Multi-scan laser forming: Synchrotron strain scanning and microstructure evolution

Abstract

Residual elastic strain and microstructural transformations resulting from high thermal gradients introduced by industrial-strength laser forming of mild steel are reported in this article. An 8 mm thick steel plate was bent to a total bending angle of 1.2° by running a laser three successive times across the length of the plate. Thin through-thickness slices of the plate were prepared for synchrotron energy-dispersive X-ray diffraction experiments from which lattice strains were calculated by measuring peak shifts in the diffraction patterns. The diffraction patterns were analysed by means of Rietveld refinement using the general structure analysis system allowing the spatially resolved mapping of relevant strain components needed for full-field eigenstrain determination in the plate. Comparison of the measured residual elastic strain fields and metallographic analyses of the steel plate suggests that a correlation exists between the residual elastic strains and metallurgical processes. The present study serves the purpose of developing a better understanding of the laser forming process and its implications on structural integrity and in-service reliability of components. It also provides a foundation for further in-depth studies into the interaction between lasers and structural materials © IMechE 2007.