Deep cryogenic treatment of plain-carbon and low-alloy steels

Abstract

To improve the mechanical properties of steels, cryogenic treatment is often carried out as an intermediate step between quenching and tempering. The transformation of retained austenite into martensite is the main objective and principle behind the cryogenic treatment. Generally, high-alloy and high-carbon steels are subjected to cryogenic treatment, as they produce a high fraction of retained austenite during quenching as compared with low- and medium-alloy steels. This work analyses the effect of cryogenic treatment on EN8, a plain-carbon steel, and EN47, a low-alloy steel, through microstructural characterization, hardness measurements, and tensile tests. The work shows that influence of cryogenic treatment carried out after tempering is only marginal, whereas cryogenic treatment carried out before tempering yields much better mechanical properties. Experimental results obtained in this work confirm that EN47 responds slightly better than EN8 suggesting that low-alloying additions influence the cryogenic treatment of steels. This work established that by properly applying cryogenic treatment, the strength and hardness of both EN8 and EN47 steels can be increased by about 50 MPa and 3 HRC, respectively, as compared with conventional hardening and tempering treatment. © 2021 ASTM International. All rights reserved.