600MPa级汽车大梁钢疲劳极限确定和疲劳断裂原因分析

为确定薄板坯连铸连轧(flexible thin slab rolling,FTSR)短流程生产线生产的600 MPa级汽车大梁钢是否满足装车要求,利用升降法研究了汽车大梁钢的抗疲劳性能。研究结果表明,采用对数试验应力-对数疲劳寿命拟合的方法要优于直接采用试验应力-疲劳寿命,计算得到了不同存活率下的P-S-N曲线,由图得到疲劳极限强度为294 MPa,经过数值计算得到的疲劳极限强度为287. 1 MPa。采用扫描电子显微镜对疲劳试样进行了断口分析,发现疲劳断裂为韧性断裂,夹杂物为裂纹的起源,结合试验钢的性能指标和装车试用考核结果,确认FTSR生产线开发的600 MPa级汽车大梁钢满足装车使用要求。

Determination of Fatigue Limit and Analysis of Fatigue Fracture of 600MPa Automobile Frame Steel

The 600MPa class steel for automotive frame have developed on Flexible Thin Slab Rolling line, and then fatigue performance of this steel was studied by using up-and-down method. It was found that lgS-lgN fitting was better than S-N fitting, and P-S-N curves under different survival rates were calculated. The fatigue limit obtained through accurate calculation is 287.1MPa .The fatigue fracture was analyzed and observed, and it was found that the fatigue fracture was ductile fracture and the inclusion was the original of the crack source. So the developed steel can meet with the operating requirement by combined with performance indicators and loading trial.