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What's The QPQ And The Advantage Of QPQ

Dec 09, 2015

Quench polish quench (QPQ) is a specialized type of nitrocarburizing case hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer or Melonite.Three steps are involved: nitrocarburize ("quench"), polish, and post-oxidize ("quench").

This process is often used when two or more of the following properties are required in a workpiece:

wear resistance

corrosion resistance


fatigue strength.

Common applications of the process are for piston rods of shock absorbers, cylinders and rods for hydraulic systems, pumps, axles, spindles and valves.


The process starts with a standard salt bath nitrocarburizing cycle, which produces a layer of ε iron nitride. Next, the workpiece is mechanically polished; typical polishing processes include vibratory finishing, lapping, and centerless grinding. Finally, the workpiece is re-immersed into the salt quench bath for 20 to 30 minutes, rinsed, and oil dipped. This last step optimizes the corrosion resistance by creating a layer of iron oxide about 3 to 4 micrometers thick.It also gives the workpiece a black finish.