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Microstructure of Welding Slag and Its Effects on the Usability of Electrode

Author: ZhangKai
Tutor: ZhangYuanBin
School: Shandong Institute of Architecture
Course: Materials Processing Engineering
Keywords: electrode welding slag microstructure detachability arc restriking
CLC: TG422.1
Type: Master's thesis
Year: 2011
Downloads: 135
Quote: 0
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Abstract


With the development of welding materials, electrode usability improved. But the research on slag especially on the characteristics of acid slag is uncompleted, and the theory about slag structure should be further explored. In this paper, characteristics of the welding microstructure and performance were investigated by self-making electrode and comparing with the domestic high quality products. For different electrode coating, the microstructure, chemical composition and phase compositions were analyzed. The electrical conductivity of the slag and its effect on restriking ability of arc were also studied in this paper, and the electric mechanism of solid slag was supposed.The slag was observed under the optical microscope. For electrode, with different slag detachability, the slag had different microstructure. The slag mainly composed of white strip crystal phase and dark gray phase alternately arranged; the wider of the white strip phase the better of the slag detachability. And the better directions of the white strip phase the better of the slag detachability. Mean time, the content of TiO2 in coating greatly affected the slag detachability.By using SEM, EDS and X-Ray, the composition of organization and the phase component of the slag were further analyzed. It indicated that:Ti, Mn and Fe congregated in the white strip phase, while the Si, Ca congregated in the dark gray phase. Almost no Si, Ca were detected in the white strip phase for the electrode with better slag detachability, while too much Si, Ca had adverse effects for slag detachability.X-Ray analysis showed that the phase components of slag were complex. However crystal phase such as Fe2MnTi3O10, Fe2TiO4 and FeTi5O10 were detected in the slag of the entire electrode with better slag detachability. It was supposed that Fe2MnTi3O10 crystal phase in the slag is the variable structure of anosovite [m(M2+O-2TiO2)·n(M3+2O3·TiO2)](M represent metallic element) which consisted of TiO2 and other oxides. Fe2MnTi3O10 could exist stable because ions such as Fe3+, Mn4+ could combine with oxygen deficiency TiO2 to form stable structure. The co-edge alignment of Fe2MnTi3O10 based on rutile structure determined the shape of the white crystals phase, especially the width of the crystal phase.The arc restriking ability and the electric conductivity of the slag were evaluated. The arc restriking ability is not only associated with the coating composition, but also the electric conductivity of the slag. It was indicated that slag is electric conductive at room temperatures, and the electric conductive related to the slag structure. The electric conductivity character of slag was different from that of metal, whereas it is similar to that of the semiconductor, the conductivity increased as the temperature increasing.The mechanism of slag electric conductivity was discussed, it was supposed that crystal defects in the oxygen losted compound produced electriferous hole and surplus electron which acted as current carrier and could move directionally in the electric field. As the temperature increasing, the number of electirc hole and electron increased, then the conductivity improved. This conclusion could instruct the design of the electrode coating to improve the arc restriking ability of electrode by improve the electric conductivity of the slag. The measure was restricting the content of materials that could release oxygen atom in the electrode coating to control the oxidation ability of the welding atmosphere.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Welding, metal cutting and metal bonding > Welding materials > Arc welding material > Welding rod
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