2016 年 56 巻 11 号 p. 2047-2056
A 0.4C-2Cr-1Mo-2Ni steel (in mass%) was austenitized at 1123 K, followed by ausforming (AF) using multi-pass caliber rolling with a rolling reduction of 74%. The AF samples were subsequently tempered at 773 K and deformed by multi-pass caliber rolling (i.e. warm tempforming, WTF) with a rolling reduction of 46%. Their microstructures and mechanical properties were investigated and compared to those of the quenched and tempered samples (non-AF samples) which were subjected to the sequent WTF with rolling reductions of 46% and 74%. The WTF with rolling reductions ranging 46 to 74% resulted in the strengthening and toughening of the AF and non-AF samples through the evolution of anisotropic and ultrafine grain structures with strong <110>//rolling direction (RD) fiber textures. The AF sample demonstrated the faster kinetics of the microstructural changes, i.e. refinement in the transverse grain size and development of highly elongated grains than the non-AF sample. As a result, the AF sample exhibited a better combination of ultra-high strength and toughness than the non-AF sample, when compared at the rolling reduction of 46%. The combined effect of AF and WTF was especially pronounced in the enhancement of toughness resulting from delamination.
