MICROSTRUCTURE AND MICROHARDNESS OF NANO/ULTRAFINE (n/UFG) GRAINED COLDROLLED 0.06C STEEL

Abstract

This present study is aimed to examine the microstructure and microhardness of nano/ultrafine grained (n/UFG) of 0.06C steel which had been cold-rolled, quenched and annealed. The process started with three different initial microstructures with the condition of 1) austenization at 1000°C for 30 min soaking and air cool (AC), 2) austenization at 1000°C for 30 min soaking and ice-water quench (IQ) and, 3) same treated as IQ but the quench specimen was tempered at 750°C for 30 min soaking and icewater quench once again (IQT). All quenched specimen, then cold-rolled by 75% and annealed at different temperatures ranging from 500°C to 600°C for 30 min soaking. From the analysis, it was found that the specimens annealed at 550ºC exhibit nano/ultrafine ferrite grained size with similar microhardness value for AC, IQ, and IQT. It has also found that acceptable UFG microstructure formed with of IQT specimen performs faster that IQ and AC specimens in terms of microstructure recovery, re-crystallization and grain growth during annealing after cold rolling.