Materials
There are many ferrous and non-ferrous metals and alloys of great importance to manufacturing industry and used in fabrication today. Some of the most commonly used are listed above. Pure aluminium is a relatively soft, ductile material and for most engineering applications it is alloyed with a range of materials to improve its properties. Each alloy is given a four number designation dependent on the main alloying element, for example 4xxx series alloys have silicon as the main alloying element, 6xxx series are alloyed with magnesium and silicon. Some alloying elements, such as copper, can make an alloy difficult if not impossible to weld. Carbon steels cover a wide range of commonly used engineering materials including the so-called, mild steels. The term carbon steels is also taken to include carbon-manganese steels, structural steels, HSLA steels and Q&T Steels which includes HY and QT types. Galvanised and coated steels are a very specific group of normally low carbon steels, which have undergone a surface treatment either to improve some property, such as corrosion resistance or to improve its appearance. In a welding and cutting context these coating materials can often create problems with both weld and cut quality and health hazards in terms of fumes created as they are vapourised. Alloy Steels are carbon and carbon manganese steels which have other alloying elements such as nickel, chromium and molybdenum added to them to improve their mechanical properties. Low temperature alloy steels have small amounts of nickel added. Creep resisting steel are alloyed with chromium and molybdenum, these steels are often used in high temperature environments such as steam boilers. High manganese steels can contain 14% Mn giving these materials high hardness making them suitable for application such as railway lines. Stainless steels are defined as steels containing more than 13% Cr. There are four basic categories of stainless steel of which the most common are the austenitic steels such as 316, and 304 alloys which contain both chrome and nickel. Ferritic stainless steels are chrome containing alloys with low levels of carbon, such as 409 and 430 grades. Martensitic are also chrome containing but have much high levels of carbon, 410 and 416 are examples of these materials. Duplex stainless steels have a mixed microstructure of ferrite and austenite and properties to match. The main types of cast iron are Grey cast iron this contains 2 to 4%C and over 2%Si. White cast iron has the same range of carbon as grey but has less than 1%Si. Malleable cast irons are basically heat-treated white cast iron. Alloy cast irons may be alloyed with chromium, nickel, molybdenum, and other elements to give specific strength, corrosion, or high temperature properties. Copper can be used as an engineering material in its pure form but is normally alloyed with other materials to improve its mechanical properties. The most common alloys of copper are brasses in which zinc is the main alloying element and bronzes, which contain tin. Another widely used alloy group are the Cupro-nickel's, which are nickel containing alloys used mainly for their excellent salt water corrosion properties. Nickel alloys are used in a wide variety of applications including marine environments, aerospace and high temperature areas. Inconel's and Nimonic's are nickel chrome alloys, while Incoloy's are nickel iron alloys. Hastalloy's are nickel, chrome and iron alloys, while Monel's are nickel rich copper containing alloys. Titanium is an attractive engineering material because of its low density, excellent corrosion resistance and the high strengths that can be obtained through alloying. Its reactive nature, however, can give problems when it is welded and keeping oxygen levels very low is of fundamental importance.
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