Steel Powders

Fully prealloyed steel powders have been made by several manufacturers since the late 1960s. Because the alloying elements are homogeneously distributed throughout their powder particles, the overall compressibility is usually moderate-poor due to increased strength of the powder particles. This is a drawback when powders are pressed at room temperature as in traditional P/M process, but this characteristic becomes irrelevant for hot powder forging applications. That is why fully prealloyed powders are widely used in powder forging applications.

Both gas- and water-atomization processes are available to produce low-alloy steel, tool steel, 12% Cr steel, high-speed steel, and stainless steel powders. The method of production preference is determined to a large extent by the powder properties desired. Water-atomized powders generally are quite irregular in shape and have relatively high surface oxygen contents. Gas-atomized powders, on the other hand, generally are more spherical or rounded in shape and, if atomized by an inert gas, generally have lower oxygen (oxide) contents. There are, of course, exceptions in each type. For highvolume, low-cost production, water atomization generally is preferred over gas atomization, providing powder characteristics are compatible with the application. In spite of these important differences, the two processes are similar in many other respects.

Atomized ferrous powders must be softened by reducing annealing at 900 °C (1652 °F) in dry, purified hydrogen to facilitate pressing and to achieve the required green density and strength necessary for subsequent processing.

0 0

Post a comment