These are high carbon steel alloys that have been designed to provide wear resistance and toughness combined with high strength.Tool steels typically have excess carbides (carbon alloys) which make them hard and wear-resistant. Most tool steels are used in a heat-treated state, generally hardened and tempered.

Tool Steel Types:
 

Water Hardened tool steels
Cold worked tool steels
Shock resisting Tool Steels
High-Speed Tool Steels
Hot-Worked Tool Steels
Plastic Mold Tool Steels
Special-Purpose Tool Steels

Water Hardened tool steels
(W grade)high carbon plain carbon steels, Water-Hardening Tool steels include all class W tool steels, and while they do not retain hardness well at elevated temperatures, they do have high resistance to surface wear. Typical applications include blanking dies, files, drills, taps, countersinks, reamers, jewelry dies, and cold-striking dies.

Advantages:

_ Account for a large percentage of all the tool steels

_ Least expensive.

Disadvantages

_ Usually the parts are quite small

_ Not used in severe usage or elevated temperatures.

_ Because their hardenability is low, they should be used only for thin sections.

_ They are brittle, especially at their higher hardness.

_ Prolonged exposure to temperatures over 300F usually results in undesired softening. Typical uses depending on the carbon content

_ 0.60-0.75% carbon: medium hardness with good toughness and shock resistance. Examples: machine parts, chisels, setscrew

_ 0.75-0.90%- forging dies, hammers, sledges

_ 0.90-1.1% - general purpose tooling - good wear resistance and toughness. Examples of drills, cutters, shear blades, heavy duty cutting edges.

_ 1.10-1.30% extremely hard, but little toughness. Examples are small drills, lathe tools, razor blades, and other light duty applications.

Cold worked tool steels
(O for Oil, A for Air, D for diffused) these contain certain alloys to help hardenability without severe quenching.: Cold-work tool steels include all high-chromium class D, medium-alloy air-hardening class A alloys, water hardening W alloys, and oil hardening O alloys. Typical applications include cold working operations such as stamping dies, draw dies, burnishing tools, coining tools, and shear blades.

Advantages

_ for larger parts because the quench is not as severe

_ better dimensional stability

_ cracking tendency is reduced

Disadvantage

_ generally require annealing treatment before they can be machined. After machining, they are hardened and tempered and can retain full hardness at temperatures up to 800F

Typical Uses

_ forging dies, die casting die blocks, drawing dies

Shock resisting Tool Steels (S)
Cold-work tool steels include all class S alloys. They are among the toughest of the tool steels, and are typically used for screw driver blades, shear blades, chisels, knockout pins, punches, and riveting tools.

Advantages

_ Low carbon content for toughness, but the alloys have carbide for good abrasion resistance, hardenability, and hot-work.

Typical Uses

_ Hot and cold impact use

High-Speed Tool Steels
(T for tungsten based and M for molybdenum based) High-speed alloys include all molybdenum (M1 to M52) and tungsten (T1 to T15) class alloys. High-speed tools steels can be hardened to 62-67 HRC and can maintain this hardness in service temperatures as high as 540 °C (1004°F), making them very useful in high-speed machinery. Typical applications are end mills, drills, lathe tools, planar tools, punches, reamers, routers, taps, saws, broaches, chasers, and hobs.

For modern industrial production, in particular mass production, machining is one of the most important shaping and forming processes. Almost all tools employed for this purpose are made from high speed steels.In recent times, the use of high speed steels has gained increasing importance for chipless shaping, e.g. for extrusion, blanking and punching tools.

With regard to chemical composition, a clear distinction is made between 'Tungsten', 'Molybdenum' and 'Tungsten-Molybdenum' alloyed high speed steel grades, which depending on the dominant stresses they will be exposed to, contain different amounts of Carbon, Vanadium and Cobalt.
The characteristic properties of all high speed steel grades include:

- High working hardness

- High wear resistance

- Excellent toughness

- High retention of hardness and Red hardness

The influence of alloying elements on steel properties:

Carbon
Forms carbides, increases wear resistance, responsible for the basic matrix hardness.
Tungsten & Molybdenum
Improves red hardness, retention of hardness and high temperature strength, forms special carbides of great hardness.
Vanadium
Forms special carbides of supreme hardness, increases high temperature wear resistance, retention of hardness and high temperature strength.
Chromium
Promotes depth hardening, produces readily soluble carbides.
Cobalt
Improves red hardness and retention of hardness.
Aluminum
Improves retention of hardness and red hardness

 

Advantages

_ Can be used for red-hot (1400F) applications

_ Good shock resistance

_ Good abrasion resistance

Typical Uses

_ wide variety of cutting applications

Hot-Worked Tool Steels (H)
Hot-work tool steels include all chromium, tungsten, and molybdenum class H alloys. They are typically used for forging, die casting, heading, piercing, trim, extrusion, and hot-shear and punching blades. Generally the term 'hot work steels' includes tool steels which adopt a constant temperature about 200°C during application. Consequently, hot work applications involves the usual stresses which tool steels are subjected to, plus, thermal stresses due to the contact between tools and hot materials during forming.

Hot work steels must exhibit good heat checking resistance in order to delay the formation of chill cracks appearing on the surface in reticulate shape as a consequence of frequent temperature changes in the surface region.
To avoid hot cracks, i.e. tension cracks developing primarily in tools with deep cavities at sectional transitions and edges, hot work steels have to feature good high temperature toughness.

For tools subjected to high impact, pressure, or tensile stresses at elevated temperatures, special attention must be paid to high strength at the various working temperatures. If the structural state is changed by the influence of heat, the strength at ambient temperature and consequently the strength at working temperature are reduced. This is why good high temperature strength and superior retention of hardness are prerequisites for stability of shape.
Excellent high temperature wear resistance is necessary for ensuring satisfactory tool life.

Further demands that must be met by hot work steels are low tendency to adhere to parts being processed, high resistance to erosion, high temperature corrosion and oxidation, dimensional stability during heat treatment, good machinability, and in some cases also good cold hobbing properties

Advantages

_ Strength at elevated temperatures

_ Hardness at elevated temperatures

Plastic Mold Tool Steels  (P)
Designed to meet plastic injection molding dies.Mold steels include all low-carbon and one medium-carbon class P tool steels. They are typically used for compression and injection molds for plastics, and die-casting dies.
Plastic mould steels generally fall into two specific groups, namely those for:
'bolsters and larger tools' and those for 'inserts and smaller tools'.
These groups may be further subdivided into stainless and non-stainless groups.

Requirements for bolsters and large tools include:

- Pretoughened or prehardened so as not to require subsequent heat treatment.
- Good machinability
- Good impact strength
- Good polishability

Requirements for inserts and smaller tools include:

- Good hardenability
- Enhanced wear properties
- Dimensional stability during heat treatment
- Good polishability

*Mold steels include all low-carbon and one medium-carbon class P tool steels. They are typically used for compression and injection molds for plastics, and die-casting dies

Special-Purpose Tool Steels
Special-Purpose Tool Steels include all low-alloy class L Tool steels. They are usually quenched, which makes them relatively tough and easily machinable. They are typically used for arbors, punches, taps, wrenches, drills, and brake-forming dies.