To investigate the mechanisms of grain boundary embrittlement, sustained load tests were conducted on a medium carbon, high strength martensitic steel at slightly elevated temperatures. Slow crack growth was observed from 185°C to 500°C.
Fracture surfaces of the specimens tested were examined by scanning electron microscopy after sustained load tests. It was found that severe grain boundary embrittlement occurred in this material with the predominant fractographic feature being intergranular fracture.
Auger electron and x-ray photoelectron spectroscopy of the intergranular facets were utilized to analyze the embrittling species. Prior suggestions for this “strain-aging embrittlement” phenomena have centered around carbide precipitation. The present results suggest that it is carbon, driven by thermal energy and the stress field, that segregates on the grain boundaries and weakens them.