Application of Koistinen and Marburger's athermal equation for volume fraction of martensite to diffusional transformations obtained on continuous cooling 0.13%C high strength low alloy steel

Koistinen and Marburger's (KM) equation for the variation of volume fractio n of athermal martensite y with temperature T below the M-s has been applie d to continuous cooling diffusional data. The data consisted of dilatometer curves obtained on continuous cooling of a 0.13%C high strength low alloy steel. The KM equation takes the form, In(1 - y) = alpha(M-s - T), Plots of -In(1 - y) against temperature for what are thought to he grain boundary f errite, intragranular ferrite, proeutectoid ferrite, and pearlite give a se ries of straight lines of increasing slope alpha. Intersections of these li nes give the temperature of transformation points in good agreement with th ose on the dilatometry curves. Values of alpha obtained for each transforma tion are compared with those previously obtained for martensite in plain ca rbon and alloy steels and ferrite in Fe-9%Ni. MST/4510.