热轧和热处理U75V钢单轴棘轮--疲劳交互作用实验研究

Experimental Study on Ratcheting-fatigue Interaction of Hot-rolled and Heat-treated U75V Steels

钢轨服役过程中,由循环滚动载荷诱发的棘轮效应是其疲劳失效的主要原因之一。针对现役的热轧和热处理U75V钢开展单调拉伸、应变和应力控制疲劳实验,揭示热处理工艺对材料基本力学性能、循环特性和棘轮行为的影响,进而讨论棘轮效应与疲劳失效行为之间的交互作用。实验结果表明:热处理U75V钢的屈服强度和抗拉强度较热轧态有显著提升,二者均表现出循环软化特性。在相同载荷水平下热处理U75V钢抗棘轮变形能力和疲劳性能明显优于热轧态,当应力幅与屈服应力之比恒定时,相同平均应力下热轧U75V钢棘轮效应更显著。加载的平均应力和应力幅对U75V钢疲劳寿命的影响存在竞争作用,较强的棘轮行为使两种U75V钢疲劳寿命均降低。

Ratcheting effect induced by cyclic rolling loading is one of main causes for fatigue failure of rails in service.Monotonic tension,strain-controlled and stress-controlled fatigue tests are carried out for the hot-rolled and heat-treated U75V steels.The effects of heat treatment process on basic mechanical properties,cyclic characteristics and ratcheting behavior of steels are revealed,and the interaction between ratcheting effect and fatigue failure behavior is discussed.The results show that the yield and tensile strengths of heat-treated U75V steel are significantly higher than that of the hot-rolled steel,and both steels show cyclic softening characteristics.Under the same load level,the ratcheting resistance and fatigue performance of the heat-treated U75V steel are significantly better than that of the hot-rolled steel.When the ratio of stress amplitude to yield stress is constant,the ratcheting effect of the hot-rolled U75V steel under a same average stress is more significant.The effect of the mean stress and stress amplitude on the fatigue life of U75V steel is competitive,the stronger ratcheting behavior decreases the fatigue life of both of the hot-rolled and the heat-treated U75V steels.