Troisiéme Conférence Européenne sur les Matériaux et les Procédés Avancés
J. Phys. IV France 03 (1993) C7-93-C7-95
Brittle fracture characteristics of a 50 mm boron containing HSLA steelN.S. WRIGLEY1, G. JOLLEY1 and J.J. BUTLER2
1 University of Salford, Salford M5 4WT, U.K.
2 Defence Research Agency, Dunfermline, Fife, U.K.
Previous work on a boron containing HSLA steel has shown a variation in the impact fracture transition temperature through the thickness of a 50 mm plate. The inferior properties of the surface regions were attributed to cooling rate effects. This paper describes an extensive metallographic study which shows that the effects can be related to microstructural variations. Surface regions are shown to contain significant amounts of tempered autotempered martensite while central regions were mainly bainitic. Transmission electron microscope studies revealed the presence of dislocation substructures in the bainitic regions which were not found in areas of autotempered martensite. Careful studies of the fracture path in the transition region showed that the large autotempered martensite laths facilitated brittle crack propagation. The mechanics of formation of autotempered martensite in these steels and its significance are discussed.
© EDP Sciences 1993