*3.2. Phase Transformation Start Calculation for Arbitrary Cooling Path*

When the ideal TTT diagram has been determined for a given steel composition, it can be used to calculate the phase transformation start for an arbitrary cooling path. To give an example of this, we calculated transformation start diagrams for two different kinds of cooling paths: (1) for linear cooling paths, *<sup>T</sup>*(*t*) = *<sup>A</sup>*e3 <sup>−</sup> ˙ *θt*, where the constant cooling rate, ˙ *θ*, was varied; and (2) for modified cooling paths, *<sup>T</sup>*(*t*) = *<sup>A</sup>*e3(<sup>1</sup> − (*t*/*t*0)2), where the time constant, *<sup>t</sup>*0, was varied. The transformation start curves as well as two examples of the cooling paths are shown in Figure 6 for both types of cooling paths.

**Figure 6.** Phase transformation start calculated for two different types of cooling paths: (1) the linear cooling paths exemplified by linear plots and (2) the modified cooling paths given by the Equation *<sup>T</sup>*(*t*) = *<sup>A</sup>*e3(<sup>1</sup> <sup>−</sup> (*t*/*t*0)2) shown by the curved plots.
