Relationships governing slip in the structure of the weld metal of welded joints in heat-resisting pearlitic steels

Summary

Previous papers have shown the high‐current AC‐MIG welding process to be superior to the conventional DC‐MIG process in terms of welding efficiency and welded joint performance. The authors have used the AC‐MIG process to weld heavy‐gauge steel plates at a tensile strength level of 980 MPa. Weld metal with a very low hydrogen content is obtained by the newly developed process, resulting in a reduced preheating temperature during welding of high‐strength steels. The AC‐MIG process also produces an arc climbing effect with electrode negative polarity ‐ a desirable effect in narrow‐gap welding. AC‐MIG weld metal further contains low oxygen, conferring high toughness. As a result, a narrow‐gap AC‐MIG welding process has been developed to ensure high efficiency in processing and metallurgically high‐quality welds in welding of 980 MPa high‐strength steels for penstocks (pressure shafts) in hydroelectric power stations. Welding wires with chemical compositions satisfying suitable strength and toughness criteria have been trial‐manufactured. Suitable welding parameters have also been determined for narrow‐gap welding of penstocks.     

工业纯钛光纤激光-MIG复合焊接工艺及性能

采用光纤激光与熔化极惰性气体保护电弧焊(MIG焊)复合焊接工业纯钛,分别对激光焊、MIG焊和复合焊接头的焊缝表面成形、横断面进行了观察,并进行了激光焊和复合焊接头的拉伸试验及杯突试验.结果表明,复合焊的电弧稳定性比MIG焊显著提高,焊接速度可提高7倍;复合焊与激光焊接头的抗拉强度高于母材;复合焊接头的杯突值优于激光焊接头的杯突值,这是因为复合焊焊缝的微观组织有利于接头的塑性.因此,采用光纤激光-MIG电弧复合焊接方法很好地实现了工业纯钛的高速焊接,焊缝成形良好,接头的塑性优于单一激光焊的塑性.

Abstract：

Fiber laser-metal inert gas (MIG) arc hybrid welding was used to weld the commercial pure titanium (CP-Ti). The weld appearance, cross section, tensile strength, Erichsen value and microstructure of the CP-Ti welded joints were studied. The results show that the arc stability is substantially improved and the welding speed can be increased to 7 times by fiber laser-MIG hybrid welding. The welded joints by laser welding and the hybrid welding exhibit the higher ultimate tensile strength than those of the base metal. In addition, the welded joint by the fiber laser-MIG hybrid welding has higher Erichsen values than that by laser joints. The difference in plasticity is attributed to the microstructure changes in the welded joint of hybrid welding. Thus, the fiber laser-MIG hybrid welding of CP-Ti can be carried out suecessfully at higher welding speed with a good combination of weld bead appearance and plasticity.     

10Ni3CrMoV钢CO2激光多层焊的接头组织与性能

与传统电弧焊相比,激光焊接厚板优势明显。采用纯激光焊和激光电弧复合焊等多道焊接技术实现了28 mm厚10Ni3CrMoV钢的高效焊接,采用光学显微镜分析焊缝、热影响区和焊缝重叠区的组织,激光复合焊缝组织主要为针状铁素体,纯激光焊缝、粗晶区和细晶区组织主要为板条马氏体,激光复合焊缝重叠区组织为粒状贝氏体+马氏体,纯激光焊缝和激光复合焊缝重叠区组织为马氏体+少量粒状贝氏体。测试了焊接接头的力学性能,结果表明,激光复合焊缝金属的冲击韧性较高,焊接接头的抗拉强度和屈服强度与母材相当,延伸率略小于母材,焊接接头的最大硬度小于360 HV,弯曲性能合格。     

高速列车6N01侧墙激光复合焊接头软化行为分析

采用激光-电弧复合焊工艺焊接高速列车侧墙6N01铝合金型材,并对焊接接头的软化行为进行分析. 通过拉伸试验、显微硬度测试、微观金相试验和拉伸断口SEM试验,系统分析激光-电弧复合焊焊接接头软化行为,并与目前生产中应用的MIG焊接头的性能进行对比. 结果表明,采用复合焊,焊接接头强度均较MIG焊接头的强度提升10%以上,HAZ的软化区较MIG焊的减小了40%～60%;激光复合焊接头金相组织晶粒更细小,第二相质点数量多而且弥散细小,MIG焊热影响区晶粒长大倾向较大,强化相质点数量少并且尺寸较大. 采用激光-电弧复合焊方法对高速列车车体的侧墙所发生的焊接接头软化有较大的改善.     

