Welding - 4140 material

[pancho400cid]

Hey guys -

I have a general question about welding. I know there is a lot of "real" welding knowledge around here so here goes:

If you needed to build up material on a 4" diameter 4140 round bar how would you go about it, generally speaking? Let's say the O.D. is damaged and the idea is to build up the O.D. and then re-machine.

I'm talking in terms of pre-heat (yes? no? temperature?), filler material, and post-weld heat treatment ((yes? no? temperature? soak time?).

Any input appreciated.

 

[dr_clyde]

Preheat to 500 degrees or so, weld with appropriate filler, post heat to ensure even cooling, and then you want to cool slowly and consistently. I wrap in welding blankets.

Rapid temperature changes cause cracks.

 

[matt_i]

An easy preheat is typical residential gas grill. Place on grate and go wide open if you have no thermometer.

Post welding, its then possible to slow-cool the part with the grill, just put it back on and ramp down the temp in 15 minute stages.

There are suggestions to bury the part in vermiculite for slow cooling, I think I'd be tempted to put it between some pieces of Roxul until the next day. Some protection needed if the grit (which I think is abrasive) from the Roxul could mess up an "assembly".

 

[pancho400cid]

Thanks guys -

I'm really just trying to get to a point where I can have a quasi-informed discussion.

Any guesses as to filler material? We would presumably be MIG welding as I assume that would be easiest/fastest. We could stick weld if there was a reason it would be better.

 

[MoonRise]

Preheat? Yes. temp depends a bit on material size/thickness. Usually a minimum of 500F and for thicker sections you might have to go up to 700-800F.

Post-weld heating? Yes. Might have to also include a post-weld stress relief treatment as weld as the 'standard' Cool-it-really-really-really-really-slowly-so-you-dont-crack-it -instantly procedure. And then possible a complete quench-and-temper treatment if you want to get back to full strength/hardness.

Filler? Depends a bit on if you want to match the properties of the base 4140 after welding (need a matching filler then) or just want to build up the surface.

http://weldinganswers.com/how-to-weld-4140-steel/

https://www.hobartbrothers.com/news/286/523/welding-4130-and-4140-low-alloy-steel.html

 

[pancho400cid]

Those links were great. Thanks!

 

[welder4956]

We sometime weld 4140 to build up worn bearing surfaces in pumps and electric motors. 4140 can be hardened by heat treatment, usually a quench harden and tempering to restore ductility. My experience has been that very few manufacturers of pumps and electric motors actually specify a heat treatment and the material is typically used in the annealed condition. You would need to have hardness testing and metallographic examination of the grain structure to verify the actual heat treatment condition of the material.

As far as welding, the closest commercially available alloy we have found is ER80S-B2 for tig or mig, or E8018-B2 for stick welding. There is a matching alloy E4140 rod available, but it is hard to find. For preheat, the carbon equivalent has to be calculated from a chemical analysis and the 0.40% carbon along with manganese, chromium, molybdenum and vanadium additions usually push the preheat temperature up to at least 300 F. If you preheat to 400 F and maintain until the welding is complete, then slow cool under insulation it will be fine. Rapid cooling in air or water will increase the hardness and make final machining more difficult. Postweld heat treatment will reduce the hardness and restore any lost ductility. Typical postweld heat treatment temperature would be heating to 1200 degrees F at no more than 600 degrees F per hour, hold at 1200 F for one hour per inch of thickness (4 hours for a 4" diameter shaft), then slow cool at no more than 600 degrees F per hour down to below 600 F, and remove from the furnace and slow cool under insulation to ambient.

Good luck with the repair.

 

[pancho400cid]

Outstanding. I sincerely appreciate the info!