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Influence of primary cooling conditions and austenite conditioning on the hot ductility of the simulated continuous cast peritectic steels
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posted on 2020-09-18, 13:51 authored by Kedibone LekganyaneStage 1:The first approach to the project was to generate the coarse and abnormal prior austenite grain size to approximate the industrial as-cast microstructure. Please refer to the thermal path followed to generate the as-cast microstructure in Figure 3:4 in chapter 3 (dissertation). The method used to reveal the prior austenite grain boundaries was explained in details in chapter 3 of the dissertation section 3.3.1.1.
Stage 2: 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.
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 Figure 4:3 in chapter 4 (dissertation).
Stage 3: It was reported that during the rapid primary cooling, the surface of the strand corner drops to a minimum temperature, Tmin followed by the surface reheating to the Tmax as the surface position studied moves away from the mould. The secondary cooling cycle from the Tmax 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 Tmin values were generated from the non-equilibrium and equilibrium austenite to ferrite start transformation temperatures.
The first set of Tmin values were generated at 10 °C below the Ae3 temperatures (Figure 4:5) whilst the second set of Tmin values was generated at 70 °C above the Ar3P temperatures (Figure 4:7).
Stage 4: In
order to evaluate the influence of the magnitude of the rebound step on the hot
ductility, two values of ∆Tr, were selected for each of the two Tmin-values
employed, ∆Tr values of 200 °C and 300 °C respectively, resulting
in the four Tmax -values.
It was decided that the secondary cooling rate from the Tmax 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 Tmax -value to a temperature 272 °C below the Tmax value. This was done in order to investigate the influence of the magnitude of the undercooling below the Tmax -value on the hot ductility.
Please refer to Figures 3:9-3:12 in chapter 3 of the dissertation. All the conditions used to generate the thermal paths are tabulated in Table 3:2.
