Investigation on the residual stress of AISI 4047 low alloy steel laser welded

The residual stress in steel welding can highly influences the performance of the joint during its working life. Both boundary conditions and metal phase transformations have influence on the levels of the residual stress in the weld. In this paper the residual stress for AISI 4047 bead-on-plate samples were measured by strain gage method after laser welding with different values for the laser speed and power, and focus height. The laser used for this project was the ROFIN DC 015 Industrial CO2 Slab Laser. This laser, registered as class 4 laser product in accordance with the European Norm EN 60825 is an high frequency excited, diffusion cooled CO2 gas laser, designed to be used for processing materials in a industrial environment. The measurement procedure was performed on all the welded specimens taking notes of 3 strains (epsilon(1) epsilon(2) epsilon(3)) relative to as many gages at different depths, following the American Society for Testing Materials (ASTM) standard. Thereafter the residual stresses were calculated by means of a non-linear finite element analysis. The analysis took in account the thermo-mechanical phenomena with temperature dependent steel properties. The other considered also the phase transformation and phase-dependent thermal and mechanical properties.