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Title: Alloy Steel: Everything you need to know about alloy steels and their role in building and construct

Posted on: 24th July 2019

When other elements comprising metals and non-metals are added to carbon steel, alloy steel is formed. The composition and proportion of alloying elements determine the various properties of alloy steel. 
An overview of ‘steel’

Steel is among the most popular materials used in the construction industry. According to the World Steel Association, in 2018 around 1,808 million tons of crude steel was produced worldwide and about 50% of this production was utilized by the construction industry. Further, they also state that there are as many as 3,500 different grades of steel and each grade offers environmental, chemical and physical properties unique to that grade of steel. Steel has undergone significant evolution through time and around 75% of all the types of modern-day steel were developed in the past 20 years. It is interesting to note that had the Eiffel Tower (constructed in 1887) been constructed in today’s times, it would require only one-third of the steel used back then. 

Types of steel 
Fundamentally, steel is an alloy of iron with low amounts of carbon. There are thousands of different types of steels which are created to suit different kinds of applications. These broadly fall into 4 types – carbon steel, tool steel, stainless steel and alloy steel. Carbon steels form the majority of steels produced in the world today. Tool steels are used to make machine parts, dies and tools. Stainless steels are used to make common household items. Alloy Alloy steels are made of iron, carbon and other elements such as vanadium, silicon, nickel, manganese, copper and chromium. 

Alloy steel 
When other elements comprising metals and non-metals are added to carbon steel, alloy steel is formed. These alloy steels display various environmental, chemical and physical properties that can vary with the elements used to alloy. Here the proportion of alloying elements can provide different mechanical properties. 

Effects of alloying 
Alloying elements can alter carbon steel in several ways. Alloying can affect micro-structures, heat-treatment conditions and mechanical properties. Today’s technology with high-speed computers can foresee the properties and micro-structures of steel when it is cold-formed, heat treated, hot-rolled or alloyed. For instance, if properties such as high strength and weldability are required in steel for certain applications, then carbon steel alone will not serve the purpose because carbon’s inherent brittleness will make the weld brittle. The solution is to reduce carbon and add other elements such as manganese or nickel. This is one way of making high strength steel with required weldability. 

Types of alloy steel 
There are two kinds of alloy steel – low-alloy steel and high-alloy steel. As mentioned earlier, the composition and proportion of alloying elements determine the various properties of alloy steel. Low-alloy steels are the ones which have up to 8% alloying elements whereas high-alloy steels have more than 8% alloying elements.

Alloying elements 
There are around 20 alloying elements that can be added to carbon steel to produce various grades of alloy steel. These provide different types of properties. Some of the elements used and their effects include: 

  • Aluminium – can rid steel of phosphorous, sulfur and oxygen
  • Chromium – can increase toughness, hardness and wear resistance
  • Copper – can increase corrosion resistance and harness
  • Manganese – can increase high-temperature strength, wear resistance, ductility and hardenability
  • Nickel – can increase corrosion, oxidation resistance and strength
  • Silicon
  • can increase magnetism and strength
  • Tungsten – can increase strength and hardness
  • Vanadium – can increase corrosion, shock resistance, strength and toughnes

Other alloying elements that provide varied properties include bismuth, cobalt, molybdenum, titanium, selenium, tellurium, lead, boron, sulfur, nitrogen, zirconium and niobium. These alloying elements can be used singly or in various combinations depending on the properties desired.