Microstructures and properties of laser/arc hybrid welds and autogenous laser welds in pipeline steels

Abstract

Lasers are capable of producing welds with deep penetration, low distortion and faster travel speeds, compared to arc welding. More recently, laser/arc hybrid welding processes have also been generating interest for industrial fabrication. In this paper, six carbon–manganese, mainly pipeline, steels were welded using both autogenous Nd:YAG laser welding, and Nd:YAG laser/MAG hybrid welding. The improvements in weld microstructures and weld metal toughness that are possible when using the hybrid process are described and illustrated. Laser/arc hybrid welding is shown to be a process that can generate good quality welds in commercially available pipeline steels. It also has the potential to complete girth welds in these steels with significantly fewer welding passes than are currently required for arc welded pipelines, reducing the joint completion time.     

Microstructural and strength study of MIG welded joints of AW7020 aluminium alloy,as a function of joint geometry

Summary

Medium strength AW7XXX aluminium alloys are widely used as welded structures and in transportation. The applications of these alloys are limited by the behaviour of the welded joints. There is no agreement on the joint geometry that must be used on 5 mm welds. The microhardness evolution is one of the most important strength indicators. For this reason, the aim of this work is to study the influence of welded joint geometry on microhardness profile and on the microstructure of a MIG welded AW7020 aluminium alloy, using AW5256 filler.     

铝合金/镀锌钢板脉冲MIG电弧熔-钎焊接头组织与性能

采用数字化脉冲MIG焊机,以ER4043焊丝为填充材料.实现了6013-T4铝合金薄板与镀锌钢板的熔-钎焊接,研究了焊接热输入对接头组织和性能的影响,结果表明,在熔-钎焊接头熔化焊缝焊趾处存在主要由Zn-Al共晶体、富A1的α固溶体和Fe3Al组成的富Zn区:钎焊界面上的Fe-Al金属间化合物层厚度在1.05-4.50μm之间.且随焊接热输入的增加而增大.Fe-Al金属间化合物呈"锯齿"或"舌"状向焊缝内生长,主要为FeAl₂,Fe₂Al₅和Fe₄Al₁₃.随着焊接热输入的增大,熔-钎焊接头的抗拉强度先增大而后减小.在850 J/cm的热输入下达到229 MPa,拉伸后在铝合金焊接热影响区发生断裂,为塑韧性断裂;当焊接热输入较小时接头在钎焊界面断裂,属于脆性断裂.     

Study of laser MIG hybrid welded AZ31 magnesium alloy

Abstract

The laser metal inert gas (MIG) hybrid welded AZ31 magnesium alloy is discussed in weld shape, microstructure characteristics and mechanical properties in comparison of single laser and arc welding. The stable MIG arc, reliable droplet transfer and regular weld that are hardly obtained in single MIG welding can be obtained in hybrid welding by laser arc synergic effects. The ultimate tensile strength and elongation of hybrid weld are far higher than those of laser weld and reach 97·8 and 87·5% of base metal respectively. Under this experimental condition, the efficiency of hybrid welding is 1·20 times faster than that of single laser welding. Between the wide upper part (arc zone) and the narrow lower part (laser zone), obvious difference is observed. Arc zone has coarser grain size and wider partial melted zone than laser zone. Finally, the porosity reduction mechanism of hybrid weld is discussed according to the weld pool shape and the acting forces on it.     

Laser and laser assisted arc welding processes for DH 36 microalloyed steel ship plate

Abstract

A series of laser and laser assisted metal inert gas (MIG) welds was produced from a common plate. Each weld was mechanically tested, and the welds showed broadly similar properties, except for the autogenous CO₂ laser weld metal, which had poorer toughness. This was related to a harder weld metal microstructure. Toughness and hardness were related to the lath width of the ferrite, for the welds involved. The weld metal area/volume was used as an indicator of potential distortion. In this instance, the autogenous CO₂ laser weld was superior to the CO₂ laser assisted MIG weld which was better than the Nd:YAG laser assisted MIG weld. Each weld was examined using carbon extraction replicas in the TEM, and also using an SEM with an EDAX attachment. A number of inclusions and precipitates were observed, identified and sized. It was concluded that the particles observed were not detrimental in this specific case. A tentative relationship was established between parent plate inclusion size distribution and weld metal inclusion size distribution.     

