Quench polish quench

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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. [1] Three steps are involved: nitrocarburize ("quench"), polish, and post-oxidize ("quench"). [2]

Contents

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 of shock absorbers, cylinders and rods for hydraulic systems, pumps, axles, spindles, firearm slides and barrels and valves. [3]

Process

The process starts with a standard salt bath nitrocarburizing cycle, which produces a layer of ε iron nitride. [4] 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. [5] It also gives the workpiece a black finish. [3] [6]

Corrosion resistance

Field immersion

Field immersion comparison chart QPQ field immersion comparison chart.png
Field immersion comparison chart
ASTM B117 Salt Spray Test QPQ ASTM B117 comparison chart.png
ASTM B117 Salt Spray Test

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 of hydrogen peroxide for 24 hours.[ citation needed ]

Salt spray test

The chart on the right shows a comparison of the corrosion resistance of surface treated steel automotive steering columns based on the ASTM B117 salt spray test.[ citation needed ]

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Ferritic nitrocarburizing or FNC, also known by the proprietary names Tenifer, Tufftride and Melonite as well as ARCOR, is a range of proprietary case hardening processes that diffuse nitrogen and carbon into ferrous metals at sub-critical temperatures during a salt bath. Other methods of ferritic nitrocarburizing include gaseous processes such as Nitrotec and ion (plasma) ones. The processing temperature ranges from 525 °C (977 °F) to 625 °C (1,157 °F), but usually occurs at 565 °C (1,049 °F). At this temperature steels and other ferrous alloys remain in the ferritic phase region. This allows for better control of the dimensional stability that would not be present in case hardening processes that occur when the alloy is transitioned into the austenitic phase. There are four main classes of ferritic nitrocarburizing: gaseous, salt bath, ion or plasma, and fluidized-bed.

References

  1. "Melonite/QPQ". HEF Group (USA). 14 June 2012. Retrieved 16 February 2014.
  2. Davis, Joseph R., ed. (2002). Surface Hardening of Steels: Understanding the Basics. ASM International. pp. 203–204. ISBN   9781615032501 . Retrieved 16 February 2014.
  3. 1 2 Easterday, James R. (1996). "The Kolene QPQ(SM) Process". Detroit, Michigan: Kolene Corporation. Retrieved 14 February 2014.
  4. Liapina, T.; Leineweber, A.; Mittemeijer, E. J. (June 2003). "Nitrogen redistribution in ε/γ′-iron nitride compound layers upon annealing". Scripta Materialia . Elsevier. 48 (12): 1643–1648. doi:10.1016/s1359-6462(03)00136-2.(subscription required)
  5. "Use Salt Bath Nitriding for Uniform & Consistent Layers". Kennebunk, Maine: Northeast Coating. Retrieved 16 February 2014.
  6. "QPQ Liquid Nitriding". Edmonton, Alberta: Thermex Metal Treating Ltd. 2010. Retrieved 16 February 2014.