Analysis of the effect of Deep Cryogenic Treatment on the hardness and microstructure of X30 CrMoN 15 1 steel

The heat treatment response and the microstructure of a high-chromium steel alloyed with nitrogen was investigated. Deep Cryogenic Treatment after quenching and prior to tempering was confirmed to be crucial in order to maximise the hardness of the steel. The different contributions to hardness of the various constituents (martensite, retained austenite, carbides and carbonitrides) were quantified by an equation based on the composite model. Although simple, the model was able to describe the experimentally observed variation in hardness as a function of the austenizing temperature, and could also be used to estimate the volume fraction of the different constituents for a given austenizing temperature.

► The quenching behaviour of a high N 15%Cr–1%Mo steel has been investigated.
► Quenching temperature above 1100 °C result in high fraction of retained austenite.
► Deep Cryogenic Treatment transforms retained austenite.
► Tempering of the Deep Cryogenic treated steel results in higher hardness.
► The hardness after quenching can be modelled by the composite model.