Quench polish quench (QPQ) is a specialized type ofnitrocarburizingcase hardening that increases corrosion resistance. It is sometimes known by the brand name of Tufftride, Tenifer or Melonite.[1] Three steps are involved: nitrocarburize ("quench"), polish, and post-oxidize ("quench").[2]
This process is often used when two or more of the following properties are required in a workpiece:
Common applications of the process are for piston rods ofshock absorbers, cylinders and rods forhydraulic systems,pumps,axles,spindles,firearm slides andbarrels andvalves.[3]
The process starts with a standard salt bathnitrocarburizing cycle, which produces a layer of ε iron nitride.[4]Next, the workpiece is mechanically polished; typical polishing processes includevibratory finishing,lapping, andcenterless 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 ofiron oxide about 3 to 4 micrometers thick.[5] It also gives the workpiece a black finish.[3][6]
The chart on the right shows a comparison of corrosion resistance against other surface treatments, based on field immersion tests. Test conditions for the immersion test are full immersion in 3%sodium chloride plus 3 g /L ofhydrogen peroxide for 24 hours.[citation needed]
The chart on the right shows a comparison of the corrosion resistance of surface treated steel automotive steering columns based on the ASTM B117salt spray test.[citation needed]
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