Microstructure and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel

Two post weld heat treatments (PWHT), 900 ℃ oil quenched and low temperature tempered (PWHTA) and high temperature tempered and then 900 ℃ oil quenched and low temperature tempered (PWHTB), are employed to treat the weldment. Then the effect of two post weld heat treatment processes on the microstructure,mechanical properties and fracture toughness of electron beam welded joints of 30CrMnSiNi2A steel have been discussed. The results show that, after two kinds of PWHT the microstructure and hardness at every zones of EBW joints are nearly same. Although the welds have good mechanical properties, fracture toughness of both weld and heat affected zone (HAZ) is low, the CTOD values of welds are comparatively higher than that of HAZ. Microstructure and fracture toughness of two EBW joints have no evident differences.

Effects of Electron Beam Local Postweld Heat Treatment on Microstructure and Properties of 30CrMnSiNi2A Steel Welded Joints

To improve the microstructure and properties of the electron beam welded joints, the vacuum or furnace whole post weld heat treatment (FWPWHT) usually should be done on it. The electron beam local post weld heat treatment (EBLPWHT) is a rather new heat treatment procedure that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. In this paper, the microstructure, mechanical properties, fracture toughness and fatigue properties of electron beam welded joints of 30CrMnSiNi2A steel in as-welded (AW) and EBLPWHT conditions have been investigated respectively. The results show that the microstructures of different zones of joints in as-welded condition are changed by EBLPWHT procedure, in which the welds from coarse needle martensite into lath-shaped martensite; the main structures of heat affected zones (HAZ) from lath-shaped martensite into lower bainite. The properties of welded joints can be improved by the EBLPWHT in some extent, especially the fracture toughness of the welds and the fatigue crack resistance of welded joints can be sufficiently improved. However, more appropriate heat treatment parameters of the EBLPWHT have to be studied in order to increase the mechanical properties of base metal near by the HAZ.

Fatigue behavior of AZ31B magnesium alloy electron beam welded joint based on infrared thermography

Fatigue behavior of AZ31B magnesium alloy electron beam welded joint undergoing cyclic loading was investigated by infrared thermography. Temperature evolution throughout a fatigue process was presented and the mechanism of heat generationwas discussed. Fatigue limit of the welded joint was predicted and the fatigue damage was also assessed based ontheevolution of the temperatureand hotspot zone on the specimen surfaceduring fatigue tests. The presented results show that infrared thermography can not onlyquicklypredict the fatigue behavior of the welded joint, but also qualitatively identify the evolution of fatigue damage in real time. It is found that the predicted fatigue limit agrees well with the conventionalS-Nexperimental results. The evolution of the temperatureand hotspot zone on the specimen surface can be an effectivefatigue damage indicatorfor effectiveevaluationof magnesium alloy electron beam welded joint.

Structure and mechanical properties of aluminum alloy/Ag interlayer/steel non-centered electron beam welded joints

Electron beam welding was carried out between aluminum alloy and steel with Ag interlayer. Seam morphology, structure and mechanical properties of the joints were investigated with different action positions of the electron beam spot. The results show that with the increment of the beam offset to the silver side from the interface between silver and steel, the seam morphology was improved, and the porosity in the Ag interlayer vanished. A transition layer mainly composed of Ag2Al and Al eutectic was formed at the interface between silver and aluminum, and became thin and spiccato as the beam offset increased. When the beam offset was too large, two IMC layers composed of FeAl and FeAl3 respectively were formed at the interface between steel and Ag interlayer. The optimal beam offset was 0.2 mm, and the maximum tensile strength of the joint was 193 MPa, 88.9% that of the aluminum alloy, and the fracture occurred at the interface between steel and Ag interlayer.

