Most bits are made of high-speed steel (HSS), either 100 percent or alloyed or bonded with another material. Chrome vanadium steel resists corrosion and holds its edge longer than plain HSS bits. Cobalt-alloyed steel is even harder (and more expensive) and used on steel as well as softer materials like wood, plastic and aluminum. Tungsten carbide bits have a ceramic tip bonded to the steel and are used for concrete, masonry, glass and tile. Match your bit material with your project needs.