The microstructural evolution and the tensile strength of in-situ eutectic composite in slightly hypo-eutectic Fe-27Cr-2.7C alloy

The microstructural evolution and tensile properties of directionally solidified near-eutectic Fe-27Cr-2.66C alloy were investigated under temperature gradients of 15 and 30 K/mm at withdrawal rates ranging from 5 to 160 μm/s. Two distinct solidification regimes were identified: fully aligned cellular eutectic structures at low to intermediate withdrawal rates, and primary dendrite formation with interdendritic eutectic at high rates. The critical velocity for eutectic-to-dendritic transition increased from 50-100 μm/s to 150-160 μm/s with increasing temperature gradient, in good agreement with theoretical predictions based on coupled-zone analysis (68 μm/s and 152 μm/s, respectively). Inter-fiber spacing decreased with withdrawal rate following λ ∝ V -0 · 5 , resulting in systematic microstructural refinement from approximately 14 μm at 5 μm/s to 2 μm at 150 μm/s. Directionally solidified specimens exhibited 2.1-3.6 times higher tensile strength (1405-2346 MPa) compared to conventionally cast material (654 MPa), with the finest microstructures achieving maximum strength. Microstructural analysis revealed that secondary M 23 C 6 carbides precipitated preferentially in rapidly solidified cell interiors during subsequent heat treatment. The results demonstrate that controlling temperature gradient and withdrawal rate enables production of fine, aligned M 7 C 3 /austenite eutectic composites at industrially relevant solidification rates (up to 150 μm/s), offering a viable approach for manufacturing high-strength, wear-resistant components for mining and mineral processing applications.