Effect of Austenite Grain Size on the Hardenability of Eutectoid Steel

Abstract

As a first step to obtain a theoretical prediction of hardenability based upon the theories of phase transformation, the effect of austenite grain size on the hardenability of eutectoid steel is examined.
The effect of austenite grain size on the isothermal pearlite transformation curves were first measured.
The obtained results were analysed according to the Cahn's theory and the volume fraction of pearlite can be expressed as X=1-exp(-1.31×10^-5×t⁴/d^1.76). This result indicates that the pearlite transformation in the steel in present study procceeds by nucleation and growth and dominant nucleation site is grain edge. Step quenching experiments indicates that additivity rule is almost holds.
Using these experimental data, the effect of austenite grain size on the ideal critical diameter was calculated as D_I ∝ d ^0.22. The relation between the ideal critical diameter and the diameter of the bar having any amount of martensite at the center is also calculated.