Is heat scale cosmetic only? 1

[rollingcloud]

The material is UNS S42716. It was supposed to be heated to 1925 °F (1052 °C), held at heat for 30 minutes, quenched in oil, sub-zero cooled to -100 °F (-73 °C), held for 2 hours, warmed in air to room temperature and tempered at 350 °F (177 °C) for an hour.
Is the black discoloration a heat scale? I was told that the ones on the left are not an issue and its only cosmetic. However, the one on the right looks much worse. The finish requirement is 32 Ra, would the scale make the surface too rough? Does it decrease the corrosion resistance?

 

[EdStainless]

The ones on the left look like staining from the wash water.
Any scale or tint on a stainless is bad news as it ties up Cr reducing the local corrosion resistance.
How were they supposed to be descaled?

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P.E. Metallurgy, consulting work welcomed

 

[MintJulep]

What's the size? Are they an inch, a foot, mm or kilosomethings?

So if I imagine that the things are about an inch diameter the two on the left look better than 32 Ra. The one on the right maybe not so much.

 

[mfgenggear]

Op
If part are not protect while heat treatng will have damage on the surface.
Did not mentioned these parts appear that it was run in vacuum or and protective atmosphere.

Parts should be semi finished then after heat treat then should be finished machined.

 

[TugboatEng]

Pickling or electro polishing are options IF necessary. Stainless alloys have some desirable properties involving ease of storage and wear resistance that don't necessitate a perfect surface finish. Exhaust valves in engines are a good example. They rarely have the heat scale removed.

 

[mfgenggear]

Electro polishing is a great way to polish parts. But not advisable for close tolerance dimensions.

Any time pats are heated over 800 degrees F
Parts will obtain light scale. On rough out parts parts are eighter vapor blast for close dimensions, or abrasive blast on roughed parts. Abrasive can be aggressive stock removal. Not advisable on close tolerances.
There are measures to protect parts during heat treat. To prevent scale. Copper plating, protective atmosphere, vacuum heat treat.
Bagging parts, or covering with foil.