I'm trying to electropolish a piece of Stavax ESR (from Uddeholm.com) using an ESMA E678-1 electropolisher with an electrolyte based on phosphoric acid (Cougartron CGT-550).
Stavax ESR contains 0.38% C, 0.9% Si, 0.5% Mn, 13.6% Cr and 0.3% V.
I have already successfully electropolished several stainless parts and thought that there would be no problems with the stainless Stavax ESR steel as well. However, after electropolishing by the same procedure as usual, between 5 to 25 min on 8-9 V at 50°C, the end finish made the already shiny regions on the piece matte.
However, what confuses me is that while the sawn surfaces get matte after the polishing, the rough surfaces from the raw forging actually gets shiny. I have attached a picture showing a non polished piece and an electropolished piece for reference.
My guess is that the forged surface maybe have a different composition that allows it to be polished in this certain electrolyte. But this is just a guess...
Does anyone know the cause of this problem?
And does anyone know a way that I could make it work?
My wild guess is as followed:
The electrolyte worked fine with low carbon versions of stailess steels and not suitable for high carbon VC containing alloy. The forged surface would have been decarburized and therefore got a shiny appearance after electro-polishing.
How about decreasing the electrolyte temperature to 10 deg. C or decreasing the voltage to ~ 5 V or both! If you have already tried playing with the parameters without any success then the other option is a different electrolyte!
There are 3 reasons for this problem:
1-your choice for electrical current is not correct.
2-electropolishing time is not correct.
3-your material is not suitable for electropolishing technique.
I don't think forged surface would have a very much difference in composition.
I think the reason lies in the following sequence of "as - received" or the "starting " roughness.
The sawn surface is the most roughest, the matter finish the middle roughness and the electropolished one the lowest roughness.
When all are electropolished for the same duration in identical baths, you get differences in polished finishes.
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