Plastic flow behavior of twinning induced plasticity steel from low to warm temperatures

Abstract

This work investigates the tensile behavior of twinning induced plasticity (TWIP) steel under room to warm temperatures. Stress-strain flow curves have been obtained from steady-state uniaxial tensile tests performed at different temperatures, that is, from 20 to 800°C, and different engineering strain rates, 0.003 and 0.5s−1. The yield and ultimate tensile strength, elongation at fracture, reduction of area, strain hardening exponent and strain hardening rate have been defined to describe the plastic behavior of TWIP steel. It has been found that the plastic flow behavior of TWIP steel is characterized by negative strain rate sensitivity and strain hardening, at temperatures from 20 to 300°C, until the twinning mechanism occurs. At these temperatures, dynamic strain aging starts at the beginning of plastic deformation, with the appearance of fluctuations in the work hardening rate and local strain rate. Pronounced local serrations also appear at 300°C and 0.003s−1. Plastic deformation is mainly driven by dislocation gliding at 550 and 800°C, and mechanical twins are absent. As a result, negative strain rate sensitivity and local serrations disappear in the stress-strain curves. Creep also contributes notably to plastic deformation at 800°C, as was also observed on the fracture surfaces of tensile samples. Mechanical twins were only visible for the lower temperatures. The grains in the sample tested at 800°C and 0.003s-1 were fully recrystallized.