Bainite transformation and the diffusional migration of bainite/austenite broad interfaces in Fe-9%Ni-C alloys

The processes of bainitic structure formation in Fe-9%Ni-C alloys have been investigated by means of transmission electron and hot stage optical micro scopies. The bainite laths formed initially with sharp surface reliefs grow in thickness direction rather slowly with surface rumpling-type reliefs. A pearlitic layer often forms in the carbon-enriched region between the bain itic ferrite laths. The pearlitic ferrite nucleates epitaxially on or grows directly from an adjacent bainitic ferrite lath. Such pearlite colonies al ways exhibit the Isaichev ferrite/cementite orientation relationship with t he [010](theta)parallel to < 111 > alpha parallel to < 110 > (gamma) near i nvariant line between three phases on the bainite habit plane. In the typic al upper bainite with cementite layer between ferrite laths, a cementite/fe rrite orientation relationship with the (100)(theta)approximate to parallel to {110}(alpha) bainite habit plane was recognised in addition to the (011 )(alpha)parallel to((1) over bar 03)(theta) habit. The general feature of c ementite Precipitation in such upper bainite laths is that the near invaria nt [010](theta)parallel to < 111 > (alpha)parallel to < 110 > (gamma), dire ction lies on the bainite habit plane. (C) 2001 Acta Materialia Inc. Publis hed by Elsevier Science Ltd. All rights reserved.