Some Aspects of Low Methylamine Partial Pressure Carbonitriding*

Abstract

Low pressure carbonitriding is a case hardening process under development. At temperatures between 800 °C and 1050 °C and at total pressures below 50 mbar the carbon and nitrogen concentrations in the outer layer of steel parts are increased and the parts are subsequently hardened by quenching. As state of the art, ammonia is used as the nitrogen donor, in combination with a carbon donor gas, mainly acetylene or propane [1–3]. Other possible carbonitriding gases are not mentioned in recent literature with the exception of a Soviet Union patent [4], but no information on the application of this invention was found. At the Engler-Bunte-Institut of the Karlsruhe Institute of Technology, methylamine and dimethylamine were identified as potential carbonitriding gases, and their carbonitriding behavior was experimentally studied using a thermobalance. The experiments proved an increased nitrogen uptake of the steel samples in comparison to the state of the art. The carbon uptakes were in the same order of magnitude to a comparable process with acetylene. In addition to earlier published results for methylamine as the carbonitriding gas [5], this paper focuses on some operational and kinetic effects.