Gears tooth hardness

For example, a common process encountered in industry is the heat treating of alloy steel parts to produce a locally hard surface (e.g., bearing or gear tooth wear surface). Though only a very small fraction of the material actually needs to be hardened, conventional technology has required that the entire part be heated to about 1650°F, then quenched at 350°F in oil to produce a hard martensite structure in the steel. 

Hard Formation Bits. The heel or outermost row on each cone is the driving row, that is, this row generates a rock gear pattern on the bottom of the borehole that, in the case of these strong rocks, is not easily broken away from the wall of the borehole. The numbers of heel row teeth used on each of the three cones are selected to prevent the heel teeth from tracking," or exactly following in the path of the preceding cone, which would cause abnormally deep rock tooth holes on the borehole bottom. 

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