ADVANCED WAYS OF IMPROVING THEWELDED STRUCTURES

TheprogressintheleadingbranchesofthenowadaysindustryiscloselycormectedwiththesolutionofthoseProblems,whichareencounteredintheconstrUctionOfthereliableandlong--livedweldedstrUctures.TheseProblemsincludetheaPPlicationoftheadvancedstrUcturalmaterials,updatingthestandalsandnilesOfthestructUredesiring,OPtidrizationofthedesignofjointsandmembers,thesolutionoftheproblemsofthestructUleadaptabilitytofabrication,theselectionofoptimumtechnologiesOfwelding,thedesignofnecessapeoppmentforthestructu-refa…     

Characterization of Mechanical Properties and Residual Stress in API 5L X80 Steel Welded Joints

The use of high-strength and low-alloy steels, high design factors and increasingly stringent safety requirements have increased the operating pressure levels and, consequently, the need for further studies to avoid and prevent premature pipe failure. To evaluate the possibility of improving productivity in manual arc welding of this type of steel, this work characterizes the mechanical properties and residual stresses in API 5L X80 steel welded joints using the SMAW and FCAW processes. The residual stresses were analyzed using x-ray diffraction with the sin² ψ method at the top and root of the welded joints in the longitudinal and transverse directions of the weld bead. The mechanical properties of the welded joints by both processes were characterized in terms of tensile strength, impact toughness and Vickers microhardness in the welded and shot peening conditions. A predominantly compressive residual stress was found, and shot peening increased the tensile strength and impact toughness in both welded joints.     

随焊旋转挤压对铝合金焊接接头组织和性能的影响

随焊旋转挤压是一种能够控制薄壁结构焊接应力和变形的新方法,这种方法同时能改善焊接接头的微观组织和力学性能.对2A12T4铝合金焊接接头的金相观察表明,随焊旋转挤压焊缝区晶粒明显细化,组织更加致密,气孔等缺陷大大减少.拉伸和三点弯曲试验结果表明,随焊旋转挤压之后焊接接头的抗拉强度、抗弯强度等力学性能得到不同程度的提高.由于薄弱的焊趾部位得到强化,部分试件的裂纹萌生部位由焊趾转移到焊缝.     

Effect of modifying additions in the composition of agglomerated fluxes on the structure and properties of the metal of welded joints in Cr–Mo–V heat-resisting steel

Automatic submerged-arc welding is used widely in the manufacture of nuclear power plant made of heat resisting steels. Solving the problem of producing welded joints with the strength equal to that of the parent metal, is important to replace fused fluxes in welding by high basicity agglomerated fluxes.     

Increasing the reliability of welded joints in high-strength V-1461 aluminium–lithium alloy

Filler materials for welding V-1461 alloy, ensuring high cracking resistance, corrosion resistance and mechanical properties, are selected. The results of tests of the welded joints in static tensile loading and bending and the impact toughness of the weld metal and low-cycle fatigue strength are presented. The experimental results show that the application of impact ultrasound treatment increases by an order of magnitude the values of low-cycle fatigue resistance of the welded joints as a result of the formation of the nanostructured surface layers. The level of residual stresses in welded joints is determined.     

Fatigue properties of longitudinal attachments welded using low transformation temperature filler

Abstract

In welded structures, fatigue properties are normally considered to be independent of mean stress owing to the presence of tensile residual stresses with a magnitude close to yield level. Introduction of compressive residual stresses by use of low transformation temperature welding consumables has been reported in the literature to have a positive influence on the fatigue strength. In this investigation new low transformation temperature welding consumables have been evaluated with respect to static strength, impact toughness, residual stresses and fatigue properties. Welds were produced in the base material Domex 700 MC, an extra high strength cold forming steel with minimum yield strength of 700 MPa. The improvement of fatigue strength was found to be 25 - 90% at 2 × 10⁶ cycles.     

