"Roy J" wrote in message
...
If you would substitute the word 'deflection' into your arguments
in place of elasticity, it would make more sense. If you do, I
would agree.

Ok, whatever works.


As for the fatigue resistance, ductility arguments, take a look
at these frames:
http://www.jeraldsulky.com/horsecart...GoldJCart.html
4130 tube, heat treated to the 200kpsi range on tensile, 12 %
elongation in 2" (BETTER ductility than 6061-T6 !!!)

Nice frames! Are you making them? Have you been at it for a while? If so, do
the names Rich Muntz or Charlie Kobash mean anything to you? They were
pretty well-known harness-race drivers on the East Coast. They were my
uncles.

These have
no springs, the driver just bounces along on a rough dirt track,
letting the frame flex. They have 'mixups' occasionally, not good
for horses, drivers, or frames. Typical sulky might get used for
1000 races (1250 miles) of race conditions. Never see any fatigue
issues.

All good reasons to use 4130. Its impact strength, fatigue strength, and
general toughness are all excellent, and it can produce excellent properties
even when you're dealing with a lot of welded joints, thanks to the low
carbon percentage.

That's what it's for. Specifically, the alloy was developed in the 1920s for
aircraft applications that required those mechanical properties, plus easy,
reliable weldability. Airplanes were both gas-welded and stick-welded (yes,
stick) from 4130 tube through the 1930s.


One got bent 90 degrees when a semi backed over it, still
didn't break. But the heat treating on these is precise. Pull
coupons attached to each batch.

Well, you're getting some interesting properties from your 4130. Getting
back to this application, the 12% elongation you're getting (are you
actually testing it for elongation?) is what SAE claims for 4130 hardened to
a yield strength of between 125 and 130 ksi, not 200 ksi. And the comparable
figure (13% elongation) for AISI 1060, for example, occurs at a heat-treated
yield strength of 112 ksi. Even 1040, which is a lot easier to get than
1060, comes close enough that it probably would do the job.

That's why I say it's unlikely you'd need or even notice the advantages of
4130, if you're going to heat treat it, in a race car or other
high-performance car. Ironically, the more demanding the racing, the less
strength you need in your anti-roll bar, because you're going to design it
for more than normal stiffness. Sizing it for greater stiffness results in
lower specific torsional loads on the bar. It's unlikely, say, in a road
racing application, that you'd even come close to challenging the steel in
that bar in terms of its yield strength. If you did, it would mean that it's
producing relatively low roll resistance.

Now, your point about off-road vehicles is a good one, and it's also true
that a racing anti-roll bar for a production car may put you in a bind for
space, and you have to use relatively short arms. In that case the bar has
to twist more for a given amount of suspension travel (actually, for a given
amount of differential displacement for the left- and right-side wheels, but
I hate talking like that g), and that could dictate the use of a
high-strength anti-roll bar.

It's like a lot of issues in racing: You're usually after stiffness rather
than strength, and, if you have adequate stiffness, you aren't even
beginning to load the part close to its yield strength. Tubular space frames
made for racing perform equally well if they're made from 1020 as from 4130.
Lotus, Porsche, and many other race cars of the 1960s proved the point
beyond any doubt. If the frame is properly designed, it never approaches the
yield strength of the material. It's all about stiffness, and that's
virtually the same for all grades of steel.


I would agree that the need for a full high strength sway bar is
debatable in standard practice. But a couple things to consider:
heat treated parts tend to be much more uniform in
characteristics. I would much rather have a 4130 bar treated to a
low value than an equivilent CR bar if I wanted an accurate point
of stress beyond yield. The other thing is if the bar might need
to take a huge overload, say from a baja buggy landing on one
corner in a movie style launch. I have a picture sequence on a
buggy launching upward, 5' of air, slowly going nose down and
tilting off to one side, and coming down on one front tire. Next
pic in the sequence is the tire going a rather unusual direction.

If it's a Baja buggy, then use what you have to. I don't even remember what
the subject was here g, so I don't know if that's the case or not.

But let's assume that the subject is what's in the header: Heat treating
4130 steel at home. My first response is, no way, Hose-A. Unless you have
some really terrific facilities, this is one steel you don't want to try
heat treating. It's right on the edge of air-hardening in terms of its
quench rate, and annealing, for example, requires ramping down the
temperature at 50 deg. F per hour. If you overquench 4130 from the
transformation temperature, you wind up with a disaster waiting to happen --
if it doesn't split lengthwise while you're looking at it.

It is almost never heat treated in normal transportation applications:
aircraft, cars, motorcycles. The bicycle guys sometimes order it heat
treated to greater hardness, but that's an exception. Then they silver-braze
or bronze-braze it into a frame, creating a structure of questionable
overall integrity. The tubes resist permanent bending better but the joints
can be really screwy.

Neither is it usually used in the annealed condition, as you suggested in
your last post. By far the most common heat-treat state of 4130 tube and bar
is normalized: somewhat stronger than annealed, but not as strong as
heat-hardened. In that state it's easy to work, it has close to 100 ksi
yield strength (in practice; official minumums are lower), and it has
terrific elongation -- over 25%. It's a very ductile material, easy to weld,
and it's reliable in a welded structure. It's actually tougher, with much
greater impact strength, than an identical structure made of annealed 1020.

The margin of strength between normalized 4130 and the same steel heat
treated to an acceptable level of ductility (elongation), IMO, is maybe 30%
or so. That may make a difference in the Baja buggy but it shouldn't make a
difference in most applications. As I said, you shouldn't be anywhere near
its yield strength in actual practice.

What you get by leaving it normalized is a rather large cost savings and a
lot less complication, unless you're buddies with someone who knows what
he's doing and who has a heat treating oven long enough to fit your bar. If
you try to heat treat it at home, I'll give you dollars to donuts that the
end result will be *worse* than if you just left the steel in its normalized
state.

And if you really need heat treated 4130 for your anti-roll bar, next time
do a better design job. g

--
Ed Huntress
(remove "3" from email address for email reply)