I definitely disagree with the statement that chromoly is not stronger than mild steel. It is called "mild" steel for a reason
Who made the statement it wasn't stronger?
"Mild" steel is called mild for a few reasons. Although it has lower tensile strength, it is also "mild" in the sense that it is more affordable, more ductile, easier to machine, and easier to weld than the fancier alloys. "Mild" isn't a bad thing.
The strength advantage doesn't exist if the material is damaged in the welding process. Who cares if the tube itself is 20 times stronger than mild steel if the joint is weaker due to improper welding? Where do most frames break?
The material is touted for being stronger, so you can use less and get a lighter part. Taking that to a limit, you can use less material until you have the same strength but less weight. Great! Except your thinner/lighter part is more flexible now. Lighter, just as strong, but more flexible. Is that a desirable trade off? It could be but it's certainly not a given.
Long winded point being, the advantages of chromo to the home builder are almost entirely theoretical. Virtually no one does the math to optimize the design. They buy whatever is available from a convenient supplier, have no idea what the final strength or stiffeness will be, build the frame, and then use it the same way they'd use it no matter what the material is. In reality, the main advantge of chromo becomes the tubing doesn't dent as easily as mild steel, and even that is only if they don't go super thin to save weight.
For someone who is just learning to weld I'll give the advantage to mild steel. In fact I'll give mild steel the advantage in 95% of homebuilt situations but that's an even longer post.
