Types of Steels

Fe-Fe3C Phase Diagram — The figure shows the iron–iron carbide (Fe–Fe3C) phase diagram. The percentage of carbon present and the temperature define the phase of the iron-carbon alloy and its physical characteristics and mechanical properties. The percentage of carbon determines the type of ferrous alloy: iron, steel, or cast iron. Source: wikipedia.org Läpple, Volker – Wärmebehandlung des Stahls Grundlagen. License: CC BY-SA 4.0

Steels are iron-carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for greater strength. Due to its very-high strength but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloys in modern use. Thousands of alloys have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. According to our AISI classification, carbon steel is divided into four classes based on carbon content.

Typical applications for low-carbon steel include automobile body components, structural shapes (e.g., I-beams, channel and angle iron), and sheets used in pipelines and buildings.

Steel. Steels are iron-carbon alloys that may contain appreciable concentrations of other alloying elements. Adding a small amount of non-metallic carbon to iron trades its great ductility for greater strength. Due to its very-high strength but still substantial toughness, and its ability to be greatly altered by heat treatment, steel is one of the most useful and common ferrous alloys in modern use. Thousands of alloys have different compositions and/or heat treatments. The mechanical properties are sensitive to the content of carbon, which is normally less than 1.0 wt%. According to our AISI classification, carbon steel is broken down into four classes based on carbon content:
- Low-carbon Steels. Low-carbon steel, also known as mild steel, is now the most common steel because its price is relatively low. At the same time, it provides material properties that are acceptable for many applications. Low-carbon steel contains approximately 0.05–0.25% carbon making it malleable and ductile. Mild steel has a relatively low tensile strength, but it is cheap and easy to form; surface hardness can be increased through carburizing.
- Medium-carbon steel is mostly used to produce machine components, shafts, axles, gears, crankshafts, coupling, and forgings. It could also be used in rails, railway wheels, other machine parts, and high-strength structural components calling for a combination of high strength, wear resistance, and toughness.
  
  Medium-carbon Steels. Medium-carbon steel has approximately 0.3–0.6% carbon content, balances ductility and strength, and has good wear resistance. This grade of steel is mostly used in the production of machine components, shafts, axles, gears, crankshafts, coupling, and forgings and could also be used in rails and railway wheels.
- High-carbon Steels. High-carbon steel has approximately 0.60 to 1.00% carbon content, and hardness is higher than in the other grades, but ductility decreases. High carbon steels could be used for springs, rope wires, hammers, screwdrivers, and wrenches.
- Ultra-high-carbon Steels. Ultra-high-carbon steel has approximately 1.25–2.0% carbon content. Steels that can be tempered to great hardness. This grade of steel could be used for hard steel products, such as truck springs, metal cutting tools, and other special purposes like (non-industrial-purpose) knives, axles, or punches. Most steels with more than 2.5% carbon content are made using powder metallurgy.
Alloy Steels. Steel is an alloy of iron and carbon. Still, the term alloy steel usually only refers to steels that contain other elements— like vanadium, molybdenum, or cobalt—in amounts sufficient to alter the properties of the base steel. In general, alloy steel is alloyed with various 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.
- High-alloy Steels.
Steam Turbine Blade. Superalloys (typically face-centered cubic austenitic alloys) based on Co, Ni, and Fe can be engineered to be highly resistant to creep and have thus arisen as an ideal material in high-temperature environments. Source wikipedia.org License: CC BY-SA 3.0

Stainless Steel. Stainless steels are low-carbon steels with at least 10% chromium with or without other alloying elements. Strength and corrosion resistance often make it the material of choice in transportation and processing equipment, engine parts, and firearms. Chromium increases hardness, strength, and corrosion resistance. Nickel gives similar benefits but adds hardness without sacrificing ductility and toughness. It also reduces thermal expansion for better dimensional stability.
Superalloys.

Special Ferrous Metals

Tool Steels
High-speed Steels
Shock-resisting Steels
Silver Steel

References:

Materials Science:

U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 1 and 2. January 1993.
U.S. Department of Energy, Material Science. DOE Fundamentals Handbook, Volume 2 and 2. January 1993.
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Gaskell, David R. (1995). Introduction to the Thermodynamics of Materials (4th ed.). Taylor and Francis Publishing. ISBN 978-1-56032-992-3.
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Ashby, Michael; Hugh Shercliff; David Cebon (2007). Materials: engineering, science, processing, and design (1st ed.). Butterworth-Heinemann. ISBN 978-0-7506-8391-3.
J. R. Lamarsh, A. J. Baratta, Introduction to Nuclear Engineering, 3d ed., Prentice-Hall, 2001, ISBN: 0-201-82498-1.

See above:
Steels