SiO 2 and CaF 2 Behavior During Shielded Metal Arc Welding and Their Effect on Slag Detachability of the CaO-CaF 2 -SiO
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NICKEL-BASE alloys are very important engineering materials that can be used in a wide range of environments and applications due to their high resistance to the aqueous and high-temperature corrosion in complex atmospheres, and their high strength over a large temperature range from cryogenic up to high temperatures.[1] The Ni-base alloy welding consumables also can be used for welding the structures that serves in various harsh environments, because their weld metals can always maintain strength and ductility in a large temperature interval, despite significant dilution by other alloying elements.[1,2] ENiCrFe-7 is a typical nickel-base alloy covered electrode, which was recommended to be used for welding Inconel 690 and other similar applications to produce excellent as-welded HUANG WANG and RENYAO QIN, Ph.D. Students, are with the Shanghai Key Laboratory of Materials Laser Processing and Modification and State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China. GUO HE, Professor, is with Shanghai Key Laboratory of Materials Laser Processing and Modification and State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, and also with the Collaborative Innovation Center for Advanced Ship and Deep-Sea Exploration, Shanghai 200240, China. Contact e-mail: ghe@sjtu. edu.cn Manuscript submitted November 23, 2014. Article published online July 8, 2016 4530—VOLUME 47A, SEPTEMBER 2016
strength and impact toughness and good corrosion resistance.[2,3] In welding practice, the covered electrodes (conforming to AWS A5.11/A5.11M ENiCrFe-7 specification) manufactured by different producers may exhibit very different weldability and operability including arc stability, weld contour, slag detachability, spatter and fume, etc. This is because different flux formulations have been used in each factory. Generally, the acidic flux system provides very good welding operability but relatively high-cracking susceptibility; while the basic flux system results in lower hydrogen in the weld metal but unfavorable welding operability.[4,5] For the nuclear power applications, low hydrogen and low cracking susceptibility are extremely important, so that the basic flux system should be the first choice. However, the welding operability becomes the main problem in this case. One of the concerns is poor slag detachability that seriously affects productivity. It has already been recognized that the slag detachability has very close relations with both the physical and chemical properties of the flux.[4–7] One of the mechanism of slag adhesion to weld metal is the chemical bond via forming a thin layer of oxides of elements of the metal phase on the weld metal surface.[6] This chemical bond can be eased or eliminated if a slag system with the minimal oxidizing ability was used (e.g., basic flux system).[4–6] The other factors affecting the slag detachability are the differences between the thermal expansion coefficients of the slag and the
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