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Corrosion of precipitation hardenable stainless steel

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We are supplying a manufacturer of connecting pins with 17/4PH (AISI 630) type of steel bars. They are ground to his finished size and tolerance. After part machining he sends them to a heat treatment shop for precipitation hardening at 482°C for 1 hr in vacuum.
Some of these parts appear after heat treatment to have a lightly corroded surface.

Do you have any ideas what this surface corrosion could be and where it could come from.

Best regards

Barrington Tennant
- Germany

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The oxidation is likely due to incomplete evacuation of the vacuum chamber, or due to a less than perfect seal. Contamination on the door seals can cause the latter. Also, make sure that the surface of the stainless steel component is clean and dry, with no residual oil prior to placement in the furnace.

Toby Padfield
- Michigan

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