Join Al–steel dissimilar metal by novel high frequency electric cooperated arc welding

ABSTRACT

A novel high frequency electric cooperated arc welding method (HFAW) was developed to join aluminium and steel of 3.0?mm thickness without groove. Owing to the skin effect and proximity effect of high frequency current, a part of welding heat was directly distributed all over weld side wall. Consequently, sound double-sided weld formation was achieved under a low MIG heat input and high welding speed. The average thickness of interfacial layer was limited to 2.3?µm. Benefitted from the balanced heat input and thin interfacial layer, the failure mode of the HFAW joint was necking at Al base metal. For traditional MIG joint, however, poor back weld formation and thick interfacial layer resulted in spontaneous fracture at interface.     

异种钢LMHW与MIG焊接头力学性能对比分析

激光-MIG复合焊（LMHW）由于结合了激光和电弧两个独立热源各自的优点,极大程度地避免了二者的缺点,因此成为在汽车、船舶、石油化工等领域具有极大应用前景的新型焊接方法. 以25CrMo4和33MnCrB5-2异种钢试样为研究对象,对比研究了LMHW和MIG焊的焊接接头金相组织差别与硬度分布差异. 结果表明,LMHW焊缝成形均匀饱满,焊接成形效果好于MIG焊接. LMHW接头焊缝中心的组织比MIG焊的组织更细,整体硬度比MIG焊接头整体硬度高,接头的质量较MIG焊的接头质量好. LMHW的接头整体硬度高出MIG焊接头的整体硬度30%.     

高速列车用厚板铝合金CMT焊接工艺

针对低热输入、高质量焊接技术的需求,研究厚板铝合金多层多道冷金属过渡技术(cold matal transter,CMT)焊接工艺和脉冲MIG焊接工艺的区别,对CMT焊接和脉冲MIG焊接进行热循环曲线测量,焊接接头拉伸、弯曲、硬度等常规力学性能试验和接头微观组织分析.结果表明,铝合金厚板焊接时相对脉冲MIG焊接方法,CMT方法焊接温度场低,焊接接头软化明显减弱,冲击韧性得到提高,厚板多层多道焊接接头组织明显改善,晶粒明显细化.试验表明CMT焊接方法可获得相对脉冲焊接更加优良的铝合金焊接接头.     

Electromagnetic impact welding of Mg to Al sheets

Abstract

Magnesium (Mg) and aluminium (Al) alloys have been lap welded using an electromagnetic impact welding technique. Metallographic examination of the welds has revealed sound and defect free interfaces. Complete metal continuity has been observed with a characteristic wavy interface. X-ray diffraction analysis has shown no intermetallic phases and suggested that this electromagnetic technique is a solid state welding process. All the shear strength samples welded with discharge energy of 6·7 kJ failed away from weld either in the plastically deformed zone or in the base metal. Optimum discharge energy has been determined as 6·7 kJ based on the shear strength results of the welds.     

铁道车辆用铝材的焊接特性

对高速列车用６０６３、６０６１、９１９（相当于７００５）铝合金母材及与之相匹配的焊丝（４０４３、５１８３、５３５６铝合金丝）施以ＭＩＧ焊接之后的焊区强度、硬度以及焊接接头的腐蚀倾向、残余应力水平和常见的焊接裂纹与气孔等缺陷进行了分析和研究。结果表明，由于产生了软化，焊缝及热影响区的强度和硬度均低于母材；从综合效果来看，以母材６０６１合金匹配４０４３焊丝为佳；从焊后强度和刚度看，中空型材的截面以斜筋截面为优；从焊接接头的可靠性看，以纵向ＭＩＧ自动焊接对接为最好     

6061铝合金FSW接头与MIG焊接头对比试验

采用搅拌摩擦焊(FSW)和MIG焊分别对6061铝合金板进行了焊接试验,测试了焊接接头的强度,观察了焊接接头的金相组织,并进行了接头的硬度分布测试.结果表明,搅拌摩擦焊接头抗拉强度高达212.05 MPa,是母材抗拉强度的86％,比MIG焊的接头强度略高.焊接接头软化区宽度比MIG焊接头软化宽度窄.6061铝合金母材为典型的轧制组织,焊核区为细小的等轴晶组织,MIG焊接头焊缝为柱状晶组织.     

高强钢CO2激光-MAG复合焊接性能

为了研究CO₂激光-熔化极活性气体保护焊（MAG）复合焊接性能,采用CO₂激光和CO₂激光-MAG复合焊接590MPa级高强度钢,对其焊接接头的显微组织和力学性能进行了研究.结果表明,激光-MAG复合焊接的焊缝金属中,MAG电弧作用区主要为珠光体和贝氏体,激光作用区主要为马氏体;激光-MAG复合焊接的焊缝金属中Mo和Mn合金元素的分布具有不均匀性;激光和激光-MAG复合焊接的试件焊接接头拉伸性能完全满足要求,焊缝强度高于基体强度;激光-电弧复合焊缝金属在-60℃～+15℃试验温度范围内的冲击韧性比激光焊缝金属高;激光-MAG复合焊接焊缝金属硬度在250～400 HV之间,高于基体金属的硬度.     

