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The in‐situ V8C7‐V3B4/Fe45 composites were fabricated by vacuum sintering using ferrovanadium, carbon black and Fe45 alloy powders as raw materials. The microstructure, phase structure and hardness of sintered Fe45+x wt.% (FeV+C) composite specimens (x = 0, x = 5, x = 10, x = 15, x = 20) were investigated. The results show that the type and shape of in‐situ borides and carbides depend on the content of (FeV+C) mixed powders. When x = 5, the composite consists of α‐(Fe, Cr, V) solid solution, strip M7C3 carbides and block M2B borides. When x = 10, the V3B4 particles initiate inside the M2B borides by in‐situ precipitation, and the excess vanadium reacts with carbon to in‐situ form V8C7 particles. When x≥15, the M2B completely transform into V3B4. Furthermore, the V8C7 and V3B4 particles coarsened and tended to be spheroidal and rectangle shape respectively. The V3B4 particles coarsen possibly by contacting and merging of the small V3B4 particles. However, the V8C7 particles coarsen possibly by the Ostwald ripening. The hardness of the composites increases firstly and then decreases with the increase of (FeV+C) mixed powders. The Fe45+10 wt.% (FeV+C) composite has the highest hardness value (54.2 HRC), which is due to the fine boride and carbide reinforcement and little pore defect.