Level 2 Model as a
Some thin grades often experiences high force errors in the last pass. It seems that the distribution of measured flow stress is off the trend: the measured value in the last pass is a bit too low. As in the case showed in the Figure 3, the measured flow stress was calculated into a reference condition with strain 0.3 and strain rate 10/s; the only effect left was the temperature for the given grade. From the second last pass to the last pass, the flow stress reduced with the decreasing temperature.
It is very likely that there was an α-γ phase transformation in the last pass, so the much softer ferrite was produced.
Research report from Suzuki, et al  shows that for low and medium carbon steel there may be phase transformation in the temperature 800-1000°C (1470-1830°F), sometimes it could be in the range 900-1000°C (1650-1830°F). Frequently some low carbon steels and some HSLA grades conduct phase transformation in the temperature range 850°-900°C (1560-1650°F). This is the temperature range for the second last passes or the last pass of quite a number of grades rolled in many mills. The phase transformation temperatures for the newer grades rolled in recent years are much more difficult to determine, especially for those with addition of micro-alloys.
Figure 3 Measured flow stress at strain 0.3 and strain rate 10/s
<To be continued>
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Part 2 |
Part 3 |