Enhanced toughness in a medium-carbon low-alloy steel processed by tempforming

Innovative Materials Engineering Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan The deformation of a tempered martensitic structure, namely tempforming was applied to a high purity 0.4%C-2%Si-l%Cr-l%Mo steel at 500 °C using multi-pass caliber rolling with an accumulative reduction in area of 77%. Charpy impact properties were investigated for the tempformed sample. An excellent combination of strength and toughness without the addition of a large amount of alloying elements such as Ni was demonstrated in the ultrafine fibrous grain structure that was processed by the tempforming. The yield strength of 1.84GPa and the V-notch Charpy absorbed energy of 226J at room temperature and the ductile-to-brittle temperature of less than -60 °C that we obtained in the medium-carbon low-alloy steel are the most optimal values that have been reported in low-alloy steels.