There are many ways to categorise steel, however, according to the American Iron & Steel Institute (ASIS), steel is primarily categorised based on chemical composition. A useful way to remember each of the different types of steel is to remember the acronym ‘CAST’.
‘CAST’ stands for: Carbon, Alloy, Stainless and Tool. In this article we are going to discuss these four types of steel used by major steel suppliers and outline the properties of each
As discussed before, steel can either be made of Carbon, Alloy, Stainless and Tool. However, there are many properties that distinguish what grade the steel belongs to. These grades are determined by properties such as physical, chemical and environmental. Having a qualified steel supplier will assist in determining what type of steel you need for your project.
All steel shares the same compounds of iron and carbon. The amount of carbon, and additional alloys are what distinguish each grade and type.
Different Classifications of Steel
Types of steel, provided by steel suppliers, can be identified by various factors. Some of these include:
- Composition – Steel can either be composed of carbon, alloy or stainless steel;
- Production method – The production method can have a big impact on the final product, therefore steel can also be identified by whether it has been continually cast or through an electric furnace;
- Finishing Method – There are various ways to finish the steel, some of these include cold rolled, hot rolled, or cold drawn;
- Shape – The shape of the steel is another common way of classifying different products. Some common forms are Bar, Rod, Tube, Plate, Sheet and Structural;
- De-oxidation Process – The de-oxidation process means that steel can either come as killed or semi-killed;
- Microstructure – The microstructure of steel can either be Ferritic, Pearlitic and Martensitic;
- Physical Strength – The physical strength is measured by ASPM Standards;
- Heat Treatment – Temperature plays a large role in the production of steel, as a result, if it annealed, quenched or tempered will help identify it;
- Nomenclature – The quality of the nomenclature means that steel can either be identified as commercial, drawing or pressure vessel quality.
Steel Numbering Systems
There are two primary numbering systems used by steel suppliers in the production of steel. The American Iron and Steel Institute (ASIS) developed the first, whilst the Society of Automotive Engineers (SAE) prepared the second.
The first digit (1) is designated as carbon steel. All carbon steels for both ASIS and SAE take the form (1xxx). They are then further subdivided due to the below properties:
- 10xx – Plain carbon steel with 1.00% Manganese maximum;
- 11xx – Re-sulfurized carbon steel;
- 12xx – Re-sulfurized and re-phosphorized steel;
- 15xx – Non-re-sulfurized, high Manganese (up to 1.65%) carbon steel.
If the first digit is not a (1) it will be one of nine other options listed below:
- 2xxx – Nickel steel;
- 3xxx – Nickel-chromium steel;
- 4xxx – Molybdenum steel;
- 5xxx – Chromium steel;
- 6xxx – Chromium steel;
- 7xxx – Tungsten-chromium steel;
- 8xxx – Nickel-chromium-molybdenum steel;
- 9xxx – Silicon-manganese steel, as well as other SAE grades.
The second digit, often, but not always, will indicate the concentration of the major elements as a percentile ie. 1 equals 1%.
The last two digits indicate the carbon concentration to 0.01%.
An example may be SAE 5130. This type of steel is chromium alloy steel with about 1% chromium and 0.3% carbon.
There are three main types of steel, provided by steel suppliers; they are known as Low Carbon Steel (or Mild Steel), Medium Carbon Steel and High Carbon Steel.
Mild Steel will typically contain 0.04% to 0.3% carbon. This is the largest category, covering a diverse range of steels in different shapes from Flat Steel to Structural beam.
Medium Carbon Steel typically has a range between 0.31% to 0.6%. This product is stronger than mild steel, yet harder to weld or cut.
High Carbon Steel is the hardest and most brittle type of steel. It is very difficult to cut
Rather than just having carbon, Alloy steel will have varying trace amounts of another alloying element; these might be manganese, silicon, nickel, titanium, copper, chromium or aluminium.
Depending on the type of alloy, the steel will have different properties. Alloy steels are the most common types of steel available in the industry, as they are economic, widely available and have several good mechanical properties.
Stainless steel is more corrosion resistant compared to Carbon and Alloy steel types. Stainless steel is typically made of at least 11% Chromium, Nickel or Molybdenum. The Alloy content will fall somewhere between 15-30%.
Stainless steel is applied in a variety of household goods, medical instruments, hardware and appliances.
Tool steel is extremely hard and abrasion resistant. As such it is typically involved in the production of tools for cutting steel and even in the production of knives.