焊接热循环对1 000 MPa级焊缝金属组织性能的影响

为研究多层多道焊对1 000 MPa级焊缝金属组织性能的影响,采用热模拟试验对末道焊缝金属进行一次及二次焊接热循环,并通过冲击、硬度试验,利用金相显微镜、扫描电镜、透射电子显微镜和电子背散射衍射技术分析热循环后焊缝金属组织性能的变化规律.结果表明:单次热循环下,随着峰值温度(Tp)的升高,冲击韧性逐渐下降,显微硬度先上升后下降;TP为800℃时出现了软化现象,显微硬度326 HV,冲击韧性较高为64 J;TP为950℃时,其奥氏体晶粒相对细小,具有良好的综合力学性能;TP为1 350℃时,显微硬度最高为383 HV,冲击吸收功只有19 J,其脆化原因是冷却时获得粗大原奥氏体晶粒以及粗大的、且方向性较为一致的板条马氏体和贝氏体硬脆组织;经800℃的二次循环后,再次出现软化现象,显微硬度为313 HV,并且焊缝热影响区中残余奥氏体体积分数为1.39%,冲击韧性得到改善为59 J.     

Effects of electropulsing assisted ultrasonic impact treatment on welded components

Abstract

The effect of electropulsing assisted ultrasonic impact treatment (EUIT) on the mechanical properties and microstructure evolution of S50C steel welded components has been investigated. The present paper presents the application of a relatively new post-weld treatment method to eliminate the residual stress and improve the surface mechanical properties. The results show that EUIT exhibits better surface modification capability than does conventional ultrasonic impact treatment. After EUIT, plastic deformation layer with strengthened grains formed on the sample surface, and residual tensile stress was converted into residual compressive stress.     

Modification of residual stress and microstructure in aluminium alloy by cryogenic treatment

The effect of cryogenic treatment (CT) combined with solution and ageing treatment on the residual stress and microstructure of 7050 aluminium alloy was investigated. The relationship between residual stress and microstructure was discussed. The results showed that compared to solution–ageing treatment (SA), CT after solution and before ageing (SCA) exhibited lower level and higher uniformity of residual stress. The highest dimensional stability was also obtained by the process of SCA. It was found that CT induced the fine precipitates through the lattice contraction under cryogenic temperature. Furthermore, the execution of CT in advance would also promote the uniform distribution of precipitates in the subsequent ageing by releasing and homogenising the residual stress.     

电脉冲辅助超声冲击技术对焊缝残余应力及显微硬度的影响

焊接结构件中存在焊接残余应力,使得焊接构件在使用过程中容易发生断裂,缩短构件的使用寿命.以D36钢焊缝为研究对象,使用电脉冲辅助超声冲击技术处理D36钢焊接件,研究了电脉冲辅助超声冲击技术对焊缝残余应力和显微硬度的影响.研究结果表明:电脉冲辅助超声冲击技术在适当的电流密度和处理时间下消除焊接残余应力和表面强化的作用优于传统的单一超声冲击技术,不仅能够比单一超声冲击技术降低焊缝的残余应力最多达23 MPa,提高焊缝表层的最大硬度达109HV,同时增加强化层深度最多达250μm.     

强化处理对GCr15钢球残余应力和微观组织的影响

实验研究了强化处理后钢球残余应力和微观组织的改变.本文研究了经强化处理后,钢球沿径向表面残余应力大小、残余奥氏体含量及硬度分布;用光学显微镜、扫描电子显微镜对经表面形变强化后的轴承钢球进行显微组织及裂纹观察.研究表明:轴承钢球次表层残余应力为压应力,随电解抛光深度的增加,逐渐会出现一个最大压应力的峰值,而后压应力值逐渐减小.强化处理过程中会发生应力诱发残余奥氏体转变为马氏体,但对压应力分布影响不大.将静态Herzt接触理论应用于钢球的动态碰撞强化中,分析探讨钢球裂纹的形成,与实验结果相一致,具有重要指导意义.     

Numerical simulation of weld tab length influence on welding residual stress and distortion of aero-engine disk

In order to control the welding residual stress and distortion to the greatest extent, based on the MSC. MARC software platform and adopting the impending critical value methods gradually, the welding residual stress and distortion are calculated through varying the weld tab length values. The results show that different weld tab lengths only have a slight effect on welding residual stress but a significant effect on welding distortion. According to the calculation results with different weld tab lengths, the critical length value for the 100 mm-length TC4 alloy weld for electron beam welding of an integral disk should be 50 mm or so.     

激光冲击处理对AISI304钨极氩弧焊接接头残余应力的影响

利用激光冲击波对AISI304不锈钢氩弧焊接接头进行了表面强化处理,用X-350A型X射线应力仪测定了其激光冲击处理后残余应力,分析了残余应力的产生机理.结果表明,激光冲击处理后AISI304焊接接头残余应力为110MPa左右,其强化效果十分明显,显著地降低了焊接接头残余拉应力,并使残余应力分布趋向均匀.     