异种钢焊接接头失效机制的研究进展

由于异种钢理化特性的差异,在焊接过程中导致焊接接头的界面分布和裂纹失效机理与同种钢有所不同。文中从异种钢焊接接头的失效机制入手,介绍碳迁移导致熔合区出现软化和脆化现象,分析在焊接过程中导致其力学性能降低的本质原因,详细解释Type-II晶界和“白亮层”的形成机理,分析在高应力水平下异种钢焊接裂纹的形成机理和抑制措施。通过对异种钢焊接接头失效的本质原因进行系统性论述,为异种钢焊接失效机制的深入研究和工程应用提供理论指导,并提出针对异种钢焊接接头常见失效问题的解决方案。 创新点： (1)从焊缝过渡区域的特性着手,分析异种钢焊接接头失效机制的研究进展,提出抑制过渡区域中Type-II晶界的形成、缩小“白亮层”的宽度是提高焊接接头性能的关键措施。通过整理前人对异种钢焊接过程中的碳迁移过程的定量研究,明确了由于碳迁移造成的异种钢焊接接头软化和脆化机理。(2)提出基于精确施加冷源从而定量控制焊接热应力和残余应力的分布情况,是可能改善异种钢焊接裂纹失效问题的有效措施。     

爆炸法消除三峡工程高强钢压力钢管焊接残余应力

对三峡工程采用的６０ｍｍ厚ＮＫ－ＨＩＴＥＮ６１０Ｕ２调质高强钢对接和角度均焊接度板进行爆炸处理。结果表明爆炸处理不仅显著消除试板表面的拉伸残余应力,而且能使残余应力沿厚度方向分布均匀且显著降低。     

Strength of straight‐seam and spiral‐seam pipes in transmission gas and oil pipelines

It is shown that it is important to improve further the technology for welding oil and gas equipment produced from materials with high weldability (low-alloy steels) and working in the conditions of steep temperature gradients in the environment. The results of microstructural analysis, the tests of the impact bend strength of the specimens at different temperatures, and also the data obtained in the determination of the level of residual stresses of the third kind are used to show the possibility of increasing the parameters of the reliability of the welded oil and gas equipment produced from low-alloy steels.     

Improving the fatigue performance of longitudinal welded joints by low transformation temperature electrodes

0　IntroductionAfatigueisoneofthemainfailurescausesofweldedstructures.Manyexperimentshaveshownthatfatiguestrengthsofweldedjointsaremuchlowerthanthoseofbasemetal.Thefatiguecrackmainlyinitiatesatweldtoe ,becausetherearetensileresidualstressesandstressconcentrationinthisregion ,sothatthefatiguestrengthcanbeincreasedbybothmodifyingstressdistributionatweldtoeanddecreasingstressconcentration .Therearemanymethodstoimprovethefatiguestrengthsofweldedjoints[1,2 ] ,forexample ,TIGdress ing,hammerpeenin…     

Suppressing type IV failure via modification of heat affected zone microstructures using high boron content in 9Cr heat resistant steel welded joints

Abstract

Creep rupture strength at 923 K and microstructural evolution of welded joints have been investigated for high boron–low nitrogen–9Cr heat resistant steels developed at the National Institute for Materials Science (Japan). Welded joints were prepared from plates containing 47–180 ppm boron using gas tungsten arc welding and Inconel type filler metal, and showed superior creep properties to those of welded joints of conventional high chromium steels such as P92 and P122. No type IV failure was observed in the boron steel welded joints. A large grained microstructure was observed in the heat affected zone heated to Ac ₃ (Ac ₃ HAZ) during welding, whereas the grains are refined at the same location in conventional steel welded joints. The simulated Ac ₃ HAZ structures of the boron steels have a creep life almost equal to that of the base metal. Large grained HAZ microstructures and stabilisation of M₂₃C₆ precipitates are probable reasons for suppression of type IV failure and improved creep resistance of the boron steel welded joints.     

