Alloy Steels

Topics: Stainless steel, Steel, Steels Pages: 19 (5469 words) Published: March 15, 2013
Any metallic element added during the making of steel for the purpose of increasing corrosion resistance, hardness, or strength. The metals used most commonly as alloying elements in stainless steel include chromium, nickel, and molybdenum.  Characteristic of alloying elements

Very important elements for alloy steels are manganese, nickel, chromium, molybdenum, vanadium, tungsten, silicon, copper, cobalt and boron. All commercial steels contain 0,3-0,8% manganese, to reduce oxides and to counteract the harmful influence of iron sulphide. There is a tendency nowadays to increase the manganese content and reduce the carbon content in order to get a steel with an equal tensile strength but improved ductility. Nickel and manganese are very similar in behaviour and both lower the eutectoid temperature. Nickel steels are noted for their strength, ductility and toughness, while chromium steels are characterized by their hardness and resistance to wear. Chromium can dissolve in either alpha- or gama-iron, but, in the presence of carbon, the carbides formed are cementite (FeCr)3C in which chromium may rise to more than 15%; chromium carbides (CrFe)3C2 (CrFe)7C3 (CrFe)4C, in which chromium may be replaced by a few per cent, by a maximum of 55% and by 25% respectively. The chrome steels are used wherever extreme hardness is required, such as in dies, ball bearings, plates for safes, rolls, files and tools. The combination of nickel and chromium produces steels having all these properties, some intensified, without the disadvantages associated with the simple alloys. Molybdenum dissolves in both alpha- or gama-iron and in the presence of carbon forms complex carbides (FeMo)6C, Fe21Mo2C6, Mo2C. Molybdenum is also a constituent in some high-speed steels, magnet alloys, heat-resisting and corrosion-resisting steels.| |

B. Alloy steel

Alloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low-alloy steels and high-alloy steels. The difference between the two is somewhat arbitrary: Smith and Hashemi define the difference at 4.0%, while Degarmo, et al., define it at 8.0%.[1][2] Most commonly, the phrase "alloy steel" refers to low-alloy steels. -------------------------------------------------

Every steel is truly an alloy, but not all steels are called "alloy steels". Even the simplest steels are iron (Fe) (about 99%) alloyed with carbon (C) (about 0.1% to 1%, depending on type). However, the term "alloy steel" is the standard term referring to steels with other alloying elements in addition to the carbon. Common alloyants include manganese (the most common one), nickel,chromium, molybdenum, vanadium, silicon, and boron. Less common alloyants include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, tin, zinc, lead, and zirconium. -------------------------------------------------

The following is a range of improved properties in alloy steels (as compared to carbon steels): strength, hardness, toughness, wear resistance, corrosion resistance hardenability, and hot hardness. To achieve some of these improved properties the metal may require heat treating. -------------------------------------------------

Some of these find uses in exotic and highly-demanding applications, such as in the turbine blades of jet engines, in spacecraft, and in nuclear reactors. Because of the ferromagnetic properties of iron, some steel alloys find important applications where their responses to magnetism are very important, including in electric motors and in transformers.

Low-alloy Steels
Low-alloy steels are usually used to achieve better...
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