M2 Tool Steel surface anomaly post heat treat

[Frank2020]

This M2 shaft gets hardened in vacuum furnace 2220F for 5-10 minutes and 2 bar gas quench. Defect is being witnessed on surfaces not ground after heat treat. Ground surfaces are fine.
Defect looks like a crater, approx .050-.075 in diameter. Could this be related to surface roughness or incomplete degrease prior to HT?

 

[Compositepro]

It looks like some liquid was expelled from a pore and deposited solids in a ring around the pore.

 

[Frank2020]

Thank you for input. Another batch getting processed today - we'll see if it duplicates.

 

[EdStainless]

Pay attention to the orientation of the parts in the load, see if it a top surface or a bottom surface.
We used to see similar, but since these surfaces were either not critical or to ground latter we didn't care.

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P.E. Metallurgy, consulting work welcomed

 

[Frank2020]

Thank you. Parts are oriented with that small hex up,with opposite face of that slotted diameter resting on screen. there is about 3" long shaft approx .200 in diameter extending beyond the slotted diameter shown.
A batch ran yesterday and the condition did not duplicate. We reduced the partial pressure in the vacuum by 25% and used a new pc. of screen for racking.

 

[EdStainless]

I am going to guess that it was debris on the surface.

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P.E. Metallurgy, consulting work welcomed