Gas Nitriding Stainless Steel
Gas Nitriding of stainless steel is possible but is not commonly available due to the complexity involved.
AIHT is uniquely capable of gas nitriding stainless steel! This specialty process improves on the more commonly used salt-bath (liquid) nitriding method by offering deeper case depths and higher quality case hardening
The second challenge with stainless steels is the high amount of Chromium. Chromium has a high affinity for nitrogen and slows diffusion, thereby limiting the achievable case depth. Max case depth is typically 0.005-0.008” depending on the alloy. Conversely, the hardness of the nitrided layer in stainless steels is very high, typically >68HRC.
Stainless steel nitriding requires careful control to ensure a suitable microstructure forms at the surface. Nitriding of stainless steel is a complex metallurgical problem, as an understanding of the layer growth kinetics is key. If the process is not carefully managed, the white layer can grow uncontrollably and could cause the nitrided surface to become brittle.
Care should also be taken when developing a stainless nitriding recipe as using a one-size-fits-all approach can cause problems for some alloys. Austenitic stainless steel like 316L should not be subjected to the same treatment as precipitation hardened stainless steel like 17-4PH as there may be unintended consequences such as sensitization. AIHT leverages the understanding of its team of Ph.D. metallurgists to ensure that customers receive the right treatment for their application.
Stainless gas nitriding can be tailored to mimic liquid nitriding, but is also capable of deeper cases and superior white layer control.
For some recipes and stainless steels, a Post-Oxidation Reaction (PROTM) will result in the formation of a black surface as with alloy steels.