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

Abstract

Koistinen and Marburger’s (KM) equation for the variation of volume fraction of athermal martensite y with temperature Tbelow the M s has been applied 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, ln(1 - y) = α(M s - T ). Plots of -ln (1 - y) against temperature for what are thought to be grain boundary ferrite, intragranular ferrite, proeutectoid ferrite, and pearlite give a series of straight lines of increasing slope α. Intersections of these lines give the temperature of transformation points in good agreement with those on the dilatometry curves. Values of α obtained for each transformation are compared with those previously obtained for martensite in plain carbon and alloy steels and ferrite in Fe–9%Ni.