The main use of vanadium is in steel. It is used where great toughness and torsional strength are required, as in automobile parts, gears, piston rods, tubes, boiler plates, transmission shafts, bolts, gun barrels, gun shields and forgings of any kind which have to withstand heavy wear and tear. The vanadium content of such steels varies from 0.1 to 0.4 per cent. Vanadium is occasionally used in certain tungsten alloys for making high-speed tool steel, the introduction of a small proportion of vanadium decidedly reducing the proportion of tungsten required to give such alloys the desired hardness and toughness. Arnold has given some illustrations of the effect of vanadium on steels of different types: One plain carbon steel containing about 1 per cent. of carbon had a yield point of 35 tons per square inch, a maximum stress of 60 tons per square inch, an elongation of 10 per cent. on 2 inches, and a reduction of area of 10 per cent. The addition to this steel of about 0.6 per cent. of vanadium raised the yield point from 35 to 65 tons, the maximum stress from 60 to 86 tons per square inch, still leaving an elongation of 7 per cent. and a reduction of area of 8 per cent. A steel containing 0.25 per cent. of carbon and 3.3 per cent. of nickel gave a yield point of 33 tons, a maximum stress of 42 tons per square inch, an elongation of 26 per cent. on 2 inches, and a reduction of area of 53 per cent. A practically identical steel, containing in addition about 0.25 per cent. of vanadium, gave a yield point of 50 tons instead of 33, and a maximum stress of 68 instead of 42 tons per square inch. The elongation was 17 per cent. on 2 inches and the reduction of area 36 per cent. A steel containing 0.25 per cent. of carbon and about 1 per cent. of chromium registered a yield point of 27 tons and a maximum stress of 41 tons per square inch, with an elongation of 36 per cent. on 2 inches and a reduction of area of 55 per cent. The addition of 0.25 per cent. of vanadium raised the yield point from 27 to 40 and the maximum stress from 41 to 55 tons per square inch. The elongation was lowered from 36 to 26 per cent., and the reduction of area from 55 to 53 per cent. Vanadium, therefore, differs from tungsten in having an extremely beneficial effect, not only on tool but also on structural steel. Arnold has shown that vanadium seemingly does not form a double carbide with iron, but gradually takes the carbon from the carbide of iron until, if about 5 per cent. of vanadium is present, Fe₃C can not exist, and only a vanadium carbide, V₄C₃, containing 15 per cent. of carbon, is present; and this constituent is constant, at least in tool steels containing 5 to 14 per cent. of vanadium. The micrographic analysis of such alloys has resulted in the discovery of three new constituents, namely, vanadium pearlite, vanadium hardenite, and vanadium cementite.