The Influence of Deep Cryogenic Treatment on Precipitation Phenomena during Tempering and Ageing

The paper presents results of comparative studies of tempering processes of quenched and conventionally treated tool steel vs. the same steel quenched and cryo-treated. Also ageing processes of Al-4.7%Cu alloy after conventional and cryo-treatments are analyzed and the results presented. It has been observed that in both cases cryogenic treatment has an effect on the development of the tempering and ageing processes. The mechanisms of the influence are different in each case. In the cryo-treated steel, the tempering processes already begin in the process of reaching ambient temperature from 196°C and accelerate the increase in hardness because of tempering. In conventionally treated Al-Cu alloy the processes of dissolving precipitates and the resulting decrease in hardness occur earlier than in the cryo-treated alloy. Reazons of such changes have been analyzed.