13th International Conference on Fracture June 16–21, 2013, Beijing, China 10 4.6 Effect of welding process Table 6 lists the values of Charpy V impact toughness and relevant parameters measured at -50oC for weld metals of T100 and T5-21. Table 6 Parameters relevant to Ni content and toughness No. E-50 o C (J) Nickel (%) Average grain size(μm) Width of Bainite lath(nm) Average value (nm) Area fraction of M-A(%) T5-21 163 5.74 30 65-186 113 39 T100 61.2 6.36 60 59-578 151 26 As listed in Table 6, while the Ni content of 6.36% in T100 weld metal is comparable with that of 5.74% in T5-21. However, the impact toughness of 61.2J of the former is much less than that of 163J in the latter. In addition, the grain sizes and the width of bainitic laths of T100 are larger than that of T5-21, the area fraction of M-A flakes is less for T100 than for T5-21. The reason which causes the inferior toughness and the factors deteriorating the toughness is attributed to the welding process. Fig. 17 displays the fracture surface (a) and the macrostructure (b and c) of the weld metal T100. From Fig. 17 it is evident that the coarse directional columnar grains exhibited in Fig. 17 (c) produce the coarse embossing fracture strips shown in Fig.17 (a) which cause the inferior toughness of weld metal T100. Table 7 lists the metallographic parameters measured in T100 and T5-21 weld metal which shows that the width of the weld of T100 is appreciably larger than that of T5-21. It is considered to be welded by horizontal weaving of the welding torch. This procedure produces high heat input at same welding current and causes larger columnar grains and segregation of impurities on the boundaries of the crystalline cells as shown in Fig. 17(b) and (c). Therefore, regardless of the higher nickel content the large columnar grains with impurity segregating boundaries make the impact toughness of the T100 weld metal inferior. The similar phenomenon was observed in the case of M100. (a) (b) (c) Fig 17. The fracture surface (a) and the macrostructure (b and c) of the weld metal T100 Table 11 Metallographic parameters measured in T100 and T5-21 weld metal Weld metal Weld Width (mm) Weld depth (mm) Columnar grain width (mm) Sizes of fine grain (mm) T5-21 15.9 7.4 0.29 0.11 T100 20 7.6 0.41 0.45 M100 14.3 8.5 0.47 0.16 Acknowledgements This work was financially supported by National Nature Science Foundation of China (No. 51035004 and 51265028). References [1] D. Chae, C. J. YoungD. M. Goto and D. A. Koss, Metall. Mater. Trans. A, 32A(2001)2229-2237 [2] R. Cao, W.Feng, Y. Peng, W. S. Du, Z. L. Tian, J. H. Chen, Mater.Sci.Eng A. 528(2010) 631-642. [3] J. R. Low, Deformation and fracture in solids, Springer-Verlag, Berlin, (1956) 163-176. [4] Kamada, N. Koshizuka, T.Funakoshi, Transaction ISIJ, 16(1976)407-416. [5] G. T. Hahn, Metall. Trans. A. 15(1984)947–959. [6] A.Echeverria, J. M. Rodriques-Ibabe, Mater.Sci.Eng A. 346(2003)149-158. [7] L.Rancel, M. Gomez, S. F. Medina, I. Gutierrez, Mater.Sci.Eng A. 530(2011) 21-27. [8] R. Cao, Y. J. Yan, W. S. Du, Z. L. Tian, Y. Peng, J. H. Chen, 2011, Mater.Sc.Techno, 27(2011)145-155. [9] J. H. Chen, G. Z. Wang, C. Yan, H. Ma, and L. Zhu, Inter. J. Fract. 83(1997)105-120. 1
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