Our team also did a bunch of research as to whether or not 4130 gets brittle
in the HAZ.
I did a few "tests" on MIG welded .049" wall chromoly tubing, in which i
welded some sample pieces at about 70F ambient, with little cross-breeze,
and smashed the hell out of the welded joint with a sledgehammer. (The joint
was a butt joint on two tubes - i flattened the tubes and bent the flattened
assembly in a u-shape) The weld didn't tear...
We ended up buying 4130 .049 wall cause it was easier to find than 1020 .049
wall. Our tubing supplier had 4130 in stock but 1020 was a special order.
They ended up costing the same for us.
We used .065 wall 1020 last year, and the frame was rugged (and heavy) as
hell. I guess the nice thing about using 4130 as opposed to 1020 for thinner
walled tubing is its increased resistance to local impact (like Shawn points
out).
-Ross
Boston u
-----Original Message-----
From: owner-mini-baja@autox.team.net
[mailto:owner-mini-baja@autox.team.net]On Behalf Of Perrin, James (J.M.)
Sent: Wednesday, October 08, 2003 1:41 PM
To: 'Paterson S'; mini-baja@autox.team.net
Subject: RE: 4130 Steel
There actually isn't any weight savings compared to 1020 steel for the
frame.
1020 and 4130 still have the same modulus of elasticity so for the same "I"
value
the bending stiffness is still the same. Where 4130 can gain is with the
bending strength.
But the rules say we need to have equivalent to bending stiffness and
strength to 1"X0.083.
I like to use 1020 DOM 1 1/4"X0.049 because it is a lot cheaper...
Anyway, getting back to you question about heat treating, I've read that for
thin wall tubing such as these frames (I hope your not using anything .120"
thick) that heat treating/stress releaving is not required:
http://www.lincolnelectric.com/knowledge/articles/content/chrome-moly.asp
However, if you still want to do it, this is a good article on how to do it:
http://archive.metalformingmagazine.com/2001/01/Lincoln.pdf
Hope this helps.
James
University of Michigan - Dearborn
-----Original Message-----
From: Paterson S [mailto:paters6@uwindsor.ca]
Sent: Wednesday, October 08, 2003 9:31 AM
To: mini-baja@autox.team.net
Subject: 4130 Steel
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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