Non-destructive testing by acoustic signature of damage level in 304L steel samples submitted to rolling, tensile test and thermal annealing treatments

Acoustic signatures are used to detect in a non-destructive way the damage of rolled and drawn plates of 304L stainless steel from measurements of the propagation velocity VR of ultrasonic Rayleigh waves. This parameter is compared with the relative thickness decrease ‘ε’ of the sample. Upon rolling, VR decreases gradually for ε exceeding 5%. The corresponding evolution of wave attenuation and standard deviation of velocity indicate the damage of the sample structure as ε increases. Dynamic Young’s moduli calculated from acoustic velocity measurements show a small evolution. Under tensile tests, VR reduces more rapidly as a function of ε than for rolled samples. A tempering process of 2 h at 250°C applied to a sample with ε=48% produces no detectable variations of the Rayleigh velocity, while annealing for 30 min at 850°C induces large changes.