焊趾TIG熔修对10Ni5CrMoV钢焊接节点疲劳性能的影响

对焊趾氩弧(tungsten-arc inert-gas welding,TIG)熔修与否的10Ni5CrMoV钢大角度焊接节点进行了疲劳试验,比较了相同加载条件下的疲劳寿命、载荷与位移关系及疲劳裂纹启裂位置,同时测量了焊接接头残余应力,并采用有限元计算方法对承载条件下焊接节点的应力应变场进行了分析.结果表明,焊趾TIG熔修显著提高了10Ni5CrMoV钢焊接节点的疲劳性能,在相同承载条件下使焊接节点的疲劳寿命提高了34%.其主要原因在于TIG熔修能有效改善焊趾处的几何形状、降低应力集中程度,从而降低焊趾在承载条件下的应力应变水平,使焊接接头疲劳性能得到提高.     

Suggestion of welding procedure for compressive residual stress induction by using low transformation temperature welding materials

ABSTRACT

To understand the cause of compressive residual stress in welded joints, we analysed by numerical analysis the effect of welding pass sequence using low transformation temperature (LTT) welding materials on residual stress around the weld toe of boxing fillet welded joints. It was determined by numerical analysis that the produced compressive residual stress and the influence of the stiffeners are reduced in the equivalent position of the weld toe in a fillet welded joint because of the influence on the behaviour of the stiffener in the weld being due to residual stress distribution around the weld toe. The residual stress reduction method of extending the length of the welded bead and releasing the weld toe from the stiffener, similar to the concept of discarding a bead to reduce tensile residual stress, was effective in fillet welded joints. Numerical analysis of the relationship between residual stress around the weld toe and width of the weld bead in the bead-on-plate welding model clarified that compressive residual stress can be introduced around the weld toe by having a wide width weld bead. In addition, a fully penetrated welded joint was very effective for causing compressive residual stress around the weld toe.     

Microstructure and Fatigue Properties of Laser Welded DP590 Dual-Phase Steel Joints

In this paper, cold-rolled DP590 dual-phase steel sheets with 1.5 mm thickness were butt-welded by a fiber laser, and the evolution and effect on microhardness, tensile property and fatigue property of the welded joint microstructure were studied. The results showed that the base metal is composed of ferrite and martensite, with the martensite dispersed in the ferrite matrix in an island manner. The microstructure of the weld zone was lath-shaped martensite that can be refined further by increasing the welding speed, while the heat-affected zone was composed of ferrite and tempered martensite. The microhardness increased with increasing welding speed, and the hardness reached its highest value—393.8 HV—when the welding speed was 5 m/min. Static tensile fracture of the welded joints always occurred in the base metal, and the elongation at break was more than 16%. The conditional fatigue limits of the base metal and the weld joints were 354.2 and 233.6 MPa, respectively, under tension–tension fatigue tests with a stress rate of 0.1. After observation of the fatigue fracture morphology, it was evident that the fatigue crack of the base metal had sprouted into the surface pits and that its expansion would be accelerated under the action of a secondary crack. The fatigue source of the welded joint was generated in the weld zone and expanded along the martensite, forming a large number of fatigue striations. Transient breaking, which occurred in the heat-affected zone of the joint as a result of the formation of a large number of dimples, reflected the obvious characteristics of ductile fracture.     

TC11钛合金电子束焊接接头超高周疲劳性能

采用天津大学自行研制的TJU-HJ-I型超声疲劳试验系统研究了TC11钛合金电子束焊焊接接头的超高周疲劳性能. 试验结果表明,TC11钛合金电子束焊接接头在107周次以上仍然会发生疲劳失效,S-N曲线呈现连续下降的趋势,没有明显的转折. 试件的断裂位置大多数为母材处,焊缝和热影响区的疲劳性能要比母材好,这与焊接接头的微观组织有关. 通过SEM对超声疲劳断口形貌进行观察发现,断裂试件的疲劳裂纹大部分在表面萌生,然而在应力范围较低时,疲劳裂纹的萌生位置有从表面转向次表面的趋势.     

