Tool steels are composed of various combinations of carbide-forming metals such as chromium, molybdenum, tungsten, and vanadium. These iron-based alloys have relatively high carbon content for strength and carbide formation. Substitutional solutes like nickel and cobalt are added for high-temperature strength. Carbide-forming metals like: chromium, molybdenum, tungsten, and vanadium are added for hardness and wear resistance. They are divided into different categories based on their composition and characteristics including: cold work tool steels, hot work tool steels, and high-speed tool steels.
The carbon percentage in tool steels is typically in the range of 0.7 to 1.5 wt% carbon. However, some tool steels can contain up to 2.1% carbon, while others contain less than 0.25 % carbon. Hardness, strength, and hardenability are enhanced with an increase in carbon concentration. However, because of its propensity to create martensite, carbon also makes materials more brittle and less weldable.
Tool steel is made in a variety of ways. One of the main methods is through an electric arc furnace (EAF). EAF is done by melting recycled steel scrap in an electric arc furnace together with alloying components. To stop oxidation, the molten mixture is combined with chemicals and thrown into a huge ladle. The steel can then flow down into enormous molds to form ingots once the impurities have been eliminated during this refining stage.
An alternative to EAF is electroslag refining (ESR). With this method, ingots with smooth surfaces and no tubes (holes) or porosity (imperfections) are created using a progressive melting technique. This creates very high-grade steel with few imperfections. Other common steps in the manufacture of tool steel includes:
Tool steels are used in a variety of different industries and applications, including: cutting, forming, shearing, and stamping of metals and plastics; extrusion of plastic components, such as pipes and vinyl window frames; and the manufacture of dies for pressing metal powder into shapes like gears.
The three key properties associated with tool steel are: wear resistance, heat resistance, and toughness. Alloying elements are added to increase strength, wear resistance, hardness, and toughness. The degree of resistance to deformation of steel is measured by its hardness. The Rockwell C test is most frequently used to gauge the hardness of tool steels. Depending on the grade, hardened cold work tool steels have a hardness of around 58/64 HRC (Rockwell C). The majority are normally between 60/62 HRC, while some are occasionally utilized up to 66 HRC.
The temperature used to harden tool steel depends on the chemical composition of the steel. The different types of tool steel are usually heat treated at critical temperatures, which are determined by the type of steel and are typically in the range of 760-1300 °C. This step is then followed by a controlled cooling step.
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