On the peculiarities of steel fracture at quenching and possibilities of its channeling

The propagation of a martensite plate during austenite-martensite transformation is considered as a process having a ballistic character. In these conditions, the martensite plate growth should cause dynamic impact on any barrier in front of the plate. The leading edge of the martensite plate moving with a velocity close to the sound wave velocity is represented as a flying body with mass launched by the austenite-martensite phase transition. The body can exert mechanical effect on any barriers, perforate and break them. As a result, extended fracture zones as channels within the material should appear in the barriers. During martensitic transformation one should expect the formation of the elastic and inelastic Rose channels of the first and second type. At lath martensite formation the so-called martensite anvils with negative (tensile) stresses of about 20... 70 GPa are formed between martensite laths. Tensile stresses of this kind can cause fracture of austenite layers in packets with the formation of channels, either void or filled with fractured material. Such structure of lath martensite may turn to be the key one for understanding processes occurring in creep of quenched high-chromium steels P91 and P92. The channels in fractured austenite layers formed during lath martensitic transformation could be the main source and thoroughfare for the delivery of alloying elements and carbon to the austenite grain boundary. The delivery rates exceed many times the rates of any diffusion process. This scenario leads to an abnormally rapid formation of inclusions of different nature in prior austenite grain boundaries. It could be the main cause of degradation and early fracture of high-chromium steels.