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Banded Structure Control and Effect on Mechanical Properties of Gear Steel 18CrNiMo7-6

Effect of normalized cooling treatment on banded structure of gear steel 18CrNiMo7-6 was analyzed through metallographic microscope. Effects of banded structures with different degree on micro hardness uniformity, composition segregation, mechanical properties of test steels after quenching and tempering were analyzed through microhardness tester, scanning electron microscope, tensile testing machine, impact testing machine and metallographic microscope. The results show that, banded structure can be reduced to 1.5 degree after austenizing heat preservation at 930??, Strong wind cooling to 610??, furnace cooling to 400?? and then air cooling. But continuous rapid cooling can result in the formation of a large amount of bainite; Micro hardness range of test steels with different banded structure degree is between 30~35 HB after quenching at 850?? and tempering at 180??. Hardness uniformity and anisotropy of mechanical properties are comparable.