Microstructure and mechanical properties of Y-modified low-activation austenitic steel after aging

Abstract

The features of microstructure and mechanical properties of yttrium-modified low-activation austenitic steel after high-temperature aging at 700 °C during 100 h are investigated. Using transmission and scanning electron microscopy, it is shown that aging results in the precipitation of dispersed particles of M₂₃C₆ carbides (M–Cr, Mn, Fe). These particles are found along the grain boundaries and inside the grains in the form of shells on dispersed particles of MC carbides (M–Ti, Ta, V), as well as at the boundaries of micro- and nanotwins. The strength properties of the steel are studied in tensile tests at 20, 650 and 700 °C. It is shown that an intense precipitation of carbides has a significant effect on the mechanical properties of this steel. After aging of the quenched state, the yield strength increases at all test temperatures used in this study, while the elongation to failure decreases by a factor of 1.6. This is due to the precipitation of carbide particles. After aging of the cold-rolled state, the yield strength decreases by 1.3–2 times, while the values of elongation to failure do not practically change. This is due to the intensive recovery of the dislocation substructure and the prevailing precipitation of carbides along the boundaries of micro- and nanotwins under aging of the cold-deformed state.