On the Oxidation Behaviour of Si and Mn During CO2-O2 Are Welding
1976 Volume 45 Issue 11 Pages 960-966
Details
1976 Volume 45 Issue 11 Pages 960-966
The CO2-O2 arc welding process is done in strong oxidation atmosphere with a wire containing Si and Mn which are deoxidizing elements. Dr. H. Sekiguchi pointed out that mechanical properties of welded metal were significantly influenced by the content of these elements and there was a proper range of their contents. Therefore, an investigation was made on the oxidation behaviour of Si and Mn. Six kinds of wire containing different amounts of Si and Mn were used. Their compositions correspond to the ranges in which SiO2 of solid state (Field I) and liquid solution of FeO-MnO-SiO2 unsaturated with SiO2 (Field II), respectively, form as a deoxidation product from molten steel just above the solidification point. The multi-pass welding was made with all of the wires under various conditions of arc voltage and oxygen content of shielding gas. Samples taken from upper layer of deposited metal were analyzed. Furthermore, slag covering the weld bead of upper layer was also analyzed.
Thus, the following results were obtained.
(1) It was recognized that the oxidation consumption curve of Si and Mn shows the same tendency regardless of wire composition in Field I or II.
(2) Si and Mn are oxidized with a fixed ratio when welding is performed with different oxygen content of shielding gas or arc voltage. The ratio is dependent on the wire composition. That is, the relation between Si and Mn content of wire and those of deposited metal can be shown as follows.
log (w/o Si) =A log (w/o Mn) +B
constant A is about 1.7 and constant B is determined from the wire composition.
(3) Accordingly, the composition of wire to be used is to correspond with constant B determined from the aimed composition of deposited metal.
(4) Thermodynamic considerations show that, although equilibrium between Si or Mn in weld metals and SiO2 or MnO in slags is not completely achieved, their deviation from equilibrium is relatively small, and the deviation in oxidation of Si and that in oxidation of Mn are of similar level.