Development of electrodes for welding transmission pipelines and marine equipment made of high-strength low-alloy cold-resistant steels

The problems of production of welding electrodes with basic coatings in Russia is associated with the changes in the raw materials base used as components for electrode coatings, in particular, the electrodes of the UONII-13 series used extensively in industry in welding important structures made of cold-resistant low-alloy steels of different strength categories are examined. A promising composition of the electrode coating with a new deoxidation alloying system is proposed. The system results in high welding and technological characteristics of the electrodes and stable mechanical properties of the metal of welded joints in low-alloy steels with a strength of up to 560 MPa. The high-quality parameters are achieved as a result of using Minal (mineral alloy) in the electrode coating for adding through this coating the mineral and rare-earth components. The compositions of the coatings of the developed electrodes are calculated using the phase equilibrium diagrams of non-metallic systems.     

Influence of Multi-Thermal Cycle and Constraint Condition on Residual Stress in P92 Steel WeldmentEI北大核心CSCD

P92 steel is a typical 9%similar to 12% Cr ferrite heat-resistant steel with good high temperature creep resistance, relatively low linear expansion coefficient and excellent corrosion resistance, so it is one of important structural materials used in supercritical thermal power plants. Fusion welding technology has been widely used to assemble the parts in thermal power plant. When the supercritical unit is in service, its parts are constantly subjected to combination of tensile, bending, twisting and impact loads under high temperature and high pressure, and many problems such as creep, fatigue and brittle fracture often occur. It has been recognized that welding residual stress has a significant impact on creep, fatigue and brittle fracture, so it is necessary to study the residual stress of P92 steel welded joints. The evolution and formation mechanism of welding residual stress in P92 steel joints under multiple thermal cycles were investigated in this work. Based on SYSWELD software, a computational approach considering the couplings among thermal, microstructure and mechanics was developed to simulate welding residual stress in P92 steel joints. Using the developed computational tool, the evolution of residual stress in Satoh test specimens was studied, and welding residual stress distribution in double-pass welded joints was calculated. In the numerical models, the influences of volume change, yield strength variation and plasticity induced by phase transformation on welding residual stress were taken into account in details. Meanwhile, the hole-drilling method and XRD method were employed to measure the residual stress distribution in the double-pass welded joints. The simulated results match the experimental measurements well, and the comparison between measurements and predictions suggests that the computational approach developed by the current study can more accurately predict welding residual stress in multi-pass P92 steel joints. The simulated results show that the longitudinal residual stress distribution around the fusion zone has a clear tension-compression pattern. Compressive longitudinal residual stresses generated in the fusion zone and heat affected-zone (HAZ) in each pass, while tensile stresses produced near the HAZs. In addition, the numerical simulation also suggests that the transverse constraint has a large influence on the transverse residual stress, while it has an insignificant effect on the longitudinal residual stress.     

高强度结构钢药芯焊丝气体保护焊工艺设计与开发

为了研究用于高强度结构钢(屈服强度为420 MPa、460 MPa)的焊接工艺,采用药芯焊丝气体保护焊工艺对国产高强度钢(EH420-Z35和EH460-Z35)进行了焊接试验、力学性能试验及CTOD试验测试。试验结果表明,焊接接头的各项性能均满足相关标准的要求,且具有较好的断裂韧性和疲劳性能,满足标准的设计要求,能有效降低海洋结构物总体重量、施工难度和开发成本。     

Application of the local approach to the fatigue assessment for welded joints

The fatigue behavior of welded structures is currently determined by means of recommendations defined in terms of S-N curve corresponding to the detail classes of welded joints without taking account of the actual geometry of the weld. A new fatigue strength assessment method based on Dang Van multiaxial fatigue limit criterion was introduced, which is named the local approach and presented by lnstitut de Soudure recently. The local approach has advantages in taking welding residual stresses and the geometry of the weld toe and weld root into consideration. The application of the local approach to the fatigue strength assessment of low carbon steel Q235B welded joints was studied. The fatigue tests and finite element analysis results show that the local approach parameters recommended by lnstitut de Soudure were incorrectly for low carbon steel Q235B welded joints. With aluminum alloy welded joints being used widely, the parameters of the local approach used for aluminum alloy welded joints were obtained and verified on bases of the fatigue tests and finite element analysis.     

