## 3 Results
### Mass Balance
The inputs for Equation (8) were the weld metal mass (Mwm) and the dilution ratio value (\(\%\)DR\({}_{\text{(wire+MP)}}\)), from Table 5, for the base case, and the \(\%\)Mn in the weld metal, from Table 3. The square bracketed terms in Equation (8) represent the calculation of the BC weld metal nominal composition:  
\[\text{M}_{\text{Mn}}=(\text{M}_{\text{WM}})\bigg{(}\frac{\%\text{Mn}_{\text{ WM}}}{100}-\bigg{[}\frac{\%\text{DR}_{\text{wire}}}{100}\ast\frac{\%\text{Mn}_{\text{wire}}}{100} \bigg{]}-\bigg{[}\bigg{(}1-\frac{\%\text{DR}_{\text{wire}}}{100}\bigg{)} \ast\frac{\%\text{Mn}_{\text{BP}}}{100}\bigg{]}\bigg{)} \tag{8}\]  
M = mass (gram); M\({}_{\text{WM}}\) = mass Mn (gram); \(\%\)Mn\({}_{\text{WM}}\) = \(\%\)Mn in weld metal; \(\%\)DRwire = \(\%\) of weld metal contributed by weld wire in the base case (BC); \(\%\)Mnwire = \(\%\)Mn in weld wire; \(\%\)Mn\({}_{\text{BP}}\) = \(\%\)Mn in base plate (BP); WM = weld metal; BP = base plate; Wire = weld wire. The exothermic heat from reactions (2) and (3) can be calculated from the reaction enthalpy values displayed next to reactions (2) and (3). The simplified translation of the kJ values was made by using the heat capacity of steel (0.460 kJ/kg K) to calculate the expected increase in weld metal temperature from the exothermic heat released in reactions (2) and (3) according to the mass of SiO\({}_{2}\) and MnO reacted, as calculated in Equation (8) and displayed in Table 6. The reaction heat values from the calculations are summarised in Table 6. Although only small quantities of SiO\({}_{2}\) and MnO were involved in reactions (2) and (3), the exothermic heat added into the weld metal was significant as an instantaneous increase of 58 \({}^{\circ}\)C in the weld metal temperature was generated. This exothermic heat may contribute to the melting of metal powders for incorporation into the weld pool. It has been established that the weld pool solidification time plays an important role in the control of total oxygen content in the weld pool. This effect is due to an increase in the weld pool cooling time, which then in turn provides more time for oxide inclusions to float from the weld pool to the slag-veld-pool interface and be absorbed into the molten slag [32]. The weld pool cooling time, set by the difference between the weld pool liquidus and solidus temperatures, may be different for differing weld-pool chemistries. Figure 3 displays the solidification curves for the BC and MP7 weld-metal chemistries; see Table 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **SiO\({}_{2}\)** & **MnO** & **Al** & **Reaction (2)** & **Reaction (3)** & **Reactions** & **Weld metal** \\  & **(g)** & **(g)** & **(g)** & **(kJ)** & **(kJ)** & **(2) \& **(3) \& **(kJ)** \\ \hline MP7 & 0.53 & 0.67 & 0.49 & \(-\)0.96 & \(-\)1.57 & \(-\)2.53 & 58 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: exothermic heat added to the weld pool from reactions (2) and (3). \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **Al** & **Co** & **Powder** & **Wire (g)** & **Base Plate** & **Weld Metal** & \(\%\)DR\({}_{\text{(wire+MP)}}\) & \(\%\)**AI** & \(\%\)**Co** \\  & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **(g)** & **Yield** & **Yield** \\ \hline Base Case & 0 & 0 & 0 & 33.8 & 33.8 & 67.6 & 50 & 0 & 0 \\ \hline MP7 & 3.9 & 5.0 & 8.9 & 51.1 & 33.5 & 93.5 & 64 & 55 & 70 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mass balance numbers for percentage yield calculation. FactSage 7.3 thermochemical software, using the Equilib module and the FFoxid and FSstel databases, was used to calculate the solidification curves displayed in Figure 3[31]. Comparison of these curves confirms that the solidus temperature of MP7 weld metal is lower than the solidus temperature of the base case (BC) weld metal. Consequently, the longer cooling time of the MP7 weld pool, compared with the BC weld pool cooling time, contributed to a lower total ppm O in the MP7 weld metal at 230 ppm O compared with the BC weld metal at 499 ppm O, see Table 3.