Optimization of TMCP strategy for microstructure refinement and flow-productivity characteristics enhancement of low carbon steel

Abstract

Improving the mechanical properties of low carbon steel through the microstructural refinement without adding alloying elements is a complicated scientific and technical mission. This challenge can be overcome by using thermo-mechanical controlled processing (TMCP) technology. Most researches have examined the influence of TMCP on the microstructure development without shed light on the flow characteristics. The current work aims at studying the effect of applying different TMCP strategies on the microstructure refinement, flow-productivity characteristics, i.e. peak stress, flow stress, strain hardening index, Zener–Hollomon parameter and total strategy time, of low carbon steel. These TMCP strategies involve applying heavy deformation in single-pass TMCP strategy versus light deformation/pass in multi-pass TMCP strategy through applying different plane-strain hot compression regimes using Gleeble 3500 thermo-mechanical simulator. The proposed TMCP strategies have been involved application of heavy accumulative strain of 45–57% through: (1) single pass TMCP strategy at various strain rates (0.01, 0.1 and 1.0 s−1), (2) double pass TMCP strategy at different strain rates and (3) multi-pass TMCP strategy at strain rate of 0.1 s−1. Microstructures after the diverse TMCP strategies reveal ferrite grain refinement and the flow curves show typical strain hardening. This denotes that the working grain refinement mechanism during all TMCP is dynamic strain-induced transformation of austenite to ferrite. It has been found that the strain rate plays a considerable role in determining the flow characteristics regardless the applied TMCP strategy type. Double-pass TMCP strategy is the optimum TMCP strategy that promotes the ferrite refinement and enhances the flow and productivity characteristics. Keywords: Single/double/multi-pass TMCP strategy, Microstructure refinement, Flow/peak stress, Strain hardening index, Zener–Hollomon parameter, Strategy time