KOLENE QPQ Liquid nitriding (also known as salt bath nitriding) is a cost-effective process for producing a thin, high-hardness case that is wear and corrosion resistant.

In the liquid nitriding process, the part is first immersed in a molten salt bath, then polished, then re-immersed in the salt bath (hence the name QPQ, for quench-polish-quench).

The resulting lustrous black coating is an effective replacement for both chrome and nickel plating, outperforming both at a lower cost. Liquid nitriding introduces more nitrogen to the part’s surface creating in superior corrosion resistance.

Liquid nitriding is suitable for a wide variety of carbon steels, low alloy steels, tool steels, cast irons, and stainless steels. Because liquid nitriding is a relatively low-temperature form of case hardening, part distortion is reduced.

Liquid nitriding requires precise control of the treatment process. Thermex operates under an ISO 9001:2000 Registered Quality Management System. Process quality control measures include:

• complete control of process sequence, including salt bath temperature and composition, polishing, and post-treatment parts handling
• test coupons of matching material are run with all nitriding loads. Coupons can then be used for metallurgical analysis in Thermex’s in-house metals testing laboratory. Random microhardness case depth surveys ensure that process specifications are being met.
• daily accuracy checks of all hardness testers

Contact Thermex for more information on our liquid nitriding services.