It wouldn’t be inaccurate to define the last two centuries as a Steel Age similar to antiquity’s Bronze or Iron Age. Since Bessemer simplified steelmaking in 1856, the modern world has been built upon reliable, strong, and inexpensive steel. Although the benefits of steel compared to metals like copper or iron have been known for around 4,000 years, it wasn’t until its price came down that it found its full potential.
Today steel is probably the most common and inexpensive industrial metal there is, and, as a result, it is used in pretty much everything. If you are reading this in an office chair there is steel in the wheels, base, and frame. Walk into any large building and the walls and roof are both held up by steel. The benefits of steel make it ubiquitous, and, while its low cost may be chief among those benefits, there are others of equal significance that have made steel the standout material of the modern era.
Types of Steel
The most important thing to realize about steel is that there is more than one type. Steel refers to a broad class of alloys of iron and carbon. Depending on the exact blending of these elements, the final steel can take on a range of properties that are suitable for a dizzying array of uses. As the carbon content of the steel rises the material gets harder and can be hardened further with heat treatment, but this comes at the cost of some of its ductility or flexibility.
Essentially, as the carbon content rises, the steel can cut through more things more often but becomes more brittle and prone to chipping or cracking. These carbon steels make up over 90% of the steel produced, and their general categories are as follows:
- Low-Carbon Steels: Steel with 0.05% – 0.15% carbon are considered low-carbon steels. They maintain a high degree of ductility but are relatively soft and can be subject to corrosion and surface wear more than higher carbon steels. The most common use for these steels is in sheet metals for things like auto body panels and containers.
- Medium-Carbon Steels or Mild Steels: Steels with 0.3% – 0.5% carbon content. These are perhaps the most versatile range of steels that offer an excellent balance between hardness and ductility. These are the steels that are used for structural members like i-beams and girders as well as for forgings like automotive driveshafts and other industrial machinery components.
- High-Carbon Steels: A carbon content of 0.6% – 1% makes up high-carbon steel. These steels are most commonly found in the tooling used to work other metals and steels: the blade in a shear brake used to cut sheet metal or the tooling used to machine steel components.
- Ultra-High Carbon Steels: A relatively new class of steels in the industry are those with 1.25% – 2% carbon content. These are steels that can be heated to exceptional hardness and used for very specialized tooling. While not technically new, some swords and knives in history provide examples of ultra-high carbon steel. The difficulty in making these alloys means that they weren’t seriously explored for use in modern industry until the 1970s, and they didn’t find more widespread use until the advent of powder metallurgy made production more feasible.
It is these carbon steels that most people mean when they talk about steels. In particular, medium-carbon or mild steels are popular because those are the most versatile, produced, and familiar to both metal workers and everyday people. Mild steels are what most steel extrusions like angle iron are made of.
And yet, an entire class of alloy steels can be added to these steels. Alloy steels are those which receive a significant amount of an additional alloying element. Stainless steels, which have a 10% – 20% chromium content are examples of alloy steels. This class of steels also includes a wide variety of tool steels which are alloyed with tungsten, molybdenum, cobalt, vanadium, and other metals. The use case for these alloys is so wildly different from carbon steels with such little overlap that they may as well be an entirely different class of metals. The biggest benefit of steel is that it is a relatively inexpensive material that can serve almost any purpose with the right alloying elements and heat treatments. Although, the biggest benefits of steel are found in mild steel.
Benefits of Steel for Fabrication, Industry, and Structures
When structural welders build a stairway for an office building, a mezzanine for seats in a stadium, or the joists that hold up the concrete floor of a commercial building these will be made of mild steels—specifically, extruded mild steel profiles and bar stock and rolled steel plate and sheet. Similarly, when auto shops want to build a custom battery bracket or fix a classic car’s steel frame, they’ll most often use mild steel to form, fabricate, and weld these structures. Mild steel is used to build the jigs and frames to hold these assemblies in shape as they are welded, although they are most often used in the form of strong, solid, but ultimately temporary frameworks angle iron. New iterations of mild steel rolled out into sheets thin enough that a nail or screw can be driven through are starting to be used as a replacement for timber in residential construction once they are folded into shape for strength and galvanized to resist corrosion.
The versatility of mild steel cannot be overstated. One of the issues that can emerge is that there is such a wide range of quality and properties in steels as a whole, and even sub-categories like mild steel, that the weldability and workability of steels can differ significantly even among steels that are notionally the same grade. This can be compounded by the quality of the work by the foundry that produced the steel in the first place. Any hobbyist fabricator that has picked up steel from their local hardware store can attest to the unpredictable behavior of steel that barely qualifies as mild steel compared to the stuff that’s more solidly in the middle of the category. More serious structural or mechanical engineering firms that need their steel to meet qualifications have lost a significant amount of time trying to make borderline steel meet the needed standards through additional work and care. Many have also incurred additional costs when it became clear that no amount of extra effort could make the steel meet the requirements and new materials would need to be purchased.
The many benefits of steel can only really be enjoyed when the qualities of the steel are known and can be counted upon. This is why a supplier of metal that can be relied on is so important not just for high-specification materials like nickel-based superalloys and MIC-6 aluminum plate but also for the most basic materials like the angle iron and other steel profiles that any industrial shop keeps around both for fabricating into finished products and for odd jobs as needed. It is important to have a quality steel supplier from the start rather than find weldments are being contaminated from the poor quality of the steel while under the pressure to meet a deadline under budget.