Papers by Keyword: Weld Joint

Abstract: The X70 pipeline steel welded joint was processed to strengthen with laser shock wave, the structures of welded joint by laser shock wave were observed with Scanning Electric Microscope (SEM), and its surface residual stresses was analyzed with X-ray diffraction (XRD), the residual stress distributions of welded joint by laser shock processing were discussed, and the strengthened mechanism of X70 pipeline welded joint by laser shock processing was investigated. The experimental results shown that the phenomenon of grain fine is produced in the surface of X70 pipeline steel welded joint by laser shock processing, and compressive residual stress is formed in its surface layer, and improves the distribution of residual stress, which is benefit to increasing the capability of stress corrosion resistance for X70 pipeline steel welded joint.

Abstract: A steel footbridge with a 27m net span, a worm-shaped curve and a vine bridge style was proposed to be constructed in Diexi city of Sichuan, China. Considering the appearance and the functional requirement, the bridge is designed as follows: the section outline is composed of 21 different ellipse-shaped transverse ribs with 1.5m spacing, and the transverse ribs are connected by 12 longitudinal ribs. Comparison between two optional structure schemes is carried out. Considering the mechanical performance and economy, the structure scheme, a truss structured system at lower part of the bridge, is adopted. Internal force analysis, member design and deformation calculation of the structure are accomplished. Finite elements analysis with ANSYS shows that the welded joints can meet the bearing capacity requirement. Connection between the bridge and the foundation platform is also presented in this paper.

Abstract: Laser Shock Processing (LSP) has become an advanced method for improving the mechanical properties such as hardness, residual stress and fatigue life. Nanosecond laser pulses of extreme intensity generated subsequent plasma. The rapid expansion of high pressure plasma creates a shock wave that propagates through the material, creating dislocations and inducing plastic deformation. Thus it can effectively eliminate welding residual tensile stress and improve fatigue capability of welding joints. The two kinds of welding experiment of 12Cr2Ni4A were designed to prove it. The experimental results showed that LSP has abroad application prospects in post-processing welding field.

Abstract: Hot spot stress (HSS) approach is more applicable for fatigue evaluation, because it is more closer to the real stress at the welded notch than nominal stress.This paper studies a typical welded joint, fillet welded joint, which is used widely in high-speed car. Hot spot stress concentration factor is calculated under different nominal stress and loading methods. The S-N curves belong to nominal stress and hot spot stress were analysized. The result show that the difference between the S-N curves under different load style can be reduced greatly by hot spot stress. The hot spot stress characteristic variable was put forward, which is used to describe the influence from the welding size of the joint.

Abstract: The creep rupture behaviour,hardness distribution and microstructure of weldment made by submerge arc welding for W strengthened P92 steel are described in this paper. The cross-weld creep tests were carried out at 923K under stresses in the ranges 130-100MPa. For stress below 120MPa, weld-joints were ruptured by the Type crack, which located in their fine-grained heat affected zone(FGHAZ)with the smallest measured cross-weld hardness. A strong drop in creep rupture strength of weldment was induced by brittle type failure. In addition to coarsening of M23C6 carbides and an equiaxed fine grains in FGHAZ, intermetallic Fe2(Mo,W)Laves phase precipitated on grain boundaries during creep is probably the significant factor caused the type failure.

Abstract: The influence of weld heat input on weld joint between B610CF and 16MnR steel using shielded metal arc welding method was investigated by metallographic experiment and mechanical properties experiment. Metallographic experimental results show that in welded metal with the increasing of weld heat input the quantity of bainite is decreased and crystalline grain is larger; but in both B610CF and 16MnR steel heat affected zone, with the increasing of weld heat input there is no distinct difference in microstructure. Mechanical property experimental results show that in weld metal with the increasing of weld heat input the impact toughness decreases, but in both B610CF and 16MnR heat affected zone, there is less difference in impact toughness; and there is no distinct difference in tensile strength and plasticity of weld joint, which is consistent with the metallographic experiment results.

Abstract: Alloy-designing of high-strength ferritic heat resistant steels has been investigated for application to highly efficient, low emission ultra-supercritical power plant with maximum steam temperature of 700 oC. Ferritic heat resistant steels can be applied to the next highest temperature components and are strongly desired to expand their temperature range up to 650 oC in order to minimize the requirement of expensive nickel base superalloys. A dispersion of nanometer size MX nitrides along boundaries and the addition of boron significantly improve long-term creep strength. Newly alloy-designed 9Cr-3W-3Co-0.2V-0.05Nb steel with 160 ppm boron and 85 ppm nitrogen exhibits excellent creep strength of base metal and no degradation in welded joints at 650 oC. The protective Cr2O3-rich scale forms on the surface of 9Cr steel by pre-oxidation treatment in Ar gas, which significantly improves the oxidation resistance in steam at 650 oC.

Abstract: Comparing with traditional welding technology, there are many advantages of magnesium laser welding, for example, high welding speed, low line energy, small welding distortion, easy to achieve automate production et al. It is widely used in the area of magnesium welding. Fine microstructure and excellent weld shape can be obtained by choosing reasonable technology parameters and the mechanical properties of welding joint can also be promoted. But there are some defects in the process of welding magnesium alloys with laser, such as, stomas, cracks, impurities and so on. Some actions can be taken to improve or prevent those defects. For example, choosing the appropriate process parameters can solve the problem of cracks, impurities. In this paper, the status of laser welding magnesium alloy is reviewed in recent years, and some problems in magnesium laser welding were analyzed and some suggestions of solving the problems were put forward.

Abstract: Weldability analysis, metallographic experiments and mechanical property experiments were carried out on weld joint between B610CF and 16MnR steel using shielded metal arc welding method and mixed active-gas arc welding method. Weldability analysis shows that the weld joint has some tendency to cold crack, and preheat is needed before welding. Metallographic results show that there are ferrite and bainite in weld metal, and in heat-affected zone of B610CF side there are ferrite and bainite, on which there is much dispersed slight Fe3C, and in heat-affected zone of 16MnR side there are ferrite, pearlite. There is no quenching microstructure resulting in crack in weld joint. From mechanical property results, it can be concluded that the weld joints have excellent impact toughness at low temperature and the tensile strength and plasticity of weld joints is matched to the ones of 16MnR steel. So the welding parameters in this paper are appropriate to get qualified weld joints.

Abstract: Experimental and numerical investigation on the dimensional stability of aluminum alloy welded joint in thermal cycling conditions are presented. Accumulated deformation have been found during the tests. Analytical results demonstrated that the dimensional instability of the welded joint under thermal cycling is governed by the internal plastic flow rather than creep mechanisms. A finite element unit cell model is used to predict the behaviors of dimensional instability.