Diffusion Layer Growth Mechanism in ASPN Method Using an Iron Cage for St52 Steel

The mechanism of diffusion layer growth in plasma nitrided coatings applied on a St52 steel using an active screen is investigated. The nitriding was performed at 450,500 and 550 degrees C temperature nitriding times of 5, 10 and 15 h, in a gas mixture containing 20 vol. % H2: 80 vol. % N2 and DC-pulsed plasma nitriding unit. The surface, cross section and the thickness of diffusion of specimens was studied in terms of optical and scanning electron microscopy. According to the measurements of diffusion layer thickness, values of Q and DO for nitrogen diffusion in substrate were calculated as 50585 (j/mol) and 4.11x 10-10 (m2/s)respectively. The variations of depth of hardness during nitriding period was determined.