Weld hot crack in Fe-36%Ni alloy which is used as elements of'membrane-type container for liquefied gas was studied. One of the characteristics of the hot crack is that it occurs in weld metal reheated by the following welding pass. Its dynamic behavior in Cross-bead tensile hot cracking test was analyzed with direct observation technique (MISO technique). Regression analysis was done on chemical composition in relation to total crack length in Cross-bead tensile hot cracking test conducted for 24 different materials. Materials insusceptible to the hot crack were produced on practical production line, and used for practical fabrication of model tanks. Main conclusions are as follows: 1) Weld metal reheated to the range of 600°C to 1000°C by the following welding pass is susceptible to reheated hot crack. 2) Microstructural and fractographic features suggest that the reheated hot crack is ductility-dip crack. 3) S, O, N and Al are crack-promoting elements, while P shows a slight trend of crack-promoting. 4) Model tanks fabricated with materials insusceptible to the hot crack showed favorable result in inspections.
