Originally posted by stevebfl
Yes, this is the heart of the repair. Yhliem is right on about the metallurgical changes that take place. It doesn't matter how quick to welder is, as whats more important is how quick it cools.
In a weld every form of heat treating takes place from the hardening of rapidly quenched martensitic transformation to the annealing properties of a slow treatment. Hard and brittle to soft and pliable. But as csnow points out, metal is cheap and structural reinforcing from the adding of material to the thickening of the fractured area can easily make the end result stronger than the original clean sheet.
Exactly, and speaking as a certified welder and pipe fitter from long ago(before changing careers), I don't think I ever had a repair job go bad. And if it can hold together battleships, I think the odds of it holding a spring in place are pretty good. Mercedes used good steel in their cars, mig good steel back to it, and I would be willing to bet that it will be every bit as solid as OE. Maybe not as pretty(depending on the welders skill and detail orientation), but definately as strong.