Preparation process of fatigue-resistant alloy steel for automobile hollow stabilizer bar

Abstract

The application discloses a preparation process of fatigue-resistant alloy steel for automobile hollow stabilizer bars and relates to the technical field of automobile part manufacturing. The application connects overload pre-torsion and inner wall ultrasonic impact in series and inserts low-temperature tempering in the middle. The overload pre-torsion makes the full-section residual tensile stress be redistributed into a uniform compressive stress field. The ultrasonic impact extends into the inner cavity through a flexible rod, forms a 1.5 mm deep compressive stress layer in the inner arc of the bend angle and the inner wall, realizes double locking of the inner and outer walls and overcomes the problem that the hollow inner wall cannot be treated by shot blasting. The cooperation of the two makes the cross section free of residual tensile stress concentration. The overload pre-torsion can be completed by using an existing torsion testing machine, the ultrasonic impact device is a standard commercial product and only needs to be customized with a flexible clamp to realize automation, the transformation cost is extremely low and the single-piece increment is less than 2 minutes. The pre-torsion amount of 5% to 9% is matched with low-temperature tempering to eliminate the micro-crack risk, and the ultrasonic parameters can be adjusted. The whole process is free of water, acid and dust, and meets the green manufacturing.

Description

Technical Field

[0001] This invention relates to the field of automotive parts manufacturing technology, specifically to a process for preparing fatigue-resistant alloy steel for automotive hollow stabilizer bars. Background Technology

[0002] As a key anti-roll component in automotive suspension systems, the performance of hollow stabilizer bars directly affects the vehicle's handling stability and driving safety. Under alternating torsional loads, fatigue fracture of stabilizer bars typically originates from stress concentration areas on the surface or inside the bar, particularly on the inner arc side of bends and near welds. Therefore, surface strengthening processes are commonly used in engineering to extend their fatigue life. Currently, the mainstream strengthening method for solid stabilizer bars is shot peening of the outer wall. This process can introduce a residual compressive stress layer on the bar surface and refine the surface grains, thereby effectively inhibiting crack initiation and propagation. However, with the increasing urgency of automotive lightweighting, hollow stabilizer bars are gradually replacing solid structures due to their weight reduction advantages. But the hollow configuration presents a significant obstacle to traditional shot peening processes—the shot peening medium cannot effectively enter the narrow inner cavity, nor can it uniformly impact the inner arc side of bends and the entire length of the inner wall. This results in the inner wall surface being in a state of no or weak strengthening for a long time, becoming a potential weak point for fatigue failure.

[0003] To address this issue, some manufacturers have attempted to use dedicated internal wall shot peening equipment. However, due to limitations in the reachability of the shot gun and the shot scattering angle, significant reinforcement blind spots still exist in the bend transition area. Furthermore, internal wall shot peening is prone to causing excessive impact in localized areas, introducing micro-damage and ultimately reducing reliability. On the other hand, overload pre-torsion technology is used in the manufacture of solid bars. It applies an over-yield torque to induce plastic deformation across the entire cross-section of the bar and create a residual compressive stress field. However, for hollow bars, the conventional pre-torsion is often too large. Although it can achieve macroscopic stress improvement, it is highly likely to induce micro-cracks within the material. Especially when there is a lack of subsequent transition treatment to eliminate stress concentration, these micro-defects will rapidly expand during service, severely weakening the fatigue gain effect. In addition, existing processes mostly implement external wall reinforcement and internal wall treatment independently, lacking a systematic design concept from the perspective of full-section stress distribution. This results in an alternating distribution of residual tensile and compressive stresses on the cross-section of the bar, leading to significant batch-to-batch performance fluctuations and making it difficult to meet the stringent reliability requirements of OEMs. Therefore, current technology has not yet proposed a systematic solution that can simultaneously take into account the outer and inner walls of the hollow stabilizer bar, the macroscopic stress field and the microscopic surface structure, and the overall strengthening effect and local damage control. Summary of the Invention

[0004] The purpose of this invention is to provide a manufacturing process for fatigue-resistant alloy steel for hollow stabilizer bars in automobiles, so as to solve the problems existing in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a fatigue-resistant alloy steel for automotive hollow stabilizer bars, comprising the following steps: (1) Prepare a quenched and tempered hollow stabilizer bar workpiece. The workpiece is made of 42 chromium molybdenum steel or 50 chromium vanadium steel through smelting, hot rolling, forming, welding and quenching and tempering. The microstructure is tempered sorbite, the Rockwell hardness is 38-42, and the yield strength is 800MPa-1000MPa. (2) Implement the overload pre-torsion process, clamp both ends of the heat-treated hollow stabilizer bar onto the torsion loading device, apply a unidirectional ultimate torsion load at room temperature, the applied equivalent torque is 105%-109% of the torque value corresponding to the yield limit of the workpiece, the torsion rate is 5° / min-15° / min, after reaching the preset torsion angle, maintain the load for 30s-60s, remove the load to allow the bar to elastically recover, so that a uniform residual compressive stress field is formed in the entire cross section of the bar; (3) After the pre-twist cleaning process, the outer surface of the rod body is sprayed with industrial hydrocarbon cleaning agent, and the inner hole is blown with compressed air to remove oil and metal debris. (4) Implement a low-temperature tempering process. Place the cleaned hollow stabilizer into the tempering furnace and keep it at 180℃-250℃ for 90min-150min. After taking it out, let it cool naturally to room temperature in still air. (5) Implement the internal cavity blowing and cleaning process, use high pressure compressed air to repeatedly blow the internal cavity, and then use a flexible guide rod to pull the non-woven cloth soaked in anhydrous ethanol to wipe the inner wall and blow dry the surface of the internal cavity. (6) Implement the ultrasonic impact process on the inner wall, install the impact needle on the front end of the flexible guide rod and extend it into the inner cavity, and push it along the inner cavity axis to perform high-frequency mechanical impact on the inner wall of the straight section and the inner arc side of the curved section. After the impact, a residual compressive stress layer with a depth of 1.5mm is formed on the metal surface. (7) Implement the final inspection process, use magnetic particle testing to detect whether there are cracks or defects on the inner and outer surfaces of the pole body, use a residual stress tester to detect whether the residual stress value meets the design requirements, and after passing the inspection, transfer to the finished product packaging process.

