Si-Mn系超高强度热成形淬火钢板的点焊性能

 采用不同的点焊工艺参数对研发的1700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊,并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明,焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响,而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区,即在靠近母材处存在一个硬度明显低于母材的软化区,其组织为回火马氏体;在靠近熔核处存在一个硬度明显高于母材的硬化区,其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织,其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织,使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。     

Characterization of a friction-stir-welded aluminum alloy 6013

The aluminum alloy 6013 was friction-stir welded in the T4 and the T6 temper, and the microstructure and mechanical properties were studied after welding and after applying a postweld heat treatment (PWHT) to the T4 condition. Optical microscopy (OM), transmission electron microscopy (TEM), and texture measurements revealed that the elongated pancake microstructure of the base material (BM) was transformed into a dynamically recrystallized microstructure of considerably smaller grain size in the weld nugget. Strengthening precipitates, present before welding in the T6 state, were dissolved during welding in the nugget, while an overaged state with much larger precipitate size was established in the heat-affected zone (HAZ). Microhardness measurements and tensile tests showed that the HAZ is the weakest region of the weld. The welded sheet exhibited reduced strength and ductility as compared to the BM. A PWHT restored some of the strength to the as-welded condition.     

Properties of friction-stir-welded 7075 T651 aluminum

Friction stir welding (FSW), a new welding technique invented at TWI, was used to weld 7075 T651 aluminum, an alloy considered essentially unweldable by fusion processes. This weld process exposed the alloy to a short time, high-temperature spike, while introducing extensive localized deformation. Studies were performed on these solid-state welds to determine mechanical properties both in the longitudinal direction, i.e., within the weld nugget, and, more conventionally, transverse to the weld direction. Because of the unique weld procedure, a fully recrystallized fine grain weld nugget was developed. In addition, proximate to the nugget, both a thermomechanically affected zone (TMAZ) and heat affected zone (HAZ) were created. During welding, temperatures remained below the melting point and, as such, no cast or resolidification microstructure was developed. However, within the weld nugget, a banded microstructure that influences room-temperature fracture behavior was created. In the as-welded condition, weld nugget strength decreased, while ductility remained high. A low-temperature aging treatment failed to fully restore T651 strength and significantly reduced tensile ductility. Samples tested transverse to the weld direction failed in the HAZ, where coarsened precipitates caused localized softening. Subsequent low-temperature aging further reduced average strain to failure without affecting strength. Although reductions in strength and ductility were observed, in comparison to other weld processes, FSW offers considerable potential for welding 7075 T651 aluminum.     

The effect of friction stir processing on 5083-H321/5356 Al arc welds: Microstructural and mechanical analysis

Friction stir processing (FSP) is used locally to modify the microstructure and thus mechanical properties of 5083-H321/5356 aluminum gas metal arc welds (GMAWs). Four specimen approaches were examined: as-arc welded, weld toe FSP (with arc weld on either the advancing or the retreating side of tool), and weld crown FSP. Microstructures within the fine-grained FSP region contained smaller constituent particles. Mg₂Si and Al₆(Fe,Mn), than those particles found in the arc weld nugget, heat-affected zone (HAZ), and base-metal (BM) locations. The FSP improved the monotonic tensile strength, yield strength, and elongation of 5083-H321/5356 Al arc welds by 6 to 9 pct, 7 to 13 pct, and 46 to 80 pct, respectively. The addition of FSP produced a 30 pct increase in the load necessary to reach 10⁷ cycles during four-point bending fatigue. An analysis of strengthening mechanisms determined that solid-solution, grain-size, and precipitation strengthening made contributions to the calculated yield strength of the BM, are weld nugget, and FSP regions. In addition, the strength mechanism analysis demonstrated that FSP increased the amount of grain-size strengthening and precipitate strengthening by nearly 110 MPa, when compared to the arc weld nugget.     

Microstructure,Tensile and Impact Toughness Properties of Friction Stir Welded Mild Steel

 Microstructure, tensile and impact toughness properties and fracture location of friction stir welded AISI 1018 mild steel are revealed in this paper. The 5 mm thick AISI 1018 mild steel plates were friction stir welded with tool rotational speed of 1000 rpm and welding speed of 50 mm/min with tungsten base alloy tool. Tensile strength of stir zone is higher (8%) when compared to the base metal. This may be due to the formation of finer grains in the weld nugget region under the stirring action of the rotating tool. The ductility and impact toughness of the joints are decreased compared to the base metal and this is due to the inclusion of tungsten particles in the weld region.     

