METALLURGICAL STRUCTURE AND THE BRITTLE BEHAVIOR OF STEEL.
Abstract:
By means of surface-replication and three-dimensional metallography, it has become possible to delineate the interrelated processes of slip, twinning, carbide cracking, void formation and microcleavage in the tensile testing of iron and mild steels at subatmospheric temperatures. The cracking of intergranular carbides is an especially potent means of microcleavage initiation, and can be used as a tell-tale to follow the fracturing sequences. There are indications that the amount and size of intergranular carbides in mild steels are reduced by decreased carbon content, increased manganese content, increased cooling rate from the austenitizing temperature, and decreased grain size. The initiation of microcleavage via carbide cracking can be treated statistically, on the assumption that the number of carbide cracks per unit volume is proportional to the plastic strain, and that the size distribution of carbide cracks at any given strain is parabolic up to the maximum size present. Author