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I Forge Iron

Axles, what metal?


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What type metal is used to make axles in vehicles? The 1-1/4 inch or larger solid bars that go from the wheel to the gears that drive the wheel. Usually has a spline on one end.

It would seem there is some good resource material there.

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The Transmission drive shafts I am familiar with are usually made from a high carbon steel, different manufacturers use different specifications, however all the steel ones should be heat treatable, and make excellent hammer heads, drifts, anvil tools etc.

If you consider their function, they have to withstand shock loads and torsion, so they should be of a good quality steel capable of functioning to these parameters.

Also what used to be good quality steel were the inside gears and shafts in vehicle gearboxes, some of which can be used to make interesting shapes in hot metal, I would suggest normalising/ annealing them first, and just surface harden the working face by whichever method you prefer.

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I've got the axles out of a Ford Ranger (smaller than Glenn's 1 1/4 inches though), two chunks of semi truck axle (one Volvo and one Kenworth IIRC) and one chunk out of a Bobcat skid loader. The semi axles spark test somewhere in the 1040-1060 range, the Bobcat axle sparks a little more like 4140ish. I can't remember what the Ranger axles sparked like, and they're at the bottom of a resource pile so they aren't getting checked anytime soon! ;)

-Aaron @ the SCF

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I am sure that there is a variation in steel selected by the design engineers based on the exact application. But most any of them would be appropriate hammers and tooling as they are a high strenth steel with good hardenability

I do know that John Deere Tractor axles were made of 1045/1050 steel based on a discussion with a retired John Deere Engineer. (at least this is what was used during the time he worked at Deere)

Historically blacksmiths looked at axle shafts as good stock for hammers and tools. So have at it. Just make certain you stress relieve prior to hardening and temper back to reduce potential for chipping.

On a side issue temper colors, which are oxides of iron formed on the surface of the steel, are a function of not only temperature but of time. So if you are using an oven or kiln for heat treatment, as some of the earlier posters have mentioned, the temper colors may appear hotter than actual temperature that they were exposed to.

As an example at one of previous jobs we had tooling that operated at 400 deg F with tooling temperatures controlled by a electronic temperature controller. This is less than "pale yellow" at 450 deg F. However these tools appeared "dark blue" which is nearly 600 deg F inspite of the fact they never saw temperatures more than 400 def F.

I am not familiar with exactly how long exposure it takes at 400 deg F to turn the tool blue, but the first time new tools came back in the shop they were all dark blue.

So I guess bottom line is that if you have access to oven or kiln, and leave your steel in the oven trust the oven not the color.

Remember the commercial heat treater's rule of thumb. 1 hour at temeperature per inch of thickness. This is hard to do in a forge but with an oven or kiln is easy.

For best outcome many industrial tooling and dies are "double drawn" that is double tempered, Heated to tempering temperature, cooled and reheated to tempering temperature again and cooled.

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The steel specs have changed a lot in the last 30 years, maufacturing processes have improved, and new industrial heat treating processes are becoming commonplace and this changes the materials that we are salavaging from different applications. The salvaged metal charts can declare authoritatively that a particular whatsit is a particular alloy, and unless it is published by the manufacturer as a current product spec it is only a good educated guess. 4140 used to be a common steel used for lots of applications where toughness and a bit of wear resistance was needed, like shafting. My impression is that even though it is still commonly available and spec'ed in a ton of older reference books, I think in many applications it has been replaced with alloys better suited to induction forging and hardening. I trust Jeff's Reinhart's information on the alloy on new forged axils, but I also know that some of the 800ton Cat dump truck axils are being cast at Harrison Steel just down the road from me, I don't know what alloy they are using but they are hollow (the hollow in the axil is the brakefluid reseviour, and lightens the axil and they don't have to find a 12" upsetter and machine them for a day or two, to change to a new design... Saves Cat time and money, but it is a pain for Harrison, because the casting have a bad tendency to crack in heat treat, and then the cracks have to be ground out and welded solid then back to heat treat to roll the dice again... Bad stress risers between thick and thin sections of the casting... due I would venture to guess because of specs from Cat, they are trying to cast too close to finished demensions to save on machining costs and weight...) Just an example of how manufacturing technics are changing to fit changing design requirements and that includes the alloys they use. I can't help but be dubious of "KNOWING" what a certain steel is. The charts are a good guideline to start with, but what it comes down to is, heat it, beat it, then try and heat treat it... Then test it to see how it proforms. A simple heat treat test is all you need to do, draw out a thin section of the unknown material, allow it to air quench or normalize, test it with a file, if the file skates then great its an air hardening alloy, try and temper it. If the file bites after the air quench, then it is mostlikely not an air hardening alloy, and you should heat it back up to critical and quench in warm oil, file test it again, if it skates try and temper it, if the file still bites, then try a water or salt water quench, if the file still bites its a mild steel with limited hardenablity, you may need to try superquench or just a cold hose and a lot of water. You can also do this same testing, by using 4 identical test bars, then you can try and break the test bars after heat treat to give you better idea of the working characteristics of the steel. It is good to know how a particular supply of scrap will react in your shop, to your technics...

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Finn; Jeff is the fellow I was quoting; his tales over at anvilfire of the giant upsetters have always been awe inspiring to say the least.

We gotta remember that manufacturers are not in the business of making the *best* stuff but are trying to make the cheapest stuff that will meet specs. So they can change alloys/processes at the drop of a hat. I myself have run into a low alloy strain hardened leafspring---meaning not enough carbon to harden even in water!

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