[0006] Furthermore, the weld formed in step (1) is located on the outside of the bend section of the rod or at the longitudinal joint of the tube. After welding, the weld reinforcement is controlled at 0.3mm-0.5mm by grinding process, and the heat-affected zone width is controlled at 3mm-5mm.

[0007] Furthermore, in step (2), the torsional loading device applies torsional load using a dual control method with torsion angle as the main control parameter and torque monitoring as a supplement. The preset torsion angle is calculated in advance based on the measured value of the torsional stiffness of the batch of workpieces.

[0008] Furthermore, the residual compressive stress field formed by the overload pre-torsion in step (2) simultaneously covers the outer and inner walls of the rod body and includes the surface of the weld area.

[0009] Furthermore, in step (4), the temperature uniformity within the effective heating zone of the tempering furnace is controlled within ±5℃.

[0010] Furthermore, in step (6), the ultrasonic shock generator operates at a frequency of 20kHz, outputs a current of 3A-6A, has an axial mechanical amplitude of 0.02mm-0.05mm, is made of tungsten-cobalt hard alloy, and has a tip radius of 0.5mm-1.5mm.

[0011] Furthermore, in step (6), the outer diameter of the flexible guide rod is 2mm-4mm smaller than the inner diameter of the hollow stabilizer rod, the contact pressure between the impact pin and the inner wall surface is 100N-200N, the axial feed speed of the flexible guide rod is 100mm / min-300mm / min, and the overlap rate between two adjacent impact paths is 40%-60%.

[0012] Furthermore, in step (6), the dwell time of the impact needle on the inner arc side of the bend is extended to 1.5 times the dwell time of the straight section.

[0013] Furthermore, in step (6), when the impact needle passes through the inner wall portion corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight section, and the dwell time in this local area is extended to twice that of the straight section.

[0014] Furthermore, the residual compressive stress layer formed in step (6) and the full-section residual compressive stress field formed in step (2) superimpose to ensure that there is no area of ​​concentrated residual tensile stress on the entire cross-section of the hollow rod.

[0015] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) In this invention, overload pre-torsion and ultrasonic impact on the inner wall are connected in sequence, and low-temperature tempering is inserted between the two as a transition process. First, a unidirectional ultimate torsional load exceeding the yield limit of 5% to 9% is applied to the tempered hollow stabilizer at room temperature, so that the residual tensile stress area of ​​the whole cross section is redistributed into a uniform residual compressive stress field. Then, the ultrasonic impact needle is inserted into the inner cavity through the flexible rod to perform high-frequency mechanical impact on the inner arc side of the bend and the entire length of the inner wall, forming a residual compressive stress layer with a depth of about 1.5 mm on the metal surface, realizing the dual compressive stress locking of the outer wall and the inner wall, and solving the technical problem that the traditional shot peening process cannot handle the inner wall of the hollow rod.

[0016] (2) The present invention utilizes the macroscopic compressive stress reshaping effect of overload pre-torsion on the entire cross section of the rod, and the deep compressive stress strengthening effect of ultrasonic impact on the inner wall surface. The two work together to ensure that there is no residual tensile stress concentration area on the entire hollow rod cross section.

[0017] (3) The overload pre-torsion process used in this invention can be completed using existing torsion fatigue testing machines or end forming machines without the need for additional large equipment; the inner wall ultrasonic impact device is a commercially available standard part, and only a set of flexible clamps that extend into the inner cavity needs to be customized to achieve automated operation. The cost of the entire process modification is extremely low, and the increase in working time per piece is less than 2 minutes, which is suitable for large-scale continuous production.

[0018] (4) This invention controls the overload pre-torsion at 5%~9%, and with the low-temperature tempering treatment after pre-torsion, eliminates the risk of microcrack initiation; the ultrasonic impact parameters are adjustable to avoid excessive impact causing surface damage. The entire process is water-free, acid-free, and dust-free, meeting the requirements of green manufacturing. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The following embodiments describe a method for testing various properties of fatigue-resistant alloy steel used in automotive hollow stabilizer bars: Residual stress testing: Residual stress values ​​at specified locations on the outer wall, inner wall, and inner arc side of the bend section of the rod were determined using X-ray diffraction. The testing equipment used was a Proto iXRD residual stress analyzer with a tube voltage of 30kV, a tube current of 25mA, Cr target Kα radiation, diffraction plane {211}, a scanning step of 0.1°, and a collimator diameter of 1mm. Before testing, the surface to be tested was electrolytically polished to remove the processing layer, with a polishing depth of approximately 0.1mm. The depth of the residual compressive stress layer was determined using a layer-by-layer electrolytic ablation method, with each ablation depth of 0.2mm until the residual stress approached zero, and the actual depth of the compressive stress layer was recorded.

