There are many different types of steel that cover varying properties. These properties can be physical, chemical and environmental.
All steel is composed of iron and carbon. It is the amount of carbon and the additional alloys that determine the properties of each class.
Steel Ratings
Steel grades can also be classified by a variety of different factors:
- Composition: Gamma carbon, league, stainless steel.
- The production method: continuous casting, electric oven, etc.
- Finishing method used: coldrolled, hot rolled, drawn cold (cold finished), etc.
- Shape or shape: Bar, Rod, Tube, Tube, Plate, Sheet, Structural, Etc.
- Deoxidation process (oxygen removed from the steel making process): Killed & Semi-Killed Steel, Etc.
- Microstructure: Ferritic, Pearlitic, Martensitic, Etc.
- Physical strength (as per ASTM standards).
- Heat treatment: Annealed, quenched and tempered, etc.
- Quality Nomenclature: Commercial Quality, Design Quality, Pressure Vessel Quality, etc.
Steel numbering systems
There are two main numbering systems used by the steel industry.Both systems are based on four-digit code numbers when identifying base carbon and alloy steels. There are league selections that have five-digit codes.
If the first digit is a (1) in this designation, it indicates a carbon steel. All carbon steels are in this group (1xxx) in the SAE and AISI systems. They are also subdivided into four categories due to specific underlying properties between them. See below:
- Plain carbon steel is included in the 10xx series (containing 1.00% Mn maximum)
- Re-sulfurized carbon steel is included in the 11xx series
- Re-sulfurized and re-phosphorized carbon steel is included in the 12xx series
- High manganese (up to 1.65%) non-resulfurized carbon steel is included in the 15xx series.
The first digit in all other alloy steels (in the SAE-AISI system) is classified as follows:
2 = Nickel steels.
3 = Nickel-chromium steels.
4 = molybdenum steels.
5 = Chrome steels.
6 = Chrome-vanadium steels.
7 = Tungsten-chromium steels.
8 = Nickel-Chromium-Molybdenum Steels
9 = Silicon manganese steels and various other SAE grades
The second digit of the series (sometimes, but not always) indicates the concentration of the main element in percentiles (1 is equal to 1%).
The last two digits of the series indicate the carbon concentration at 0.01%.
For example: SAE 5130 is a chromium alloy steel that contains approximately 1% chromium and approximately 0.30% carbon.
carbon steel
Carbon steel can be segregated into three main categories: low carbon steel (sometimes known as mild steel); Medium carbon steel; and high carbon steel.
Low carbon steel (mild steel) : typically contains 0.04% to 0.30% carbon content. This is one of the largest carbon steel groups. It covers a great diversity of forms; from the flat sheet to the structural beam. Depending on the desired properties needed, other elements are added or augmented. For example: Design Quality (DQ) - The carbon level is kept low and aluminum is added, and for structural steel the carbon level is higher and the manganese content is increased.
Medium carbon steel: normally has a carbon range of 0.31% to 0.60% and a manganese content ranging from 0.060% to 1.65%. This product is stronger than low carbon steel and is more difficult to form, weld and cut. Medium carbon steels are often hardened and tempered using heat treatment.
High carbon steel: Commonly known as “carbon tool steel”, it typically has a carbon range between 0.61% and 1.50%. High carbon steel is very difficult to cut, bend and weld. Once heat treated, it becomes extremely hard and brittle.
