X‐Ray Line Profile Analysis of Surface Microstrain and Dislocation Evolution in Laser Shock‐Peened Carburized M50NiL Steel

This study examines how laser shock peening (LSP) modifies the near‐surface micromechanical state of carburized M50NiL bearing steel, with emphasis on the evolution of microstrain, internal stress, strain energy density (SED), and dislocation state in retained austenite (RA) and martensite. X‐ray line profile analysis (XLPA) based on classical and modified Williamson–Hall methods was employed to quantify these parameters. LSP markedly increases microstrain, internal stress, and SED, with RA showing a stronger response than martensite. In RA, microstrain rises from 0.155% to 0.464%, internal stress from 674 to 888 MPa, and SED from 522 to 2060 kJ·m −3 as the laser energy increases to 13 J. The corresponding values in martensite change from 0.164% to 0.312%, 814–924 MPa, and 667–1441 kJ·m −3 , respectively. Dislocation density in RA increases from 1.35 × 10 15 to 3.65 × 10 15 m −2 , compared with a more moderate rise from 3.46 × 10 15 to 5.14 × 10 15 m −2 in martensite. Moreover, RA exhibits a clear shift toward a higher edge‐dislocation component, whereas the dislocation character in martensite remains essentially unchanged. These results demonstrate the strong impact of LSP on surface mechanical properties and establish XLPA as a simple and efficient tool for evaluating LSP‐induced effects in metallic materials.