Prediction of welding distortion in butt joint of thin plates

This paper investigates distortions and residual stresses induced in butt joint of thin plates using Metal Inert Gas welding. A moving distributed heat source model based on Goldak’s double-ellipsoid heat flux distribution is implemented in Finite Element (FE) simulation of the welding process. Thermo-elastic–plastic FE methods are applied to modelling thermal and mechanical behaviour of the welded plate during the welding process. Prediction of temperature variations, fusion zone and heat affected zone as well as longitudinal and transverse shrinkage, angular distortion, and residual stress is obtained. FE analysis results of welding distortions are compared with existing experimental and empirical predictions. The welding speed and plate thickness are shown to have considerable effects on welding distortions and residual stresses.     

近等原子比钛镍合金氩弧焊接接头的组织和性能

借助金相显微镜、拉伸实验和弯曲回复法等手段研究了近等原子比钛镍形状记忆合金氩弧焊接接头的组织和性能。研究结果表明,近等原子比钛镍形状记忆合金氩弧焊接接头的显微组织可分为三个区,分别是粗大柱状晶区、细小柱状晶区和热影响区。由于焊接接头显微组织与母材之间的差别,在相同的应变下,近等原子比钛镍形状记忆合金氩弧焊接接头的回复温度明显高于母材,记忆性能变差。焊接后的近等原子比钛镍形状记忆合金的屈服强度与母材相近,但抗拉强度和延伸率远低于母材。氩弧焊接近等原子比钛镍合金的显微组织在热处理后不会发生明显变化,经过形变后,焊接接头的回复温度与母材仍有差别,显微组织的不同是造成这一现象的原因之一。     

Joint properties of friction stir welded AZ31B– H24 magnesium alloy

Abstract

The weldability of friction stir welded hot rolled AZ31B-H24 magnesium alloy sheet, 4 mm in thickness, was evaluated, varying welding parameters such as tool rotation speed and travel welding speed. Sound welding conditions depended mainly on sufficient heat input during the welding process. Insufficient heat input, which was generated in the case of higher travel speed and lower rotation speed, caused an inner void or lack of bonding in the stir zone. The microstructure of the weld zone was composed of five regions: base metal, heat affected zone, thermomechanically affected zone, stir zone I and stir zone II. Unlike the general feature of friction stir welded aluminium alloys, the grain size of the weld zone was larger than that of the base metal. Stir zones I and II were characterised by partial dynamic recrystallisation and full dynamic recrystallisation, respectively. The hardness of the weld zone was lower than that of the base metal owing to grain growth. A wider range of defect free welding conditions was acquired at higher tool rotation speed and lower welding speed. The maximum tensile strengh was 240 MPa, which was ~85% of the base metal value of 293 MPa. The fracture location was close to the stir zone.     

On the influence of wet underwater welding on CTOD-δ5

The influence of wet underwater welding on the crack tip opening displacement CTOD-δ₅ is investigated in this paper. The welding process is numerically simulated. The instationary temperature field and welding residual stresses are calculated using the finite element method (FEM). The crack tip opening displacement for a sharp, stationary crack on the surface of a bead-on-plate weld under bending is determined. The results for an underwater wet welded specimen and a dry welded specimen are compared. The welding residual stresses are considered in the 3D fracture mechanics FE calculation as well as the material heterogeneity due to the different material properties of weld metal, heat-affected zone and base metal. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micrometre scale residual stress measurement in fusion boundary of dissimilar steel welded joints using nanoindenter system

Abstract

In the present paper, an approach for measuring the micrometre scale residual stress around the fusion boundary in dissimilar steel welded joints was introduced. An as welded joint and a post-weld heat treated joint were examined using a nanoindenter system. The results revealed that a compressive residual stress existed around the fusion boundary in a range 200 μm extending to the overheated heat affected zone (HAZ) and 300 μm to the weld metal, and the compressive stresses were reduced after post-weld heat treatment. The maximum compressive stress occurred in the fusion boundary and then dramatically decreased in the adjacent HAZ base metal and weld metal. In comparison with the regular approaches for macrometre scale measurement, the nanoindentation has the advantages of high resolution and precision for effectively evaluating the residual stresses in a narrow region. The measuring error was analysed.     

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm⁻¹, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.     

