QPQ process suitability 2

[BrianBT]

We have a component that operates subsea at a depth of 100m

It is a latch mechanism whose trigger plate is subject to point low load abrasive wear by locks which slide over it. The wear takes the form of grooves in the edge of the trigger plate which is also subject to corrosion

Due to longevity of originals we were considering replacing these triggers with stainless steel. However, we are being offered units which have been surface treated using QPQ ( I assume melonite-QPQ)

I can see how it may improve corrosion resistance but will we see and improvement in wear rates

 

[arunmrao]

I have made similar parts for subsea applications. Ofcourse the use of trigger was only once and not often. The parts were made in 316 grade and were tested after placing them under sea water for varying times upto a period of 1 year. No deterioration in performace was observed.I hope this information is helpful.

" All that is necessary for triumph of evil is that good men do nothing".
Edmund Burke

 

[TVP]

First QPQ is a generic description of a process involving ferritic nitrocarburizing + polishing + oxidation treatment. Melonite is only one version, Kolene is another. Regarding wear resistance, the hard nitride layer (~800-1000 HV hardness) improves wear resistance of steels, and the polishing and oxidation treatment generally reduce friction. However, in a seawater environment I am not sure how much if any friction reduction would be possible. The last point is regarding corrosion resistance: while the QPQ process does impart improved corrosion resistance to carbon and alloy steels, it is only on the order of hundreds of hours during salt spray tests. Constant wear in a seawater environment will almost certainly cause a corrosion failure.