What is Alloy Steel?: Composition, Types, Properties, Applications

By BYJU'S Exam Prep

Updated on: September 25th, 2023

Before getting into the specifics of Alloy Steel, let’s first define steel. Steel is an iron and carbon alloy with a maximum carbon content of 2% (with higher carbon content, the material is defined as cast iron). Most of the world’s businesses and infrastructure are built with this substance, which is used to make anything from oil tankers to sewing needles.

To enhance its mechanical qualities, steel is alloyed with several elements in total amounts ranging from 1.0% to 50% by weight. Low and high alloy steels are the two categories into which alloy steels are divided. It is disputed what separates the two. Low-alloy steels are typically used when the term “alloy steel” is used.

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What is Alloy Steel?

Alloy steel has been alloyed with other elements, ranging from 1 to 50 weight percent, in addition to carbon, to improve the material’s various qualities. Various types of alloy steel are being produced today, such as High-strength low alloy (HSLA) steel, Stainless steel, Microalloyed steel, etc.

Steel Alloy Composition

These substances frequently contain boron, silicon, manganese, nickel, chromium, molybdenum, vanadium, and nickel. Less common elements include aluminum, cobalt, copper, cerium, niobium, titanium, tungsten, lead, zinc, and zirconium.

For example, stainless steel is an alloy of:

  • iron,
  • chromium and
  • nickel( in some cases) and other metals.

Types of Alloy Steel

Steel is mostly made of iron, comparable in hardness to pure copper. Like all other metals, iron is polycrystalline, which means that its crystals are joined at their boundaries, except a few extreme cases. Alloy steel is divided into several subcategories. These consist of:

  • Low-alloy steel
  • High-strength low alloy (HSLA) steel
  • High-alloy steel
  • Stainless steel
  • Microalloyed steel
  • Advanced high-strength steel (AHSS)
  • Maraging steel
  • Tool steel

Steel Alloy Properties

Alloy steels can contain various elements, each of which can improve the material’s resistance to corrosion, heat, and mechanical stress. While higher additions of up to 20 wt.% boost corrosion resistance and stability at high or low temperatures, smaller additions of less than 5 wt.% tend to improve mechanical qualities, such as hardenability and strength.

Production & Processing of Alloy Steel

The desired outcome determines the procedures for alloying and processing alloy steel. The necessary mixture of components is first fused for eight to twelve hours at temperatures above 1600°C. After that, the steel is annealed at more than 500 °C to remove impurities and modify its chemical and physical properties.

Before repeating the annealing and descaling procedure, the mill scale (a combination of iron oxides), a byproduct of the annealing process, is first cleaned from the surface of the steel with hydrofluoric acid. The steel is finally melted and cast before being rolled and shaped into its final form.

Applications & Examples of Alloy Steel

Since alloy steel refers to various steel types, its application varies. Due to their extreme strength, machinability, affordability, and availability, low alloy steels are used in various industries. They can be found in ships, pipelines, pressure vessels, oil drilling platforms, military vehicles, construction equipment, and structural elements. HY80 and HY100 are two examples.

High-alloy steels can be expensive to produce and challenging to work with. However, they are perfect for structural components, automotive applications, chemical processing, and power generation equipment due to their high hardness, toughness, and corrosion resistance. The grades HE, HF, HH, HI, HK, and HL are a few examples of high-alloy steels.

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