正火预处理对42CrMoVNb高强度螺栓钢耐延迟断裂性能的影响

Effect of Normalizing Pretreatment on Delayed Fracture Resistance of 42CrMoVNb High Strength Bolt Steel

通过拉伸试验、恒载荷缺口拉伸试验(CLT)、慢应变速率拉伸试验(SSRT),研究了42CrMoVNb高强度螺栓钢经不同工艺热处理后的耐延迟断裂性能,并与42CrMo螺栓钢进行了比较。结果表明:1400和1500 MPa强度级别的42CrMoVNb螺栓钢的恒载荷延迟断裂强度比均大于0.62,其耐延迟断裂性能优于1200 MPa级的42CrMo螺栓钢。调质处理前增加一道正火处理,可使V、Nb等合金元素形成的碳化物更加细小弥散,从而提高钢的强度和塑性。此外,细小弥散的合金碳化物可以增强氢陷阱作用,提高恒载荷延迟断裂强度比,降低氢脆敏感系数,提升42CrMoVNb高强度螺栓钢的耐延迟断裂性能。

Delayed fracture resistance of 42CrMoVNb high strength bolt steel heat treated by different processes were studied by tensile test,constant load notch tensile test(CLT)and slow strain rate tensile test(SSRT),and compared with those of 42CrMo bolt steel.The results showed that the constant load delayed fracture strength ratio of 42CrMoVNb bolt steel of tensile strength levels of 1400 MPa and 1500 MPa was greater than 0.62,and its delayed fracture resistance was better than that of 42CrMo bolt steel of strength level of 1200 MPa.Adding a normalizing process before quenching and tempering could make the carbides containing V,Nb and other alloy elements finer and uniformly dispersed,thus improving the strength and plasticity of the steel after quenching and tempering.In addition,fine dispersed alloy carbides could enhance the hydrogen trapping effect,increase the constant load delayed fracture strength ratio,reduce the hydrogen embrittlement sensitivity coefficient,and improve the delayed fracture resistance of 42CrMoVNb high strength bolt steel.