Dynamic Strain Induced Transformation of Austenite to Ferrite during High Temperature Extrusion of Low Carbon Steel

Abstract

Ultra fine grained materials exhibit superior mechanical properties compared with the conventional coarse grained one. In the present work, the hot extrusion process was conducted on plain low carbon steel to achieve ultra fine ferritic structure. At first, with the aid of 3D finite element simulation an appropriate preheating temperature for the initiation of dynamic strain induced transformation of austenite to ferrite was predicted to be 930 C. After hot extrusion, the results of microstructural analysis by optical microscopy showed that the predicted temperature was suitable. Extruded samples showed ultra fine ferrite structure with average grain size of 1 mm on a plane perpendicular to material flow. Also, the microstructural developments with strain in the extrusion zone confirmed the occurrence of dynamic strain induced transformation of austenite to ferrite during deformation process. Tensile strength of processed steel is two times higher than coarse grained one.

Dynamic Strain-Induced Ferrite Transformation during Hot Compression of Low Carbon Si-Mn Steels

“…In recent years, several thermomechanical controlled processing (TMCP) routes have been developed to produce ultrafine ferrite grains in hot-rolled microalloyed or plain low carbon steel strips. [1][2][3][4] The dynamic strain-induced transformation (DSIT) has been reported to be one of the most promising fabrication processes for ultrafine-grained (UFG) metallic materials because of its simplicity and efficiency in grain refinement with a low cost. 1,[5][6][7][8] Grain refinement by the DSIT process is strongly dependent on the chemical composition of steels, prior austenite grain size (AGS), undercooling of austenite (ÁT), and rolling conditions such as temperature, thickness, and strain rate.…”