Introduction

When it comes to industrial fabrications, there are a variety of metals that can be used. Each metal has its own unique properties that should be considered when deciding which one to use for a particular job.

There are thousands of types and grades of metals, so it’s impossible to discuss them all in one article. So, in this series of articles, we will focus on the most common sheet metals we use, i.e. mild steel, stainless steel, and aluminium.

First up – mild steel.

What are carbon steels?

When people talk about steel, they’re really referring to a group of materials. So in that respect, “steel” is an umbrella term covering a wide range of metals.

Carbon steel is an alloy of iron and carbon. Carbon steels are usually categorised by their carbon content, so you have:

  • Low-carbon steel (mild steel) contains less than 0.3% carbon. It’s the cheapest to produce and easiest to fabricate due to its low carbon content. They are used extensively for general sheet metal fabrications due to their versatility and ease of forming.
  • Medium-carbon steels range in carbon content up to 0.6%. The additional carbon makes them a harder and more wear-resistant metal. However, they still retain some malleability. Typical applications are for gears, shafts, and civil engineering projects requiring a higher tensile strength than mild steel.
  • High-carbon steels have a carbon content between 0.6% and 1.5%. The addition of carbon at that level makes an extremely hard metal that is difficult to form or fabricate. Therefore, these steels are mainly used in industrial tooling and are often known as “tool steel”.

Mild Steels

Mild steels are low-carbon steels made from iron and carbon. They’re the most common type of steels we use and are perfect for general fabrication work. Mild steels are robust, durable and can be easily machined and welded. They are also relatively cheap, making them a popular choice for many applications.

Main types of mild steels

The two most common mild steel sheets we use are Hot Rolled (HR) or Cold Rolled (CR). While they are the same primary material, they are made in two different ways:

  • Hot Rolled steels are produced at temperatures of around 900 degrees Celsius, which is above the recrystallisation point of mild steel. Rolling at this point means the steel is more malleable and can be formed into large sizes.
  • Cold Rolled steels are formed after hot rolling when the steel has cooled to room temperature. So in that respect, CR is HR that’s had further processing.

HR steels are cheaper than CR as they have a wider dimensional tolerance and a lower quality surface finish. On the other hand, CR is more expensive but has a more uniform surface finish and higher dimensional accuracy.

Advantages of Mild Steel

  • Cost – both HR and CR mild steels are relatively cheap materials, making them cost-effective for many applications.
  • Range – there is an enormous variety of mild steel products from sheet and plate to bar and sections of all shapes and sizes.
  • Recyclable – mild steel is extensively recycled and can be efficiently melted down and reused.
  • Weldable – mild steel is easy to weld with all methods of welding processes.
  • Ductile – mild steel can be easily stretched and formed, making it perfect for deep-drawing processes.

Disadvantages of Mild Steel

  • The main disadvantage of mild steel is its meagre corrosion resistance. As a result, it needs a further finishing process to extend its lifespan to provide long-term protection.
  • As it has a low carbon content, it doesn’t have high tensile strength, so it is unsuitable for load-bearing applications such as buildings or other civil engineering projects.

How to finish mild steel fabrications

As mild steel has low corrosion resistance, it must have a final finishing operation to provide long-term protection and longevity to the finished product. The most common finishing operations are:

  • Powder Coating – a dry powder is applied to the surface of the steel and then baked on. This forms a hard, durable finish that is resistant to mechanical and chemical attacks.
  • Wet Painting – a layer of paint is applied to the surface of the steel to protect it from the elements.
  • Hot Dip Galvanising – the steel is dipped in molten zinc and then allowed to cool. This forms a protective barrier that prevents corrosion and rust.
  • Electroplating – a thin layer of metal (usually copper, nickel or chromium) is applied to the surface of the steel. This protects it from corrosion and rust.

Many other finishes can be used, but these are the most common. For more information on surface coatings, please refer to this previous article.

Summary

Mild steel is a low-carbon steel that is easy to weld and form. It is often used for general fabrication work due to its low cost and recyclability. While it has low corrosion resistance, it can be finished with various coatings to protect it from the elements.

Pegasus Precision specialise in producing high-quality, precision sheet metal fabrications for the instrumentation industry