Thermo-metallurgical and thermo-mechanical computations for laser welded joint in 9Cr-1Mo(V, Nb) ferritic/martensitic steel

Transient thermo-metallurgical and thermo-mechanical computations for laser welded joint, in 9 mm thick 9Cr-1Mo(V, Nb) ferritic/martensitic steel plate, in square-butt configuration, have been carried out by simulating the laser welding process on the 3-dimensional (3D) solid model using a finite element based welding and heat treatment simulation solution package - SYSWELD. The heat source has been modeled as a combination of a 3D Gaussian and a double ellipsoid profiles for realistic representation of fusion zone morphology. Phase and temperature-dependent physical and mechanical properties of this material were used in these computations. The results show very short residence time (<0.5 s) for the material in the heat affected zone (HAZ). The results clearly delineate the effects of different thermo-metallurgical processes like heating, softening, cooling and solid state phase transformation (SSPT) on temporal evolution of the stress-field resulting from laser welding. Longitudinal component of the residual stress is the most significant followed by the normal component and the transverse component is the least significant. Cross-weld residual stress profiles show a trough in the fusion zone and the heat affected zone (HAZ) with a peak in the parent metal region bordering the metallurgical HAZ. Also, the longitudinal and the normal components of the residual stress show nearly similar profile with different magnitudes. The computed residual stress profiles show reasonably good agreement with that measured by neutron diffraction. The results also show significant plastic deformation and strain-hardening of the austenitic phase-field prior to its transformation into martensite.