Stainless Steel is a more difficult substrate to coat than mild steel or aluminium and therefore requires more care in order to achieve successful adhesion.
Pre-Treatment Is Non-Negotiable
Stainless steel forms a passive oxide layer that will actively resist the attempt of the plating solution to bond to it. This layer has to be broken down in a controlled manner prior to plating, either by an acid activation process or a specialist Woods nickel strike process.
Adhesion Testing After Plating
For stainless steel parts the adhesion of the coating needs to be verified even after the correct pre-treatment has been carried out. Simple tests such as bend tests or cross-hatch tests can be performed on samples or even on complete parts prior to release. Flaking of the coating in these tests will indicate a problem with the activation of the substrate and not a problem with the plating chemistry.
Choosing the Right Phosphorus Content
Electroless Nickel Coating comes in Low Phosphorus (3-6%), Medium Phosphorus (6-10%) and High Phosphorus (10% +) versions. The main factor to consider is corrosion protection vs. wear resistance / hardness. While High Phosphorus coatings give the best corrosion protection they may not be required for parts that are exposed to chemicals only from time to time. Medium Phosphorus coatings are suitable for general engineering applications. Low Phosphorus coatings give higher hardness and improved wear resistance.
Uniform Coverage on Complex Geometry
Electroless Nickel tends to cover recessed areas, bores, holes and threads etc. very evenly due to it’s chemical nature. This makes it an ideal coating for components of stainless steel with complex geometries etc. However, a dimensional allowance of 10 to 25 microns per surface would be expected.
Using a Specialist Plater
Stainless steel plating requires a close control of the plating bath and, above all, good knowledge of the activation processes to obtain good results.
If you are looking for Electroless Nickel Coating, see Poeton.
Getting the substrate right the first time helps to avoid expensive re-work.
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