T91/HR3C异种耐热钢焊接接头蠕变失效有限元模拟

采用有限元方法建立马氏体T91/新型奥氏体HR3C异种耐热钢焊接接头蠕变数值模型,模拟600℃/42.26 MPa内压作用下的蠕变最大主应力、von Mises等效应力和应力三轴度分布.结果表明,最大主应力峰值位于接头内表面的焊缝/T91和HR3 C/焊缝界面以及距外表面2.96 mm处的焊缝/T91界面附近区域.内表面焊缝/T91界面区域von Mises等效应力数值最大,依次为距内表面1.29 mm处焊缝/T91界面区域、外表面和距外表面2.96 mm处焊缝/T91界面区域.内表面焊缝/T91界面处的应力三轴度数值较高,孔洞易于扩张、形成界面蠕变裂纹.而距内表面1.29 mm处和距外表面2.96 mm处的细晶HAZ内应力三轴度数值较高,两部位的孔洞容易连接形成Ⅳ型蠕变裂纹.采用应力三轴度分析T91/HR3C钢接头焊缝/T91界面失效和T91细晶HAZ蠕变孔洞扩张及裂纹扩展特性更为准确,与加速试验结果比较一致.     

超超临界机组奥氏体/马氏体异种钢接头蠕变数值模拟

采用有限元方法对超超临界火电机组中新型奥氏体耐热钢HR3C/马氏体耐热钢T91异种钢接头在600℃/42.26 MPa内压作用下的最大蠕变主应力、von Mises等效应力和应力三轴度进行了数值模拟.结果表明,对于HR3C/T91异种钢接头,最大主应力峰值位于焊缝/T91界面附近区域,蠕变孔洞易于在焊缝/T91界面区域...     

HR3C/T91异种耐热钢焊接接头界面蠕变失效有限元模拟

利用有限元方法对HR3C/T91接头在温度为600℃、内压为42.26 MPa作用下的最大蠕变主应力、von Mises等效应力和应力三轴度进行数值分析,并采用温度—应力双参数加速试验对模拟结果进行验证. 结果表明,最大主应力峰值位于管接头内表面焊缝/T91界面附近区域,von Mises等效应力峰值同样位于内表面焊缝/T91界面附近区域,因而焊缝/T91界面区域内孔洞易于形核、扩张. 内表面应力三轴度峰值分别位于HR3C/焊缝和焊缝/T91界面处,与两界面重合. 内表面焊缝/T91界面处的应力三轴度数值较大,而焊缝/T91界面的蠕变强度较HR3C/焊缝弱,因此焊缝/T91界面为接头的薄弱环节,与加速试验结果一致.     

有关钢焊接的文献

<正>焊接残余应力对P92钢IV型蠕变开裂的影响/姜运建,等.焊接学报,2011,32(1):16-20.P92钢焊接接头在高温长时服役条件下易于在细晶热影响区(FGHAZ)或临界热影响区(ICHAZ)产生IV型裂纹。但对于IV型开裂的机理,至今尚未达成一致认识。为了科学地认识IV型开裂,文中采用大型有限元软件ABAQUS对P92钢焊接接头的温度场、应力场以及蠕变进行了有限元模拟,并且通过X射线测量试验对残余应力模拟值进行了验证。结果表明,通过温度     

马氏体/珠光体异种耐热钢焊接接头蠕变失效数值模拟

采用有限元方法对马氏体/珠光体异种耐热钢接头在560℃条件下,外加轴向应力水平分别为100,120和140 MPa时界面附近的最大主应力、Von Mises等效应力进行了数值模拟,通过恒应力加速蠕变试验对模拟结果进行了验证.结果表明,对于低匹配接头,焊缝/低强母材界面附近最大主应力很高,蠕变孔洞易于在焊缝/低强母材界面处形成,随着外加应力水平的提高,焊缝/低强母材界面附近最大主应力升高较快,但VonMises等效应力较低,孔洞不易扩张.加速模拟试验后界面的蠕变损伤较轻,晶界仅存在少量分散蠕变孔洞,失效倾向较小.对于高匹配接头,焊缝/低强母材界面的最大主应力数值大,界面附近的Von Mises等效应力很高,孔洞易于形核、扩张.加速模拟运行后,高匹配接头中焊缝/12Cr1MoV界面的蠕变损伤及失效倾向大,发生了界面蠕变断裂.因此,对于马氏体/珠光体异种耐热钢接头,采用低匹配焊缝较高匹配合理.     

