M-2 is the tungsten-molybdenum high speed steel that has become the favorite for all general purpose applications. It has a wider heat treating range than most of the molybdenum high speed steels, and has the resistance to decarburization that is characteristic of the tungsten types. It offers an excellent combination of good red hardness, toughness, and wear resistance.
Heating for forging must be done slowly and uniformly, with care being taken not to put cold steel into a hot furnace. Soak through at 1700-1800°F and then heat to 1900-2050°F for initial forging. Do not forge below 1600-1700°F, and when forging is completed, cool slowly in lime, mica, dry ashes or furnace.
Heat slowly to 1500-1550°F, hold until the entire mass is heated through, and cool slowly in the furnace (30°F or hour) to about 1000°F, after which the cooling rate may be increased. Suitable precautions must be taken to prevent excessive carburization or decarburization.
Cool in air, oil, or molten salt bath operating at 1000-1100°F. In the case of oil quenching, it is usually good practice to interrupt the quench by removing the tool after it has reached about 1000°F, and allow the cooling to continue in still air. Where a salt bath is used, the tool should be held only long enough to equalize at the bath temperature, and then should removed and cooled in air. Any necessary straightening should be done while cooling in the range of 850-450°F. Tools should be allowed to cool to 150°F, or to where they can be held in the bare hand, and then tempered immediately.
The tempering temperature may be varied according to the desired hardness, but is usually in the range of 1000-1100°F. Double tempering is always recommended. The response to tempering is shown in the following chart.
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