Correlation between Tetragonality and the Residual Stress in Cryotreated Spring Steels

Abstract

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

Keywords

• Steel
• Cryogenic
• Residual stress
• Rietveld