Approximate Grades carbon range Common uses Extra soft 0.08-0.18 Pipe, chain and other welding purposes; (dead soft) case-hardening purposes; rivets; pressing and stamping purposes. Structural (soft) 0.15-0.25 Structural plates, shapes and bars for (medium) bridges, buildings, cars, locomotives; boiler (flange) steel; drop forgings; bolts. Medium 0.20-0.35 Structural purposes (ships); shafting; automobile parts; drop forgings. Medium hard 0.35-0.60 Locomotive and similar large forgings; car axles; rails. Hard 0.60-0.85 Wrought steel wheels for steam and electric railway service; locomotive tires; rails; tools, such as sledges, hammers, pick points, crowbars, etc. Spring 0.85-1.05 Automobile and other vehicle springs; tools, such as hot and cold chisels, rock drills and shear blades. Spring 0.90-1.15 Railway springs; general machine shop tools. CHAPTER II COMPOSITION AND PROPERTIES OF STEEL It is a remarkable fact that one can look through a dozen text books on metallurgy and not find a definition of the word "steel." Some of them describe the properties of many other irons and then allow you to guess that everything else is steel. If it was difficult a hundred years ago to give a good definition of the term when the metal was made by only one or two processes, it is doubly difficult now, since the introduction of so many new operations and furnaces. We are in better shape to know what steel is than our forefathers. They went through certain operations and they got a soft malleable, weldable metal which would not harden; this they called iron. Certain other operations gave them something which looked very much like iron, but which would harden after quenching from a red heat. This was steel. Not knowing the essential difference between the two, they must distinguish by the process of manufacture. To-day we can make either variety by several methods, and can convert either into the other at will, back and forth as often as we wish; so we are able to distinguish between the two more logically.