Effects of Gas Nitriding on the Mechanical and Corrosion Properties of SACM 645 Steel
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Abstract
The effects of the nitrided case produced by gas nitriding processes on the mechanical and corrosion resistance properties of the JIS SACM 645 steel were studied in this paper. JIS SACM 645 steel specimens with different substrate hardness were gas nitrided at 530?C for various nitriding durations. Nitrided specimens were characterized by means of optical and scanning electron microscopy, X-ray diffraction, glow discharge optical spectrometry, microhardness profiling, wear test, torsion mode fatigue test as well as electrochemical corrosion test in an aerated 3.5% NaCl solution. The surface hardness values of the nitrided specimens with Fe3N and Fe4N phases precipitated in the case layer were observed higher than 1000 HV0.1. Mass loss measurement of the wear test showed increases of wear resistance of the nitrided specimens, and the mass losses of the specimens were strongly influenced by nitriding durations. Electrochemical measurements showed that corrosion current density of the specimens was significantly decreased after nitriding and the corrosion potential was shifted to the noble direction as the increase of the nitriding durations. The fatigue limit of the specimen nitrided for 96 h rose 44% to 600 MPa in exceeding the untreated specimen in this study.
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