About 1018|The default mild steel for machine shops. If someone says 'cold rolled steel' without specifying a grade, it's probably 1018. Good machinability, easy to weld, takes case hardening well. The main complaint is chip control. It's gummy enough to produce long stringy chips that bird's-nest around your tooling. Use a chipbreaker or bump up the feed. Cold drawn 1018 gives you tighter tolerances and a better surface finish off the bar than hot rolled, but it has internal stresses that can cause warping if you machine heavily from one side. Quality varies by supplier. Compare to
12L14 (dramatically easier to machine but can't weld it),
A36 (cheaper and fine for structural work but worse surface finish and less consistent chemistry), and
1045 (stronger but harder to machine when you need more carbon).