Microcrack Formation During Gas Metal Arc Welding of High-Strength Fine-Grained Structural Steel

The recent development of high-performance-modified spray arc processes in gas metal arc welding due to modern digital control technology and inverter power sources enables a focused spray arc,which results in higher penetration depths and welding speed.However,microcracks occurred in the weld metal while approaching the process limits of the modified spray arc,represented by a 20-mm double layer DV-groove butt-weld.These cracks were detected in structural steel exhibiting a yield strength level of up to 960 MPa and are neither dependent on the used weld power source nor a consequence of the modified spray arc process itself.The metallographic and fractographic investigations of the rather exceptional fracture surface lead to the classification of the microcracks as hot cracks.The effects of certain welding parameters on the crack probability are clarified using a statistical design of experiment.However,these microcracks do not impact the design specification for toughness in the Charpy V-notch test(absorbed energy at —40 ℃ for the present material is 30 J).     

熔化极气体保护焊发展中的问题及对策

熔化极气体保护焊（ＧＭＡＷ）是焊接生产中最常采用的焊接方法这一。目前ＧＭＡＷ工艺的研究着重于：抑制焊接飞溅，提高焊接效率，以及实现焊接设备的脱技能化。本文综述了该领域近年来的研究成果，并对将来的研究方向和重点作一展望。     

Multiphysics Modeling and Simulations of Mil A46100 Armor-Grade Martensitic Steel Gas Metal Arc Welding Process

A multiphysics computational model has been developed for the conventional Gas Metal Arc Welding (GMAW) joining process and used to analyze butt-welding of MIL A46100, a prototypical high-hardness armor martensitic steel. The model consists of five distinct modules, each covering a specific aspect of the GMAW process, i.e., (a) dynamics of welding-gun behavior; (b) heat transfer from the electric arc and mass transfer from the electrode to the weld; (c) development of thermal and mechanical fields during the GMAW process; (d) the associated evolution and spatial distribution of the material microstructure throughout the weld region; and (e) the final spatial distribution of the as-welded material properties. To make the newly developed GMAW process model applicable to MIL A46100, the basic physical-metallurgy concepts and principles for this material have to be investigated and properly accounted for/modeled. The newly developed GMAW process model enables establishment of the relationship between the GMAW process parameters (e.g., open circuit voltage, welding current, electrode diameter, electrode-tip/weld distance, filler-metal feed speed, and gun travel speed), workpiece material chemistry, and the spatial distribution of as-welded material microstructure and properties. The predictions of the present GMAW model pertaining to the spatial distribution of the material microstructure and properties within the MIL A46100 weld region are found to be consistent with general expectations and prior observations.     

Gas Metal Arc Welding Process Modeling and Prediction of Weld Microstructure in MIL A46100 Armor-Grade Martensitic Steel

A conventional gas metal arc welding (GMAW) butt-joining process has been modeled using a two-way fully coupled, transient, thermal-mechanical finite-element procedure. To achieve two-way thermal-mechanical coupling, the work of plastic deformation resulting from potentially high thermal stresses is allowed to be dissipated in the form of heat, and the mechanical material model of the workpiece and the weld is made temperature dependent. Heat losses from the deposited filler-metal are accounted for by considering conduction to the adjoining workpieces as well as natural convection and radiation to the surroundings. The newly constructed GMAW process model is then applied, in conjunction with the basic material physical-metallurgy, to a prototypical high-hardness armor martensitic steel (MIL A46100). The main outcome of this procedure is the prediction of the spatial distribution of various crystalline phases within the weld and the heat-affected zone regions, as a function of the GMAW process parameters. The newly developed GMAW process model is validated by comparing its predictions with available open-literature experimental and computational data.     

连续管管-管对接自动焊电弧偏吹现象的探讨

在连续管全位置自动TIG对接焊中,经常会出现电弧偏吹现象.分析表明,引起电弧偏吹的主要原因有小线能量、送丝不稳定、地线连接不正确、焊道成型差、坡口加工不规范、热对流、焊接工艺参数不合适等.根据分析,提出了避免或减小电弧偏吹的措施.     

熔化极气体保护焊保护气体选择研究

系统总结了保护气体物理特性、混合种类与比例、气体流量等参数对熔化极气体保护焊焊缝外观与性能的影响。结果表明,保护气体对焊缝力学性能、化学组成和表面成型性有重要影响,正确选择保护气体种类、混合种类与比例和气体流量,对于熔化极气体保护焊至关重要。     

Modeling of AA5083 Material-Microstructure Evolution During Butt Friction-Stir Welding

A concise yet a fairly comprehensive overview of the friction stir welding (FSW) process is provided. This is followed by a computational investigation in which FSW behavior of a prototypical solution-strengthened and strain-hardened aluminum alloy, AA5083-H131, is modeled using a fully coupled thermo-mechanical finite-element procedure developed in our prior study. Particular attention is given to proper modeling of the welding work-piece material behavior during the FSW process. Specifically, competition and interactions between plastic-deformation and dynamic-recrystallization processes are considered to properly account for the material-microstructure evolution in the weld nugget zone. The results showed that with proper modeling of the material behavior under high-temperature/severe-plastic-deformation conditions, significantly improved agreement can be attained between the computed and measured post-FSW residual-stress and material-strength distribution results.     

