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Steel and its alloys

25/06/2024

Introduction

Steel is an alloy of iron and carbon that represents one of the most versatile and used materials in modern industry. Due to its exceptional mechanical properties, corrosion resistance and ability to be machined into a wide range of shapes and sizes, steel is essential for numerous industrial and everyday applications. This article explores the various types of steel, their characteristics, chemical compositions, physical properties and main applications, with reference to AISI (American Iron and Steel Institute) specifications.

Types of Steel

Carbon Steel

Characteristics: Carbon steel is the most common type of steel, consisting mainly of iron and carbon. It can be divided into three categories based on carbon content: low, medium and high carbon. The amount of carbon present directly affects the mechanical properties of the steel.

Chemical composition

  • Low Carbon Steel: 0.05-0.25% C
  • Medium Carbon Steel: 0.25-0.6% C
  • High Carbon Steel: 0.6-1.5% C

AISI specifications

  • Low Carbon Steel: AISI 1010, AISI 1020
  • Medium Carbon Steel: AISI 1040, AISI 1050
  • High Carbon Steel: AISI 1095

Applications: Low carbon steels are used in the manufacture of tubes, sheets and lightweight structures due to their ductility and ease of machining. Medium carbon steels are used in the production of mechanical components such as shafts and gears, where a balance between hardness and ductility is required. High carbon steels, due to their high hardness, are used for cutting tools, springs and high-strength wires.

Stainless steel

Characteristics: Stainless steel is an iron alloy with at least 10.5% chromium, which forms a passivating layer of chromium oxide on the surface, protecting the material from corrosion. It may also contain other elements such as nickel and molybdenum to further improve properties.

Chemical composition

  • Chromium (Cr): >10.5%
  • Nickel (Ni): 0-20%
  • Molybdenum (Mo): 0-4%
  • Manganese (Mn): 0-2%

AISI specifications

  • 200 series: AISI 201, AISI 202 (contain manganese)
  • Series 300: AISI 304, AISI 316 (containing nickel)
  • Series 400: AISI 410, AISI 430 (containing chromium)

Applications: Stainless steel is used in corrosive environments, such as in the chemical, food and pharmaceutical industries. It is used in the production of kitchen utensils, surgical instruments, water treatment equipment and architectural components.

AISI 410
AISI 410

Alloy Steel

Characteristics: Alloy steel contains other alloying elements in addition to carbon, such as manganese, chromium, vanadium, tungsten and molybdenum. These elements improve specific mechanical and physical properties of steel, making it suitable for specialized applications.

Chemical composition

  • Manganese (Mn): 0.5-2%
  • Chromium (Cr): 0.5-18%
  • Vanadium (V): 0.1-2%
  • Tungsten (W): 0.1-18%
  • Molybdenum (Mo): 0.1-10%

AISI specifications

  • AISI 4130: Cr-Mo, low alloy steel
  • AISI 4340: Ni-Cr-Mo, alloy steel
  • AISI 6150: Cr-V, alloy steel

Applications: Alloy steels are used in applications requiring high mechanical performance, such as cutting equipment, tools, gears, crankshafts, bearings and heavy machinery parts. Thanks to their improved properties, they are ideal for extreme environments and severe operating conditions.

Construction Steel

Characteristics: Structural steel is designed to be used in building structures. It is characterized by a good balance between strength, ductility and workability, making it ideal for use in load-bearing structures.

Chemical composition

  • Carbon (C): 0.2-0.25%
  • Manganese (Mn): 0.5-1.6%
  • Silicon (Si): 0.2-0.6%
  • Small quantities of sulfur (S) and phosphorus (P): <0.05%

AISI specifications

  • AISI 1018: low carbon construction steel
  • AISI 1026: medium carbon content construction steel

Applications: Structural steel is widely used to make building frames, bridges, skyscrapers and other infrastructure. Its strength and ductility ensure that structures can withstand heavy loads and adverse environmental conditions.

AISI 1018
AISI 1018

Tool Steel

Characteristics: Tool steel is designed to resist wear, deformation and fracture during use. It is characterized by high hardness, wear resistance and the ability to maintain a sharp cutting edge.

Chemical composition

  • Carbon (C): 0.5-1.5%
  • Tungsten (W): 0.5-18%
  • Molybdenum (Mo): 0.5-10%
  • Vanadium (V): 0.1-2%
  • Chromium (Cr): 0.5-12%

AISI specifications

  • AISI O1: oil-hardened tool steel
  • AISI D2: high wear resistance tool steel
  • AISI M2: high-speed tool steel

Applications: Tool steels are used in the production of cutting tools, dies, punches, blades and metalworking equipment. Their mechanical properties make them ideal for applications requiring precision and wear resistance.

Spring steel

Characteristics:

Spring steel is designed to offer high elasticity and fatigue resistance. It is used to manufacture springs that must withstand repeated stress without permanently deforming.

Chemical composition

  • Carbon (C): 0.6-1.0%
  • Silicon (Si): 1.5-2.0%
  • Manganese (Mn): 0.5-1.0%

AISI specifications

  • AISI 1074: carbon steel for springs
  • AISI 1095: high carbon steel for springs

Applications: They are used in the production of springs for cars, trains, industrial equipment and electronic devices. Their ability to return to their original shape after being compressed or extended makes them ideal for these applications.

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