ELECTROSLAG WELDING METHOD FOR FIRE RESISTANT STEEL

PROBLEM TO BE SOLVED: To obtain a welded metal excellent in ductility at a high temperature by controlling the depth of a molten slag bath to a prescribed range, controlling the oxygen content of the weld metal to a prescribed range, and controlling the content of Al and B to a prescribed value or below. SOLUTION: In the electroslag welding method for fire resistant steel and steel of weatherability with fire resistant properties, which contain Al and B, the depth of the molten slag bath is made to 20 to 30mm, and the oxygen content of the weld metal is controlled to 130 to 180ppm by weight and Al is controlled to 130ppm or below. Since ductility the in a high temperature is impeded by B in the weld metal, it is necessary to suppress B to 5ppm or below. When the depth of the slag bath becomes shallower than 50mm which is usual welding condition, the oxygen content in the weld metal is increased. When the slag bath is made extremely shallow, the oxygen content in the weld metal is increased. However, a defect such as a blowhole, occurs in a weld zone. To the contrary, when the slag bath is made extremely deep, the oxygen content in the weld metal can not be increased, and the ductility in a high temperature can not be secured.