how to make tool steel

How Tool Steel is Made

Tool steel, as the name suggests, is often used to produce and repair machine tools and hand tools (among other applications). Known for its extreme hardness, tool steel has good abrasion resistance and can hold a cutting edge at high temperatures.

Different grades of tool steel are made by adding different amounts of carbon, as well as other elements such as chromium, tungsten, and molybdenum. Each type and form of steel is produced with different methods, depending on the characteristics desired.

The most popular forms of tool steel are O-1 and A-2 tool steels, which are both part of the cold-work group of tool steels.

  • O-1 is a general purpose oil-hardening steel with good hardness, strength, and wear resistance. It is mainly used for items like knives and forks.
  • A-2 is an air hardening steel with good machinability along with a balance of wear resistance and toughness. A-2 is the most common variety of air-hardening steel and is often used for blanking and forming punches, trimming dies, and injection mold dies.
  • How to Make Tool Steel

    The basic process of making tool steel starts with recycled steel scrap which is melted in an electric arc furnace, along with any alloying elements. The molten mixture is poured into a giant ladle and mixed with chemicals to prevent oxidation. After impurities are removed through this refining stage, the steel is allowed to flow down into large molds to make ingots.

    After un-molding, the red-hot ingots are forged with huge mechanical dies to press them into the desired size and shape. The finished forgings are annealed by re-heating to reduce internal stresses formed during the forging process. Then they are allowed to cool slowly either in water, air, or an oil bath, allowing the metal crystals to re-form. This annealing process keeps the steel soft enough to work without cracking. It can then be cold- or hot-rolled into the desired shape.

    Advanced Methods

    An alternative method of making tool steel is to position the ladle of hot molten steel over a vertical open-ended mold. The molten steel runs down through the cooled mold, and begins to harden near the mold’s inner surface. As more steel passes through the mold, the partially hardened metal continues to move down and then out onto water-cooled rollers. The result is a long, continuous bar or rod of steel.

    For a tool steel with better surface quality and fewer imperfections, manufacturers use a process called electro-slag re-melting (ESR). Giant water-cooled molds are filled with a pool of heated slag containing reactive chemicals. A consumable steel ingot, called an electrode, is lowered down into the slag. An electric current passed through the electrode causes it to melt, its liquid drops of steel pulled by the current towards the bottom of the mold. As the drops flow downward through the hot slag, impurities react with chemicals in the pool and float to the top. Only pure steel droplets reach the bottom, where they solidify and eventually build up a homogeneous steel ingot inside the mold.

    Another, more advanced process uses powdered metal to form tool steel with improved hardening and machinability. This process has better results for tool steel with higher percentages of carbon and alloying material, required for applications such as aerospace components.

    Industrial Metal Supply offers tool steel bar in O-1 and A-2 grades. Note that not all sizes and alloys are stocked in every IMS location, but we can get it to you in any case.


    Selecting Tool Grade Steel

    4 Things To Consider When Selecting a Tool Grade Steel

    Known for their distinct hardness, tool steels are used to make cutting tools including knives and drills, as well as to create dies that stamp and form sheet metal. Though selecting a tool steel may seem straightforward, the process requires tradeoffs – making the task an art as well as a science. Choosing the optimal tool steel grade will depend on many factors, including:

    1. Characteristics of available tool steel grades
    2. The specific application
    3. The history of failures in similar applications
    4. Tool steel cost

    Tool Steel Grades and Corresponding Applications

    Tool steels are available in a wide range of grades, based on their composition, the temperature range in which they were forged or rolled, and the type of hardening they have undergone. The AISISAE general purpose grades of tool steel are O-1, A-2, and D-2. These standard grade steels are considered “cold-working steels,” that can hold their cutting edge at temperatures up to about 400°C. They exhibit good hardness, abrasion resistance, and deformation resistance.

    O-1 is an oil-hardening steel with high hardness and good machinability. This grade of tool steel is mainly used for items like cutting tools and drills, as well as knives and forks.

    A-2 is an air-hardening steel containing a medium amount of alloying material (chromium). It has good machinability along with a balance of wear resistance and toughness. A-2 is the most commonly used variety of air-hardening steel and is often used for blanking and forming punches, trimming dies and injection mold dies.

    D-2 steel can be either oil-hardened or air-hardened, and contains a higher percentage of carbon and chromium than O-1 and A-2 steel. It has a high wear resistance, good toughness and low distortion after heat treating. The higher carbon and chromium levels in D-2 steel make it a good choice for applications requiring a longer tool life.

    Other tool steel grades contain a higher percentage of different types of alloys, such as high-speed steel M2, which can be selected for high-volume production. A variety of hot working steels can maintain a sharp cutting edge at much higher temperatures of up to 1000°C.

    How Does Tool Steel Fail?

    Before selecting a tool steel grade, it’s important to consider which type of tool failure is most likely for this application by examining failed tools. For example, some tooling fails due to abrasive wear, in which the material being cut wears down the tool surface, though this type of failure is slow to occur and can be anticipated. A tool that has become worn to failure needs a tool steel with greater wear resistance.

    Other types of failure are more catastrophic, such as cracking, chipping, or plastic deformation. For a tool that has broken or cracked, the toughness or impact resistance of the tool steel should be increased (note that impact resistance is reduced by notches, undercuts, and sharp radii, which are common in tools and dies). For a tool that has deformed under pressure, hardness should be increased.

    Keep in mind, however, that tool steel properties are not directly related to each other, so for instance, you may need to sacrifice toughness for higher wear resistance. This is why it’s so important to understand the properties of different tool steels, as well as other factors such as the geometry of the die, the material being worked, and the manufacturing history of the tool itself.

    Cost Of Tool Steel

    A final issue to consider when selecting a tool steel grade is cost. Cutting corners on the choice of material may not result in lower overall production cost if the tool proves to be inferior and fails prematurely. A cost-benefit analysis should be undertaken to ensure that the tool steel material chosen will provide the performance required.

    Industrial Metal Supply offers a variety of shapes and sizes of tool steel bar in O-1 and A-2 grades.