Studies on Effect of Parent Metal Condition on the Room Temperature Mechanical Properties of Ti6Al4V Friction Welds

The influence of parent metal condition on the microstructure and mechanical properties of friction welds of Ti6Al4V alloy has been investigated. Welds are observed to contain predominantly martensite. Stress relieving results in improvement in the strengths of α + β and β treated parent metal and their welds. β welds are observed to contain coarser prior β grains. Studies reveal that welds of α + β solution treated parent metal exhibit higher strength than all the other welds. In plain tensile tests, the location of failure is away from the welds in all the conditions, suggesting that the welds are stronger than their respective parent metals. Parent metal in α + β and β solution treated conditions is observed to respond to stress relieving such that, hardness is improved after stress relieving. Stress relieving results in reduced ductility and improvement in the strength of the welds. Notch tensile strength of the welds is observed to be higher than their parent metals and stress relieving results in further improvement. The notch tensile ratio of the welds has been observed to be ~1.4 in all the conditions indicating that the welds are not notch sensitive.     

含铝304和316L奥氏体不锈钢热轧板材焊接性能

 对加Al质量分数为4%的304、2%的316L不锈钢热轧板材的焊接性能进行了研究。采用手工氩弧焊（TIG）的焊接方法,利用光学显微镜对焊缝的显微组织进行分析,利用电子探针（EMPA）分析焊接母材的元素分布,并对焊接接头进行力学性能测试。组织和力学性能的研究结果表明：含铝304和含铝316L合金热轧板分别选用ER308L,ER316L作为焊接材料,经TIG焊接后,焊缝无裂纹、气孔等缺陷,接头具有良好的强度和塑性,焊接接头力学性能接近于其母材;热影响区组织与母材组织基本一致,焊缝与母材熔合良好,组织良好,加铝304和316L不锈钢具有良好的焊接性能。     

A Comparison of Residual Stress Development in Inertia Friction Welded Fine Grain and Coarse Grain Nickel-Base Superalloy

The effect of the base material microstructure on the development of residual stresses across the weld line in inertia friction welds (IFWs) of high-strength nickel-base superalloy RR1000 was studied using neutron diffraction. A comparison was carried out between tubular IFW specimens generated from RR1000 heat treated below (fine grain (FG) structure) and above (coarse grain (CG) structure) the γ′-solvus. Residual stresses were mapped in the as-welded (AW) condition and, after a postweld heat treatment (PWHT), optimized for maximum alloy strength. The highest tensile stresses were generally found in the hoop direction at the weld line near the inner diameter of the tubular-shaped specimens. A comparison between the residual stresses generated in FG and CG RR1000 suggests that the starting microstructure has little influence on the maximum residual stresses generated in the weld even though different levels of energy must be input to achieve a successful weld in each case. The residual stresses in the postweld heat treated samples were about 35 pct less than for the AW condition. Despite the fact that the high-temperature properties of the two parent microstructures are different, no significant differences in terms of stress relief were found between the FG and CG RR1000 IFWs. Since the actual weld microstructures of FG and CG RR1000 inertia welds are very similar, the results suggest that it is the weld microstructure and its associated high-temperature properties rather than the parent material that affects the overall weld stress distribution and its subsequent stress relief.     

Effect of Post-weld Heat Treatment on Microstructure and Mechanical Properties of Laser Beam Welded TiAl-based Alloy

Post-weld heat treatment is carried out on the laser beam welded γ-TiAl-based alloy Ti-48Al-1Cr-1.5Nb-1Mn-0.2Si-0.5B (at. pct). The macro/microstructure and mechanical properties of both as-welded and heat-treated specimens are investigated by radiography, SEM, and tensile tests. Moreover, high energy synchrotron X-ray diffraction is performed to measure the residual stresses and evaluate the microstructure evolution. It is found that the residual stresses are distributed in a three-peak shape in the region of the weld zone and heat-affected zone of the as-welded specimen due to the microstructural transformation and heat softening. The residual stresses are largely relieved after the heat treatment. The heat-treated specimens have a near fully lamellar microstructure and show balanced mechanical properties of strength and ductility. The diffraction shows that the phase transformation from α ₂ to γ takes place under tensile load at 1023 K (750 °C), and the grain size and lamellar spacing are refined in the weld zone. Finally, the fracture mechanisms are found to be controlled by the local stress concentration-induced strain misfit between α ₂ and γ phases in the near γ grains and delamination and debonding in the lamellae. Boride ribbons of 5 μm in the near fully lamellar microstructure are found not to be detrimental to the tensile properties.     

