Effect of Multi-Step Tempering on Retained Austenite and Mechanical Properties of Low Alloy Steel

The effect of multi-step tempering on retained austenite content and mechanical properties of low alloy steel used in the forged cold back-up roll was investigated. Microstructural evolutions were characterized by optical microscope, X-ray diffraction, scanning electron microscope and Feritscope, while the mechanical properties were determined by hardness and tensile tests. The results revealed that the content of retained austenite decreased by about 2% after multi-step tempering. However, the content of retained austenite increased from 3.6% to 5.1% by increasing multi-step tempering temperature. The hardness and tensile strength increased as the austenitization temperature changed from 800 to 920 °C, while above 920 °C, hardness and tensile strength decreased. In addition, the maximum values of hardness, ultimate and yield strength were obtained via triple tempering at 520 °C, while beyond 520 °C, the hardness, ultimate and yield strength decreased sharply.