EFFECT OF CRYOGENIC TREATMENT ON MICROSTRUCTURE OF T - 15 TOOL STEEL

Cryogenic treatment process uses sub - zero temperatures down to - 184°C to modify the micro - structure and properties of material. This process is an extension of heat treatment which further improves the properties of material. This paper focuses on the effect of cryogenic treatment on High Speed Steel (T - 15) tool material. Cryogenic treatment at - 184°C is conducted in this research and its properties compared with untreated mate rial. It has been found that as the temperature is decreased, microstructure of material is refined and more number of carbide precipitates appeared on the surface after the treatment. Interestingly to note that the retained austenite is completely convert ed into martensite after subjecting the T42 HSS specimen to cryogenic treatment. The micro structural changes results in improvement of properties of HSS, (T - 15) tool material. The X - Ray diffraction pattern showed that the presence of retained austenite in CT HSS has been found to be very less as compared to UT HSS specimen. During cryogenic treatment contraction in lattice of martensite and austenite took place. Due to super saturation martensite with carbon and thermodynamic instability, the carbon atoms squeezed out of martensite, migrated to the neighbouring lattice defects and acted as nucleation sites for the growth of fine carbides