PURPOSE: To form boron nitride coating having high purity and high density on a substrate contg. iron group metals at ordinary press. and at a temp. lower than that for conventional method, by introducing a reaction gas contg. NH3, BCl3 etc. on the substrate so as to metallize the substrate chemically.

CONSTITUTION: A reaction gas is brought into contact with a heated substrate contg. iron group elements in respective ranges of flow rate of components, i.e., 0.2W3.0ml/sec. NH3 or N2H4, 0.5W1.0ml/sec. BCl3 or B2H6, 0.2W4.0ml/sec. H2, and 0.2W4.0ml/sec. inert gas such as Ar. Hereby a coating of hexagonal system crystals of boron nitride 2 μm in thickness are formed on the substrate by chemical metallizing. The thickness of the coating increases linearly with increase in the metallizing time to form a coating not smaller than 500μm in thickness. For the substrate is used an alloy or a cpd. including a single iron group element, e.g., iron, cobalt, or two or more members of iron group elements.