Carburizing : What Is LPC???
Low pressure carburizing (LPC), also known as vacuum carburizing or vacuum case hardening is achieved under vacuum, in a vacuum furnace.
The carbon donator gas is Acetylene C2H2 – used during the enrichment phases, and nitrogen N2 is used during the diffusion phases. The process temperature is generally higher than traditional carburizing, between 880 and 1050°C thanks to the vacuum technology. The high temperature processes help to drastically reduce carburizing cycle time in comparison to traditional atmosphere carburizing: up to 50%, depending on the carburizing depth.
ECM Technologies’ ICBP® low pressure carburizing installations use the Infracarb® patented process. Infracarb® consists in an alternation of enrichment phases and diffusion phases (C2H2 hydrocarbon and a neutral gas N2 for diffusion). The number and the length of the phases depend on the targeted carburizing depth.
Infracarb® process includes a simulation software CBPWin to allow precise adjustment of recipe parameters to achieve perfect control of the carburizing depth. Acetylene is a synthesis gas, its purity can be controlled providing exceptional chemical reactivity (dissociation rate is over 60%) which allows very complex parts such as diesel injection components to be carburized.
Very simple physical parameters (temperature, length of the gas injection phases, flows and pressures) enable to reach precise and optimal results. Large surface areas can be carburized thanks to acetylenes’ high enrichment power.
Vacuum carburizing brings in many advantages in comparison with traditional atmosphere carburizing. This process allows to avoid oxidation of parts, a better carburizing homogeneity, an excellent repeatability of the process from load to load, and to fit in tight metallurgical tolerances regarding the carburizing depth, and finally, hardness parameters. This process is environmentally friendly as it significantly reduces CO2 emissions and harmful chemical products.
The LPC process is followed by a martensitic oil or gas quenching to obtain the desired hardness at the core and at the surface of the parts. The selection of the quenching media depends of the quenching ability and the geometry of the materials and parts to be treated.
INFRACARB® ADVANTAGES COMPARED TO ATMOSPHERIC PROCESSES
Better carburizing efficiency due to the use of acetylene
No inter-granular oxidation thanks to the absence of oxygen (IGO)
Perfectly controlled and repeatable case depth with limited tolerances
Regarding Gear case hardening, better pitch to root consistency of case depth
Ability to choose the recipe and the surface carbon content independently for each load
Environmentally friendly process: less gas consumption, no CO/CO2 rejection
Mixing of C2H2 with N2 to adjust carbon penetrability
Heat treatment time drastically reduced with the use of higher temperatures
Excellent esthetic aspect of the parts
Improved fatigue resistance with combination of low pressure carbonitriding and stop quench.
