Effects of W on microstructure of as-cast 28 wt.%Cr-2.6 wt.%C-(0-10)wt.%W irons

• Main Authors: S. Imurai, C. Thanachayanont, J. T.H. Pearce, K. Tsuda, T. Chairuangsri
• Format: Journal
• Published: 2018
• Subjects: Agricultural and Biological Sciences
• Online Access: https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=84911867500&origin=inward; http://cmuir.cmu.ac.th/jspui/handle/6653943832/44759
• Institution: Chiang Mai University

© 2014 Elsevier Inc. All rights reserved. Microstructures of as-cast 28 wt.%Cr-2.6 wt.%C irons containing (0-10)wt.%W with the Cr/C ratio about 10 were studied and related to their hardness. The experimental irons were cast into dry sand molds. Microstructural investigation was performed by light microscopy, X-ray diffractometry, scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. It was found that the irons with 1 to 10 wt.%W addition was hypereutectic containing large primary M 7 C 3 , whereas the reference iron without W addition was hypoeutectic. The matrix in all irons was austenite, partly transformed to martensite during cooling. The volume fractions of primary M 7 C 3 and the total carbides increased, but that of eutectic carbides decreased with increasing the W content of the irons. W addition promoted the formation of W-rich M 7 C 3 , M 6 C and M 23 C 6 . At about 4 wt.%W, two eutectic carbides including M 7 C 3 and M 6 C were observed together with primary M 7 C 3 . At 10 wt.%W, multiple carbides including primary M 7 C 3 , fish-bone M 23 C 6 , and M 6 C were observed. M x C where x = 3 or less has not been found due possibly to the high M/C ratio in the studied irons. W distribution to all carbides has been determined increasing from ca. 0.3 to 0.8 in mass fraction as the W content in the irons was increased. W addition led to an increase in Vickers macro-hardness of the irons up to 671 kgf/(mm) 2 (HV30/15) obtained from the iron with 10 wt.%W. The formation of primary M 7 C 3 and aggregates of M 6 C and M 23 C 6 were the main reasons for hardness increase, indicating potentially improved wear performance of the as-cast irons with W addition.