Induction harden ?

[mfgenggear]

Spline Shaft with external spline.

Material AISI 9310 core hardness 33-43 HRc

External Spline is carburized to 58 min HRc hardness
case depth .018-.025

I want to a run a test with one part that has been carburized, Harden & tempered.

I want to see if this would be a viable repair or am I
chasing up a tree.

I want to Induction anneal the spine area dead soft.
Then I want to Induction harden & temper the spline.

then I want to cut the ahaft down the middle and run hardness test verifing the core & case.

question ? would be it possible to maintain the core & case hardness, and the martensite properties?
can a transition/heat affected zone be prevented.

Please advise
Thanks in Advance

 

[arunmrao]

The carbon content is too low for it to be amenable to induction harden. Hence the carburzing process is done. This increases the surface carbon level thereby during hardening the case gets hardened.

Save water Drink Beer

 

[CoryPad]

When you say anneal, do you mean austenitize? You intend to limit this to only the splined area?

I suppose in theory this is possible, but likely difficult to set up correctly.

The testing procedure is straightforward.




Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[dbooker630]

I have had cases where there is some rework to do on the spline or keyway geometry, hence the reason for induction anneal, or furnace subcritical anneal, soft enough to cut the keyway or hob a spline. Then I would give the part a slightly shorter recarb cycle to put minimum case depth where I cut but without saturating what already had a full case.

Assuming that your surface carbon is .90%, the annealed shaft COULD be induction hardened again but you would have to be careful about cracking. You should raise your quench concentration if you try this. As far as a transition, it depends on how deep your anneal cycle went into the part. You are going to have a transition zone ranging from martensite, to intermediate products, perhaps your annealed structure, and then the original Q&T core.

 

[redpicker]

I am not sure what you are trying to accomplish, but I think you are "chasing up a tree"

If you induction anneal the splined area, you will get both the case and core dead soft, with the case always remaining harder than the core (because of the higher carbon content). When you re-harden the splined area, there are two ways to go.

1) You could use a high frequency induction coil that would only austenitize the surface (carburized case) in which case, you would not re-harden the core, it would remain as soft as it got when you annealed it.

2) You could use a lower frequency induction coil that could through harden the splined area. This would allow you to restore both the hardness of the case and the core. The edges of the re-hardened area (Heat Affected Zone), however, would not achieve adequate austenitization, so this may cause a problem. Depending on the geometry of the splined area and the remaining area of the shaft, you might be able to get extent of the HAZ small enough so it wouldn't matter. I would want to give the entire shaft a furnace temper after this operation and, being 9310, a sub-zero treatment and second temper would probably be needed.

The better way would be to furnace anneal the shaft, perform whatever repair you need, then re-heat treat the entire shaft.

rp

 

[mfgenggear]

arunmrao

Part would be carburized & harden. prior to induction Harden.

CoryPad

Part is carb, Harden(austenitize) & tempered
so I do mean anneal, repair then reinduction harden.

dbooker630

exactly or very similar to my situation.
I need to rework the spline

"You should raise your quench concentration"

Please advise on the above comment.

redpicker

I am researching new ground here, this is why I posted on this board before proceeding with my experiment.


"you might be able to get extent of the HAZ small enough so it might not matter"

This is what my concern would be, if it is enough to be detrimental to the product.

How would you process so the HAZ would be minimal.

Thanks for all your Post

mfgenggear

 

[dbooker630]

mfgenggear,

Normally when induction hardening alloy steel the concentration of polymer is enriched to guard against quench cracking, as opposed to if you were working with carbon steel.

If I were to attempt to salvage a carburized shaft using IH, I agree with redpicker that high frequency should be used, and I would use it on both the anneal and reharden, with the intent of leaving the core intact through both ops. The trick is going to be minimizing the HAZ in both IH steps.