Study On Seamless Flux Cored Welding Wire Of 0.5Ni System With Super Low Hydrogen And High Toughness

The purpose of the paper was to develop a seamless flux cored welding wire(TME711NiSF)which was compatible with the 420 Mpa grade steel used in marine platform and meeted the requirements of the marine platform on the performance of the welding materials,and study the mechanism of toughening and reducing hydrogen.The development process and performance tests of the seamless flux cored welding wire were studied in the following aspects:1.Based on the performance requirements of the construction of the marine platform on the flux cored wire for 0.5Ni system,the Ti-based alkaline slag and Mn-Ni-Si-Ti-B alloy system were determined and a kind of seamless flux cored wire named TME711 NiSF was developed on the seamless flux cored wire production line imported from Germany.2.In order to improve the mechanical properties of the welding wire,the contents of deoxidizer and alloying agent in the formulation were optimized.The results showed that when the oxygen content in the deposited metal was low,the contents of Ti and B were suitable,and the content of Mn and Si were at the optimized levels,the microstructure was mainly composed of uniform and fine acicular ferrite with good ductility and toughness.The impact absorbing energy at-40℃ can be reached up to 154 J.3.In order to meet the needs of high heat input welding and post welding heat treatment in the construction of offshore platform,the adaptabilities of the welding wire on the heat input and post weld heat treatment were studied.The experimental results showed that the welding wire had good adaptability to the heat input of 14 ~ 30 kJ/cm with most of acicular ferrite microstructure,which can obtain excellent mechanical properties.The post welding heat treatment had little effect on the properties of the welding wire,and the welding wire was adapted to the post welding heat treatment in engineering.4.In order to study the crack resistance of the welding wire,the G-BOP test,Y-groove cracking test and the fillet weld cracking test with thick plate designed by ourselves were carried out.The results showed that the welding wire had good crack resistance due to its high toughness and low hydrogen content(2.4m L/100g).Because the fillet weld cracking test with thick plate contained the three elements affecting the cold cracking sensitivity and the experimental results were in good agreement with the results of the G-BOP test and Y-groove cracking test,it was believed that this method could be applied to the detection of cold cracking sensitivity of fillet welds in engineering.5.In order to study the fracture toughness of the welding metal,CTOD test was carried out.The results showed that the welding joint had good fracture toughness due to the uniform and fine acicular ferrite microstructure with good ductility and toughness which can effectively prevent the crack propagation.