STM STUDY ON THE SURFACE-RELIEF AND MECHANISM OF BAINITE TRANSFORMATION

Scanning tunneling microscopy (STM) has been first employed to study t he surface relief accompanying bainite transformation in a Fe-2.17C-12 .18Cr-0.31Si-0.26Mn (wt pct) steel. With the exclusive vertical resolu tion of STM, we observed that the surface relief associated with baini te is a group of surface reliefs related to subplates, subunits and su b-subunits. As a whole, the relief group is in a tent shape, not of in variant plane strain (IPS) type, which is obviously different from tha t of martensite, and implying that bainite is not formed by shear mech anism. The fine structure of bainite in Fe-1.0C-4Cr-2.0Si (wt pct) all oy has also been studied with STM and TEM. It is found that the bainit e plate is composed of subplates, subunits and sub-subunits. On the ba sis of the fine structure inside a bainitic ferrite plate observed und er STM, a sympathetic-ledgewise mechanism of bainite formation is prop osed.