FV520B钢十字焊接接头的疲劳性能

用金相显微镜和扫描电镜观察了FV520B钢焊接接头母材、焊缝及热影响区的微观组织;并通过透射电镜给出了母材和焊缝的微观形貌。结果表明:母材组织为细小均匀的回火马氏体、弥散分布的析出相及高密度位错,而焊缝为粗大的板条马氏体及少量的析出相,说明母材力学性能优于焊缝。利用疲劳实验获得了高平均拉应力下接头的疲劳强度及S-N曲线等。通过对疲劳断口的观察,发现疲劳断裂主要有两种形式:破坏于焊趾处和焊接缺陷处,由于这里严重的应力集中,加速了疲劳裂纹的萌生。     

Analysis of martensite transformation behaviour in welded joint using low transformation temperature welding wire

Abstract

Low transformation temperature welding (LTTW) wire has been found to improve the fatigue strength in welded joints. In the present study, the temperature dependence of the mechanical properties in a dual phase microstructure of austenite and martensite was estimated using the properties of full austenite and full martensite in numerical analyses. A welding method effective for residual stress reduction and fatigue strength improvement was shown by applying a calculation method under transformation superplasticity and transformation induced plasticity in high strength steel welded joints. With this method, the influence of the welding pass sequence on the residual stress distribution and fatigue strength was examined in a boxing fillet welded joint using LTTW. The transformation tensile residual stress in the weld toe was decreased by sectioned welding, and the fatigue limit by sectioned welding with LTTW improved in comparison with the fatigue limit of a joint welded with conventional wire in the same process.     

机械整形新技术对铝合金焊接接头疲劳性能的影响

以提高焊接结构的疲劳强度为目标,通过有限元计算获得焊缝整形的最优方案,研制了相应的专用机械冲击碾压装置,采用机械冲击碾压新技术优化处理焊趾处的过渡圆弧,对整形前后的试件在低频疲劳试验机上进行疲劳寿命测试.结果表明,机械冲击整形新技术采用专用装置对焊缝及其附近区域进行冲击作用,有效减小焊缝余高,增大焊趾曲率半径.疲劳寿命测试发现,机械整形新技术通过优化焊趾几何形状降低了焊趾位置的应力集中、提高铝合金焊接接头疲劳强度,整形处理后疲劳破坏多发生于焊缝和母材的缺陷处.     

转向架用SMA490BW钢焊接接头超高周疲劳性能

采用超声疲劳试验方法对SMA490BW钢焊接接头的超高周疲劳性能进行研究,通过X射线应力仪对焊接试样残余应力进行测试,采用扫描电镜对疲劳裂纹的萌生、扩展及疲劳断裂机理进行观察和分析. 结果表明,SMA490BW钢母材的疲劳性能远高于焊接接头,在1 × 108循环周次条件下,接头的疲劳强度为141 MPa,仅为母材的44.2%. 接头裂纹主要萌生于焊趾表面缺陷处,疲劳断裂机理表现为准解理断裂, 并伴有塑性变形痕迹. 焊趾处几何不连续造成的应力集中和焊缝及其附近区域一定的残余拉应力,以及接头各微区组织和性能的不均匀性,是导致焊接接头疲劳性能偏低的主要原因.     

Fatigue behavior of welded joint spray fused by nickel-base alloy powder

Modification of spray fusing (MSF), which is a new method, was used to improve the fatigue strength of welded joints. Cruciform welded joint of Q235B steel was processed by MSF with nickel-base alloy powder of Ni60A and Ni25A. The bonding layer between coating and weld was studied by optical microscopy, scanning electron microscopy (SEM) and energy spectrum analysis. The results show that flame spray fusing can produce a coating layer with finer microstructure, lower impurities content, less air hole and higher bonding strength. Stress concentration at weld toe was significantly reduced due to smooth coating of high curvature after MSF. High cycle fatigue test results indicate that fatigue strength of welded joint spray fused by Ni60A is higher than that of welded joint spray fused by Ni25A owing to the good effect of MSF. Low cycle fatigue test results show that fatigue life of welded joint spray fused by Ni25A dose not affected by the poor effect of MSF compared with welded joint spray fused by Ni60A.     

