Tool Steel M2
M2 tool steel is a molybdenum high-speed steel of the M group according to the AISI classification, representing more than 95% of high-speed steels manufactured in the United States. It has a high carbon content and superior wear resistance compared to M1 high-speed steel. Its combination of molybdenum, tungsten, and vanadium gives it excellent cutting ability at high temperatures, maintaining hardnesses above 60 HRC even under severe working conditions. It is normally supplied in the annealed condition and can be coated with titanium nitride or titanium carbide by physical vapor deposition to further improve its service life.
Chemical Composition
Section titled “Chemical Composition”| Element | Content (%) |
|---|---|
| Carbon (C) | 0.78 – 1.05 |
| Manganese (Mn) | 0.15 – 0.40 |
| Silicon (Si) | 0.20 – 0.45 |
| Chromium (Cr) | 3.75 – 4.50 |
| Nickel (Ni) | ≤ 0.30 |
| Molybdenum (Mo) | 4.50 – 5.50 |
| Tungsten (W) | 5.50 – 6.75 |
| Vanadium (V) | 1.75 – 2.20 |
| Copper (Cu) | ≤ 0.25 |
| Phosphorus (P) | ≤ 0.03 |
| Sulfur (S) | ≤ 0.03 |
Physical Properties
Section titled “Physical Properties”| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density | 8.16 g/cm³ | 0.294 lb/in³ |
| Melting point | 1425 °C | 2600 °F |
Mechanical Properties
Section titled “Mechanical Properties”| Property | Condition | Value (SI) | Value (Imperial) |
|---|---|---|---|
| Rockwell C hardness | Quenched at 1204 °C (2200 °F) | 65 HRC | 65 HRC |
| Rockwell C hardness | Tempered at 621 °C (1150 °F) | 62 HRC | 62 HRC |
| Compressive strength | Tempered at 149 °C (300 °F) | 3250 MPa | 471 000 psi |
| Unnotched Izod impact | Tempered at 149 °C (300 °F) | 67 J | 49.4 ft·lb |
| Abrasion loss (ASTM G65) | As-quenched condition | 25.8 mm³ | 25.8 mm³ |
| Abrasion loss (ASTM G65) | Tempered at 691 °C (1275 °F) | 77.7 mm³ | 77.7 mm³ |
| Elastic modulus | – | 190 – 210 GPa | 27 557 – 30 458 ksi |
| Poisson’s ratio | – | 0.27 – 0.30 | 0.27 – 0.30 |
Thermal Properties
Section titled “Thermal Properties”| Property | Temperature range | Value (SI) | Value (Imperial) |
|---|---|---|---|
| Coefficient of thermal expansion (CTE) | 20 – 100 °C | 10.0 μm/m·°C | 5.56 μin/in·°F |
| Coefficient of thermal expansion (CTE) | 20 – 500 °C | 12.2 μm/m·°C | 6.78 μin/in·°F |
| Coefficient of thermal expansion (CTE) | 20 – 850 °C | 12.6 μm/m·°C | 7.00 μin/in·°F |
| Thermal conductivity | 20 °C | ~ 24 W/m·K | – |
Other Designations
Section titled “Other Designations”| Standard / Country | Designation |
|---|---|
| AISI / ASTM (USA) | M2 |
| UNS | T11302 |
| EN (Europe) | HS6-5-2 (1.3339) |
| DIN (Germany) | 1.3343 |
| AFNOR (France) | 06-05-04-02 / Z85WDCV06-05-04-02 |
| JIS (Japan) | SKH51 (similar SKH9) |
| SS (Sweden) | 2722 |
| BS (United Kingdom) | BM2 |
| UNI (Italy) | HS6-5-2 |
| ISO | HS6-5-2 |
Manufacturing and Heat Treatment
Section titled “Manufacturing and Heat Treatment”Machinability
Section titled “Machinability”The machinability of M2 steel in the annealed condition is approximately 65% to 75% that of water-hardening tool steel of group W, which corresponds to a moderately low rating. The use of cemented carbide cutting tools and reduced cutting speeds compared to low-alloy steels is recommended.
