result in an improved surface finish on parts machined therewith the present invention and its advantages can be more completely understood from the following example a series of cemented carbide inserts were prepared having a boron carbide external coating atop sequential titanium nitride titanium carbide alumina and titanium nitride layers the cemented carbide inserts were sandvik ab type rnma 43gc415 tapered tool inserts 3 16 inch 4 7 mm high by 1 2 inch 12 7 mm diameter the inserts had an inner layer less than 1 micron thick of titanium nitride a 2 micron layer of titanium carbide atop the titanium nitride layer a 5 micron layer of alumina atop the titanium carbide layer and an external one micron layer of titanium nitride all of the layers had been applied by chemical vapor deposition the inserts were then coated by d c magnetron sputtering the sputtering target was b 4 c formed by hot pressing 99 percent pure crystalline b 4 c powder disordered boron carbide coatings approximately 2 5 microns thick were deposited atop the titanium nitride titanium carbide alumina titanium nitride coated cemented tool inserts the inserts were tested for their ability to remove a 0 100 inch 964l weldment from a four inch 10 cm high 25 inch 63 5 cm diameter die the weldment had a rockwell c hardness of 54 to 58 metal removal was carried out to remove a 0 100.