The Influence of Deformation-Induced Microvoids on Mechanical Failure of AISI A8-Mod Martensitic Tool Steel.

Tool steels are considered as hard to deform materials since they have a mixture of soft ferritic matrix with hard carbides as secondary particles. In this study, 5 mm thick plates of AISI A8-Modified tool steel were subjected to cold rolling prior to the quench-temper cycle with the view to investigate the work hardening behavior of this steel during rolling and to reduce the brittleness of the product after the quench-temper cycle. 5mm thick samples were rolled 10, 20, 30, 40, and 50 (%) under similar conditions and then cut parallel to the rolling direction. Microstructure evolution, deformation-induced microvoids, and hardness evolution as a function of prior deformation were investigated. Electron microscopy was used to investigate the root causes for the formation of microvoids and potential alligatoring failure. The influence of microvoids on mechanical properties after the quench-temper cycle was evaluated through bending tests. Results showed no failure for 50% cold rolled sample in comparison with fracture for non-deformed sample indicating that prior deformation could be a novel route for improving the in service properties of these alloys. Hardness of 50% cold rolled after thermal hardening was lower than that for non-deformed sample. The analysis of prior austenite grain size, volume fraction of retained austenite, and volume fraction of carbides for both testing conditions showed that hardness reduction can be related to the presence of microvoids formed in the microstructure during rolling. [ABSTRACT FROM AUTHOR]