Maraging 300 turned brown. 2

[RoarkS]

Howdy,

I'm working with some parts made from Maraging 300... parts came out of the CNC with some burrs. They went in a wet tumbler, and after about an hour with water and ceramic tumble media... they turned a light tinge of brown. Almost anodize looking in appearance.
Instant reaction is that it is rust. simplest answer right. But we tumble 17-4, 303, 400 stainless parts all the time. based on the nickel content I would expect it to behave like a stainless.

Is there something well known about mar300 that we are unaware of?

It has a lot of Cobalt in it...and I have no idea what that does as far as corrosion. Did it react with the water? a contaminate in the media such as aluminum, iron oxide from other parts so on? React with the rust inhibitor (we use PDN-50 Detergent... okay now that I looked that up that's my primary suspect).

Thanks!

 

[EdStainless]

Ni has no impact on rust resistance, that is a function of the Cr content.
M300 is a steel, it will rust.

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P.E. Metallurgy, Plymouth Tube

 

[btrueblood]

There is not necesarily any chromium in maraging steels, so they can rust.

 

[RoarkS]

Rgr that!

Thanks!

 

[ornerynorsk]

Make sure any chemicals used will not leach cobalt.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[EdStainless]

Watch out for strong caustics. You can clean in alkaline cleaners, but minimize the temp and time.

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P.E. Metallurgy, Plymouth Tube