The origins of acicular ferrite in gas metal arc and submerged arc welds
Brothers, Daniel G.
Fox, Alan G.
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The nature of weld metal inclusions in relation to the formation of acicular ferrite was investigated. Gas-metal arc welds (GMAW) on High Strength Low Alloy (HSLA) plate with varying amounts of oxygen and/or carbon dioxide added to the argon cover gas and submerged arc welds (SAW) on HY-100 plate with five different fluxes were analyzed. This analysis determined the effect of weld metal composition on non-metallic inclusion composition and the ultimate effects on the formation of acicular ferrite. Scanning and transmission electron microscopy with energy dispersive x-ray analysis were used to determine inclusion size distribution, concentration and composition. This investigation revealed that the inclusions were complex MnO-A1203-SiO2-TiO2 oxides which contain a titanium-rich compound, Pyrophanite (MnTi03), existing as a faceted particle in those inclusions promoting acicular ferrite formation. From these results and the research of others such as Grong/Matlock and Ramsay/Matlock/ Olson it is concluded that the formation of acicular ferrite does depend on non- metallic inclusion composition demonstrating the importance of weld wire composition for achieving welds with optimum mechanical properties.
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