Investigation on Electron Beam Welded Copper to AISI 316 Stainless Steel Joints

Joints of copper and stainless steels are used in a er ospace applications. Production of these joints by fusion welding faces many dif ficulties. This may be due to the differences in their physical, metallurgical a nd mechanical properties. Electron Beam Welding (EBW) process has been found to be especially well suited in this area. Selection of the appropriate welding par ameters needs thorough investigations. These parameters include: preheat tempera ture (℃), welding current (I w), focusing current (I F), welding spee d (V), height between the gun and workpiece surface (H), scan width (S w) and shift distance (S). The present work aims firstly, setting the pr oper welding conditions to get sound joint between commercially pure copper (C10 200) and AISI 316 stainless steel plates 8 mm thickness. Secondly, investigate t he effect of Electron Beam (EB) shift, single-sided and double-sided welds on the mechanical, metallurgical and chemical properties of the weld bead. Due to t he high difference in thermal conductivity between copper and stainless steel, E lectron Beam (EB) was shifted towards copper with different values. These values were ranged from 0.3 to 0.9 mm in welding without preheating of copper plate an d from 0.1 to 0.4 mm with preheating. Number of joints were welded using variabl e EBW parameters in view to obtain the sound weld bead. These parameters are as follows: gradual reduction I w=51 to 49 mA, I F=845 mA, V=8 mm/sec , H=130 mm, S w=500 μm and S=0.4 mm. The investigation has shown t hat, the copper (C10200) plate must be preheated to get sound welded joint with AISI 316 stainless steel using the EBW process. The tensile fracture in all wel ded samples occurred in copper plate away from the weld bead. This reflects that the weld bead tensile strength is greater than the copper strength. The EB shif t has slight effect on hardness distribution through weld bead. The hardness val ue (H v) reduces in gradual manner from stainless steel hardness to copper one. The EB shift distance has no significant effect on the impact toughness.

Effects of electron beam welding parameters on the microstructure of titanium to aluminum alloy joints

Electron beam welding of titanium alloy to aluminum alloy was carried out by melting and melt-brazing to investigate the effects of welding parameters on microstructure of the joint. The results indicated that the joint of the specimen welded by melting was well-formed but contained a large amount of intermetallic compounds. These intermetallic compounds were mainly composed of brittle phases such as TiAl and TiAl3 that decreased the ductility of the joints and resulted in a tensile strength 50 % lower than that of the base metal. In the melt-brazing experiment, direct heat was applied to the aluminum alloy to melt the aluminum rather than the titanium alloy, creating a well-formed joint. The weld was mainly composed of Al element and only a 3 ~m thickness of intermetallic compounds formed near the fusion line at the Ti side. The ductility and the performauce of the joint were significantly improved compared with those of the melting-only joint. In addition, the tensile strength of the joint reached 80 % of that of the aluminum base metal.

Research on microstructure and property of electron beam welding joints of titanium alloy sheets

This paper reports research into the microstructures and properties of electron beam welding （EBW） joints of a Ti alloy sheet. To control the TC4 sheet joint formation during electron beam welding is not an easy task. However, the electron beam current has a significant influence on joint formation and a good appearance of a T-joint can be obtained by increasing the heat input and using the electron beam scan method. It was found that all acicular martensite in the fusion zone （FZ） consisted primarily of α＇ phase titanium, with some β phase present. Grain coarsening occurred in the heat-affected zone （HAZ） due to transformation of the β phase. Butt joints possessed high strength, hardness of the fusion zone, and the heataffected zone of these joints performed better than that of the parent metal. The highest shear strength of T-joint was 615 MPa and the fracture mechanism was a gliding fracture.

Electron beam welding of 304 stainless steel to QCr0.8 copper alloy with copper filler wire

Electron beam welding （EBW） of 304 stainless steel to QCr0.8 copper alloy with copper filler wire was carried out. Orthogonal experiment was performed to investigate the effects of process parameters on the tensile strength of the joints, and the process parameters were optimized. The optimum process parameters are as follows：beam current of 30 mA, welding speed of 100 mm/min, wire feed rate of 1 m/min and beam offset of-0.3 mm. The microstructures of the optimum joint were studied. The results indicate that the weld is mainly composed of dendriticαphase with little globularεphase, and copper inhomogeneity only occurs at the top of the fusion zone. In addition, a melted region without mixing exists near the weld junction of copper side. This region with a coarser grain size is the weakest section of the joints. It is found that the microhardness of the weld decreases with the increase of the copper content in solid solution. The highest tensile strength of the joint is 276 MPa.

A survey on future research about electron beam welding for aerospace applications

Electron beam welding plays an important role in the aerospace industry where components like sensors,gears,actuators and air frames used in aircraft and rocket engines were welded using this technique.Welding is normally performed in a vacuum to avoid the scatter of electron due to the presence of gas molecules in the atmosphere and hence electron beam welding process provides the greater results.But still joining of dissimilar metals is challenging.This paper represents review of process,generation and distribution of heat source various input parameters,materials,microstructure,mechanical strength and the possibilities of joining dissimilar metals using electron beam welding.

