球状黒鉛鋳鉄の破壊じん性値に及ぼす黒鉛粒径と温度の影響

概要

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In order to study the effects of graphite nodule size and testing temperature on the fracture toughness of ferritic spheroidal graphite cast iron, two series of specimens with different silicon content whose mean graphite nodule size was adjusted to four levels were examined. The fracture toughness test was carried out by three point bending of notched bar specimen at the temperature of 20°C, −60°C and −130°C. Tensile strength and 0.2% proof stress increases with lowering the testing temperature. On the contrary elongation tends to decrease. When the testing temperature are 20°C and −60°C, the fracture toughness KIC increases with increasing the graphite nodule diameter. However, at −138°C, KIC decreases with increasing the graphite nodule diameter. When the testing temperatures lower the fracture mode changes from ductile to brittle. βc (1/B⋅KCI2/σys2) is used as a standard for such a transition of fracture mode. And the stress condition at the apex of the crack draws to a plain strain when the βc decreased. When the testing temperature were 20°C and −60°C, this βc decreases with decreasing the mean graphite nodule diameter. However, at −130°C, βc decreases with increasing the mean graphite nodule diameter.
日本鋳造工学会の論文