Microstructural and Mechanical Characterisation of Quenched, Quenched and Tempered AISI M2 High-Speed Steel Subjected to Deep Cryogenic Treatment

AISI M2 HSS from the family of tool steels are well known for their wide industry usage due to its strength, hardness and ability to retain red hardness at high temperature. AISI M2 HSS were investigated following different heat treatment processing sequence, such as Q, Q + DCT, Q + T, Q + T + DCT and Q + DCT + T (where Q—Quenched, T—Tempered, DCT—Deep Cryogenically Treated). The different sequence employed was chosen to better understand the effects of DCT on the studied material. The microhardness test results for DCT samples revealed an increase in hardness measurement. The level of increase was dependent on the processing sequence employed. A clear trend observed was that employing DCT following quenched and prior tempering (Q + DCT + T) resulted in a 4.1 pct improvement in hardness compared to the conventional quenched and tempered (Q + T) samples with a high degree of statistical confidence (p = 3.0919E−06). A comparison with other processing sequences indicates that introducing DCT after quenching and prior tempering could contribute to improved hardness better than after tempering. Furthermore, microstructure analysis of the X-ray diffraction data indicates a low amount of retained austenite for all DCT samples when compared to non-DCT samples counterparts, with the lowest amount of retained austenite found to be 3.1 pct in Q + DCT + T samples.