| 摘要 |
A process for heat treating a steel bar to produce a grinding rod having a softer core of at least 99% pearlite and having a hardness of less than 45 Rockwell C, an outer shell of martensite having a hardness of at least 50 Rockwell C and softer end portions having a hardness of less than 35 Rockwell C, where the softer end portions each having an engineered heat treated length less than 15 cm, comprises repeating a formed steel bar to above its austenitising temperature, transferring with minimal cooling the repeated bar to an open tubular quench vessel while securing the bar in the vessel to minimize bar warping in the vessel during quenching, introducing quench water into an inlet end of the vessel and passing the quench liquid along the vessel at high surface velocities exceeding 4 meters per second relative to bar surface to minimize thereby production of steam along the bar length and ensure uniform heat removal and removing quench water at an outlet end of the vessel, quenching the bar in the vessel for a period of time which provides a uniform annular layer for the hard outer shell of tempered martensite and the softer core of pearlite, and repeating each end portion of the bar in a furnace to elevate the end portion to above the austenitising temperature and air cooling each end portion to provide the engineered end portion hardness of less than 35 Rockwell C.
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