The significant impact of pre-strain on the structure-mechanical properties relationship in cold-rolled medium manganese TRIP steel

We elucidate here the impact of pre-strain on the structure on mechanical properties of cold-rolled Fe-0.2C-5.5Mn-1.0Al (wt%) transformation induced plasticity (TRIP) steel. The steel was intercritically hardened at 650 °C and exhibited excellent combination of total elongation (TEL) of 45.2%, ultimate tensile strength (UTS) of 1100 MPa, and UTS×TEL of 50.2 GPa%. Pre-strain increased both yield strength (YS) and ultimate tensile strength (UTS), while it decreased total elongation (TEL). Product of strength and elongation (PSE) was similar with 10% pre-strain (50.4 GPa%) and 0% pre-strain (50.2 GPa%). However, the 10% pre-strain had lower yield-to-tensile ratio. The increase in YS is attributed to the increased dislocation density and transformed martensite, while the continuous increase in UTS was associated with increase in the fraction of transformed martensite and enhanced work-hardening rate. On the other hand, the increase in the average stability of retained austenite, increased density of dislocations in ferrite and increased volume fraction of transformed martensite induced by pre-strain led to decreased ductility. The desired mechanical properties can be obtained by optimizing the amount of pre-strain.