CN114134291A - Method for prolonging fatigue life of high-strength variable-cross-section transverse plate spring - Google Patents
Method for prolonging fatigue life of high-strength variable-cross-section transverse plate spring Download PDFInfo
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- CN114134291A CN114134291A CN202111454576.1A CN202111454576A CN114134291A CN 114134291 A CN114134291 A CN 114134291A CN 202111454576 A CN202111454576 A CN 202111454576A CN 114134291 A CN114134291 A CN 114134291A
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Abstract
The invention discloses a method for prolonging the fatigue life of a high-strength variable-section transverse plate spring, which comprises the following steps of carrying out stress surface grinding and cold rolling on the high-strength variable-section plate spring after flaw detection of flat steel produced by a steel mill is qualified and before variable-section rolling, and specifically comprising the following steps of: s1: cutting the flat steel into required length, selecting the surface with better surface quality of the flat steel as a stress surface, and removing impurities on the stress surface; s2: polishing the stress surface to expose the internal metal, wherein the polishing depth is 1-3mm, and the polished surface has no obvious fluctuation and step; s3: cold rolling the polished flat steel by using a rolling mill, wherein the pressing height is 0.5-1 mm; wherein, the stress surface is used as a concave surface for bearing tensile stress after variable cross-section rolling and during service. After the method is used, the fatigue life of the plate spring bench test is obviously prolonged, and the fluctuation of the fatigue life is obviously reduced.
Description
Technical Field
The invention belongs to the technical field of steel materials, relates to a manufacturing method of a variable cross-section transverse plate spring, and particularly relates to a method for prolonging the fatigue life of a high-strength variable cross-section transverse plate spring.
Background
The transverse leaf spring is an important component of a suspension system for a vehicle such as a commercial vehicle. With the increasing demand for lighter weight of automobiles, the horizontal plate spring is developed toward a few leaf springs with high stress and variable cross sections. With the improvement of the load stress of the few-leaf spring in service, the problems of low fatigue life and large life fluctuation are gradually exposed. The higher the material strength, the greater the susceptibility of the fatigue life to defects, and slight fluctuations in the mass of the leaf spring can lead to a significant reduction in the fatigue life of the leaf spring. The 60Si2CrVAT is a typical mark of the prior high-strength variable-section less leaf spring, the tensile strength after heat treatment can reach 1800MPa, and the alternating load borne during service can reach more than 900 MPa.
Surface quality is an important factor affecting the fatigue life of leaf springs. Defects such as decarburization and microcrack on the stress surface of the plate spring tend to become a fatigue source, and the fatigue life is reduced. Shot blasting is a common method for improving the surface quality, and fine steel shots are used for blasting the surface of the plate spring at a high speed, so that the surface quality of the plate spring can be improved, the surface strength is improved, the surface is in a compressive stress state, and the fatigue life of the plate spring is prolonged. However, when the surface of the plate spring is uneven, the side walls of the dimples left after the steel shots hit the surface of the plate spring may be folded finely by the impact of the subsequent steel shots. Low tensile strength leaf springs are not sensitive to such micro-scale folding, but the fatigue life of high stress leaf springs may be significantly reduced upon such folding.
The variable cross-section transverse plate spring is made of flat steel produced by a steel mill through the processes of variable cross-section rolling, heat treatment, stress shot blasting, electrophoresis and the like. Due to the limitation of shape, the flat steel cannot be scalped before leaving the factory, and the surface has large height fluctuation. If the quality of the casting blank or the roller is not good, the surface defects of the flat steel are more. The deformation of each part of the billet is different during variable cross-section rolling, and the inconsistent deformation further increases the undulation degree of the surface of the plate spring. This becomes an important factor affecting the fatigue life stability of the high stress variable cross section plate spring.
Disclosure of Invention
The invention aims to provide a method for improving the fatigue life and the fatigue life stability of a plate spring by reducing the surface undulation degree of flat steel aiming at the problem of large fatigue life fluctuation of a high-stress variable-section transverse plate spring. The method for polishing and cold rolling the stress surface before the flat steel variable cross-section rolling is utilized to improve the surface quality of the stress surface of the plate spring before stress shot blasting, avoid shot blasting folding, and further improve the fatigue life and fatigue life stability of the plate spring.