16MnR钢激光冲击工艺及对焊接结构应力腐蚀性能的影响EI北大核心CSCD

对16MnR母材进行激光冲击工艺实验,获得优化的激光冲击工艺参数。对激光-MAG复合焊焊接接头进行表面处理,分析接头激光冲击前后状态的残余应力分布及抗应力腐蚀性能变化。结果表明:对16MnR钢平板经激光冲击处理后,在材料表面最大可引入475μm厚度的塑性变形层,并同时引入-593 MPa的压应力分布。采用优化激光冲击工艺对16MnR钢焊接接头进行表面处理后,可有效减小焊接接头表面的残余拉应力分布。在3.5%NaCl(质量分数)条件下对激光冲击处理前后的接头试样进行慢应变速率应力腐蚀实验,发现激光冲击处理前后16MnR钢焊接接头的应力腐蚀敏感指数I_(SSRT)分别为0.106和0.104,表明激光冲击可以提高接头的抗应力腐蚀能力。     

Crack aspect development curves and fatigue life prediction for surface cracks at weld toes in the presence of residual stress

An engineering procedure is proposed for estimating the crack growth behaviour and fatigue lives of semi-elliptical surface cracks at weld toes, based on a database of stress intensity factors. Some examples of crack aspect development curves (CADC) are given for some typical cracked welded joints subjected to service loading and residual stress conditions. The significance for predicting fatigue life according to the natural crack growth path, namely along the CADC, is emphasized through examples.     

Pulse current treatment effect on the strength of reinforcing steel and its weld joint under impact loading

We present results of static and impact tension tests of as-received reinforcing steel specimens, specimens with weld joints in their test portion, as well as specimens pretreated by high-density pulse current. As test results demonstrate, an increased strain rate enhances strength, and the pulse current treatment greatly influences the strength and plasticity of a defect-containing weld metal under static and impact tension. Translated from Problemy Prochnosti, No. 3, pp. 89–96, May–June, 2009.     

U形试块残余应力超声检测及有限元分析

为验证超声检测残余应力的精度与检测深度问题,该文提出并设计一种能够施加定值载荷应力的U形试块来模拟构件中的残余应力。通过残余应力超声检测系统激励5 MHz、4 MHz等其他不同频率的超声换能器,对U形试块在缺口施加拉压载荷,使试块处于闭合、张开的不同状态来模拟构件中的拉压状态,对U形试块的上表面不同位置和后侧面不同深度处的应力值进行超声残余应力无损检测。同时将其检测结果与同等条件下ABAQUS有限元仿真分析的结果进行对比,验证该系统对表面残余应力及试块内部梯度残余应力检测的准确性。另外,该试块也为残余应力超声检测系统的校准提供方法。     

Numerical evaluation of temperature fields and residual stresses in butt weld joints and comparison with experimental measurements

This paper presents a novel numerical model, based on the finite element (FE) method, for the simulation of a welding process aimed to make a two‐pass V‐groove butt joint, paying attention on the prediction of residual stresses and distortions. The ‘element birth and death’ technique for the simulation of the weld filler supply has been considered within this paper. The main advancements with respect to the state of the art herein proposed concern: (i) the development of a modelling technique able to simulate the plates interaction during the welding operation when an only plate is modelled. This phenomenon is usually neglected in literature; (ii) the heat amount is supplied to the FEs as volumetric generation of the internal energy, allowing overcoming the time‐consuming calibration phase needed to use the Goldak's model, commonly adopted in literature. Predicted results showed a good agreement with experimental ones.     

Surface modification of D36 steel by ultrasonic impact with electropulsing

ABSTRACT

The present work investigated the effect of ultrasonic impact treatment (UIT) assisted with electropulsing (EP) on the microstructure of D36 low-carbon steel. Optical microscope and scanning electron microscope were employed to reveal the microstructural evolution of the specimen subjected to the treatment. In comparison with UIT solely, a higher hardness on the superficial layer was obtained by EP-UIT and the fracture on treated surface was avoided effectively which meant a better plasticity. The electron back scatter diffraction analysis indicated a high density of low-angle boundary network owing to the large strain introduced. The distinguishing features of EP-UIT were ascribed to the athermal effect of drifting electrons which facilitate the mobilising of dislocations in the deformation.

This paper is part of a themed issue on Materials in External Fields.     

Effects of TiC formation on the microstructure and hardness of wear-resistant steel

In this study, as-cast low alloy wear-resistant steels with Ti contents of 0.6 and 3.0?wt-% were prepared at different solidification cooling rates, and the effects of TiC formation on their microstructures, hardness values, and wear resistances were investigated. The obtained phase diagrams and experimental data revealed that the TiC phase was formed via a divorced eutectic reaction in a residual liquid phase during solidification. The larger Ti content promoted the formation of TiC particles, while the solidification cooling rate represented the main influencing factor. Moreover, the produced TiC phase increased the wear resistance of the studied steel and decreased the matrix hardness, suggesting a new method for enhancing its mechanical properties through the formation of a hard ceramic phase.     

