Toughening of X100 pipeline steel welded joints

Submerged arc welding tests were carried out on X100 pipeline steels with its special wire by using different heat inputs.The microstructure of the welded zones consists of quasi-polygonal ferrite and carbide-free bainite.The difference lies in the ratio,size,shape and distribution of different phase.With welding heat input 15.75 kJ/cm,the temperature of weld pool field is most suitable,and the content of quasi-polygonal ferrite and carbide-free bainite of the welded zone is 70.5% and 28.8%,respectively,and the strength and toughess of the welded joints reaches the maximum.In slag system,the content of MnO should be strictly controlled in less than 8%;When the content of Al2O3 is between 22% and 28%,it is beneficial to deslagging,and does not increase the oxygen content and oxide inclusions of joint.