[0021] Torsional fatigue life test: Hollow stabilizer bars treated with the process of this invention and untreated quenched and tempered hollow stabilizer bars (control group) were respectively installed on an MTS 858 torsional fatigue testing machine. Sinusoidal cyclic torsional loads were applied with a stress ratio R=-1, a loading frequency of 5Hz, and the maximum torque was set at 1.2 times the design rated load of the stabilizer bar. Each group contained no fewer than 10 specimens, and the fatigue fracture cycles of each specimen were recorded. The median fatigue life was calculated using a log-normal distribution statistical method, and the coefficient of variation (CV) was used to characterize the batch dispersion.

[0022] Microstructure and surface integrity testing: Samples were cut transversely along the shaft, mounted, ground, and polished, then etched with a 4% nitric acid alcohol solution. The morphology of the tempered sorbite structure was observed under a Zeiss Axio Observer metallographic microscope. The surface morphology of the inner wall after ultrasonic impact and the interface characteristics between the compressive stress layer and the substrate were observed using a FEI Quanta 650FEG scanning electron microscope. Fluorescent magnetic particle testing (model MAGNAFLUX Y-6) was used to inspect the inner and outer walls of the shaft and the weld area to determine the presence of cracks or microcracks.

[0023] Hardness and mechanical property verification: Points were taken on the outer and inner walls of the straight and curved sections of the rod, and the HRC value was measured using a Wilson UH250 Rockwell hardness tester. Three measurements were taken at each location, and the average value was recorded. Standard tensile specimens were cut from the same batch of workpieces and subjected to room temperature tensile tests on a universal testing machine according to GB / T 228.1-2010 to determine the yield strength and tensile strength.

[0024] Process stability evaluation: 100 products were produced continuously, and 20 products were randomly selected for full-item testing according to the above method. The mean and standard deviation of each indicator were statistically analyzed to verify whether the coefficient of variation was less than 15% and whether the single-piece time increment was controlled within 2 minutes. Example 1

[0025] (1) Prepare a quenched and tempered hollow stabilizer bar. The bar is made of 42 chromium molybdenum steel through smelting, hot rolling, forming, welding and quenching and tempering. The weld formed by the welding process is located on the outside of the bend of the bar or at the longitudinal joint of the tube. The whole bar is quenched and tempered so that the microstructure of the bar is tempered sorbite, the Rockwell hardness value is 38, the yield strength value is between 800 MPa, the inner hole diameter is 8 mm, and the wall thickness is 4 mm. (2) The two ends of the quenched and tempered hollow stabilizer are clamped on the torsion loading device. The device uses the torsion angle as the main control parameter and the torque monitoring as a dual control method to apply the torsion load. After the workpiece is clamped, it is subjected to unidirectional torsion under room temperature conditions. The preset torsion angle is calculated in advance based on the measured value of the torsion stiffness of the batch of workpieces. The applied equivalent torque value is controlled at 105% of the torque value corresponding to the yield limit of the workpiece. The torsion rate is controlled at 5° / min. After the torsion angle reaches the preset angle, the load is maintained for 30s. Then the load is removed to allow the rod to recover elastically. After this process, the residual tensile stress area of ​​the entire cross section of the rod is redistributed into a uniform residual compressive stress field. This compressive stress field covers both the outer and inner walls of the rod and includes the surface of the weld area. (3) The hollow stabilizer bar that has been pre-torsed is removed from the torsion loading equipment and placed in the cleaning station. Industrial hydrocarbon cleaning agent is used to spray the outer surface of the bar to remove clamping marks and attached oil stains. At the same time, 0.6MPa compressed air is used to blow the inner hole from one end of the bar to the other end to blow away the trace metal debris and residue generated by plastic slippage from the inner wall. After blowing for 30 seconds, observe whether the airflow at the outlet of the inner hole carries impurities. After confirming that it is clean, proceed to the next process. (4) Place the cleaned hollow stabilizer bar into the tempering furnace. The temperature uniformity in the effective heating zone of the tempering furnace is controlled within ±5℃. The tempering temperature is set to 180℃ and the holding time is set to 90min. After tempering, the workpiece is taken out and naturally cooled to room temperature in still air. This process is used to eliminate the local micro-stress concentration caused by overload pre-torsion and reduce the probability of micro-crack initiation in the weld area and heat-affected zone. (5) Fix the hollow stabilizer rod after low temperature tempering to the ultrasonic impact processing station. Use 1.0MPa high pressure compressed air to repeatedly blow the inner cavity from one end of the rod to the other three times to remove the loose oxide scale and particulate impurities generated on the inner wall during the tempering and quenching process. Then use a flexible guide rod with the same length as the rod to pull the non-woven cloth roll soaked in anhydrous ethanol to wipe the inner wall once. After wiping, blow the inner wall dry again with high pressure air to ensure that the inner cavity surface is dry and free of residual liquid. (6) Turn on the ultrasonic shock generator. Set the working frequency of the ultrasonic shock generator to 20kHz, the output current adjustment range to 3A, and the axial mechanical amplitude of the ultrasonic shock needle to 0.02mm. The shock needle is made of tungsten cobalt hard alloy and the radius of the shock needle tip arc is 0.5mm. Install the shock needle on the front end of the flexible guide rod and extend the flexible guide rod from the end of the rod body into the inner cavity. The outer diameter of the flexible guide rod is 2mm smaller than the inner diameter of the hollow stabilizing rod to ensure that the single-sided gap is 1mm. The flexible guide rod is pushed axially along the inner cavity so that the shock needle passes through the inner wall of the straight section and the bend in sequence. On the inner wall of the inner arc side of the corner section, the contact pressure between the impact pin and the inner wall surface is controlled at 100N, the axial feed speed of the flexible guide rod is controlled at 100mm / min, the overlap rate between two adjacent impact paths is controlled at 40%, the dwell time of the impact pin on the inner arc side of the corner section is extended to 1.5 times the dwell time of the straight section, and when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight section and the dwell time in this local area is extended to 2 times that of the straight section, in order to compensate for the influence of the hardness difference in the weld area on the uniformity of the strengthening effect; (7) Place the hollow stabilizer bar that has been treated as described above at the testing station and use magnetic particle testing to check whether there are cracks or defects on the inner and outer surfaces of the bar. Use a residual stress tester to check whether the residual stress values ​​at specified positions on the outer and inner walls of the bar meet the design requirements. After passing the test, the bar is transferred to the finished product packaging process. Example 2

