Inclusion behavior and microstructure of weld metal with Ce in twin wire high heat input submerged-arc welding

In this study, the welding thermal cycle curve exhibited two temperature peaks in high heat-input twin-wire separate-pool submerged-arc welding and coarse-grained heat affected zone existed in the welded joint.The inclusions of primary weld metal and coarse-grained heat affected zone of Ce-added SAW should be Al2O3, MnO, SiO2, TiO, Ce2S3, CeS, Ce2O2S and Ce2O3.Under the effect of welding thermal cycle, oxy-sulfides inclusions of Ce, the diameter of which was less than 2.0 μm, slightly grew larger, but the composition and type of the inclusions didn't change.The microstructure of the large heat input weld metal had acicular ferrite that Ce oxide sulphide particles induced nucleation and proeutectoid ferrite.In the coarse-grained heat affected zone of weld metal, home-position precipitation of acicular ferrite and sympathetic acicular ferrite were both observed.It was supposed that previous crystal cells of acicular ferrite in austenite grain promoted home-position precipitation of acicular ferrite.Meanwhile, sympathetic acicular ferrite tended to nucleate at the primary acicular ferrite grain boundaries, where high dislocation density was located, and grew inside the neighboring carbon-depleted austenitic regions.The granular bainite nucleated in the austenitic zone with high carbon content close to acicular ferrite and sympathetic acicular ferrite.