Hardening metal

[Mcgyver]

http://www.deform.com/displayapp.php?appsel=11

Curious to learn more about this… I've seen induction welding of tube and this looks similair - isn’t this more production process – ie can you get this done for one of parts at the local heat treat shop?

Although they say it’s a case hardening process, it done to tool/heat treatable steel, right? i.e. only the outer part of the tool steel is changed…..but you're are still starting with a steel that can be heat treated....or is carbon added (or leached from surrounding material) to mild steel?

Finally, as a quench is still involved, isn’t warping still an issue?

[Geof]

To answer a few questions from different people. Case hardening, the old fashioned style was done by packing the low carbon steel part in charcoal and heating to red heat for many hours. The powders that came available made the process a bit easier but no matter what technique is used the depth of the hardening is only a few thousandths. It is not deep enough to grind to the type of finish needed to run needle roller bearings on nor is the underlying material strong enough for the concentrated roller loads. Remember the rollers only contact for a very small portion of their circumference. Think of a log on a layer of ice half an inch thick over soft mud.

Induction hardening only heats the surface of the shaft material being treated and a high carbon or alloy steel is needed because nothing is added. The case depth here can be several hundredths of an inch, it is deep enough for a ground finish and the hardened depth is thick enough to handle the concentrated roller loads. Distortion is minimised with induction hardening because the heated region does not extend all the way through the material, the heating is very even and the quenching is arranged to be even also.

For the shaft in question it may be possible to make it from low or medium carbon steel and press on hardened steel sleeves for the roller bearings to run on. The sleeves should be available from the same source as the rollers.

[ViperTX]

Geof...I agree with you on that...."bearing races" are the way to go...

[Mcgyver]

Geof, thanks for better my understanding on induction hardening.

Have to disagree on the case hardening though. even the old pack hardening could have thicker cases, the box had to be airtight, after that it was a matter of how long it soaked for. Nowaday it just sits a vat of nasty (cyanide?) stuff and the depts of 50 thou are possible. using the powders however will only get you a few thou

Carbonnitriding starting with low carbon steel (SAE 1008):

1 hour @ 1425 to 1450°F results in a case .004" deep.
2 hours @ 1425 to 1450°F results in a case .006" deep.
3 hours @ 1425 to 1450°F results in a case .009" deep.
4 hours @ 1425 to 1450°F results in a case .011" deep.

1 hour @ 1600 to 1625°F results in a case .015" deep.
2 hours @ 1600 to 1625°F results in a case .021" deep.
3 hours @ 1600 to 1625°F results in a case .026" deep.
4 hours @ 1600 to 1625°F results in a case .030" deep.

for Heat Treaters Guide

[Geof]

Mcgyver;

I concede; more than 0.010 does not qualify as a few thou.

[Mcgyver]

ah, your a gentleman. no need for the duelling pistols then