum to ensure that the hardenability of the steel meets the cross-sectional performance requirements of industrial shafts and avoid the risk of fracture caused by insufficient hardness in the core.

[0037] A regenerative heating furnace is used for heating in three stages. The holding time is calculated by the heat diffusion formula to make the temperature difference between the center and the surface of the billet less than 50°C. The high temperature is maintained during the soaking stage to promote the full dissolution of carbides, prepare for the formation of fine austenite grains in subsequent controlled rolling, and avoid structural segregation caused by insufficient heating.

[0038] Based on the large diameter characteristics of industrial shaft steel, multiple groups of water tanks are used to alternately and intermittently irrigate the steel. The water tank spray angle is designed using fluid dynamics formulas to ensure that the cooling water evenly covers the surface of the round steel. At the same time, the water irrigating interval is calculated using temperature field simulation formulas to prevent excessive surface cooling. The core temperature changes are monitored in real time to ensure a reasonable temperature field distribution when entering the Kocks rolling mill, providing good plastic conditions for large deformation rolling.

[0039] A multi-stand continuous rolling method is adopted, and the pressure distribution of each stand is calculated in sections through the rolling force formula. The rolling mill speed is adjusted in conjunction with the speed gradient formula to form a pass-by-pass compression ratio control. In response to the high strength requirements of industrial shaft steel, a low-temperature and large reduction process is adopted in the finishing rolling stage. The effect of deformation on grain refinement is estimated through the dislocation strengthening formula to ensure the uniformity of the final structure and the consistency of hardness.

[0040] Equipped with a high-pressure cooling system, the relationship between cooling intensity and phase transformation time is calculated using heat transfer formulas, allowing the final rolling temperature to be precisely controlled within the weak quenching range. Upper and lower spraying methods are used to ensure uniform cooling of the round steel cross section, avoiding excessive internal stress caused by uneven cooling. At the same time, the phase transformation process is monitored using the martensite transformation amount calculation formula to ensure that the depth of the surface hardened layer meets the wear resistance requirements of industrial shafts.

[0041] The cooling bed insulation cover adopts a double-layer insulation structure. The temperature maintenance capacity of the insulation cover is calculated by the heat balance formula. The steel billet moves at a slower speed to extend the self-tempering time so that the martensite can be fully decomposed into tempered bainite. The cross-sectional hardness distribution is evaluated by the hardness gradient detection formula, and the stacking method and residence time are adjusted to ensure that the hardness difference from the surface to the core of large-size steel does not exceed the standard range.

[0042] The integrated multi-parameter monitoring system uses the temperature-time curve formula to analyze the thermal efficiency of each section of the heating furnace in real time, and optimizes the continuous rolling rhythm through the rolling force-speed formula. When the water temperature in the water cooling system is abnormal, it automatically switches to the backup cooling circuit and locates the source of the problem through the fault diagnosis formula. The entire process data is stored in the MES system to form a process traceability database, providing a basis for subsequent process optimization.

[0043] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art can, without departing from the scope of the technical solution of the present invention, make some changes or modifications to equivalent embodiments using the technical contents disclosed above. However, any brief modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A rolling process method for increasing the hardness of steel for motor shaft, characterized in that: The specific steps of this method are: S1. Optimize the heating process: increase the soaking temperature to 1200°C; S2. Water cooling before controlled rolling: Use a water tank to intermittently cool the round steel before controlled rolling to reduce the core temperature of the round steel and control the Kocks temperature at 790-830℃, with a target of 805℃. S3. Strong water cooling after rolling: After rolling, strong water cooling is carried out in a water tank to control the final rolling temperature between 640-670℃ to achieve a weak quenching effect; S4. Self-tempering treatment on cooling bed: The cooling bed is put into use with a heat preservation cover in advance. The steel moves on the cooling bed at a speed of 15-20 seconds / step. The steel is slowly cooled on the cooling bed for self-tempering.

