Influence of Deep Cryogenic Treatment on the Mechanical Properties of AISI 440C Bearing Steel

摘要

This research paper focuses on the influence of shallow and deep cryogenic treatment on the mechanical properties of AISI 440C bearing steel. Hardness of this material is increased by 7% when subjected to Deep Cryogenic Treatment (DCT); and by 4% for Shallow Cryogenic Treatment (SCT) compared to the Conventional Heat Treatment (CHT). 'ImageJ' software has been used to analyse the optical microscope image of the conventional and cryogenic treated samples to estimate the retained austenite percentage. The retained austenite percentages of these samples were 29%, 8% and 5.7% for the conventional, shallow cryogenic and deep cryogenic treated samples respectively. DCT sample shows relatively higher hardness than CHT samples due to higher conversion of retained austenite to martensitic structure. DCT sample shows minor increment in hardness when compared to SCT. DCT and SCT samples show improved hardness by 7% and 4% than that of the CHT sample. Fractography analysis of the cryogenically and conventionally heat treated bearing steel were performed using Scanning Electron Microscope (SEM). SEM analysis clearly indicates the formation of flat facets in SCT specimens and micro cracks in DCT specimens.