As someone who does a lot of cage fabrication for SCCA,NHRA and mini
sprint racing I feel compelled
to add my .02.
Depending on its condition 1020 has a yield strength of 40-50kpsi and an
ultimate strength of 50-60kpsi, these numbers are for normalized or
annealed conditions .
4130, has yield numbers of about 65-70kpsi and ultimate numbers of about
8105kpsi, again these are for
nomalized or annealed conditions, normalized and annealed are two
different conditions.
Most fabrcators use a welding wire or rod that results in 70-80kpsi
strength no matter if it's 1020 or 4130 so
the welded joints have the same elongation propperties.
Cages built with 1020 tubing usually use .120-.135 wall thickness while
4130 cages use .083-.095 wall thickness, 4130 represents about a 30%
weight savings.
Stress relieving a 4130 weldment by heating it to cherry red is
considered unnecessary these days, it is used
for much thicker wall thickness weldments though.
The biggest downside to 4130 is its cost and the time it takes to tig
weld, there have been many times where it has taken me 20 minutes to get
comfortable inside a car to complete a 2 minute weld, also if I'm not
satisfied with a bend I might be discarding $80-$90 versus $20-$25 for
1020.
Besides cost, I think 4130 is a superior material if you go real fast.
OK I've rambled on enough.
Ron Meek
Alb. NM
On Fri, 14 May 2004 22:46:12 -0600 portermd@zianet.com writes:
> MARK J WEATHERS writes:
>
> > low carbon steel and mild steel and 1020 etc are the same basic
> thing. I
> > have no idea what chrome-moly steel is either but it sounds cool
> when you
> > say it.
>
> Sounds like a need for a terminology post. You're correct that
> low-carbon
> steel, mild steel and 1020 are roughly the same thing. But, 1020 is
> a
> specific grade of mild steel, just as 1010 and 1012 are. The 1000
> series is
> composed of all low-carbon, malleable steels, with slightly varying
> amounts
> of carbon and alloying elements.
>
> "Chrome-moly" steel is usually the term for AISI 4130, although it
> can also
> mean 4140. Ask for chrome-moly tubing and you'll likely get 4130,
> since 4140
> is normally used not for tubing (doesn't draw quite as well as 4130)
> but is
> used in billet form for cranks, etc.
>
> ERW stands for electric resistance welded. This grade is probably
> permissible under some rules for roll bars, but will probably
> require a
> thicker wall to meet the rules than seamless. Seamless, of course,
> is
> considerable more expensive. If you can't afford the weight, check
> the rules
> and see if a lighter wall seamless is equivalent to a heavier wall
> ERW. ERW
> is rolled and the seam electrically welded--therefore, it's not
> quite as
> strong as seamless, if all other specifications are the same.
>
> I may have mentioned previously that while the rules may allow 4130
> for roll
> bars, it's not recommended, for a couple of reasons. Because of the
>
> extremely low elongation of the material, the difference between the
> points
> of yield and failure is small--that means that if it fails, it
> doesn't bend
> much--it snaps. Pieces of it can break loose and become spears. Not
>
> something I'd like in a roll cage. The other detriment in
> fabrication is
> that the material work-hardens with welding, and requires rather
> uniform and
> precise annealing for at least a foot each direction from each weld.
>
> Difficult to do with a large piece such as a roll bar or cage, and
> especially so if some of the welding has to occur in the car.
>
> Mild steel, because of its malleability, yields much more easily,
> but it
> doesn't fail catastrophically--it gives, bends, bends some more, all
> the
> while absorbing energy. It welds easily and doesn't require
> extensive
> annealing because it doesn't have enough carbon in it to noticeably
>
> work-harden.
>
> Cheers.
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