Manual Del Ingeniero Mecanico

1 MATERIALS
PART

Mechanical Engineers’ Handbook: Materials and Mechanical Design, Volume 1, Third Edition. Edited by Myer Kutz Copyright  2006 by John Wiley & Sons, Inc.

CHAPTER 1 CARBON AND ALLOY STEELS
Bruce L. Bramfitt
International Steel Group, Inc. Research Laboratories Bethlehem, Pennsylvania

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INTRODUCTION STEEL MANUFACTURE DEVELOPMENT OF STEEL PROPERTIES ROLE OFALLOYING ELEMENTS IN STEEL

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HEAT TREATMENT OF STEEL CLASSIFICATION AND SPECIFICATIONS OF STEELS 6.1 Carbon Steels 6.2 Alloy Steels SUMMARY BIBLIOGRAPHY

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1 INTRODUCTION
Steel is the most common and widely used metallic material in today’s society. It can be cast or wrought into numerous forms and can be produced with tensile strengths exceeding 5 GPa. Aprime example of the versatility of steel is in the automobile where it is the material of choice and accounts for over 60% of the weight of the vehicle. Steel is highly formable as seen in the contours of the automobile outerbody. Steel is strong and is used in the body frame, motor brackets, driveshaft, and door impact beams of the vehicle. Steel is corrosion resistant when coated with thevarious zinc-based coatings available today. Steel is dent resistant when compared with other materials and provides exceptional energy absorption in a vehicle collision. Steel is recycled and easily separated from other materials by a magnet. Steel is inexpensive compared with other competing materials such as aluminum and various polymeric materials. In the past, steel has been described as an alloyof iron and carbon. Today, this description is no longer applicable since in some very important steels, e.g., interstitial-free (IF) steels and type 409 ferritic stainless steels, carbon is considered an impurity and is present in quantities of only a few parts per million. By definition, steel must be at least 50% iron and must contain one or more alloying elements. These elements generallyinclude carbon, manganese, silicon, nickel, chromium, molybdenum, vanadium, titanium, niobium, and aluminum. Each chemical element has a specific role to play in the steelmaking process or in achieving particular properties or characteristics, e.g., strength, hardness, corrosion resistance, magnetic permeability, and machinability.

Reprinted from Handbook of Materials Selection, Wiley, New York,2002, by permission of the publisher.

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Carbon and Alloy Steels

2 STEEL MANUFACTURE
In most of the world, steel is manufactured by integrated steel facilities that produce steel from basic raw materials, i.e., iron ore, coke, and limestone. However, the fastest growing segment of the steel industry is the ‘‘minimill’’ that melts steel scrap as the raw material. Both types offacilities produce a wide variety of steel forms, including sheet, plate, structural, railroad rail, and bar products. Ironmaking. When making steel from iron ore, a blast furnace chemically reduces the ore (iron oxide) with carbon in the form of coke. Coke is a spongelike carbon mass that is produced from coal by heating the coal to expel the organic matter and gasses. Limestone (calcium carbonate) isadded as a flux for easier melting and slag formation. The slag, which floats atop the molten iron, absorbs many of the unwanted impurities. The blast furnace is essentially a tall hollow cylindrical structure with a steel outer shell lined on the inside with special refractory and graphite brick. The crushed or pelletized ore, coke, and limestone are added as layers through an opening at the top ofthe furnace, and chemical reduction takes place with the aid of a blast of preheated air entering near the bottom of the furnace (an area called the bosh). The air is blown into the furnace through a number of water-cooled copper nozzles called tuyeres. The reduced liquid iron fills the bottom of the furnace and is tapped from the furnace at specified intervals of time. The product of the furnace is...