埋弧焊焊接T型焊缝时产生气孔的原因分析及对策

针对埋弧自动焊焊接吊车粱T型焊缝时产生焊缝内气孔影响工期和工程质量的问题,分析了铁锈、水分、焊剂中的造气剂、焊接工艺参数及清根操作情况可能对气孔造成的影响,并分别采用不同的焊剂粒度和焊剂堆高进行试验.结果表明,产生焊缝内气孔的主要原因是焊接电流与焊接速度的匹配不合理.采用单边V形坡口及改变焊接顺序后,焊缝内部和表面均没有发现气孔,焊接质量稳定.     

颗粒度对焊剂约束电弧超窄间隙焊接焊缝成形的影响

用超细颗粒焊剂约束电弧,可阻止电弧在超窄间隙埋弧焊中沿侧壁攀升,能获得良好成形良好的超窄间隙焊缝。焊剂颗粒度不是影响焊缝成形的唯一因素,在其它焊接参数一定的情况下,焊剂颗粒目数增加,焊缝横截面形状呈现出由凹形到凸形的变化。     

Q235 B螺旋焊管焊缝气孔缺陷浅析

针对Q235B螺旋焊管焊缝气孔缺陷质量异议,采用SEM-EDS对气孔缺陷微观形貌及夹杂物成分进行了分析,结果显示,导致焊缝气孔缺陷的主要原因有卷板分层、卷板焊接端面不平。另外,焊剂因受潮发生粉化,吸收空气中水分,也会增大焊缝产生气孔的几率。通过减少分层、减宽轧制等措施,此类缺陷明显减少。     

BHW35钢电渣焊缝冲击断裂研究

本文研究了酸性和碱性两种焊剂焊接的BHW35厚板电渣焊缝的冲击性能,测试了转变温度FATT_(50)。在转变温度附近进行了示波冲击试验,从冲击功、断口形态和示波冲击的各种特征值考察了焊剂对冲击性能的影响;并从断裂过程分析了冲击断口各区与相应特征能量的关系。     

大热输入焊接材料的研究开发现状

阐述了大热输入焊接对焊缝金属组织和力学性能的影响,分别介绍了590和780MPa以上级别焊接材料的不同韧化机制。列举了日本现有超大热输入电渣焊焊接材料开发实例中,通过改变焊剂碱度以调整氧化物粒子数量并使其在850～1000kJ/cm的焊接热输入条件下,仍能得到针状铁素体组织并使0℃冲击功达到123J的成功经验。指出目前中国大热输入焊接材料研究开发中存在的问题和今后的发展方向。     

新型埋弧焊烧结焊剂的研制

研究了各种成分对MgO CaF2 Al2O3 MnO渣系焊剂焊接工艺性能和熔敷金属中扩散氢含量影响的规律,并在此基础上研制出了一种碱度BⅡW为2 3、脱渣性良好、焊缝成形美观、熔敷金属中扩散氢含量达到低氢水平、与合适的焊丝配合适于焊接有-20℃低温冲击韧度要求、且抗拉强度达到650MPa级的低合金钢埋弧焊焊剂。     

耐蚀钢轨U68CuCr铝热焊工艺试验

耐蚀钢轨U68Cu Cr是新研发的钢轨品种,通过对铝热焊接工艺试验,制定出耐蚀钢轨铝热焊接工艺。试验结果表明,采用国产焊剂,轨头预热7 min,预热温度达到880℃,预留轨缝27 mm条件下进行铝热焊,焊接后焊缝组织为珠光体+铁素体,焊缝处抗拉强度Rm为815 MPa,断后伸长率为2.3%,钢轨熔合区冲击功Aku为7.1 J,焊缝布氏硬度为285 HB,软化区宽度不大于20 mm,静弯和实物疲劳性能合格,焊头各项性能满足TB/T 1632-2005《钢轨焊接》的要求。采用闪光焊工艺焊接的这种钢轨,已在京广铁路上使用。     

埋弧焊剂含水率与熔敷金属扩散氢关系研究

埋弧焊熔敷金属扩散氢的含量对焊缝质量有较大影响,其含量多少主要取决于焊剂中的含水率多少.通过控制焊剂含水率的方式控制熔敷金属扩散氢含量,可有效提高焊缝质量.选取某进口焊剂为研究对象,采用卡尔费休法测定焊剂含水率,采用热提取法测定扩散氢含量,建立熔敷金属扩散氢与焊剂含水率之间的关系曲线,有效地为焊管生产过程中的焊剂质量管控提供了技术支撑.     

