Cumulative second-harmonic analysis of ultrasonic Lamb waves for ageing behavior study of modified-HP austenite steel

► We analyze the nonlinear Lamb wave for ageing behavior study in Fe-Cr-Ni steels. ► Nonlinear Lamb wave increases with formation of precipitate at early ageing time. ► It keeps as a plateau with precipitate dynamic balance for a long-term ageing. ► It reduces at final ageing time for precipitate coarsening and microvoids initiation. ► Variation of nonlinear Lamb wave follows same trend as that of hardness in samples.