Improvement of corrosion and wear resistances of 300M ultra high strength steel by low temperature cathode assisted plasma nitriding

This study intends to systematically study the influence rule and mechanism of low temperature cathode assisted plasma nitriding (LTCPN) on the corrosion and wear properties of 300M steel. The research results were as follows: LTCPN technology effectively improved the nitride efficiency by accelerating the ionization rate of the working medium and the activity of nitrogen ions, so that the 300M steel could obtain the nitrided layer of 4 μm, 10 μm, 60 μm, 170 μm and 210 μm at 250 °C, 300 °C, 350 °C, 400 °C and 450 °C. LTCPN technology effectively improved the corrosion resistance of samples at 250 °C ~ 450 °C. Among them, more excellent corrosion resistance could be produced on the sample surface by LTCPN-treated at 350 °C, which attributed to introducing more ε-Fe₃N phases, higher residual compressive stress, and lower surface roughness. In addition, LTCPN technology also reduced the wear damage of 300M steel at different temperatures. LTCPN-treated sample at 300 °C achieved the best wear resistance due to the introduction of the higher hardness and surface compressive residual stress (CRS), deeper nitride layer, and lower surface roughness on the sample surface. The above results showed that LTCPN treatment had a great application prospect in synchronously improving the wear and corrosion behavior of martensitic ultra-high strength steel.