DEEP CRYOGENIC TREATMENT OF P/M S390MC HIGH SPEED STEEL

摘要

Deep cryogenic treatment is claimed to be an efficient technique to improve the properties of tool and high speed steels. Sometimes the influence of subzero treatment could be directly ascribed to a specific metallurgical transformation. It is the case of the transformation of retained austenite into martensite, causing a general increase in hardness and higher wear resistance (but lower toughness!). In other cases, however, the increase in wear resistance is not supported by a higher hardness and a lot of theories were proposed to justify the observed results. However, poor experimental evidences were reported in literature for this phenomenon. Specific attention is paid to the influence of subzero treatment placed just after quenching and solubilization in the vacuum heat treatment or nitriding cycle of the P/M S390MC high speed steel, respectively. Special emphasis was put on abrasive wear resistance and resistance to galling under dry sliding conditions. Abrasive wear resistance was tested under reciprocating sliding conditions using alumina ball, while galling resistance against austenitic stainless steel was determined in a load-scanning test rig. From obtained results it can be concluded that the application of deep-cryogenic treatment results in significantly higher wear resistance of high speed steels, but no significant improvements in toughness have been noticed.