The Development Of Submerged Arc Welding Material For X80 Pipeline Steel

According to the requirement for the properties of X80 pipeline steel, The submerged arc welding wire for X80 pipeline steel and a new agglomerated flux for high strength-toughness steels were developed based on the technological route of strengthening acicular ferrite with bainite. The submerged arc welding deposited metals by this welding wire in couple with agglomerated flux SJ101-G possesses quite high yield strength (σ_s≥551MPa) and excellent toughness(A_KV(-20℃)≥160J), which meet the mechanic performance requirement for X80 welding pipe. The submerged arc welding deposited metals by this alkali agglomerated flux in couple with welding wire H08C possesses higher yield strength and toughness than those using SJ101-G,and Charpy impact value is A_KV(0℃)≥170J), which meet the mechanic performance requirement for X80 welding pipe.The analysis of X80 pipeline steel weldability show that X80 pipeline steel has low cold crack sensibility and there are different changes in microstructure and properties at heated affected zone (HAZ). The toughness of CGHAZ decreases because carbide and martensite-austenite constituents appear in coarse-grained heat affected zone (CGHAZ) which consist of coarse grain proeutectoid ferrite and granular bainite. There is a softened zone between the intercritical heat affected zone (ICHAZ) and the subcritical heat affected zone(SCHAZ).The nucleation of acicular ferrite is studied in this paper, and the results indicate that the inclusions in welding deposited metals are chemical heterogeneous compound inclusions which includes various phases such as Al₂O₃, MnO, Ti₂O₃, and α-MnS so on. There is alloy elements (such as Mn, Ti, etc.) depletion around inclusion, and multiple acicular ferrite plates nucleate at one inclusion and grow radially. Excessive Mn element content is adverse to the acicular ferrite in the weld, however, the weld containing more Ni element content can obtain more high-strength and toughness for promoting acicular ferrite nucleate effectively. There is a low content of acicular ferrite in the fusion area because of lacking of valid nucleating particles for acicular ferrite. Comparing to alloy elements, there is faintish Mn and Ni elements segregation phenomenon in the weld, so, the weld ensuring Mn and Ni element content can promoting the...