INFLUENCE OF CRYOGENIC TREATMENT ON MICROSTRUCTURE CHARACTERISTICS AND MECHANICAL PROPERTIES OF AISI D2 TOOL STEEL

Significant improvement in mechanical properties of tool steels may be obtained by cryogenic heat treatment at temperatures as low as 77K. However, the selection of the cryogenic temperature can significantly influence the final properties. In the present study, AISI D2 tool steel was cryogenically treated at 183K and 77K. Microstructural studies using scanning electron microscope (SEM) and image analyzing process revealed higher volume fraction of fine secondary carbides for both cryogenically treated alloys in comparison with conventionally treated one. Higher volume fraction of fine secondary carbides was observed when the cryogenic treatment temperature was reduced to 77K. Also, the volume fraction of large carbides has been reduced after both cryogenic treatments. Tensile test results revealed simultaneous enhancement of ultimate tensile strength, higher elastic modulus (E) and increased ductility for cryogenically treated alloy at 183K. More improvement was observed when the cryogenic temperature reduced to 77K.