CISKI Aleksander Institute of Precision Mechanics

Deep Cryogenic Treatment of High Speed Steel

This experimental study investigates the properties of HS6-5-2 high speed tool steel subjected to deep cryogenic treatment (DCT) carried out at -180 °C for 32 hours. Microstructures of conventionally and DCT treated samples were examined with aid of scanning electron microscopy. The characteristic feature of deep cryogenically treated steel, distinguishing it from steel heat treated in a conventional way, was significant refinement of martensite plates. Material processed in this manner was found to exhibit slight decrease in hardness and considerable increase in impact strength. Deep cryogenic treatment caused the decrease of steel’s wear rate for about 42 %. However, this result was obtained during wear test carried out under a load of 100 MPa, while under four times higher load, there were no significant differences between wear resistance of heat treated samples. In the study, performance of deep cryogenically treated twist drills in drilling of ISO C45 constructional steel was evaluated in terms of tool in-service life. The assessment of the durability of drills was based on the occurrence of acoustic emission, as a symptom of obtaining the critical dulling. A general worsening of drills durability was observed after DCT treatment.