Influence of primary cooling conditions and austenite conditioning on the hot ductility of the simulated continuous cast peritectic steels

<b>Stage 1</b>:The first approach to the project was to generate the coarse and abnormal prior austenite grain size to approximate the industrial <u>as-cast microstructure</u>. Please refer to the thermal path followed to generate the as-cast microstructure in <b>Figure</b> <b>3:4</b> in <b>chapter 3 </b>(dissertation). The method used to reveal the prior austenite grain boundaries was explained in details in <b>chapter 3</b> of the dissertation <b>section 3.3.1.1.</b><div><b><br></b></div><div><b>Stage 2: </b>In this stage, the conditions (i.e. heating rate, austenite conditionings and the soaking times) that were used to generate the as-cast microstructure were then reserved for further procedures. </div><div><br></div><div>The austenite to ferrite start temperatures during primary cooling stage were established. In this case, the specimens were cooled at the rate of 10 °C/s from the austenite conditionings. This cooling rate was associated with the harsh cooling rate experienced by the strand beneath the mould (in the primary cooling stage). Please refer to <b>Figure 4:3</b> in <b>chapter 4 </b>(dissertation). </div><div><br></div><div><b>Stage 3: </b>It was reported that during the rapid primary cooling, the surface of the strand corner drops to a minimum temperature, T_min followed by the surface reheating to the T_max as the surface position studied moves away from the mould. The secondary cooling cycle from the T_max to the unbending was slow due to the strand's interior and the cooling intensity being lower here than in the water cooled mould region. The T_min values were generated from the non-equilibrium and equilibrium austenite to ferrite start transformation temperatures. </div><div><br></div><div>The first set of T_min values were generated at 10 °C below the Ae₃ temperatures (<b>Figure 4:5</b>) whilst the second set of T_min values was generated at 70 °C above the Ar_3P temperatures (<b>Figure 4:7</b>). </div><div><br></div><div><b>Stage 4: </b>In order to evaluate the influence of the magnitude of the rebound step on the hot ductility, two values of ∆T_r, were selected for each of the two T_min-values employed, ∆T_r values of 200 °C and 300 °C respectively, resulting in the four T_max -values.</div><div><br></div><div>It was decided that the secondary cooling rate from the T_max values be kept constant at the rate of 0.1 °C/s and the simulated unbending temperatures were chosen to range from a temperature being 72 °C below the T_max -value to a temperature 272 °C below the T_max value. This was done in order to investigate the influence of the magnitude of the undercooling below the T_max -value on the hot ductility. </div><div><br></div><div>Please refer to <b>Figures 3:9-3:12 </b>in <b>chapter 3 </b>of the dissertation. All the conditions used to generate the thermal paths are tabulated in <b>Table 3:2.</b></div>