A study on mechanical and microstructure characteristics of the STS304L butt joints using hybrid CO2 laser-gas metal arc welding

In order to examine mechanical characteristics of the stainless steel (STS304L) hybrid welded butt joints, two-dimensional thermal elasto-plastic analysis has been carried out. To this end, a 2D simulation model has been developed considering hybrid welding features. Based on thermal history data obtained from this heat source model, the residual stress distribution in weld metal (WM), heat affected zone (HAZ) and base metal (BM) characteristics have been calculated and found to be in reasonable agreement with the experimentally measured values. In order to investigate the effect of welding process, thermal elasto-plastic behaviour of the hybrid welded joints was compared with a welded joints obtained by conventional submerged arc welding (SAW) process. The results show that the longitudinal residual stress in the hybrid welded joints is less (13–15%) than that of the SA welded joints. Weld metal formed in both welding processes shows very fine dendritic structure. Due to higher heat input in SAW, the HAZ size of the SA welded joints is more than twice that of the hybrid welded joints. Therefore, from mechanical and metallurgical point of view, it could be confirmed that it makes a good sense to use SAW instead of hybrid CO₂ laser-gas metal arc welding (GMAW) for butt joint of the STS304L thick steel.     

Characterization of mechanical properties,fatigue-crack propagation,and residual stresses in a microalloyed pipeline-steel friction-stir weld

The influence of the friction-stir welding process on microstructure and mechanical properties of API 5L X80 skelp was investigated. Friction-stir welds were produced using welding parameters optimized to promote weld toughness. The solid-state welding process produced microstructures that significantly varied from those observed in the base metal, namely the redistribution and resizing of Martensite–Austenite constituent in the heat-affected zone and stir zone regions of the welds. Mechanical properties of the welds and base metal were evaluated with uniaxial tension testing and microhardness testing revealing overmatching welds and a hard zone within the weld stir zone. Residual stresses were determined in several directions with respect to the joint revealing that stress in the longitudinal direction is highest, yet well below material yield strength. Fatigue-crack propagation behavior was characterized in the different weld regions and base metal by testing with the compact tension specimen configuration showing that welds have impeded fatigue-crack growth compared to the base metal mostly due to welding-induced residual stress fields interacting with the crack.     

高强度钢加劲板焊接残余应力测试及分析

为研究高强度钢的板肋加劲板焊接残余应力分布特点,该文利用切割法对板肋加劲板试件进行了应力测试研究,建立了三维实体热弹塑性有限元模型,采用单元生死和动态约束技术模拟焊缝填充和焊接热输入过程,对比分析了高强度钢和普通钢的应力分布特点,比较研究了母板厚度、肋板厚度、肋板间距和高度对焊接残余应力的影响。研究结果表明:板肋加劲板T型接头角焊缝的焊接顺序与残余应力的分布不相关;高强度钢非焊接区域残余压应力小于普通钢;板件厚度和肋板高度是影响高强度钢的板肋加劲板焊接残余应力的主要因素。     

Application of low Ms temperature consumable to dissimilar welded joint

Abstract

The welding of dissimilar joints is very common in systems used in oil exploration and production in deep sea waters. Commonly involves welding of low carbon steel pipes with low alloy steel forgings both with inner Inconel clad. The forged steel part undergoes a process of buttering with Inconel or carbon steel electrode before the weld of the joint. The buttering process is followed by a process of residual stresses relief. The conventional way of reducing the level of residual stresses in welded joints is to apply post welding heat treatments. Depending on the size and complexity of the parts to be joined, this can become a serious problem. An alternative technique for reducing residual stresses is to use an electrode that during the cooling process undergoes a displacive transformation at a relatively low temperature so that the deformation resulting from the transformation compensates the contraction during the cooling process, and, although many papers have been published in this direction using Fe–Cr–Ni alloys, most of them report a loss of toughness in the weld metal. Maraging steel is a family of materials with M_s temperature below 200°C and even without the final heat treatment of aging has superior mechanical properties to low alloy steels used in forgings. In this work, forged piece of AISI 4130 was buttered with Maraging 350 weld consumable and subsequently welded to ASTM A36 steel using Inconel 625 filler metal. In addition, the dissimilar base metal plates were welded together using Maraging 350 steel weld consumable. The levels of residual stress, and the toughness and microstructures of heat affected zone and weld metal were investigated.     

氨水储槽泄漏原因分析

应用X射线法对氨水储槽的残余应力状态进行了检测与分析,对焊缝,热影响区、母材等部位进行了重点测试,并对热处理效果进行了检测与评价,结果表明,氨水储槽的泄漏由多种原因造成,残余应力过大是主要因素。     

Susceptibility of 7050-T7451 electron beam welded specimens to stress corrosion

Susceptibility to stress corrosion tests were carried out on electron beam welded specimens made from 7050-T7451 aluminium alloy. As a comparison, specimens made from base material were tested too. The resistance of the welded material was high: the tensile properties were only slightly lower than those of the base material. After 30 day exposure to a corrosive environment (alternate immersion in a 3.5% NaCl solution), the tensile properties of the welded material were considerably reduced, while the same properties were only slightly affected in the base material. The combined effect of stress and corrosion was only slightly detrimental for the base material and very detrimental for the welded material. At the lowest stress level tested, about 25% of the ultimate stress, the welded specimens failed after a mean life of 90 days. Considerable residual stresses associated with the welding process were measured in a plate. A test was performed to verify the possibility of stress corrosion cracking promoted by the welding residual stresses. In actual fact, no cracks were observed, but the corrosion rate increased, particularly in the areas affected by the higher residual stresses.     

