Oxide inclusions in mild steel weld metal were investigated. Oxide inclusions isolated from mild steel weld metal by ultrasonic agitating dissolution method using I2-CH3OH solution were classified according to the size (5 microns over and under) by ultrasonic sieving method, and observed by optical microscope.
Larger inclusion particles over 5 microns were analysed by electron-probe X-ray microanalyzer.
It was found that inclusion particles over 5 microns were spheroidal (MnO·SiO2, SiO2, and (Mn, Fe) O), angular (SiO2), lumpy (SiO2), platy-shaped (SiO2), prismatic (Al-silicate), pine needle- or stick-shaped (Ca-silicate), and string-shaped (Ca-phosphate) in shapes (and compostions).
The amount of inclusion particles less than 5 microns was about 90% in oxide inclusions, and the greater portion of these was MnO·SiO2, the size of which was about 1 micron.
Ti-oxides which were confirmed by X-ray diffraction in inclusion particles less than 5 microns were α-Ti2O3, Ti2O3, and FeO·TiO2 when Fe-Ti was added to the flux of low hydrogen type, while TiO2 (anatase), Ti2O3, and FeO·TiO, when TiO2 (rutile) was added to titania and cellulose type in the compositions.
The mechanism of formation of various oxide inclusion particles in the weld metal was considered.