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Published June 1989 | public
Journal Article

Micromechanisms of Dynamic Crack Propagation in an AISI 4340 Steel

Abstract

The present work is aimed at understanding the micromechanisms of dynamic crack growth at room temperature and a low temperature (−100°C) in an AISI 4340 steel studied by Ravichandran and Clifton. For this purpose, a fractographic and metallographic examination of the specimens used by Ravichandran and Clifton was carried out. Results showed that the steel contained an appreciable amount of upper bainite (about 15%). The study suggests that dynamic crack propagation in the 4340 steel occurs in two stages, i.e. nucleation of microcracks in the upper bainite followed by propagation of these microcracks into the surrounding martensite. At low temperatures, failure of the martensite occurs by cleavage whereas, at room temperature, it occurs by shear localization, leading to microvoid growth and coalescence. At both temperatures, bainitic microcracks serve as failure initiation sites and reduce the dynamic fracture toughness of the steel.

Additional Information

© 1989 Elsevier Sequoia. Received July 18, 1988; in revised form November 10, 1988. This research was supported by the Army Research Office. Central facilities support was provided through the National Science Foundation Materials Research Group at Brown University.

Additional details

Created:
August 19, 2023
Modified:
October 20, 2023