Influence of prior cold deformation on microstructure evolution of AISI D2 tool steel after hardening heat treatment

• Cold rolling was applied prior to quench hardening on AISI D2 steel.
• Prior austenite grain size was reduced after cold rolling and hardening.
• The dissolution rate of carbides was accelerated in cold rolled alloys.
• Prior deformation reduces the maximum hardness achievable in the alloy.

4 mm thick plates of AISI D2 steel were subjected to two different percentage of cold rolling prior to quench hardening. Prior austenite grain size and volume fraction of carbides were reduced after hardening heat treatment for both 10% and 20% cold-rolled samples in comparison with non-deformed one. Hardness measurements revealed that pre-deformation resulted in a 3 to 4 HRC decrease. Scanning electron microscopy images revealed more uniform mean plate size of martensite for the cold rolled samples. The obtained results are analyzed in the framework of the existing theories on martensitic transformation and the influence of strain on second phase dissolution kinetics. The drop in hardness is related to the effect of pre-deformation on the dissolution rate of carbides. The volume fraction of martensite compared to non-deformed condition didn’t show dominant reduction.

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