Influence of cold plastic deformation of austenitic grain size in steel

Abstract

1. The ferritic grain size Lα of 15Kh steel depends upon the degree of deformation ɛ and the original grain size before deformation. In fine-grained steel deformation with degrees close to the critical leads to coarsening of the grains according to the coalescence mechanism and in coarse-grained to refinement of them. This determines the different character of the Lα=f(ɛ) relationship for original fine- and coarse-grained steel. 2. At the investigated heating rates regardless of the degree of deformation with the exception of ecr the initial austenitic grain size in the fine-grained steel agrees with the grain size of the α-phase at the point Ac1. In deformation with ecr the substructure formed during coalescence influences the austenitic grain size. As the result, after such deformation the austenitic grain size is finer than the ferritic before the start of austenitization. 3. In the austenitic area strongly deformed steel in which a fine grain size was formed before the α→γ-transformation reveals a strong tendency toward grain growth regardless of heating conditions. In accelerated and rapid heating this makes it possible to obtain a more uniform grain size in the cross section of nonuniformly deformed blanks. 4. The generally accepted opinion of refinement of the austenitic structure in deformed steel is valid for original coarse-grained steel but is not confirmed for fine-grained.