Surface Treatment of Mild Steel

We all use a lot of mild steel in model engineering and so I thought I would list and discuss the surface treatment options:

  • galvanizing
  • electroplating
  • powder coating
  • nitriding
  • flame spraying
  • electrocoating
  • painting

Black Surface – there are a number of ways of achieving a black surface on mild steel, one way is to quench the parts in a bath of old engine oil. The other way is to use a chemical gun blue treatment.

Gun Blue – a chemical treatment of the surface that leaves a black finish. This can look slightly rusty and so depending on the use of the resultant part I find it best to lightly oil the surface or use a bees wax after I have a good solid black colour.

Commercially available products such as Perma Blue work rather well, I use a small paint brush to apply it to a well cleaned and degreased surface. Sometimes 2 applications are necessary.

Brown / Copper Surface – heat the part with a blow torch to around 500°C and then quench in a solution of copper sulphate, you will get some areas of copper forming on the surface. Then re-heat the parts to around 500°C and allow to cool. I then just cleaned them with detergent and water before buffing with a small amount of beeswax and a cloth.

Chess men made in mild steel and then hot quenched in copper sulphate solution

References

  • finishing.com – a community forum for all sorts of different surface finishes including electroplating.
About Nigel 228 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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