Finite element analysis of residual stress in the welded zone of a high strength steel

The distribution of the residual stress in the weld joint of HQ130 grade high strength steel was investigated by means of finite element method (FEM) using ANSYS software. Welding was carried out using gas shielded arc welding with a heat input of 16 kJ/cm. The FEM analysis on the weld joint reveals that there is a stress gradient around the fusion zone of weld joint. The instantaneous residual stress on the weld surface goes up to 800 ∼ 1000 MPa and it is 500 ∼ 600 MPa, below the weld. The stress gradient near the fusion zone is higher than any other location in the surrounding area. This is attributed as one of the significant reasons for the development of cold cracks at the fusion zone in the high strength steel. In order to avoid such welding cracks, the thermal stress in the weld joint has to be minimized by controlling the weld heat input.     

超声作用下的电铸铜微观结构与机械性能

为了改善电铸微细部件的机械性能,通过改变电铸工艺参数以及在电铸铜过程中引入超声场,得到具有不同微观结构特征的电铸铜材料.采用金相显微镜、扫描电子显微镜观察电铸铜层微观形貌,用X射线衍射分析铸层晶面择优取向,并用维氏硬度计和拉伸试验机分别测试电铸铜层机械性能.实验结果表明,超声作用下电铸和普通电铸得到的铜层表面均为(220)晶面择优取向,并且超声电铸铜层的择优取向程度更强.超声电铸铜层晶粒为细小柱状晶结构,与普通电铸铜相比,其抗拉强度和显微硬度均提高约30%.在电铸溶液中氯离子(Cl-)质量浓度为60mg/L时,铸铜层晶粒比其他Cl-质量浓度时晶粒更细小,抗拉强度和塑性也更高.在电铸过程中引入超声场能改善电铸铜层的微观结构,并提高电铸铜的机械性能.     

Effects of ultrasonic treatment on microstructure and mechanical properties of 6016 aluminium alloy

Ultrasonic treatment was applied during solidification forming of 6016 aluminium alloys. The effects of ultrasonic vibration on the microstructure and mechanical properties of the 6016 aluminium alloy ingot were studied. Compared with conventional casting, the ingot prepared with ultrasound applied to the molten metal had a fully refined microstructure and greater material homogeneity. Ultrasonic treatment reduced the amount of porosity developed by embedded gas and also resulted in an obvious decrease in solidification defects, like shrinkage. In addition, component segregation was minimised and the mechanical properties were enhanced.     

Fatigue crack initiation assessment of welded joints accounting for residual stress

The impact of residual stresses on the fatigue crack initiation life of welded joints is evaluated by the finite element method. The residual stresses of nonload‐carrying cruciform joints, induced by welding and ultrasonic impact treatment, are modelled by initial stresses, using the linear superposition principle. An alternative approach of using modified stress‐strain curves in the highly stressed zone is also proposed to account for the residual stress effect on the local stress‐strain history. An evaluation of the fatigue crack initiation life of welded joints based on the local strain approach is carried out. The predicted results show the effect of residual stresses and agree well with published experimental results of as‐welded and ultrasonic impact treated specimens, demonstrating the applicability of both approaches. The proposed approaches may provide effective tools to evaluate the residual stress effect on the fatigue crack initiation life of welded joints.     

Finite element analysis of temperature field, microstructure and residual stress in multi-pass butt-welded 2.25Cr–1Mo steel pipes

An attempt was made to develop a thermal–metallurgical–mechanical computational procedure based on ABAQUS code to simulate welding temperature field, microstructure and residual stress in multi-pass butt-welded 2.25Cr–1Mo steel pipes. In the present work, our emphasis was to predict welding residual stress considering the influence of solid-state phase transformation. In the proposed computational procedure, the Johnson–Mehl–Avrami–Kolmogorov equation was used to track the austenite–bainite transformation, and the Koistinen–Marburger relationship was employed to describe austenite–martensite change. Effects of volumetric change and yield strength change due to solid-state phase transformation on welding residual stress were investigated. The simulation results show that both volumetric change and yield strength change have significant effects on welding residual stress in 2.25Cr–1Mo steel pipes. The simulation results were compared with the experimental measurements, and the effectiveness of the developed computational producer was confirmed.     

Numerical sensitivity analysis of welding-induced residual stress depending on variations in continuous cooling transformation behavior

The usage of continuous cooling transformation (CCT) diagrams in numerical welding simulations is state of the art. Nevertheless, specifications provide limits in chemical composition of materials which result in different CCT behavior and CCT diagrams, respectively. Therefore, it is necessary to analyze the influence of variations in CCT diagrams on the developing residual stresses. In the present paper, four CCT diagrams and their effect on numerical calculation of residual stresses are investigated for the widely used structural steel S355J2+N welded by the gas metal arc welding (GMAW) process. Rather than performing an arbitrary adjustment of CCT behavior, four justifiable data sets were used as input to the numerical calculation: data available in the Sysweld database, experimental data acquired through Gleeble dilatometry tests, and TTT/CCT predictions calculated from the JMatPro and Edison Welding Institute (EWI) Virtual Joining Portal software. The performed numerical analyses resulted in noticeable deviations in residual stresses considering the different CCT diagrams. Furthermore, possibilities to improve the prediction of distortions and residual stress based on CCT behavior are discussed.