(1) Spring?
The most effective way to reduce the weight of suspension spring is to increase the allowable design stress of spring. However, in order to realize this lightweight under high stress, high-strength materials are essential. On the basis of traditional Si-Mn spring steel, a steel with high strength and toughness was developed by reducing carbon content and adding alloying elements such as nickel, chromium, molybdenum and vanadium. The allowable design stress can reach 1270MPa, and the application of this spring steel can realize 40% lightweight. Adding Nb to the traditional Cr-V spring steel can improve the delayed fracture resistance of the steel. Combined with the improved austenite rolling forming, the tensile strength of the steel can reach the level of 1800MPa. ?
V is added to Si-Cr steel for valve spring, and toughness is ensured by grain refinement, and strength is improved by adding C. After this improvement, the high cycle fatigue strength of spring is increased by about 8%, and the weight loss can be reduced by 15%. Through finite element analysis, the lemon-shaped cross-section spring steel wire with uniform internal and external stress distribution is developed, which makes the spring realize 7% lightweight. The effective methods to improve the fatigue strength of springs are shot peening and nitriding. In addition to the traditional stress shot peening, two-stage shot peening has developed into spring shot peening. Shot peening and nitriding can also be used in combination. ?
(2) gear?
Automobile engines tend to have high power, while transmissions tend to be compact and miniaturized. This is bound to increase the load of transmission gear, so the requirements for bending fatigue strength and contact fatigue strength of gear steel are also improved accordingly.
Increasing the content of Ni, Cr, Mo and other alloying elements in steel can improve the hardenability and strength of gear steel, but only strengthening gear steel with alloying elements will make the machinability of steel worse, the heat treatment process is complicated, and the raw material cost and production cost will be greatly increased. In order to prevent or reduce the appearance of abnormal layer and reduce the content of Si and P in steel, the content of Mo was increased to 0.35%~0.45% during gear carburizing, and an improved carbonitriding process was adopted. The improved steel grade can increase the impact life of gears by 3~5 times. If strong shot peening is added to the steel grade to reduce the abnormal surface layer, the fatigue limit of gears can be increased by 20%~30%.
Non-metallic inclusions in gear steel are the starting point of fatigue cracks, which will reduce the strengthening effect of strong shot peening. Therefore, high-purity gear steel has been developed. For example, for SCM420HZ steel, when the oxygen concentration is reduced below 9ppm and the phosphorus concentration is reduced below 90ppm, compared with low Si and high Mo steel, the gear tooth root bending fatigue life is increased by 10%~ 17%, the contact fatigue life is increased by 25%, and the abnormal surface layer is reduced.
Million car purchase subsidy