Mo对高强度钢延迟断裂行为的影响

在含V和Nb的40Cr钢中添加不同质量分数(0-1．54％)的Mo元素,采用缺口拉伸试样和改进的M—WOL型试样研究了Mo对高强度钢延迟断裂行为的影响．结果表明,随着Mo含量的增加,实验钢的延迟断裂抗力逐渐提高;当Mo含量超过1．15％时,延迟断裂抗力不再提高．EDS分析结果表明,钢中Mo元素在晶界发生偏聚,偏聚范围在几个纳米尺度内．通过电子能量损失谱(EELS)证明,Mo元素在原奥氏体晶界的偏聚能够提高钢的晶界结合强度．在钢中添加Mo能够显著提高钢的回火抗力和晶界结合强度,这是其具有高的延迟断裂抗力的主要原因．碳化物Mo2C对氢的捕集作用亦能够提高钢的延迟断裂抗力．Mo和V元素的二次硬化碳化物在半共格和非共格状态时,实验钢的延迟断裂抗力显著提高．

EFFECT OF MOLYBDENUM ON DELAYED FRACTURE BEHAVIOR OF HIGH STRENGTH STEEL

Four heats of V and Nb microalloyed 40Cr steel containing 0 to 1.54% Mo were used to study the effect of Mo on delayed fracture resistance. Trie results of both notched tensile sustained load test and stress corrosion cracking test show that the delayed fracture resistance increases with increasing Mo content. Maximum delayed fracture resistance is obtained at a Mo concentration of about 1.15%. The result of EDS (energy dispersive spectroscopy) analysis shows that Mo tends to segregate in the grain boundary in a scale of no more than a few nanometers. EELS (electron energy loss spectra) measurement indicates that the segregation of Mo in grain boundary tends to increase the strength of grain boundary. The pronounced effect of Mo in raising the tempering resistance and the ability to strengthen prior austenite grain boundary are the main reasons for the beneficial effect of Mo on delayed fracture resistance. Hydrogen trapping effect caused by fine Mo2C precipitation could also improve the delayed fracture resistance. It is also confirmed that the tested steels could have a much higher delayed fracture resistance when the secondary hardening carbides of V and Mo are in the condition of slight over-raging.