Types of Steel
Steel is one of the most versatile and widely used metals today. Ever since a man named Henry Bessamer invented the process to cheaply mass produce steel in the 19th century, it has become a valuable metal in many industries due to its low cost and high tensile strength. Steel is an alloy of iron and carbon, along with other metals depending on the intended use and desired properties of the end product, such as heat or corrosion resistance.
There are many different types of steel. There are over 3,500 types, each with its own unique properties. These can be divided into four main categories, according to the American Iron and Steel Institute (AISI). The categories are:
- Carbon Steel
- Alloy Steel
- Stainless Steel
- Tool Steel
When you are designing a project that includes steel, it is important to choose the steel with the right hardness, flexibility, workability, economic value, tensile strength, and more. This article will cover the basics of the four types.
Four Main Types of Steel
Carbon Steel
Carbon steel constitutes about 90% of all steel production. It contains iron and carbon as its main alloy along with other metals, and can be classified into three groups depending on the amount of carbon in it.
- Low Carbon (Mild Steel)
Low carbon, or mild steel, contains less than .3% carbon. It is the most commonly used type of steel because it is cost effective and highly workable. - Medium Carbon
Medium carbon steel contains about .3% – .6% carbon as well as up to 1.65% manganese. It is stronger than mild or low carbon steel, so it is often used in buildings and larger structures. - High Carbon
High carbon steel contains .61% – 1.5% carbon, and is incredibly hard, brittle, and difficult to weld and cut. It is often used for knives, hammers, axles, and other tools.
Alloy Steel
Alloy steel is a steel with a small amount of alloying elements other than carbon, such as manganese, silicon, nickel, titanium, copper, chromium and aluminum. This gives it a wider variety of properties than carbon steel, and makes it more heat and mechanical treatments. It is inexpensive and easy to work with, and it is used in car parts, electric motors, generators, and pipelines.
Stainless Steel
Stainless steel is a carbon alloy steel that contains 10-20% chromium as well as other alloying elements. It is attractive and incredibly resistant to corrosion (200X more resistant than mild steel), making it popular for appliances, food handling, piping, medical instruments and equipment, and all types of utensils. Based on the crystalline structure, stainless steel can be divided into three groups:
- Austenitic
Austenitic steel is the most commonly used type of stainless steel, comprising a large portion of the food processing industry. It is non magnetic and resistant to heat treatments. - Ferritic
Ferritic steels are high chromium, and have low carbon and nickel content. They are magnetic, resistant to heat oxidation and corrosion, and are used in furnaces, food processing, exhaust systems, and more applications where light, thin materials are needed. - Martensitic
Martensitic stainless steel has a moderate carbon and chromium content. It is magnetic and responsive to heat treatment, and is used in dental and surgical treatments, as well as knives and cutting tools.
Tool Steel
Tool steel is steel alloyed at a high temperature with a variety of hard metals including tungsten, cobalt, vanadium, molybdenum. It’s hardness and resistance to wear and abrasion makes it excellent for tools such as drilling equipment. It is often used to form other steel tools and equipment.
Steel Identification Numbers
With all of these types of steel, what is a good way to quickly tell what it’s made out of without having to do extensive detective work? Well, thankfully, The SAE International uses a numbering system to help us quickly determine which kind of steel it is.
Carbon and Alloy Numbering System
Carbon and alloy steels use a 4 digit numbering system. The first number indicates which alloying elements were used, the second number tells us the concentration of the major element in percentiles (1% = 1) and the last two indicate the carbon concentration in hundredths of a percent (ie., .5% carbon = XX50).
Stainless Steel Numbering System
The stainless steel numbering system uses a three digit series to indicate the alloying metals and the process by which it was made (the 200 series consists of austenitic chromium-nickel-manganese alloys, the 500 series consists of heat resistant chromium alloys, etc.). The most commonly used stainless steel grade is Grade 304, due to its corrosion resistance.
Conclusion
As you can see, there are many, many different types of steel, and they each have unique properties. No matter what your project is, there is a type of steel that can do the job.
