Investigation On Corrosion Behaviors Of Anti-corrosion Steels Joints For Cargo Oil Tanks

In order to study the corrosion behaviors and the effects of compositions,inclusions and microstructures on corrosion resistance of joints, new type anti-corrosionE36steels were welded by the5kinds of anti-corrosion solid wires which made bymyself.The differences of the solid wires were Ni,Cr,Mo,W elements of add anddifferent additives.It was concluded that the homemade solid wires and the original flux-cored wirescompared to the overall mechanical properties are not significant.The homemade solidwires were good enough to satisfy the standards of international association ofclassification societies. Although flux-cored wires have the advantages of little splash,welding path to shape, but the price is expensive, and corrosion resistance of them isnot good enough.The microstructures of the deposited metal are all for acicular ferrite+a few bainite+a few lath ferrite.Because comprehensive mechanical performance of the depositedmetal is better which contained a large number of acicular ferrite could improve thedeposited metal.Due to elastic model of the substrate and inclusion is different, so in impact, itaround inclusions produce stress concentration phenomenon, make inclusions becomecrack source. Research shows that ball inclusion on the influence of the impacttoughness minimum, short strip inclusion affected by, the influence of the slenderinclusion is the largest. Each joint of weld metal has many small and distribution ofuniform Si-Al-Mn-Ti composite spherical inclusions,which are the key of acicular ferrite nucleate. Research shows that size in0.2-0.8um spherical inclusion can induceacicular ferrite in the nucleation. Besides, inclusions served as the pitting initiation inweld metal.In the weld addition of suitable amount of Ni,Cu,Mo,W etc alloy elements that canbe a good strong toughness and enhance corrosion resistance role.Alloy element Cr inacidification pitting the stability of the pit is bad to make acid hydrolysis andenhanced,so for corrosion resistance is adverse.The difference contant of acicular ferrite is the main reason about the difference ofthe corrosion resistance between the different joint. Because of acicular ferrite has highdensity dislocation,and pitting corrosion induced and expanded easily,so it has largetendency of corrosion.Acicular ferrite,s grain boundaries is rich carbon layer,and ascathode by the protection when with other organizations in corrosion battery,and richcarbon layer will reduce the effects of acicular ferrite chemical corrosion rate.Therebyacicular ferrite is good for the corrosion resistance of the weld metal.