Fatigue Crack Growth Behavior of Gas Metal Arc Welded AISI 409 Grade Ferritic Stainless Steel Joints

The effect of filler metals such as austenitic stainless steel, ferritic stainless steel, and duplex stainless steel on fatigue crack growth behavior of the gas metal arc welded ferritic stainless steel joints was investigated. Rolled plates of 4 mm thickness were used as the base material for preparing single ‘V’ butt welded joints. Center cracked tensile specimens were prepared to evaluate fatigue crack growth behavior. Servo hydraulic controlled fatigue testing machine with a capacity of 100 kN was used to evaluate the fatigue crack growth behavior of the welded joints. From this investigation, it was found that the joints fabricated by duplex stainless steel filler metal showed superior fatigue crack growth resistance compared to the joints fabricated by austenitic and ferritic stainless steel filler metals. Higher yield strength and relatively higher toughness may be the reasons for superior fatigue performance of the joints fabricated by duplex stainless steel filler metal.     

多丝气体保护焊电弧干扰研究现状

介绍了常见多丝焊的电弧形态研究,着重分析了电弧干扰机理及影响电弧稳定性的因素.综述了国内外解决电弧干扰问题的常见方案     

CO2焊、MAG焊焊接对比试验及其在工程机械制造中的应用

通过对CO2焊、MAG焊、焊条电弧焊三种焊接方法的焊接工艺对比试验，表明CO2焊具有成本低、效率高、焊接质量好等优点。介绍了CO2焊、MAG焊对接焊缝工艺和角焊缝工艺在工程机械制造中的应用     

CO_2焊、MAG焊焊接对比试验及其在工程机械制造中的应用

通过对CO2焊、MAG焊、焊条电弧焊三种焊接方法的焊接工艺对比试验,表明CO2焊具有成本低、效率高、焊接质量好等优点。介绍了CO2焊、MAG焊对接焊缝工艺和角焊缝工艺在工程机械制造中的应用     

Prediction of Grain Growth Behavior in HAZ During Gas Tungsten Arc Welding of 304 Stainless Steel

In this study, the thermal cycles and the grain structure in the weld heat-affected zone (HAZ) are predicted. At the first stage, a combined heat transfer and fluid flow model is employed to assess the temperature fields during and after welding of 304 stainless steel and then, the evolution of grain structure is conducted using the predicted temperature distribution and an analytical model of grain growth. The grain sizes of the CGHAZ (coarse grain heat affected zone) achieved from the model are basically in agreement with those obtained from experimental measurement under different heat inputs in the range of 0.33-1.07 MJ/m. Both the experimental data and the calculated results show that the average grain size near the fusion plane is about two to four times larger than the average grain size in the base plate depending on the applied heat input.     

Ballistic-Failure Mechanisms in Gas Metal Arc Welds of Mil A46100 Armor-Grade Steel: A Computational Investigation

In our recent work, a multi-physics computational model for the conventional gas metal arc welding (GMAW) joining process was introduced. The model is of a modular type and comprises five modules, each designed to handle a specific aspect of the GMAW process, i.e.: (i) electro-dynamics of the welding-gun; (ii) radiation-/convection-controlled heat transfer from the electric-arc to the workpiece and mass transfer from the filler-metal consumable electrode to the weld; (iii) prediction of the temporal evolution and the spatial distribution of thermal and mechanical fields within the weld region during the GMAW joining process; (iv) the resulting temporal evolution and spatial distribution of the material microstructure throughout the weld region; and (v) spatial distribution of the as-welded material mechanical properties. In the present work, the GMAW process model has been upgraded with respect to its predictive capabilities regarding the spatial distribution of the mechanical properties controlling the ballistic-limit (i.e., penetration-resistance) of the weld. The model is upgraded through the introduction of the sixth module in the present work in recognition of the fact that in thick steel GMAW weldments, the overall ballistic performance of the armor may become controlled by the (often inferior) ballistic limits of its weld (fusion and heat-affected) zones. To demonstrate the utility of the upgraded GMAW process model, it is next applied to the case of butt-welding of a prototypical high-hardness armor-grade martensitic steel, MIL A46100. The model predictions concerning the spatial distribution of the material microstructure and ballistic-limit-controlling mechanical properties within the MIL A46100 butt-weld are found to be consistent with prior observations and general expectations.     

