The influence of concentration of nitrogen dissolved in the steel and the small additions of nitride-forming elements on the hardenability of boron-treated manganese-vanadium steel 40GF-VI was studied. It is shown that an increase of nitrogen concentration from 0.004 % to 0.015 % increases the hardenability of steel. It has been found that a small amount of titanium (about 0.02 %) in steel with a low content of nitrogen (0.004 %) is enough to bind the latter to nitrides, which allows to save most of the boron in the active state (in the solid solution). The residual amount of titanium and aluminum in the range of 0.015-0.020 % of each in steel with nitrogen content in the range of 0.010-0.015 %, which is typical for an electric arc melting steel, is insufficient to bind all nitrogen. As a result, a part of nitrogen is spent on the formation of boron nitrides, which reduces the effect of boron on hardenability of the manganese-vanadium steel micro-alloyed with boron. In conclusion, some methods of protecting boron in steel are briefly described.