Abstract
Effect of grain boundary precipitates on the high speed deformation of Hadfield steel was studied. The Hadfield steels with carbide on the grain boundaries or not were prepared by heat treatment. The tensile tests at various strain rates from 10^<-3>/sec to 10^3/sec were examined at room temperature. At slow strain rate (10^<-3>/sec), the both samples with/without carbide were large work-hardening with serration due to the dynamic strain aging, followed by fracture without local elongation. With the increasing of strain rate, the uniform elongations of both the samples are recovered and, furthermore, the local elongation can be found at strain rate higher than 10^0/sec. At the highest strain rate (10^3/sec), the both samples show large ductility. Observation of the fracture surface at slow strain rate indicate mainly inter granular fracture in the sample without carbide, whereas the grain boundary fracture can be found in the sample with carbides. On the other hand, the fracture surface of the sample show dimple pattern whichever the carbide exists or not. This indicates that the ductility of Hadfield steel at high speed deformation is attribute to something else than brain boundary carbide, such as solute carbon.
