## 3 Results
The standard error is similar for Methods 4 and 5, and slightly higher in Methods 1, 2, and 3. A difference of about 1.4 \({}^{\circ}\)C in the RPT with deviation percentages of about 0.4% are acceptable when the approximative RPT temperature is about 565 \({}^{\circ}\)C.  
In order to know the significant effect of each alloy element on the RPT, the values of the Student's t-distribution (t) were used. In our case, if the t value is \(>\)2.17, the selected alloy element will have a significant influence on the studied parameter. If the value of a coefficient in the RPT calculation formulas is negative, the selected alloy element will promote a decrease in the RPT value, and a positive value will promote an increase in the RPT value. In Table 3 the individual values for the t student of every alloying element are resumed. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Description of the** & **Coefficient of** & **Standard** & **Maximum and** \\  & **Determination of the RPT** & **Determination R2** & **Error** & **Minimum Deviation** \\ \hline \multirow{2}{*}{Method 1} & Second Minimum of d2T/dt2 & \multirow{2}{*}{0.77} & \multirow{2}{*}{1.48 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.40/+ 0.30\%} \\  & curve versus time & & & \\ \hline \multirow{2}{*}{Method 2} & First minimum of dT/dt curve & \multirow{2}{*}{0.77} & \multirow{2}{*}{1.5 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.39/+ 0.36\%} \\  & versus time & & & \\ \hline \multirow{2}{*}{Method 3} & Crossing point of the second & \multirow{2}{*}{0.78} & \multirow{2}{*}{1.55 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.48/+ 0.39\%} \\  & and third derivative dT/dt & \multirow{2}{*}{0.77} & \multirow{2}{*}{1.29 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.35\%/+ 0.29\%} \\  & versus time & & & \\ \hline \multirow{2}{*}{Method 4} & Sudden deviation from the & \multirow{2}{*}{0.77} & \multirow{2}{*}{1.29 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.35\%/+ 0.29\%} \\  & horizontal tangent in the & \multirow{2}{*}{0.77} & \multirow{2}{*}{1.29 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.35\%/+ 0.29\%} \\  & elbow area of dT/dt curve & & & \\ \multicolumn{2}{c}{versus temperature} & & & \\ \hline \multirow{2}{*}{Method 5} & Second and third derivative of & \multirow{2}{*}{0.82} & \multirow{2}{*}{1.35 \({}^{\circ}\)C} & \multirow{2}{*}{\(-\)0.44\%/+ 0.32\%} \\  & dT/dt versus temperature & & & \\ \hline \end{tabular}
\end{table} 
Table 2: Description of the determination of the rigidity point temperature by every method and the corresponding coefficients of determination, standard error, and maximum and minimum deviation. Figure 7: Comparison of the RPT values for each alloy with the methods studied. We can observe in Table 3 that the obtained results show that magnesium was determined as the main element impacting on the RPT values and it is the element with the highest t student coefficient and with statistical relevance. Silicon also has a statistical signification in the case of Method 5, with average values in the rest of the studied methods quite close to the limit of also having statistical signification. In Figure 8 we can observe the representation of the Mg effect over RPT values employing the calculation of method 5. Higher Mg percentages promote smaller RPT values.