Effect of inclusions on microstructure and toughness of deposited metals of self-shielded flux cored wires

The effect of inclusions on the microstructure and toughness of the deposited metals of self-shielded flux cored wires was investigated by optical microscopy, electron microscopy and mechanical testing. The deposited metals of three different wires showed different levels of low temperature impact toughness at −40 °C mainly because of differences in the properties of inclusions. The inclusions formed in the deposited metals as a result of deoxidation caused by the addition of extra Al-Mg alloy and ferromanganese to the flux. The inclusions, spherical in shape, were mixtures of Al2O3 and MgO. Inclusions predominantly Al2O3 and 0.3-0.8 μm in diameter were effective for nucleation of acicular ferrite. However, inclusions predominantly MgO were promoted by increasing Mg in the flux and were more effective than Al2O3 inclusions of the same size. These findings suggest that the control of inclusions can be an effective way to improve the impact toughness of the deposited metal.