Issue 47

P. Ferro et al., Frattura ed Integrità Strutturale, 47 (2019) 221-230; DOI: 10.3221/IGF-ESIS.47.17 225 R ESULTS AND DISCUSSION ig. 4 shows the weld toe geometry before and after TIG-dressing. As supposed, the V notch angle was 135° while the weld toe radius was found to be close to zero after welding and about 6.7 mm after TIG-dressing. It shows the effectiveness of such post-welding operation in promoting a smoother transition between the plate and the weld crown. Figure 4 : Macrograph of the fillet welding before (a) and after (b) TIG-dressing. Comparison between real and modeled geometry (c) . The FZ microstructure consists of acicular and Widmanstätten ferrite with islands of allotriomorphic ferrite both in the as-welded and post-welding treated joint (Fig. 5). It is in agreement with the microstructure observed in low carbon steels welded joints [20]. In the range between 800-300 °C the austenite decomposes to different ferrite morphologies. The austenite to ferrite decomposition starts with the formation of allotriomorphic ferrite at the prior  boundaries. With continued cooling, the Widmanstätten ferrite nuclease at ferrite/austenite boundaries and extends into the untransformed austenite-grain interiors. Further cooling to low temperatures, the acicular ferrite would nucleate on the inclusion. If there are no potent inclusions, bainitic ferrite might form instead of acicular ferrite, from the remaining austenite. Figure 5 : Micrograph of the fusion zone before (a) and after (b) TIG-dressing. The heat affected zone (HAZ) of the as-welded joint was mainly composed of bainite while after TIG-dressing a mixture of bainite and tempered bainite was detected between the FZ and the parent metal (Fig. 6). Fig. 7 shows the microhadness profile across the weld bead of the joint after TIG-dressing. It is noted that the different carbon amounts contained in the two plates result in a non-symmetric microhardness profile. The lower the carbon content, the lower the measured hardness values both in HAZ and parent metal. F