Materials for a bit

A material for a bit for drilling igneous rock having a bit leg, cutters rotatably mounted in said bit leg, bearing means interposed between said cutters and said bit leg, and ring seals arranged in said cutters near bearings, whereby said cutter is peripherally provided with cutting teeth either formed integrally therewith or separately by embedding therein cutting teeth made of hard metal such as tungalloy, said material to be used for said bit leg, said cutter, said bearing, said ring seal, etc. being steel consisting essentially of 0.10 to 0.20 wt% C, up to 0.5 wt% of Si, up to 1.0 wt% Mn, 3.0 to 5.0 wt% Cr, 0.8 to 2.0 wt% Mo, 0.10 to 0.70 wt% V, the balance being Fe, and adapted to be used after its surface layer is hardened by a carburizing process.