Morphology and distribution of precipitates in the Fe-6.5Si-0.02B alloy were characterized, and these effects on room-temperature compression cracks were investigated. The results showed that the precipitate in the Fe-6.5Si-0.02B alloy is Fe2B with body-centered tetragonal structure, and its nano-hardness is 15.0 GPa which is higher than that of the matrix (~ 8.5 GPa). In the as-cast alloys, most of the intragranular precipitates are coarse lath-like with the length of 5–15 μm and width of 2–5 μm, and the precipitates formed at the grain boundaries are of about 2–3 μm in width. After oil quenching followed by heat treatment at 1100 °C for more than 30 min, the precipitates inside grains are refined with a size of several hundred nanometers and the precipitates at the grain boundaries are refined with a size of < 1 μm. After compression test, transgranular and intergranular cracks occur in the as-cast alloys with coarse precipitates. For the quenched alloys with fine precipitates, the number of cracks decreases significantly, and no transgranular cracks happen because some cracks are blocked or the propagation direction is changed by grain boundary.
Fe-6.5 wt% Si alloy Precipitates Nano-hardness Room-temperature compression
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This research was funded by the Major States Basic Research Development Program of China (973 Program, No. 2011CB606300) and China Postdoctoral Science Foundation (Nos. 2012M520263 and 2013T60110).