Mechanical properties of electron beam welded dissimilar joints of TC17 and Ti60 alloys

Microstructure, hardness, tensile and high cycle fatigue （HCF） properties of the welded dissimilar joints of Ti60 and TC17 titanium alloys had been investigated in this study. A significant microstructural change was observed to occur after welding, with rod-like α and β phases in the fusion zone （FZ）, equiaxed et phases, fine α laths and β phases in the heat-affected zone （HAZ） of TCl7 side and acicular martensite α＇ phases＋＂ghost＂ α phases in the HAZ of Ti60 side, The microhardness across the joints exhibited an inhomogeneous distribution with the highest hardness of ~404 HV in FZ and the lowest hardness of ~304 HV in base material （BM） of Ti60. All the joints tested in tension fractured at BM of Ti60 side. Fatigue limits of the joints at 107 cycles were 425 MPa at room temperature and 380 MPa at 400 ℃, respectively. Welding micropores were found to be the main source of fatigue crack initiation.

Study on the J-Integral and Failure Assessment Line of Electron Beam Welded Thick TC4-DT Alloy Joints

The effects of strength mis-matching on J-integral and failure assessment line (FAL) of electron beam welded thick TC4-DT titanium alloy joints have been investigated.Elastic and elastic-plastic finite elements (FE) calculations on centre crack tensile (CCT) specimens were made,and the condition of 20% strength mis-matching was considered.The results indicate that the limit load of the joint can be substituted by that of the base metal.The error of substitution is less than 5%.The failure assessment lines for both over-matching and under-matching joints are increasingly close to that of the base metal,with the ratio of weld width to specimen width (H/W) decreasing.Moreover,the failure assessment lines of the joints can be devised using the stress-strain curves of the base metal,which will be convenient for the practical application of engineering

接头性能差异对Zr-Sn-Nb合金电子束焊接头残余应力的影响

为了提升Zr-Sn-Nb合金电子束焊残余应力计算精度,对Zr-Sn-Nb合金及焊接接头热物性参数与力学性能进行测量,研究接头性能差异对电子束焊接头残余应力影响规律,建立了电子束焊复合热源模型,采用热弹塑性有限元方法对4.45mm厚Zr-Sn-Nb合金电子束焊应力进行数值模拟,并进行焊缝形貌验证.结果表明,考虑焊缝与母材属性差异时,试板上表面焊缝及热影响区区域的横向残余应力峰值高于二者属性相同时的模拟结果,峰值分别为319 MPa和296 MPa,进一步考虑热影响区属性与母材及焊缝差异对接头残余应力影响不大,峰值纵向应力为318 MPa.

基于DIABEAM法的电子束能量密度测试分析

为了充分发挥电子束焊接技术在航空航天领域的作用,对反映束流品质的关键因素—电子束能量密度开展了研究;基于法拉第传感原理,通过DIABEAM测试法对真空电子束焊机电子束能量密度分布进行测试分析;结果表明:电子束能量密度分布呈非对称的近高斯分布,随着聚焦电流的增加,电子束能量密度趋于发散分布,达到焦点状态时dP90区域内电子束能量密度均值最高;电子束能量密度峰值随着灯丝加热电流增加而增加,但受灯丝尺寸等因素的影响,灯丝加热电流达到稳定值后能量密度分布不变。

45钢特厚复合坯真空电子束焊接头裂纹倾向分析

采用真空电子束焊接方法封焊并制备45钢特厚复合坯,通过金相显微镜(OM)、扫描电子显微镜(SEM)、维氏硬度计、冲击试验机等设备,分别分析了45钢复合坯封焊过程中不同位置(1#起弧处、2#中部、3#收弧处)接头组织与力学性能。结果表明,焊接位置由起弧处向收弧处变化时,接头熔深几乎不变,热影响区域面积逐渐减小。1#接头焊后冷却速度相对较慢,焊缝根部无裂纹产生,组织为针状马氏体与团块状托氏体混合物,硬度为588 HV,焊缝根部冲击性能为25.7 J,断口呈韧性断裂;2#及3#试样焊后冷却速度快,焊缝根部产生明显的穿晶裂纹,组织均为针状马氏体,随着焊后冷却速度的加快,马氏体数量增多尺寸变细;硬度分别升高至674 HV与729 HV,冲击性能下降,分别为18 J与13.7 J,并呈脆性断裂。

TC4钛合金EBW和TIG焊接头断裂韧性对比分析

采用电子束焊和氩弧焊方法制备的TC4钛合金接头,在4种温度条件下,测试了其焊缝、热影响区及母材的断裂韧性,并结合断口形貌、硬度分布及微观组织对比分析了断裂韧性测试结果.结果表明,TC4钛合金TIG焊接头焊缝及热影响区的断裂韧性优于钛合金母材,CTOD值随温度下降而降低;相较之下,EBW焊接头焊缝断裂韧性值较母材更低,热影响区断裂韧性与母材较接近,温度变化对其CTOD值无显著影响.钛合金TIG焊接头焊缝区域具有较低硬度值,其网篮状α相和较低比例的马氏体分布是其断裂韧性较高的根本原因;而钛合金EBW焊接头焊缝中针状马氏体的分布导致其局部硬度较高,并降低了断裂韧性.

