Deep Cryogenic Treatment of Alloy Steels : A Review

The word, “Cryogenics” is taken from two Greek words – “kryos” which means cold or freezing, and “genes” meaning born or generated. Technologically, it means the study and use of materials (or other requirements) at very low temperatures. In general cryogenic treatment consists of slow cooling already heat treated part to approximately -196C, holding at low temperature up to prescribed period, reheating without thermal shock to room temperature and reheat to a moderately elevated temperature (150 to 315C) for about 1 or 2 hours, to "temper" the part for the stated purpose of reducing its brittleness. It has been tried with several materials and the results in some cases are fascinating and for certain materials cryogenic treatment did had small changes or no change at all. At present also the initial mistrust about cryogenic treatment has not been cleared up, because it imparts no apparent visible changes to the metal. Alloy steels especially high speed steels, stainless steel, cast iron did show beneficial results where as carbide inserts showed results to certain extent. Even though in case of certain materials due to cryogenic treatment some of the properties are improved, still there is need of systematic investigation to make of the process in commercial sense. In this paper an attempt is made to review the investigations made and published for the effects of the cryogenic treatment on properties of alloy steels.