转向节用贝氏体型非调质钢的高周疲劳性能

High-Cycle Fatigue Properties of Medium-Carbon Microalloyed Bainitic Steels for Steering Knuckle

利用旋转弯曲疲劳试验方法对比研究了新开发的两种转向节用贝氏体型非调质钢的高周疲劳性能。结果表明,两种不同碳含量的贝氏体型非调质钢具有细小均匀的贝氏体铁素体+M-A岛组成的粒状贝氏体组织;两者具有相当的强度水平和疲劳性能,但其疲劳性能低于同等强度水平的调质钢。与锻态相比,正火处理后,试验料的抗拉强度和疲劳强度均有一定程度的降低,但屈强比和疲劳极限比明显提高。对疲劳断口的分析表明,试验料的疲劳裂纹均起源于表面基体,疲劳裂纹以准解理机制扩展。裂纹扩展速率试验表明,含碳量较低的试验料的疲劳裂纹扩展速率da/d N明显低于含碳量较高的试验料。

High-cycle fatigue properties of two newly developed medium-carbon microalloyed bainitic steels for steering knuckle were investigated using rotating-bending fatigue test.The results show that the developed two bainitic steels have fine granular bainitic structure and therefore comparable strength level and fatigue property in both as-forged and as-normalized conditions.However,the fatigue properties of the two bainitic steels are lower than that of the quenched and tempered steel.Compared to as-forged condition,both tensile strength and fatigue limit decrease,whereas both yield strength ratio and fatigue limit ratio increase when the steels were normalized.Further SEM examination of fatigue specimen fracture surfaces revealed that all the fatigue cracks initiated form specimen surface matrix and propagated in forms of quasi-cleavage.The fatigue crack growth rate da/dN of the lower cabon content steel is slower than that of higher carbon content.