热输入对Ti180钛合金电子束焊接接头组织和力学性能的影响

焊接热输入量会影响双相钛合金接头热影响区α/β相转变以及次生α′相的析出,进而改变接头力学性能。对7 mm厚Ti180钛合金电子束焊接接头组织分析发现,近熔合线热影响区和中部热影响区由“ghost”状初生α相、次生针状α′相和残余β相组成,近母材热影响区由初生α相、残余β相和少量次生α相组成。热输入量升高会导致初生α相比例减少,进而接头拉伸性能发生变化。当热输入由120 J/mm增加到177 J/mm时,接头的伸长率由16.7%降低到11.6%,抗拉强度均达母材强度(970 MPa);而焊缝区与热影响区的硬度始终高于母材硬度(341HV)。因此,可以通过改变焊接热输入量来控制热影响区微观组织,进而实现对Ti180钛合金接头力学性能的调控。

高碳铬不锈钢电子束焊接头性能研究

针对高碳铬不锈钢焊接接头性能差的问题,采用电子束焊接技术对厚度为5 mm的调质态的高碳铬不锈钢进行焊接。利用光学显微镜(OM)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和拉伸试验机等设备对其接头进行显微组织与性能分析。结果表明,在加速电压150 kV、束流强度17 mA、焊接速度850 mm/min的条件下,可获得成形良好、无气孔和裂纹等缺陷产生的焊接接头。碳及合金元素以固溶态形式存在于焊缝中,熔合区均为马氏体和残余奥氏体,呈现出非平衡凝固组织,焊接热影响区中碳化物颗粒发生部分溶解。焊接接头硬度分布呈现典型的“M”型,焊接热影响区硬度最高,可达750HV;焊接接头抗拉强度为699 MPa,在焊接热影响区发生脆性断裂,接头的塑性变形能力急剧下降。

AlCoCrFeNi_(2.1)高熵合金电子束焊接接头耐蚀性

为明确高熵合金焊接接头耐腐蚀行为,采用电子束方法对共晶双相AlCoCrFeNi_(2.1)高熵合金进行焊接,并运用电化学腐蚀方法研究了接头耐蚀性。结果表明,焊缝区域(FZ)自腐蚀电位相比母材(BM)提高0.16 V左右,耐蚀性增强,自腐蚀电流减小了一个数量级,腐蚀速率明显降低。焊接接头母材区域腐蚀坑呈纵深扩展趋势,而焊缝区域腐蚀坑呈横向扩展,并表现出明显的相选择性腐蚀现象。焊缝区域的晶粒细化显著,硬度升高,两相分布呈现密集的“网络”状,元素分布更加均匀,大角度晶界增加,这都增强了焊接接头的耐点蚀穿孔的能力。

电子束焊接钼接头的微观结构与力学性能研究

为进一步提升钼接头的力学性能,采用电子束焊接方法,并分析接头的微观结构、力学性能和缺陷。实验结果表明:焊缝的平均硬度为210 HV,热影响区的平均硬度为202 HV,均高于母材;接头的均匀抗拉强度为280 MPa;断裂位置位于焊缝处,属于脆性断裂;断口位置位于焊缝中,被确定为准劈裂断裂;在焊接区观察到气孔和裂纹缺陷,气孔由熔池中未逸散的氧气形成,裂纹被确认为凝固裂纹和低塑性脆化裂纹。该研究结果可为钼接头力学性能的提升提供参考依据。

TC4钛合金的电子束焊

采用真空电子束焊接工艺焊接TC4钛合金,通过显微组织观察、显微硬度测试以及进行冲击试验,分析了焊接接头显微组织、性能以及焊缝中气孔的形成。结果表明:采用真空电子束焊焊接TC4合金时焊缝中有气孔产生,焊缝金属的硬度值比母材金属的高,但冲击值低于母材的;焊缝和热影响区中较粗大的原始β相一部分转变为过饱和的针状马氏体;焊缝中心有少量的针状α′相,并形成了编织状α组织。