Borating

the impregnation of the surface of objects made from steel and certain other metals with boron in order to increase the hardness (up to a Vickers hardness of 1,400), heat resistance, and wear resistance (particularly for abrasion). Electrolytic borating in molten borax (the object is the cathode and the anode is made of graphite) is the chief method employed. When soaked for six to eight hours at a temperature of 930° C, a borated layer of 0.15 to 0.25 mm is obtained (the outer zone of the layer consists of the boride FeB and the inner of the boride Fe₂B). A less frequently used method for borating involves molten borax with the addition of powdered boron carbide (30 to 40 percent) or silicon carbide (30 percent). Sometimes the borating is performed in a vacuum furnace or in a gaseous medium (H₂B₆ + H₂); after borating the surface is hardened or given an isothermal heat treatment. Borating is employed in the manufacture of bushings for drilling pumps and for small tools for bending, forming, and drawing, as well as for dies, compression molds, shafts, studs, rollers, and so on.