Effect of Mo on mechanical properties of modified ultrahigh carbon steels after heat-treatment

Microstructure and mechanical properties of modified ultrahigh carbon(1.6%C)steels with different Mo additions(0,0.3%,0.5%,and 0.8%,mass fraction)were studied in their as-cast and quenched then tempered conditions by optical microscopy,scanning electronic microscopy,X-ray diffraction and hardness and toughness tests,respectively.The results show that the continuous eutectic carbide network structure has been broken down and changed to partial isolated and finer particles embedded in matrix of as-cast alloy by modification.Carbides in both quenched and tempered specimens have been refined effectively after the addition of Mo.Specimen containing 0.5% Mo shows the finest microstructures with carbides dispersed homogeneously in martensite matrix and demonstrates highest impact toughness of 18.4 J/cm2 and hardness of 50 HRC.