Fast Temporal and Spatial Resolved Stress Analysis at Laser Surface Line Hardening of Steel AISI 4140

Local and temporal strain and stress evolution is recorded by synchrotron X-ray diffraction during laser line hardening of SAE 4140 steel in the quenched and tempered states at different measuring positions with respect to the process zone. The in-situ diffraction experiments were performed at beamline P05@Petra III at DESY, Hamburg (Germany). The steel samples were line hardened using a 4 kW high-power diode laser (HPDL) unit at a constant laser feed of 800 mm/min. Using a specially designed process chamber that incorporates symmetrically attached fast silicon micro-strip line detectors, stress analysis using the sin²ψ-method in single-exposure mode, enabled measuring rates at 20 Hz. As a result of the temporal and spatial resolved analyses, the elastic strains were separated from the thermal strains