Thermochemical heat treatment of steel substrates using borane–amine adducts as precursors

Abstract

A novel approach to gas boronising has been carried out to systematically test organoboranes as precursors for low pressure gas boronising. The precursors of the group of borane–amine adducts were synthesised and subsequently applied to gas boronising of steel 42CrMo4 (AISI 4140). Characterisation of the boride layers was performed using glow discharge opticalemission spectroscopy, X-ray photoelectron spectroscopy, SEM, and metallography. Ultramicrohardness was also determined and the wear behaviour was simulated. With the precursors borane–triethylamine adduct and borane–diethylamine adduct gas boronising was possible. Single phased iron boride layers of type Fe₂ B with a thickness of several micrometres were generated. The carbon, nitrogen, and oxygen contamination of the boride layers was low. The boride layers are not completely compact which results in a lower hardness compared with commercial powder pack boronised samples. The wear behaviour is similar to powder pack boronised steels and is significantly better than the untreated samples.