Prediction of hardenability effects from isothermal transformation kinetics

Abstract

The relationship between the size of material, fraction of martensite and austenite grain size is considered for a certain eutectoid steel under a certain cooling condition. It is assumed that the isothermal pearlite transformation can be expressed as X =1 -exp {-k(T) (tⁿ/d^m )} for the whole transformation temperature range and that the transformation is additive over the whole transformation range. The cooling rate is determined as a function of section size (which is commonly found in actual quenching). With the application of the obtained relation, the Jominy curve, D_I vs D_I,X (the diameter of the bar with X pct martensite at the center after an ideal quenching) and the effect of austenite grain size on the D_I and Jominy distance are shown to be predictable.