Using Stainless Steel Grub Screws in 4140 Alloy

I would consult with a supplier for best grade of 4140 material for your purpose....

..."Alloy Steel AISI 4140 Fasteners in all possible major grades such as A193 B7, B7M, A320 L7, L7M and many more."...

https://www.multinoxinc.com/alloy-steel-aisi-4140-fasteners.php

Municipal sewage presents similar challenges to <...oil...> as similar substances are present. Mild <...carbon steel...> offers little resistance to corrosion there, so it isn't used.

To maintain corrosion resistance the <...Grub Screws...> are best in the same material into which they are screwed.

Try this.

Agreed, with the exception of stainless steel. In my experience an adjacent spec for the fastener (eg 316 SS bolt with 304 SS nuts) greatly reduces the problems with galling. A friend that does fleet truck and van outfitting does exactly this; even though the spec normally only requires 304 SS they use 316 SS nuts as the price difference is less than the time wasted when one of the 500 fasteners on a truck locks up two threads before tightening.

The big problem we had with any stainless screw was galling, the use of an anti-seize compound helped quite a bit. In the oil fields we had a lot of H2S and sulfur as well as sulfur and water forms sulfuric acid. Try the various types of stainless screws and the copper and nickel anti seize compounds. Question I have is what size are you using and how tight (torque) are you using.

Another option would be to Helicoil the threads using Inconel or Nitronic inserts (not sure what would be best in your environment). This would allow the use of stainless screws but remove the risk of galling.

The threads using Inconel or Nitronic insert are safe to use in the oil wells.

Maybe you could use copper alloy grub screws for your particular tasks.

I did find that there are several articles on tests on different alloys pertaining to your question on the following website.

https://www.onepetro.org/

They provide extracts on the tests and the full evaluation can be downloaded after paying a fee which seems to be USD20.

Previous comments for sewer environment corrosion are correct. Practice here is to use 304 SS with 312 SS since have observed galling when use same grade for external and internal threads even with coverage of anti-seize. I saw threads gall and lock when being tightened before engaging pressure onto flange being clamped.

Suggest that you talk to material supplier and get similar metallurgy (4140 Alloy) but in a different hardness and grain size.

Yes, confirming from a material supplier would be a great idea. They know everything.