Many developments have been carried out in carburizing technology. Carburizing is simply defined as adding carbon to iron or steel by heating in the presence of carbon to harden the surface of a component. Depending on the metallurgical recipe, the hardness can vary with carbon content. This process can be achieved by a low-pressure carburizing furnace (LPC).
LPC Process
Low pressure carburizing (LPC) is run without any oxygen and with injections of carburizing gas. The LPC process has been chosen for its tight process control, repeatability, optimized metallurgy and shorter cycle time at higher temperature versus older carburizing processes.
LPC Technology
The development of a new carburizing technology for new applications requires an understanding of the standard processes. The LPC process is a thermal treatment using alternative boosts of carburizing gas and neutral gases without causing intergranular oxidation. This process also provides uniform homogeneity of carburizing case depths thanks to a precise control during the recipe development. The target is to develop carburizing recipes at higher temperatures and with a higher enrichment capability without affecting the material properties.
LPC Features
The main features of LPC are:
Hydrocarbon thermal cracking at low pressures (7-13 mbar) in a vacuum cold-wall furnace
Alternate injection of hydrocarbon gas boosts (carburizing) and of neutral gas (diffusion)
Number and duration of the steps are determined by the case depth required
LPC Advantage
While older technology is more familiar, there are many benefits to new, advanced low pressure carburizing technology. The newer technology of vacuum carburizing is based on the enrichment of carbon on the surface by the cracking of a single carburizing gas (typically propane or acetylene) at a low pressure. Thus, the vacuum has the advantage to improve the absorption of carbon. This absorption of carbon is simulated during the validation of the process and is tracked each time the recipe is run.
LPC Function
The low pressure carburizing furnace uses a cold-wall technology, so the exterior surface of the furnace stays at a low temperature, reducing the amount of heat emitted into the plant. Without any flames or hot walls, the furnace can be located in the middle of the machining area within the plant. This allows for better part flow and eliminates the need for a fireproof wall enclosing the heat-treat area.