Different Types of Mild Steel and Their Common Uses

The term mild steel is applied to low carbon forms of ‘basic’ steel. All steel consists of iron with no more than 2 per cent carbon content, and mild steels have no more than 0.25% carbon in their composition. Crucially, mild steels have no other elements or chemicals forming a more complex alloy.

Mild steel is one of the basic industrial materials of the modern world, made in huge quantities and used for countless purposes by everyone and everything, from the largest car manufacturers and grand civil engineering to hobbyist engineers and fabricators in a back garden workshop.

There are actually many different types of mild steel, and what a ‘type’ is can be defined in many different ways. Let Rapid Metals, one of the UK’s leading metal stockists and suppliers, explain what types of mild steel there are and what they are used for.

Grades of Mild Steel

When considering the different types of mild steel, one of the clearest ways of defining those types is by looking at the different grades. There are many international standards and grading systems for steel, but the most widely used is the European one, which assigns each grade a number (increasing with carbon content) after the initials ‘En’. When looking at different types of mild steel grades, we’ll only be looking at low numbers below 10.

Starting at the bottom, En1a is a type of mild steel specifically formulated to be ‘free machining’ – with a very low carbon content and added sulphur or lead gives it excellent, smooth and precise machining properties. It is well suited to use in lathes and CNC machines. It is ideal for the rapid production of turned parts such as nuts and bolts, hydraulic fittings, pins and low-stress shafts. The very composition that gives En1a its good machineability also gives it very poor welding characteristics, and it is not suitable for situations of high mechanical or thermal stress.

En3b is the grade for what is probably one of the most versatile and commonly used types of mild steel. It is suitable for a huge range of applications, so long as the ultimate stresses are not high. These uses can include structural beams, vehicle chassis, threaded bars, machinery components and casings, fasteners like nuts and bolts. En3b has good machineability and weldability, making it a very common choice for all kinds of general fabrication and engineering.

For a type of mild steel offering greater strength and hardness, there is En8. It has a higher carbon content than En3 (typically 0.4%, or more than double that of En3), which gives it higher tensile strength and improved hardness. In use cases like axles, cranks, bolts and studs, locking keys, rollers and other parts for machinery and equipment, En8 can offer the performance needed without going to the expense of engineering steel alloys.

Finishes of Mild Steel

Mild steel can also be classified by the finish of the metal, and that finish can either be deliberately applied or as a result of the process by which the product was made.

When considering the uses and types of mild steel, the finish also affects the properties of the steel, and so also the applications for which it’s best suited.

Cold reduced mild steel is rolled and flattened to sheets when cold (i.e. at room temperature) – it’s more normal for the metal to be worked hot. This produces strong metal with a smooth finish that makes a suitable base for all kinds of finishes and surface applications. But it’s far less ductile than other types of mild steel – so it’s good for construction and structural purposes.

The more commonly used type of mild steel is hot rolled. Working and forming the steel when hot means it is more ductile and malleable, producing a strong and versatile product with good welding, cutting and drilling characteristics. It has a rougher finish than other finishes, often with a black or blue/grey colour from the heating. It can require further finishing or coating to have an attractive appearance. The metal shrinks and deforms slightly as it cools after finishing, so it shouldn’t be used where absolute dimensional accuracy and consistency are required. But it’s a good choice for fabrication, construction and engineering, where the unfinished metal won’t be visible.

A disadvantage of all forms of mild steel is that they are prone to rusting if not properly protected. One of the most effective forms of protection is to have mild steel hot-dip galvanised. The metal is placed in a bath of molten zinc. This reacts with the oxygen in the atmosphere, forming a strong surface layer of zinc oxide all around the mild steel, preventing corrosion of the metal. The galvanised surface is deep and tough enough to withstand weathering and mild abrasion or scratching. This all makes galvanised mild steel ideal for outdoor or all-weather structures such as building frames, vehicle and trailer parts and fence posts and wires. Mild steel can also be protected with zinc by electroplating – this produces a thinner, smoother and more accurate coating, so it is used for protecting the threads and heads of bolts, nuts, screws and other fasteners.

For a type of mild steel with a distinctive functional finish, there’s also tread plate. This is a form of cold rolled mild steel, where one of the rollers has the distinctive cross-hatch diamond pattern embossed into it. This works one side of the metal, leaving the high-grip texture suitable for stairs and walkways, trailer and vehicle floor plates and industrial aesthetic touches.

Mild steel in round bar forms can be bright drawn, which is a form of cold finishing. As well as being drawn (pulled and extruded through a narrow die), the round bar is turned, ground and polished to produce a bright, smooth, shiny and extremely accurate surface finish. This makes them ideal as the basis for parts like shafts, axles, bearings, pins, pumping elements, locks and more.

Forms of Mild Steel

Different types of mild steel can also be classified by their form, with different forms being suitable for different uses, such as:

• Angle:Formed with a right-angle bend in long strips, used for structural reinforcement such as building and roof frames, heavy-duty industrial racking and shelving and outdoor structures.
• Box:A versatile section combining strength and minimal weight, steel box sections are used for structural frameworks in buildings and vehicles, as well as pieces like furniture, gates and fences.
• Channel:Effectively ‘half’ a box, a mild steel channel serves many structural purposes, such as door and window lintels and floor joists. This form can also be used for structural frames for vehicles and machinery, railings and signposts.
• Cut Block:Supplied as a regular solid block, mild steel can be cut, milled, machined and otherwise finished into almost any number of objects.
• Flat:Mild steel flat bar is often used for structural supports and bracing. It can be made into various types of mechanical components and fittings, general fabrication and also for decorative metalwork.
• Hexagon:Hexagonal-section is a type of mild steel with some specific uses – especially as the centre spindle for the rollers on conveyor systems and similar machinery. They can also be used to make bolt and screw heads, or for decorative pieces due to their distinctive shape.
• Oval Tube:Oval tube is one of the other types of mild steel with a few specific uses – it’s ideal for wall rails, balustrades, clothes rails, shelving and similar applications.
• Round:Mild steel in round bars has almost countless applications. With relatively little further machining, it can be used for rollers, dowels and many other machinery parts. It can form driveshafts, axles and spindles, or it can be turned down and cut to make pins, screws, bolts and other fasteners. It can be used ‘as is’ for structural purposes.
• Round Tube:Round tube mild steel combines strength, accuracy and low weight. It can be used for making hydraulic and plumbing fittings, pipework, tools and dies, structural supports, frameworks, fencing, railings and more.
• Sheet:Sheet is the basic form of how much of the world’s mild steel is made and used. It can be put to many uses, from car body panels and shipping containers to forming tools and utensils and making cabinets.
• Square:Square bar mild steel has generally the same applications as round bar, although it is not as suitable for making fixings and bearings. It serves more structural purposes such as frameworks, general fabrication, furniture and ornamental metalwork.
• Threaded Rod:While round bar can have threads cut in them, mild steel can also be supplied with threads cut and zinc coating applied, making it ready for cutting into screws and bolts of any length.

Every Vital Type of Mild Steel at Rapid Metals

We hope this blog has revealed and explained the many types and uses of mild steel – one of the fundamental materials of the modern world. All these different types of mild steel, whether by grade, finish or form, are available in Rapid Metals’ online store, to be ordered cut to size and in a wide selection of diameters, finishes and dimensions.