Impacts of allowed tolerances in temperature on nitriding results

In recent years, nitriding and nitrocarburizing have gained more and more importance in the heat treatment of components. While only a few years ago, it has been common to perform these processes with fixed set temperatures and gas flows, today so-called potential control became state of the art. Consequently, besides appropriate temperature uniformity nowadays also permissible tolerances in atmosphere potential control are required. The article uses the example of the American aerospace specifications SAE AMS2759/10 and 2750D on the extent to how the therein required tolerance bands allow for staying within the specified tolerances of given compound layer thickness. Intensive experiments were conducted using pure iron, carbon steels AISI 1018 and 1070 , the high-tensile steel AISI 4140 and the hot work tool steel AISI H13, where potentials and temperatures have been varied over a wide range in order to make qualified conclusions. As a follow up on an article about the impact of measurement errors on nitriding and nitrocarburizing results (Gaswärme International (60) No. 3/2011 and Heat Processing (9) No. 3/2011) requirements for measurement instruments and furnace equipment are additionally considered. In a second series of experiments, process setup has been varied, in order to quantify the influence of heating and cooling with inert gas or process gas and nitrogen diluted atmospheres.