固态相变对10Ni5CrMoV钢焊接残余应力的影响

10Ni5CrMoV钢属于低合金高强钢,固态相变效应在其焊接热-力耦合分析中不可忽略.固态相变效应表现为体积变化和屈服强度"滞后"现象,通过热膨胀试验测试相变参数,建立固态相变的数学模型,开展了考虑固态相变效应的10Ni5CrMoV钢焊接热-力耦合分析.结果表明,考虑固态相变效应后,焊缝及焊缝附近（相变区域）纵向拉应力大幅度降低,相变区域相邻位置拉应力仍然较高;横向应力的分布状态变化明显,应力峰值变化较小,约为室温屈服强度的25%.应力测试结果与数值模拟结果较吻合,验证了固态相变模型的准确性.     

固态相变对P91钢激光对接接头残余应力的影响

基于SYSWELD软件,模拟了P91钢激光对接焊时的温度场和焊接残余应力,并探讨了固态相变产生的体积膨胀、屈服强度变化和相变塑性对焊接残余应力的影响. 数值模拟结果表明,体积膨胀和屈服强度变化对焊接残余应力的大小与分布有显著的影响; 相变塑性在相变过程中有"应力松弛"效应,对焊缝和热影响区的纵向和横向残余应力的值有一定程度的影响. 对比数值模拟结果与试验结果可知,采用文中建立的有限元模型计算得到的残余应力与中子法测量得到的结果基本吻合,在考虑相变塑性的情况下,计算结果与实测值吻合更好.     

相变塑性对低温相变钢焊接接头残余应力计算精度的影响

基于JWRIAN焊接数值模拟软件,开发了考虑固态相变的热-冶金-力学耦合的数值计算方法来模拟低温相变钢的焊接残余应力.重点讨论了固态相变中的体积变化、屈服强度变化和相变塑性对焊接残余应力的影响.结果表明,相变引起的体积变化和屈服强度变化对最终的焊接残余应力分布和大小有显著影响,相变塑性与前两者相比较影响相对较小,但它对焊缝和热影响区在相变过程中的应力变化趋势有一定的减缓作用,从而适度"松弛"了残余应力.     

不同焊接顺序的汽车用S355J2G3钢工字梁焊接结构变形和残余应力的有限元预测

基于焊接热弹塑性有限元分析理论,采用焊接专用有限元分析软件对不同焊接顺序的汽车用S355J2G3钢工字梁焊接结构手工MAG焊接过程进行了数值仿真,获得不同焊接顺序下焊接结构的变形和残余应力分布.模拟时,选择双椭球焊接热源模型,考虑了材料热物理性能与温度的非线性关系,以及相变潜热对温度场的影响.重点研究了焊缝及临近焊缝区域焊接残余应力和变形的分布特征,并进行了理论分析.     

固态相变对P92钢焊接接头残余应力的影响

采用光学显微镜、显微硬度仪和盲孔法研究了P92钢平板焊接接头的微观组织、显微硬度和表面残余应力分布.同时,基于SYSWELD软件开发了考虑材料固态相变的热-冶金-力学耦合的有限元计算方法,并采用该方法模拟了P92钢的Satoh试验和单道堆焊接头的温度场及应力场分布,探讨了固态相变引起的体积变化、屈服强度变化和相变塑性(TRIP)对焊接残余应力形成过程及最终残余应力分布的影响.实验结果表明,P92钢平板焊接接头焊缝组织为淬火马氏体,其平均显微硬度为440 HV,母材(BM)组织为回火马氏体,其显微硬度为240 HV.Satoh试验的数值模拟表明,固态相变引起的体积变化和屈服强度变化不仅对残余应力的形成过程及最终应力的分布和峰值大小有显著影响,甚至可以改变应力的符号;而TRIP效应则具有减缓因体积膨胀和屈服强度变化所引起应力变化趋势的作用.进一步的计算结果表明,P92钢堆焊接头焊缝和热影响区(HAZ)的纵向残余应力为压应力,而靠近HAZ的BM上存在较大的纵向拉应力,峰值为600 MPa,该值超过了P92钢的室温屈服强度;整个焊接接头的横向残余应力峰值为130 MPa,远小于其纵向残余应力的峰值.数值计算结果与盲孔法测量得到的结果比较吻合,表明了所开发的热-冶金-力学耦合的有限元计算方法有较高的计算精度.     

低合金高强钢焊接固态相变力学行为及模拟技术研究

热弹塑性有限元法是焊接等热加工过程力学行为研究的主要数值方法之一。然而,对于低合金高强钢焊接固态相变力学行为的研究,传统的热-力耦合求解方法受到了一定限制。根据固态相变的单一耦合模型和多耦合模型的研究现状,分析了焊接固态相变力学行为模拟中存在的问题。基于温度-组织-应力耦合模型,建立了T91钢管接头焊接残余应力分析的三维有限元模型。计算结果表明,管接头马氏体相变伴随焊接移动过程逐步发生,分析了马氏体相变对焊接残余应力的影响。管子外表面残余应力分布的计算结果与实验测试结果一致。     

转向架用S355J2W钢MAG焊接接头残余应力研究

利用X射线衍射法和超声临界折射纵波法测量和分析S355J2W钢MAG焊接接头的起弧区、中心区和收弧区残余应力。结果表明:超声波法和X射线衍射法均可用于S355J2W钢MAG焊接接头的残余应力测量,在焊缝和热影响区,超声波法的应力测量值比X射线法的大30~40 MPa。各测试区残余应力分布趋势相近,在焊缝及近缝热影响区为数值较大的残余拉应力,远离焊缝中心的母材为压应力。中心区的残余应力峰值大于起弧区和收弧区。     

