Donald Dillies wrote:
>
> Anyway, because 531 is not good for welding that's why just about all
> the seamed tubing in the world is chromoly, which loses less strength
> after welding.
> - Don Gillies
> San Diego, CA, USA
Most seamed tubing is made with low quality, low carbon steel like SAE/AISI 1018. They can be used as welded after a step to mechanically remove the protruding seam.
Higher alloy, higher carbon steels like 531 and 4130 require subsequent heat treatment after welding.
A simple explanation why:
At the temperature that welding takes place, carbon from the parent metal migrates to the molten weld zone. When cooled, the area of the parent metal has been de-carburized, thus weaker. The weld itself has extra carbon added to the metal and with fast cooling can result in embrittlement resulting in cracking.
In thin wall bike tubing this can be a real problem!
Two solutions:
Used heavier steel components to offset the problems caused by welding, or heat treat the parts after welding.
I haven't looked into the metallurgy of the newer weldable steel tubes (haven't had an interest) but they may contain lower levels of carbon.
Chas. Colerich
Oakland, CA USA