| 10Ni5CrMoV steel is a kind of high strength low alloy steel for warship manufacture. Rotating arc NG-GMAW is a kind of highly efficient welding method, which is used in the large-scale structural welding. A welding test system which includes a robot, a 2 axles positioner and a rotation arc welding torch was established, based on synergetic control of robot and 2D positioner, automatic track of space curve welding can be realized. In the paper, based on PC,DAQ PCI-6023E data acquisition card and LabVIEW platform, an acquisition system was established to synchronously gather welding parameters, images of arc and droplet transfer , which will be used to analyze arc behavior and welding bead shape feature. Correlation between the microstructure distribution feature, change rule and mechanical property of welding joint was studied through computation simulation, physical simulation, welding experimental and theoretical analysis step by step. The research results have important theoretical significance and provide a powerful support to promoting welding technical level, decreasing the cost, and shorten production cycle.In this works, based on the collected data of welding current and voltage, the influence of rotation frequency on the stability of welding process can be discussed by U-I analysis, time domain analysis and time-frequency domain analysis. In regard to U-I analysis, the smaller the varying extent of welding current and voltage is, the smaller the area of U-I triangle is, it means the more stable the welding process is. Moreover, the narrower the cluster width of triangle sides is, it means the more stable the welding process is. In regard to time domain analysis, when the amplitude of the characteristics spectrum is small and the number of the random frequency spectrum is few, that means the length of the arc and droplet transfer feature have no obvious change, and the welding process is stable relatively. In regard to time-frequency analysis, the lower the density of spectral line is, the smoother the spectral line is, it means the more stable the welding process is. Based on above analysis, the following conclusion is got that the stability of spray transfer or small droplet transfer is higher than that of big droplet transfer.In the paper,the rule of influence of welding technological parameter on weld shape has been investigated, applying the dimensional analysis to set a relationship model of weld shape and welding technological parameter. The dimensionless (?)has been put to characterize the weld surface forming of rotation arc NG-GMAW. And the weld surface shape characteristics calculating equation is given as the following,pool width =2.4828×10-3×(?6)0.0460×(?7)0.1017pool depth=3.7641×10-22×(?6)-0.7139×(?7)1.9783bend depth of pool=2.66.9×10-8×(?6)0.0228×(?7)0.6088.The TTT and CCT curve of 10Ni5CrMoV steel and Js80 wire were calculated by using of the JMatPro software. The key temperature points such as A3, A1, Ms and Mf were obtained. The microstructure and phase distribution characteristics in every zone of welded joint of the 10Ni5CrMoV and Js80 as well as its microstructure change rule under different cooling rate were predicted through the numerical simulation calculation, meanwhile the mechanical properties of welding joint were calculated. It is found that the microstructure change with increasing cooling velocity according to the following rule: bainite + ferrite?Ma+ bainite + ferrite?Ma+ bainite + retained austenite. The higher the cooling velocity is, the bigger Ma transforming trend is. The yield strength of HAZ is between 708.1?875.6MPa with different cooling velocity.The microstructure change under different thermal input can be obtained by thermal simulation with the Gleeble3500. It is found that the microstructure evolution rule with increasing t8/5 is as following: lath Ma + acicular Ma?lath Ma?lath Ma + granular bainite?lath Ma +granular bainite + a little acicular ferrite, meanwhile the Martensite, as the main phase in CGHAZ, will become bigger in the lath width ( from1.3?2.4um to 2.4?3.3um) and the size of Ma lath cluster ( from 7.6?18.9um to 30.2?43.9um). With increasing t8/5, the side of grain becomes bigger in the size ( from 34.6?37.9um to 80.5?119.7um). From above thermal simulation analysis, the microstructure distribution feature and change rule of HAZ is almost same as that of simulation calculation.The microstructure and phase distribution feature of real welding joint have been analyzed through OM, SEM and TEM. The rule of microstructure evolution when the initial temperature is between 25?250?is as following: the lath martensite, as the only phase in the completely quenching area, the lath width and the size of lath cluster becomes bigger with the increasing of initial temperature; the granular bainite, as one phase of multiphase zone which included Ma+granular bainite+ tempered Ma in the incomplete quenching area, becomes more slightly with the increasing of initial temperature. Based on thermodynamic calculation, the formation mechanism of the acicular ferrite is analyzed. In the rotation arc NG-GMAW process, the content of pool element may fluctuate greatly. The activity of element C decreases with reducing transformation temperature, and the driving force of ferrite nucleation increase to promote the formation of acicular ferrite.The mechanical properties of the NG-GMAW welded joints of 10Ni5CrMoV steel had been investigated through tensile strength tests, bending tests, Charpy impact tests and microhardness tests. It is found that the welding fusion zone was weak zone through the tensile strength tests. The fracture position of the tensile joint with different initial temperature is fusion zone or fusion zone + welding seam. The initial temperature has an obvious effect on the bending performance of joints. When the bending 120°, no cracks is found in the bending sample with 150?, and the bending sample have not ruptured when the bending 180°. The bending performance of joints cannot satisfied with GB standard when the initial temperature is 25?or 250?. The -50?Akv is low to 27J when the initial temperature is 250?. The low Akv is concerned with coarse grain and Ma microstructure.The hardness of the joint increases gradually from the root to up of weld seam. The reason is concerned with heat effect of later pass on prior pass during multipass welding. |
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