Tool steel is often used to manufacture and repair machine tools and hand tools. The tool steel is renowned for its severe hardness and has excellent abrasion resistance, which can hold a cutting edge at elevated temperatures.
By adding various amounts of carbon, as well as other materials such as chromium, tungsten, and molybdenum, different grades of tool steel are made. Based on the required characteristics each form and type of steel is manufactured using various methods.
Types of Tool Steel
Tool steels are classified into five groups. Each of them has specific features, such as surface hardness, strength or ductility, working temperature, shock resistance, and price.
These five groups are:
- Water-hardening
- Cold-working
- Shock-resisting
- High-speed
- Hot-working
The cold-working group is further divided into three grade types: air-hardening, D-grades, and oil-hardening.
- Water Hardening or W-Grades
This category includes low-cost, high-hardness carbon steels. The price factor renders it the most commonly used steel tool.
Although Fragility, is a short come of the W-grade hardness. They are therefore not ideal for operating at high temperatures.
All the steels in this category are quenched in water and that how the name is derived. More often Water quenching can result in cracking and warping compared to the other cold working methods like oil quenching or air hardening. That is also why sales, while still leading, have declined in comparison to other groups.
The most common applications of W-grade tool steels include Cutters and knives, Cutlery, Embossing, Drills, Razor blades, and Lathe tools.
- Cold-Working
- Air Hardening or A-Grades
A-grade tool steels have higher chromium content resulting in a better response to heat treatment. The performance of the A-grade tool steel is very good. They have outstanding properties like wear resistance and toughness.
A-grade tool steels are most commonly used in Dies used for Bending, Blanking, Coining, Embossing, and Lamination, and also used in Cams, Chipper knives, Lathe centers, Plastic injection molds, Cold extrusion punches.
- D-Grades (Cold-Working)
In this category, we identify tool steels that combine the characteristics of W-grade and A-grade. They contain a higher level of carbon compared to the water hardening type but the properties mentioned above are common in the air hardening type.
Due to their high chromium content, D series tool steels are often also known as stainless steel. But the protection against corrosion is actually quite limited.
D grade Tool Steel are used in applications such as Burnishing tools, Lamination dies, Cutters, Cold extrusion dies, Lathe centers, Woodworking knives, Drawing punches, Seaming and Forming rolls, etc.
- Oil Hardening or O-Grades (Cold-Working)
This tool steels category has high abrasion resistance and high strength properties. It is regarded as the general-purpose steel, making it highly adaptable.
The majority of applications in which Oil Hardening or O-Grade Tool Steel are applied are identical to A-grade and D-grade steels, but they also include Bushings, Gauges, Punches Chasers for thread cutting, Collets, Master engraving rolls.
- Shock-Resisting or S-grades
Shock-Resisting or S-grades Tool Steels are comprised of low carbon tool steels and has very high toughness values. These properties enables them to be highly shock-resistant at both high and low temperatures.
However, owing to the same low carbon content they aren’t quite resistant to abrasion.
S-grade tool steels are found in applications like Jackhammer parts, Blacksmith chisels, Cold and Hot-working chisels, Hot forming dies, Hot stamps, Cold gripper dies, Chipper knives, Clutch parts, Pneumatic tools.
- High-Speed Tool Steel
High-Speed tool steels are common particularly in cutting tools.
Mechanical methods of cutting result in a lot of heat production. However, high-speed steels do not lose their hardness making them an ideal choice for high temperature applications.
High-speed steels are used for variety of application some of which include Power-saw blades, Drill bits, Milling and Gear cutters, Router bits, etc.
- Hot-Working or H-Grades
Hot-Working or H-Grades tool steel from this group may be used when cutting material at extremely high temperatures. The high qualities of durability and strength, which preserve their attributes when operating over long periods at elevated temperatures. All these qualities are inherited by a low carbon content, but a high content of other alloying elements.
H-grade tool steels are most commonly used in Casings, Hot forging, Dummy blocks for hot extrusion, Plastic injection molds, Hot-working punches.
The choice of the tool steel depends on what properties are required by your project. The most common mechanical properties to evaluate are the hardness of a surface, working temperature, durability, and resistance to shock. At the same time, it is necessary to include the expense of each material while making the assessment.
It is also very helpful in addressing questions about the specifications of sharp edges or cutting, how critical the resistance to abrasion is, and the type of heat treatment needed.
You should be ready to go with all this information, and make your choice!
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