Axle hardening

[churchill]

I tried to cut an old axle I had lying around so I could make a breakaway torque tester for an LSD I bought. I put it in the power hacksaw turned it on a watched the blade skid over the axle a few time a leave almost no mark on it. It was hardened. Out comes the cutoff blade on the grinder and within a minute the axle was cut, next I placed it in the lathe and faced it using a carbide tool.





The shiney outer is hard as the hobbs of hell and the duller inner feels soft in comparison. Interesting how thick the hardened layer is and how the inner is not hardened, it makes sense as the inner of the axle is the neutral axis and not much torque is transferred through it. It looks like the harder the steel the is the higher the yield stress so basically it'll be stronger but the downside is that it's more brittle.

A bit of metallurgy for everyone.

[Sketchy_Racer]

The surface texture could also be affected by the surface cutting speed reducing at the smaller diameter of cutting, this would be especially noticeable if using a carbide insert tool.

It's impossible to get a true hardness scale by looking at that but I would say that it would be a alloy steel axel that has been heated and then quenched in a temperature controlled environment letting the outer surface of the material turn into martinsitic structure and transforming through steel depth to pearlitic and ferritic structures to give a hard outer tensile strength but with a tough flexible core.

Axel metallurgy is a massive topic with many, many different compromises between strength vs flex and materials

To hard equals to brittle and under and shock load the axel will simply crack at a fracture.

To soft and the axel will twist under load and shear, seems simple enough but where the balance lays is the challenge.

[churchill]

I'm fairly confident that the colour change represents a hardness change after machining other materials on that lathe using the same tip. Also the core drills a lot easier than the outer.

Thank you for the metallurgical description. It sounds like the typical engineering problem of balancing material characteristics. I got the title wrong and have amended it, your right, they are heated and quenched and not case hardened.

[zukmeista]

My brain might explode if I try and understand that!

[churchill]

:shock: My brain might explode if I try and understand that!

Haha, once it's exploded it cant do it again...

He's explaining whats happening to the steel structure as it gets hardened (I assume you're talking about sketchy's comment).

[kbjj]

Has anyone tried the "chryogenically frozen" treatment to the likes of axel's, cv's, crown wheel's, pinion's, and maybe even gbox bearing's?
Apparently it's ment to align the metal structure and toughen it, hardened or not.

[churchill]

I've heard about this but don't really know a lot about it, don't know if it works.

[De-Ranged]

From what I've read on the subject (cryo)
without going into the brain exploding stuff it dosn't treat the steel its sort of like a tempering phase
When you harden steel you make it very hard but brittle... not really usable like this the next phase is to temper this will remove some of the hardness but make it less brittle
These changes happen because the cystaline structure of the metal changes with heat, you trap these changes by quenching to cool the metal and hold the changed structure
The cryo re leaves some of the stress between these structures making it more resilient but without removing any of the hardness

Oh and for the books I've used it on lathe tools and diff gears... noticable differance in life on the lathe tooling but the diff gears I didn't use in the end so no idea if it was worthwhile

Cheers Reece