Tool Steel Grades, Applications and Production Methods

Tool steels are a group of alloy steels that are particularly well-suited for applications requiring high hardness, wear resistance, and the ability to retain shape at elevated temperatures. These properties make them ideal for manufacturing tools, dies, moulds, and other components subjected to mechanical stress or thermal cycling. However, their use extends beyond tools alone – Tool steels are the most common group of metals used in engineering today.

In this article, we’ll take a closer look at what defines tool steel, explore its key subcategories, and explain how different grades are selected for specific industrial applications.

What Is a Tool Steel?

Judging by the name, you may have an idea of the main purpose of a tool steel. Whether you are manufacturing hand tools or machine tools, like dies or drill bits, tool steel is the perfect choice. Some of the main properties that make this alloy steel the go-to option for tool manufacturing include:

• A fairly high material hardness makes it resistant to deformation and flattening (58–64 HRC on the Rockwell C scale, some specialised grades may even exceed 66 HRC after heat treatment).
• Great toughness, which makes it resistant to breakage and chipping.
• Wear resistance, which includes resistance to abrasion and erosion
• Good thermal properties provide it with the ability to retain its shape and sharp cutting edges even at very high temperatures.

These properties make them highly suitable for applications such as cutting, forming, stamping, and moulding. Unlike standard carbon steels, tool steels are designed to retain their shape and strength under repeated mechanical stress and heat exposure.

A defining characteristic of tool steel is its carbon content, typically ranging from 0.5% to 1.5% by weight, though some grades may fall slightly outside this range. Higher carbon levels increase hardness and strength but also tend to reduce ductility and weldability.

Besides carbon, tool steels incorporate alloying elements such as chromium, vanadium, molybdenum, tungsten, cobalt, manganese, and nickel. These elements serve distinct purposes — for instance, vanadium and tungsten form stable carbides that improve wear and corrosion resistance, cobalt and nickel enhance strength retention at high temperatures, and small amounts of manganese reduce the possibility of cracks during quenching. The specific alloy blend and subsequent heat treatment determine a tool steel’s behaviour in service, whether it’s resisting deformation in a stamping die or maintaining a cutting edge on a drill bit.

How Are Tool Steels Made?

There are different processes that can be used to produce tool steels, but all of them have something in common. The production of tool steel has to be carried out in environments with controlled conditions to ensure high quality.

Some of the most used processes in tool steel production include:

• Electric arc furnace melting
• Electroslag refining
• Primary breakdown
• Rolling
• Hot and cold drawing
• Continuous casting

Electric Arc Furnace (EAF) Melting

This process is also known as primary melting. It is based on the melting of metal chips that are obtained from milling processes and suppliers. Basically, EAF melting uses leftovers of different metal processing methods.

Electric arc furnace melting is widely used because the production costs are low. Still, some extra treatment may be needed to achieve the highest possible quality and properties. An example of this is annealing to prevent cracking.

The process consists of two steps:

• Melting the scrap quickly in the furnace.
• Refining the melted metal in a separate vessel, which allows the possibility of processing great amounts of metal.

It is necessary to avoid the contamination of the melt during the process. That is why controlled conditions are extremely important.

Electroslag Refining (ESR)

Electroslag refining is also known as electroslag remelting. Throughout the process, the metal is melted progressively. The resulting ingots have good surface quality without notable imperfections.

Moreover, the tool steel produced through this process provides other great qualities unnoticeable to the naked eye:

• Better hot workability
• Higher cleanliness
• Improved ductility
• Increased fatigue resistance

Although a rather expensive process, electroslag refining is a good choice for the most specialised applications.

Primary Breakdown

This tool steel manufacturing process requires certain machinery. Such as open-die hydraulic presses or rotary forging machines.

However, the variety of cross-sections achievable with the primary breakdown process makes up for the cost of the machines. It is possible to produce square, rectangular, hollow and stepped profiles. The maximum lengths range somewhere between 6…12 metres.

Most importantly, tool steel manufactured by primary breakdown provides increased quality, few to no imperfections and great straightness.

Rolling

Modern tool steel production frequently relies on continuous rolling mills arranged in series — sometimes with more than 20 stands in a row. The process begins with heating the steel in an induction furnace, though walking-beam furnaces are also commonly used. Rapid and controlled heating is crucial to minimise decarburisation, the loss of carbon at the surface, which can weaken the steel.

Hot rolling follows to form the steel into its basic shape. Each pass through the rollers reduces the thickness incrementally until the desired dimensions are reached. For applications requiring tighter dimensional tolerances and a smoother finish, cold rolling may be performed as a secondary step.

Thanks to automation and advances in control systems, modern rolling lines are highly efficient. The process can produce coils of steel in as little as 12 minutes per unit, supporting both high output and precision.

Hot and Cold Drawing

Drawing is used to produce tool steels with tighter tolerances, smaller cross-sections, and specific profiles. However, due to the high strength and relatively low ductility of tool steels, cold drawing is typically limited to a single light pass to prevent cracking.

Hot drawing, conducted at temperatures up to approximately 540°C, allows for multiple passes. It not only increases strength through work hardening but also enables more complex shapes to be formed without compromising material integrity.

