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Tham khảo tài liệu 'arc welding 2011 part 16', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Chemical and Physical Properties of Fluxes for SAW of Low-Carbon Steels 291 The latter compounds were detected in the fluxes A C and T but only a small content may be as impurity and were observed in the flux B. Thus a problem of flux fluidity might be present in this flux. The manganese oxide and quartz have been observed to have a beneficial effect on the mechanical properties of welds Lancaster 1999 . Manganese oxide and quartz were included in the formulation of fluxes A and C but not for flux B. Titanium oxide has been observed to promote the formation of acicular ferrite which is less susceptible to cracking Evans 1996 . Fluxes C and T are expected to produce the better weld since they contain quartz manganese oxide titanium oxide and the content of oxygen ions calculated by X-ray diffraction is smaller than A and B. 2.4 Influence of chemical composition on the microstructure and tensile properties of SAW welds The mechanical properties of welds are determined by the microstructure developed during the submerged-arc welding process Joarder et al. 1991 . It was suggested that the acicular ferrite provided a good toughness and tensile strength to the welds because its fine size has a higher resistance to the crack propagation Liu Olson 1986 . Thus it seems to be convenient to increase the volume fraction of ferrite in welds. Widmanstatten equiaxial and acicular ferrite can be developed by the welding process. A method for promoting the formation of acicular ferrite consists of the additions of oxides into the flux such as boron oxide vanadium oxide and titanium oxide Evans 1996 . The oxides in the flux may contribute to different metallic element dissolution and oxygen into the weld. These elements may react to form oxide inclusions which are trapped into the weld and facilitate the nucleation of acicular ferrite during the weld cooling Dowling et al. 1986 and Vander et al. 1999 . The main factors that determine the microstructure of a weld are chemical .