Researchers say that modern engine components need to be made of highly stable materials, citing the example of diesel injection systems in dowsized engines that face higher mechanical and thermal loads than ever before while still needing to maintain accuracy.
Steels hardened using low-pressure carbonitration with methylamine are suited for use in components subjected to high mechanical and thermal loads in energy-efficient and low-emission engines of the future, according to the research which was presented by KIT scientists in the Journal of Heat Treatment and Materials.
The researchers say their process can be used to develop processes where cheaper low-alloy steels can be machined in the soft state and then hardened for final use. The carbonitration process involves the metal being heated to temperatures between 800 and 1050°C and total pressures below 50 millibars. The component surface is specifically enriched with carbon and nitrogen and subsequently hardened by quenching.
“Low-pressure carbonitration combines the advantages of low-pressure processes with those of atmospheric carbonitration,” explains project leader David Koch, who also says that atmospheric carbonitration damages the surface of the components treated by oxidation, which can be prevented by low-pressure processes.
So far, the low-pressure carbonitration process has been carried out nearly exclusively using ammonia as a nitrogen donor together with a carbon donor, but the KIT scientists have been studying other gases too. Together with researchers from Bosch, they found that methylamine and dimethylamine worked well and only require one gas instead of two. Work continues on improving the process and developing a pilot study outside of the laboratory.
December 2, 2015