Formation of austenite in Fe-10Cr-0.2C alloy

Abstract

The formation of austenite from a ferrite–carbide microstructure in an Fe-10Cr-0.2C (wt-%) alloy has been investigated by optical and transmission electron microscopy and microanalysis of partially transformed and quenched samples. Although nucleation of austenite is relatively sluggish (compared to low alloys steels), growth of austenite is rapid and the reaction is complete within 100 s at temperatures above AC ₃. The transformation proceeds more rapidly as the temperature increases. Fine undissolved carbides have little effect on the movement of the austenite growth front while closely spaced coarse carbides can pin the interface. Carbides do not dissolve in ferrite or in the ferrite/austenite interface (unless the interface is stationary owing to pinning) but the higher solubility of carbon in austenite allows dissolution of carbides in austenite to occur. The rate of dissolution is controlled by the rate of removal of chromium. Austenite inherits the chromium content of the ferrite and no partitioning of chromium between austenite and ferrite accompanies the transformation. Local increases in the chromium content of austenite are associated with carbide dissolution.