Fatigue crack propagation behaviour of a single crystalline superalloy : Lerch, B.A. and Antolovich, S.D.Metall. Trans. A Aug. 1990 21A, (8), 2169–2177

Abstract

The relationships between the austenitizing temperature, the quenching medium, and the plane strain fracture toughness have been investigated for the following quenched and tempered low alloy commercial steels: 4130, 4330, 4140, 4340, 300-M and 3140. The specimens were tested in both the as quenched condition, and after tempering at temperatures up to 390°C. By increasing the austenitizing temperature from 870°C to 1200°C, the fracture toughnesses of these alloys was significantly increased and for some alloys increasing the severity of the quench from oil to ice brine, when used after austenitizing at 1200°C, led to still further increases in the fracture toughness. Using a ‘step quench’, which consisted of auitenitizing at 1200°C for 1 hr followed by furnace cooling to 870°C and holding for 12hr before quenching, did not, in general, result in as high a fracture toughness as when the specimens were directly quenched from 1200°C. Associated with the increase in toughness were changes in both the microstructure and the fracture morphology. Alloys 4130, 4340, 4140, and 3140, showed severe intergranular embrittlement when austeoitized at 1200°C and tempered above 200°C, while alloys 4330 and 300-M did not.