高碱度烧结焊剂的初步研究——碱度、强度和熔敷金属的扩散氢含量

随着低合金高强度钢的广泛应用,获得高韧性焊缝的难度越来越大。提高埋弧焊焊剂的碱度被证明是有效措施之一,但随之会使焊缝中的扩散氢含量增高,导致由氢而引起的冷裂纹倾向增大。因此,研制高碱度而含氢量低的非熔炼型焊剂,是高强度钢和对低温韧性要求高的钢焊接发展的需要。我们研究出了几种碱度(B)在1.5～2.5范围内的焊剂,其焊剂的化学成份为:CaO MgO BaO=40～60％,CaF_2=15～30％,Al_2O_3 TiO_2=20～40％,MnO=0～20％,K_2O Na_2O=3～7％,SiO_2=8～15％,其它≤10％,其熔敷金属扩散氢含量小于2ml/100g。这种高碱度烧结焊剂具有焊接工艺性能良好、碱度高、强度足够和氢含量低的特点,适用高强度钢和对低温韧性要求高的钢的焊接。     

429铁素体不锈钢焊接微观组织和晶间腐蚀行为研究

本文通过高频焊对429铁素体不锈钢管进行焊接,观察相应的焊缝组织。通过金相组织观察、布氏硬度检测和晶间腐蚀实验等,分析了该铁素体不锈钢焊接处组织和性能,以及其晶间腐蚀对该铁素体不锈钢腐蚀行为的研究。实验结果表明,429铁素体不锈钢的焊接会使得焊缝区、热影响区处铁素体组织受热高温发生奥氏体化并且会析出碳化物颗粒。焊接后焊缝的硬度高于原材的硬度。晶间腐蚀结果表明,429铁素体不锈钢经焊接后的焊缝区域耐腐蚀性能很强。焊缝区晶粒细小均匀,在表面形成致密钝化膜保护焊缝免受晶间腐蚀影响,提高了该不锈钢稳定性。     

Quality of weld seams produced with flux based on silicomanganese slag

The use of metallurgical wastes in welding fluxes is considered. A new welding flux based on slag from silicomanganese production is proposed, along with the corresponding manufacturing technology. The quality of the weld seams is studied by metallographic analysis. The grain size and content of nonmetallic inclusions are determined. An Olympus GX-51 optical microscope is used for metallographic analysis (magnification ×100–1000). The influence of the fractional composition on the performance of the fluxes is studied. The optimal fraction is chosen, ensuring low content of nonmetallic inclusions (in particular, nondeforming silicates and oxides) in the weld seam. If 30–40% of the small fraction of welding flux is employed, the content of nonmetallic oxide inclusions in the weld seam is reduced. Metallographic analysis shows that introducing the small fraction has no effect on the structural components of the weld seam. The seam is characterized by ferrite–pearlite structure. The ferrite is present in the form of grains extended in the direction of heat transfer. The optimal content of the <0.45 mm fraction in the welding flux is 30–40%. To improve flux performance, the small fraction may be mixed with liquid glass. The use of ceramic flux produced from the dust of silicomanganese slag (<0.45 mm fraction) bound by liquid glass reduces the content of nonmetallic inclusions in the weld seam. However, increase in the content of liquid glass from 15 to 40% has little effect on the content of nonmetallic oxide inclusions in the weld seam or on the microstructure. The microstructure in the weld seam consists of pearlite and ferrite. The optimal flux consists of the small fraction with 15–20% liquid glass.     

Effect of controlled arc motion on the surface of a weldpool on the quality of a weld during argon-arc welding of a 1565chM aluminum alloy

The effect of the rotation of an arc on the weld formation in welding 1565chM alloy sheets is studied. The arc rotation is shown to induce controlled low-frequency perturbations, which depend on the tungsten electrode rotation frequency, in a weldpool. Periodic changes in the value and direction of temperature gradient favor misorientation and refining of the weld structure. The arc rotation in welding intensifies the release of gas bubbles and oxide inclusions from a weld.     

氧化物冶金技术在大线能量焊接用钢的应用

随着大线能量焊接技术的发展,对相应的钢板也提出了抗大线能量焊接的要求。通过合理调整成分和采用氧化物冶金技术开发大线能量焊接用钢已经被广泛使用。总结了在大线能量焊接用钢开发中合金元素的作用、脱氧剂的选择及各钢铁厂对氧化物冶金技术在生产中的应用,为大线能量焊接用钢的开发提供借鉴。     

Slag-metal reactions during welding: Part II. Theory

A kinetic model is developed to describe the transfer of alloying elements between the slag and the metal during flux-shielded welding. The model accounts for changes in alloy recovery based on the geometry of the resulting weld bead. It also distinguishes compositional differences between single-pass and multiple-pass weld beads. It is further shown that the final weld metal oxygen content is directly related to the weld solidification time as well as the type of flux used.     

