17-4 Bolts to Replace 12.9 Zinc Coated Bolts

Q:  We are trying to move away from zinc plated 12.9 bolts due to hydrogen embrittlement problems and the geomet finish is giving us problems due to the diameter of the screw. As a better solution, we have thought about using Super Duplex screws or Nimonic 80A screws.  I understand that we would achieve tensile strength with both materials and at the same time avoid having to use a coating.

Do you think the solution I propose is correct?

A:  The concept of replacing coated material with a higher performance alloy is a good idea, however both Nimonic 80A and Super Duplex will not have the minimum strength requirements of 12.9 which is  1100MPa  (159KSI) minimum yield strength and 1220MPa (177 KSI) minimum tensile strength.  You could see a material strength comparison table at: https://www.extreme-bolt.com/high-strength-fasteners.html#Metals

From a strength perspective, a material you could consider as a replacement for 12.9 would be 17-4 PH Stainless Steel H900 bolts.  This will have 190KSI min Tensile and 170KSI min Yield.  Learn more at: https://www.extreme-bolt.com/17-4-ph-fasteners-flanges.html

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