Effects of temperature, strain rate and silicon content on dynamic strain ageing of modified chromium-molybdenum steel

Martensitic T91 grade steels exhibited a susceptibility to dynamic strain aging (DSA) by virtue of gradually reduced failure strain (ef) and formation of serrations within a susceptible temperature range, irrespective of the silicon (Si) content. Since DSA is a thermally-activated process involving diffusion of solute elements, the effects of temperature and strain rate have been investigated. The activation energy associated with the diffusion process was gradually enhanced with increasing Si content at comparable temperatures. A maximum dislocation density was determined at 400°C at which lowest ef was observed in the engineering stress versus engineering strain diagram. The resistance to plastic deformation in terms of work-hardening index was gradually enhanced with an increase in temperature up to 400°C, independent of the Si content. The presence of higher Si content in the T91 grade steels resulted in reduced impact resistance and fracture toughness. Steel containing 2.0 weight percent Si exhibited predominantly ductile failures under tensile loading at all tested temperatures. However, the other materials showed a combination of brittle and ductile failures.