17-4 stainless rusting problem need help

[skipperspride]

this is most likly a Metallurgy question I am using 17-4 stainless steel to make a mechinical fishing gaff it has moving parts and used in saltwater. I am tig welding a 1/4 round bar to a 1/8 x 3/4 flat bar the flat bar is 3 inchs long, the flat bar and about 2 inches up the round bar is rusting very fast like 1 use in saltwater what can I do to stop this. I know it must have something to do with welding it I am using wire for 17-4 ph stainless so I know it is not the wire

[wildwestpat]

Hi

This is not my area of expertise but I have been a bystander whilst this caused bother.

The 'rusting' was due to using a wire brush that was not s/s. On doing dye penetration test there were signs of cracks in the weld which were thought to indicate that the weld had been contaminated possibly by hydrogen getting to the metal whils it was still molten. The parts were removed as they looked bad but would probably have failed if left in use.

Using a stainless steel brush - well cleaned parts and an adequate gas shield and the problem went away! Not scientific but got the problem to go away.

Regards - Pat

[Geof]

Using the stainless brush as suggested is essential. You can also 'passivate' it after welding; Google '17-4 stainless steel passivation' and you should get a few hits about passivating.

[little bubba]

The only time I've ever seen rust on 17-4 is on a raw investment casting.

Passivation should do it. Look for QQP-35. Basic spec for passivation. DO NOT pay for it. Its been superceded, probably by SAE-QQP-35, which means its the same spec that now costs $50.

If you need a copy, I'm 95% sure I have an electronic copy here somewhere.

Basically, clean metal, degreased, descaled, 40% nitric acid for 20 minutes, and rinse, rinse, rinse. Doing the final rinse in hot water heats the part up and it dries really fast, if you care about it drying fast.

Saltwater is one of the ways to test for proper passivation, its in QQP-35. Might be worth a look.