View Full Version : What makes a weld hard?

dan s
02-03-2008, 04:10 PM
I have a project coming up that will require me to weld some nuts to threaded rod, and then turn it down for a clean appearance. I have that bead is really hard and almost impossible to turn, and I have also read that it turns easily.

If you know the base metal and wire (flux core in my case), how can I tell if it’s going to be hard to turn?


02-03-2008, 04:18 PM
Dan, it mostly boils down to how fast the weld cools. That seems to determine how hard it will be. Little short tacks with mig turn out very hard. Tig and stick welds are usually softer as they impart more heat into the steel.
Now if I want to turn something that has these hard spots on them, I put the torch to it and anneal the weld area. Makes a big difference.
But that's just me...

02-03-2008, 04:28 PM
If you have a steel bucket fill it with wood ashes and stick the heads in the ash to let them cool slowly.

Thats how we anneal small parts or castings.

02-03-2008, 04:32 PM
It's the carbon content of the base metal and the rate of cooling from critical temperatures. Below about .025% the weld will not harden, above it will get hard but you should be able to cut it with high speed tools. Some welds like cast iron can't be easily cut with carbide tools. Annealing after welding will make welds machinable.

02-03-2008, 04:40 PM
High tensile steel can become almost impossible to turn or drill after welding,
in your case depending on the application of the threaded rod, if standard
hardware rod and nuts are used welding will make little difference, higher grade nuts or rod may need annealing or the use of a tool post grinder.

02-03-2008, 05:37 PM

If you have time, buy some silicon bronze rod and TIG weld a test piece. I use it a lot but haven't tried turning it. I've tapped through it without a hitch.


02-03-2008, 09:33 PM
Just weld it and turn it. I just got through rebuilding some antique spring shackles by building them up and turning them down. I didn't do anything special except keep them out of the draft in the barn. They sat on the concrete floor until cool enough to handle. These are made from forged Vanadium steel. I doubt your threaded rod and nut even come close. The weld itself will turn down with HSS. Get busy and quite dilly-dallying. ;)




02-03-2008, 10:03 PM
Beautiful job Ken!

Yeah, I've never quite understood what the rod manufacturers mean by "machineable" welding rod/wire.

Most welding wire (ER70S-6, for example) is mild steel anyway (0.07 - 0.15% carbon), but I've even machined nickel filler wire for cast iron, and didn't have to break out the carbide.

02-04-2008, 02:07 AM
I've welded up a lot of stuff w/ the MIG and turned it down, including some worn-out spinning wheel shafts for my wife. The welds from MIG seem softer than the weld from a stick, but that's gut feel, not a controlled experiment.

- Bart

02-04-2008, 09:28 AM
The welds from MIG seem softer than the weld from a stick, but that's gut feel, not a controlled experiment.

No doubt! MIG has the lowest heat affected zone of any of the welding processes. The HAZ is even less than TIG, because you're moving the bead so fast compared to TIG.