Let's not forget acetylene torch brazing. Dissimilar metals and hard-to-weld stuff like cast iron can be joined by brazing. I extended the fork tubes on a scooter using 1" diameter stainless steel boat railing brazed to chrome plated steel fork tubes. I used nickel-silver rods and they worked great. Many, many, moons go I also fixed my Wife's big frying pan broken handle using a brass rod to braze it together. 45 years later it is still in use.
They also come in handy for frozen bolts.