Abstract: In order to study the microstructure change and the phase transformation of the austenitic~bainitic ductile iron weld metal,a Formastor ~F phase transformation apparatus has been used to measure the cooling curves and volume expansion curves of the weld under different cooling rate.Through analy zing the characterization of these curves and in combination with the data obtained from the quantitative metallog raphic analysis and hardness measurement,all the critical points of the phase transformation were determined and a continuous cooling transformation diagram (CCT diagram) of the weld metal was developed.The diagram will be used to help the choice of the welding technology.