Q: Looking for a bolt rated 320 psi for use at a temperature of 1292F on an Incoloy 80oHT flange? Suggestions?
A: Assuming you want hex head bolts and Inconel 625 is probably your best choice at those temperatures. At about 1300F, Inconel 625 bolts (per the chart below) should be able to withstand a yield of 60,000psi. If that seems overkill you could look at Alloy 330 bolts which will have about 20,000psi at 1300F.