In the longitudinal direction, the best fit was achieved for the cluster nucleation model with f0=0.001 (Figure 4 left). 3.0 2.0 1.0 0.4 Notch radius mm 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 Critical strain mm/mm Ductility WM−transversal smooth 3.0 1.0 0.4 Notch radius mm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Critical strain mm/mm Ductility All weld metal experiment top/bottom experiment mid f0=0.005 f0=0.001 f0=0.002 Experiments top/bottom mid A=0.002 A=0.005 A=0.03 A=0.01 Figure 4: Ductility diagrams for WM. Longitudinal direction and cluster model (left), transversal direction and continuos model (right). Both nucleation models, however, gave poor fit for the smooth and R=0.4 mm notched specimens with respect to ductility. In the transversal direction, good fit for the mid-section specimens was achieved for the continuos model with A = 0.03 (Figure 4 right), and for the cluster model with f0 = 0.005. Volume fraction of non-metallic inclusions in weld metal was measured in the range of 0.002 - 0.004 [5], which is approximately in the same range as the void volume fraction established by the model. Regarding to these results the cluster model with f0= 0.001 gives a good description of longitudinal weld metal. In the transversal direction f0=0.005 gives better representation of the ductility behavior. The obtained values for f0 in BM and WM agrees well with the findings in a previous SINTEF investigation of a welded joint in X-65 pipeline steel [6]. Heat affected zone As for weld metal, there is a tendency of higher load levels and lower ductility for the mid section specimens (Figure 5). This tendency is slightly more pronounced in the transversal than in the longitudinal direction. However, comparing the tensile testing results of the longitudinal and transversal direction, the overall load and ductility level is quite similar. Higher hardness values were found in the mid-section HAZ than in the top and bottom area. Higher hardness and lower ductility in the mid-section is proposed related to the welding procedure. Welding of the first passes (on both sides) were performed with lower heat input (1.5 MJ/m) compared to the rest of the weld (3.0 MJ/m). This will give shorter ∆t8/5 in the mid-section HAZ, and influence hardness and tensile properties [5][7]. 3.0 2.0 1.0 0.4 Notch radius mm 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00 Critical strain mm/mm Ductility HAZ transversal 0.4 1.0 3.0 smooth Notch radius mm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Critical strain mm/mm Ductility HAZ− longitudinal top/bottom mid f0=0.0001 f0=0.0003 f0=0.0005 top/bottom mid f0=0.0001 f0=0.0003 f0=0.0005 Figure 5: Ductility diagrams for HAZ. Longitudinal direction and cluster model (left), transversal direction and cluster model (right).
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