In order to achieve the above object, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section horizontal plate spring, wherein the plate spring is made of flat steel produced by a steel mill through the steps of variable cross-section rolling, heat treatment, stress peening and electrophoresis, and the method of the present invention has the following characteristics: to high strength variable cross section leaf spring, after the band steel that the steel mill produced is detected a flaw qualified, before carrying out variable cross section rolling, carry out stress surface and polish and cold roll-in, concrete step is:
s1: cutting the flat steel into required length, selecting the surface with better surface quality of the flat steel as a stress surface, and removing impurities on the stress surface;
s2: polishing the stress surface to expose the internal metal, wherein the polishing depth is 1-3mm, and the polished surface has no obvious fluctuation and step;
s3: cold rolling the polished flat steel by using a rolling mill, wherein the pressing height is 0.5-1 mm;
wherein, the stress surface is used as a concave surface for bearing tensile stress after variable cross-section rolling and during service.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: the high-strength variable cross-section plate spring is a plate spring with the tensile strength of more than 1800MPa and the maximum alternating stress of more than 900MPa in service after quenching and tempering heat treatment.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: wherein the qualified flaw detection standard of the flat steel is as follows: there were no cracks or folds at the surface with a depth exceeding 2 mm.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: wherein the heat treatment is quenching and tempering heat treatment.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: the flat steel after polishing and cold rolling is heated and rolled with variable cross section, the polished surface (i.e. stress surface) is rolled to form the concave surface of the plate spring, the plate spring with variable cross section is heated at 850-950 ℃, oil quenched, tempered at 450-550 ℃, air cooled and stress shot-blasted.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: wherein the shot blasting prestress is more than 800MPa, and the shot blasting strength is more than 0.2; and (5) carrying out electrophoresis drying after shot blasting cleaning.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: in S2, the specific polishing method comprises the following steps: fixing the flat steel with the stress surface facing upwards, and using a grinding wheel machine to remove oxide skin and a small amount of metal on the stress surface to expose the metal inside.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: wherein, in S1, the way of cutting the flat steel into length is cold break.
Further, the present invention provides a method for improving the fatigue life of a high-strength variable cross-section transverse leaf spring, which may further have the following features: the high-strength variable cross-section plate spring comprises the following chemical components in percentage by mass: c: 0.56-0.64%, Si: 1.40-1.70%, Mn: 0.40-0.70%, S: < 0.03%, P: < 0.03%, Cr: 0.90-1.20%, V: 0.20 to 0.25%, Ni: < 0.30%, Cu: < 0.20%, the balance being Fe and unavoidable impurities.
The processing method is designed for the high-strength variable cross-section plate spring. The strength of the stress surface of the common plate spring is improved after shot blasting or stress shot blasting, the common plate spring is in a compressive stress state, insensitive to tiny folding caused by shot blasting, and stable and high in fatigue life. And the high-stress plate spring is very sensitive to shot blasting folding due to high strength, strong crack sensitivity and large alternating stress in service. But it is very difficult to ensure the stress surface to be flat and free of defects before shot blasting. Firstly, the flat steel produced by a steel mill cannot be scalped, and the thickness of each position of a plate spring is different after the flat steel is rolled with a variable cross section, and the whole plate spring is arched, so that the stress surface can be processed only before the rolling with the variable cross section, but the traditional surface processing mode is very limited due to the shape limitation of the flat steel. The specific grinding and cold rolling of the invention can remove oxide skin with different thickness of the flat steel stress surface, so as to flatten the metal surface, and can also remove possible defects of micro cracks, micro folds and the like of the flat steel stress surface, thereby obviously reducing the probability of shot blasting folding and other surface defects and improving the fatigue life of the plate spring.
It should be noted that the method of the present invention places definite requirements on the polishing position and the polishing method. When in service, only one surface of the variable cross-section plate spring can bear large alternating tensile stress. Therefore, the side with better surface quality of the flat steel is selected for polishing, the workload is reduced, and the requirement for placing the flat steel in the subsequent variable cross-section rolling is provided. The stress surface is polished by a grinder for 1-3mm to remove oxide skin and possible defects, and meanwhile, the flatness of the polished surface is an important technical guarantee that micro-folding is not generated during shot blasting. After polishing, cold rolling can further improve the flatness of the stressed surface and remove polishing burrs, so that a small amount of un-peeled burrs are oxidized and peeled off during variable cross-section rolling and heating, and are not rolled into a plate spring to form folding.
