C-HRA-1镍基支吊架焊接工艺研究

C-HRA-1是我国自主开发的25Cr-20Co-Al-Ti-Nb镍基高温合金并首次被应用到我国700℃超超临界试验平台中,由其焊接制造的镍基支吊架在焊后及时效后出现大量裂纹。返修后裂纹依然无法去除。通过改变焊接顺序、焊道排列、焊接参数及起收弧位置解决了C-HRA-1镍基支吊架角焊缝裂纹问题,焊后及800℃×4h时效热处理后100%PT检查无任何缺陷。     

国产F92耐热钢焊接接头性能试验与研究

对国产F92钢焊接热影响区的粗晶区进行热模拟试验.不同热处理条件后试样的硬度试验,冲击韧性试验和组织分析表明,焊后热处理对改善焊接接头的塑韧性具有显著作用.焊接工艺试验表明,国产F92钢存在一定的冷裂倾向,实际生产宜采用多层多道焊,层间温度的控制也很重要.     

ASTM A387 GR22 CL2钢的焊接

根据ASTM A387 GR22 CL2珠光体耐热钢的焊接性和工艺性特点，为避免在焊接过程中出现热影响区硬化、冷裂纹、回火脆性、软化以及焊后热处理或高温长期使用中的再热裂纹问题，结合燃气轮机排气缸进行了工艺评定，制定了合理的焊接工艺参数和工艺措施，最终使焊接接头性能达到设计要求，取得了良好的效果。     

驻厂监检中应加强压力容器焊接工艺的审查

焊接工艺评定是为验证所拟订的焊接工艺的正确性而进行的试验过程及对试验结果的评价。为了保证焊接工艺的正确性和产品质量，TSGR0004-2009《固定式压力容器安全技术监察规程》明确规定，“压力容器产品施焊前，受压元件焊接接头、与受压元件相焊的焊接接头、熔入永久焊缝内的定位焊接接头、受压元件母材表面堆焊与补焊以及上述焊接接头的返修焊缝都应当进行焊接工艺评定或者具有经过评定合格的焊接工艺支持”。     

Cr-Mo与Cr-Mo-V钢铸件在精加工后缺陷焊补

论述了汽缸等Ｃｒ－Ｍｏ与Ｃｒ－Ｍｏ－Ｖ钢铸件在精加工及在电厂运行中所产生的裂纹等缺陷修复问题。为避免焊后回火、减少焊后变形,需要采取冷焊技术;而为防止低合金耐热钢的淬硬倾向而产生冷裂纹,采取敷焊层操作技术,同时保证焊补区的综合机械性能,减少合金元素的稀释、碳迁移所采取的奥氏体焊条焊接的冷焊工艺,证明采用合理的冷焊技术并在操作中严格控制是能够满足机组安全运行需要的。     

12Cr1MoV钢焊接接头蠕变、蠕变～疲劳交互作用裂纹开裂和扩展特性研究

结合火力发电设备大型锅炉集箱管座焊接接头破裂情况,本文重点研究了12Cr1 Mov钢母材、手工焊的焊缝、热影响区的蠕变、蠕变～疲劳交互作用下裂纹开裂和扩展特性,同时也测定了母材、焊缝和热影响区的蠕变断裂韧性值,用来评定焊接接头抗蠕变脆性特性的好坏.另外还研究了回火温度对12Cr 1 MoV钢母材,焊缝和热影响区裂纹开裂和扩展及蠕变断裂韧性影响,从改善焊接接头抗裂纹开裂和扩展能力新观点出发,来确定焊后最佳热处理。     

某电厂阀门无损检测及其补焊修理的实践研究

对在用锅炉主汽阀门进行无损检测,阀体发现大量表面裂纹,结合企业实际,分析缺陷状况,确定补焊的修理方法,制定修理方案和科学的补焊工艺.经检测确认缺陷消除后,通过焊前准备、实施焊接、焊后检测、焊后热处理、验收确认以及施工资料整理汇总等相关工作,恢复阀门的使用功能.通过补焊修理,改变以往发现缺陷就更换阀门的不合理处理模式,延长阀门的使用寿命,同时引申阀门延寿运行的其他方法.实践证明阀门修理后的使用对用户创造的经济效益十分可观.     

