Abstract
The effects of the chemical composition of base metal on the toughness, hardness and microstructure of weld metal was studied in order to get higher toughness of submerged arc weld metal of high grade line pipes produced from controlled rolling process. As a result the authors clalified the optimum micro-alloy content of base metal which would make the high toughness weld metal.
(1) Low C-0.2 Si-1.6 Mn system of base metal was the best material for toughness of weld metal. Microalloy element should be added to this basic composition to make high toughness weld metal.
(2) Combined addition of nickel and molybdenum was best as micro-alloy element. Copper and Chromium was effective if a small amount.
(3) The reason was due to preventing proeutectoid ferrites of weld metal and making them fine.
