Here is the real deal on carbon absorption:
Casehardening: The box must be packed full with charcoal then sealed. The steel must be clean (scale free) to start. 1425°F is the minimum recommended case hardening temperature and it takes a lot less time at the maximum of 1625°F.
Carbonnitriding is done by using a liquid salt bath (cynaide was commonly used) and the time/temperature ratio is supposed to be more or less the same for case hardening by carbon packing and gas methods. The results are the same.
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.
Heat Treaters Guide, 1982, ASM, p.25 chart (referenceing Metals Handbook 8th ed., Vol 2, ASM.
So to get only 20 thou of case on virgin mild steel (or case-hardened steel that has been filed or polished), you need 2 hours at 1600F and that's too hot to quench from and still get color, hence the need to come down to a lower temp (precisely what temp is what we are trying to ascertain) and stabilize before we quench.
Last edited by doublegunhq; 12/31/06 01:42 AM.
