Stelco Inc.

Robert William Pugh

A grinding rod chemistry enhances wearability and durability of a steel rod and comprises levels of carbon to achieve a surface hardness in excess of 55 Rockwell C and levels of chromium which achieve significant depth in the formed outer martensite shell. The grinding rod has a core greater than 99% pearlite with a hardness less than 45 Rockwell C and the end portions of the rod are soft and have a hardness less than 35 Rockwell C. The steel bar of the selected chemistry is treated by reheating to above its austenitising temperature, transferring with minimal cooling to an open tubular quench vessel while securing the bar in the vessel to minimize bar warping, introducing quench water into the inlet end of the vessel and passing the liquid through the vessel to ensure uniform heat removal. The outer martensite shell is tempered by allowing the bar to soak back after quenching. The bar end portions are reheated in a furnace to elevate the end portions above the austenitising temperature and air cooling each end portion to provide the engineered end portion hardness of less than 35 Rockwell C.

Grinding rod chemistry and method of heat treatment to enhance

A grinding rod having a hardened outer shell of tempered martensite is adapted for use in heavy duty grinding environments. The rod is stress relieved to reduce internal compressive stresses in the tempered martensitic shell to less than 60 ksi and greater than 15 ksi. Such stress relieve stabilizes the rod against break-up as caused by the balancing tensile stresses in the pearlitic core exceeding tensile strength of the core.

Stress relieved grinding rod having hard outer shell

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 reheating a formed steel bar to above its austenitising temperature, transferring with minimal cooling the reheated 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 reheating 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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Sherwood Park, Canada

Robert William Pugh