The Effect of Microcracking in Martensite on the Deformation and Fracture Behavior of Fe-C Alloys and Commercial Steels.

摘要

The fracture pf hardened SAE/AISI 52100 steel was examined as a function of austenitizing and the early stages of tempering of the martensite in an Fe-1.22C alloy were examined as a function of tempering time and temperature. The fracture toughness of the 52100 steel was improved by the presence of residual proeutectiod carbides in specimens austenitized below Acm. Specimens austenitized above Acm showed increasing fracture toughness with increasing austenitizing temperature, a result explained by the initial crack extension during the fracture toughness test through the martensite-austenite microstructure of the grains rather than along the prior austenite grain boundaries as was observed on the balance of the overload fracture surface. Mossbauer examination of the Fe-1.22C martensite showed changes in the martensite, cementite the austenite components of the Mossbauer spectra as a function of tempering time and temperature and yielded evidence for transition carbide formation. Transmission electron microscopy verified the presence of the transition carbide, and showed it to be eta-carbide rather than epsilon-carbide. (Author)