Researchers from Solar Atmospheres, Souderton, Pa., will discuss the influence of nitrogen and hydrogen as diluting gases during nitriding of iron and low-alloy steels at the ASM International Heat Treat 2019 conference in October.
In many large industrial furnaces, atmospheric ammonia gas nitriding processes use nitrogen as the diluting gas for safety, economic, and environmental reasons. The widely published Lehrer phase diagram for ammonia/hydrogen gas nitriding of pure iron has been used as a reference guide for selecting ammonia/nitrogen mixtures for nitriding of alloy steels. However, when the diluting gas is not hydrogen, the diagram is not precise or accurate.
Recent R&D gas nitriding studies on pure iron powders indicate that the use of nitrogen as the diluting gas produces considerably different compound layer (white layer) phase ratios when compared to the standard Lehrer ammonia/hydrogen mixtures, according to XRD analysis. Current data reveals that nitrogen shifts the Lehrer diagram phase boundaries to the left. This is pertinent to the topic, as only the gamma prime phase (Fe4N) is desired, not epsilon (Fe2-3 N). Literature indicates that Fe4N has uniquely sought-after magnetic properties in some specialized industries.
Materials are currently being tested to compare the pure iron results to those obtained when nitriding common low-alloy medium-carbon steel.
Presentation title: “The Influence of Nitrogen versus Hydrogen Diluting Gas on the Compound Layer Phase Formation During Ammonia Gas Nitriding of Iron and Low Alloy Steels.”
Authors: Dr. Virginia Osterman, Mr. Donald Jordan; Solar Atmospheres, Souderton, Pennsylvania. www.solaratm.com
Heat Treat 2019: 30th Heat Treating Society Conference & Exposition
October 15-17 in Detroit
Conference website: https://www.asminternational.org/web/heat-treat-2019/home
