Abstract: Described is the heat treatment of the N80 black casing by means of the on-line internal-external water spray quenching process and the off-line temper process on the hot rolling production line in Tianjin Municipal Seamless Steel Tube Plant based on the application of the forging heat treatment process theory and the relevant process simulation tests.The operation practice proves the quenching and tempering process is capable of ensuring the consistence of the overall mechanical properties thus meeting the expected targets in the massive production of the N80 casings.Moreover the said heat treatment process is also an energy saving one.