The Transformation Behaviour Of High Strength CMn Steels

摘要

The isothermal transformation kinetics of CMn steels, exhibiting an austenite grain size in the region of 16 mu m, have been examined through dilatometry. It was found that the Avrami equation can suitably describe the progress of ferrite formation during isothermal holding. The equation's constants have been fitted to the experimental data. The value of the constant K, and hence the speed of ferrite formation, increases as the transformation temperature falls. In general, the value of the Avrami co-efficient, n, was found to be in the region of 0.9 for these steels. The experimental results have been discussed in terms of their implications, regarding stepped run-out table cooling profiles. During hot mill processing, cooling can be interrupted for a time long enough for a given volume of ferrite of form isothermally. It has been found that a lower transformation temperature offers the advantages of a finer microstructure and faster ferrite formation. However, a higher transformation temperature allows greater control over microstructural consistency. Future work will concentrate on the laboratory hot rolling and cooling of CMn steel grades. These studies will provide further information regarding the effect of isothermal transformation temperature on ferrite microstructure and mechanical properties.