Hardness distribution of multipass weld metal has been evaluated with numerical simulation. Fraction of microstructure and cooling rate during weld thermal cycle has been taken into consideration in evaluation of hardness. Continuous cooling transformation diagram (CCT diagram) has been used in calculation of microstructure. Simulated weld thermal cycle tests has been conducted to create CCT diagram for multipass weld metal. Microstructure of the weld metal after reheating has been more dependent on the peak temperature than the previous microstructure before reheating. Therefore calculation of microstructure has been conducted based on two different CCT diagram for the different peak temperature. Hardness distribution has been estimated based on the rule of mixture. Fraction of each microstructure has been calculated with CCT diagram, and hardness of each microstructure has been estimated from cooling rate. Hardness distribution of multipass weld metal has nicely reproduced with numerical simulation.
