Research Of Martensite Formation On The Steel Grain Boundary

The martensitic transformation of several industrial steels have been studied in the article , include low carbon steel, medium carbon steel and high carbon steel. The results show that, in low carbon steel, first martensite plate is formed not only at the intracrystalline but also at the boundaries of austenitic grain in the experiment; first martensite plate is formed at the boundaries of austenitic grains among the medium carbon steel and high carbon steel.The formation mechanism of low carbon steel, medium carbon steel and high carbon steel grain-boundary martensite from the thermodynamic aspects of conduct in-depth analysis in the paper. In our opinion, the atom arrangement, dislocation density and quenching stress of original austenite promote martensite priority in the grain boundary nucleation. Dislocation slip provide the facilitation for the formation of martensite nucleation. The elastic energy produced by dislocation slipping can provide the driving force for the martensite nucleation, martensite rowth and induced martensite formation. The arrangement of grain boundary is incompact, which supply enough space for the volume change and strain energy produced by shear deformation of the nuclear. The stress arising from quenching easily concentrate on the grain boundary, which provide nuclear energy for the martensite priority in the grain boundary.The results show that , the first martensite plate formed at the boundaries of austenitic grains in the experiment is lamellar martensite. According to the Principle of phase-chang, compare with lath martensite, the lamellar martensite has lower surface energy and the higher strain energy, and has lower resistance force during the nucleation, so make it easier to proceed.