Hot Forming
Hot forming operations include forging, extrusion, hot upsetting, piercing, and any other operations involving deformation of solid hot metal at relatively high temperatures. Generally, the environment is at least 600/800°F, and may exceed 2000°F, as in forging of ferrous alloys. Tools and dies will typically be required to run at temperatures of 800/1200 F.
Tool steels should be chosen according to the specific conditions of the forming process. Generally, forming of non-ferrous alloys requires lower temperatures, and thus permits a wider selection of tooling material. Up to about 900/1000 F, all of these steels are capable of maintaining reasonable properties. In general, CPM 9V, Halcomb 218, Chro-Mow, Nu-Die V (Nu-Die XL), and Crucible 161 may be used up to about 1000/1100 F; WR-95 is usable to about 1100/1200 F; and Halcomb 425 and Peerless A may be required for die temperatures up to about 1250 F. When tools will be expected to operate for long times at tool temperatures above about 1300 F, non-ferrous high-temperature alloys may be required, as such temperatures may be high enough to cause severe softening of most die steels, sometimes to the point of completely eradicating the original heat treatment at the surface of the die. Refer to the charts and individual datasheets for more specific information.
Die Casting
The die casting process consists of forcing molten metal under pressure into a machined steel die. After solidification, the metal part is ejected from the die, the die is cooled, and the cycle is repeated. Die steels for die casting must be able to withstand the thermal shock of extreme temperature swings, from the heat of molten aluminum, magnesium, zinc, or brass, to the cooling effects of internal water lines, die lubricants, and die surface coolants. These environments require a combination of heat check (thermal fatigue) resistance, toughness, and high temperature strength (hot hardness, temper resistance).
Die steels should be chosen to accommodate the appropriate service temperatures. Generally, molten aluminum and magnesium (1100/1300°F) subject the die steel surfaces to maximum temperatures of about 900/1000°F, but occasionally higher in the case of thin die sections, uncooled inserts, heavy castings, special alloys, etc. Molten zinc presents a less severe thermal load, with casting temperatures of 800/900 F, and thus zinc casting dies do not require as high properties as aluminum or magnesium casting dies. Copper and brass, with casting temperatures of over 1700 F, may create special problems, because the molten metal temperature is high enough to cause severe softening of most die steels, sometimes to the point of completely eradicating the original heat treatment at the surface of the die.
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