Nitriding of stainless steel in a glow discharge in crossed electric and magnetic fields

A nitriding process is described in which a deeper hardened layer is obtained and the treatment time is shortened. The workpiece is the cathode in a glow discharge in a mixture of nitrogen and hydrogen at low pressure; a magnetic field is applied perpendicular to the electric field. Because of the magnetic field it is possible to obtain a glow discharge at gas pressures much lower than those in conventional ion nitriding. In consequence, ions bombarding the workpiece have a very high energy, leading to efficient nitriding. The process was applied to ion nitriding of AISI 304 stainless steel where, as an example, a case depth of 200 μm was achieved with a treatment time of 1 h.