Continuous Casting

Continuous casting is a cost-efficient method for producing tool steels in large volumes. In this process, molten steel is solidified into a semi-finished billet, bloom, or slab, which is then processed further. To improve the final properties, the cast material is usually subjected to downstream treatments such as annealing, hammer forging, or rolling.

Other Processes

Traditional methods for producing tool steels often involve long cooling periods, which can lead to coarse grain structures. These structures negatively impact the material’s overall performance by reducing toughness, machinability, and dimensional stability.

Powder Metallurgy

To address these limitations, more advanced manufacturing techniques have been developed. Among the most notable are powder metallurgy and the Osprey process. These methods enable the production of tool steels with higher carbon and chromium content, along with significantly improved material properties, including:

• Enhanced machinability
• Better response to heat treatment
• Increased grindability

The primary drawback of these modern processes lies in their higher production costs, driven by the need for specialised equipment and expertise. However, as adoption increases and technology matures, these costs are expected to decline, making the benefits of these methods more accessible to a broader range of applications.

Most Common Tool Steel Grades with Applications

Tool steels are divided into 5 groups. Each of them has specific features regarding aspects like surface hardness, strength or toughness, working temperature, shock resistance and cost.

These five groups are:

• Water-hardening
• Cold-working
• Shock-resisting
• High-speed
• Hot-working

The cold-working group consists of three grade types: oil-hardening, air-hardening and D-grades.

Water Hardening or W-Grades

This group contains low-cost, high-carbon steels with high hardness. The price factor makes it the most widely used group of tool steels in steel fabrication.

However, fragility is a side-effect of the W-grade’s hardness. Also, they are not suitable for working at elevated temperatures.

The name derives from the fact that all steels in this group are water-quenched. Water quenching may result in cracks and warping more often than oil quenching or air hardening. This is also why the sales, although still leading, have been decreasing compared to other grades.

The most common applications of W-grade tool steels include:

• Cutters and knives
• Cutlery
• Embossing
• Drills
• Razor blades
• Lathe tools

Air Hardening or A-Grades (Cold-Working)

A-grade tool steels have a higher content of chromium, which results in a better response to heat treatment. The machinability of A-grade tool steels is quite good. In addition, they have great wear resistance and toughness properties.

The most common applications of A-grade tool steels include, but are not limited to:

• Cams
• Bending dies
• Blanking dies
• Coining dies
• Embossing dies
• Lamination dies
• Chipper knives
• Lathe centres
• Injection moulding and die casting moulds
• Cold extrusion punches

D-Grades (Cold-Working)

In this group, we find the tool steels that combine W-grade and A-grade characteristics. On one hand, they contain a higher amount of carbon compared to the water-hardening type. On the other hand, they have the properties described above which are typical of the air-hardening type.

Because of their high chromium content, D series tool steels are often also categorised as stainless. But the corrosion protection is actually pretty limited.

The most common applications include:

• Burnishing tools
• Cutters
• Cold extrusion dies
• Lamination dies
• Woodworking knives
• Lathe centres
• Drawing punches
• Plastic injection moulds
• Seaming rolls
• Forming rolls

Oil Hardening or O-Grades (Cold-Working)

This tool steel group has great resistance to abrasion and high toughness properties. It is considered to be a general-purpose steel, making it very versatile.

Most of the applications are similar to those of A-grade and D-grade tool steels, but also include:

• Bushings
• Chasers for thread-cutting
• Collets
• Master engraving rolls
• Gauges
• Punches

Shock-Resisting or S-grades

This group contains low-carbon tool steels that have very high toughness values. That allows them to be very resistant to shock at both low and high temperatures.

However, they are not very resistant to abrasion because of the same low carbon content.

The most relevant applications of S-grade tool steels are:

• Jackhammer parts
• Blacksmith chisels
• Cold working chisels
• Hot working chisels
• Clutch parts
• Hot forming dies
• Cold gripper dies
• Chipper knives
• Pneumatic tools
• Hot stamps

High-Speed Tool Steel

These tool steels are especially common in cutting tools.

Mechanical cutting methods result in a lot of heat generation. High-speed steels do not lose their hardness at high temperatures, though, making this a perfect use case for them.

Common applications for high-speed steels:

• Power-saw blades
• Drill bits
• Milling cutters
• Gear cutters
• Router bits

Hot-Working or H-Grades

When cutting material at very high temperatures, you may want to use a tool steel from this group. The high toughness and hardness values keep their characteristics while working at high temperatures for long periods.

This is achieved by having a low carbon content, but a high content of other alloying elements. 

The most common applications of H-grade tool steels include:

• Casings
• Hot forging
• Dummy blocks for hot extrusion
• Plastic injection moulds
• Hot working punches

The choice of the tool steel you really need depends on the properties your specific application requires. The most common mechanical properties to consider are surface hardness, toughness, working temperature and shock resistance.

At the same time, it is important to include the cost of each material in the assessment matrix.

Also, it is very useful to answer questions about the requirements of sharp edges or cutting, how important abrasion resistance is, and the heat treatment method required.

With all this information, you should be ready to go and make your choice!