40CrNiMoA钢同质焊条焊接接头组织和性能研究

分析了焊接电流70A、80A、90A对40CrNiMoA钢焊缝接头组织和力学性能的影响。随着焊接电流的增大,焊缝外观质量较好。随着焊接电流的增大,熔池区温度升高,奥氏体晶粒尺寸增大,导致马氏体组织粗大。焊缝的显微组织为马氏体及少量残余奥氏体。焊缝的硬度远高于母材的硬度,且波动较大。热影响区的硬度从母材向沿焊缝方向逐渐升高。焊接接头纵向应力在焊缝中心为压应力,向外压应力减小。焊接颜色区边界处纵向应力为拉应力,且该点拉应力最大。焊接接头横向应力在焊缝中心为拉应力,向外逐渐增大,焊接颜色区边界处变横向拉应力达到最大。焊接电流和热输入增大,降低了材料的韧性,组织中铁素体增多及焊接残余应力是诱发脆性断裂的原因。焊接电流80A是40CrNiMoA同质焊条平板对接焊接工艺的最佳的焊接电流。     

热处理对GH3128合金接头组织及力学性能的影响

 核能已经逐渐取代化石能源成为新一代能源,作为重要构件的高温气冷堆中间换热器得到了广泛关注。由于GH3128合金具有较好的焊接性、较高的高温抗氧化性能和组织稳定性,有望成为超高温气冷堆中间换热器的候选材料,但基于换热器结构复杂性以及密封性的要求,焊接是其生产和制造的关键成形手段。采用脉冲钨极氩弧焊(GTAW)对GH3128合金2 mm板材进行对接焊,研究了热处理对焊接焊接接头显微组织以及应力的影响。结果表明,在优化焊接工艺参数下,固溶态板材接头表现出最高的强塑性,室温及高温拉伸断裂位置均为母材。由于热轧态与固溶态板材接头热影响区在焊接过程中产生残余应力,导致该区硬化,在高温变形过程中残余应力诱发热影响区μ相析出,对接头持久、蠕变性能造成不利影响。焊后热处理消除了接头热影响区的残余应力,减少了持久、蠕变过程中μ相的析出,接头持久寿命得以改善。在1 200 ℃下,残余应力可为焊后热处理过程中静态再结晶提供激活能,接头热影响区发生再结晶,硬度下降,接头塑性变形能力不协调,导致室温拉伸与950 ℃拉伸断裂位置均为焊接接头。对固溶态板材试样进行不同的焊后热处理,EBSD扫描结果分析发现,接头经过1 100 ℃×10 min热处理后,残余应力明显消失,温度升高至1 140 ℃后,热影响区开始发生再结晶。     

Microstructure and mechanical properties of friction stir welding of AZ31B magnesium alloy added with cerium

The AZ31B magnesium alloy sheet added with 0.5 wt.% Ce was welded with friction stir welding(FSW).The microstructures and mechanical properties of the welded joint were investigated.The results showed that the microstructures in the weld nugget zone were uniform and with small equiaxed grains.The grains in the heat-affected zone and the thermo-mechanical affected zone were coarser than those in the base metal zone and the weld nugget zone.The ultimate tensile strength of AZ31B magnesium alloy added with 0.5...     

Laser Welding of Ultra-Fine Grained Steel SS400

Steeliswidelyusedbecauseofitsgoodcompre hensive properties ,plentyofresourceandlowerprice .Thestrengthandtoughnessaretwoimpor tantpropertiesofsteels ,andpeoplemakeeffortstoincreasetheirvalues .Addingalloyingelementandcontrollingmicrostructurearetwobasicwaystoac complishtheaim .Therefinedmicrostructureob tainedbyprocessingtechniqueenablesthestrengthandtoughnessofsteeltobeincreasedwithoutaddingalloyingelementandtheratioofperformance costtobeincreased .Theultra finegrainedsteelshavefer ritegrains…     

Effect of Arc Welding Processes on the Weld Attributes of Type 316LN Stainless Steel Weld joint

The present study aims at understanding the effect of various arc welding processes on the evolution of microstructure, mechanical properties, residual stresses and distortion in 9 mm thick type 316LN austenitic stainless steel weld joints. Weld joints of type 316LN stainless steel were fabricated by three different arc welding processes which were commonly employed in the nuclear industry. All the weld joints passed radiographic examination. Microstructural characterization was done using optical and scanning electron microscope. Volume fraction of δ-ferrite was lowest in the A-TIG weld joint. The A-TIG welded joint exhibited adequate strength and maximum impact toughness values in comparison to that of weld joints made by SMAW and FCAW processes. The A-TIG weld joint was found to exhibit lowest residual stresses and distortion compared to that of other welding processes. This was attributed to lower weld metal volume and hence reduced shrinkage in the A-TIG weld joint compared to that of weld joints made by FCAW and SMAW processes which involved v-groove with filler metal addition. Therefore, type 316LN stainless steel A-TIG weld joint consisting of lower δ-ferrite, adequate strength, high impact toughness, lower residual stresses and distortion was suited better for elevated temperature service compared to that of SMAW and FCAW weld joints.     

