There's really not a huge advantage to using 4130 in that most of the
tubing sizes are mandated by the rules. Additionally as you stated, the
weld causes 4130 to lose it's strength around the weld and actually has
similar strength to a mild steel from what I've read. If your FEA shows
that your maximum stresses occur near joints then the fact that you're
using 4130 makes essentially no difference unless you heat-treat. The main
case that I can think of where 4130 would be an advantage is if you load a
tube in bending such as hitting a rock with the midpoint of an a-arm, roll
over with impact at the middle of a tube. However, due to the strict
requirements in the rules on roll cages, it seems that cars that do roll
experience very minor damage regardless of which type of steel used. I've
discussed this with many professors on campus and our opinion is that
using 4130 in general is not worth the cost for this application except
for on certain components (possibly the a-arms). Ultimately though it's
your decision as to the trade-off of time/money to analyze your design and
optimize tubing sizes based on material properties and loading conditions.
Shawn
On Wed, 8 Oct 2003, Paterson S wrote:
> Hey guys,
>
> I know some teams last year used chrome-moly steel for
> their roll cage. I understand that we can save a lot of
> weight using this type of steel as it can maintain the same
> strength as plain carbon steel however using a thinner
> tubing. My question is, is it really necessary to
> post-weld heat treat? I have read in some books that it
> would be stupid not to do this because the weld will become
> brittle and can crack without heat treatment. However, I
> have also read that it is not necessary. Does anyone have
> any thoughts or commments on this? I would really
> appreciate it.
> Thanks,
>
> Sarah Paterson
> Team Manager
> 2004 Midwest Mini-Baja
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