308,346. Mannesmannr÷hren-Werke March 22, 1928, [Convention date]. Annealing and tempering.-In a process for heat-treating boring or drilling tubes or rods the tubes &c. are quenched in oil or water and annealed by heating above the Ac3 point, e.g. 810‹ C., and cooling or quenching, the tubes or rods to be treated coming direct from the rolling mills or being subsequently raised to the rolling temperature. The tube &c. may be heated again to 570‹ C. and cooled as before.