Effects of Cr addition and cold deformation on the mechanical properties of a FeNi bainitic steel

Abstract

ABSTRACT The effects of Cr addition and cold deformation in increasing strength and altering the austempered structure of a FeNi steel is discussed. Cr content in the steel was varied from 2 to 3 wt% whilst cold deformation was undertaken on the material at either, 10% or 50%. The cold deformed steel was then subjected to austempering treatment at 400 °C for 30 min to obtain bainite structure in the samples. Post-austempering scanning electron microscopy (SEM) images of the FeNi-Cr samples showed the formation of lower bainite (LB) and martensite/retained austenite (M/RA) in the microstructure, whilst, in the FeNi sample showed the presence of ferrite in addition to LB and M/RA. The hardness and strength of the austempered FeNi-Cr samples increased significantly with increasing Cr content. Hardness and strength values of up to 46 HRC (from ⋘<20 HRC in FeNi) and above 1400 MPa (from ~800 MPa in FeNi), respectively, were obtained in 50% cold-deformed austempered FeNi-3 wt% Cr sample. However, the elongation decreased with increasing Cr content from 22% in the FeNi to 17% in the FeNi-3 wt% Cr sample. These findings suggest that while strength and hardness increase in cold-deformed austempered FeNi with increasing Cr content, the ductility decreases.