[0026] (1) Prepare a quenched and tempered hollow stabilizer bar. The bar is made of 42 chromium molybdenum steel through smelting, hot rolling, forming, welding and quenching and tempering. The weld formed by the welding process is located on the outside of the bend of the bar or at the longitudinal joint of the tube. The whole bar is quenched and tempered so that the microstructure of the bar is tempered sorbite, the Rockwell hardness value is 39, the yield strength value is between 850 MPa, the inner diameter is 11 mm, and the wall thickness is 5.5 mm. (2) The two ends of the quenched and tempered hollow stabilizer are clamped on the torsion loading device. The device uses the torsion angle as the main control parameter and the torque monitoring as a dual control method to apply the torsion load. After the workpiece is clamped, it is subjected to unidirectional torsion under room temperature conditions. The preset torsion angle is calculated in advance based on the measured value of the torsion stiffness of the batch of workpieces. The applied equivalent torque value is controlled at 106% of the torque value corresponding to the yield limit of the workpiece. The torsion rate is controlled at 7.5° / min. After the torsion angle reaches the preset angle, the load is maintained for 37.5s. Then the load is removed to allow the rod to recover elastically. After this process, the residual tensile stress area of ​​the entire cross section of the rod is redistributed into a uniform residual compressive stress field. This compressive stress field covers both the outer and inner walls of the rod and includes the surface of the weld area. (3) The hollow stabilizer bar that has been pre-torsed is removed from the torsion loading equipment and placed in the cleaning station. Industrial hydrocarbon cleaning agent is used to spray the outer surface of the bar to remove clamping marks and attached oil stains. At the same time, 0.6MPa compressed air is used to blow the inner hole from one end of the bar to the other end to blow away the trace metal debris and residue generated by plastic slippage from the inner wall. After blowing for 30 seconds, observe whether the airflow at the outlet of the inner hole carries impurities. After confirming that it is clean, proceed to the next process. (4) Place the cleaned hollow stabilizer bar into the tempering furnace. The temperature uniformity in the effective heating zone of the tempering furnace is controlled within ±5℃. The tempering temperature is set to 197.5℃ and the holding time is set to 105min. After tempering, take out the workpiece and let it cool naturally to room temperature in still air. This process is used to eliminate the local micro-stress concentration caused by overload pre-torsion and reduce the probability of micro-crack initiation in the weld area and heat-affected zone. (5) Fix the hollow stabilizer rod after low temperature tempering to the ultrasonic impact processing station. Use 1.0MPa high pressure compressed air to repeatedly blow the inner cavity from one end of the rod to the other 4 times to remove the loose oxide scale and particulate impurities generated on the inner wall during the tempering and quenching process. Then use a flexible guide rod with the same length as the rod to pull the non-woven cloth roll soaked in anhydrous ethanol to wipe the inner wall once. After wiping, use high pressure air to dry the inner wall again to ensure that the inner cavity surface is dry and free of residual liquid. (6) Turn on the ultrasonic shock generator. Set the working frequency of the ultrasonic shock generator to 20kHz, the output current adjustment range to 3.75A, and the axial mechanical amplitude of the ultrasonic shock pin to 0.0275mm. The shock pin is made of tungsten-cobalt hard alloy, and the radius of the shock pin tip arc is 0.75mm. Install the shock pin on the front end of the flexible guide rod and extend the flexible guide rod from the end of the rod body into the inner cavity. The outer diameter of the flexible guide rod is 2.5mm smaller than the inner diameter of the hollow stabilizing rod to ensure a single-sided gap of 1.25mm. The flexible guide rod is pushed axially along the inner cavity so that the shock pin passes through the straight... For the inner wall of the line segment and the inner arc side of the bend segment, the contact pressure between the impact pin and the inner wall surface is controlled at 125N, the axial feed speed of the flexible guide rod is controlled at 150mm / min, the overlap rate between two adjacent impact paths is controlled at 45%, the dwell time of the impact pin on the inner arc side of the bend segment is extended to 1.5 times the dwell time of the straight segment, and when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight segment and the dwell time in this local area is extended to 2 times that of the straight segment, in order to compensate for the influence of the hardness difference in the weld area on the uniformity of the strengthening effect. (7) Place the hollow stabilizer bar that has been treated as described above at the testing station and use magnetic particle testing to check whether there are cracks or defects on the inner and outer surfaces of the bar. Use a residual stress tester to check whether the residual stress values ​​at specified positions on the outer and inner walls of the bar meet the design requirements. After passing the test, the bar is transferred to the finished product packaging process. Example 3

