What’s Tool Steel?

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Tool steel is a type of steel used for tools due to its hardness, ability to hold a sharp edge, and resistance to abrasion and deformation. It is produced in many grades and can be used for stamping dies, construction equipment, and axles. The different grades are classified under SAE or AISI/SAE steel grades. The most common form is W-grade, which is a low-cost carbon steel. Other grades include A, O, D, H, T, M, and S. Some types of tool steel have very specific characteristics or purposes, such as F-grade for superior wear resistance, P-grade for injection molding and die casting machines, and L-grade for high iron content.

Tool steel is a type of steel with mechanical properties that make it a desirable material for tools. Tool steels are notable for their hardness, ability to hold a sharp edge, or resistance to damage from abrasion and deformation. There are a number of carbon and alloy steels, usually made through a product of heat treatment and quenching, which are suitable as tool steels. Tool steel is produced in many different grades and can be used to make tools such as stamping dies, construction equipment, and axles. In addition to tool making, it is also used in other applications that require materials with mechanical properties of tool steel.

The different grades of tool steel are often classified under a system called SAE steel grades or AISI/SAE steel grades, created by the Society of Automotive Engineers (now SAE International) and the American Iron and Steel Institute. Classifies each steel grade with a letter that indicates its properties or method of production, such as W-grade for water-hardened steel or S-grade for impact resistant steels. Each steel grade within these broad categories then receives an individual number following the letter.

The most common form of tool steel is W-grade, a form of carbon steel popular due to its low cost. Some types of W-grade steel also include silicon, molybdenum or manganese to increase the toughness of the steel. It is called water hardened because water is used during quenching, a step in the manufacturing process of many steels in which heated steel is rapidly reduced in temperature. Grade W tool steel is hard, but tends to be brittle and does not withstand temperatures above 302°F (150°C) well. Grade W tool steels are commonly used to make blades such as edged blades and razors; machine parts for machines that do not encounter or produce high temperatures; and tools such as hammers, drills, and chisels.

Grades A, O and D are steels produced by cold working, a process in which the steel is subjected to mechanical stress until it undergoes plastic deformation, a permanent change in the microstructure of the steel. This process increases the tensile strength and hardness of the steel while reducing its ductility, and the resulting steel shapes are commonly used for purposes such as saw blades and machine tools. Grade O steel is oil hardened while Grade A is air hardened, methods that produce less distortion in the steel than water hardening. Grade D steel contains a large amount of chromium, which makes up 10 to 18 percent of the alloy. In addition to chromium, grade A, O and D steels are often alloyed with other metals, including manganese, tungsten and vanadium, and with nonmetals such as sulfur and phosphorus.

H steel is a hot work tool steel, created by causing plastic deformation of the steel through prolonged exposure to high temperatures. These steels have high strength and hardness, but slight distortions due to the cooling process and thermal contraction make them less suitable than cold work steels for applications with very tight engineering tolerances. Chromium, tungsten and molybdenum are common alloying elements in steels of this grade.

Grades T and M are types of high speed steel, which are distinguished by their ability to maintain high hardness at high temperatures. This property makes it suitable for use in powered cutting tools and blanking dies, where its resistance to frictional heat allows it to work at higher speeds than other steels. T-grade steel gets its name from its high tungsten content, while M-grade steel contains a high amount of molybdenum. Additional common alloying elements in these steels include vanadium, chromium and cobalt.
Grade S steels are tool steels characterized by high impact resistance. They have less carbon than other steel alloys, which decreases their resistance to abrasion but increases their toughness. S-grade steel is used in equipment such as jackhammers that must be able to withstand heavy impact.

Some types of tool steel have very specific characteristics or purposes. Grade F steel is a type of water hardened steel, like Grade W steel, but has superior wear resistance. P-grade steel, or plastic mold steel, is used in injection molding and die casting machines. L-grade, or low alloy special purpose steel, is a very hard type of steel that has little alloying material and a very high iron content.

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