The study on the ultrafine mechanism of steels: strain-induced phase-transform ation form austenite to ferrite

Abstract

The models of interphase boundaries of austenite/ferrite(γ/α) in the undeformde austenite and deformed austenite, and the model of 12[1 1 0] edge dislocation in austenite matrix were set up with computer programming. The interfacial energ y of γ/α interphase boundaries in the undeformde austenite and deformed austen ite, the environment sensitive embedding energies (EESEESE) of C, N a nd microalloying elements Nb, Ti or V (in the form of air mass) in the area of e dge dislocation in austenite were calculated by using recursion method. The refineme nt mechanism of steels in the deformation process was discussed. Interfacial ene rgy calculation results show that the most preferred ferrite nucleation sites ar e the area of high density dislocations such as deformation bands, the austenite grain boundaries and subbounaries, which leads to a considerable increase in th e nucleation rate. This is why ferrite grains formed in the deformed austenite a re far more smaller than those in undeformed austenite. The EESEESE calcu lation results show that C,N microalloying elements (Nb, Ti or V) in form of the air mass, C,N together with microalloying elements (Nb or Ti) in the form air m ass are all easy to aggregate to the area of edge dialocations, which results in the carbonitride precipitation in there (deformation band, grain boundary or gr ain subboundary). The growth of ferrite grains is considerably suppressed by def ormation due to impingement with carbonitride particles and other ferrite grains , which leads to the further refinement of ferrite grains.