Ferrous metals share some basic properties, including being prone to rust and being magnetic. The list of common ferrous metal properties include:
- Good tensile strength
- Good electrical conductivity
- Low corrosion resistance
- Silver in colour
- Usually magnetic
Ferrous metals can include a wide range of different alloying elements, including chromium, nickel, manganese, molybdenum, and vanadium, manganese. These alloying elements give ferrous materials different properties that allow them to be used in a variety of engineering and other applications including tools, pipelines, containers, cutlery and larger fabrications like skyscrapers.
Due to the different properties of ferrous materials, they have a variety of applications that differ depending on the metal being used:
Also known as carbon steels, non-alloy steels use carbon as the alloying element. These steels do include other elements, such as manganese, silicon, sulphur, and phosphorus, but the content of these elements is so low that they do not impact the material properties. Non-alloy steels are classified as having either a low, medium or high carbon content, and each has different characteristics and treatment methods:
1. Low Carbon Steel
Low carbon steels, also called mild steels, contain just 0.05-0.25% carbon. Low cost and malleable, these steels are widely used for items such as nuts and bolts or forgings. The surface hardness of these steels can be increased by carburising.
2. Medium Carbon Steel
Medium carbon steels contain 0.25-0.6% of carbon. This higher carbon content provides an increase in strength and hardness over low carbon steels. However, these steels have reduced ductility compared to low carbon steels. Increased levels of carbon and manganese in medium carbon steels mean that they can be tempered and quenched. These steels are widely used for making components for the automotive industry, such as gears, axles and shafts, but are also suitable for use on railway applications.
3. High Carbon Steel
High carbon steels contain 0.6-1% carbon and are the strongest of the non-alloyed steels. This strength makes them ideal for applications requiring resistance to mechanical wear, while they are also good at maintaining their shape. On the negative side, these steels are inferior to lower carbon steels when it comes to weldability, ductility and impact toughness. High carbon steel is used for springs, blades, rail steels, wire rope, wear resistant plates, tools and more.
Alloy Steels and the Alloying Elements
Alloy steels make up another subgroup of ferrous metals, with each alloying element having its own effect on the material properties. These alloying elements include chrome, copper, nickel, and silicon, but can be combined to provide a range of properties. Here are the properties of the most common of these alloying elements:
Chromium is used to make stainless steel, with chromium levels of over 11% making metals corrosion-resistant. An oxidised chromium layer on top of the metal will prevent the underlying metal from coming into contact with oxygen, thereby greatly reducing the chance of corrosion. Chromium also increases the hardness, tensile strength, toughness and wear resistance of a metal.
Manganese can be used as an alloying element to prevent iron sulphides from forming, as well as increasing strength at high temperatures, improving ductility and wear resistance. Manganese can also improve hardenability through quenching, reducing the danger of defect formation and making the metal more stable.
Nickel, when used with other elements, can increase ductility and corrosion resistance. For example, a mix of 18% chromium and 8% nickel creates extremely durable stainless steels.
Silicon can be used to increase the magnetic properties of a metal as well as improving strength and providing elasticity for applications like springs.
Vanadium carbides also limit the grain size of a metal, increasing the ductility of the alloyed material. Vanadium also improves the strength, hardness, wear and shock impact resistance. However, if used in quantities that are too high it can have a negative impact on material properties.
Molybdenum offers a good effect on steel alloys operating at high temperatures. It not only improves mechanical properties, but also provides higher resistance to rust and corrosion, and amplifies the effects of other alloying elements.
7. Cast Iron
Cast iron is produced when a carbon content of 1.5-4% is alloyed with iron. Other elements including silicon, manganese, sulphur and phosphorus will be present, but only in small quantities. Cast iron is brittle, but has a good wear resistance due to its hardness. It is also easy to cast, relatively cheap, has high compressive strength, and a low melting point.
Ferrous metals such as cast and wrought iron or carbon steel are known for their tensile strength and durability. As a result, materials such as carbon steel are widely used in the construction industry to build the structures of bridges and skyscrapers.
Ferrous metals are also found in shipping containers, pipework, automobiles, railways and a range of both commercial and domestic tools.
The high carbon content of ferrous metals means that they are vulnerable to rust when exposed to moisture, and therefore generally unsuitable for applications such as water pipes. Wrought iron is an exception to this as its purity means it resists rust, while alloying elements can also be used, such as chromium in stainless steel, to prevent rusting.
Since most ferrous metals are magnetic, they are often used in electrical and motor applications, as well as in other less obvious places, such as in your refrigerator door, so you can use a magnet to attach your shopping list to it!
Ferrous metals have been in use for thousands of years and have a huge range of different applications, from the largest structures to the smallest nuts and bolts.
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