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On the nature of eutectic carbides in Cr-Ni white cast irons.
Metall Trans, A, Phys Metall Mater Sci 1991 Aug; 22A:1709-1720
The mechanical and tribological properties of white cast irons are strongly dependent on whether they contain m7c3 or m3c carbides (m = fe, cr, etc.). In an effort to improve the wear resistance of such materials, the U.S. Bureau of Mines has studied the effects of adding 0.3 to 2.3 Wt pct (throughout) si to hypoeutectic irons containing approximately 8.5 pct cr and 6.0 pct ni. The eutectic carbides formed were identified by electron microprobe analysis, x- ray diffraction, and scanning electron (sem) and optical microscopies. In addition, differential thermal analysis (dta) was used to study the process of solidification. At si contents of 0.3 and 1.2 pct, the eutectic carbides exhibited a duplex structure, consisting of cores of m7c3 surrounded by shells of m3c. Additionally, the microstructure contained ledeburite (m3c + vfe(austenite)). At the higher si content of 1.6 pct, the eutectic carbides consisted entirely of m7c3, and some ledeburite remained. Lastly, when the si content was raised to 2.3 pct, the eutectic carbides again consisted entirely of m7c3, and some ledeburite remained. Lastly, when the si content was raised to 2.3 pct, the eutectic carbides again consisted entirely of m7c3, but ledeburite was no longer formed. These observations can be explained in terms of the effects of si and, to a lesser extent, of ni on the shape of the liquidus surface of the metastable fe-cr-c phase diagram. The addition of si reduces the roles played by the four-phase class IIp reaction l + m7c3 -> m3c + vfe and the ledeburitic eutectic reaction l -> m3c + vfe in the ov
OP; Journal Article
Metallurgical Transactions. A. Physical Metallurgy and Materials Science
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