Computer-aided experiment on arc welding

Fatigue properties of cast aluminium welded joints by friction stir welding (FSW) and MIG welding were investigated, comparing with that of the base plate. Fatigue crack propagation tests for the da/dN ? ΔK relation and bending fatigue tests for the S–N relation were carried out. Fatigue cracks in both FSW and MIG specimens were accelerated, when the fatigue crack tip reached the stir zone or the weld metal. This behaviour was discussed based on the crack closure induced by the crack surface roughness and the residual stress. In the S–N properties, the influence of specimen surface finishing on fatigue life was also examined. Fatigue lives of the FSW and MIG specimens in the ‘as weld’ condition were in the range of the largely scattered base plate fatigue lives, in spite of the different fatigue crack initiation sites in each specimen such as the porosity in the base plate, the tool mark bottom in the FSW and the weld toe in the MIG. The FSW specimens with the polished surface showed the particular improvement in fatigue strength for finite fatigue life.     

焊接参数对铝合金激光——MIG电弧复合焊缝熔深的影响

以5A06(LF6)铝合金为研究对象,研究了铝合金激光-MIG电弧复合焊(HYBRID焊)时焊接参数的变化对焊缝熔深的影响规律,并将焊接参数的变化对激光-MIG电弧复合焊、MIG电弧焊、激光焊的焊缝熔深的影响进行了综合比较分析.结果表明,若以等效于激光焊熔深的MIG电弧功率为分界线,可以把MIG电弧的功率分成高、低能量两个区,当激光与低能量电弧区的电弧复合时,激光对焊缝的熔深起主导作用,HYBRID焊的熔深大于该区的MIG电弧焊;当激光与高能量电弧区的电弧复合时,电弧对焊缝的熔深起主导作用,HYBRID焊缝主要体现为MIG焊缝的特点,加入激光的优势主要体现在增加焊接速度方面,即高速焊时也可获得良好的焊缝成形.     

焊丝成分对SiCp/6061 Al复合材料MIG焊焊缝组织及性能的影响

采用Al-Mg及Al-Si两种焊丝分别对SiCp/6061Al复合材料进行了MIG焊及脉冲MIG焊,利用光学显微镜、电子显微镜及MTS-810试验机对焊缝的组织及性能进行了分析.结果表明,采用Al-Mg焊丝焊接时,无论是MIG焊还是脉冲MIG焊,熔池中Al-SiC间的界面反应程度均较大,生成了较多的针状Al4C3,且Al4C3的尺寸较大.采用Al-Si焊丝时,MIG焊熔池中的界面反应程度显著降低,仅生成了少量尺寸较小的针状Al4C3;而采用Al-Si焊丝的脉冲MIG焊焊缝中没有发现针状Al4C3.同时,利用Al-Si焊丝可有效地防止焊缝熄弧处的宏观结晶裂纹.力学性能试验表明,采用同样焊丝时,脉冲MIG焊接头的强度及伸长率比MIG焊接头的高,而用Al-Si焊丝焊接的接头强度比用Al-Mg焊丝焊接的接头强度高.     

Structural evolution of pulsed Nd-YAG laser welds of AISI 1006 steel

Abstract

Although correlations of welding parameters with the metallurgical features of conventional fusion welds in low carbon steels are well established, information on process–structure–property relationships associated with pulsed laser welds is more limited. This paper presents results on the characterisation of weld metal and heat affected zone (HAZ) microstructures observed in laser welded AISI 1006 steel. Pulsed Nd-YAG laser welds in the bead on plate configuration were used for this purpose, both in overlapping and non-overlapping bead configurations. As very rapid heating and cooling cycles occur during laser welding, the microstructures observed in the weld metal are the result of rapid solidification producing thin columnar austenite grains extending from the fusion boundary, which transform to martensite and bainite during fast cooling to ambient temperature. The HAZ structure in the base plate can also be rationalised in terms of the rapid thermal cycling experienced. The HAZ is narrow with the intercritical reheated subzone being dominant. As microstructural development has a critical effect on the mechanical properties of welds, microstructural characterisation plays an integral role not only in the understanding of pulsed laser welding, but also in the selection of optimum welding conditions for the material of interest.