Hi Doug,
<<Does anyone know the weight per foot of mild steel (DOM)>>
Here's a handy little formula I found in my library:
Weight/foot = 10.68 (D-t)t
where D is O.D. and t is wall thickness. All in inches and pounds, of course.
<<Has anyone had any experience welding 4130 or using it as a roll cage. It
was my understanding that it was more brittle than mild steel ?>>
4130 is readily weldable provided you use proper welding procedures. You
should purchase it in the proper condition (normalized, annealed, etc., NOT
hardened and tempered), preheat it prior to welding, maintain a maximum
interpass temperature, and post weld heat treat it to insure uniform
properties. You should also, of course, use the proper filler metal and
welding process. GTAW or tig, heli-arc, etc. is the preferred method.
It is not inherently more "brittle" than plain low carbon (mild) steel, its
just more sensitive to the thermal cycles generated during welding.
The cage I welded into my car is low carbon steel. To me its just not worth
the extra effort fo what I see as an insignificant weight savings (I have a
small car). But hey, because I'm a Metallurgical Engineer, I worry about how
my welds and other metal parts more than the average guy :). Some call it
paranoia!
Feel free to contact me off-list if you want the specifics.
Chuck Gee
Spitfire Racer
Paranoid Metallurgical Engineer
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