Jul 16 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal propertiesOther DesignationsFabrication and Heat Treatment Machinability Heat Treatment Forging Annealing Tempering HardeningApplications
Introduction
High-speed tool steels are divided into molybdenum high-speed steels and tungsten high-speed steels. Molybdenum high-speed tool steels are known as Group M steels. These steels have lower initial cost even though both types of high-speed steels are equivalent in performance. Tools made using high-speed tool steels can be coated with titanium carbide, titanium nitride, and other coatings by physical vapor deposition process for enhancing performance and prolonging life of the tool. There are different types of molybdenum high speed tool steels. Types M 1 to M 10 (except M6) consist of some tungsten, but no cobalt.
Chemical Composition
The chemical composition of M1 molybdenum high speed tool steels is tabulated below:
| Element |
Content |
| C |
0.78-0.88% |
| Mn |
0.15-0.40% |
| Si |
0.20-0.50% |
| Cr |
3.50-4.00% |
| Ni |
0.30% |
| Mo |
8.20-9.20% |
| W |
1.40-2.10% |
| V |
1.00-1.35% |
| Cu |
0.25% |
| P |
0.03% |
| S |
0.03% |
Physical Properties
The following table shows physical properties of M1 molybdenum high speed tool steel.
| Physical Properties |
Metric |
Imperial |
| Density |
7.89 g/cc |
0.285 lb/in3 |
| Melting Point |
1427°C |
2600°F |
Mechanical Properties
The mechanical properties of M1 molybdenum high speed tool steels are outlined in the following table.
| Mechanical Properties |
Metric |
Imperial |
| Hardness, Rockwell C |
60.0 - 65.0 |
60.0 - 65.0 |
| Poisson's ratio |
0.27-0.30 |
0.27-0.30 |
| Elastic modulus |
190-210 GPa |
27557 – 30457 ksi |
Thermal Properties
The following table shows thermal properties of M1 molybdenum high speed tool steels.
| Thermal properties |
Metric |
Imperial |
| CTE, linear |
10.1 μm/m °C |
5.61 μin/in °F |
Other Designations
Other designations that are equivalent to AISI M1 molybdenum high speed tool steel include:
- AFNOR 08-04-02-01
- DIN 1.3346
- UNI X 82 MoW 09 KU
- B.S. BM 1
- FED QQ-T-590
- SAE J437
- UNS T11301
- ASTM A600 (M-1)
- SAE J438 (M-1)
Fabrication and Heat Treatment
Machinability
M1 steels are medium machinable alloys. Machining should be carried out before performing hardening by heat treatment. The machinability of M1 molybdenum high speed tool steels is 50% of that of the W group or water-hardening low alloy tool steels.
Heat Treatment
M1 steels are preheated at 760°C (1400°F ) before heat treatment. They are then heated rapidly to 1190°C (2175°F) for 3 to 5 min followed by oil-quenching, salt bathing or cooling in air. It is then subjected to tempering.
Forging
M1 molybdenum high speed tool steels are forged from 1093 to 927°C (2000 to 1700°F). They should not be forged below 927°C (1700°F).
Annealing
M1 steels are annealed at 857°C (1575°F). They are then furnace cooled at less than 4°C (40°F) per hour.
Tempering
M1 molybdenum high speed tool steels are tempered at 565°C (1050°F) for a long time in order to allow complete heating and cooling in air. The tempering process can be repeated for a second time in order to achieve best results and produce a part with hardness of 63 HRC.
Hardening
M1 steels can be hardened by heat treatment and quenching.
Applications
M1 molybdenum high speed tool steels are suitable for all types of cutting tools.