The Effect of shock hardening on the impact resistance of low-carbon steel

Abstract

Mild steel plates were deformed by explosive loading prior to the testing of notched specimens in slow and impact bending and of plain specimens in uniaxial tension. The shock loading produced a significant increase (up to 25 ksi) in tensile yield strength σ Y . The increase resulted from both a high dislocation density and a high density of mechanical twins that were introduced by shock loading. At the same time, the slow-bend and impact transition temperatures were unaffected by the shock hardening. Elastic-plastic analysis showed that the shock loading results in an increase inσ ƒ * , the critical tensile stress required to initiate cleavage below the notch root. It is this increase inσ ƒ * that is responsible for preventing a rise in the brittleness transition temperature in shock-hardened plates, despite the increase inσ Y . The increase inσ ƒ * was attributed to the increase in twin density, hence an increase in the number of twin boundaries. Although grain boundaries have a primary role in preventing the initiation or propagation of microcracks, extensive testing and analysis demonstrated that the twin boundaries also serve as barriers in this regard.