[0027] (1) Prepare a quenched and tempered hollow stabilizer bar. The bar is made of 42 chromium molybdenum steel through smelting, hot rolling, forming, welding and quenching and tempering. The weld formed by the welding process is located on the outside of the bend of the bar or at the longitudinal joint of the tube. The whole bar is quenched and tempered so that the microstructure of the bar is tempered sorbite, the Rockwell hardness is 40, the yield strength is between 900 MPa, the inner diameter is 14 mm, and the wall thickness is 7 mm. (2) The two ends of the quenched and tempered hollow stabilizer are clamped on the torsion loading device. The device uses the torsion angle as the main control parameter and the torque monitoring as a dual control method to apply the torsion load. After the workpiece is clamped, it is subjected to unidirectional torsion under room temperature conditions. The preset torsion angle is calculated in advance based on the measured value of the torsion stiffness of the batch of workpieces. The applied equivalent torque value is controlled at 107% of the torque value corresponding to the yield limit of the workpiece. The torsion rate is controlled at 10° / min. After the torsion angle reaches the preset angle, the load is maintained for 45s. Then the load is removed to allow the rod to recover elastically. After this process, the residual tensile stress area of ​​the entire cross section of the rod is redistributed into a uniform residual compressive stress field. This compressive stress field covers both the outer and inner walls of the rod and includes the surface of the weld area. (3) The hollow stabilizer bar that has been pre-torsed is removed from the torsion loading equipment and placed in the cleaning station. Industrial hydrocarbon cleaning agent is used to spray the outer surface of the bar to remove clamping marks and attached oil stains. At the same time, 0.6MPa compressed air is used to blow the inner hole from one end of the bar to the other end to blow away the trace metal debris and residue generated by plastic slippage from the inner wall. After blowing for 30 seconds, observe whether the airflow at the outlet of the inner hole carries impurities. After confirming that it is clean, proceed to the next process. (4) Place the cleaned hollow stabilizer bar into the tempering furnace. The temperature uniformity in the effective heating zone of the tempering furnace is controlled within ±5℃. The tempering temperature is set to 215℃ and the holding time is set to 120min. After tempering, the workpiece is taken out and naturally cooled to room temperature in still air. This process is used to eliminate the local micro-stress concentration caused by overload pre-torsion and reduce the probability of micro-crack initiation in the weld area and heat-affected zone. (5) Fix the hollow stabilizer rod after low temperature tempering to the ultrasonic impact processing station. Use 1.0MPa high pressure compressed air to repeatedly blow the inner cavity from one end of the rod to the other 4 times to remove the loose oxide scale and particulate impurities generated on the inner wall during the tempering and quenching process. Then use a flexible guide rod with the same length as the rod to pull the non-woven cloth roll soaked in anhydrous ethanol to wipe the inner wall once. After wiping, use high pressure air to dry the inner wall again to ensure that the inner cavity surface is dry and free of residual liquid. (6) Turn on the ultrasonic shock generator. Set the working frequency of the ultrasonic shock generator to 20kHz, the output current adjustment range to 4.5A, and the axial mechanical amplitude of the ultrasonic shock pin to 0.035mm. The shock pin is made of tungsten-cobalt hard alloy and the radius of the shock pin tip arc is 1.0mm. Install the shock pin on the front end of the flexible guide rod and extend the flexible guide rod from the end of the rod body into the inner cavity. The outer diameter of the flexible guide rod is 3mm smaller than the inner diameter of the hollow stabilizing rod to ensure that the single-sided gap is 1.5mm. The flexible guide rod is pushed axially along the inner cavity so that the shock pin passes through the straight section in sequence. For the inner wall of the inner arc side of the wall and the bend section, the contact pressure between the impact pin and the inner wall surface is controlled at 150N, the axial feed speed of the flexible guide rod is controlled at 200mm / min, the overlap rate between two adjacent impact paths is controlled at 50%, the dwell time of the impact pin on the inner arc side of the bend section is extended to 1.5 times the dwell time of the straight section, and when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight section and the dwell time in this local area is extended to 2 times that of the straight section, in order to compensate for the influence of the hardness difference in the weld area on the uniformity of the strengthening effect; (7) Place the hollow stabilizer bar that has been treated as described above at the testing station and use magnetic particle testing to check whether there are cracks or defects on the inner and outer surfaces of the bar. Use a residual stress tester to check whether the residual stress values ​​at specified positions on the outer and inner walls of the bar meet the design requirements. After passing the test, the bar is transferred to the finished product packaging process. Example 4

