Abstract
The purpose of this study was to reveal the changes in properties of deep cryogenic treatment (DCT) processed high speed steel, in comparison to conventional heat treatment for secondary hardness. Tool properties were assessed in terms of hardness, and tensile strength. Statistically significant enhancement in the mechanical properties was observed. Cryogenic processing of HSS tool steel eliminated the retained austenite, and hence increased the hardness of the material. This treatment initiated nucleation sites for precipitation of large numbers of very fine carbide particles.Tensile values for cryogenically treated HSS samples can be attributed to the fact that the tool becomes more brittle after the treatment. XRD analysis illustrated the contraction in lattice of martensite and austenite. Deep cryogenic treatment practically removed all traces of austenite in the sample. The superior performance of cryogenically treated HSS can be attributed to the transformation of almost all retained austenite into martensite, a harder structure and precipitation of fine and hard carbides.
Highlights
Application of cryogenic treatment in enhancing properties of tool materials has received wide acceptance by researchers and industries
The present experiment was carried out to assess the enhancement in the mechanical properties of HSS tool and the compositional analysis by X-ray diffraction (XRD) analysis
The mean values pertaining to hardness were 29.5,65.5 and 68 HRc for raw,CHTand deep cryogenic treatment (DCT) toolbits, respectively; depicting about 3.81% improvement in the hardness of the toolbits on cryogenic processing.Increase in hardness of cryogenically treated samples is due to the conversion of retained austenite to martensite and due to the presence of fine carbides in the metal matrix
Summary
Application of cryogenic treatment in enhancing properties of tool materials has received wide acceptance by researchers and industries. Conventional heat treatment gives hardness, wear resistance and ductility to steel. It cannot remove all of the retained austenite (large, unstable particles of carbon carbide) from steel. Cryogenic treatment commonly referred to as cryotreatment, is an add-on process to the conventional heat treatment of tool/die steel It consists of controlled cooling of conventionally hardened steel specimens to some selected cryogenic temperature (–500c to–1960c) and holding there for sufficiently long duration Cryogenic treatment improves wear resistance, hardness, toughness, resistance to fatigue cracking, microstructure of metal (retained austenite to marten site), dimensional stability and decreases residual stresses. Cryogenic treatment gives machining, grinding and polishing finish due to little soft austenite[6] In this direction, the present experiment was carried out to assess the enhancement in the mechanical properties of HSS tool and the compositional analysis by XRD analysis
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