Classifications of Steel

Steels are grouped into five main classifications.

Carbon Steels

More than 90 percent of all steels are carbon steels. They contain varying amounts of carbon and not more than 1.65 percent manganese, 0.60 percent silicon, and 0.60 percent copper. Machines, automobile bodies, most structural steel for buildings, ship hulls, bedsprings, and bobby pins are among the products made of carbon steels.

Alloy Steels

These steels have a specified composition, containing certain percentages of vanadium, molybdenum, or other elements, as well as larger amounts of manganese, silicon, and copper than do the regular carbon steels. Automobile gears and axles, roller skates, and carving knives are some of the many things that are made of alloy steels.

High-Strength Low-Alloy Steels

Called HSLA steels, they are the newest of the five chief families of steels. They cost less than the regular alloy steels because they contain only small amounts of the expensive alloying elements. They have been specially processed, however, to have much more strength than carbon steels of the same weight. For example, freight cars made of HSLA steels can carry larger loads because their walls are thinner than would be necessary with carbon steel of equal strength; also, because an HSLA freight car is lighter in weight than the ordinary car, it is less of a load for the locomotive to pull. Numerous buildings are now being constructed with frameworks of HSLA steels. Girders can be made thinner without sacrificing their strength, and additional space is left for offices and apartments.

Stainless Steels

Stainless steels contain chromium, nickel, and other alloying elements that keep them bright and rust resistant in spite of moisture or the action of corrosive acids and gases. Some stainless steels are very hard; some have unusual strength and will retain that strength for long periods at extremely high and low temperatures. Because of their shining surfaces architects often use them for decorative purposes. Stainless steels are used for the pipes and tanks of petroleum refineries and chemical plants, for jet planes, and for space capsules. Surgical instruments and equipment are made from these steels, and they are also used to patch or replace broken bones because the steels can withstand the action of body fluids. In kitchens and in plants where food is prepared, handling equipment is often made of stainless steel because it does not taint the food and can be easily cleaned.

Tool Steels

These steels are fabricated into many types of tools or into the cutting and shaping parts of power-driven machinery for various manufacturing operations. They contain tungsten, molybdenum, and other alloying elements that give them extra strength, hardness, and resistance to wear.

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