Crystallography of spheroidite and tempered martensite

Abstract

Convergent beam Kikuchi line diffraction patterns, which have an accuracy more than an order of magnitude better than the more widely used conventional selected area diffraction, have been used to determine the orientation relationship between cementite and the ferrite matrix in spheroidite and tempered martensite. It has been shown that when pearlite spheroidized in plain carbon eutectoid steel, the original orientation relationship between cementite and ferrite is maintained in some cases. In other pearlite colonies in the later stages of the spheroidization the cementite particles rotate into a different orientation relationship with respect to the surrounding ferrite. In twinned martensite tempered in the range 450–650°C, the Isaichev orientation relationship between ferrite and cementite is obeyed, until recrystallization of the ferrite occurs. After full recrystallization the strict orientation relationship is destroyed, but the cementite particles still maintain a pseudo orientation relationship, in which close packed planes are approximately parallel, while the angle between corresponding close packed directions varies widely.