0.0 1.0 2.0 3.0 4.0 Diameter reduction mm 0.0 5.0 10.0 15.0 20.0 25.0 30.0 Load kN Load vs diameter reduction Base material longitudinal R=0.4 mm R=1.0 mm R=2.0 mm R=3.0 mm Smooth −0.2 0.2 0.8 1.2 1.8 2.2 2.8 Diameter reduction mm 0.0 10.0 20.0 30.0 Load mm BM_R10 Experiment f0=0.0001 f0=0.0005 f0=0.001 a b Figure 2: Load vs diameter reduction for base metal a) overview of all results b) f0 fitted curves for R=1.0mm The level of non-metallic inclusions in the base metal has been evaluated by Olden [5]. By counting of particles larger than 1 µm a volume fraction of 0.00014 was found. If one assume that voids primarily nucleate from these inclusions, the obtained f0 value of 0.0001 matches the inclusion level very well. smooth 3 2 1 0.4 Notch radius mm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Critical strain mm/mm Ductility Base material top/bottom Mid A=0.0003 A=0.0005 A=0.001 smooth 3 2 1 0.4 Notch radius mm 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 Critical strain mm/mm Ductility Base material top/bottom Mid f0=0.0001 f0=0.0005 f0=0.001 Figure 3: Ductility diagrams for the base metal. Continuos nucleation model (left) and cluster nucleation model (right) Weld Metal Weld metal was tested in longitudinal and transversal direction. In longitudinal direction the specimen geometries were smooth and notched with R=3.0 mm, R=1.0 mm and R=0.4 mm. In the transversal direction smooth specimens were omitted and the notch geometry R=2.0 mm was included in the test program. Weld metal results were more scattered than the base metal results. The results also showed more scatter in the transversal direction than in the longitudinal direction. The transversal mid-section specimens had the overall lowest ductility, with a critical strain of about 0.2 for all notched geometries (Figure 4). This may indicate that other factors than the stress triaxiality level have influenced the ductility. Investigations of the welded joint [5] have revealed coarse dendrite austenite grain boundaries in weld metal. Measured hardness was also somewhat higher in the mid-section (230 - 250 HV) than in the “top” and “bottom”- region (200 - 220 HV). Accordingly there is a possibility that the brittle nature of the microstructure has influenced the results more than the stress conditions. The tensile testing produced a large scatter in ductility results. The mid section R0.4 longitudinal specimens (all weld) achieved clearly lower ductility values than the R1.0 specimens, while the top/bottom specimens showed the same or slightly higher values.
RkJQdWJsaXNoZXIy MjM0NDE=