Heat Treatment
Section titled “Heat Treatment”M2 steel achieves its maximum performance through a controlled thermal cycle that includes preheating, high-temperature austenitizing, quenching, and multiple tempers. Tempering at temperatures between 540 °C and 600 °C produces significant secondary hardening, raising the hardness several HRC points above the as-quenched value.
Annealing
Section titled “Annealing”Heat uniformly to 870 – 900 °C, hold for 2 to 4 hours, and cool slowly in the furnace at a rate ≤ 10 °C/h until reaching room temperature, obtaining a typical hardness of 230 – 250 HB. This condition is suitable for machining and forming operations.
Quenching
Section titled “Quenching”Preheat in two stages: 550 – 600 °C and 850 – 900 °C. Austenitize at 1190 – 1230 °C (ideally 1210 – 1220 °C) with a soak time of 2 to 5 minutes for thin sections and up to 15 minutes for large sections. Quenching can be performed in oil, molten salt (550 °C), or by pressurized air cooling for large parts.
Tempering
Section titled “Tempering”Perform at least two tempers (preferably three) at 540 – 600 °C, each lasting 1 to 2 hours, cooling in air between cycles. The resulting hardness varies from 62 to 65 HRC depending on the exact tempering temperature. Tempering at 550 °C usually offers the best combination of hardness and toughness.
Applications
Section titled “Applications”M2 steel is widely used in the manufacture of cutting and forming tools that operate at high speeds and moderate temperatures. Typical applications include:
- Drills, milling cutters, and reamers.
- Taps.
- Blades and circular saws.
- Punches, stamping dies, and cold extrusion tools.
- Cutting tools for wood and reinforced plastics.
- Surgical and dental instruments (when high wear resistance is required).
Comparison with Similar Materials
Section titled “Comparison with Similar Materials”| Property | M2 | M1 | M7 | T1 |
|---|---|---|---|---|
| C content (%) | 0.85 | 0.80 | 1.00 | 0.75 |
| Total Mo + W (%) | 11 | 9.5 | 10.5 | 18 (only W) |
| Maximum hardness (HRC) | 65 | 65 | 65 | 65 |
| Wear resistance | High | Good | Very high | High |
| Toughness | Good | Very good | Moderate | Good |
| Relative cost | 100 % | 110 – 120 % | 130 – 140 % | 150 – 180 % |
| Primary application | Universal use | Small drills and mills | Extreme wear tools | Heavy-duty work |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the maximum hardness that M2 steel can achieve after heat treatment?
Section titled “What is the maximum hardness that M2 steel can achieve after heat treatment?”The maximum hardness in the quenched condition is 65 HRC, and after a typical temper at 540 – 600 °C, 62 – 65 HRC is obtained.
What maximum working temperature can M2 steel withstand without losing its edge?
Section titled “What maximum working temperature can M2 steel withstand without losing its edge?”It can work continuously at temperatures up to 560 °C while maintaining hardness above 58 HRC, which corresponds to a significantly higher cutting speed than carbon steels.
How much molybdenum and tungsten does the M2 alloy approximately contain?
Section titled “How much molybdenum and tungsten does the M2 alloy approximately contain?”The nominal content is 5% molybdenum and 6% tungsten, totaling about 11% by weight of carbide-forming elements.
Which European standard is directly equivalent to M2 steel?
Section titled “Which European standard is directly equivalent to M2 steel?”The closest equivalent is steel HS6-5-2 according to EN ISO 4957, also identified with material number 1.3339.
What is the typical coefficient of thermal expansion between 20 °C and 500 °C?
Section titled “What is the typical coefficient of thermal expansion between 20 °C and 500 °C?”The linear coefficient of thermal expansion is 12.2 μm/m·°C in that range, which places it at a moderate value among tool steels.
What is the compressive strength of M2 after tempering at 149 °C?
Section titled “What is the compressive strength of M2 after tempering at 149 °C?”The compressive strength reaches 3250 MPa, indicating an excellent ability to withstand loads in deformation and cutting tools.
References
Section titled “References”- azom.com: https://www.azom.com/article.aspx?ArticleID=6174
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/engineering-materials-properties-d_1225.html
- steelnumber.com: https://www.steelnumber.com/en/equivalent_steel_iron_eu.php?zname_id=11913