Effect of aging at 700 °C on the microstructure, phase transformations, and mechanical properties of low-activation austenitic steel

Abstract

The effect of aging at 700 °C for 100 h on the microstructure, phase transformations, and mechanical properties of a new high-manganese low-activation austenitic steel is studied. It is shown that a long-term high-temperature exposure results in the precipitation of dispersed particles of M₂₃C₆ carbides. The formation of these particles occurs at grain boundaries, incoherent and coherent twin boundaries, and inside grains. Particles precipitated along grain boundaries have the form of discontinuous or continuous thin films. At incoherent twin boundaries, M₂₃C₆ carbides precipitate in the form of parallel thin plates lying along the {111} crystallographic planes of austenite at a certain angle to these boundaries. At coherent twin boundaries, these particles have the form of thin plates parallel to the twinning plane, and their transverse dimensions are limited by the thickness of twins. Inside grains, M₂₃C₆ particles can have the shape of rhomboids or cuboids. The grain and twin structure remains stable during aging. The precipitation of dispersed carbides affects the strength and plastic properties of the steel. After aging of the quenched steel, the yield strength increases slightly, while the elongation decreases by 1.5–1.8 times. After aging of the cold rolled steel, the yield strength decreases by 1.3 times at all studied temperatures (20, 650, and 700 °C). In this case, the elongation to failure at 20 °C decreases by 1.7 times, while at high temperatures its values change little. The effect of dispersed M₂₃C₆ particles on the strength and plastic properties of the steel is discussed.