Strain rate and temperature dependence of low temperature superplastic deformation in a nanostructured microalloyed steel

The low temperature plasticity behavior of a nanostructured microalloyed steel was studied at varied deformation temperatures and strain rates. Tensile condition of 500 degrees C (0.33 melting point) and 0.00005 s (1) led to superplastic flow with a low peak stress of 140 MPa and a high elongation of 202%. The ultra-fine equiaxed ferrite kept high misorientation grain boundaries and absent of dislocations subjected to superplastic strain, accounted for grain boundary sliding mechanisms. Slip deformation was required at strain rate of 0.00025 s (1) or deformation temperature of 450 degrees C based on a relatively high dislocation density. Low temperature superplasticity in NG/UFG steel was highly strain rate and temperature dependent. (C) 2019 Elsevier B.V. All rights reserved.