Microstructure Evolution and Toughness Variation of Simulation HAZ with Large Heat Input Welding for E40 Ship Plate Steel

This Charpy impact toughness and microstructure evolution of simulated heat affected zone (HAZ) for E40 ship plate steel have been investigated in this experiment. Simulation of large heat input welding was conducted by thermal simulator to research microstructure evolution of HAZ at 1400°C peak temperature. Results show that microstructure at HAZ was mainly composed of high intensity of acicular ferrite (AF) and intragranular ferrite (IGF), and grain boundaries ferrite (GBF). Hardness of HAZ decreases with heat input (HI) increasing. Impact toughness for steel specimens with HI of 500 kJ/cm was 141 J. TiN precipitates nucleation and growth at HAZ was analyzed by TEM, indicating that TiN size increases and the number of TiN decreases at HAZ with HI increasing. The reason is that the specimens with HI of 400 kJ/cm has longer cooling time from 800°C to 500°C than 120 kJ/cm, which is favorable to growth of TiN particle at HAZ. (paper)