オースフォームした9%W-2.5%Cr鋼の破壊靭性について

Abstract

The notch tensile strength and the fracture toughness of 30% and 60% ausformed 9%W-2.5%Cr steels (SKD 5) and the conventionally heat treated one were examined, in order to study the effects of ausforming and subsequent tempering on the characteristics of brittle fracture caused by sharp notches or small cracks. The results obtained are as follows:(1) The ultimate tensile strength and the yield strength of the 60% and 30% ausformed steels and the conventionally heat treated steel become smaller in that order up to the tempering temperature of 700°C, and though the ultimate tensile strength is not so changed with tempering temperature up to 500°C, the yield strength is largest at the tempering temperature of 300°C.(2) The notch tensile strength of the 60% and 30% ausformed steels and the conventionally heat treated steel become larger in that order up to the tempering temperature of 400°C. But at the tempering temperature of 600°C, the notch tensile strength of the 60% ausformed steel is much larger than that of the 30% ausformed or the conventionally heat treated steel, because the former increases slightly at that tempering temperature while the latters decrease remerkably.(3) The fracture toughness Kc versus tempering temperature relationship is very similar to the notch tensile strength versus tempering temperature relationship.(4) The pop-in fracture toughness KIC of the 60% and 30% ausformed steels and the conventionally heat treated steel become larger in that order, but it is not so influenced by tempering as the fracture toughness Kc.(5) The strong interrelation is found between the fracture toughness Kc and the notch tensile strength regardless of the ausform reduction and the tempering temperature.