转速对 7075-T651 铝合金搅拌摩擦焊接件内部残余应力分布的影响

目的掌握铝合金搅拌摩擦焊接板内部残余应力的分布,为控制焊接残余应力、改进焊接工艺和提高焊接件质量。方法以13.6 mm厚的7075-T651铝合金为研究对象,用短波长X射线衍射技术,对在不同搅拌头转速下搅拌摩擦焊接板内部的残余应力进行了无损测试,并对焊接接头在板厚中心层上的微观组织和显微硬度进行了研究。结果在垂直于焊缝截面上的显微硬度均呈"W"型分布,焊核区的显微硬度高于其两侧的热机械影响区和热影响区,但低于母材区的硬度;随着转速的增大,接头硬度的最小值减小,低硬度区的范围越大。横向残余应力绝对值整体小于焊接方向;焊核区为正应力,热机械影响区残余应力减小且变化梯度最大;残余应力的极大值位于热影响区和热机械影响区的交界处;残余应力极大值与硬度最小值的位置重合。结论通过残余应力的无损检测分析,不仅可以直接获得加工件内部应力分布,还可以间接获得加工件内部的加工缺陷情况,为改进加工工艺、提高成形精度提供依据。     

Microstructural evolution in AZ91D magnesium alloy during electron beam welding

Vacuum electron beam welding can have a low heat input, which means there is a minimum heat affected zone during welding of AZ91D magnesium alloy. From the observed microstructure, the weld of the AZ91D magnesium alloy can be divided into four regions, which are the weld metal zone, a partially-melted zone adjacent to the fusion boundary, a partially-melted zone adjacent to the base metal and the base metal zone. A sharp transition from the fusion zone to the non-melted zone, especially the characteristic partial melting microstructure and nature of the alloy elements, was observed. It was found that significant partial melting had taken place in the very narrow region around the weld metal of the AZ91D magnesium alloy. The Al content of eutectic β-Mg₁₇Al₁₂ in the partially-melted zone adjacent to the fusion boundary was close to the content in the continuously precipitated eutectic β particles in the fusion zone and much lower than the eutectic β in the base metal. The fully melted eutectic β-phase coexisted with the partially melted eutectic β phase in the partially-melted zone adjacent to the base metal.     

高频焊管焊缝冲击韧性异常原因分析

为查明J55钢高频焊管焊缝处的冲击功差异较大的原因,对母材,焊接热影响区及焊接区进行了微观分析,结果表明,冲击功低者,其母材,热影响区和焊缝区分别存在较严重的带状组织,粗大的过热组织和夹杂物等。     

Comparison of creep behaviour of 2.25Cr–1Mo/9Cr–1Mo dissimilar weld joint with its base and weld metals

Abstract

Evaluation of the creep behaviour of 2.25Cr–1Mo and 9Cr–1Mo ferritic steel base metals, 9Cr–1Mo steel weld metal, and 2.25Cr–1Mo/9Cr–1Mo ferritic–ferritic dissimilar weld joints has been carried out at 823 K in the stress range 100–260 MPa. The weld joint was fabricated by shielded metal arc welding using basic coated 9Cr–1Mo electrodes. Investigations of the microstructure and hardness variations across the joint in the as welded, post-weld heat treated (973 K/1 h), and creep tested conditions were performed. The heat affected zone (HAZ) in both the steels consisted of a coarse prior austenitic grain region, a fine prior austenitic grain region, and an intercritical structure. In the post-weld heat treated condition, a white etched soft decarburised zone in 2.25Cr–1Mo steel base metal and a black etched hard carburised zone in 9Cr–1Mo steel weld metal around the weld fusion line developed. Hardness troughs also developed in the intercritical HAZ regions of both the steels. The width of the carburised and decarburised zones and hardness differences of these zones were found to increase with creep exposure. The 9Cr–1Mo steel weld metal showed higher creep strength compared to both the base metals. The 9Cr–1Mo steel base metal exhibited better creep resistance than the 2.25Cr–1Mo steel base metal at lower applied stresses. The dissimilar joint revealed lower creep rupture strength than both the base metals and weld metal. The creep strain was found to concentrate in the decarburised zone of 2.25Cr–1Mo steel and in the intercritical HAZ regions of both the steels. Creep failure in the stress range examined occurred in the intercritical HAZ of 2.25Cr–1Mo steel even though this region showed higher hardness than the decarburised zone. Extensive creep cavitation and cracks were observed in the decarburised zone.     

