An examination of the formation of adiabatic shear bands in AISI 4340 steel through analysis of grains and grain deformation

Results from an experimental investigation showed that the formation of adiabatic shear bands (ASBs) in heat treated AISI 4340 steel is a microstructural phenomenon which depends highly on the grain size, shape, and orientation in the microstructure prior to deformation. Prior heat treatment (at various austenizing and tempering temperatures), as well as testing parameters, such as initial temperature and deformation strain rate, were shown to affect grain size in the steel tested. Optical microscopic examination of the microstructure showed that ASBs, formed in heat treated steel, exhibited zones of high hardness and small grain size. In specimens where ASBs formed, a progressive reorientation and elongation of the grain structure in the direction of maximum shear was observed. A much more refined grain structure was observed at the center of the bands.