Simultaneous ion nitriding and tempering after deep cryogenic treatment of PM S390MC HSS

摘要

Vacuum heat treatment, deep cryogenic treatment and pulse plasma nitriding are efficient techniques 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. This is the case in the transformation of retained austenite into martensite, causing a general increase in hardness and higher wear resistance. In other cases, however, the increase in wear resistance is not supported by higher hardness and several theories were proposed to explain the observed results. However, poor experimental evidence was reported in literature for this phenomenon. Specific attention is paid to the influence of subzero treatment just after quenching and solubilisation in the vacuum heat treatment or simultaneous pulse plasma nitriding and tempering (PPNT) cycle of PM S390MC high speed steel, respectively. Special emphasis was put on resistance to galling and abrasive wear resistance under dry sliding conditions. From results obtained it can be concluded that the application of deep cryogenic treatment results in a significantly higher wear resistance of high speed steels, but no significant improvements in toughness have been noticed.