The relationship between microstructure and toughness of API 5L-X70 weld deposits was studied by means of full metallographic and mechanical on the specimens cut transversely to the weld beads. The best combination of microstructure and impact properties was obtained in the weld metal contained 0.02% Ti. With more increasing of the titanium content, the microstructure has changed from a mixture of acicular ferrite, grain-boundary ferrite, Widmanstätten ferrite to a mixture of acicular ferrite, grain-boundary ferrite, bainite, martensite and microphases. Therefore, the mode of fracture also changed from ductile to quasi-cleavage and cleavage. Also, the observed increasing of titanium content in the inclusions, due to the addition of titanium, led to change the nature of inclusions and decrease the amount of MnS inclusions in the microstructure.

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