熔滴过渡类型光谱信号自动识别软件系统

根据模式识别原理和方法,在Windows环境下以Visual Basic为开发语言,成功地开发了一套熔化极气体保护焊（MIG、MAG、CO2）熔滴过渡模式识别软件系统,通过试验在特征谱线下,采集了大量熔化极气体保护焊五种熔滴过渡光谱信号波形。该软件系统根据熔滴过渡与光谱信号的对应关系,以及溶化极气体保护焊五种熔滴过渡的光谱信号波形的几何特征,经数据的预处理,创造性地抽取了多个关键性的特征参数,建立了相应的识别函数和最小距离法分类器,结果表明,利用该系统较好地对MIG、MAG和CO2焊熔滴过渡类型进行自动识别,具有较高的准确性和识别精度,为实现熔化极气体保护焊溶滴过渡自动控制提供了信号处理基础。     

20钢蒸汽管道氩电联焊焊接工艺

本文分析了对20钢蒸汽管道采用的TIG打底焊、SMAW焊条填充、盖面时的焊接工艺,采用该工艺减少了气孔、夹渣和未焊透等缺陷,提高了焊接接头的射线检验合格率,保证了焊接质量。     

A Study of Microstructure and Mechanical Properties for the Autogenous Single-Pass Butt Weldment of a Ferritic/Martensitic Steel Using Gas Tungsten Arc Welding

A 12%Cr ferritic/martensitic steel,HT-9,has been used as a primary core material for nuclear reactors.The microstructure and mechanical properties of gas tungsten arc butt welded joints of HT-9 in as-welded,and as-tempered conditions have been explored.In as-welded condition,the fusion zone (FZ) contained a fresh martensite matrix with delta (δ)-ferrite.Theδ-ferrite was rich in Cr and depleted in C compared with the matrix.The heat-aff ected zone (HAZ) could be divided into three areas as the distance from the fusion line increased:δ-ferrite/martensite duplex zone,fully recrystallized zone,and partly recrystallized zone.Prior austenitic grains did not coarsen in theδ-ferrite/martensite duplex zone due to the newly nucleatedδ-ferrite grains and incompletely ferritizing (δ-ferrite) during the welding thermal cycle.The weldment microhardness distributed heterogeneously with values above 600 HV _(1.0 )in the HAZ and FZ and 250 HV _(1.0 )in the base metal (BM).Solute C in the matrix,induced by the dissolution of carbide during the welding process,dominated the microhardness variation.Low toughness was observed in the FZ with a quasi-cleavage fracture tested from-80 to 20℃.The tensile fracture occurred in the relatively soft BM tested from 20 to 600℃.In as-tempered condition (760℃ for 1 h),M _(23 )C _6-type carbides precipitated within the martensitic laths,the lath boundaries,and theδ-ferrite/martensite interfaces.Moreover,V,Cr,Mo-rich nitrides with very small size also precipitated in theδ-ferrite/martensite interface.The tempering treatment improved the homogenous distribution of weldment hardness significantly.Tensile fracture still occurred in the BM of the weldment specimens tested from 20 to 600℃.The impact toughness improved significantly,but the ductile–brittle transaction temperature was-12℃ which was higher than that of the normalized and tempered (NT) BM.δ-ferrite was considered to be one of the major factors aggravating the impact toughness in the FZ.     

天然气管线对接接头的焊接

介绍了天然气管线的焊接工艺并提出了焊接质量控制的方法和要求。     

锅炉20G钢和12CrMo钢的对接焊工艺

某造纸厂热力发电使用的锅炉,牌号为P35/39-P,蒸汽流量35 t/h,压力4.2 MPa,属大型中压锅炉.该锅炉从投产使用以来,经常因生产不稳定,造成汽机甩负荷而引起过热器温度急剧升高,压力增大,致使过热器与过热器联箱连接处焊缝区产生龟裂鼓包,周而复始形成裂纹,引起蒸汽泄漏.     

碳钢板埋弧自动焊贯穿性气孔问题的解决方法

碳钢板埋弧自动焊时经常出现贯穿性气孔问题,本文通过多次试验,采用强规范,圆满地解决了问题,取得了令人满意的效果.     

Modeling of the Weld Shape Development During the Autogenous Welding Process by Coupling Welding Arc with Weld Pool

A numerical model of the welding arc is coupled to a model for the heat transfer and fluid flow in the weld pool of a SUS304 stainless steel during a moving GTA welding process. The described model avoids the use of the assumption of the empirical Gaussian boundary conditions, and at the same time, provides reliable boundary conditions to analyze the weld pool. Based on the two-dimensional axisymmetric numerical modeling of the argon arc, the heat flux to workpiece, the input current density, and the plasma drag stress are obtained. The arc temperature contours, the distributions of heat flux, and current density at the anode are in fair agreement with the reported experimental results. Numerical simulation and experimental studies to the weld pool development are carried out for a moving GTA welding on SUS304 stainless steel with different oxygen content from 30 to 220 ppm. The calculated result show that the oxygen can change the Marangoni convection from outward to inward direction on the liquid pool surface and make the wide shallow weld shape become narrow deep one. The calculated result for the weld shape and weld D/W ratio agrees well with the experimental one.