Q: I am looking to eventually get a quote for some 3/8″ studs and nuts. I need to have a min yield stress of 29 ksi at 700F. SA-540 Grade B22 Class 2 or SB-637 should work. Is this something you can provide?

A: These are very different materials: A-540 Grade B22 Class 2 and SB-637 (Inconel 718). For sure the Inconel 718 studs will give you the strength you need of 29 KSI at 700F but it may be a bit overkill. Inconel 625 should be a good fit for your application providing all the strength you need. Inconel 625 studs offer 144ksi ultimate tensile strength and 84ksi yield strength. It is also usable to approximately 1800F. Inconel 625 fasteners will also be more economic than Inconel 718 fasteners. In addition, they may offer a shorter leadtime.

17-4 Corrosion Resistance to Sulfuric Acid & Inconel

Q: Are there any materials I can use with the strength of 17-4PH in the H1150 heat treat, but with better corrosion resistant properties. I have low levels of sulfuric acid and chlorides that seem to be attacking the 17-4 steel.

A: The best choice for both extreme strength and corrosion would be Inconel 718 bolts. Inconel 718 may be overkill as it can provide excellent corrosion resistance to concentrated acids and chlorides at high temperatures while boasting min yield of 175KSI. However if you are looking for a big improvement in both corrosion and strength this will do it. Another material worth considering would be Inconel 625. This is basically the un-aged sister material of Inconel 718 having good corrosion resistance and a strength similar to that of 17-4 H1150. Inconel 625 would a significant improvement in corrosion resistance to sulfuric acid over 17-4 PH while maintaining a similar strength.

TZM for High Strength Bolting for 1500F Vacuum

Q:

I’m looking into a bolt which will be used to create vacuum seal with graphite and hold vacuum of 1 Pa. I’ve tried Inconel 718 but they seem to fail loosen at high temperatures, and my system requires 1500 F. Because I am trying to seal a vacuum system, it requires very high internal strength to compress the gasket. Ideas? The bolts are inside process / Vacuum an not on the outside.

A:

Inconel 718 bolts are age hardened, so at 1300 F, they will be re-annealed and lose the strength from the hardening treatment. For the highest strength at 1500 F, in vacuum, I would recommend TZM alloy screws or perhaps tungsten. They should have excellent room temperature strength as well as high strength at 1500 F. As long as there is NO oxygen in the system this would be a good choice.