The results of determining the average corrosion rate of nickel, molybdenum and vanadium in fused sodium tetraborate in the presence of B2O3 are generalyzed and the physicochemical state of H2O molecules at elevated temperature is estimated. By the method of DTA, the corrosion destruction of metals with simultaneous formation of gaseous hydrogen, oxides and borides is ascertained at 1273 K. The theoretical conceptions on the nature of lowering the corrosion resistance in row of mentioned metals are given.