New Insights into the Aging Embrittlement Mechanism of 30Cr2Ni4MoV Steel Containing Si and Mn

The aging embrittlement of 30Cr2Ni4MoV steel during service at high temperature has been attributed to the segregation of Si and Mn at grain boundary (GB). We report an alternative mechanism of aging embrittlement of 30Cr2Ni4MoV steel. Using atom probe tomography, it is found that the quenched and tempered (QT) 30Cr2Ni4MoV steel has already contained obvious Si and Mn segregations at GB, which means that the Si and Mn segregations at GB are not sufficient to induce aging embrittlement. It is discovered for the first time in aged 30Cr2Ni4MoV there newly precipitate many G-phases along GB, and Si and Mn segregations at GB of QT30Cr2Ni4MoV steel are the main reason for the precipitation of G-phase. The hard and brittle G-phase helps to promote crack initiation during impact deformation. Subsequently, the cracks can rapidly propagate along GB due to the distribution of G-phase and the segregation of Si and Mn along the GB, which leads to intergranular cracking and low impact energy as for aged 30Cr2Ni4MoV steel.