Types
High speed steels belong to the Fe-C-X multi-component alloy system where X represents chromium, tungsten, molybdenum, vanadium, or cobalt. Generally, the X component is present in excess of 7%, along with more than 0.60% carbon. (However, their alloying element percentages do not alone bestow the hardness-retaining properties; they also require appropriate high-temperature heat treatment in order to become true HSS; see History above.)
In the unified numbering system (UNS), tungsten-type grades (e.g. T1, T15) are assigned numbers in the T120xx series, while molybdenum (e.g. M2, M48) and intermediate types are T113xx. ASTM standards recognize 7 tungsten types and 17 molybdenum types.
The addition of about 10% of tungsten and molybdenum in total maximises efficiently the hardness and toughness of high speed steels and maintains these properties at the high temperatures generated when cutting metals.
| Grade | C | Cr | Mo | W | V | Co | Mn | Si |
|---|---|---|---|---|---|---|---|---|
| T1 | 0.65–0.80 | 3.75–4.00 | - | 17.25–18.75 | 0.9–1.3 | - | 0.1–0.4 | 0.2–0.4 |
| M2 | 0.95 | 4.2 | 5.0 | 6.0 | 2.0 | - | - | - |
| M7 | 1.00 | 3.8 | 8.7 | 1.6 | 2.0 | - | - | - |
| M35 | 0.94 | 4.1 | 5.0 | 6.0 | 2.0 | 5.0 | - | - |
| M42 | 1.10 | 3.8 | 9.5 | 1.5 | 1.2 | 8.0 | - | - |
| Note that impurity limits are not included | ||||||||
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