The Effects of Si and Deformation on the Phase Transformation in Dual Phase Steels

초록

It is well known by up-to-date references that the role of Si in dual phase steels is the increase of fraction of ferrite, the refinement of ferrite grain size, the formation of polygonal ferrite and the carbon enrichment in untransformed austenite. In order to quantitatively clarify the effects of Si in dual phase steels on the austenite-to-ferrite phase transformation and the carbon enrichment, the phase boundaries of /(+) and (+)/(+Pearlite) were calculated by the use of TCFE-database. Para-Ae3(`C)=911-502.50C+535.12C^2-285.95C^3-53.61Mn+65.40Si+73.71CMn+76.31CSi+16.42MnSi(wt%) Para-Ael(`C)=727-18.54Mn+17.96Si-3.36MnSi(wt%) The ferrite transformation kinetics and the martensite start temperature were investigated by the analysis of dilatation curve and microstructure. In the continuous cooling test, Ar3 in 0.9wt%Si steels was about 30~50`C higher than that of Si-free steels. Moreover, the difference of Ms after the shut isothermal heat treatment was about 50~60`C by the effect of Si.