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Stainless Steel Rusting

Stainless Steel Rusting

Stainless Steel Rusting

(OP)
I was wondering if anyone could describe what is happening in the attached picture.  The parts are cast stainless CF8 as per ASTM A351 and then machined. We obtained data from an independent lab that showed that the chemisty and physicals were per the standard.  The parts were put through an environmental test with humidity and temperature (80°C).  Out of 12 units only 3 showed signs of this corrosion.

Could suggestion be made on how to remedy this issue?

RE: Stainless Steel Rusting

What is the post machining processing? Are the parts passivated? What type of machining fluid is used?

RE: Stainless Steel Rusting

(OP)
There are no post processing steps after machining.  I am unaware of what type machining fluids were used?

RE: Stainless Steel Rusting

It looks like you may have machined into inclusions or unmixed metal in the casting.  Are there pits at these locations?
Clean them up and passivate in nitric acid and see it you still get the same response.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Stainless Steel Rusting

free iron ions are everywhere, cutting fluids, dirty hands, shop dust, compressed air used for drying,dirty rags,etc...

RE: Stainless Steel Rusting

Do all the pieces have the same type of discontinuity or are the other 2 in different areas... can you send pictures of the other 2... if possible?
Thanks

RE: Stainless Steel Rusting

Hi Timbow123

The last picture looks more like a casting defect to me.

desertfox

RE: Stainless Steel Rusting

Agree with desertfox. Looks like you machined into casting flaws.

RE: Stainless Steel Rusting

These are definitely inclusions in the cast material.
 

----------------------------------------
Paul van der Heijden
Composite Engineer
Vekoma Rides Manufacturing BV
Internet: www.vekoma.com
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RE: Stainless Steel Rusting

That is  a slag or sand  defect observed. . Probably this went unnoticed by the foundry, else they could have salvaged it. Actually defect is over a large surface area, and should have been noticed while grinding or after shot blasting.

I have not failed. I've just found 10,000 ways that won't work." — Thomas Edison
_____________________________________
 

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