CM:
Let me pose a question & see if you have any input on this aspect. First it has been my understanding for the absorption of carbon & for hardening at the quench the steel has to be above it's critical temp. Since we are speaking here of re-hardening a steel previously carburized it is in efect already a high carbon steel on the surface, to the depth of the original case. However once the steel has been carburized the hardening effects are essentially those of any other carbon steel.
Quenching temps from an old (we are speaking of old techniques here) are as follows for various carbon steels;
.65-.80% C = 1450-1550°F
.80-.95% C = 1410-1460°F
.95-1.10% C = 1390-1430°F
1.10%+ C = 1380-1420°F
To obtain a "File Hardness" with a quench of 1250°F or lower certainly seems surprising to me. As the parts are already carburized & likely to a rather high % working in the extreme low end of the above ranges would seem plausible, but temps of 1350°F & down would seem questionable as to hardening.