焊接残余应力对P92钢Ⅳ型蠕变开裂的影响

P92钢焊接接头在高温长时服役条件下易于在细晶热影响区(FGHAZ)或临界热影响区(ICHAZ)产生Ⅳ型裂纹.但对于Ⅳ型开裂的机理,至今尚未达成一致认识.为了科学地认识Ⅳ型开裂,文中采用大型有限元软件ABAQUS对P92钢焊接接头的温度场、应力场以及蠕变进行了有限元模拟,并且通过X射线测量试验对残余应力模拟值进行了验证...     

蠕变对应力腐蚀裂纹尖端应力应变的影响

裂尖应力和应变是影响核电关键焊接接头应力腐蚀开裂速率的主要因素之一,裂尖高应变区的金属蠕变会造成裂尖力学场的变化,并对应力腐蚀开裂速率产生影响。本文以紧凑拉伸试样为研究对象,采用ABAQUS有限元软件,分析了裂尖高应变区蠕变对裂尖应力和应变的影响。结果表明,蠕变能显著缓解裂尖区域的应力集中现象,而对裂尖区域的等效塑性应变影响较小。裂纹尖端不同方向处的应力随蠕变时间的增加而减小,裂尖蠕变量随着裂尖距离的增大而减小,0°方向的应力值和蠕变量最大。     

蠕变空洞尺寸对镍基高温合金应力场的影响规律

为研究在热等静压作用下蠕变空洞大小对镍基高温合金的应力场分布的影响,采用有限元方法分别计算了不同尺寸的蠕变空洞附近的应力场分布情况。结果表明,空洞顶点距离γ′相中心越近,镍基高温合金中最大von Mises应力和最高弹性应变能密度越小;当蠕变空洞的顶点到γ′相中心距离相同时,在垂直方向上,基体垂直通道上von Mises应力和弹性应变能密度从上到下递增,基体水平通道上递减。而且随着蠕变空洞半径增大,合金中基体通道上的von Mises应力和弹性应变能密度递增和递减的趋势越明显。     

P92钢焊接接头蠕变本构关系

通过热处理方法模拟焊接热循环,在 3.53 K/s 的升温速度下制备 P92 钢焊接热影响区各微区的模拟组织试样,通过单轴蠕变试验获得 923K 下 P92 钢熔敷金属、热影响区各微区和母材组织不同应力水平下的单轴蠕变数据,用最小二乘法拟合得到 P92钢焊接接头各区域组织在稳态蠕变条件下的蠕变本构方程.结果表明,相比焊接接头其它微区组织,试验应力较低时,细晶区的蠕变应变率最大,因此在低应力下细晶区容易发生蠕变开裂;随着应力水平的增加,焊接接头和母材蠕变速率逐渐超过细晶区,蠕变断裂易发生在焊缝或母材上.

Abstract：

The welding heat thermal cycle was simulated through the heat treating method, and the simulated microstructures of the coarse grain heat-affected zone (CGHAZ), fine grain heat-affected zone (FGHAZ) and intercritical heat-affected zone (ICHAZ)of P92 steel were prepared by using a furnace at 3.53 K/s of heating rate. The uniaxial creep data of the base metal, deposited metal and simulated CGHAZ, FGHAZ and ICHAZ specimens were obtained through the creep tests under the temperature of 923 K, and the creep constitutive equations of each material were obtained too. The result shows that the creep strain rate of FGHAZ is higher than the other zones of the welded joint under the low stress. So the creep rupture is easy to occur in te FGHAZ. In addition, the creep properties are obviously different among the CGHAZ, FGHAZ and ICHAZ, which indicate the HAZ has the obvious material heterogeneity.     

T92/HR3C异种钢接头的蠕变损伤演化

对T92/HR3C异种钢焊接接头进行温度为650℃、应力为90 MPa的系列蠕变中断试验,利用光学显微镜、扫描电子显微镜对经过不同蠕变寿命分数试样的显微组织和蠕变孔洞损伤进行了观察与定量,并测试了接头蠕变断裂后的硬度分布.结果表明,T92/HR3C异种钢接头断裂在T92侧细晶粒热影响区(FGHAZ),断裂方式为IV型开...     