[0028] (1) Prepare a quenched and tempered hollow stabilizer bar. The bar is made of 50 chromium vanadium steel through smelting, hot rolling, forming, welding and quenching and tempering. The weld formed by the welding process is located on the outside of the bend of the bar or at the longitudinal joint of the tube. The whole bar is quenched and tempered so that the microstructure of the bar is tempered sorbite, the Rockwell hardness value is 41, the yield strength value is between 950 MPa, the inner diameter is 17 mm, and the wall thickness is 8.5 mm. (2) The two ends of the quenched and tempered hollow stabilizer are clamped on the torsion loading device. The device uses the torsion angle as the main control parameter and the torque monitoring as a dual control method to apply the torsion load. After the workpiece is clamped, it is subjected to unidirectional torsion under room temperature conditions. The preset torsion angle is calculated in advance based on the measured value of the torsion stiffness of the batch of workpieces. The applied equivalent torque value is controlled at 108% of the torque value corresponding to the yield limit of the workpiece. The torsion rate is controlled at 12.5° / min. After the torsion angle reaches the preset angle, the load is maintained for 52.5s. Then the load is removed to allow the rod to recover elastically. After this process, the residual tensile stress area of ​​the entire cross section of the rod is redistributed into a uniform residual compressive stress field. This compressive stress field covers both the outer and inner walls of the rod and includes the surface of the weld area. (3) The hollow stabilizer bar that has been pre-torsed is removed from the torsion loading equipment and placed in the cleaning station. Industrial hydrocarbon cleaning agent is used to spray the outer surface of the bar to remove clamping marks and attached oil stains. At the same time, 0.6MPa compressed air is used to blow the inner hole from one end of the bar to the other end to blow away the trace metal debris and residue generated by plastic slippage from the inner wall. After blowing for 30 seconds, observe whether the airflow at the outlet of the inner hole carries impurities. After confirming that it is clean, proceed to the next process. (4) Place the cleaned hollow stabilizer bar into the tempering furnace. The temperature uniformity in the effective heating zone of the tempering furnace is controlled within ±5℃. The tempering temperature is set to 232.5℃ and the holding time is set to 135min. After tempering, take out the workpiece and let it cool naturally to room temperature in still air. This process is used to eliminate the local micro-stress concentration caused by overload pre-torsion and reduce the probability of micro-crack initiation in the weld area and heat-affected zone. (5) Fix the hollow stabilizer rod after low temperature tempering to the ultrasonic impact processing station. Use 1.0MPa high pressure compressed air to repeatedly blow the inner cavity from one end of the rod to the other 4.5 times to remove the loose oxide scale and particulate impurities generated on the inner wall during the tempering and quenching process. Then use a flexible guide rod with the same length as the rod to pull the non-woven cloth roll soaked in anhydrous ethanol to wipe the inner wall once. After wiping, blow the inner wall dry again with high pressure air to ensure that the inner cavity surface is dry and free of residual liquid. (6) Turn on the ultrasonic shock generator. Set the working frequency of the ultrasonic shock generator to 20kHz, the output current adjustment range to 5.25A, and the axial mechanical amplitude of the ultrasonic shock pin to 0.0425mm. The shock pin is made of tungsten-cobalt hard alloy, and the radius of the shock pin tip arc is 1.25mm. Install the shock pin on the front end of the flexible guide rod and extend the flexible guide rod into the inner cavity from the end of the rod body. The outer diameter of the flexible guide rod is 3.5mm smaller than the inner diameter of the hollow stabilizing rod to ensure a single-sided gap of 1.75mm. The flexible guide rod is pushed axially along the inner cavity so that the shock pin passes through the straight... For the inner wall of the line segment and the inner arc side of the bend segment, the contact pressure between the impact pin and the inner wall surface is controlled at 175N, the axial feed speed of the flexible guide rod is controlled at 250mm / min, the overlap rate between two adjacent impact paths is controlled at 55%, the dwell time of the impact pin on the inner arc side of the bend segment is extended to 1.5 times the dwell time of the straight segment, and when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight segment and the dwell time in this local area is extended to 2 times that of the straight segment, in order to compensate for the influence of the hardness difference in the weld area on the uniformity of the strengthening effect; (7) Place the hollow stabilizer bar that has been treated as described above at the testing station and use magnetic particle testing to check whether there are cracks or defects on the inner and outer surfaces of the bar. Use a residual stress tester to check whether the residual stress values ​​at specified positions on the outer and inner walls of the bar meet the design requirements. After passing the test, the bar is transferred to the finished product packaging process. Example 5

