Formation and Morphology of M₇C₃ in Low Cr White Iron Alloyed With Mn and Cu

ISSN： 1059-9495

Source： Journal of Materials Engineering and Performance, Vol.12, Iss.1, 2003-02, pp. : 14-18

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Abstract

The presence of M ₇C₃ carbide in white iron enhances its wear resistance because of high hardness. Scanning electron microscopy (SEM) revealed its morphology as a pencil-like hexagonal structure. On the basis of the SEM observations, elemental distribution studies, and differential thermal analysis (DTA) of some heat-treated hypoeutectic white irons alloyed with Cr, Mn, and Cu, it is concluded that M₇C₃ carbides form as a result of attainment of a favorable condition in the liquid phase present at the austenite grain boundaries. Segregation of phosphorus in the intercellular regions and formation of a copper-rich intermetallic is responsible for the formation of this liquid phase. Austenite was found to nucleate first, followed by the nucleation and growth of M ₇C₃ carbide in its vicinity, because of rejection of C and Cr during formation of austenite. The rosette structure generally observed is formed from the joining of M₇C₃ carbides by precipitation of secondary carbides.