EFFECT OF AUSTENITIZING TEMPERATURE ON THE MICROSTRUCTURE AND FRACTURE TOUGHNESS OF A MEDIUM CARBON CrMnMo STEEL
Lou Bingzhe;Chen Xicheng Shaanxi Mechanical Engineering Institute Institute of Physics; Academia Sinica
Cite this article:
Lou Bingzhe;Chen Xicheng Shaanxi Mechanical Engineering Institute Institute of Physics; Academia Sinica. EFFECT OF AUSTENITIZING TEMPERATURE ON THE MICROSTRUCTURE AND FRACTURE TOUGHNESS OF A MEDIUM CARBON CrMnMo STEEL. Acta Metall Sin, 1979, 15(4): 498-589.
Abstract An investigation of the effect of austenitizing temperature on the microstruc-ture, strength and fracture toughness of a quench-tempered 0.5% C CrMnMo steelhas been carried out. The fracture toughness (K_(IC)) of this steel in fully temperedcondition was improved by adequately increasing the austenitizing temperature inwhich the amount of lath martensite was increased and the rupture was mainlyductile. When the austenitizing temperature went up beyond 950℃, films of retainedaustenite began to appear at the lath boundaries. Such a distribution of retainedaustenite would seem to be liable to continuous precipitation of carbide platesaround the lath boundaries owing to its decomposition on being tempered at 500℃.Such carbide plates would seriously deteriorate the fracture toughness of the steeland enhance its tendency to intergranular fracture. After protracted tempering at500℃, spheroidization of the carbides and disappearance of the twins in acicularmartensite resulted. Both would contribute to the improvement of the fracturetoughness (K_(IC)) of the steel, as well as to an improvement of the ductile behaviouron fracturing. The effect of carbide size on the propagation behaviour of cracksare discussed tentatively. The variation of the plane strain fracture toughness (K_(IC))caused by an increase of austenitizing temperature would seem to agree well withthe Hahn-Rosenfield relation.
[1] Lai, G. Y., Wood, W. E., Clark, R. A., Zackay, V. F. and Parker, E. R., Met. Trans., 5 (1974) , 1663． [2] Zackay, V. F., Parker, E. R. and Wood, W. E., Microstructure and Design of Alloys, International Conference on the Strength of. Metals and Alloys, 3d, Cambridge, Eng., 1973, Vol. 1, p. 175． [3] Beachem, C. D., Met. Trans., 4 (1973) , 1999． [4] Thomas, G., Iron and Steel Inter., 46． (1973) , 451． [5] Das, S. K. and Thomas, G., ASM Trans. Quart., 62 (1969) , 659． [6] Hahn, G. T. and Rosenfield, A. R., Applications Related Phenomena in Titanium Alloys, Amer. Soc. Test. Mater., Spec. Tech. Publ. №. 432, 1968, p. 5