Influence of Inter-Pass Temperature on Residual Stress in Multi-Layer and Multi-Pass Butt-Welded 9%Cr Heat-Resistant Steel PipesEI北大核心CSCD

9% Cr heat-resistant steels have been abundantly used in boilers of modern thermal plants. The 9% Cr steel components in thermal plant boilers are usually assembled by fusion welding. Many of the degradation mechanisms of welded joints can be aggravated by welding residual stress. Tensile residual stress in particular can exacerbate cold cracking tendency, fatigue crack development and the onset of creep damage in heat-resistant steels. It has been recognized that welding residual stress can be mitigated by low temperature martensitic transformation in 9% Cr heat-resistant steel. Neverthe-less, the stress mitigation effect seems to be confined around the final weld pass in multi-layer and multi-pass 9% Cr steel welded pipes. The purpose of this work is to investigate the method to break through this confine. Influence of martensitic transformation on welding stress evolution in multi-layer and multi-pass butt-welded 9% Cr heat-resistant steel pipes for different inter-pass temperatures (IPT) was investigated through finite element method, and the influential mechanism of IPT on welding residual stress was revealed. The results showed that tensile residual stress in weld metal (WM) and heat affected zone (HAZ), especially the noteworthy tensile stress in WM at pipe central, was effectively mitigated with the increasing of IPT. The reasons lie in two aspects, firstly, there is more residual austenite in the case of higher IPT, as a result, lower tensile stress is accumulated during cooling due to the lower yield strength of austenite; secondly, the higher IPT suppresses the martensitic transformation during cooling of each weld pass, thus the tensile stress mitigation due to martensitic transformation was avoided to be eliminated by welding thermal cycles of subsequent weld passes and reaccumulating tensile residual stress. The influence of IPT on welding residual stress relies on the combined contribution of thermal contraction and martensitic transformation. When the IPT is lower than martensite transformation finishing temperature (M-f), thermal contraction plays the dominant role in the formation of welding residual stress, and tensile stress was formed in the majority of weld zone except the final weld pass. While, compressive stress was formed in almost whole weld zone due to martensitic transformation when the IPT is higher than martensite transformation starting temperature (M-s).     

Study on the strength and failure modes of laser welded galvanized DP980 steel lap joints

The mechanical properties of different sections of the laser welded galvanized high strength dual phase (DP) 980 steel lap joint such as the hardened zone (fusion zone and the grain coarsened heat affected zone (HAZ)), the softened zone (subcritical HAZ), and the base material were determined through mini-tensile tests. The numerically-predicted load–displacement curve and the sample rotation angle were verified by experimental measurements. The FE model considering the non-homogeneous mechanical properties was built based on the weld cross section geometries that were obtained under various laser welding conditions. The numerically-predicted von Mises equivalent strain concentrations and failure modes of the galvanized DP980 lap joints with respect to different laser welding conditions exhibit reasonable agreement with the experimental results.     

焊缝强度匹配对铝合金焊接接头三向应力度分布的影响

用有限元软件ABAQUS对不同焊缝强度匹配的6063铝合金焊接接头进行拉伸模拟,研究了焊缝强度匹配对焊接接头中三向应力度分布的影响.同时,在每种强度匹配条件下,研究了HAZ宽度对焊接接头中三向应力度分布的影响.结果表明,与母材相比,不同焊缝强度匹配的焊接接头中应力状态较为复杂,三向应力度在母材与HAZ交界处和焊缝与HAZ交界处存在突变;高强匹配接头中三向应力度最大值最高,低强匹配接头中三向应力度最大值最小;等强匹配条件下,随着HAZ宽度的增大,三向应力度最大值的位置从母材与HAZ交界处转变为焊缝与HAZ的交界处;高强匹配条件下,三向应力度的最大值都出现在焊缝与HAZ的交界处,随着HAZ宽度增大,三向应力度的最大值逐渐减小;低强匹配条件下,三向应力度的最大值都出现在母材与HAZ的交界处,随着HAZ宽度增大,三向应力度的最大值逐渐减小.     

6063铝合金TIG焊接头的变形行为及等效模型

用有限元软件ABAQUS对平板对接6063铝合金TIG焊接头进行拉伸模拟,研究了HAZ宽度及板厚对焊接接头变形的影响规律,进而建立TIG焊接头有限元等效模型,并用带焊缝的6063铝合金薄壁方管的压缩模拟来验证等效模型的精确性.结果表明,与母材相比,力学性能不均匀的焊接接头中应力状态较为复杂,三向应力度在母材与HAZ交界处和焊缝与HAZ交界处存在突变,三向应力度最大值的位置从母材与HAZ交界处转变为焊缝与HAZ的交界处;力学性能不均匀的焊接接头中的三向应力度不仅取决于试样的厚度,还取决于接头的几何尺寸;铝合金TIG焊接头有限元等效模型宽度为20 mm;带焊缝铝合金薄壁方管的精细模型和等效模型的载荷-位移曲线吻合较好.     