搅拌摩擦焊和熔化极气体保护焊6082铝合金疲劳性能分析

对10 mm厚6082-T6铝合金进行搅拌摩擦焊(FSW)和熔化极气体保护焊(MIG焊)焊接,利用疲劳性能试验机、光学显微镜、扫描电子显微镜等手段对6082铝合金FSW和MIG焊接头的疲劳力学性能、微观组织、裂纹扩展特征、疲劳断口进行了分析. 结果表明,在疲劳寿命为2×106周次时,6082铝合金母材及其FSW和MIG焊接头的名义应力分别为126.3,110.2,84.2 MPa;在高应力水平下(Δσ=160 MPa),FSW接头疲劳寿命明显大于MIG焊接头、与母材的疲劳寿命相当. MIG焊疲劳断口均位于焊趾处,焊缝内的气孔缺陷为其主要裂纹源;FSW疲劳断口大多发生在轴肩边缘. 接头的微观断口具有准解理特征,断口中存在疲劳条纹和韧窝.     

Improving the fatigue property of welded joints for AZ31 magnesium alloy by ultrasonic peening treatment

The fatigue property of AZ31 magnesium alloy and its TIG welded joints were investigated. The ultrasonic peening treatment (UPT) was used to improve the fatigue property of the TIG welded joints, which was treated at the weld toe by the UPT process. The test results show that the fatigue strength of the base metal of AZ31 magnesium alloys is 57.8 MPa, and those of the fillet joint and the transverse cross joint are respectively 20.0 MPa and 17.2 MPa at 2×106 cycles. The fatigue strengths of two kinds of welded joints treated by the UPT are respectively 30.3 MPa and 24.7 MPa, which have been improved by 51.5% and 43.6%, respectively. The fatigue life of the fillet joint specimens is prolonged by about 2.74 times and the fatigue life of the transverse cross joint specimens is prolonged by about 1.05 times when the stress range is at 40.0 MPa.     

高温合金焊接接头动态拉伸变形断裂行为

借助扫描电子显微镜(SEM)的专用拉伸台,通过取自相同焊接接头疲劳试件的原位拉伸试验和疲劳试验,分析了高温合金焊接接头原位拉伸的动态断裂过程,讨论了原位拉伸断裂行为与疲劳断裂的关系。结果表明,高温合金熔化焊接接头强韧性良好,断裂前应变可达17．5％,具有明显的形变强化效应;焊缝断裂形貌与应力状态密切相关,在平面应力状态下,裂纹形成于熔合区晶内缺陷和晶界交汇处,以延性剪切型断裂为主,在应力集中的棱角处,易诱发穿晶脆断;焊缝熔合区的微观组织不均匀性和焊趾应力集中的联合作用将使焊接接头在疲劳试验过程中发生应变硬化,引发疲劳裂纹。     

Micro-mechanical properties of 2219 welded joints with twin wire welding

Nanoindentation method was adopted to investigate the distribution regularities of micro-mechanical properties of 2219 twin wire welded joints, thus providing the necessary theoretical basis and guidance for joint strengthening and improvement of welding procedure. Experimental results show that in weld zone, micro-mechanical properties are seriously uneven. Both hardness and elastic modulus distribute as uneven sandwich layers, while micro-mechanical properties in bond area are much more uniform than weld zone;In heat-affected zone of 2219 twin wire welded joint, distribution regularity of hardness is similar to elastic modulus. The average hardness in quenching zone is higher than softening zone, and the average elastic modulus in solid solution zone is slightly higher than softening zone. As far as the whole welded joint is concerned, metal in weld possesses the lowest hardness. For welded specimens without reinforcement, fracture position is the weld when tensioning. While for welded specimens with reinforcement, bond area is the poorest position with joint strength coefficient of 61%. So, it is necessary to strengthen the poor positions--weld and bond area of 2219 twin wire welded joint in order to solve joint weakening of welding this kind of alloy.     

