Heat Treatment

[georgebarr]

How much does it cost to get me mild steel that was welded using a MIG to remove the heat stresses? Where can I get it heat treated (e.g. metal shop, etc)?

Thanks,

[Ken_Shea]

George you can stress relieve it (Anneal) by heating to a cherry red and simply let it cool naturally.

Ken

[duluthboat]

In most cases stress relief can be accomplished by annealing. To anneal small parts you can stick them in the kitchen oven and bake at 450 for two hours. The key is even heating and slow cooling. Parts can also be stress relieved by shot peening, which will not affect the parts hardness, but requires special equipment. If it’s a large part you can do as described above with a torch, work the heat out away from the weld and cool slowly.

Gary

[georgebarr]

I am trying to stress relieve parts too large for a kitchen oven. How long does it take for 1/8" thick mild steel to turn cherry red under a hand operated propane torch? What areas should I heat up (e.g. the weld area, near the weld area, etc)? Is a propane torch bought at a hardware store a good diy way to do this? Will this process weaken the mild steel or welds?

Also, will this process remove the warp that occurs after the welds are done?

Thanks,

[lt paul]

Realisticaly the propane torch will not be sufficent to do this. if you still wand to do this yourself you would neen either an oxy acetelyne $$$ or an oxyMAPP torch. an oxyMAPP torch can be had from the home depot for about $40 it uses an Oxygen cylinder that looks pretty much like a propane cylinder and a MAPP gas cylinder tha can be interchanged with a propane for lighter jobs. some professional plumbers use these to speed up their work compared to plain propane.

[TyRex]

I've got a bernzomatic oxymapp setup......works great for little jobs here and there, but the oxygen tanks sure dont last long. If you plan on using it more often, I would infest in a nice oxyacetylene setup. Or even a mid size oxymapp setup. There are many advantages to using mapp over acetylene in my opinon, but i'm no expert though.

[HuFlungDung]

George,

Stress relieving will not remove weld warp. It will remove the stress in the weld zone, but since there is nothing "pulling it back" during the anneal, it just sits there

You don't have to go as high as a red heat for stress relief. Maybe 800 to 1000° F.

Pre heating before welding can be beneficial to reduce the amount of warpage. However if the part is of a small cross section, the best way to reduce warpage is to clamp the parts firmly to a massive backplate. Other than that, planning for warpage can help too. Purposely place the parts slightly out of position, and "hope" that the welding will pull it into line. Also, if you use several tack welds on the parts before you burn in the big one, this can help reduce warpage. If the weld is a double sided joint, welding alternately on both sides will help. Try to avoid big long nonstop stringer welds. Using a MIG process will also help reduce warpage because it is at least 2 or 3 times faster than stick, so less heat is input into the weld zone.

[InventIt]

To add to Hu's comment,
It is also helpful to allow a small gap between the parts when tack welding your pieces. Make a tack weld on one side and then recheck to make sure the parts are where you want them. If they are not (and they ussually aren't) the small gap allows enough movement to reposition the piece without breaking the tack weld, then tack the other side.