Study On Microstructure And Performance Of SAF2507 SDSS Welding Thermal Simulation

Compared with conventional duplex stainless steel, the super duplex stainless steel SAF2507 has higher content of Cr, Mo, N element and a lower carbon content, meanwhile, the PREN of SAF2507 is more than 40. With the excellent resistance to pitting corrosion, crevice corrosion, chloride corrosion resistance and high mechanical strength, SAF2507 has been widely used in high corrosion resistance and high strength requirements of extremely environment, such as shipbuilding industry, marine oil and gas field exploitation, desalination and submarine pipeline laying. According to the research of domestic and abroad, the heat affected zone(HAZ) is usually the most vulnerable area of the welded joint. It is hard to accurately evaluate the microstructure and properties of HAZ with the general welding methods due to the size of HAZ is very small, while the thermal simulation experiment has provided a good technical means to study this area. Therefore, the welding thermal cycle process has been simulated by thermal simulation method to study the influence of different parameters on microstructure evolution, corrosion resistance and mechanical properties of SAF2507 heat affected zone. Subsequently, shielded metal arc welding(SMAW) test was used to evident the correctness of simulation. The results show that welding thermal simulation test can provide theoretical basis for the actual welding production.Firstly, the effects of the cooling time t12/8 on microstructure, phase proportion, precipitated phases, corrosion resistance and mechanical properties of SAF2507 high temperature HAZ were studied through single-pass welding thermal simulation tests. The results indicated that with the increase of cooling time t12/8, microstructure transforming from ferrite to austenite of high temperature HAZ was more sufficient. Thus, austenite content increased, austenite grain gradually became more coarser,microhardness decreased, impact value increased and the corrosion resistance first reduced and then rised. When the cooling time t12/8 was up to 34 s, microstructure was relatively small, bipolar proportions was appropriate, intermetallic precipitated phase was inexisted, corrosion resistance was better and the corresponding heat input was 1.789kJ/mm, which provided theoretical guidance for practical production.Secondly,the effects of the interpass temperature on microstructure, phase proportion, precipitated phases, corrosion resistance and mechanical properties of SAF2507 high temperature HAZ were studied through the multi-pass welding thermal simulation tests. The results indicated that with the increase of interpass temperature in the range of 150~250?, the ferrite content of high temperature heat affected zone(HAZ) decreased, while austenite content increased, microhardness decreased, impact value increased and corrosion resistance also gradually decreased. When the interlayer temperature was 300?, a lot of sigma phase precipitated, meanwhile, the microhardness increased, impact value decreased, and the corrosion resistance declined further.In the end, the actual welding experiment of shielded metal arc welding(SMAW) surface overlaying was conducted according to the thermal simulation test datas. The results demonstrated that, when the welding heat input was comparative approaching, the microstructure and corrosion resistance of shielded metal arc welding(SMAW) experiments was similar to the microstructure and corrosion resistance of thermal simulation.In this paper, the thermal simulation and actual shielded metal arc welding(SMAW) surfacing welding of SAF2507 were tested. The comprehensive results showed that in the single-pass welding thermal simulation tests, corrosion resistance and mechanical properties at high temperature heat affected(HAZ) were relatively superiored when the cooling speed of t12/8 was 34s(corresponding to the heat input is 1.696kJ/mm). In the multi-pass welding thermal simulation tests, corrosion resistance and mechanical properties at high temperature heat affected(HAZ) were relatively superior when the interpass temperature was 150?. The surface overlaying of shielded metal arc welding(SMAW) showed that welding thermal simulation tests can provide theoretical guidance for practical welding test.