Q: I have equipment that requires a high strength bolt. Temperature and corrosion are not an issue, solely strength. I had tried Super Duplex thinking that would do the trick, but I’m still having breakage. Any ideas?

A: For an application that exclusively requires high strength, you might want to consider 17-4PH bolts. 17-4PH is an age hardened steel that provides extreme strength ranging from 160-200ksi (ultimate tensile strength) depending on the level of heat treatment. 17-4PH bolts have a yield strength that can be up to 2-½ times greater than Duplex 2205 and over 4+ times greater than 316 stainless steel.

Q: Looking at options to increase the tensile strength for a socket head cap screw. We
are currently using grade 8. Would Waspaloy be a good option?

A: If you are looking for a fastener with higher strength than Grade 8 Alloy Steel (150 KSI Tensile, 130 KSI Yield), and are only interested in strength (not corrosion resistance or high temperature stability etc.) you should consider 17-4 PH. This is a precipitation hardened stainless steel that lets you fine tune the strength depending on the heat treatment. 17-4PH bolts can deliver strength of 160-220ksi UTS.

Beyond this you are getting into some very special alloys that do more than just offer high strength, like Inconel 718, Waspaloy and MP35N. These materials relative to alloy steel are very expensive and typically used for high strength applications that have other requirements such as corrosion resistance or high temperature usage.

Q: I need a material that offers about 80-90ksi yield but is also corrosion resistant to low concentrations of sulfur acid. I’m tried 17-4Ph but its not working? Any ideas.

A: Yes, 17-4PH fasteners are excellent for high strength like you need, but are not really geared for corrosion resistance in acids. For this situations, I would suggest Inconel 625 bolts. If offers about 84ksi yield strength and 144ksi UTS. It also offers good resistance to many corrosive environments including sulfuric acid. If more strength is needed you may want to try Incoloy 925 or Inconel 718. Both do when in corrosive situations and offer will over 100ksi yield strength.