A new process for hardening steel develop scientists at the Karlsruhe Institute of Technology (KIT): Use of methylamine enrich it to low-alloy steels with carbon and nitrogen. The low-pressure carbonitriding with methylamine saves time and process gas. The so hardened steels are suitable for mechanically and thermally highly stressed components in energy-efficient and low-emission engines of the future.
Hard surfaces, tough core
However, bringing the so-called downsizing with that highly stressed components, such as components of diesel injection, even higher mechanical and thermal loads. Diesel injection systems have higher injection pressures and injection better accuracies have to meet the requirements of downsizing. Therefore, the injectors must be made from highly resistant materials.
An attractive and cost-effective way is the use of low-alloy steels, ie steels containing a maximum of five percent by mass other metals other than iron. You can edit soft well and are then cured for use in order to obtain a hard surface with a tough core. Scientists at the Engler-Bunte-Institut of KIT are working on a new method of case hardening steels, the low-pressure carbonitriding: the outer layer of about curing components is enriched selectively with carbon and nitrogen at temperatures between 800 and 1050 degrees Celsius and total pressures below 50 millibars and then hardened by quenching.
United advantages of previous methods
The aim of the current project led by David Koch, together with partners from research and industry, the basics of low pressure carbonitriding to elaborate and develop this ready for volume production. “The low-pressure carbonitriding combines the advantages of low-pressure process by which atmospheric carbo” said David Koch. When atmospheric carbonitriding the surface of the treated components from being damaged by surface oxidation; This can be avoided at low-pressure process. In addition, a more uniform hardness profile is generated in the component, especially in complex component geometries.
Heretofore, almost exclusively ammonia, used in the low-pressure carbonitriding as a nitrogen donor, in combination with a carbon donor, usually acetylene or propane. The KIT researchers have now investigated other gases and gas mixtures for their suitability for the low-pressure carbonitriding and tested their effectiveness in enriching a component surface layer with carbon and nitrogen in a thermobalance experiment. The KIT scientists presented in collaboration with researchers of the Robert Bosch GmbH in Stuttgart found that methylamine lead (CH3NH2) and dimethylamine ((CH3) 2NH) as process gases to a good enrichment of the surface layer with carbon and nitrogen.
Shorter process at higher temperatures
When using methylamine to low-pressure carbonitriding is instead of two gases only a necessary, and the usual two process steps can be reduced to one. In comparison with the ammonia as a nitrogen donor in combination with a carbon donor methylamine reaches a higher nitrogen enrichment of the surface layer. Same Since carbon is introduced, the process time is reduced significantly. Methylamine allows moreover the carbonitriding at significantly higher temperatures, which in addition reduces the processing time. Also, the methylamine is utilized better as a process gas, which allows a reduction in the amount of gas used.
The KIT scientists are now working with amines to optimize the low-pressure carbonitriding on. Above all, it comes to improve the uniformity and the free adjustability of the entry of carbon and nitrogen. The next goal is to transfer the process from the laboratory scale to pilot scale. (Journal of Heat Treatment and Materials, 2015; doi: 10.3139 / 105.110263)