PLASTICITY AND TRIAXIALITY IN STRUCTURAL STEEL AND ASSOCIATED WELD METALS

为了评价应力状态对低强度结构钢及其焊缝金属塑性和韧性的影响,采用20G低碳锅炉结构钢及其全焊缝金属的圆周缺口拉伸试样进行试验.结果表明结构钢及其焊缝金属的初始断裂应变受到三轴应力状态的强烈影响.在同样的三轴应力状态条件下,J427焊缝金属的断裂应变值最高,J422焊缝金属的断裂应变值最低.同时,就实验所用结构钢及其焊缝金属确定了反映其冶金特征的材料常数C值。     

含表面裂纹非匹配焊接接头的断裂行为

测试了两种超高强度钢低匹配接头母材、焊缝和热影响区的表面裂纹断裂韧性,比较了母材与热影响区的断裂韧度概率分布.同时采用有限元方法分析了匹配因子和裂纹位置对裂纹尖端张开应力和应力三轴度的影响.结果表明,当裂纹位于热影响区时,由于软焊缝使其应力三轴度降低,其断裂韧性明显好于母材;而当裂纹位于焊缝一侧时,匹配因子越高,距熔合线越远,则应力三轴度越低,断裂韧性越好;当裂纹位于焊缝中心时,两种匹配的断裂韧度相当.从而解释了试验结果.     

Quantification of creep cavitation damage around a crack in a stainless steel pressure vessel

In this paper, metallographic sectioning and non-destructive small angle neutron scattering (SANS) are used to map the level of creep cavitation around a surface breaking crack in a stainless steel pressure vessel. The cracking developed during 65,000 h service at an operating temperature of around 525 °C and was promoted by the accumulation of creep strain resulting from relaxation of tensile residual stresses associated with a nozzle attachment weld. The distribution and evolution of the cavities is discussed in terms of existing models of creep cavitation failure based on a ductility exhaustion model in which the corresponding multi-axial creep ductility, expressed as the von Mises strain at failure, is a function of the strain rate and stress state. An empirical approach has been adopted for describing the effects of stress state on ductility, which takes into account cavity nucleation as well as cavity growth by creep deformation, and is similar to local approach models for ductile crack growth. Crack initiation is conceded when the creep damage parameter D_c⩾1. The measured creep cavitation results are found to be in reasonable accordance with such a model.     

热影响区软化焊接接头应力分布特征及强度预测

细晶粒钢焊接接头热影响区晶粒粗化引起强度的局部下降，对接头承载能力的影响需要做出定量评价。有限元分析发现，在热影响区软化焊接接头的拉伸试样上，Mises等效应力分布具有确定的特征：在软化的热影响区减小，在与之相邻的焊缝区和母材区相应升高，分布规律符合指数函数规律，在热影响区与焊缝及母材的交界面上发生突变，突变的幅度与交界面两侧材料的屈服应力差值及外加载荷有一定相关性；在焊缝及母材区Mises等效应力增加量的积分等于热影响区减少量的积分。在此基础上提出了预测热影响区软化焊接接头强度的方法，其预测结果与有限元分析有很好的一致性，可用于热影响区软化焊接接头强度的预测和高匹配接头的强度设计。     

Ferrite to austenite reverse transformation process in B containing 9%Cr heat resistant steel HAZ

Abstract

Creep properties of the high Cr heat resistant steel welded joint can be improved by adding B due to prevention of the grain refinement in heat affected zone (HAZ). In the present study, phase transformation behaviour of the B steel HAZ has been investigated to understand suppression mechanism of the grain refinement. During reverse transformation, fine austenite was formed through diffusional transformation at the prior austenite grain boundary in the first stage, and then coarse austenite was formed at the same location of the original austenite. The volume fraction of the fine austenite increased with increasing perk temperature of the weld thermal cycle. This phenomenon can be explained if the coarse austenite contains high density of dislocations. Clear surface relief was observed during the reverse transformation by a confocal laser microscope. These results indicate that martensitic or displacive reverse transformation takes place during welding and it prevents the grain refinement in HAZ.     

600MPa级耐火钢焊接热模拟研究

对一种600MPa级耐火钢焊接性能进行模拟研究，绘制了热影响区连续冷却转变曲线SHCCT。计算了钢的碳当量，并预测了25mm板的止裂温度、HAZ最大硬度。结果表明，该钢具备低的冷裂纹敏感性。