焊接接头强度组配对CTOD的影响

利用模拟焊接接头试样三点弯曲试验的方法,就焊接接头强度组配对其断裂性能的影响进行了研究。发现不同的焊接接头强度组配对其断裂韧性和裂纹扩展驱动力有不同程度的影响,在考虑强度组配对焊接接头的断裂性能的影响时,必须从材料的断裂韧性变化和裂纹扩展驱动力变化的两个方面来考虑。     

基于局部应变能密度的厚板T形接头焊趾和焊根疲劳性能分析

以装载机前车架疲劳寿命评估为目的,从前车架焊接结构关键部位中提取三种典型焊接接头,对其进行疲劳试验和分析.以局部应变能密度法为理论基础,对获得的试验数据进行处理,得到了基于局部应变能密度的疲劳寿命曲线,并采用文献中十字接头的疲劳数据验证该理论的准确性和适用性.结果表明,局部应变能密度法既可用于焊根失效疲劳评估,也可以用于焊趾失效疲劳评估;不同位置的疲劳裂纹会影响结构的刚度,进而影响结构的疲劳寿命.此外,研究了焊脚尺寸和熔深对焊接接头疲劳寿命的影响,推导了基于局部应变能密度法的疲劳失效位置转换区间.并通过文献中的疲劳数据验证了文中提出的焊趾失效和焊根失效转换区间的准确性,为合理设计未焊透厚板T形接头抗疲劳性能提供依据.     

Improvement mechanism of fatigue strength of weld joints by hammer peening on base metal

New peening technology is proposed to improve the fatigue strength of welded joints. By using this technology, compressive residual stress is introduced at weld toe by the developed peening procedure which plastic deformation is only applied to the base material near the weld toe. In this study, improvement mechanism of fatigue strength of weld joints by hammer peening on base metal was clarified by FEA. It was clarified that increasing of stress at weld toe is controlled by depression formed near the weld toe. Not only compressive residual stress at weld toe but also decreasing stress concentration at weld toe by plastic deformation on base metal was indicated as the factor of improving fatigue strength of weld joints.     

TA15钛合金焊接接头性能与断裂行为研究

对TA15钛合金氩弧焊和电子束焊焊接接头的性能与微观组织进行了分析研究,并结合断口观察,对其断裂行为进行了研究.结果表明,两种焊接接头强度均与母材相当,而塑性明显降低.焊接接头热影响区组织均呈现从粗大等轴组织到魏氏组织的过渡变化特征.疲劳断裂位置一般位于靠近熔合线的焊缝区域,主要原因是此区域存在组织突变和熔合线气孔.焊接气孔对接头疲劳性能影响较大.两种焊接接头疲劳断口特征存在明显区别.     

Application of the local approach to the fatigue assessment for welded joints

The fatigue behavior of welded structures is currently determined by means of recommendations defined in terms of S-N curve corresponding to the detail classes of welded joints without taking account of the actual geometry of the weld. A new fatigue strength assessment method based on Dang Van multiaxial fatigue limit criterion was introduced, which is named the local approach and presented by lnstitut de Soudure recently. The local approach has advantages in taking welding residual stresses and the geometry of the weld toe and weld root into consideration. The application of the local approach to the fatigue strength assessment of low carbon steel Q235B welded joints was studied. The fatigue tests and finite element analysis results show that the local approach parameters recommended by lnstitut de Soudure were incorrectly for low carbon steel Q235B welded joints. With aluminum alloy welded joints being used widely, the parameters of the local approach used for aluminum alloy welded joints were obtained and verified on bases of the fatigue tests and finite element analysis.     

Fatigue behaviour of load-carrying, fillet-welded, cruciform joints with plates of different thickness

Large numbers of fillet-welded cruciform joints are extensively employed at the connection zones of steel structural members because of their superiority from consideration of ease of construction and economy. Where this welded cruciform joint becomes a load-carrying type, the fatigue fracture starting point will be either at the weld toe zone, the root zone or both, so the fatigue behaviour becomes complex. In particular, when root fracture takes place, the fatigue strength is low compared with other welded joints and also it is difficult to detect by means of non-destructive inspection at the initial stage of crack occurrence; consequently there are some cases where fatigue becomes a problem.     

TA5钛合金焊接接头的低周疲劳性能

分析了TA5钛合金不同余高焊接接头的低周疲劳性能。结果表明，当TA5钛合金焊接接头工作在应变值小于0．35％时，焊接接头的低周疲劳寿命随焊接接头余高的增加而降低，当应变值高于0．35％时规律不明显。在较高应力应变条件下，呈循环软化特性，在低应力应变条件下的循环硬化特性不明显。同时，给出了焊接接头的循环应力应变曲线的表达式。以及焊接接头光滑试样的低周疲劳寿命表达式。