Abstract
Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW). The in situ visualization of austenitization upon welding and subsequent α’-martensite formation during cooling could be achieved with a temporal resolution of 2 s for monochromatic imaging using a single neutron wavelength and of 0.5 s for polychromatic imaging using the full spectrum of the beam (white beam). The spatial resolution achieved in the experiments was approximately 200 µm. The transmitted monochromatic neutron beam intensity at a wavelength of λ = 0.395 nm was significantly reduced during cooling below the martensitic start temperature Ms since the emerging martensitic phase has a ~10% higher attenuation coefficient than the austenitic phase. Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye–Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging.
Highlights
Welding residual stresses can have a crucial influence on the crack resistance of a steel component under service load
Polychromatic and wavelength-selective neutron transmission radiography were applied during bead-on-plate welding on 5 mm thick sheets on the face side of martensitic low transformation temperature (LTT) steel plates using gas tungsten arc welding (GTAW)
Neutron imaging was significantly influenced by coherent neutron scattering caused by the thermal motion of the crystal lattice (Debye– Waller factor), resulting in a reduction in the neutron transmission by approx. 15% for monochromatic and by approx. 4% for polychromatic imaging
Summary
Welding residual stresses can have a crucial influence on the crack resistance of a steel component under service load. It was found that phase transformations during the cooling of the weld seam can have a significant influence on the residual stresses around the weld seam. It is advantageous to control such phase transformations during cooling to minimize residual stresses and improve the crack resistance of the welds [1]. Compressive residual stresses can thereby have a positive influence on crack prevention. A unique possibility of generating compressive residual stresses already during the welding procedure is offered by so-called low transformation temperature (LTT) filler wires [2,3,4]. Distinct compressive residual stresses can be observed within the weld and adjacent areas
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