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Will heating destroy case hardening

Will heating destroy case hardening


So have a gear thats a interference fit on a shaft. (by 0.08mm)
Both gear and shaft are some sort of nickel - chromium steel simular to en36a (but not necessarily so, detected composition by XRF and found closest match).

There case hardened, but not through hardened. (cutting a old gear is soft inside) But do not know the process used to harden. (suspect carburised, but its a mass produced item from a motorcycle gear box so who knows)

What to try and shrink fit assembly instead of press, But to expand the gear over the shaft would have to heat gear to a calculated 360C. Will this damage the case hardening of the gear? and any ideas as to what max temperture could be used used.

RE: Will heating destroy case hardening

Assuming you have a steel close to EN36A, see the attachment. You have core hardness data after carburizing and another table showing the typical hardness after tempering at 200 deg C. These is a slight drop in hardness at 200 deg C.

I would limit the heat to less than 200 deg C to avoid softening the case.

RE: Will heating destroy case hardening

Instead of heating the gear, why not deep freeze the shaft instead?

RE: Will heating destroy case hardening

or both

RE: Will heating destroy case hardening


I don't think slip fittings going to fly, after all.

Heating to 200C will expand by +.04mm
Freezing with dry ice -78C contract by -.02mm
Not enough need at least .09mm difference to be desirable easy slip on.
Could freeze with liquid nitrogen at -195C will contract maybe -.05mm,
so heat and freeze potentially works, BUT would have to buy nitrogen, not worth the expense, can just press it on... (Dang! need a bigger press!)

RE: Will heating destroy case hardening

and if a bigger hammer won't fix it, your problem is electrical

RE: Will heating destroy case hardening

Liquid nitrogen should be relatively cheap - in central FL, the suppliers sell it by low volume amounts (less than 2 liters) for shipping bull semen.

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