Structure and mechanical properties of 1570C alloy welds produced by friction stir welding

The effect of the conditions of friction stir welding (FSW) of 1570C aluminum alloy sheets on the structure and mechanical properties of the welded joints is studied. A recrystallized fine-grained structure with a grain size changing with the rate of welding tool rotation forms in a weld during FSW. As compared to the base metal, the yield strength of the weld metal decreases by 9–22% depending on the rate of welding tool rotation, and the ultimate tensile strength is almost independent of the FSW conditions and accounts for ～90% of the ultimate tensile strength of the base metal. The plasticity of the weld metal is >13% for all rates of welding tool rotation. The microstructure and mechanical properties of the weld zone are discussed.     

热处理对B1500HS钢激光拼焊板力学性能的影响

利用单轴拉伸试验机、扫描电子显微镜、能量色散谱仪、光学显微镜、维氏硬度仪等研究了热处理前后B1500HS钢激光拼焊板的淬火性能.结果表明:热处理前B1500HS钢拼焊板焊缝强度远高于母材区,硬度分布极不均匀;热处理后,B1500HS钢拼焊板的元素分布几乎没有变化,整体强度有了大幅的提高,但塑性下降程度较大,其中横向塑性最差,经维氏硬度测试,发现焊缝至母材区的硬度过渡平滑.硬度值平滑过渡使得应力和应变分布更加均匀,保证了母材和焊缝力学性能的良好连续性,可以显著提高B1500HS钢拼焊板的成形性能.      

Microstructural damage and residual mechanical properties in helium-bearing gas metal Arc weldments

The influence of entrapped helium on microstructural damage and residual mechanical properties subsequent to applying low-penetration gas metal arc (GMA) weld overlays was examined for an AISI Type 304 stainless steel. Two helium levels were examined: 22.5 and 85.0 atomic parts per million (appm) He. Detailed scanning electron microscopy (SEM) revealed the presence of intergranular cracks in the weld heat-affected zone (HAZ). The crack surfaces exhibited a dimple structure that was characteristic of a gas bubble embrittled material. Transmission electron microscopy (TEM) revealed that the size and spacing of the grain boundary helium gas bubbles remained virtually unchanged (relative to that established by the charging and aging procedure) at distances greater than 1 mm from the fusion line. Within this first millimeter, the diameter of the bubbles increased rapidly, and the bubble spacing increased to the characteristic spacing of the dimples that decorated weld-induced cracks. Mechanical testing revealed a loss in strain-to-fracture and ultimate tensile strength (UTS) at the higher helium level. While the majority of the fracture occurred in a transgranular, ductile manner, some deformation-induced intergranular cracking was observed. This cracking occurred over a very narrow region localized to the HAZ of the weldment. At the lower helium level, ductility and strength were unaffected compared to helium-free specimens.     

Characterization of Structure–Property Relationship of Incoloy 825 and SAF 2507 Dissimilar Welds

This study was carried out to investigate the evaluation of dissimilar welding between Incoloy 825 Ni-based alloy and SAF 2507 super duplex stainless steel. Welding was conducted by pulsed current (PC) and continuous current (CC) gas tungsten arc welding (GTAW) methods using ERNiCrMo-3 filler wire. The microstructure of weld zones and base metal/weld interfaces as well as mechanical properties of weldments were characterized. The results detailed the formation of Nb, and Mo-rich phases in the inter-dendritic regions of weld metals leading to a decrease in impact resistance of weld zones in comparison to parent metals. Presence of more secondary phases at the CCGTA weld metal resulted in higher hardness and lower toughness than that of the PCGTAW sample. During tensile tests, fracture occurred at the Incoloy 825 base metal, and both weldments also underwent ductile mode of fracture. The research addressed the microstructure–property relationship for dissimilar weld joints.     

SPCC冷轧钢胶焊连接工艺研究及数值模拟

 为了研究胶焊工艺对接头力学性能的影响,并分析胶焊接头的温度场演变规律,针对1.5 mm厚的SPCC冷轧钢薄板,开展胶接点焊和电阻点焊的正交试验,并应用极差和方差分析得到最佳工艺参数,借助材料性能试验机对两种接头进行单向静拉伸试验获得接头的失效载荷,对比分析点焊和胶焊接头的力学性能,建立胶焊接头的仿真模型,分析接头熔核区温度场的演变规律,采用超声波C扫描成像检测熔核直径。结果表明,影响胶焊接头拉剪载荷的主、次因素依次为焊接电流、焊接时间、电极压力;胶焊接头和点焊接头的平均失效载荷分别为11 071.12和10 179.72 N,胶层的引入提高了接头的失效载荷;随着焊接时间的增加,熔融的金属液增多,熔核沿着径向和轴向呈椭圆形扩张,熔核中心的径向温度均高于轴向温度,模拟获得的熔核尺寸与超声C扫描测得熔核直径分别为6.17、5.61 mm。     

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.