Selecting Tool Steel Grades

When it comes to industrial machinery such as drills, dies and cutting tools, tool steel is the favored choice. As you can tell by the name, it’s designed for this very purpose. High amounts of carbon and other alloying elements gives tool steel enhanced hardness and strength, qualities which allow it to weather the repeated stresses of manufacturing. But while all tool steel is tough, selecting the right grade of tool steel is important to ensuring you have the type best suited for the job. A good starting point is to first determine the exact purpose of the tool steel you plan to use:

1. Will it be doing work at low temperatures?
2. Will be doing work at high temperatures?
3. Do you intend to use it at high speeds?
4. Will the tool steel be involved in repeated impacts?
5. Will it be used for plastic molding?
6. What is your budget?

Low Temperature Work
For work performed at very low temperatures, the tool steel group known as cold work steel best fits the bill. All tool steels are very hard, but extreme hardness tends to be accompanied by increased risk of cracking. With extreme cold, metal can become even more brittle. So cold work steels are carefully quenched, using methods that allow the steel to retain some degree of flexibility. Quenching in oil (O-series), air (A-series), or adjusting the chemical composition to include more chromium (D-series) produces cold work steel that can perform well in low temperatures. While these cold work steels are pricier than water-hardened types, the mechanical benefits justify the higher cost.

High Temperature Work
Whatever the type of steel, any prolonged exposure to high temperatures will begin to affect its mechanical properties. As the temperature climbs, the atoms in the steel will increase their movement, creating structural changes within the metal. Because tools steels are already heat-treated prior to use, the application of more heat makes them even more vulnerable to structural changes. At worst, it can affect the steel’s crystal structure to the point of reversing the initial heat treatment. To avoid this, hot work steels are formulated with lower carbon and higher alloying content. The increased amount of molybdenum and tungsten produces a steel that can retain its hardness and wear resistance at extreme high temperatures.

High Speed Work
Tool steel used at high speeds are put under a great deal of pressure. High speed tool usage leads to increased friction, which means the steel will be exposed to both heavy wear and high temperatures. This means a metal must possess the durability of hot work steel, and even more resiliency to hold up to the friction. High speed tool steels typically include tungsten, chromium, and vanadium as their alloying elements to produce a very hard steel. This protects it against the pressure and abrasion of high speed work, while its hardness allows it to retain a sharp cutting edge during use.

High Impact Work
To undergo repeated major impacts, the necessary grade of tool steel must have a high degree of shock resistance. Tool steel is prized for its hardness, but that hardness means the metal can crack, chip, or lose its shape with impact. Shock resistant tool steels generally have a lower carbon content along with alloys such as silicon, sacrificing some hardness to give it more ductility and tensile strength. However, this does come at the cost of lower wear resistance. This means high impact tool steels are best suited for impacts only, rather than machinery that will experience more friction and wear.

Plastic Molding Work
The tool steels used for plastic molding are known as the P-series, or special purpose steels. These are much softer than the other types of tool steel due to alloying elements such as nickel, which impedes hardening during the forging process. While the hardness is decreased, P-series tool steel possesses enough malleability to allow it to be shaped into a variety of molding dies. After being heat treated, the tool steel molds can be used to produce plastic items. Theis grade of tool steels are rarely used for any other purpose, because the lengthy and complex manufacturing process makes it more costly to produce.

Cost of Tool Steel
As you can see, the more specialized the task of a tool steel, the more you should prepare yourself to spend. The price tag is well worth it: purchasing the right type of tool steel means it will perform better for its intended work and will last longer while doing it. Choosing the wrong type of tool steel can result in more frequent repairs or even replacements, both requiring an additional cost. However, for general usage not involving any extreme conditions, W-series tool steel will perform well. Due to being water quenched, these steels are the least expensive of all tool steels to produce or purchase. Hand tools, springs, and other small steel goods are typically made of this grade of tool steel.