Specifically, firstly, after the steel sheet is polished by a grinding machine, the surface flatness of the steel sheet is improved, and the defects of uneven oxide skin on the surface of the steel sheet, potential microcracks, folding and the like on the surface are overcome. But the grinder still produces a slight step at the seam, with the risk of forming a slight fold in the subsequent variable cross-section rolling. The cold rolling process is carried out, so that the steps can be flattened, and the possible micro folding at the edges of the steps can generate obvious work hardening and even fracture with the matrix, and further the steps are peeled off after rolling or oxidized and peeled off during variable cross-section rolling and heating. Secondly, the side of the flat steel is arc-shaped and cannot be polished. However, since the surface irregularities of the flat steel side surface are more pronounced and the irregularities are more pronounced as the flat steel side surface approaches the flat surface, severe undulations at the boundary between the arc edge and the stress surface or folds formed after shot blasting also become fatigue fracture source regions after the final plate spring is rolled. After the polishing and the cold rolling, the most severe shape sudden change at the junction of the flat steel can be removed or the rolling is gentle, so that the surface quality of the transition of the stress surface and the arc surface is obviously improved, the quality of the junction of the arc edge and the stress surface of the plate spring is further improved, and the fatigue life is prolonged.
In addition, the method of the invention puts clear requirements on the variable cross-section rolling, the heat treatment and the stress peening process. The variable cross-section rolling and quenching and tempering heat treatment process is to ensure the shape and basic mechanical property of the plate spring. Different from common variable cross-section rolling, the invention needs to roll the polished stress surface into a concave surface to ensure the polishing and cold rolling effect. The strength level of the plate spring is ensured by the limit of quenching and tempering temperature and cooling medium. The stress shot blasting process is to perform shot blasting on the plate spring under the condition of bearing tensile stress, after external stress is removed, the compressive stress and the pre-stress caused by the shot blasting on the stress surface are superposed to generate larger compressive stress, so that the difficulty of fatigue crack initiation in the service process of the stress surface is further improved, and the fatigue life of the plate spring is prolonged. The stress surface after polishing and cold rolling is smoother, the defects are fewer, and the probability of micro-folding generated during stress shot blasting is obviously reduced, so that the fatigue life and the fatigue life stability of the plate spring are obviously improved.
The invention has the beneficial effects that:
the method improves the flatness of the stress surface of the plate spring before stress shot blasting through grinding and cold rolling, reduces the number of surface defects, improves the strength and the compressive stress of the stress surface after stress shot blasting, obviously reduces micro-folding caused by shot blasting, and finally obviously improves the fatigue life and the fatigue life stability of the plate spring;
the invention solves the problem that the flat steel produced by a steel mill cannot be scalped, and the surface of the plate spring cannot be polished in batch after variable cross-section rolling, so that the performance of the plate spring is influenced, and the surface quality and the service safety of the plate spring are improved on the basis of not greatly improving the cost.
Drawings
FIG. 1 is a metallographic structure of a stress surface of a plate spring with a fatigue life of 3.04 ten thousand times in comparative example 1 of the present invention;
FIG. 2 is a metallographic structure of a stress surface of a plate spring with a fatigue life of 3.96 ten thousand times in comparative example 1 of the present invention;
FIG. 3 is a metallographic structure of a stress surface of a plate spring of comparative example 1 of the present invention, which has a fatigue life of 10.45 ten thousand cycles near a fracture;
FIG. 4 shows the metallographic morphology of the boundary between the side edge and the stressed surface of the leaf spring with a fatigue life of 3.04 ten thousand times in comparative example 1 of the present invention;
FIG. 5 shows the metallographic morphology of the stress surface of the plate spring with the fatigue life of 22.55 ten thousand times in the vicinity of the fracture in example 1 of the invention;
FIG. 6 shows the metallographic morphology of the stress surface of the plate spring in the vicinity of the fracture, the fatigue life of which is 26.20 ten thousand times in example 2 of the invention;
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention and the accompanying drawings, and it is obvious that the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention. The conditions not specified in the examples are generally those in routine experiments.
