| The influence of incorporating different cryogenic phases in the heat treatment sequence of D series cold working tool steels is reviewed. The micro structural changes taken place for different grades of cold working steels under this series, by incorporating a cryogenic treatment process within the conventional heat treatment cycle is focused for this review analysis. Also, the changes in mechanical as well as tribological properties of these steels due to this additional treatment are discussed with emphasis on the factors contributing to the enhancement of these properties. AISI D series represents tool steels with high carbon and high chromium contents which exhibit good post treatment hardness and are having good machinability in the pre treated conditions. Hence, they are widely used for making press tools, plastic moulds, knifes, blades etc which need good wear characteristics. D2, D3, D5, D6, and D7 are the grades of tool steel selected for this review. The improvements obtained by the deep as well as shallow sub zero treatments conducted in various sequences of operations are noted. Comparisons within the material and within the series are reviewed for different cases. The advantages and disadvantages of having cryogenic treatment as a secondary heat treatment for D series tool steels are highlighted. |
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