Critical Conditions for the Formation of A-segregation in 9Cr1Mo Steels

Laboratory scale casting experiment in 9Cr1Mo steel of 20 kg in mass was carried out and critical conditions for the formation of A-segregation was investigated. Critical values of cooling and solidification rates of the casing for the formation of A-segregation were evaluated based on the thermal analysis and metallographic examination. The influence of the addition of Mo, V and W on the formation of A-segregation was examined and it was shown that A-segregation was reduced in order of V, Mo and W addition. Phase-field simulations were carried out for the evolution of dendrite in Fe–C–V, Fe–C–Mo and Fe–C–W ternary alloys. It was shown that the effect of the adding elements on the promotion of the branching of dendrite is in order of V, Mo and W. Based on the simulation results, dendrite morphology becomes finer in V addition, then interdendritic fluidity decreased and the formation of A-segregation was suppressed.