THE NATURAL FRAGMENTATION OF STEEL CYLINDERS WITH TEMPERED MARTENSITE MICROSTRUCTURES

摘要

Small steel cylinders with martensitic microstructures produced by heat treating steels of three different carbon contents have been explosively fragmented. Some effects of material properties on the fragmentation behaviour are assessed by correlating recovered fragment mass distributions with observations made on the operative fracture modes. The fracture modes are determined from optical microscopy of fragment cross sections and from scanning electron microscopy of fracture surfaces. It is shown, for the cylinder sizes used, that coarse fragmentation is associated with predominant ductile shear fracture whereas increases in the contributions from radial tensile fracture and adiabatic shear fracture lead to finer fragmentation. The relationships between the modes of fracture and the martensite compositions and heat treatment are discussed, and particular reference is made to the fractography of adiabatically sheared surfaces.