D. F. Jordan, Solar Atmospheres, Inc, Souderton, PA
The rate of compound layer formation (white layer) was determined during nitriding of AISI 4140 steel. Nitriding was accomplished in a vacuum furnace with an all graphite hot zone using a pre-nitriding heat up in hydrogen. Nitriding was performed at a slightly positive pressure with an ammonia plus nitrogen gas mixture at 510°C (950°F) and 538°C (1000°F). White layer thickness and depth of the nitrided diffusion zone were determined from metallography and microhardness measurements. The diffusion coefficients of nitrogen in alpha ferrite and gamma-prime were calculated for the above two temperatures. These data were utilized in establishing nitriding cycles to provide the desired structures in the minimum cycle time. Processes were established for structures that required the presence or absence of white layer.
Summary: The rate of compound layer formation (white layer) was determined during nitriding of AISI 4140 steel. Nitriding was accomplished in a vacuum furnace with an all graphite hot zone using a pre-nitriding heat up in hydrogen. Nitriding was performed at a slightly positive pressure with an ammonia plus nitrogen gas mixture at 510°C (950°F) and 538°C (1000°F). White layer thickness and depth of the nitrided diffusion zone were determined from metallography and microhardness measurements. The diffusion coefficients of nitrogen in alpha ferrite and gamma-prime were calculated for the above two temperatures. These data were utilized in establishing nitriding cycles to provide the desired structures in the minimum cycle time. Processes were established for structures that required the presence or absence of white layer.
