Correlation between Tetragonality and the Residual Stress in Cryotreated Spring Steels

Abstract

In the conventional heat treatment process (CHT), a significant amount of compressive stressoccurs in the material as a result of the quenching process. After the tempering process, it is seen that thematerials lose those compressive stress. This loss can be explained by the formation of carbide structures andthe loss of tetragonality of the supersaturated martensite structure. The cryogenic treatment is a complementaryprocess that it has been given to a miscellany of materials to improve their mechanical and physical attributes. Itwas first commercially recognized as an effective method in achieving complete martensitic transformation inthe alloyed steels. In this study, microstructural investigations were carried out in order to relate themicrostructural properties to the mechanical properties following the cryogenic treatment. For this purpose, theconventional heat treatment (CHT) and the deep cryogenic treatment (DCT: -196°C) procedures were applied tovarious medium carbon spring steels. The martensite lattice parameters and the amount of retained austenitewere measured by using high-resolution X-ray diffractometer. Rietveld analysis was used to deconvolute theoverlapping peaks of martensites.