硅脱氧弹簧钢55SiCr旋转弯曲疲劳断口中外来夹杂物的研究

Study on exogenous inclusions in rotary bending fatigue fracture of Si-killed spring steel 55SiCr

借助SEM-EDS分析1 950 MPa级汽车用悬架弹簧钢丝硅脱氧55SiCr钢的旋转弯曲疲劳断口中疲劳源宏观夹杂物的尺寸、距表面距离与成分。利用FEI Explorer 4自动扫描电镜对硅脱氧55SiCr盘条内生夹杂物成分分布进行检测统计,对比分析认为疲劳断口宏观夹杂物主要是外来夹杂物。通过采用盘条凝固枝晶显示方法,判断了这些外来夹杂物在连铸坯上的分布特点。研究结果表明:外来夹杂物主要来自于结晶器保护渣卷入、水口耐材和中间包渣线耐材的侵蚀剥落;疲劳断口上的外来夹杂物在铸坯中主要分布在大方坯内弧角部位置。

The size, distance from surface and composition of macro inclusions in rotary bending fatigue fracture of 1 950 MPa-class Si-killed 55 SiCr suspension spring wire were analyzed by SEM-EDS. The composition distribution of endogenous oxide inclusions in the Si-killed 55 SiCr wire rod were analyzed by means of FEI Explorer 4 automated scanning electron microscope, and the results show that macro inclusions in rotary bending fatigue fracture are exogenous inclusions. The distribution characteristics of these exogenous inclusions in the continuous casting bloom were studied by wire rod solidification dendritic display method. The results show that exogenous inclusions in fatigue fracture mainly are caused by the entrapment of mold powder, erosion of tundish line and submerged entry nozzle, and these exogenous inclusions mainly concentrate at the bloom loose side corner.