[0029] (1) Prepare a quenched and tempered hollow stabilizer bar. The bar is made of 50 chromium vanadium steel through smelting, hot rolling, forming, welding and quenching and tempering. The weld formed by the welding process is located on the outside of the bend of the bar or at the longitudinal joint of the tube. The whole bar is quenched and tempered so that the microstructure of the bar is tempered sorbite, the Rockwell hardness value is 42, the yield strength value is between 1000 MPa, the inner diameter is 20 mm, and the wall thickness is 10 mm. (2) The two ends of the quenched and tempered hollow stabilizer are clamped on the torsion loading device. The device uses the torsion angle as the main control parameter and the torque monitoring as a dual control method to apply the torsion load. After the workpiece is clamped, it is subjected to unidirectional torsion under room temperature conditions. The preset torsion angle is calculated in advance based on the measured value of the torsion stiffness of the batch of workpieces. The applied equivalent torque value is controlled at 109% of the torque value corresponding to the yield limit of the workpiece. The torsion rate is controlled at 15° / min. After the torsion angle reaches the preset angle, the load is maintained for 60s. Then the load is removed to allow the rod to recover elastically. After this process, the residual tensile stress area of ​​the entire cross section of the rod is redistributed into a uniform residual compressive stress field. This compressive stress field covers both the outer and inner walls of the rod and includes the surface of the weld area. (3) The hollow stabilizer bar that has been pre-torsed is removed from the torsion loading equipment and placed in the cleaning station. Industrial hydrocarbon cleaning agent is used to spray the outer surface of the bar to remove clamping marks and attached oil stains. At the same time, 0.6MPa compressed air is used to blow the inner hole from one end of the bar to the other end to blow away the trace metal debris and residue generated by plastic slippage from the inner wall. After blowing for 30 seconds, observe whether the airflow at the outlet of the inner hole carries impurities. After confirming that it is clean, proceed to the next process. (4) Place the cleaned hollow stabilizer bar into the tempering furnace. The temperature uniformity in the effective heating zone of the tempering furnace is controlled within ±5℃. The tempering temperature is set to 250℃ and the holding time is set to 150min. After tempering, the workpiece is taken out and naturally cooled to room temperature in still air. This process is used to eliminate the local micro-stress concentration caused by overload pre-torsion and reduce the probability of micro-crack initiation in the weld area and heat-affected zone. (5) Fix the hollow stabilizer rod after low temperature tempering to the ultrasonic impact processing station. Use 1.0MPa high pressure compressed air to repeatedly blow the inner cavity from one end of the rod to the other end 5 times to remove the loose oxide scale and particulate impurities generated on the inner wall during the tempering and quenching process. Then use a flexible guide rod with the same length as the rod to pull the non-woven cloth roll soaked in anhydrous ethanol to wipe the inner wall once. After wiping, blow the inner wall dry again with high pressure air to ensure that the inner cavity surface is dry and free of residual liquid. (6) Turn on the ultrasonic shock generator. Set the working frequency of the ultrasonic shock generator to 20kHz, the output current adjustment range to 6A, and the axial mechanical amplitude of the ultrasonic shock pin to 0.05mm. The shock pin is made of tungsten cobalt hard alloy and the radius of the shock pin tip arc is 1.5mm. Install the shock pin on the front end of the flexible guide rod and extend the flexible guide rod into the inner cavity from the end of the rod body. The outer diameter of the flexible guide rod is 4mm smaller than the inner diameter of the hollow stabilizing rod to ensure a single-sided gap of 2mm. The flexible guide rod is pushed axially along the inner cavity so that the shock pin passes through the inner wall of the straight section and the bend in sequence. For the inner wall of the inner arc side of the corner section, the contact pressure between the impact pin and the inner wall surface is controlled at 200N, the axial feed speed of the flexible guide rod is controlled at 300mm / min, the overlap rate between two adjacent impact paths is controlled at 60%, the dwell time of the impact pin on the inner arc side of the corner section is extended to 1.5 times the dwell time of the straight section, and when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight section and the dwell time in this local area is extended to 2 times that of the straight section, in order to compensate for the influence of the hardness difference in the weld area on the uniformity of the strengthening effect; (7) Place the hollow stabilizer bar that has been treated as described above at the testing station and use magnetic particle testing to check whether there are cracks or defects on the inner and outer surfaces of the bar. Use a residual stress tester to check whether the residual stress values ​​at specified positions on the outer and inner walls of the bar meet the design requirements. After passing the test, the bar is transferred to the finished product packaging process.

[0030] Comparative Example 1 The difference between Comparative Example 1 and Example 3 is that step (2) is omitted. Step (2) is deleted, and "pre-twisted" in step (3) is changed to "tempered state". "Eliminate overload pre-twisting" in step (4) is changed to "Eliminate tempering". Comparative Example 1 is used to examine the individual strengthening effect of ultrasonic impact without overload pre-twisting, so the ultrasonic impact parameters are kept the same as those in Example 3.

[0031] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that step (4) is omitted. Step (5) is performed directly after step (3). In step (5), "after low temperature tempering" is changed to "after pre-twisting and cleaning". In step (6), "eliminating local micro-stress concentration caused by overload pre-twisting and reducing the probability of micro-crack initiation in weld area and heat-affected zone" is deleted. The remaining steps are the same as in Example 3.

[0032] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is that step (6) is omitted. After step (5) is completed, the process jumps directly to step (7), and the description of the pre-processing in step (7) is modified accordingly. In step (7), "the process that has been treated as described above" is changed to "the process that has been pre-twisted, cleaned and tempered at low temperature". The remaining steps are the same as in Example 3.

[0033] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is that the equivalent torque applied in step (2) is controlled at 115% of the torque value corresponding to the yield limit of the workpiece, the torsion rate is controlled at 15° / min, and the load is maintained for 60s after the torsion angle reaches the preset angle; the remaining steps are the same as in Example 3.

[0034] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is that the equivalent torque applied in step (2) is controlled at 102% of the torque value corresponding to the yield limit of the workpiece, the torsion rate is controlled at 5° / min, and the load is maintained for 20s after the torsion angle reaches the preset angle; the remaining steps are the same as in Example 3.

[0035] Comparative Example 6 The difference between Comparative Example 6 and Example 3 is that the tempering temperature in step (4) is set to 320°C and the holding time is set to 180 min; the other steps are the same as in Example 3.

[0036] Comparative Example 7 The difference between Comparative Example 7 and Example 3 is that the tempering temperature in step (4) is set to 120°C and the holding time is set to 60 min; the other steps are the same as in Example 3.

[0037] Comparative Example 8 The difference between Comparative Example 8 and Example 3 is that in step (6), the output current adjustment range of the ultrasonic impact generator is 8A, the axial mechanical amplitude of the ultrasonic impact needle is set to 0.08mm, and the axial feed speed of the flexible guide rod is controlled at 80mm / min; the remaining steps are the same as in Example 3.

[0038] Comparative Example 9 The difference between Comparative Example 9 and Example 3 is that in step (6), the output current adjustment range of the ultrasonic impact generator is 1.5A, the axial mechanical amplitude of the ultrasonic impact needle is set to 0.01mm, and the axial feed speed of the flexible guide rod is controlled at 400mm / min; the remaining steps are the same as in Example 3.

[0039] Comparative Example 10 The difference between Comparative Example 10 and Example 3 is that in step (6), when the impact pin passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod does not decrease and the dwell time does not increase, that is, the feed speed is always kept at 200mm / min, and the dwell time of the straight section is the same as that of the weld area; the rest of the steps are the same as in Example 3.

