铁路货车60Si2CrVAT钢弹簧疲劳试验断裂分析和工艺改进

Φ16 mm 60Si2CrVAT弹簧钢（/%:0.58C,1.76Si,0.66Mn,0.010P,0.005S,1.15Cr,0.15V）生产流程为转炉-LF-VD-220 mm×300 mm连铸-轧制-退火工艺。弹簧制造主要工艺为冲床下料-中频感应加热-热卷簧-余热淬火（890~870℃,油冷）-530℃电阻炉回火-打磨-抛丸-预压缩。分析了Φ16 mm K6弹簧在疲劳试验过程62万次发生断裂（标准要求≥300万次）的原因。结果表明,弹簧支撑圈与工作圈之间在点接触产生的硌伤而导致应力集中是弹簧早期疲劳断裂的主要原因,同时弹簧局部存在异常下贝氏体也对弹簧疲劳寿命产生了不良影响。通过改进制簧工艺,包括保证支撑圈几何尺寸和弹簧淬火温度,防止弹簧疲劳试验时发生局部点接触等措施,使60Si2CrVAT钢弹簧的疲劳试验寿命≥300万次。

Analysis on Failure of Spring of Steel 60Si2CrVAT for Railway Freight Train during Fatigue Test and Process Improvement

The production flowsheet of Φ 16mm product of spring steel 60Si2CrVAT (/% : 0. 58C, 1.76Si, 0. 66Mn, 0. 010P, 0. 005S, 1. 15Cr, 0. 15V) is BOF-LF-VD-22Q mm x300 mm bloom casting-rolling-annealing process. The main manufacturing process of spring for railway freight train is punching machine unloading-medium frequency induction heating- hot coiling spring-residual heat quenching ( 890 ~ 870 °C , oil cooling) -530 °C tempering in electric resistance furnace-grinding-shot blasting-pre-compression process. The cause of fracture of Φ16 mm K6 spring with 620 000 times in fatigue test (standard requirement ≥3 000 000 times) is analyzed. Results show that the hurt at point-contact between spring supporting ring and effective ring led to stress concentration is main cause of earlier fatigue fracture, while the abnormal lower bainite existing at local region of spring is disadvantage for spring fatigue life. With improving spring manufacturing process including insuring supporting ring size and controlling spring quenching temperature, preventing local point contact at spring fatigue test, the test fatigue life of spring of steel 60Si2CrVAT is up to ≥3 000 000 times.