Realizing Ultrafine Grained Steel by Simple Hot Deformation Using Dynamic Transformation and Subsequent Dynamic Recrystallization Mechanisms

Abstract

We have found a new strategy for ultra grain refinement without high strain deformation by combining dynamic transformation (DT) and dynamic recrystallization (DRX) mechanisms. Through simple thermomechanical processes using a total plastic strain of 0.92 at elevated temperatures, ultrafine grained microstructures having mean grain sizes down to 0.35 microns could be obtained in a 10Ni-0.1C steel. DRX phenomenon occurring in the dynamically transformed ferrite significantly reduced the strain necessary for the formation of ultrafine grains. The DRX of DT ferrite showed an unconventional temperature dependence, which suggested an optimal condition for grain refinement. The obtained UFG steel exhibited superior mechanical properties, for example, the tensile strength of 970 MPa and the total elongation over 20% at the same time.