[0040] Example of effect Tables 1 and 2 below show the performance analysis results of a fatigue-resistant alloy steel for a hollow stabilizer bar of an automobile, using Examples 1 to 5 and Comparative Examples 1 to 10 of the present invention.

[0041] Table 1

[0042] Table 2

[0043] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No markings in the claims should be construed as limiting the scope of the claims.

Claims

1. A fatigue-resistant alloy steel for automotive hollow stabilizer bars, characterized in that, Includes the following steps: (1) Prepare a quenched and tempered hollow stabilizer bar workpiece. The workpiece is made of 42 chromium molybdenum steel or 50 chromium vanadium steel through smelting, hot rolling, forming, welding and quenching and tempering. The microstructure is tempered sorbite, the Rockwell hardness is 38-42, and the yield strength is 800MPa-1000MPa. (2) Implement the overload pre-torsion process, clamp both ends of the heat-treated hollow stabilizer bar onto the torsion loading device, apply a unidirectional ultimate torsion load at room temperature, the applied equivalent torque is 105%-109% of the torque value corresponding to the yield limit of the workpiece, the torsion rate is 5° / min-15° / min, after reaching the preset torsion angle, maintain the load for 30s-60s, remove the load to allow the bar to elastically recover, so that a uniform residual compressive stress field is formed in the entire cross section of the bar; (3) After the pre-twist cleaning process, the outer surface of the rod body is sprayed with industrial hydrocarbon cleaning agent, and the inner hole is blown with compressed air to remove oil and metal debris. (4) Implement a low-temperature tempering process. Place the cleaned hollow stabilizer into the tempering furnace and keep it at 180℃-250℃ for 90min-150min. After taking it out, let it cool naturally to room temperature in still air. (5) Implement the internal cavity blowing and cleaning process, use high pressure compressed air to repeatedly blow the internal cavity, and then use a flexible guide rod to pull the non-woven cloth soaked in anhydrous ethanol to wipe the inner wall and blow dry the surface of the internal cavity. (6) Implement the ultrasonic impact process on the inner wall, install the impact needle on the front end of the flexible guide rod and extend it into the inner cavity, and push it along the inner cavity axis to perform high-frequency mechanical impact on the inner wall of the straight section and the inner arc side of the curved section. After the impact, a residual compressive stress layer with a depth of 1.5mm is formed on the metal surface. (7) Implement the final inspection process, use magnetic particle testing to detect whether there are cracks or defects on the inner and outer surfaces of the pole body, use a residual stress tester to detect whether the residual stress value meets the design requirements, and after passing the inspection, transfer to the finished product packaging process.

2. The fatigue-resistant alloy steel for a hollow automotive stabilizer bar according to claim 1, characterized in that, The weld formed in step (1) is located on the outside of the bend section of the rod or at the longitudinal joint of the tube. After welding, the weld reinforcement is controlled at 0.3mm-0.5mm by grinding process, and the heat-affected zone width is controlled at 3mm-5mm.

3. The fatigue-resistant alloy steel for a hollow automotive stabilizer bar according to claim 1, characterized in that, In step (2), the torsional loading device applies torsional load using a dual control method with torsion angle as the main control parameter and torque monitoring as a supplement. The preset torsion angle is calculated in advance based on the measured value of the torsional stiffness of the batch of workpieces.

4. The fatigue-resistant alloy steel for a hollow automotive stabilizer bar according to claim 1, characterized in that, The residual compressive stress field formed by the overload pre-torsion in step (2) simultaneously covers the outer and inner walls of the rod and includes the surface of the weld area.

5. The fatigue-resistant alloy steel for a hollow stabilizer bar in automobiles according to claim 1, characterized in that, In step (4), the temperature uniformity within the effective heating zone of the tempering furnace is controlled within ±5℃.

6. The fatigue-resistant alloy steel for a hollow stabilizer bar in automobiles according to claim 1, characterized in that, In step (6), the ultrasonic shock generator operates at a frequency of 20kHz, outputs a current of 3A-6A, has an axial mechanical amplitude of 0.02mm-0.05mm, is made of tungsten-cobalt hard alloy, and has a tip radius of 0.5mm-1.5mm.

7. The fatigue-resistant alloy steel for a hollow stabilizer bar in automobiles according to claim 1, characterized in that, In step (6), the outer diameter of the flexible guide rod is 2mm-4mm smaller than the inner diameter of the hollow stabilizer rod, the contact pressure between the impact pin and the inner wall surface is 100N-200N, the axial feed speed of the flexible guide rod is 100mm / min-300mm / min, and the overlap rate between two adjacent impact paths is 40%-60%.

8. The fatigue-resistant alloy steel for a hollow automotive stabilizer bar according to claim 1, characterized in that, In step (6), the dwell time of the impact needle on the inner arc side of the bend is extended to 1.5 times the dwell time of the straight section.

9. The fatigue-resistant alloy steel for a hollow stabilizer bar in automobiles according to claim 1, characterized in that, In step (6), when the impact needle passes through the inner wall part corresponding to the weld area, the feed speed of the flexible guide rod is reduced to 0.7 times the speed of the straight section and the dwell time in this local area is extended to 2 times that of the straight section.

10. The fatigue-resistant alloy steel for a hollow stabilizer bar in automobiles according to claim 1, characterized in that, The residual compressive stress layer formed in step (6) and the full-section residual compressive stress field formed in step (2) are superimposed to ensure that there is no concentrated area of ​​residual tensile stress on the entire cross-section of the hollow rod.

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