汽车螺旋悬架弹簧用钢55SiCrA组织和性能研究

Study on Microstructures and Properties of 55SiCrA Steel Used for Coil Springs of Automotive Suspension System

采用热膨胀法结合显微金相与硬度法,在LINSEIS L78 RITA相变仪上测定了55Si Cr A弹簧钢的临界点温度和连续冷却转变曲线,研究了冷却速度对组织和硬度的影响规律。在此基础上,进行了控轧控冷工业试验。结果表明,当冷速≤2℃/s时,转变产物为少量铁素体、珠光体,珠光体硬度随冷速增大而增大;当冷速≥5℃/s时,转变产物为珠光体、马氏体;当冷速≥20℃/s时,转变产物为马氏体,硬度随冷速增大而增大;现场控轧控冷的试验钢抗拉强度达到1 163 MPa,伸长率为13%,面缩率为49%,综合力学性能良好,满足了用户的使用要求。

By the thermal expansion method, metalloscopy method and hardness method the temperature of the 55SiCrA spring steel at critical points and its continuous cooling transformation curves （CCT） was measured on LINSEIS L78 RITA. The laws of effect of cooling rates on microstructures and hardness of the steel were studied. Based on the studies the industrial test on the thermo mechanical control process （TMCP） was carried out. The test results show that the resultants by transformation include a little bit of ferrite and pearlite as the cooling rate is less than or equal to 2 ℃/s and the hardness of pearlite increases with the increasement of the cooling rate. But the resultants by transformation turn into martensite and pearlite as the cooling rate is more than or equal to 5℃/s and the resultants by transformation turn into martensite as the cooling rate is more than or equal to 20 ℃/s and the hardness of martensite increases with the increasement of the cooling rate. The tensile strength of tested steel produced by the TMCP process on site is 1 163 MPa, the elongation rate is 13% and the reduction of area is 49%, all of which means that its comprehensive mechanical properties are good enough to meet the requirements asked by consumers.