Effect of Activated Flux on the Microstructure, Mechanical Properties, and Residual Stresses of Modified 9Cr-1Mo Steel Weld Joints

A novel variant of tungsten inert gas (TIG) welding called activated-TIG (A-TIG) welding, which uses a thin layer of activated flux coating applied on the joint area prior to welding, is known to enhance the depth of penetration during autogenous TIG welding and overcomes the limitation associated with TIG welding of modified 9Cr-1Mo steels. Therefore, it is necessary to develop a specific activated flux for enhancing the depth of penetration during autogeneous TIG welding of modified 9Cr-1Mo steel. In the current work, activated flux composition is optimized to achieve 6 mm depth of penetration in single-pass TIG welding at minimum heat input possible. Then square butt weld joints are made for 6-mm-thick and 10-mm-thick plates using the optimized flux. The effect of flux on the microstructure, mechanical properties, and residual stresses of the A-TIG weld joint is studied by comparing it with that of the weld joints made by conventional multipass TIG welding process using matching filler wire. Welded microstructure in the A-TIG weld joint is coarser because of the higher peak temperature in A-TIG welding process compared with that of multipass TIG weld joint made by a conventional TIG welding process. Transverse strength properties of the modified 9Cr-1Mo steel weld produced by A-TIG welding exceeded the minimum specified strength values of the base materials. The average toughness values of A-TIG weld joints are lower compared with that of the base metal and multipass weld joints due to the presence of δ-ferrite and inclusions in the weld metal caused by the flux. Compressive residual stresses are observed in the fusion zone of A-TIG weld joint, whereas tensile residual stresses are observed in the multipass TIG weld joint.     

Weld metal composition change during conduction mode laser welding of aluminum alloy 5182

Selective vaporization of volatile elements during laser welding of automotive aluminum alloys affects weld metal composition and properties. An experimental and theoretical study was carried out to seek a quantitative understanding of the influences of various welding variables on vaporization and composition change during conduction mode laser welding of aluminum alloy 5182. A comprehensive model for the calculation of vaporization rate and weld metal composition change was developed based on the principles of transport phenomena, kinetics, and thermodynamics. The calculations showed that the vaporization was concentrated in a small high-temperature region under the laser beam where the local vapor pressure exceeded the ambient pressure. The convective vapor flux driven by the pressure gradient was much higher than the diffusive vapor flux driven by the concentration gradient. The computed weld pool geometry, vaporization rates, and composition changes for different welding conditions agreed well with the corresponding experimental data. The good agreement demonstrates that the comprehensive model can serve as a basis for the quantitative understanding of the influences of various welding variables on the heat transfer, fluid flow, and vaporization occurring during conduction mode laser welding of automotive aluminum alloys.     

A study on weldability of zinc-coated steel sheets in lap joint configuration

The weldability of Zn-coated steel sheets 0.7 mm thick was investigated using resistance spot welding process. The effect of welding current, welding time and holding time on weld nugget characteristics, microstructure, and mechanical properties was discussed. Then, the possibility of replacing this welding process with laser beam welding was outlined. In this respect, quality of weld joints as a function of zinc removal by grinding prior to welding was evaluated. It is found that resistance spot welding current and time are the most significant parameters in affecting both expulsion and Zn-induced porosity. Expulsion was avoided and Zn-induced porosity was reduced with the decrease in welding current and/or welding time. Zn-induced porosity was completely eliminated by zinc-removal by grinding prior to welding. The best weld joint concerning nugget characteristics, soundness and tensile shear strength was obtained using welding current of 10 kA, weld cycle of 20, holding cycle of 18. Unlike resistance spot welds, high quality of CO₂ laser welds free from Zn-induced porosity could be made without zinc removal by grinding before welding.     

Influence of welding-flux moisture on welding quality

A high hydrogen content in weld produces hydrogen embrittlement,welding cold cracks,and even blowholes,which seriously affect joint performance and welding quality.Submerged-arc-welding flux has a great influence on the hydrogen content of the final weld.To simulate different flux storage circumstances and prewelding treatments,the effects of different welding-flux states on the welding quality and hydrogen content in weld were compared,using moisture content determination test and hydrogen content in deposited metal determination test.The test results reveal that to ensure the quality of welding,it is necessary to strictly control the storage of welding flux and procedures followed when using it.