G18CrMo2-6型高中压汽缸特大裂纹补焊修复

从某厂G18CrMo2．6型高中压汽缸特大裂纹结构特征及基体材料出发，对其焊接性、变形控制进行深入分析研究，制定了相应的补焊修复方案。同时采用半热焊的方法．模拟汽缸实际焊接条件进行工艺试验，并对其焊缝组织、性能进行评定。实践结果表明，对于该汽缸特大裂纹，补焊修复方案行之有效，能满足产品技术要求．为企业挽回了巨大的经济损失。     

筒体与接管相交的马鞍形焊道几何特征的研究

目前锅炉、化工等行业中压力容器接管与筒体相交的空间马鞍形相贯曲线的焊接多采用机械式马鞍形焊机。机械马鞍焊不能根据焊道实时的宽度变化自动修正焊接轨迹,因此需要人工修补导致焊接作业效率的降低;当接管与筒体的半径比较大时,由于焊道的切线与水平面的夹角较大导致下坡焊时铁水向下流淌,焊后成形变坏;并且当接管与筒体偏交时机械马鞍焊无法进行焊接作业。根据机械马鞍焊存在的问题,针对筒体与接管相交的空间马鞍形焊道的几何特征进行了研究,在两管偏交的情况下建立了焊接轨迹、焊道宽度与焊道上各点切线与水平面夹角的数学模型,为开发新一代的数控马鞍形焊机奠定了理论基础。因此,该项研究具有较强的实际意义与实用价值。     

锅炉汽包和联箱的焊接问题

锅炉汽包、联箱和厚壁管的缺陷返修补焊,是一项难度较大的工作,通过收集我国某些水电厂上述部件的缺陷修复实例,对同种钢焊接与异种钢焊接,筒体环缝补焊与管座角缝补焊的工艺、检验、热处理等过程作重点介绍。     

3D heat transfer model of hybrid laser Nd:Yag-MAG welding of S355 steel and experimental validation

A three-dimensional heat transfer model was developed to predict the temperature fields, the weld geometry and the shape of the solidified weld reinforcement surface during hybrid laser-MAG arc welding of fillet joints. Melt pool deformation due to arc pressure was calculated by minimizing the total surface energy. A series of hybrid welding experiments was conducted on S355 steel for different welding speeds and wire feeding rates. A high speed video camera was used to measure weld pool depression and surface weld pool geometry. Visualization of the weld pool during welding has also allowed for a better understanding of the interaction between the keyhole and droplets. The various weld bead shapes were explained through these observations. The arc pressure, the surface energy distribution, and arc efficiency were evaluated by comparing experimental data and numerical results for a wide range of welding operating parameters. Good correlation was found between the calculated and experimental weld bead shapes obtained for the hybrid laser-MAG arc welding process as well as for laser or MAG alone.     

Predicting the influence of groove angle on heat transfer and fluid flow for new gas metal arc welding processes

This article studies the three dimensional transient weld pool dynamics and the influence of groove angle on welding of low carbon structural steel plates using the ForceArc® process. The deformation of the weld bead is also calculated with an accurate coupling of the heat transfer with fluid flow through continuity, momentum and the energy equations combined with the effect of droplet impingement, gravity, electromagnetic force, buoyancy, drag forces and surface tension force (Marangoni effect). Different angles of V groove are employed under the same welding parameters and their influence on the weld pool behavior and weld bead geometry is calculated and analyzed, which is needed for subsequent calculations of residual stress and distortion of the workpiece.Such a simulation is an effective way to study welding processes because the influence of all welding parameters can be analyzed separately with respect to heat transfer, weld pool dynamic, and microstructure of the weld. Good agreement is found between the predicted and experimentally determined weld bead cross-section and temperature cycles. It is found that the main flow pattern is more or less the same although the groove angle increases, but it will evoke larger amount of fluid to flow downward to get deeper penetration.     

Multivariable adaptive control of the bead profile geometry in gas metal arc welding with thermal scanning

This research implements the newly introduced scan welding technique in processes with material deposition. A laboratory station is developed with robotic plasma-arc welding under infrared pyrometry sensing for thermal scanning, and with gas metal arc welding under laser profilometry feedback for material transfer. The dynamics of the weld profile geometry (i.e. the bead width and reinforcement height) are modeled experimentally with respect to the process conditions (weld speed and wire feed). This model serves as the basis for the development of a simple geometry feedback control scheme. A multivariable adaptive control system, based on a generalized one step ahead regulation algorithm is also established and validated experimentally. Application of such bead profile regulation is explored in multipass weld joining, orbital welding, coating hardfacing and rapid manufacturing methods.     

Numerical Modeling of Cold Weld Formation and Improvement in Gmaw of Aluminum Alloys

Both mathematical modeling and experiments have been conducted on the formation of cold weld in gas metal arc welding (GMAW) of aluminum alloy 6005-T4. Transient weld pool shape and the distributions of temperature and velocity were calculated by a three-dimensional numerical model. The final weld bead shape and dimensions and peak temperature in the heat-affected zone (HAZ) were obtained. Three techniques were proposed to input more energy at the initial state of welding to improve weld bead penetration. Both the simulation and the experimental results show significantly improved weld bead penetration at the start of welding.     

