Higher harmonic analysis of ultrasonic signal for ageing behaviour study of C-250 grade maraging steel

Higher order harmonic analysis of ultrasonic signal has been applied to study the precipitation kinetics of 18Ni maraging steel. The material has been solution annealed (SA) at a temperature of 1088 K for 1 h and then air quenched. Ageing of SA materials have been done at 728 K for different durations of 10 min to 100 h and air cooled. It has been found that the measurement parameter of this new technique increases with the formation of finer precipitates at the initial stage of ageing till 12 h and then decreases at longer holding time with the coarsening of precipitates.