Effects of the Pre-transformation Micro structures on the Grain Refining of Medium-carbon 5Cr-Mo-V Steels

摘要

For the purpose of obtaining refined grains over full cross section for improved ductility in heavy-gage products of a medium carbon 5Cr-Mo-V steel, the effects of pre-transformation microstructures on the grain refining during austenitizing were investigated.Samples were prepared to possess either one of three different microstructures, pearlite, bainite and martensite. These samples were heated slowly to the desired austenitizing temperature followed by rapid cooling, and the formation of new austenite grains was examined.Though austenite grains were not refined in cases of martensite and bainite microstructures, these were remarkably refined in case of pearlite. Portions of pearlite were enriched with carbon, where the transformation temperature into austenite was lower, and this is considered to be the reason that finer austenite grains were formed.Above results show that arranging pearlite microstructure before quenching heat treatment is effective for obtaining refined grains over full cross section in heavy-gage products.