Effects of Si on microstructure and phase transformation at elevated temperatures in ferritic white cast irons

• Main Authors: Wiengmoon A., Pearce J., Nusen S., Chairuangsri T.
• Format: Journal
• Published: 2017
• Online Access: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84984945107&origin=inward; http://cmuir.cmu.ac.th/jspui/handle/6653943832/41500
• Institution: Chiang Mai University

© 2016 Elsevier Inc. The effects of Si on microstructure and phase transformation at elevated temperature of ferritic 31wt.%Cr-1.1wt.%C white cast irons with up to 3wt.%Si have been studied. Applications of these irons include parts requiring heat resistance at elevated temperature. The irons were produced by sand casting. The microstructure in as-cast condition and after being subjected to high temperature (700 to 1000 °C) was investigated by light microscopy, X-ray diffraction, and electron microscopy. The results revealed that the as-cast microstructure consisted mainly of primary ferrite dendrites and eutectic (ferrite + M 7 C 3 ). Si promotes M 7 C 3 -to-M 23 C 6 transformation in the irons subjected to transformation at elevated temperature, but no sigma phase was found. The extent of M 7 C 3 -to-M 23 C 6 transformation increases proportional to the increasing transformation temperature, holding time and Si content in the irons. For the iron with 1.0wt.%Si content after holding at elevated temperatures, martensite was also found, which could be attributed to carbon accretion effects in eutectic ferrite. Si was incorporated in M 23 C 6 such that M 23 C 6 containing Si can show darker contrast under SEM-BEI as compared to M 7 C 3 ; this is the opposite to what has been observed for the cases of typical M 23 C 6 and M 23 C 6 containing Mo or W. The results obtained are important to understand the change in properties of ferritic, high chromium irons containing Si subjected to elevated temperature.