Study on time dependence fracture of weldment of steel in molten Zinc

The liquid metal embrittlement cracking (LMEC) of heat affected zone (HAZ) of steel in hot dip galvanizing was investigated. The experiment was conducted using synthetic HAZ of JIS G 3444 STK55 and Sustained Load Test (SLT) at 370°C-470°C heating range in liquid (molten) and solid Zinc.The results obtained are as follows.(1) LMEC behavior is of thermal activated process and LMEC sensitivity is affected by hardness of HAZ.(2) The coarse grain region in HAZ showed the highest LMEC sensitivity.(3) The interfacial energy of steel is reduced by the existence of Zinc.(4) The reaction rate process of LMEC of steel is controlled by grain boundary diffusion of Zinc.(5) The nucleation and the propagation of LMEC in steel are likely to have a close relation to the reduction of interfacial energy due to the grain boundary diffusion of Zinc.