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Selecting correct tube grade - live rear axle housing

Selecting correct tube grade - live rear axle housing

Hi there, I'm after some guidance with regards to selecting the correct grade of steel tube for a particular job, please.

(Hoping this is the right forum section?)

I'm fabricating a live rear axle housing for use in an off-road application, and I'm getting confused by all the different grades of tube available.

The axle tube will be under constant (and sometimes severe) bending loads. It also needs to be weldable, and machinable. I'm not interested in surface finish - and to be honest - dimensional accuracy is not too important as the tube will be turned/skimmed where size is critical.

The big tube suppliers seem to stock 2 common grades, in the required size;

Cold drawn seamless - EN10305-1 E235+c
Hot finished seamless EN10297 E355+AR/S355J2H

Now people keep advising me that the CDS will be stronger, as the cold-forming will work harden it, but according to the spec sheets - the HFS is slightly stronger (550MPa compared to 470MPa min UTS) But the HFS elongation figure is 22% whereas the CDS figure is 16%.

And how do I know which will be better in "impact"?

There are other, more exotic grades of tube available - 4130 for example - but I'm worried about the practicalities of welding this (and the PWHT) not to mention the cost.

15CDV6 looks superb - but V expensive - and i'd have to have it made in my required size, minimum order quantity makes it unreasonable.

Any suggestions or words of wisdom would be much appreciated,

many thanks


RE: Selecting correct tube grade - live rear axle housing

I think cold drawn has a higher flex mod.

High flex mod and high elongation will be your friend if this is really off road as opposed to on track as in drag or circuit.

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RE: Selecting correct tube grade - live rear axle housing

The OEM axle tubes with which I am familiar are/were roll formed and ERW from mild steel strip, cut to length, then stepwise tapered and sized by pushing a carbide die ring over both ends.  The cold working severely reduces the diameter, and increases the thickness and the overall length, but I don't think the hardness is much affected, because it's a very mild steel.

If you're only making one or a few, were I you, I'd scour junkyards for raw material.

Or just order a special from Currie or someone else who's already tooled up to make this stuff at a competitive price.

Mike Halloran
Pembroke Pines, FL, USA

RE: Selecting correct tube grade - live rear axle housing

Thanks for feedback so far. Just to clarify then, these are being used for rough terrain off road, not track. They'll be manufactured in reasonable quantities - not enough to warrant a 500metre batch of tube though.

Thanks again.

RE: Selecting correct tube grade - live rear axle housing

All else being equal, cold drawn (+C) is stronger than as hot-formed (+AR).  However, everything is not equal, because you are comparing grade E235 to E355.  E355 +AR is nominally stronger, and will be stronger in the as-welded condition, however, the diameter variation will be much greater because it hasn't been cold drawn.  If this doesn't matter, then use E355 +AR (EN 10297).

RE: Selecting correct tube grade - live rear axle housing

That's very helpful TVP, thanks very much, just the sort of info I'm after.  So E355+c would be better still, if it's available? I'll ask the question.

Is there a good source of info/data on all the different grades, designations, suffixes and properties etc that you would recommend?

Thanks again.


RE: Selecting correct tube grade - live rear axle housing

Yes, the highest strength would be E355 +C.  Keep in mind that you have only listed seamless tubes (EN 10305-1, 10297), but welded tubing is a lot more common, especially in thin wall sections.  E355 +C according to EN 10305-2 would have essentially the same strength as 10297, but would have a more consistent wall thickness, before or after the cold drawing process.  Here are some links that provide more technical information on tubes:


RE: Selecting correct tube grade - live rear axle housing

Before you get too far down that road, "stronger" is not the appropriate goal here.

Axle housings fail to perform their intended function when they deform enough to damage the gears and bearings within.

That happens long before they reach ultimate tensile strength, and before they reach yield strength, too.

You should be looking at deflection under the set of applied loads. ... which is more sensitive to geometry than to material properties.


Mike Halloran
Pembroke Pines, FL, USA

RE: Selecting correct tube grade - live rear axle housing

Good points all, but round tube axles for severe off-road use nearly always have additional support structure added.


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