微合金中碳钢48MnV曲轴连杆轴颈感应淬火工艺的优化

Induction hardening process optimization of microalloyed medium carbon steel 48MnV for crankshaft connecting rod journal

采用对比试验法,以淬火功率、回火条件、加热时间、冷却时间等作为变量,研究了微合金中碳钢48MnV曲轴连杆轴颈感应热处理的最佳工艺。结果表明,优化的感应热处理工艺为淬火功率165 kW,电流频率9 kHz,加热时间17 s,冷却间隔时间1 s,冷却时间20 s, 210℃回火2.5 h。在优化的感应热处理工艺下,连杆轴颈淬硬层显微组织为细小均匀针状马氏体;轴颈表面、两侧过渡圆角距表面0.25 mm处的最高硬度依次可达720.9、690.0和667.1 HV,耐磨性显著提高;连杆轴颈、过渡圆角表面残余应力呈现为压应力,靠芯轴端过渡圆角残余应力高达-884.0 MPa,靠法兰端过渡圆角残余应力为-831.9 MPa;试样的疲劳极限载荷最高,高达3750 N·m。感应热处理后残余压应力越大,越有利于提高曲轴连杆轴颈的弯曲疲劳强度。

Optimum process of induction heat treatment of microalloyed medium carbon steel 48MnV crankshaft connecting rod journal was studied by means of contrast test with quenching energy, tempering conditions, heating time and cooling time as variables. The results show that the optimized induction heat treatment process consists of quenching power of 165 kW, current frequency of 9 kHz, heating time of 17 s, cooling interval time of 1 s, cooling time of 20 s, and tempering at 210 ℃ for 2.5 h. Under the optimized induction heat treatment process, the microstructure of the hardened layer of connecting rod journal is fine and uniform acicular martensite;the maximum hardness of the journal surface and the position 0.25 mm from the surface of fillet on both sides can reach 720.9, 690.0 and 667.1 HV, respectively, and the wear resistance is significantly improved;the residual stress on the surface of connecting rod journal and fillet is compressive stress, the residual stress of the transition fillet near the spindle end is up to-884.0 MPa, and the residual stress of the transition fillet near the flange end is-831.9 MPa. The fatigue limit load of the specimen is the highest, up to 3750 N·m. The greater the residual compressive stress after induction heat treatment, the better the bending fatigue strength of the crankshaft connecting rod journal.