MACROSCOPIC CHARACTERISTICS OF PLASMA-NITRIDED AISI-4340 STEEL

Plasma-nitrided AISI 4340 steel, in a low-pressure abnormal glow discharge was studied. The layer formation and their characteristics, were studied as a function of the main macroscopic parameters of the gas discharge: gas flow, N2/H-2 mixture, treatment time and sample temperature. The nitrided layers were characterized using a metallographic microscope coupled to a microhardness tester and X-ray techniques. Typical results obtained for samples which were nitrided for 2 h in a gas mixture of 0.9N2 + 0.1 H-2 at 793 K, showed a white layer composed of epsilon and gamma' phases, 20 mum thick, and a 1 100 HV20 microhardness.