Morphology of the boron-rich phase along columnar grain boundary and its effect on the compression crack of Fe–6.5Si–0.05B alloy

The morphology of precipitated phases along Fe–6.5Si–0.05B columnar grain boundary and its effect on the initiation and propagation of compression cracks were investigated. Under the present experimental condition, alloy phases along the grain boundary exhibited three different morphologies, i.e., thick-strip, fish-bone like and thin-strip. These phases were all with enrichment of boron and dilution of silicon. The grain boundary with dendrite growth mode was apt to generate the thick-strip and fish-bone like phases, while the boundary with cellular growth mode was easy to form the thin-strip phase. The thick-strip phase was favorable to form “weak plane” containing numerous micropores, which ultimately led to intergranular cracks. The fish-bone like phase was one of the main crack sources under the compression processing and easily caused transgranular cracks. The thin-strip phase enhanced the bond strength of the grain boundary and detained the crack propagation.