OBSERVATIONS CONCERNING TRANSFORMATION INTERFACES IN STEELS

The transformation interfaces of pearlite, allotriomorphic cementite, M23C6, and Widmanstatten cementite plates in high-Mn high-C alloy stee ls have been studied by TEM. Linear striations in the interface have b een analysed and related to intersections with stacking faults in the parent austenite phase. Emphasis is given to the pearlite interface wh ere it is found that the striations at the interface increased as a re sult of thermomechanical treatment of the austenite prior to isotherma l transformation, consistent with an increased density of planar defec ts. The effect of heat treatment, and Si alloying additions, are also considered. Both conventional and in situ TEM of the pearlite interfac e showed that the linear defects stretched across both ferrite and cem entite phases at the pearlite interface, apparently without any deviat ion or change in image contrast. The results are compared with similar ones made of the static gamma/alpha interphase boundaries in duplex s tainless steel. The effect of prior deformation structure in the paren t austenite on the growth and interface structure of Widmanstatten cem entite plates has also been considered.