Friction weldability of aluminium alloys to carbon steel

It is established that weld metal saturation by aluminium occurs at welding steels coated by aluminium, and this decreases mechanical properties of the welded joints substantially. Application of the gaseous medium with high oxidizing ability at welding allows for refining weld metal from aluminium and for improving strength and plastic properties of the aluminium-coated steel welded joints.     

镀锌钢板的CO_2激光焊焊接性(II)

以裁焊板工业生产为背景 ,对汽车用镀锌钢板的CO2 激光切割板坯的CO2 激光焊接的焊缝性能进行了试验研究。试验中的激光焊缝屈服强度都大于母材 ,焊缝金相组织以硬度较软的针状铁素体为特征 ,包含激光焊缝的镀锌钢板仍具有优良的深冲性能 ,在焊缝附近锌层烧损小于 0 .5mm宽。镀锌层具有牺牲保护作用使得激光焊缝不易腐蚀。因此 ,裁焊板的激光焊接工艺可靠 ,从焊接角度看 ,激光切割取代裁焊板生产中剪切工艺是可行的     

Study of microstructures and properties for girth welding of domestic X70 pipeline steels

With the development of domestic pipeline steels, it is necessary to develop suitable welding technology which can improve the properties of the welded pipeline. In this paper, the microstructures and mechanical properties of domestic X70 pipeline steels and welded joints are discussed. The welding consumables of BOHLER E6010 and HOBART 81N1 are matched for girth welding. The following characteristics in heat-affected zone(HAZ) are indicated that microstructures of intercritical HAZ(ICHAZ) is finer and more uniform, the grain sizes of fine-grain HAZ(FGHAZ) and subcritical HAZ(SCHAZ) are smaller than that of coarse-grain HAZ(CGHAZ). The hardness, tensile strength and toughness of welded joints come up to the standard. The micrographs of impact specimens in welded joints are cleavage, quasi-cleavage and dimple which shows there is typical ductile rupture.     

Effects of zonal heat treatment on residual stresses and mechanical properties of electron beam welded TC4 alloy plates

Zonal heat treatment(ZHT) was conducted in situ to 14.5 mm-thick TC4 alloy plates by means of defocused electron beam after welding. The effects of ZHT on residual stresses, microstructures and mechanical properties of electron beam welded joints were investigated. Experimental results show residual stresses after welding are mostly relieved through ZHT, and the maximum values of longitudinal tensile stress and transverse compressive stress reduce by 76% and 65%, respectively. The tensile strength and ductility of welded joint after ZHT at slow scanning velocity are improved because of the reduction of residual stress and the microstructural changes of the base and weld metal. ZHT at fast scanning velocity is detrimental to the ductility of welded joint, which is resulted from insufficiently coarsened alpha phase in the fusion zone and the appearance of martensite in the base metal.     

Friction stir welding of duplex stainless steels

Duplex stainless steels are successful in a variety of applications such as the food industry, petrochemicals and plants for desalination of seawater, where high corrosion resistance and high mechanical strength are required. However, the beneficial microstructure may change during fusion welding steps, and it can compromise the performance of these materials. Friction stir welding is a solid-state process avoiding typical problems concerning solidification such as solidification cracks, liquation and segregation of alloying elements. Superduplex stainless steels can avoid unbalanced proportions of ferrite and austenite, formation of secondary deleterious phases and grain growth of ferrite in the heat-affected zone. Consolidated friction stir welded joints with full penetration 6 mm thick were obtained for UNS S32101 and S32205 duplex and S32750 and S32760 superduplex stainless steels. The friction stir welds were submitted to tensile tests indicating an improvement of strength in welded joints, showing increased yield and tensile strength for all studied cases. Regarding the microstructural characterization, an outstanding grain refinement was observed in the welded joint, achieving grain sizes as small as 1 μm. This refinement was associated with the combination of microstructural restoration mechanisms in the dual-phase microstructure promoted by severe deformation associated with a high temperature during the welding process.