Vacuum Carburizing
Vacuum carburizing, also known as low-pressure carburizing (LPC), is a case-hardening process in which steel is heated in a vacuum furnace to approximately 890–1000°C and exposed to hydrocarbon gas pulses followed by diffusion holds. Carbon diffuses into the surface, creating a hard, wear-resistant case while retaining a tougher, ductile core, then parts are oil or gas quenched.
On the shop floor, vacuum carburizing is selected for precision ferrous workpieces such as gears, shafts, and automotive drivetrain components that demand a hard case for wear and pitting resistance but cannot tolerate the scale, oxidation, or dimensional movement of conventional atmospheric carburizing. In practice, the furnace cycle uses boost/diffusion sequences: the load is heated under vacuum to carburizing temperature, hydrocarbon gas is injected at low pressure to raise surface carbon, then the vacuum is restored to allow diffusion and even out the case depth. Because distortion and surface contamination stay low, the process reduces post-heat-treat grinding and rework, helping CNC-machined parts hold tight tolerances. Load preparation is critical—residual oil, grease, coolant, or chips must be removed before load-in, or the furnace atmosphere and vacuum pump system become contaminated, producing unstable case quality and extra maintenance downtime.
What does vacuum carburizing actually change in the steel?
It increases the carbon concentration in the surface layer, which later enables hardening while the lower-carbon core remains tougher and more impact resistant.
Why use vacuum carburizing instead of conventional gas carburizing?
It is preferred when the job requires less oxidation, less distortion, higher repeatability, and better case uniformity, especially for precision parts and complex shapes.
What parts benefit most from vacuum carburizing?
Parts with demanding wear and fatigue requirements, especially gears and shafts, benefit because the process combines a hardened surface with a ductile core.