Evaluating surface hardened steels by laser-acoustics

► Surface acoustic waves can be used to determine the hardening depth of steels non-destructively. ► The hardened layer has a lower acoustic velocity than the non-hardened steel. ► This effect depends on the steel grade and is in the range from 45 to 70 m/s. ► A laser-acoustic hand-held probe was developed to measure the wave velocity. ► Hardening depth and surface hardness could be determined with an uncertainty of lower than 5%.