The Effect of Strain in Recrystallization Region on Interphase Precipitation and Mechanical Properties of Ferritic Microalloyed Steels

Abstract

High yield strength (710–862 MPa) ferritic microalloyed steels are developed through the combined contribution of Nb, Mo, V, and Cr microalloying and controlled thermomechanical treatment. Microstructures and mechanical properties are characterized using advanced microscopy techniques and uniaxial tensile testing. NbV carbonitrides with/without Mo (depending on steel composition) are formed in austenite and range from 30 to 70 nm in average diameter. However, V‐ and Cr‐rich interphase (3–7 nm range) and random (1–6 nm range) precipitates are found in polygonal ferrite. An increase in roughing strain in the recrystallization region results in finer polygonal ferrite grains, higher number density of NbV carbonitrides and VCr interphase precipitates, and their size reduction. Higher roughing strain also minimize the intersheet spacing of interphase precipitates. Finer polygonal ferrite grains and a greater number of nanosized interphase precipitates are responsible for the higher yield strength of 862 MPa in the VCrNb steel processed with a larger strain in the recrystallization region.