Heat treating nomenclature...

[Bryanbdp]

Hi. On a print from the 1940s war department, a part made from 1020 steel has a heat treating specification of C.C. .004 to .006" deep.

Can anyone tell me what C.C. stands for?

Carburize and Case harden? Or maybe something else?

Thank you,

bryan

[Moses Ludel]

Bryanbdp...This would be a 1940s specification for case hardening a 1020 part(s) by the carburizing process.  The minor case depth would provide a better/harder wear surface without affecting the part's core.  1020 is a low-carbon steel with good machining properties in an annealed or normalized state.  Machining the non-hardened part would be easier on tooling.  Case hardening usually takes place after any machining work if this is a gear, shaft or splined part.  Here is a reliable description of 1020 uses and features: 

Material Notes:	1020 steel responds well to cold work and heat treating. Weldability is fair. Applications: Shafts, lightly stressed gears, hard wearing surfaces, pins, chains and case hardened parts where core strength is not critical. 1020 is suitable for case hardened parts where core strength is not critical.

1020 would be a lighter-duty material for these kinds of parts.  An automotive transmission gear, even in that era, would likely be made of 8620 alloy steel.  8620 also responds to carburizing heat treatment.  Common uses and properties of 8620:

"8620 has a high case toughness and above average core toughness due to the nickel content. Additionally, it is the most widely used carburizing alloy steel. Typical uses include gears, cranks, shafting, axles, bushings, heavy duty pins, bolting, springs, hand tools, gears, and many other machinery parts."

Sounds like you're restoring an original part or duplicating it with 1020.  The '40s case hardening depth specification is slight and can be assured by using a heat treating shop's carburizing process.  This relatively minor depth is intentional, likely to prevent overloading the non-hardened 1020 core.  Case depth requirements for each low-carbon steel or alloy steel are different.

Moses