Studies On Composition Design,microstructure And Properties Of Ultra-high Strength Steel Weld By Twin Wire Gas Shielded Welding

With the continuous development of construction machinery to large tonnage,large-scale,lightweight and high safety,a large number of ultra-high strength steel(UHSS)have been used.With the improvement of strength grade,the contradiction between weld strength and toughness of UHSS has become more and more prominent.Therefore,new welding materials and welding processes are needed to solve this problem.According to the design concept of multi-principal element alloy,the physical and chemical parameter calculation and artificial neural network were used to assist the design.Through the coupling design of welding wire composition and welding process,the twin-wire GMAW equipment was used to prepare the nano precipitation strengthening heterogeneous weld with good comprehensive performance.According to the design concept of multi-principal element alloy,five sets of welding wires were designed.The twin-wire surfacing test was carried out on Q960E ultrahigh strength steel plate with a thickniess of 12 mm.The results showed that with the increase of the content of Al or Al and Ti,the microhardness value of the weld metal increases gradually,and cracks appear when the hardness is higher.The physical and chemical parameter calculation method was used to predict the phase structure of multi-principal element alloy.The results showed that when the?H_mixof all the alloys is between-10 and-5 k J/mol,?<0.06,?>2,stable solid solution structure can be formed.The??value of most of the alloys was greater than or equal to 0.117,which will easily cause to form TCP phases such as?and?.When VEC was between 6.88 and 7.84,FCC,BCC and?phase was easy to form.The BP artificial neural network model was established to predict the microhardness of multi-principal component alloy.24 samples were selected as the training samples of the network,and 6 samples were selected as the prediction samples of the network.The results showed that the established artificial neural network model can accurately predict the hardness of the alloy,and the absolute error was controlled within 15 HV.The microstructure of the Fe Ni Cr Co Mo Al system and Fe Ni Cr Co Mo Ti Al system and their effects on the properties were investigated by OM,SEM,TEM and XRD.The results showed that for the Fe Ni Cr Co Al multi-principal element alloy system,with the increase of Al content,the alloy structure changed from FCC phase to FCC+BCC+?phase and the hardness of the alloy increases gradually.For the Fe Ni Cr Co Mo Ti Al(Ti/Al=0.8)multi-principal element alloy system,with the increase of Al and Ti content,the microstructure of the alloy changes from FCC phase to FCC phase+?phase,and then to FCC phase+BCC phase+Laves phase+?phase,and the hardness of the alloy increases gradually.For Fe Ni Cr Co Mo Ti Al(Ti/Al=1.2)multi-principal element alloy system,with the increase of Al and Ti content,the microstructure of the alloy changes from FCC phase+?phase to FCC phase+?phase+Laves phase,and then to FCC+BCC+?phase+Laves phase,and the hardness of the alloy increases gradually.For the Fe Ni Cr Co Mo Ti Al(Ti/Al=1.6)multi-principal element alloy,with the increase of Al and Ti content,the structure of the alloy changes from FCC phase+Laves phase+?phase?phase to FCC phase+BCC phase+Laves phase+?phase,and the hardness of the alloy increases gradually.For the Fe Ni Cr Co Mo Al(Ti/Al=0.8)multi-principal element alloy system with B addition,with the increase of Al and Ti content,the microstructure of the alloy changes from FCC phase+?phase to FCC phase+BCC phase+Laves phase,and the hardness of the alloy increases gradually.Twin-wire GMAW welding was carried out on Q960E steel plastes with the optimized welding wire.The microstructure and properties of welded joint were studied by OM,SEM,XRD,tensile and impact testing machine.The results showed that the matrix of weld zone is FCC phase,and nano BCC phase is dispersed on the matrix.The tensile strength of welded joint is 1 025 MPa,the elongation is 14%,the fracture is located in the base metal,and the impact toughness at-40?is 89 J.The welded joint has good comprehensive properties.