Hypo-eutectic irons with 5%, 10%, 15% and 30% chromium and with 0.5 to 3.8% carbon were quenched during solidification, and the dendrite arm spacings were measured to clarify the growth process of the primary dendrite in Fe-Cr-C alloys. The distribution of chromium in the dendrites was analyzed with an electron probe micro-analyzer to investigate the solute redistribution during dendrite growth. The secondary arm spacing (D₂) during solidification was expressed by the empirical equation as follows: D₂=A₂θ_f^0.30, where θ_f was the solidification time. A₂ decreased with increasing chromium content, carbon content and cooling rate. The equation Ḋ₂/D₂=0.30 θ_f⁻¹ indicates that coarsening and coalescence of the secondary arms occur more frequently in the earlier stages of solidification than in the later stages. The distribution coefficient (K_Cr) of chromium in the primary dendrite decreased almost linearly with increasing carbon content. In the specimens with chromium ranging from 5 to 15%, K_Cr was little affected by the chromium content and was expressed by the next equation.
            K_Cr=−0.11(%C)+0.99
K_Cr of the 30% Cr iron was appreciably larger than that given by the above equation. The segregation ratio of chromium in the dendrite is quantitatively expressed by the ratio of the chromium content in the boundary of the dendrite (C??) to that in the core (C??). The ratio C??/C?? decreased gradually from 1.8 and 1.5 to 1.0 with increasing carbon content in the 5% and 10% chromium irons. On the other hand, C??/C?? of the 15% chromium irons was at the maximum value 1.4 at about 1.1% carbon. C??/C?? of the 30% chromium irons was less than 1.1. The results could be explained by the dependence of C??/C?? on both K_Cr and the fraction of the primary solid.