Discolouration of A286 2

[MrTibbs]

Hi Guys,
I've got my fingers crossed that someone on here can shine some light on this situation. I'm precipitation hardening some A286 and im experiencing a finish of either blue or gold (I'm after the same colour prior to treatment)?? Im processing it through a vacuum furnace but cant think as to why I'm getting such a finish??

Any ideas?

Cheers

 

[metengr]

These colors would imply heat tinting from either exposure to air or some type of surface contamination. The same blue and gold/straw colors are sometimes seen after welding austenitic stainless steels with poor shielding/backing gas.

 

[TVP]

As metengr stated, it sounds like surface oxidation that is caused either by surface contamination that is not properly cleaned prior to heating, or a leak in the vacuum furnace seal, etc.

 

[mighoser]

If I recall A-286 has a PH treatment temp of 1325F for 16hrs + Air quench. As others have said, pull the vacuum data chart. The other area to investigate is the cooling method after completion of the aging. Ideally a cooling plate is used while maintaining vacuum but this isn't that common practice. Most backfill with argon. Make sure the lines are dedicated and don't share with house air or nitrogen. Gold coloring may be an indicator of nitrogen. If argon is being used, you might want to stream gas into the furnace while pumping down and then kill the flow to achieve the desired vacuum pressure.