In-situ Monitoring of Laser Surface Line Hardening by Means of Synchrotron X-Ray Diffraction

An in-situ X-ray diffraction investigation of a power controlled laser line hardeningexperiment has been carried out at the synchrotron beamline P05 at the German electron synchrotron(DESY) in Hamburg. During the process the local strain and stress evolution is monitored usingsynchrotron radiation with a time resolution of 10 Hz. Samples made of steel grade AISI 4140 wereline hardened by means of a high-power diode laser (HPDL) unit at constant laser feed. A speciallydesigned process chamber was used, allowing the control of the inert gas atmosphere to avoid oxidescale formation. Through the symmetric application of 4 fast micro-strip line detectors various{hkl} - diffraction lines were recorded during the short-time heat treatment by means of the singleexposure approach. Thermal and elastic strains were separated and time resolved stress analysis wascarried out according to the sin2ψ-method. Stress and strain evaluation during the complete laserhardening process lead to unprecedented experimental insights