Effect of boron on microstructure of directionally solidified high chromium white irons

Abstract

This work analyses the effect of boron additions (up to 195 ppm) in a directionally solidified high chromium white iron (17Cr–2·5C). Owing to its high level of segregation during solidification, boron additions have been able to change the solidification mechanism and hence to modify the microstructure of the iron. Microprobe analysis in a scanning electron microscope was used to determine the chemical distribution within the phases forming the microstructure. Boron was observed to segregate mainly to the austenite/carbide interface, it was also detected within the eutectic carbide and rarely as a boron compound. It was found that boron additions decreased the amount of proeutectic matrix and promoted a microstructural refinement by moving the chemical composition of the alloy towards the eutectic. An increase in the carbide volume fraction was measured as boron increased; however, no increase in the density of carbides was observed. These phenomena are discussed in terms of the boron segregation during solidification.

Keywords:

• High chromium cast iron
• Boron additions
• Directional solidification

This research was supported by the National Council of Science and Technology from Mexico (CONACyT) and the Universidad Michoacana de San Nicolas de Hidalgo. We are grateful for the financial support. R. Correa, one of the authors of this paper, also acknowledges the CONACyT for the sponsorship during the carrying out of this project.