Views: 0 Author: Site Editor Publish Time: 2022-07-27 Origin: Site
Although the consumption of steel materials has decreased year by year, the consumption of high-strength steel has increased considerably.
The most effective way to lighten the weight of suspension spring is to improve the design allowable stress of spring. However, in order to achieve this lightweight under high stress, the high strength of materials is indispensable. Based on the traditional Si Mn spring steel, by reducing C and adding Ni, Cr, Mo, V and other alloy elements, a steel with high strength and toughness is developed, and the design allowable stress can reach 1270mpa. The application of this spring steel can achieve 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 used for valve spring to ensure toughness through grain refinement, and the strength is improved by increasing C. After this improvement, the high cycle fatigue strength of the spring is increased by about 8%, and 15% lightweight can be achieved. Through finite element analysis, the lemon shaped cross-section spring steel wire with uniform stress distribution on the inner and outer sides of the coil spring can be developed, so that the spring can achieve 7% lightweight.
The effective way to improve the fatigue strength of springs is shot peening and nitriding. In addition to the traditional stress peening, two-stage peening has been developed for spring peening. Shot peening and nitriding can also be combined.
The automobile engine has the trend of high power, while the driver has the tendency of compact and miniaturization. This is bound to increase the load of the transmission gear, so the requirements for the bending fatigue strength and contact fatigue strength of the gear steel are also correspondingly increased.
Increasing the content of Ni, Cr, Mo and other alloy elements in steel can improve the hardenability and strength of gear steel, but strengthening gear steel by alloy elements alone will deteriorate the cutting performance of steel, complicate the heat treatment process, and greatly increase the cost of raw materials and production costs. During gear carburizing, in order to prevent or reduce the appearance of abnormal layer and reduce the content of Si and P in steel, the amount of Mo is increased to 0.35% - 0.45%, and the improved carbonitriding process is adopted. The improved steel grade can increase the impact life of the gear by 3~5 times. If the steel grade with the above reduced surface abnormal layer is added with strong shot blasting, the fatigue limit of the gear 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, the bending fatigue life of gear root is increased by 10% - 17% and the contact fatigue life is increased by 25% compared with the low Si high Mo steel that reduces the surface abnormal layer mentioned above.