Modern salt bath nitrocarburizing units can be arranged as fully automated and contained lines and usually consist of an air-preheating furnace, one or several salt bath nitrocarburizing furnaces, which can either be heated electrically or by gas combustion, and a cooling unit that can be an oxidizing salt bath. Such oxidizing posttreatment builds up a thin and dense oxide layer on top of the compound layer that significantly increases the corrosion resistance.
Online monitoring of the chemical composition is not required due to the high stability of the melt and the automatic supply of refill salt and regenerators. The nitrocarburizing line usually ends with three- to four-step washing cascades that also act as a regeneration system for the salt.
Gas nitriding and nitrocarburizing is the most sensitive process regarding passivation effects typical for medium- to high-alloy tool steels. Therefore special attention must be paid to cleaning and pretreatment processes such as preoxidation, controlled oxinitriding, or the use of chemicals such as hydrazine. On the other hand, gas processes have the best accessibility for boreholes and thin gaps.
For more information, click on the link below (subscription required). Then scroll to Figure 21. R Schneider; R. Mesquita; W Schützenhöfer, Distortion in Tool Steels, ASM International, 2014 https://doi.org/10.31399/asm.hb.v04d.a0005958
