Elucidation of deformation mechanisms and construction of processing maps for a Ti+Nb stabilized IF steel

摘要

Deformation characteristics of a Ti + Nb stabilized IF steel have been investigated in the present study to clarify the associated strain hardening and/or dynamic restoration mechanisms. Single-hit hot compression experiments were performed in a Gleeble thermomechanical simulator in the temperature range 650-1100°C at various constant true strain rates in the range 10~(-3)-10 s~(-1) to a true strain of 0.7. The 'safe' and 'unsafe' deterministic domains were identified through the construction of processing maps and verification of mechanisms through the examination of evolved microstructures, regardless of the phase type (austenite and/or ferrite). Among different materials models employed, the 'safe' workable region at austenite and ferrite phase, predicted by a modified dynamic materials model (DMM) superimposed with Poletti instability criteria has been identified to be appropriate in accord with the experimental data. Development of a fully recrystallized fine equiaxed ferrite grain structure is ascribed to the occurrence of dynamic recrystallization (DRX). The characteristics of the onset of DRX mechanism have been further analyzed in terms of critical strain and stress required. Moreover, a kinetic model has been established to evaluate the fractional transformation through DRX. In addition, industrial optimization of hot working schedule of the IF steel could be ascertained from the processing map.