2. A rolling process method for improving the hardness of motor shaft steel according to claim 1, characterized in that: In the optimized heating process, a regenerative heating furnace is used to heat the billet. The temperature of each section of the heating furnace is strictly controlled during the heating process. During the heating process, the heating time of the billet also needs to be accurately controlled. The heating cycle is determined according to the size and material properties of the billet. The billet reaches an equalizing temperature of 1200°C to fully dissolve the alloy elements in the steel.

3. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: When using a water tank for intermittent water penetration before the controlled rolling, the valve opening degree, flow rate and pressure of the water tank need to be set according to the specifications of the round steel and the rolling speed. For round steels of different specifications, the washing machine shaft adopts Φ25-32mm steel bars. By adjusting the parameters of the water tank, the core temperature of the round steel is reduced to an appropriate range, thereby controlling the inlet Kocks temperature at 790-830℃, with a target of 805℃. The intermittent water penetration method can avoid surface crack defects caused by excessively low surface temperature of the round steel, and at the same time reduce the core temperature, so that the round steel has a suitable temperature gradient when entering the Kocks rolling mill. During the water penetration process, the temperature changes of the round steel need to be monitored in real time, and the parameters of the water tank are adjusted in time according to the actual temperature conditions.

4. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: When using a water tank for strong water penetration after rolling, it is necessary to ensure that the cooling capacity of the water tank is sufficient to quickly cool the round steel and control the final rolling temperature between 640-670°C to achieve weak quenching. During the strong water penetration process, the water flow, pressure and spray angle must be accurately controlled. In addition, the time and intensity of the strong water penetration must be adjusted according to the specifications of the round steel and the rolling speed.

5. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: The cooling bed is put into use with an insulation cover in advance, and the structural design of the insulation cover must meet the insulation performance requirements. The steel moves on the cooling bed at a speed of 15-20 seconds per step. The steel has enough time to self-temper on the cooling bed to release the residual stress inside the steel and at the same time make the martensite structure undergo tempering transformation to form tempered bainite structure. During the cooling process of the cooling bed, the temperature change of the steel needs to be monitored in real time, and the use status of the insulation cover and the moving speed of the steel need to be adjusted according to the temperature conditions.

6. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: Before optimizing the heating process, the blank needs to be pretreated, including checking the surface quality of the blank, removing the oxide scale and crack defects on the surface, and rechecking the chemical composition of the blank.

7. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: During the controlled water cooling before rolling and the strong water cooling after rolling, the water temperature needs to be controlled. If the water temperature is too high, the cooling efficiency will be reduced. If the water temperature is too low, the surface of the round steel may cool too quickly, resulting in large internal stress and even crack defects. Therefore, a water treatment system needs to be set up to monitor and adjust the water temperature in real time during the water cooling process.

8. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: During the rolling process, the rolling speed and rolling pressure of the rolling mill need to be adjusted according to the specifications of the round steel and the rolling process requirements. For steel bars for washing machine shafts with a diameter of Φ25-32mm, a reduced speed rolling method needs to be adopted during the rolling process. At the same time, the rolling mill rolls need to be regularly inspected and maintained.

9. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: During the self-tempering treatment process on the cooling bed, it is also necessary to control the stacking method of the steel on the cooling bed to avoid mutual squeezing or over-stacked steel, which will affect the cooling and self-tempering effect of the steel. The steel should be evenly distributed on the cooling bed and maintain a certain spacing. In addition, the residence time of the steel on the cooling bed needs to be arranged according to the production rhythm and the cooling condition of the steel so that the hardness of the steel reaches 20-25HRC.

10. The method for increasing the hardness of motor shaft steel according to claim 1, characterized in that: During the entire rolling process, a complete online monitoring system needs to be set up to monitor and record the key process parameters such as heating temperature, rolling speed, water penetration temperature, final rolling temperature, and cooling bed cooling temperature in real time, and automatically adjust the process parameters through the control system. The online monitoring system must also have a fault alarm function, which can promptly issue an alarm signal when abnormal process parameters or equipment failure occur.

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