For anyone who needs this info about carbon steels:
Very popular. Low carbon structural steel. Available as hot rolled or cold finished bar, as ERW tube in wall thicknesses of 0.063" and up, as cold drawn seamless and DOM tube. It welds and forms very well. It doesn't respond to heat treating but it can be case hardened by carburizing.
Best of the low carbon steels. Was used before 4130 as the standard aircraft structural tubing. Hard to find.
Known as a chrome moly steel. Excellent tensile strength, toughness and response to mild heat treatment, great welding characteristics, great for high strength fabrications. All welds must be stress relieved. Not heat treating it leaves brittle weld areas (no better than 1020). Doesn`t machine well. Deep heat treating is not good with 4130. Not good for driveshafts, spindles, axles.
A deep hardening chrome moly steel. It does machine willingly. Tough, high impact strength and fatigue strength.
Nickel chrome moly steel. Excellent deep hardening. Good for hubs, driveshafts, axles etc. Good tensile strength, toughness, fatigue resistance.
SAE 4340 modified
Similar to 4340. Added vanadium and silicone level increased. Added toughness and resistance to fatigue. Also know as 300M. Heat treating is difficult. Copper plating prior to heating reduces surface decarburization.
Chrome vanadium steel. Bad machinability. Not weldable but high tensile strength and excellent fatigue resistance!
Chrome silicon steel. Better than 6150 in tensile strength and fatigue resistance. Better heat treating.
Corrosion resistance. Contain 10.5% or more chromium and alloying elements. Retain mechanical characteristics at high temperature.