Low‐Pressure Nitrocarburizing in Standard Vacuum Furnaces—Preliminary Studies

Abstract

For the first time, low‐pressure nitrocarburizing process is performed in a minorly modified standard vacuum furnace on 16MnCr5 alloy steel samples. Ammonia and acetylene are used as a source of nitrogen and carbon, respectively. Lowering the pressure of the process ensures longer and more efficient ammonia dissociation. To prove the safety of the process, exhaust gases are investigated online using residual gas analyzer mass spectrometer, whereas reaction products deposited on the sample's surface are studied by means of time‐of‐flight secondary ion mass spectrometer. Possible reactions taking place in the atmosphere of the chamber are written down. In the results of conducted examinations, it is confirmed that no toxic gases are generated, and no cyanides and polycyclic aromatic hydrocarbons are formed during the process. Additionally, microstructure analysis of the cross sections of nitrocarburized sample is performed using scanning electron microscopy (SEM) and optical microscopy. It confirms the diffusion of nitrogen and carbon into the near surface layer. SEM/energy‐dispersive X‐ray spectroscopy analysis demonstrates precipitation of carbide and carbonitride, what is proved by X‐ray diffractometer and microhardness profile analysis. The presented low‐pressure nitrocarburizing results in an increase in hardness from about 200 to over 500 HV and the formation of an effective case depth of about 20 μm, after only 20 min of the process.