PHYSICAL or IIION .1N1) STEEL. The physical properties of iron and steel which are chiefly useful to the engineer and manufacturer are strength, hardness, weldaliility, ductility, malleability, elasticity. and homogeneity. With the exception of weldability, all of these prop erties are exhibited to sonic extent by every piece of iron or steel. The relative degrees in \villein these different properties exist in different kinds of iron and steel vary greatly. however. This i4 a familiar fact to all, and does not need proof. The variation in these properties in different kinds of iron and steel is due partly to variation in the relative amounts of the contained chemical elements. partly to the physical structure, and partly to the method and amount of working to which the metal Inas been subjected to attain its final useful form. Commercially, iron and steel may be divided into the billowing general classes: Wrought iron, soft steel. medium steel, hard steel, cast steel, hard east steel, cast iron, east iron. The chief physical prop erties of each of these classes of iron and stead will be referred to after a brief statement of the destructive effects produced by the different eli•nnical elements 111)011 1110 physical properties of iron and steel generally. The effects of 00 iron and steel are more and use ful than those of any other known chemical element: it constitutes about 4 per cent. of east iron. and from to 11!-, per cent. of steel, and is nearly entirely absent from wrought iron. The effects of increasing the carbon element in iron or steel are to increase the hardness, strength, and fusibility. and to decrease the ductility, mal leability, and •eldability. The effect of inereas ing the silicon element of iron and sled is to increase the strength and soundness of steel and the fluidity of cast iron, and to reduce the duc tility of steel. Manganese has the effect of coun teracting the injurious effects of sulphur. phos phorus, and some other impurities. and increases hardness, fluidity, elasticity, and strength. Sul phur and phosphorus are nearly unmixed evils in iron and steel, and every effort is made to remove them from these metals.
The effect of none of these elements upon the metal is independent, hut is influenced by the presence of one or more of the others. These interactions are too complicated to be discussed outside of special technical treatises. The effect of treatment during working upon the physic-al properties of iron and steel are numerous, and are referred to in the articles on ANNEALING; FORGE. FORGING; FOUNDING: ROLLING-MILL: \\ IRE.
Turning now to the physical properties of the several classes of iron and steel mentioned above, it may be noted, first, that strength may he sub divided into strength against rupture by direct pull, or tensile strength: strength against rup ture by compression. or compressive strength; strength against rupture by bending. or flexural strength: and strength against shear. or shearing strength. (For the methods of measuring these various forms of strength, see STRENGTH OF MA TERIALS.) Hardness is the capacity to resist in dentation; Weldability is the property which permits two or more separate fragments to be welded together; ductility is the property which renders the metal capable of being drawn out into rods or wire; malleability is the prop erty which permits the metal to be hammered or pressed into different shapes; elasticity is the property which gives the metal power to return to its original form after distortion: and homo geneity is the property which secures uniformity of structure and mass.
Cast iron cannot be welded like wrought iron. and its malleability and ductility are practically nil; its tensile strength is from 15.000 pounds to 35,000 pounds per square inch: its compressive strength is from 60,000 pounds to 200,000 pounds per square inch; its flexural strength is from one half to two-thirds its tensile strength; its elas ticity is small. Wrought iron is malleable. van be forged and welded, and has a high capacity to tensile strengths of from 60.000 pounds to 70, 000 pounds per square inch, with a limit of elas ticity of from 30,000 pounds to 40,000 pounds per square inch. The hard steels have a much greater strength. The compressive strength of steel is always greater than the tensile strength.