Forging Temperature of a metal

For Forging, a metal must be heated to a temperature at which it will possess high plastic properties both at the beginning and at the end of the forging process. For instance, the temperatures to begin the forging for soft, low carbon steels is 1250*C to 1300*C, the temperature to finish forging is 800 to 850*C. The respective temperatures for hard, high-carbon and alloy steels are 1100*C to 1150*C and 825*C to 875*C. Wrought iron is best forged at a temperature little below 1300*C . Non-ferrous alloys like brass and bronze are heated to about 600*C to 950*C, and aluminum and magnesium alloys to about 350 to 500*C

If the forging operation is finished at a lower temperature, this leads to cold hardening and cracks. With excessive heating the forgings suffer oxidation and much metal is wasted. The blanks should be heated uniformly all over and at a definite rate.

The temperature of heating steel for hand forging can be estimated by heat color which is the color of the light emitted by the heated steel. The heat color disappears when the steel cools down. For more determinations, optical pyrometers are used. Surface colors for iron and steels are given ,

Color and Temperature :

Faint Red - 500*C

Blood Red - 650*C

Cherry Red - 750*C

Bright Red - 850*C

Salmon - 900*C

Orange - 950*C

Yellow - 1050*C

White - 1200*C

FINISHING TEMPERATURE OF FORGING :

The temperature at which the hammering of the forging is left off has an important influence on the properties of the forging. When steel is heated well above the upper critical temperature, the grain begins to grow in size, and they will continue to grow as the temperature is increased. During forging, however , its grains are broken up and become finer. If the final forging temperature is high (above 910*C ), the grains will grow during the process of cooling in the air; the cold forging will then have a coarse - grained structure and low mechanical properties. If forging is finished at low temperature (below 910*C), the grains will not grow when the steel is cooled owing to the low temperature. The cold forging will then possess a fine-grained structure and high mechanical properties. If steel is hammered when it is below the lower critical temperature (about 723*C) it will be cold worked and may be given small hair cracks. Thus, if the forging of a piece of steel is finished within a temperature interval of 910 to 723*C, depending on its grade, the forging must be completed at a temperature at which further growth of the grain will not take place.

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