Steels (first made in China and Japan around 600-800 AC) are generally divided into the categories of carbon steels and alloy steels (including plastic mold steels).

Carbon steels

Carbon steels are used extensively in plasitc mold construction. they are those steels which ony contain iron and carbon, and small amounts of other alloying elements. they are the most common and least expensive type of steels used for tools. The three principal types of them used for tooling are low carbon, medium carbon, and high carbon steels, Low density contains between 0.05% and 0.7% carbon. And high density contains between 0.7% and 1.5% carbon. As the carbon content is increased in carbon steel, the strength, toughness, and hardness also increase when the metal is heat treated.

Low density are soft, tough rapid prototype that are easily machined and welded. Due to thrie low carbon content, these steels cannot be hardened except by case hardening.Low carbon steels are well suited for the following applications: tool bodies, handles, die shoes, and similar situations where strength and wear resistance are not required.

Medium density are used where greater strength and toughness are required. Since medium’s have a higher carbon content they can be heat treated to make parts such as studs, pins, axles, and nuts. Steels in this group are more expensive as well as more difficult to machine and weld than low density.

High density are the most hardenable types and are used frequently for parts where wear resistance is an important factor. Other applications where high density are well suited inclued drill bushings, locators, and wear pads. Since the carbon content of these plastic mold material in so high, parts made from high’s are normally difficult to machine and weld.

Alloy steels

They are basically material with additional elements added to alter the characteristics and bring about a predictable chang in the mechanical properties of then alloyed metal. They are not normally used for most tools due to their increased cost, but some have found favor for special applications. The alloying elements used most often in steel are manganese, nickel molybdenum, and chromium.