Welding sintersed/pressed steel part

I recently repaired a pump shotgun part for my nephew. One piece was a steel tube, the other a pressed (sintered?) steel block with a stepped hole to receive the tube. The assembly was originally soldered(furnace brazed?), though after cleaning there was very little evidence of any solder, hence the failure. After cleaning with a spray, non-chlorinated solvent, the repair looked simple enough. Just a careful micro-type weld around the joint where the tube entered the block. I knew the porous nature of the pressed metal might be a problem, and it was. I did manage three small stitch welds around the tube, but not as pretty as I would have liked. Oil would ooze out of the metal causing sparkles and destroying the tip of the tungsten.

I used DC TIG, 1/16" Thor. tungsten, 55-60amp max foot pedal control, no pulse, and .030" steel mig fill wire. I doubt if silicone bronze fill would have worked any better.

Any ideas as to how to clean this pressed metal part without destroying the gun blue finish, that would have allowed a cleaner weld?

As soon as you tried to weld it up, the bluing was destroyed. Along with it, you might have boiled the remaining solder away. It might have been under soldered, but solder flows due to capillary action caused by heat.

Bluing a weapon goes back to the early times of firearm making. Our first muskets were "Rust Blued". Bluing is basically allowing the weapon to be corroded in an acceptable manner to help protect it from unacceptable corrosion.

With no disrespect meant, If the welds were made close to where the round is chambered, I would be cautious about the integrity of the chamber. Proof firing it at the range at a distance from the gun would be warranted.

The best way to clean the parts is to bead blast the whole barrel, buff it, and blue it again.

Better yet, take the gun to a gunsmith you trust, and have him check it. It's far safer than losing fingers, faces and eyeballs.

I even cringe when I see those gunsmiths on the Discovery Channel weld on the guns they work on. They are trained and qualified to do so!

Best Regards!

Quote:

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Originally Posted by Grizzly1944

As soon as you tried to weld it up,
With no disrespect meant,

I even cringe when I see those gunsmiths on the Discovery Channel weld on the guns they work on. They are trained and qualified to do so!

Best Regards!

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The welded repair would see none of the pressure upon firing. This was just the connection of the action bars with the fore-end. My repair worked as desired and allowed the weapon to function correctly. I was just asking if anybody had any experience in welding pressed steel, as far as removing any oil or contaminants before attempting to weld.

Putting the parts in boiling water after degreasing it would work. The oils will rise to the surface. In fact it's done before barrels are blued.

For small bluing repairs, Birchwood Casey makes a cold bluing solution. I use a Q-tip to apply it.

Glad you got it fixed.

Happy Holidays!

Heating the parts up a bit with a torch can help to get greasy / oiled parts "clean".

If you use the "bluing" solutions, be sure to use in an area with plenty of ventilation. The chemicals typically contain selenium or some compound of selenium and should not be inhaled.

Pressed and sintered material density can very depending on how well it was pressed and how much densification took place during the sintering process. If the material is very porous there is a chance that there will be huge stress raiser due to densification of the material around the welded/heated area. I would just keep an eye on the welded area to ensure that no cracks exist or grow out of the heat affected zone.