Low pressure carburising
Low pressure carburising (CBP), carried out in vacuum furnaces with cold walls, offers many advantages compared to traditional atmosphere carburising: no oxidation, better carburising homogeneity, excellent reproducibility of the load to load processing, tightening of the metallurgical tolerances such as the carburising depth, and finally, hardness control of parts at their centre. This process respects environmental standards as it significantly reduces CO2 emissions and harmful chemical products.
ECM Technologies’ ICBP® low pressure carburising installations use the Infracarb® patented process. Infracarb® consists in alternately injecting C2H2 hydrocarbon - which enriches the surface by breaking the molecule at high temperatures - and a neutral N2 gas for diffusion.
This treatment is followed by a martensitic oil or gas quenching to obtain the hardness desired at the centre and at the surface. The quenching media is selected depending on the quenchability and the massiveness of the materials treated.
The objective is to maintain high level concentration of monoatomic carbon - obtained after the dissociation of the reactive gas on the surface of the parts - without reaching the carbon solubility limit in the steel, and therefore, without soot formation. Thus, the reaction yield is greatly superior to that obtained in traditional atmosphere carburising based on a CO/CO2 balance, while still being less prone to atmospheric changes. The absence of carbon potential notion in low pressure carburising eliminates the need for in situ atmospheric control and basically makes the process easier.
ECM Technologies’ Infracarb® process ensures precise control of simple physical parameters for optimal results: temperature, length of the gas injection phases, flows and pressures.
The process temperature is generally higher than traditional carburising, between 880 and 1,050°C, thanks to the technology used to heat graphite areas in vacuum furnaces. The cycle time is reduced significantly: up to 50%, depending on the carburising depth.
C2H2 Acetylene - used for low pressure carburising - and N2 nitrogen - used for diffusion - are the most common gases used in the Infracarb® process, under standard conditions.
Acetylene is a synthesis gas, and therefore, 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 carburised. It is also not very sensitive to possible heterogeneity in washing before treatment and prevents the occurrence of soft areas.
Large areas can be carburised and it has a high enrichment power.
The number and length of the phases depend on the carburising depth required. Simulations using Infracarb® allow precise adjustment of recipe parameters to achieve perfect control of the carburising depth.
Infracarb’s main characteristics
- Alternated injection C2H2, N2 and NH3 if carbonitriding
- Constant working pressure and temperature
- The number and duration of the enrichment phase depend on the carbon concentration and the case depth required
Infracarb® advantages compared to atmospheric processes
- Better overall efficiency for gas reaction
- No inter-granular oxidation (IGO)
- Perfectly controlled and repeatable case depth with limited tolerances
- Better pitch to root consistency of case depth
- Ability to choose the surface carbon content load to load
- Green process: much less gas consumption and no CO/CO2 rejection
- Mixing of C2H2 with N2 to adjust individual case to case penetrability
- Heat treatment time drastically reduced with higher process temperatures
- Excellent cosmetic aspect of the parts
- Enhanced fatigue strength with combination of low pressure carbonitriding and stop