304不锈钢管TIG焊接头凝固行为及热力耦合研究

目的 对2mm厚不锈钢管的焊接工艺参数进行优化,并基于模拟仿真软件对接头的热应力场进行模拟,以解决薄壁管件接头应力测试不方便的问题。方法 以TIG焊对2 mm不锈钢管进行焊接,通过对接头宏观形貌、微观组织、显微硬度等结果进行优化进而得到最佳焊接工艺参数,采用双椭球热源和温度-位移耦合方法结合最优工艺参数进行数值模拟。结果 当焊接电流为150 A、焊接速度为66 cm/min时,焊接接头全部熔透,且正面及背面焊道均匀致密,成形良好。焊缝中心上部区域和下部区域均呈现等轴晶形貌,下部区域尺寸较上部区域尺寸略大,熔合线附近为柱状晶组织。焊接接头显微硬度整体分布呈现U形,其中热影响区显微硬度（197HV）大于焊缝区域硬度（162HV）,熔合线附近显微硬度达到最低值（145HV）。模拟结果显示,在焊接过程中,当纵向残余应力从母材向焊缝中心过渡时,由压应力逐步转化为拉应力;焊缝中心横向应力呈现为压应力,向两侧母材过渡时应力值逐渐趋近于0,径向应力值变化幅度较小,模拟数据变化趋势与实测数据变化趋势接近。     

FATIGUE CRACK INITIATION LIFE PREDICTION FOR WELDED JOINTS BY LOW CYCLE FATIGUE APPROACH

Abstract— Analytical procedures based on low cycle fatigue theory are used to estimate the fatigue crack initiation life (N_i) for a cruciform welded joint in mild steel under constant amplitude tensile cyclic loading; the fatigue crack initiating at the weld toe. Effects due to welding such as residual stresses, geometrical variability and changes in material properties are handled. It is shown that for high mean stresses the discrepancies observed between the N _i estimates provided by commonly used analytical procedures exceed an order of magnitude. For the base metal (BM) the discrepancies become negligible if cyclic relaxation of notch mean stress is taken into consideration. The differences betwen the N _i estimates for heat affected zone (HAZ) material (where fatigue cracks at the weld toe usually initiate) and for BM are quantified. The applicability of HAZ material properties, estimated from hardness, to N _i prediction is evaluated.     

A572 Gr.50厚板对接焊缝断裂性能研究

A572 Gr.50厚板常用于锅炉钢结构大板梁的加工制作,其对接焊缝易存在焊接裂纹缺陷。为评定含缺陷的锅炉钢结构大板梁的安全性,通过焊接接头模拟制作实际大板梁下翼缘的A572 Gr.50厚板对接焊缝,分别对其母材、焊缝金属及热影响区材料进行了系列单轴静力拉伸试验、冲击韧性试验和直三点弯曲断裂韧度试验,并结合有限元分析对A572 Gr.50厚板对接焊缝存在裂纹缺陷时的断裂性能进行了研究。研究结果表明:厚板对接焊缝母材、焊缝和热影响区材料基本力学性能均能满足规范要求,均具有良好的塑性变形能力;随温度的降低,母材、热影响区及焊缝处的夏比冲击功减少,但均具有良好的冲击韧性;比较而言,母材的抗低温冷脆性能最好,焊缝最差;母材、焊缝和热影响区3个区域中焊缝的断裂韧度最差;厚板对接焊缝接头的焊缝区是大板梁焊接缺陷安全性评估的重点控制区域;基于断裂力学,可以运用有限元软件方便的对带裂缝的工作状态下工作的钢结构构件的断裂性能进行分析,保证其安全性。     

5083铝合金搅拌摩擦焊接头的显微组织与力学性能

对8 mm厚5083-H321铝合金板进行了搅拌摩擦焊接试验,研究了焊接工艺参数对搅拌摩擦焊接头显微组织和力学性能的影响。结果表明:该搅拌摩擦焊接头焊核区显微组织为细小的等轴晶组织,热机影响区为拉伸弯曲变形组织,热影响区非常窄,其晶粒尺寸与母材相当;综合接头表面形貌和拉伸性能得到较佳的搅拌摩擦焊接工艺参数为使用搅拌针为三棱形带螺纹、轴肩为内扣型的搅拌头,主轴转速为300 r·min^-1,焊接速率为120 mm·min^-1;在该工艺条件下接头表面成形良好,抗拉强度可达到母材的94.5%。