N2/H2 Non-thermal Transferred arc Plasma Nitriding Treatment of Stainless Steel at Atmospheric Pressure

In the paper, a novel metal surface nitriding method is presented by using an atmospheric pressure non-thermal transferred arc plasma technique. In the N-2/H(2)plasma nitriding process, the surface of stainless-steel is treated by the arc root, which shows an irregular movement in a circle-like zone with about 5 mm diameter observed by high speed camera. The discharge has characteristics of high voltage and low current, and the gas temperature of the arc column plasma is only about 2900 K determined by the diatomic molecule N-2(+)(B-2 sigma u+-> X-2 sigma g+) fitting method. It is found that the NH radical production in plasma plays an important role in the nitriding process. The thickness of nitrided layer can reach 60 mu m after processing of 120 min under the optimal experimental conditions. The surface hardness of stainless-steel increased from 220 to about 1200 HV0.1(Vickers hardness under the force of 0.1 kg) after plasma treatment. The treating saturation time for stainless-steel surface hardness reaching to 1200 HV(0.1)is around 9 min.