Iron and steel are the two most commonly used metals in our industry, and their use has become so common that we take them for granted these days. But the importance of these metals is so great that humanity has been using them for at least 2,000 years, and we have named entire periods of human history after iron and steel.
Iron is the fourth most common element in the Earth’s core, mantle, and crust by weight. It’s a very significant metal, as it helped propel human civilization through history, and it’s still used in numerous metal manufacturing processes to this day. It’s a very versatile mineral used across all industries.
Pure, refined iron is a silvery-white substance with subpar mechanical properties since it’s very soft and brittle. Despite poor mechanical properties, pure iron has excellent thermal and electrical conductivity and exceptional magnetic properties. However, pure iron is very susceptible to oxidation, as it really combines with oxygen from the atmosphere, making it exceptionally difficult to find iron in its pure form.
As previously said, pure iron isn’t really useful since it’s very soft and reactive. However, its properties are greatly enhanced when it’s alloyed with other metals and non-metals. Thus, all materials that people broadly refer to as iron are actually different types of iron-based alloys. There are several types of iron:
Iron was undoubtedly known to the ancient world, and one of the earliest examples is beads made from meteoritic iron ore dating back to 3,500 BC Egypt. Mankind didn’t extract iron from the Earth due to a lack of technological knowledge, so they associated this metal with heavenly origins. Egyptians continued to work with meteoritic iron until 2,500 BC.
At the same time, samples of smelted iron can be found in Asmar, Mesopotamia, and Syria, dating between 3,000 and 2,700 BC. The Hittites were among the first to smelt iron between 1,500 and 1,200 BC, and it’s likely that the practice of iron smelting spread throughout the rest of the ancient world, ushering in the Iron Age.
Cast iron first appeared in the 5th century BC in China but was hardly used in Europe until the medieval period. Cast iron eventually replaced wrought iron towards the end of the 18th century, when its use became incredibly widespread, furthering the development of construction, transportation, and numerous other industries.
Steel is the backbone of modern industry and quite possibly the most versatile alloy used in modern production. Steel is an alloy of iron consisting primarily of iron and carbon — a non-metallic alloying element that clearly distinguishes iron from steel. Steel contains anywhere from 0.002% to 2.14% carbon, more than wrought iron, and less than cast iron.
Admittedly, this is a small amount of carbon by weight, but it results in significant physical enhancements making steel both harder and stronger than pure iron. In its most basic form, steel is typically made of iron and carbon, with negligible traces of other elements — this is called carbon steel.
However, adding additional alloying elements, such as chromium, nickel, manganese, and vanadium, can further enhance its properties. This type of steel is mostly used in the construction industry and the production of industrial hardware, such as knobs and handles, which don’t have specific tensile strength requirements.
As an alloy, steel can be enhanced with different amounts of different chemical elements, resulting in more than 3,500 different steel grades, each with its unique properties. However, these grades are typically grouped into four different types of steel:
Carbon steel got its name because it’s primarily made of iron and carbon, with a minute and negligible traces of other elements. The resulting material is exceptionally strong but very susceptible to corrosion. Carbon steel is further categorized according to its carbon content into low-carbon or mild steel, medium-carbon steel, and high-carbon steel.
Alloy steels are made by mixing carbon steels with alloying elements that give steel distinct qualities. These elements include chromium, cobalt, molybdenum, nickel, tungsten, vanadium, and traces of other alloying elements.
Tool steels are known for their exceptional hardness and high-temperature resistance, which is why they’re used to produce various tools, including ones that would cut through other types of steel.
Stainless steel is probably the best-known steel on the market and one of the most widespread steels used in industries with high hygienic requirements due to its corrosion resistance. This is achieved by adding at least 10% of chromium to the iron-carbon mixture, resulting in steel that’s suitable for aerospace, medical equipment, residential application, cookware, etc.
The main difference between iron and steel is that the former is a naturally occurring element, while the latter is an alloy of iron and carbon — something that doesn’t naturally occur.
Steel is stronger than iron in the domains of yield and tensile strength, but it’s also significantly tougher. For applications across various industries, steel is obviously a superior material; it doesn’t crack, warp, twist, rot, or split.
Apart from stainless and galvanized steel, all steels are also susceptible to corrosion, but as they’re non-porous alloys, they don’t corrode as readily as iron. This is mostly alleviated by using a protective coating.
Overall, steel is lighter, stronger, and more durable than iron, and in most cases and parameters, using steel is cheaper and more effective than using iron.
Both of these resilient, malleable, and versatile materials are used in similar applications, but steel has obviously superseded iron due to its enhanced qualities with modern foging techniques. Ultimately, however, the applications of each greatly depend on the required properties and durability of materials and understanding the differences between the two is critical in choosing the right metal for your project.
If you want to learn more about Steel and its types, check out our Engineer Resource Guides on various types of materials and their applications throughout industries, including stainless and surgical steel.