Abstract: The effects of Fe-Si_3N_4 addition on the room temperature physical properties and hot mechanical properties of MgO-based castables using magenisite as main raw and micropowder as binder were investigated. The phase and microstructure were analysed by XRD, SEM. The results show that as the increase of Fe-Si_3N_4 addition the drying strength decreases .The immediate temperature strength increases first and then decreases and the maximum value is obtained when 3% Fe-Si_3N_4 is added. High temperature strength increases first and then drops.The hot modulus of rupture maximizes when 3% Fe-Si_3N_4 is added. Fe-Si_3N_4 partially oxidizes to produce SiO_2 and further tranforms to fibrous M_2S contributing to strength.The phase containing iron can produce solid solution with magnesia contributing to sintering .

Key words: Fe-Si_3N_4%magnesia%castable%mechanical properties%microstructure