Roles of {101}α twinnings in martensitic transformation of a 1.80 mass% carbon steel

Abstract

In order to investigate the role of {101}α type twins or faults observed at the periphery of the martensite plate, the structure of the martensite in a 1.80 mass% C steel with a high tetragonality of 1.078 was studied by transmission electron microscopy, and in terms of the phenomenological theory of martensitic transformation. The periphery of the martensite contained two or three kinds of {101}α twins or faults in addition to the transformation twins of the (112) [1̄1̄1]α system concentrated in the midrib. The possible {101}〈101̄〉α twinning systems in a b crystal were taken into consideration as follows; (011)[011̄]α, (101)[101̄]α, (01̄1)[01̄1̄]α and (1̄01)[1̄01]α. From the magnitudes of shape strain of martensite resolved to the four kinds of {101}〈101̄〉α twinning components, the (011)]011̄]α and (1̄01)[1̄01̄]α twinnings were considered to be sufficient to accommodate shape strain. (101)[101̄]α twins observed in a highly densed state occurred by the inheritance of the (112)[1̄1̄1]α transformation twinning shear strain of the lattice invariant shear. Since the (01̄1)[01̄1̄RBα twin was not observed, this twinning contributed neither to the accommodation of shape strain nor to the inheritance of the (112)[1̄1̄1]α twinning shear strain.