Comparative example 1
The flat steel for producing the high-strength variable cross-section plate spring comprises the following chemical components in percentage by mass: 0.60% of C, 1.50% of Si, 0.50% of Mn, 0.010% of P, 0.020% of S, 1.10% of Cr, 0.22% of V, 0.10% of Ni and 0.10% of Cu, and the balance of Fe and inevitable impurities. After flaw detection is qualified, the flat steel is directly rolled with a variable cross section without polishing and the like, then is subjected to heat preservation and oil quenching at 920 ℃, tempering and air cooling at 500 ℃, stress shot blasting of a stress surface is prestressed at 900MPa, the shot blasting strength is 0.3, and after shot blasting cleaning, electrophoresis drying is carried out.
The test of the bench test shows that the alternating stress amplitude of the root part of the plate spring is 950 MPa. The fatigue life of the 3 support plate springs under the same process is respectively as follows: 3.04 ten thousand times, 3.96 ten thousand times and 10.45 ten thousand times. The fatigue life is entirely low and the fatigue life fluctuation is large.
3 the appearance of the stress surface near the fracture of the support plate spring after shot blasting is respectively shown in figures 1-3, and the microscopic appearance of the junction of the side edge of the plate spring with the fatigue life of 3.04 ten thousand times and the stress surface is shown in figure 4. The side surfaces of the plate spring shot-blasting pits with fatigue life of 3.04 ten thousand times and 3.96 ten thousand times and the junctions of the side edges and the stress surfaces of the plate springs are all found with micro-folds, while the side surfaces of the plate spring shot-blasting pits with fatigue life of 10.45 ten thousand times are not found with micro-folds. It is explained that the micro-folding by shot blasting is a cause of a significant reduction in the fatigue life of the leaf spring.
Example 1
The flat steel for producing the high-strength variable cross-section plate spring comprises the following chemical components in percentage by mass: 0.58% of C, 1.45% of Si, 0.55% of Mn, 0.010% of P, 0.020% of S, 1.20% of Cr, 0.24% of V, 0.11% of Ni and 0.11Cu, and the balance of Fe and inevitable impurities. After flaw detection of the flat steel is qualified, grinding and cold rolling are carried out, then variable cross section rolling is carried out, then 900 ℃ heat preservation oil quenching and 500 ℃ tempering air cooling are carried out, stress shot blasting with stress of 900MPa and shot blasting strength of 0.3 are carried out on the stress surface, and electrophoresis drying is carried out after shot blasting cleaning.
The stress surface polishing and cold rolling method comprises the following specific steps:
s1: cold breaking the flat steel into required length, selecting the surface with better surface quality of the flat steel as a stress surface, and removing impurities on the stress surface;
s2: fixing the flat steel with the stress surface facing upwards, using a grinding machine to remove oxide skin and a small amount of metal on the stress surface, exposing the internal metal, and grinding the surface to a depth of 1-2mm without obvious fluctuation and steps after grinding;
s3: and (5) carrying out cold rolling on the polished flat steel by using a rolling mill, wherein the pressing height is 0.8 mm.
The test of the bench test shows that the alternating stress amplitude of the root part of the plate spring is 950 MPa. The fatigue life of the 3 support plate springs under the same process is respectively as follows: 22.55, 20.36 and 23.11 million times. The fatigue life is long and stable.
The appearance of the stress surface near the fracture of the plate spring after shot blasting is shown in figure 5, wherein the fatigue life of the stress surface is 22.55 ten thousand times. No micro-folding is found on the side surface of the shot blasting pit of the stress surface near the fracture of the plate spring. The grinding and cold rolling before variable cross-section rolling have obvious effect on improving the fatigue life.
Example 2
The flat steel for producing the high-strength variable cross-section plate spring comprises the following chemical components in percentage by mass: 0.62% of C, 1.60% of Si, 0.65% of Mn, 0.010% of P, 0.020% of S, 0.95% of Cr, 0.20% of V, 0.25% of Ni and 0.13Cu, and the balance of Fe and inevitable impurities. After flaw detection is qualified, the flat steel is polished, cold rolled and then subjected to variable cross section rolling, then thermal insulation oil quenching at 940 ℃, tempering air cooling at 500 ℃, stress shot blasting with stress surface stress of 900MPa and shot blasting strength of 0.3 are performed, and after shot blasting cleaning, electrophoresis drying is performed.
