The heat treatment behind most high-capacity gears. Parts made of low-carbon alloy steels such as 8620, 4320 or 9310 are held around 900 to 950 C in a carbon-rich atmosphere until carbon diffuses to the required depth, then quenched and tempered. The result is a case of about 58 to 62 HRC over a tough core, giving the highest bending and pitting capacity of common steel gear treatments, at the cost of distortion that usually needs grinding.
Carburizing load is in the pit furnace for twelve hours, so the gears won't be back for grinding till Monday.
Areas that must stay soft, such as threads and some bores, are masked with copper plate or stop-off paint before the furnace.
Also heard as
- case carburizing
- carburize
- case hardening
Related terms
Case depth
How deep the hardened surface layer of a gear tooth goes, usually measured to a set hardness such as 50 HRC.
Gear grinding
Finishing hardened gear teeth with abrasive wheels to correct heat treat distortion and reach high accuracy.
Hard gearing
Shop term for case-hardened, ground gears, as opposed to through-hardened soft gears that are cut to finish.
Nitriding
A low-temperature surface hardening that diffuses nitrogen into alloy steel gears with almost no distortion.