Sensitivity to welding positions and parameters in GTA welding with a 3D multiphysics numerical model

A three-dimensional numerical model of Gas Tungsten Arc welding has been developed to predict weld a bead shape, fluid flow in the weld pool, as well as thermal field in the workpiece. This model accounts for coupled electromagnetism, heat transfer, and fluid flow with a moving free surface to simulate different welding positions. The solution strategy of the coupled non-linear equations that has been implemented in the Cast?M finite-element code is also discussed. The capabilities of our numerical model are first assessed by comparison to the experimental results. Then, as fluid flows in a weld pool play a prominent role in the weld quality as well as in the final shape of the weld bead seam, the effect of various welding positions on the weld pool shape has been investigated. This constitutes the main novelty of this work. The performed computations point out a strong sensitivity to gravity on the weld pool shape depending on assisting or opposing the weld direction with respect to gravity. This study contributes to assessing the model capabilities that provide a deeper physical insight into a more efficient optimization of welding processes.     

Genetic algorithm for optimisation of A-TIG welding process for modified 9Cr–1Mo steel

Abstract

It is essential to set up the activated tungsten inert gas (A-TIG) welding process parameters to produce the desired weld bead geometry and heat affected zone (HAZ) width in modified 9Cr–1Mo steel weld joints. Therefore, it becomes necessary to develop a tool for optimisation of A-TIG welding process. Genetic algorithm (GA) based model has been developed to determine the optimum process parameters. In this methodology, first independent ANN models correlating depth of penetration, weld bead width and HAZ width with current, voltage and torch speed respectively were developed. Then, GA code was developed in which the objective function was evaluated using the ANN models. There was good agreement between the target and actual values of bead geometry and HAZ width obtained using the GA optimised process parameters. Thus, a methodology using GA has been developed for optimising the A-TIG process parameters for modified 9Cr–1Mo steel.     

锅筒焊接热裂纹原因分析及建议

在某厂余热发电锅炉首次检验时，发现锅筒内部环焊缝多处表面裂纹，通过化学成分、金相、硬度分析等方法确定裂纹的性质是焊接热裂纹．制造焊接过程中，化学成分不合格的工艺垫板熔入焊缝并未能消除干净，是造成锅筒内部封底焊缝表面热裂纹的主要原因针对制造工艺和质量控制出现的问题，提出改进措施和意见     

Thermo-mechanical modelling of a single-bead-on-plate weld using the finite element method

This work describes a three-dimensional thermo-mechanical finite element analysis of a single weld bead-on-plate of austenitic stainless steel performed as part of the NeT programme. The overall aim is to validate the use of finite element (FE) weld simulations to accurately predict residual stress states for use in the assessment of welded components. Here, the final residual stresses in the plate are predicted, which can later be verified through comparison with measured distributions. A one-way coupled analysis is carried out with the thermal and mechanical problems solved in sequence. For the thermal analysis, two approaches are adopted to simulate the welding process. In one case sections of the weld bead's elements are sequentially deposited, while in the other the whole bead is deposited simultaneously. A moving heat source is used to simulate the torch traversal over the weld bead in both cases. Predicted thermal profiles, residual stresses and equivalent plastic strains, due to the welding process are presented at certain locations in the plate.     

Formation of weld crater in GMAW of aluminum alloys

Both mathematical modeling and experiments have been conducted on the formation of the crater formed in a GMAW of aluminum alloy 6005-T4. Transient weld pool shape and the distributions of temperature and velocity were calculated by a three-dimensional numerical model. The final weld bead shape and dimensions were obtained. Corresponding experiments were conducted and in good agreement with modeling predictions. Metallurgical characterizations were also performed on the experimental samples. It was found that due to the fast solidification of the weld pool after the termination of the welding arc, there is no time for the molten metal to flow back towards the weld pool center and close up the crater. Thus a crater was formed at the end of the weld bead. Solidification cracking was formed at the center of weld crater. A “back-up” technique was proposed to allow extra molten metal to flow back to the crater and fill it up. The crater was successfully filled and the crater cracking was eliminated.     

NeT bead-on-plate round robin: Comparison of transient thermal predictions and measurements

The members of the European network NeT have undertaken parallel round robin activities measuring and predicting the residual stresses generated by laying a single Tungsten Inert Gas (TIG) weld bead on an AISI Type 316L austenitic stainless steel flat plate. This is a strongly three-dimensional configuration with many of the characteristics of a repair weld. The round robin finite element predictions of transient temperatures and the extent of the melted zone are compared with thermocouple measurements made during welding, and with the results of destructive metallography. The most reliable thermocouple positions for calibrating the global heat input are identified. The actual achieved weld efficiency, and hence the heat input, are deduced from the response of these far-field thermocouples. As a result, best practice recommendations are made for finite element simulation of welding thermal transients.