Effect of the Strain Rate on the Deformation Mechanism in a 12 Mn Austenitic Steel

摘要

The effect of the strain rate on the plastic deformation mechanism in Fe-12Mn-0.6C-0.06N (in mass pct) steel was investigated. After tensile testing at a strain rate of 10~(-4) s~(-1), the microstructure consisted of the austenitic matrix with e-martensite. The strain-induced formation of ε-martensite was inhibited for deformations carried out at a strain rate of 10~(-3) s~(-1). When the strain rate was higher than 10~(-2) s~(-1), mechanical twinning of strain-induced e-martensite formation occurred. This resulted in an increased work hardening rate. The change of the plastic deformation mechanism from transformation-induced plasticity (TRIP) effect at low strain rate to the twinning-induced plasticity (TWIP) effect at high strain rate resulted in an increase of the work-hardening. The stacking fault energy of the steel was calculated using a thermodynamic approach and TEM micro-characterization was used to analyze the relationship between the stacking fault energy, the strain rate, and strengthening mechanisms in the 12 pct Mn austenitic steel.