The Study On The Nucleation Of Martensitic Transformation And Lath Width Nanometre In Steel

The effect of plastic deformation and elastic strain energy induced by pre-strain on the nucleation of martensitic transformation of low alloy ultra-strength steel SOSiMnCrMoV had been studied by pre-strain quenching in austenite state. The control over deformation magnitude and deformation temperate as well as loading pattern was performed to adjust the storage of elastic strain energy in steel before martensitic transformation, using the type of Geeble-1500 thermal analogue test machine.The result showed that plastic deformation during pre-strain played an restrained role on the growth of martensite (especially in the direction of lath width) and increase the nucleation rate indirectly; The elastic energy induced by plastic deformation restrain the transformation of primary martensite but accelerate the transformation of after martensite. The reason is that the elastic energy increases the nucleation work while the formation of primary martensite can excite the release of elastic energy in austenite to promote the formation of after martensite and intensify the tendency towards homogeneous nucleation. The mechanism of elastic energy releasing wave stimulating the nucleation of martensitic transformation had been studied on the basis of the experiment result. According to the mechanism, the nucleation course of martensitic transformation requires energy (i.e. elastic energy) propagation in the form of wave in austenite. According to Solid-state Physics, the physical mode of elastic wave stimulatingthe nucleation of martensitic transformation had been established, of which the elastic energy release as elastic wave to induce particle displacement and strengthen the condition required by martensitic transformation.The lath width of martensite can be fined noticeably by pre-strained quenching at non-dynamic recrystallization to approach nanometer magnitude (the average width is 120nm). The lath martensite nanometer structure can play the role of fine-particle strengthening and dislocation strengthening as well as coordinate the distribution of dislocation. It is hopeful that the strength and toughness of material with this structure can be increased at the same time.The ultrasonic quenching of medium carbon alloy high strength steel 35CrMnSi was conducted, using H66025T ultrasonic generator. The result showed the mertensite lath was fined obviously and the nucleation rate was improved. It proved the theory that the propagation of elastic wave in austenite can promote the nucleation of martensitic transformation.