I knew I should have kept my mouth shut.
Just trying to point a few things out to help you out.
You're not telling me anything new about welding. Having a degree in welding engineering and welding for over 25 yrs on materials that you never heard of, and of technics . Working on my masters in mechanical engineering. You should do some research on stress relieving before posting. Your oil quenching is not stress relieving. It's heat treating. Totally different. If you dunk you weld right after you are done welding. It will make the weld and heat affected zone HARD and brittle. D'uh! What you want to do is a preheat of the welding area before welding, weld, then do a post teatment. This all depends on the material. Some materials require that you keep the part below 70F the whole time. To do this, you have to use chill blocks. Some, all you have to do is pass a torch over the part until you see moisture forming. Then dry it with the torch. Others require a preheat of over 700f or higher before welding. With an interpass temp within 50 degrees (650 to 750) of your preheat temp. Once welding has stopped. Some materials require only a slow cool to room temp. So you wrap the piece in Kaowool insulation and let it cool. Others require going straight into stress relieving. The process normally goes like this. Start at a temp, say 500f. Hold for an hr. Then ramp up a 100 degrees ever hr until you hit your final temp. Depends on the material. Say 1100F. Hold there for a set time. Then ramp down a 100 degrees ever hr until 400F is hit. Other stress relieving methods include peening, and vibration.
You're right on a new car about soldering wires. Because the manufacturer's don't have to do it. It's when you start to modify and add things to the system. Oh, there is a BUNCH of solder in a new car. Every circuit board in the car has soldered joints.
Have fun with your project.