Spots on cast iron

[jangolobow]

Hay

We are using CAST steel A351 CF8. After cleaning of this cast steel with acid spots like oil spots remain. I am attaching the photo. Does somebody have an idea what those spots are? We can not remove them by cleaning agent, acid, base only mechanically by grinding.

Thx

JG

 

[EdStainless]

Are they there before acid cleaning? have you tried PT?

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P.E. Metallurgy, consulting work welcomed

 

[Tmoose]

What is the scale of the picture ?
How much material do you have to remove to eliminate the spots ?

Have you tried a sequence of solvents like mineral spirits, Acetone, chlorinated brake cleaner, isopropyl alcohol, and finally hot soapy water ?
For each solvent I'd scrub using a brass or nylon brush, and may be heat the casting to 120° F or so if possible.

 

[gtaw]

Magic marker?

Best regards - Al

 

[TugboatEng]

If acid doesn't remove them, could they be related to macrostructure? There could be porosity in those regions and grinding is simply smearing metal over the porosity.

 

[mrfailure]

If you are thinking change in structure or porosity, you could make a replica after preparing the surface and etching to see. Both would show up.

 

[jangolobow]

Hay

thanks for answer!

I marked spots with marker. But spots which were marked remain on the cast. They can only be removed from cast by grinding. I tried all possible solvents without success.
Spots size is up to 5 mm.
What is suppriesingly if we put the cast ins heat own fpr 1 hour to approx 450degVC spots dissapear and after few hours they appear again.

It looks like that some fluid is penetrationg from cast out. Did you ever seen something like that?

J

 

[Dhurjati Sen]

Possibly casting defect - porosity.

DHURJATI SEN