Iron and its alloys

Introduction

Iron is a fundamental chemical element for life on Earth and one of the most abundant and used metals. It is essential for steel production, infrastructure construction and the manufacture of a wide range of industrial and domestic products. There are different types of iron, each with specific properties and applications. This article explores the various types of iron, their characteristics, chemical and physical properties, as well as main applications, with a particular focus on their chemical compositions.

Types of Iron

Pure Iron

Characteristics: Pure iron (Fe) is relatively rare in nature due to its tendency to oxidize easily. However, it is produced in the laboratory and in some specific industrial applications. It has a body-centered cubic (BCC) crystal structure at room temperature and becomes a face-centered cubic (FCC) structure at high temperatures.

Composition: Pure iron contains very few impurities, with a carbon content of less than 0.008%. Major impurities may include traces of oxygen, silicon and sulfur.

Applications: Pure iron is mainly used in scientific and experimental research applications. It serves as a reference point for studying the properties of various alloys and ferrous materials. It is also used in the production of special magnets and electronic components.

Sweet Iron

Characteristics: It is a low-carbon form of iron, containing less than 0.1% carbon. This low amount of carbon gives soft iron greater ductility and lower hardness than other types of iron. It is easily workable and can be molded into various shapes.

Composition: mainly includes iron (Fe) with a carbon percentage of less than 0.1%. Small quantities of manganese (Mn), silicon (Si) and other trace impurities may be present.

Applications: Soft iron is widely used in the production of electrical components such as transformer cores and electric motors, due to its high magnetic permeability. It is also used in the manufacture of cables and wires, as well as in the construction of lightweight structures such as building frames and machinery.

Cast Iron

Characteristics: Cast iron is an iron alloy containing between 2% and 4% carbon, as well as small amounts of silicon, manganese and other impurities. There are several types of cast iron, including gray cast iron, white cast iron and ductile cast iron, each with specific properties.

Gray Cast Iron: is characterized by the presence of graphite in the form of flakes, which gives the material a good vibration dampening capacity and ease of processing. However, it is brittle and has low tensile strength.

White Cast Iron: contains carbon in the form of carbides (cementite, Fe₃C), making the material very hard and resistant to wear. However, it is very fragile and difficult to work with.

Ductile Iron: Ductile iron, or nodular iron, contains graphite in the form of nodules, which significantly improves ductility and tensile strength compared to gray iron. It is obtained by adding magnesium (Mg) or cerium (Ce) to the melt.

Composition:

• Gray Cast Iron: 2-4% C, 1-3% Si, small quantities of Mn, P, S.
• White Cast Iron: 2-4% C, 0.5-1.5% Si, carbides (Fe₃C).
• Ductile cast iron: 3-4% C, 2-3% Si, additions of Mg or Ce.

Applications: Cast iron is widely used in multiple industrial sectors. Gray cast iron is used in the production of machinery components, engine bodies and pipes. White cast iron is used to produce wear-resistant equipment such as mills and crushers. Ductile cast iron finds application in structural components, water and gas piping and automotive parts.

Steel

Characteristics: it is an iron alloy with a variable carbon content (generally between 0.2% and 2.1%), which improves its mechanical properties compared to pure iron. There are numerous types of steel, including carbon steel, stainless steel, and alloy steel.

Carbon Steel: is the most common type of steel and can be divided into three categories: low, medium and high carbon. Low carbon steels are ductile and easy to work with, medium carbon steels offer a good balance between hardness and ductility, while high carbon steels are very hard but less ductile.

Stainless Steel: contains chromium (Cr) at least 10.5%, which forms a protective layer of chromium oxide on the surface, making the material highly resistant to corrosion. Some stainless steels also contain nickel (Ni) and molybdenum (Mo) to further improve corrosion resistance and mechanical properties.

Alloy Steel: contains other alloying elements in addition to carbon, such as manganese (Mn), chromium (Cr), vanadium (V) and tungsten (W), which give specific properties to the material. These steels are used for specialized applications where high mechanical performance is required.

Composition:

• Carbon steel: 0.2-2.1% C, small quantities of Mn, Si, P, S.
• Stainless Steel: >10.5% Cr, may contain Ni, Mo, Mn.
• Alloy Steel: variable, with elements such as Mn, Cr, V, W.

Applications: Steel is one of the most versatile and widely used materials in the world. Carbon steels are used in the construction of buildings, bridges, cars and machinery. Stainless steels are used in corrosive environments, such as chemical plants, food industries and medical applications. Alloy steels are used in precision instruments, cutting equipment and high-strength components.

Forged Iron

Characteristics: It is a type of hand-crafted iron, characterized by a low carbon content (less than 0.08%) and a unique fibrous structure that gives the material a combination of strength, ductility and corrosion resistance. Hot working allows the iron to be shaped into various shapes and sizes.

Composition: Wrought iron primarily comprises iron (Fe) with a carbon content of less than 0.08%, and may include small amounts of silicon (Si) and sulfur (S).

Applications: It is mainly used in decorative and architectural applications, such as gates, railings, furniture and ornamental elements. Its strength and ductility also make it ideal for making tools, horseshoes and other applications requiring a strong, workable material.