Salt bath nitriding, or Quench-Polish-Quench, (QPQ) is particularly important to companies such as oil field service firms whose parts operate for extended periods in highly corrosive environments and are subject to high levels of friction. 

QPQSM provides excellent corrosion protection of cast iron and steel components and is an effective and environmentally acceptable alternative to chrome and cadmium coatings.

QPQSM is a diffusion process that provides distortion-free dimensional stability while hardening the surface of the part (up to three times the strength of carbon steel) thereby producing superior wear resistance, improved fatigue strength, and surface lubricity.

The term “QPQ,” or Quench-Polish-Quench is based on a sequence of process events that occur directly following the nitrocarburizing cycle. It begins with ta pre-wash treating cycle, then a pre-heat step, and finally a nitrorcarburizing salt bath quench which produces a layer of epsilon iron nitride 

The next step is a mechanical polish of the nitride layer, thus restoring the original surface finish. This may be accomplished by vibratory polishing, lapping, centerless polishing, or by other similar means. Finally, to optimize the corrosion resistance, the component is then re-immersed in the salt quench bath for 20-30 minutes, rinsed and oil dipped. The overall process gives the work piece a cosmetically appealing matte black finish.

HP&C further enhanced its capabilities with the addition of a separate QPQSM service line in the Humble plant, thereby doubling its QPQSM capacity. 

For additional information on our Electroless Nickel, QPQ, Phosphate, Spray or other coatings services, please contact your Houston Plating & Coatings sales representative at 713.946.8920.









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