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Microstructural evaluation of PM S390 MC high- spped steel using Transmission Electron Microscopy

The research deals with the study of the impact of microstructure on the tribological properties of PM S390 MC high-speed steel (Böhler), prepared by powder metallurgy with chemical composition in weight % of 1.64 C, 0.60 Si, 0.30 Mn, 4.80 Cr, 2.00 Mn, 4.80 V, 10.40 W, 8.00 Co and the rest was Fe. Different microstructure conditions of high-speed steel were obtained by heat treatment in two ways: conventional (vacuum hardening, three high-temperature temperings) and deep cooling (vacuum hardening, deep cryogenic treatment, high-temperature tempering). In some experiments, nitriding in plasma of ionising gases was also carried out. Thin foil specimens for transmission electron microscopy (TEM) were prepared using Jeol EM-09100IS Ion Slicer and further analyzed by TEM (Jeol JEM-2100 and Jeol ARM 200F) using conventional TEM (CTEM) and energy dispersive X-ray spectroscopy (EDS, Jeol JED-2300 Series) at 200 kV electron accelerating voltage. Detailed characterization of the microstructure was performed on thin foil specimens, and electron diffraction method was used as well to carry out the microstructure–crystallographic analysis of the phases. In the martensite microstructure some nanometre sized areas of possible other phase were observed. This study tries to explain whether these areas are nanometre sized carbide precipitates. The research showed that the microstructure obtained by deep cooling and nitriding compared to conventional heat treated resulted in an increase of wear resistance of PM S390 MC high-speed steel.

TEM analysis; powder metallurgy; high speed steel; microstructure

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