The stress surface polishing and cold rolling method comprises the following specific steps:
s1: cold breaking the flat steel into required length, selecting the surface with better surface quality of the flat steel as a stress surface, and removing impurities on the stress surface;
s2: fixing the flat steel with the stress surface facing upwards, using a grinding machine to remove oxide skin and a small amount of metal on the stress surface, exposing the internal metal, and grinding the surface to a depth of 1.5-2.5mm without obvious fluctuation and steps after grinding;
s3: and (5) carrying out cold rolling on the polished flat steel by using a rolling mill, wherein the pressing height is 0.5 mm.
The test of the bench test shows that the alternating stress amplitude of the root part of the plate spring is 950 MPa. The fatigue life of the 3 support plate springs under the same process is respectively as follows: 26.20, 24.75 and 25.92 million times. The fatigue life is long and stable.
The fatigue life is 26.20 ten thousand times, and the appearance of the stress surface near the fracture of the plate spring after shot blasting is shown in figure 6. No micro-folding is found on the side surface of the shot blasting pit of the stress surface near the fracture of the plate spring. The grinding and cold rolling before variable cross-section rolling have obvious effect on improving the fatigue life.
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments, and all technical solutions belonging to the idea of the present invention belong to the protection scope of the present invention, it should be noted that, for those skilled in the art, several modifications and decorations without departing from the principle of the present invention should be regarded as the protection scope of the present invention.
Claims (9)
1. A method for improving the fatigue life of a high-strength variable-section transverse plate spring is characterized in that the plate spring is made of flat steel through the working procedures of variable-section rolling, heat treatment, stress shot blasting and electrophoresis, and is characterized in that:
aiming at the high-strength variable-section plate spring, after flaw detection of the flat steel is qualified, before variable-section rolling, stress surface polishing and cold rolling are carried out, and the method specifically comprises the following steps:
s1: cutting the flat steel into required length, selecting the surface with better surface quality of the flat steel as a stress surface, and removing impurities on the stress surface;
s2: polishing the stress surface to expose the internal metal, wherein the polishing depth is 1-3mm, and the polished surface has no obvious fluctuation and step;
s3: cold rolling the polished flat steel, wherein the rolling height is 0.5-1 mm;
wherein, the stress surface is used as a concave surface for bearing tensile stress after variable cross-section rolling and during service.
2. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
the high-strength variable cross-section plate spring is a plate spring with the tensile strength of more than 1800MPa and the maximum alternating stress of more than 900MPa in service after quenching and tempering heat treatment.
3. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
wherein the qualified flaw detection standard of the flat steel is as follows: there were no cracks or folds at the surface with a depth exceeding 2 mm.
4. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
wherein the heat treatment is quenching and tempering heat treatment.
5. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 4, wherein:
wherein, the flat steel after polishing and cold rolling is heated and rolled with variable cross section, the polished surface is rolled into a concave surface of the plate spring, the plate spring with variable cross section is heated at 850-950 ℃, oil quenched, tempered at 450-550 ℃, air cooled and then stress shot-blasted.
6. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 5, wherein:
wherein the shot blasting prestress is more than 800MPa, and the shot blasting strength is more than 0.2; and (5) carrying out electrophoresis drying after shot blasting cleaning.
7. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
in S2, the specific polishing method comprises the following steps: fixing the flat steel with the stress surface facing upwards, and using a grinding wheel machine to remove oxide skin and a small amount of metal on the stress surface to expose the metal inside.
8. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
wherein, in S1, the mode of cutting the flat steel into the required length is cold breaking.
9. The method of improving the fatigue life of a high strength variable cross section transverse leaf spring according to claim 1, wherein:
the high-strength variable cross-section plate spring comprises the following chemical components in percentage by mass: c: 0.56-0.64%, Si: 1.40-1.70%, Mn: 0.40-0.70%, S: < 0.03%, P: < 0.03%, Cr: 0.90-1.20%, V: 0.20 to 0.25%, Ni: < 0.30%, Cu: < 0.20%, the balance being Fe and unavoidable impurities.
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