Journal
JOURNAL OF MATERIALS PROCESSING TECHNOLOGY
Volume 209, Issue 8, Pages 4027-4035Publisher
ELSEVIER SCIENCE SA
DOI: 10.1016/j.jmatprotec.2008.09.021
Keywords
Titanium; Acicular ferrite; Ductile; Inclusion
Funding
- National Iranian Gas Company (NIGC)
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The effect of titanium addition on the SAW weld metal microstructure of API 5L-X70 pipeline steel was investigated. The relationship between microstructure and toughness of the weld deposit was studied by means of full metallographic, longitudinal tensile, Charpy-V notch and HIC tests on the specimens Cut transversely to the weld beads. The best combination of microstructure and impact properties was obtained in the range of 0.02-0.05% titanium. By further increasing of titanium content, the microstructure was changed from a mixture of acicular ferrite, grain-boundary ferrite and Widmanstatten ferrite to a mixture of acicular ferrite, grain-boundary ferrite, bainite and ferrite with M/A microconstituent. Therefore. the mode of fracture also changed from dimpled ductile to quasi-cleavage. The results showed an increase in the titanium content of inclusions with increased titanium levels of weld metal. Titanium-base inclusions improve impact toughness by increasing the formation of acicular ferrite in the microstructure. No HIC susceptibility was found in the weld metals with titanium contents less than 0.09%. (C) 2008 Elsevier B.V. All rights reserved.
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