Chemical Composition
The following table shows the chemical composition of M2 molybdenum high speed tool steels.
| Element | Content (%) |
|---|---|
| C | 0.78-1.05 |
| Mn | 0.15-0.40 |
| Si | 0.20-0.45 |
| Cr | 0.20-0.45 |
| Ni | 0.3 |
| Mo | 4.50-5.50 |
| W | 5.50-6.75 |
| V | 1.75-2.20 |
| Cu | 0.25 |
| P | 0.03 |
| S | 0.03 |
Physical Properties
The physical properties of M2 molybdenum high speed tool steel are given in the following table.
| Physical properties | Metric | Imperial |
|---|---|---|
| Density | 8.16 g/cm3 | 0.294 lb/in3 |
| Melting point | 4680°C | 2600°F |
Mechanical Properties
The mechanical properties of M2 molybdenum high speed tool steel are tabulated below.
| Mechanical properties | Metric | Imperial |
|---|---|---|
| Hardness, Rockwell C (tempered at 1150°F, quenched at 2200°F) | 62 | 62 |
| Hardness, Rockwell C (as hardened, quenched at 2200°F) | 65 | 65 |
| Compressive yield strength (when tempered at 300°F) | 3250 MPa | 471000 psi |
| Izod impact unnotched (when tempered at 300°F) | 67 J | 49.4 ft-lb |
| Abrasion (loss in mm3, as-hardened; ASTM G65) | 25.8 | 25.8 |
| Abrasion (loss in mm3, tempered at 1275°F; ASTM G65) | 77.7 | 77.7 |
| Poisson’s ratio | 0.27-0.30 | 0.27-0.30 |
| Elastic modulus | 190-210 GPa | 27557-30458 ksi |
Thermal Properties
The following table shows the thermal properties of M2 molybdenum high speed tool steels.
| Thermal properties | Metric | Imperial |
|---|---|---|
| CTE, linear (@20.0 – 100°C/ 68.0 – 212°F) | 10 μm/m°C | 5.56 μin/in°F |
| CTE, linear (@20.0 – 500°C/68.0 – 932°F) | 12.2 μm/m°C | 6.78 μin/in°F |
| CTE, linear (@20.0 – 850°C/68.0 – 1560°F) | 12.6 μm/m°C | 7 μin/in°F |
Fabrication and Heat Treatment
Machinability
Shaping of M2 tool steels can be carried out using grinding methods. However, they have poor grinding capability and hence they are regarded as “medium” machinability tool steel under annealed conditions. The machinability of these steels is only 50% of that of the easily machinable W group or water hardening tool steels.
Heat Treatment
M2 tool steels are pre-heated prior to hardening at 2610°C (4730°F) followed by rapid heating from 2610°C (4730°F) to 3960°C (7160°F). These steels are then cooled for 3 to 5 min and quenched in air, salt bath or oil.
Annealing
M2 tool steels are annealed at 1204°C (2200°F) and cooled at 72°C (162°F) per hour or even less.
Tempering
M2 steels are tempered at 552°C (1025°F) to obtain Rockwell C hardness from 60 to 65.
Hardening
Finally, M2 steels are hardened by heat treatment and quenching.
Applications
M2 tool steels are suitable for making cutting tools.
