Advanced Materials Research Vols. 538-541

Abstract: In this paper, the welding microstructure of Ferritic Stainless Steel sheet with different Ti, Nb elements were studied. The experiment results shows that the addition of alloying element Ti +Nb stabilization steel causes the precipitation of Nb(CN) and TiN. This can reduce the C content, so the temperature of Ac1 increases, then it would be difficult to get martensite. Due to Martensite is harmful for toughness, so Ti+Nb elements are in need.

Abstract: Welding thermal cycle simulation with the heat input of 12~25 kJ/cm and practical welding were undertaken to investigate the weldability of a Zr-Ti microalloyed pipeline steel X120. The microstructure in the simulated coarse-grained heat-affected zone was predominantly bainite. The Vickers hardness and room temperature impact toughness of simulated coarse-grained heat-affected zone is 276~297 (HV10) and 208~225 J, respectively. These results indicated that the X120 steel had good weldability. Practical plate welding with the heat input of 21 kJ/cm also showed that the Zr-Ti microalloyed pipeline steel X120 had high yeild strength (895 MPa) and low temperature (-30°C) impact toughness (183 J, 204 J and 208 J in the fusion line, coarse-grained heat-affected zone and fine-grained heat-affected zone, respectively).

Abstract: Aim to the question of laser welding easy rapture of hot rolling Si-steel strip. Utilize the Trumph TLF12000 fast-flow CO2 laser, and the method of laser welding, laser welding with filling wire and laser welding with normalize, the laser welding characteristic and mechanical performance of 50ww600 hot rolling Si-steel strip have been studied experimentally.The technology of improving the welding performance has been probed into.It include that the softing of laser welding lead to break easily. The question may be solved by the method of laser welding with filling wire.

Abstract: The present paper deals with experimental studies on the ultra-high cycle fatigue property of Q345 bridge steel. Using the ultrasonic fatigue testing technique, specimens of Q345 welded joint with hourglass shape were designed using an analytical method combining with the finite element method and then fatigue tested in air at room temperature under fully reversed cyclic loading conditions (R=-1). The results show that the S-N curves of welded joints and relative base material specimens show continuously decreasing tendency in the very high cycle regime (105-109 cycles). Fatigue property of welded joint is much lower than that of base material and the fatigue strength of welded joint is only 45.0% of base material. Fracture can still occur on welded joints beyond 5 106 cycles, which indicates the fatigue limit defined at lifetime of 5 106 cycles cannot guarantee a safe design.

Abstract: As abrupt change of the shape and elastic constant in the weld area occurs to the welding joint, there will be obvious stress concentration near the weld area when being loaded. Lifting and Lowering Method and Grouping Method prevailing in the world are applied to conduct an experiment about fatigue strength of a certain welding joint in Wuhan Iron and Steel and S-N curve is drawn in this paper based on the condition of nominal stress. In addition, the influence of weld size of the welding joint on the distribution of stress is studied through the calculation of finite element numeral value and experimental test. According to the factor of stress concentration, S-N curve is modified to provide the data support for the application of the welding joint and assessment of fatigue strength.

Abstract: In order to solve the problem of thin plate butt-welded tracking, a welding vision sensing system with a rotund facular laser has been designed. In the vision sense system, each parameter of the interior part has been designed by a variety of experiments. The designed image processing software can precisely identify the position of the joint, based on the optimal designed vision sensor system. The thin plate butt welding experiments have been taken with the designed sensing device. The experimental results show that the vision sensor system with a suitable auxiliary illuminant can obtain satisfying visual image information in stainless thin plate butt-welded.

Abstract: Crystallization of aluminum alloy directly affects the brazing beam quality. The transmission electron microscopy (TEM) was used to measure lattice parameter of aluminum in the brazing beam. And the differential scanning calorimeter (DSC) was used to measure endothermic and exothermic reaction in the vacuum brazing process. The experiment results indicate that the latent heat of crystallization in the crystallization is –370.7J/g, the critical work of nucleation is 3.82×10－17J, the critical radius of nucleation is 8.69×10－10m, the volume of critical crystal nucleus is 2.75×10－27m3 and the per unit cell in critical crystal nucleus is 43, the number of atoms is 172, in the actual crystallization the number is less than 172.

Abstract: Currently, the consistency of tailor welded blanks ( TWBs ) with the design part is receiving more attention owing to the extensive use of TWBs. An approach based on compensation principle is proposed in this paper, which reduces the deviation between the design weld line and the actual weld line after forming of TWBs. Firstly an optimization model based on the offset of the blank weld line of TWBs is built. Then a C++ program is developed as the external customized optimizer. It bases on the FEM simulation software HyperWorks. At last, a example using the approach is provided, and the results show that the method is practicable.

Abstract: Numerical simulation based on MSC.MARC was applied to predict the residual stress in double-sided double arc welding (DSDAW). The distribution of residual stress field in the welding seam was simulated and the actual situation in experiment of the residual stress was also measured. It shows that the calculated results are in good agreement with the experimental ones. The residual stress of conventional welding (CW) or a single arc welding (SAW) is calculated too. Moreover, the welding residual stress field of thick metal plates welded by DSDAW was carried out and compared with that of the CW method with back chipping. The result shows that the DSDAW technology had some excellent characteristics of smaller angular deformation, lower residual peak tensile stress, and well-proportioned stress distribution, which testifies that the welding procedures in DSDAW are reduced and the welding efficiency and quality of the welding joint are improved in great margin.

Abstract: In this paper, to investigative effects of preheating and postweld heat treatment on residual stress field in Q345 steel pipe welding, the finite element model was established. Preheating processes and postweld heat treatment process were simulated respectively. The results show that preheating can homogenize residual stress distribution of the weldment and decrease the residual stress. The heat treatment reduces the residual stress in inner and outer walls by 40% and 60% respectively and the stress distribution is more even and the stress concentration is reduced.