The unique phase transformation and carbide evolution in 9Cr18 steel were investigated during semi-solid forming and subsequent heat treatment.The functional gradient thixoforging 9Cr18 component was divided into inner area and edge area.Microstructure evolution was different at each area.After semi-solid cooling,the solid particles in the inner area were retained as meta-austenite.During annealing,M23C6 carbide began to precipitate when temperature reached 700 ℃.Martensite transformation occurred when temperature reached 800 ℃.The occurrence of M23C6 carbide and martensite structure would be harmful to the mechanical properties of inner area.In the edge area,the liquid underwent eutectic transformation to form bar-shape M7C3 carbide and secondary austenite after semi-solid cooling.The width of bar-shape carbide would decrease during annealing.By controlling the carbide evolution,we could tailor the functional gradient material with required property.