Effect of Zr on microstructures and impact toughness of deposited metal by self-shield flux cored wire on submarine pipeline steel

Four types of self-shield flux cored wires with different Zr content were prepared in laboratory and the deposited metals were made by self-shielded flux cored welding.The effect of Zr on microstructures and impact toughness of deposited metal of self-shield flux cored wire was studied.The results show that the inclusions of Zr-additioned deposited metal are mainly nitrides and oxides of Al-Mg-Zr.With the increase of Zr content,the microstructure of deposited metal is gradually uniform and refined,and the proportion of acicular ferrite increases gradually;The number of inclusions also increases with the increase of Zr content and the size of inclusions decreases with the increase of Zr content.The improvement of impact toughness of deposited metal is attributed to the increase of acicular ferrite and the refinement of inclusions and grains.When the content of Zr is 2%,the average impact toughness of deposited metal at-40 ℃is up to 132 J.