SiO sub(2) and CaF sub(2) Behavior During Shielded Metal Arc Welding and Their Effect on Slag Detachability of the CaO-CaF sub(2)-SiO sub(2) Type ENiCrFe-7-Covered Electrode

• Published in: Metallurgical and materials transactions. A, Physical metallurgy and materials science Physical metallurgy and materials science, 2016-09, Vol.47 (9), p.4530-4542
• Main Authors: Wang, Huang, Qin, Renyao, He, Guo
• Format: Article
• Language: English
• Subjects: Calcium fluoride; Coatings; Detaching; Flux; Microstructure; Shielded metal arc welding; Silicon dioxide; Slags
• ISSN: 1073-5623; 1543-1940
• DOI: 10.1007/s11661-016-3629-x

The metallurgical behavior during shielded metal arc welding (SMAW) and the slag detachability of the CaO-CaF sub(2)-SiO sub(2) type ENiCrFe-7-covered electrodes was investigated. The results indicated that the slag detachability could be improved as the SiO sub(2) in the flux coatings decreased. When the SiO sub(2) in the flux coating was 10.9 pct, about 28.3 pct CaF sub(2) resulted in the best slag detachability. The CaF sub(2) and SiO sub(2) in the flux coating interacted during SMAW to form gaseous SiF sub(4) to be evacuated. In the reactions, one SiO sub(2) consumed two CaF sub(2), leading to the reduction of the ratio of CaF sub(2)/SiO sub(2). After comparing the slag compositions, the best slag detachability was obtained at CaO:CaF sub(2):SiO sub(2) = 1.7:1.8:1, but the worst slag detachability appeared at CaO:CaF sub(2):SiO sub(2) = 1.3:0.9:1. The XRD analysis revealed that the oxides and fluorides in the slags preferred to gather together to form cuspidine and other complex phases. If the CaF sub(2) was dominant in the slags, they intended to form homogenous porous microstructures that were relatively strong and would most likely detach from the weld metal in blocks, exhibiting good slag detachability. If the cuspidine phase was dominant, the slags exhibited a 'rock strata'-like microstructure in the intergranular area. Such microstructure was very fragile and could be broken into fine powders that were easily embedded in the weld ripples, leading to slag adhesions. This work provides the researcher with a wealth of information and data, which will also be beneficial to the welding material producers and users.