For annealing, brazing or sintering, furnace atmospheres help ensure that metals thermal processors obtain the results they need. Hydrogen-containing atmospheres are used to protect surfaces from oxidation, and to ensure satisfactory thermal processing results. Hydrogen-containing atmospheres make thermal processing more forgiving because the hydrogen improves heat conduction and actively cleans heated surfaces – reducing oxides and destroying surface impurities. For powder based fabrication such as P/M, MIM or binder-jet metal AM, the use of a hydrogen-containing thermal processing atmosphere ensures the highest possible density of the sintered parts without necessitating the use of post-processing techniques. Users of pure hydrogen or hydrogen-containing gas blend atmospheres often struggle with hydrogen supply options. Hydrogen storage may create compliance problems due to its flammability and high energy content. Hydrogen generation enables hydrogen use without hydrogen storage issues. Deployment of hydrogen generation can ease the addition of thermal processing atmospheres to new and existing processing facilities.

The Lehrer diagram often serves as a guide for selecting gas mixtures for nitriding alloy steels, but it is only accurate for ammonia gas nitriding processes when hydrogen is used as the diluting gas. This paper presents the results of a study showing that the use of pure nitrogen as a diluent has a marked effect on the phase boundary lines of the standard Lehrer diagram, essentially shifting them to the left. The paper also includes examples showing where the use of nitrogen is advantageous and where it is not.