Effects of Cooling Rate on Transformations in a Fe-9 Pct Ni Steel

The transformations of a high-strength 9Ni-Cr-Mo-V steel were characterized as a function of cooling rate by dilatometry, microhardness measurements, and microstructural characterization. The results demonstrate that this steel is extremely insensitive to changes in cooling rate, generating a duplex microstructure of coarse autotempered martensite within a matrix of fine lath martensite at nearly all cooling rates. The coarse autotempered martensite is observed even at very slow cooling rates, although the lath martensite becomes replaced by lath (or bainitic) ferrite.