Background: The effect of the holding time of the deep cryogenic treatment on the strain hardening of HY-TUF, a\nlow-alloy medium-carbon steel, and a comparison with strain hardening of conventional heat-treated steel were\ninvestigated.\nMethods: For this purpose, a deep cryogenic treatment was done for different holding times of 12, 24, 48, and\n72 h. The metallographic results indicate completion of martensitic transformation; �·-carbide precipitation and\ndecrement of carbon concentration in martensitic matrix happened while carrying out a deep cryogenic process.\nResults: Observations of transmission electron microscopy indicate higher density of dislocations within martensite\nnear the cementite compared to that near the �·-carbides. The tensile flow stress data for this steel was examined in\nterms of Hollomon equation. The results show that strain hardening of conventional heat-treated steel takes place\nin two stages.\nConclusions: This evidence is related to the co-deformation of austenite and martensite. The strain hardening takes\nplace in one stage for the deep cryogenic-treated steels, and their strain hardening exponents increase (from ~0.29 to\n0.47) with an increasing holding time up to 48 h. A further increase in the holding time of the deep cryogenic treatment\nis found not to vary strain hardening exponent. The increase of strain hardening exponent and then observation of\nplateau in this parameter show an optimum value for the holding time of the deep cryogenic treatment (48 h).
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