## 3 Results
### Mass Balance
Equation (8) shows the calculation for the mass of Mn added from aluminothermic reduction, (M\({}_{\text{Mn}}\)). The inputs to Equation (8) are 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. \[\text{M}_{\text{Mn}}\ =\ (\text{M}_{\text{WM}})\bigg{(}\frac{\%\text{Mn}_{ \text{WM}}}{100}-\bigg{[}\frac{\%\text{DR}_{\text{wire}}}{100}\times\frac{\% \text{Mn}_{\text{wire}}}{100}\bigg{]}-\bigg{[}\bigg{(}1-\frac{\%\text{DR}_{ \text{wire}}}{100}\bigg{)}\times\frac{\%\text{Mn}_{\text{BP}}}{100}\bigg{]} \bigg{)} \tag{8}\]  
M = mass (gram); M\({}_{\text{WM}}\) = mass Mn (gram); %Mn\({}_{\text{WM}}\) = %Mn in weld metal; %DR-wire = % 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 is calculated from the reaction enthalpy values displayed next to reactions (2) and (3). A simplified translation of the kJ values is made by using the heat capacity of steel (0.460 kJ/kg K) to calculate the expected increase in weld metal temperature due to reactions (2) and (3). The calculation results are summarised in Table 6. It is seen that although small quantities of SiO\({}_{2}\) and MnO were reduced into the weld metal via reactions (2) and (3), the exothermic effect of these reactions is significant in increasing the weld metal temperature by 53 \({}^{\circ}\)C. This exothermic heat may contribute to the melting of metal powders for incorporation into the weld pool. Furthermore, the weld pool solidification time is an important aspect of oxygen content control of the weld pool. Increased weld pool cooling time provides more time for oxide inclusions to float from the weld pool to the molten slag-weld pool interface to be absorbed into the molten slag [29]. The weld pool cooling time, set by the difference between the weld pool liquidus and solidus temperature, may be different for differing weld pool chemistries. This effect is shown in Figure 3 for the two weld metal chemistries displayed in Table 3. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **SiO\({}_{2}\)** & **MnO** & **Al** & **Reaction** & **Reaction** & **Reactions (2) \& **(3)** & **Weld Metal \(\Delta\)T** \\  & **(g)** & **(g)** & **(g)** & **(2) (k)** & **(3) (k)** & **(k)** & **(**c)** \\ \hline MP6 & 0.46 & 0.54 & 0.41 & \(-\)0.83 & \(-\)1.27 & \(-\)2.1 & 53 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Exothermic heat added to the weld pool from reactions (2) and (3). Figure 3: Solidification curves for BC and MP6 weld metal compositions as calculated in Fact-Sage 7.3 [30]. The solidification curves in Figure 3 were calculated in FactSage 7.3 thermochemical software using the Equilib module and the FToxid and FSstel databases [30]. Figure 3 confirms that the solidus temperature of MP6 weld metal is significantly lower than the solidus temperature of the Base Case (BC) weld metal, and this aspect will contribute to a lower ppm O in the MP6 weld metal, compared to the BC weld metal, as is confirmed in Table 3.