Carbon steel consists of many different grades that provide different properties, and machinists and fabricators should select specific carbon steel grades for particular projects, as the application of the finished product may indicate. Each type of steel has different advantages over the others. However, the main difference between these steel grades is the amount of carbon mixed with the iron during the refining process. Beyond this, many additives are introduced during refining to alter properties such as tensile strength, toughness, temperature resistance, and ductility. Generally, three distinctions are made between types of carbon steel – low carbon steel, medium carbon steel and high carbon steel.
Low carbon steel — The normal range for carbon content in low carbon steel is between 0.03 and 0.08%. There are many applications where low carbon steel is used, such as the manufacture of cookware, silverware, and unplated sheet metal products. It has excellent weldability and formability.
Low carbon grades have low tensile strength and are relatively inexpensive. These are widely used in forming processes that require bending, crimping and crimping; they have high surface hardness and make low carbon steel preferable for making liners, machine parts, special bolts, ratchets, chain pins, oil tool slips, tie rods, anchor pins and dowels.
Medium carbon steel — For medium carbon steel grades, the carbon content ranges from 0.25% to 0.60%. The carbon in these products is usually introduced with alloys of high hardness elements like molybdenum, chromium or nickel. Medium carbon steels have high strength and wear resistance.
These alloys are used in the manufacture of tools and devices that require material toughness. You will find medium carbon steel specified for components such as gears, axles, studs and other mechanical equipment where strength and hardness are required.
A widely used medium carbon steel grade is AISI 1045, which is known for its superior machining characteristics. If a certain application requires hardness, AISI 1045 can be hardened by heat treatment at a uniform temperature of 820-850°C (1,508-1,562°F).
High carbon steel – High carbon steel grades are the hardest and toughest of the three types of steels discussed here. Generally, the carbon content will range from 0.60% to 1.4% of the total weight. However, high carbon steel grades are also ductile and with heating and tempering these materials can also be hardened. Typically, these steel grades are used to make the materials needed for mechanical, cutting, and bearing components.
AISI 52100 is one of the premium high carbon steel grades used for linear shift parts. To add hardness and corrosion resistance, chromium and manganese are added in the composition of 52100 steel.
Read the ratings — The two institutions that designate steel alloys are the American Iron and Steel Institute (AISI) and the American Society for Testing and Materials (ASTM). Each of these organizations has a different methodology for classifying and identifying steel alloys. The AISI method gives a four-digit designation, in which the first two digits are the alloy and the next two digits indicate the carbon content.
The ASTM system uses A to identify ferrous materials, followed by an assigned number. These classifications are very important to understand and follow, as they ensure that the correct steel grade is specified and used for particular engineering products and applications. These are the common notations agreed upon by engineers, metal producers, metal distributors and buyers, and metal fabricators, to identify and choose the right alloy.
