Ferrous metals and alloys are iron-based materials that are used in a wide variety of industrial applications.
Ferrous metals and alloys can be divided into iron, and iron alloys and materials.
Iron is a soft, silvery metal that is the fourth most abundant element in the Earth’s crust. Pure iron is unobtainable by smelting, but small amounts of impurities can make iron many times stronger than it exists in its pure form. Iron oxide compounds, when mixed with aluminum powder, are used to create thermite reactions for welding and purification processes.
Iron Alloys and Materials
There are a number of different types of alloys containing iron. Some of the most important include carbon steels, alloy steels, stainless steels, tool steels, cast iron, and maraging steel.
Carbon steels are steels in which the main alloying additive is carbon. Mild steel is the most common due to its low cost. It is neither brittle nor ductile, has relatively low tensile strength, and is malleable. Surface hardness can be increased through carburizing. High carbon steels have a higher carbon content which provides a much higher strength at the cost of ductility.
Alloy steels are steels (iron and carbon) alloyed with other metals to improve properties. The most common metals in low alloyed steels are molybdenum, chromium, and nickel to improve weldability, formability, wear resistance, and corrosion resistance.
Stainless steels are steels that contain a minimum of 10% chromium. There are many grades of stainless steel, but the most common grade used for typical corrosion resistant applications is type 304, also known as 18-8. The term 18-8 refers to the amount of chromium (18%) and nickel (8%) combined with iron and other elements in smaller quantities. The metal’s finish is depicted by a number, 3 to 8, with 3 being the roughest and 8 being a mirror-like finish. Other specifications to consider include textures and coatings.
Tool steels are particular steels designed for being made into tools. They are known for toughness, resistance to abrasion, ability to hold a cutting edge, and/or their resistance to deformation at high temperatures. The three types of tool steel available are cold work steels used in lower operating temperature environments, hot work steels used at elevated temperatures, and high speed steels able to withstand even higher temperatures giving them the ability to cut at higher speeds.
Cast iron is an iron alloy derived from pig iron, alloyed with carbon and silicon. Carbon is added to the base melt in amounts that exceed the solubility limits in iron and precipitates out as graphite particles. Silicon is added to the melt to nucleate the graphite which optimizes the properties of cast iron. Often dismissed as a cheap, dirty, brittle metal; cast iron is getting much more attention and use today because of its machinability, light weight, strength, wear resistance, and damping properties.
Maraging steels are carbon free iron-nickel alloys with additions of cobalt, molybdenum, titanium, and aluminum. The term maraging is derived from the strengthening mechanism, which is transforming the alloy to martensite with subsequent age hardening. With yield strengths between 1400 and 2400 MPa, maraging steels belong to the category of ultra-high-strength materials. The high strength is combined with excellent toughness properties and weldability.
Specifications and Properties
Selecting metal alloys requires an analysis of the desired dimensions and specifications. Dimensions to consider include outer diameter (OD), inner diameter (ID), overall length, and overall thickness. Other specifications of importance (based on application) include product shape, tensile strength, yield strength, melting point, conductivity, corrosion resistance, ductility, and malleability. These properties differ based on the forming method and alloy composition.
Applications and Uses
Ferrous metals and alloys are used in countless applications as construction materials, medical devices, tools, magnetic cores, wires, and in the aerospace, military, and medical fields.
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