| Super duplex stainless steel(SDSS) SAF2507 has not only superior corrosion resistance but also good strength and toughness, which has saved the scarcity of nickel resources in China, as a result, the steel is widely applied in petroleum chemical industry and other industries. The key technical problems of welding SAF2507 are dual phase imbalance in HAZ and a decline in joint performance which greatly led to the precipitation of brittle phase.At present, the study about thermal simulation, submerged arc welding technology and joint organization performance of SAF2507 are very little.In this paper, on the one hand, we simulate the HAZ organization of SAF2507 by GLEEBLE3800; on the other hand, we study the actual condition of SAW process.The results could provide important theoretical basis and production guidance for practical welding of SAF2507.Firstly,effects of the cooling time t8/5 on microstructure、phase proportion and precipitated phases(σ-phase) of HAZ of Super duplex stainless steel SAF2507 were studied through welding thermal simulation tests.The results indicated that with the increasing of cooling time t8/5, transformation from ferrite of HAZ to austenite was more sufficiently,content of austenite increased and austenite become more coarser,microhardness increased constantly, and the impact value of heat affected zone was reduced.When the cooling time t8/5 was between 20 s to 60 s, organization was relatively small, bipolar proportions was right, precipitated phase were very few, and the corresponding heat input was 1.141 ~ 1.977 Kj/mm, which can provide theoretical guidance for practical production.Secondly, effects of with the increasing of cooling time t8/5 on microstructure、phase proportion and precipitated phases(sigma phase) of HAZ of Super duplex stainless steel SAF2507 were studied through welding thermal simulation tests.After the multi-pass welding thermal simulation, the later pass acted a role of reheating on the previous which maked parts of ferrite transform into austenite.The results indicated that with the increasing of with the increasing of cooling time t8/5, the content of ferrite was decreasing, while austenite content was increasing, precipitated phase content was increasing at the same time, microhardness increased unceasingly,and the impact value of HAZ was decreasing.The last, the actual welding experiment of SAW was conducted under the support of simulation test data.The results demonstrated that the microstructure of SAW experiments was similar to the microstructure under the condition of thermal simulation;Additionally, precipitations(sigma phase) content by SAW were slightly greater than thermal simulation.Therefore,thermal simulation tests can provide theoretical reference for the formulation and adjustment of welding technology.The heat input of 1.141~1.977Kj/mm was recommended in this paper in practical production of SAW. |
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