Steel

(stel.) [From A. S. style.] (Metall.) Steel is intermediate between malleable iron and cast-iron, and its peculiar properties are supposed to depend upon the amount of car bom combined with it. The best steel contains about 1.5 per cent.. and when the carbon gets below this it becomes " mild steel," and approaches wrought iron in its properties, while when the carbon increases beyond this amount it a umes the properties of cast-iron. The distinguishing property of steel is that of becoming very hard and brittle when it is heated and then plunged into water, and of becoming soft again when heated and cooled slowly. When hardened steel is gradually raised in temperature and a bright surface is watched,it will be seen to pa through different shades of colors which are due to different thickne es of oxide. These colors have been found to correspond to definite temperatures, and if the steel is plunged into water at any particular color it will be found to po e a definite amount of temper, as it is called, dependent upon the temperature which it had attained. Good steel is white in color and takes a very high polish. Its fracture should be close and granular, with no appearance of fibre. Its tenacity exceeds that of any other metal or alloy. Its specific gravity varies between 7-6224 and 7-8131.It melts at a lower temperature than malleable iron, being more fusible in proportion to the carbon it contains. When near the melting-point it is capable of being welded and wrought. When di olved in acids it leaves a black carbonaceous residue. One proce for making steel is that termed Cementation, which consists in filling a suitable furnace with boxes containing alternate strata of malleable iron bars, and powdered charcoal, and keeping the whole for several days at a red heat, the atmospheric air being excluded. During this proce the texture of the iron, which was fibrous, becomes granular, and its surface a umes a blistered appearance; the product being hence termed blistered S. Several bars of the latter being welded together, and the proce being repeated, shear S. is the result; this being broken in pieces, and melted in a crucible, forms cast-S., which po e es equality of texture and a capability of being rendered extremely hard, as well as of taking a fine polish. The Be emer proce consists in blowing atmospheric air into the melted pig iron in the converting ve el, and this operation is continued until the oxygen has effected a combination with all the carbon, except the quantity required to form S. It has also been manufactured in such away that the bars contain cores of iron; this gives all the hardne of S., and the tenacity of iron; and prevents articles made of it from breaking off short, as they frequently do, when formed only of hardened S. The property on account of which S. is so valuable consists in its being rendered extremely hard by being heated to redne and quenched in water; and in this hardne being capable of modifications by tempering, so as to be accompanied, when nece ary, with great tenacity and elasticity. [s. 855]