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

摘要

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 ℃ 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 Al_2O_3 and MgO. Inclusions predominantly Al_2O_3 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 Al_2O_3 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.