[brannanjohn]

Which is better?

Is it worth the extra $ to get Cromoly or is the only diff weight savings?

I have also heard that Cromoly requires special preparation such as pre heating etc, that should only be don eby experienced persons.

vs mild steel which is easier to work with and just as strong, but heavier.

Any input?

[PeteL]

Although chrome-molybenum alloy steel SAE 4130 can have higher tensile strength...if heat treated properly...than mild steel SAE 1020, it has lower impact strength compared to mild steel. Impact strength, as measured in something like a Charpy Impact test, measures the amount of energy that a material will absorb before fracturing. Simply put, Mild steel will bend in a impact situation where cromoly will break...all else being equal. Considering what you ask of a cage in a crash is to absorb energy while maintaining as much as possible the integrity of the cockpit, the better impact strength of mild steel is an advantage.

Given the difficulty in heat treating a roll cage after welding and lack of stiffness to weight advantage, I have a difficult time seeing why one would choose cromoly over mild steel in this application.

There are certainly places on a race car where Cromoly has advantages over mild steel, suspension arms come to mind, but if I ever put a cage in my car, it will be mild steel.