Definition of terms
Tool steels are exclusively (not necessarily rust-free) stainless steels , which are mainly used for machining or processing workpieces. Tool steels can also be used to manufacture handling equipment and measuring devices .
Properties of tool steels
Tool steels have a variety of different properties. Depending on the application, a tool steel must be selected whose properties meet all given boundary conditions. This selection process can be very time-consuming if, for example, diametrically running properties, including high hardness combined with high toughness , are required. In this case, it must be considered which property has a more significant impact on tool life.
The table below lists some of the most important properties of tool steels. The tensile strength in particular relates to values in the quenched and tempered condition of tool steels.
|property||unit||Value range (approx.)|
|tensile strenght||Megapascal (MPa)||800-1500|
|Modulus of elasticity||MPa||210,000-246,000|
|Maximum hard work||Hardness Rockwell Scale C (HRC)||40-72|
|Notched impact strength||Joule (J)|
|Maximum surface temperature||Degrees Celsius (° C)||up to 615|
|Corrosion resistance||mm / year||0.001 - over 1|
In addition to these criteria, there are others. For example, the machinability in the delivery condition (see machinability of steel ) is an essential aspect of the steel selection in some applications. Computer programs are used to find the most suitable tool steel for a tool on the basis of several criteria.
Setting the properties
With many tool steels, the properties can be adapted to the requirements of the application by means of suitable heat treatment . The most frequently used heat treatment is quenching and tempering . Depending on the application, for example, a high level of hardness may be necessary and at the same time the toughness may only be relevant to a very limited extent. This means that the material can be operated close to or at maximum case hardness. The maximum useful hardness is usually given in the data sheets for the individual materials. An example of this is a data sheet from erasteel.com. It can be clearly seen how the toughness decreases with increasing hardness.
If the wear resistance of the material is insufficient, it can be increased by further measures. These are among others:
- the application of a wear-reducing layer, including CVD layer , PVD layer , DLC layer, etc. and
- the change of material properties , for example by nitriding .
In all processes, it is essential to ensure that the process temperature does not lie above the previously selected tempering temperature of the base material, in this case tool steel, as otherwise there will be a loss of hardness or strength and the component produced may under certain circumstances occur in use Cannot withstand stresses or cannot withstand stress for a long enough time.
Tool steels can be characterized according to various aspects. On the one hand, a distinction can be made according to the composition and, on the other hand, according to the temperature range which should be maintained during use. In terms of composition, tool steels are divided into unalloyed and alloyed steels. With regard to the temperature range, a distinction is made between cold and hot work steels. So-called high - speed steels are a special class of hot-work steels . Furthermore, a classification can be made according to the area of application.
Areas of application
Tool steels are used for a variety of applications. Depending on the properties of the material, the following areas of application can be considered. Tool steels are mainly used to manufacture active elements of tools, for example punches and dies. The breakdown in the following table is based on DIN 8580 (manufacturing process) .
|Forming process||Exemplary procedure||Active elements|
|Pressure forming||Rolling , extrusion , extrusion||Rollers, punches, dies, reinforcement rings|
|Tensile compression forming||Drawing through , deep drawing , hydroforming||Drawing die, punch, die, hold-down device|
|Tensile forming||Depths , lengths , widths||Punch, die|
|Bending||Free bending , die bending , roll forming||Die, rolling, bending bar|
|Shear forming||Twisting, shifting||die|
Alloyed tool steels
The main alloying elements of tool steels besides carbon can be found in the table below. Depending on the requirement profile of the steel, various alloying elements are added to the steel composition .
|Chromium (Cr)||Hardenability, corrosion resistance||Notched impact strength , weldability|
|Cobalt (Co)||Heat resistance, temper brittleness||---|
|Manganese (Mn)||Hardenability, yield point, tensile strength,||Thermal expansion|
|Molybdenum (Mo)||Hardenability, temper brittleness, yield point, tensile strength, high temperature strength||Scale resistance|
|Nickel (Ni)||Yield strength, notch toughness, toughness,
|Nitrogen (N)||Stress-cracking corrosion resistance, work hardening , strength||Blue brittleness, sensitivity to aging|
|Vanadium (V)||Wear resistance, heat resistance, tempering resistance||---|
|Tungsten (W)||Tensile strength, yield point, toughness,
heat resistance, wear resistance
Cold work steels
Cold work steels are generally used if the temperature on the surface does not exceed 200 ° C during use. If this temperature is exceeded, there is usually a drop in hardness, since cold work steels have only a very low tempering resistance. Cold work steels can be both alloyed and unalloyed tool steels. The following table lists unalloyed, low-alloy and high-alloy cold work tool steels.
|C 45 W||1.1730||Unalloyed|
|C 85 W||1.1830||Unalloyed|
|90 MnCrV 8||1.2842||Low alloy|
|100 Cr 6||1.2067||Low alloy|
|21 MnCr 5||1.2162||Low alloy|
|X 210 Cr 12||1.2080||High alloy|
|X 155 CrVMo 12 1||1.2379||High alloy|
|X 36 CrMo 17||1.2316||High alloy|
Hot work tool steels
If a surface temperature of more than 200 ° C can occur during use, the use of a hot-work tool steel is indicated. This type of steel is almost exclusively made of high-alloy steels to improve the tempering resistance and hot hardness. In addition, they must have sufficient wear resistance at hot hardness even at temperatures above 200 ° C. Hot-work steels are used in particular for the production of forging dies . A selection of hot work tool steels is listed in the table below.
|X38 CrMoV 5 1||1.2343||High alloy|
|X40 CrMoV 5 1||1.2344||High alloy|
|X32 CrMoV 3 3||1.2365||High alloy|
Unalloyed tool steels
The carbon content of unalloyed tool steels is between 0.5% and 1.5%, and often small amounts of tungsten are still contained. The hardening of the surface is drastically increased by tempering , and the hardenability is essentially dependent on the carbon content of the steel . However, unalloyed tool steels cannot be fully hardened (high critical cooling rate) and are also not suitable for high operating temperatures, since the temperature-related decrease in hardness occurs at around 200 ° C. That is why the unalloyed tool steels fall into the cold work tool steel category .
Simple cutting plates and punches as well as drawing and bending tools are made from this steel.
Examples: C85W1 → tool steel, quality class 1; C85W2 → tool steel, grade 2
- Johannes Noneder: Stress recording for the validation of FE models for the design of massive forming tools. In: Manufacturing Technology Erlangen. No. 255, Meisenbach, Bamberg, 2014, ISBN 978-3-87525-371-9
- Crucible Industries: CPM® REX® 121 (HS) * High hardness high vanadium cobalt high speed steel , accessed January 7, 2017
- Böhler-Uddeholm: Hot-work steel (PDF, 0.94 MB) ( Memento from April 22, 2014 in the Internet Archive ), accessed on January 7, 2017
- ASP®2015 ( English , PDF) erasteel.com. Retrieved November 12, 2019.