HSS M2 High Speed Steel - 1.3343 - HS6-5-2C - JIS ~SKH 51

M2, one of the most used high speed steel, is suitable for cold forming tools e.g. cold extrusion rams, its elevated wear resistance makes it suitable for e.g. plastic molds and can also be used for certain hot work applications. The added tungsten and molybdenum give this high speed steel the excellent combination of toughness, wear resistance, red hot hardness and the good edge retention, which make it suitable to a wide variety of applications.

General information to High Speed Steels

High Speed Steel a high alloyed tool steel, often used for drills, taps, turning tools and broaches, has a 3-4 times higher cutting speed without loosing its hardness up to a temperature of 1112°F (600°C). In comparison ordinary cold work tool steel loses its hardness at about 392°F (200°C). The foundation for its abilities can be found in its alloys as well as its martensitic microstructure.

Tungsten (W): Forms carbides (especially tungsten carbide) which increase the red hot hardness, tempering resistance and wear resistance.

Molybdenum (Mo): Molybdenum can replace tungsten and has the same effect as tungsten at half the mass. Molybdenum does form carbides, increases red hot hardness, temper- and wear resistance but has to undergo a more complex heat treatment.

Vanadium (V): It forms vanadium carbide, which, as in some other steels, increases wear resistance because of its hardness (601 HBN / 58 HRC).

Chromium (Cr): Is involved in carbide formation and improves through hardenability. This enables tools with large cross sections to be hardened.

Carbon (C): Is needed both to form martensite and carbides. The proportion is adjusted in line with the proportion of the other elements.

Cobalt (Co): Increases the temperature up to which the material can be used, meaning above which temperature martensite transforms. It prevents the growth of precipitated carbides.

Heat treatment

Annealing

Heat M2 uniformly to a temperature of 1600°F (871°C) and hold for 1 hour per inch (25.4 mm) of thickness but for a minimum of 2 hours. Then the parts are cooled down by 25°F (10°C) to 1000°F (538°C) in the furnace and continue to cool them to ambient temperature either in the furnace or air.

Stress relieving

After heavy machining M2 it is recommended to stress relieve the parts before hardening them to minimize distortion. Heat the material to a temperature of 1166-1202°F (630-650°C), hold for approx. 2 hours, then cool in air to room temperature.

Hardening

To harden M2 first preheat the material, in an air circulating furnace, uniformly to a temperature of 752°F (400°C), then increase the heat uniformly to 1562°F (850°C) and for the final preheating stage increase the heat from 1562°F (850°C) to 1922°F (1050°C). Then rapidly take the temperature to 2174-2246°F (1190-1230°C) and soak for 5-15 minutes.

Quenching media

• Salt bath – quench to a temperature of 1000-1100°F (538-593°C), then cool further to 150°F (66°C). After the quench the material has to be tempered immediately.
• Vacuum – quench to a temperature below 1000°F (538°C) at a rate of 50°F (10°C), then cool to ambient temperature.
• Air

Tempering

Heat the material to 986-1040°F (530-560°C) and hold for a minimum of 2 hours. It is recommended to double temper this material.

Machinability

In the annealed condition, M2 is considered a “medium” machinability steel with poor grindability capabilities.

Forging

Preheat the material slowly to 1562-1652°F (850-900°C) and then continue to increase the temperature more quickly to the forging temperature of 1922-2102°F (1050-1150°C). Do not let the temperature drop below 1616-1652°F (880-900°C) and larger parts can be cool slowly in the furnace when finished forging. Small and uncomplicated forgings can be cooled in lime or ashes.

Note, this is not an annealing, when cooled down properly, the parts should be annealed.