PSI - Issue 17

Jan Kec et al. / Procedia Structural Integrity 17 (2019) 230–237 Jan Kec / Structural Integrity Procedia 00 (2019) 000 – 000

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Macrostructure of the seam weld is depicted in Fig. 3, where a very good matching of weld beads and sheets is visible. Microstructure is oriented preferentially along the direction of the solidification gradient. Microstructure of the weld metal is formed by acicular ferrite, grain boundary ferrite, polygonal ferrite and Widmanstätten ferrite – Fig. 4a. Along the fusion boundary, coarsening of the ferrite grains is observed; the structure of heat affected zone consists of a mixture of bainite, ferrite and pearlite – Fig. 4b.

Fig. 3. macrostructure of longitudinal submerged arc weld

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b)

Fig. 4. (a) weld metal microstructure; (b) microstructure of heat affected zone.

Charpy impact transition curves for transversal (T-L) and longitudinal (L-T) orientation of BM specimens are shown in Fig. 5. To eliminate the effect of scatter, three specimens were tested for each orientation and temperature. The rate of shear fracture was evaluated on the fractured specimens with the help of Olympus SZ-61 microscope equipped with QuickPHOTO INDUSTRIAL software. The values of absorbed energy are markedly higher in case of specimens in L-T orientation, particularly in upper shelf energy region (USR) and ductile-brittle transition temperature (DBTT), what is typical for the hot rolled materials. Taking in account the results of many works (Haskel et al. 2014, Joo et al. 2012, Yang et al. 2014, Khalid et al. 1999 and etc.) it can be said that the differences in absorbed energy and