Some Considerations on Austenite Grain Growth Kinetics from High-Temperature Laser Scanning Confocal Microscopy Observations

For more than 20 years, high-temperature laser scanning confocal microscopy (HT-LSCM) has become worldwide a proven technique for observing various metallurgical phenomena in situ. HT-LSCM turns out to be a reliable and effective method for the observation of quantification austenite grain growth kinetics in steel, being highly relevant in casting and steel processing. In the present article, the measurement technique is briefly introduced followed by some basics on austenite grain growth. Finally, selected examples of recent research activities are discussed, including investigations into pure iron and the systems Fe-P, Fe-C, Fe-Al-N, and Fe-C-Nb-N. The influence of P on the grain growth kinetics is remarkable. At 1350 degrees C, the final grain size decreases from 255 mu m in pure iron to 145 mu m by adding 0.044 wt% P. In contrast, C enhances the grain growth in specific alloying ranges (0-0.30 wt%C), particularly at elevated temperatures. For a Al content of 0.025 wt% and only 50 wt ppm N, AlN loses the pinning effect above 1150 degrees C. In case of Nb(C,N), an elevated Nb content (0.085 wt%) provides stabilization of Nb(C,N) at 1150 degrees C, but at 1250 degrees C, no pinning of Nb(C,N) is visible anymore.