Effects of Cooling Rate by Double Austenitizing Tempering Treatment on the Microstructure and Mechanical Properties in Low Alloy Steel

Spent nuclear fuel is stored and transported in cask bodies, but they become embrittled with the passage of time resulting in lattice defects due to neutron irradiation. Cask bodies made by the quenching and tempering (QT) treatment are not safe and are hard to store because of embrittlement caused by high levels of radiation and heat over long periods. Recently, it was shown that the double austenitizing tempering (DAT) treatment resulted in a significant improvement in strength and toughness as a result of austenite grain refinement. In this study, we evaluated the effects of DAT treatment for improving the mechanical properties of low alloy steel. We also investigated the effects of cooling rate on the DAT treatment. It was found that the charpy impact properties of the alloy were improved by the DAT treatment, which used water cooling comparing, compared to the QT heat treated specimen. As a result of microstructure analysis, it was determined that the grain size and carbide morphology were affected by mechanical properties such as the tensile, hardness and impact property.