Influence of boron and nitrogen on tempered martensite embrittlement

The propensity of boron-containing and molybdenum-containing steels to tempered martensite embrittlement was carried out. Investigation conducted by serial curves of impact strength and fractographical studying of samples fracture obtained with a scanning electron microscope (SEM). Fracture of samples depending on conditions of their tempering (temperature and cooling rate) is determined. The study has shown that commercial boron-containing steel does not show a tendency to tempered martensite embrittlement. It was found that addition of boron into steel with a low concentration of nitrogen (0.004 mass%) leads to a decrease of impact strength, but does not embrittle steel. An increase of the nitrogen concentration to 0.016 wt. % leads to embrittlement, regardless of the boron concentration introduced up to 0.025% by weight. (paper)