Abstract
The formation mechanism of intermediate transformation products and the effects of B as well as carbide forming elements such as Cr, Nb and Ti on the isothermal transformation characteristics of low carbon 3 wt% Mn steels have been investigated and the following results have been obtained.
(1) Widmanstatten ferrite and bainite exibit both the diffusional and the displacive aspects in their formation processes.
(2) The addition of the above described elements markedly retards the formation of primary ferrite, Widmanstatten ferrite and bainite in the specimens directly quenched to isothermal transformation temperatures from 1200°C, while the precipitation of coarse carbide particles in austenite accelerates the fololowing transformations.
(3) Ferrite nucleation on coarse carbide particles can be explained in terms of the decrease in the activation energy for nucleation by the lattice correspondence at the interface.
(4) The coarse carbide particles precipitated at austenite grain boundaries are related to the ferrite enclosing these particles with Kurdjumov-Sachs relationship.
