These four groups include carbon steel, alloy steel, stainless steel, and tool steel. All steel is composed of both iron and carbon, but vary in type depending on certain physical, chemical, and environmental properties; all of which are determined by the amount of carbon and any additional alloys. Below are the descriptions of the four categories of steel, and facts about each.
Carbon steel can be further categorized into three groups: 1) Low carbon, 2) Medium carbon, and 3) High carbon. Low carbon, also called mild steel, is one of the largest categories of carbon steel, and generally contains anywhere from 0.04% to 0.30% carbon content. Depending on its intended use, other additives and alloys can be added to create desired properties. Medium carbon generally contains anywhere from 0.31% to 0.60% carbon content, as well as, a range of 0.60% to 1.65% of manganese content. High carbon steel is informally known as “carbon tool steel” and contains 0.61% to 1.50% carbon content. It is difficult to manipulate, and becomes very brittle when heat-treated.
Alloy steel also contains carbon, since all steel contains both carbon and iron. But alloy steel also contains a marginal amount of additional elements, such as Nickle (Ni), Chromium (Cr), and Manganese (Mn). This type of steel is popular and commonly used due to their wide availability, economical costs, ease of processing, and quality mechanical properties. In comparison to carbon steel, alloy steel is more responsive to mechanical and heat treatments. Heated alloy steel comes in wither annealed or normalized.
Stainless steel contains added alloys that make is extremely resistant to corrosion in comparison to carbon and alloy steel. This is why it is commonly used in the medical/surgical industries, appliance industry, hardware manufacturing industry, food processing/handling industry, architectural industry, and more. It contains both carbon and iron, as mentioned before, but stainless steel generally contains other alloys as well, such as Chromium (Cr), Molybdenum (Mo), or Nickel (Ni).
Tool steel is a general term to describe a variety of steels that retain high-hardness and abrasion-resistance properties. Specific applications for tool steel include stamping, extrusion, dies, cutting, mold-making, or impact applications (i.e. hammers).