预热温度对S355钢L型焊接接头温度场、应力场、应变场和微观组织的影响研究

本文主要研究典型结构钢材料S355作为焊接母材时,在不同预热温度条件下L型焊接接头的温度场、应力场、应变场以及焊缝区的微观组织变化。使用Simufact.welding软件进行焊接过程的数值模拟,采用更为符合电弧焊实际情况的双椭球热源模型。研究结果给出了预热温度对L型焊接接头温度场、应力场和应变场的影响,显示了材料S355在焊接冷却过程中的贝氏体相变对焊缝区应力场变化的影响。     

固态相变对2.25Cr1Mo钢多道焊组织及残余应力的影响

基于Abaqus及其子程序，提出了考虑包括奥氏体相变、贝氏体相变和马氏体相变在内的固态相变的2.25Cr1Mo钢焊接模拟方法。模拟考虑了固态相变产生的相变潜热、体积变化和屈服强度改变，对2.25Cr1Mo钢平板多道焊模型的温度场、组织分布及焊后残余应力进行了计算，并研究了其规律。研究结果表明：相变潜热使得焊后贝氏体生成量增多，马氏体生成量减少。相变导致的屈服强度改变使得焊后残余应力大幅下降，相变导致的体积变化减小了焊缝内部残余应力。     

湿H2S环境下低合金钢焊接接头氢扩散数值模拟

利用电化学渗透法测定了氢在16MnR低合金钢焊接接头处的焊缝金属、热影响区金属以及母材中的扩散系数.利用有限元软件ABAQUS,对16MnR钢焊接接头氢扩散进行数值模拟,考虑焊接残余应力、不同组织对氢扩散的影响,得到焊接接头扩散氢的浓度随时间的分布.结果表明,在焊缝和热影响区,氢的扩散系数和焊接残余应力较大,使氢在焊缝和热影响区聚集,降低材料的力学性能,使得焊接接头部位成为最薄弱环节,在湿H2S环境下很容易发生与氢有关的损伤和破坏.     

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).     

Studies on multipass welding with trailing heat sink considering phase transformation

A two pass butt welding of 6 mm mild steel plates was simulated using 3D finite element model using temperature and phase dependent material properties. Material phase transformations were simulated using suitable phase transformation kinetic models. Mechanical analysis is carried out using nodal temperature and phase proportions as input. Experiments were carried out using liquid nitrogen (LN2) as trailing heat sink. Trailing heat sink helped to reduce the residual stress in the fusion zone (FZ) and heat affected zone (HAZ) although distortions were found be increasing. A parametric study was conducted to study the effect of distance between weld arc and trailing heat sink. The heat sink closer to weld arc reduced both distortions and residual stresses.     

Microstructure,hardness and residual stress distribution in maraging steel gas tungsten arc weldments

Abstract

The distribution of residual stresses due to welding has been studied in maraging steel welds. Gas tungsten arc welding process was used and the effect of filler metal composition on the nature of residual stress distribution has been investigated using X-ray diffraction technique with Cr K_α radiation. Three types of filler materials were used, they include: maraging filler, austenitic stainless steel and medium alloy medium carbon steel filler metal. In the case of maraging steel weld, medium alloy medium carbon filler, the residual stress at the centre of the weld zone was more compressive while, less compressive stresses have been identified in the heat affected zone of the parent metal adjacent to the weld metal. But, in the case of austenitic stainless steel filler the residual stresses at the centre of the weld and heat affected zone were tensile. Post-weld aging treatment reduced the magnitude of stresses. The observed residual stress distribution across the weldments has been correlated with microstructure and hardness distribution across the weld.     

Distribution Features of the Residual Stress For T-Joints by Laser Welding

The residual stress of T-joints for SUS304 stainless steel by YAG laser welding was measured by the method of hole-drilling,and the effects of heat treatment and hardness distribution of weld joints on the distribution of residual stress for T-joints were analyzed.The results showed that the maximum of longitudinal residual tensile stress for T-joints was about 140MPa.The maximum of residual stress was not more than 40MPa after heat treatment,the peak of residual stress reduced obviously.The gradient of residual stress distribution was also reduced significantly.Strain hardening phenomenon occurred for T-joints,and the hardness of weld and heat affected zone was both higher than the hardness of base metal,the peak of hardness occurred in the fusion line.The effect of strain hardening phenomenon of weld and heat affected zone on the residual stress distribution of T-joints for SUS304 stainless steel was obvious,which made longitudinal residual tensile stress become higher.     

9%Cr-1%Mo耐热钢焊缝金属显微组织特征解析

提出了“焊道热影响区”的概念。通过对多层多道焊缝中焊道热影响区特征区域的划分,不同区域中各特征点所经历的焊接热循环曲线的绘制,解析了9％Cr-1％Mo耐热钢焊缝金属显微组织特征。焊缝金属中各点距其后续焊道熔池的距离,决定了其所经历的焊接热循环的峰值温度、焊接热循环次数;不同的峰值温度决定了各点所处的相变区域不同、所发生的组织转变不同;不同的焊接热循环次数也决定了发生的组织转变不同;各点所经历的焊接热循环可分为不同类型,根据焊接热循环的类型可全面完整解析焊缝金属组织。文中方法为针对9％Cr-1％Mo耐热钢提出的,但它同样适用于其它Cr-Mo高合金钢焊缝金属的组织分析,     

不同工艺下超强钢点焊残余应力的试验分析

为了分析在不同工艺下电阻点焊对超强钢焊接构件内部残余应力的影响,文中试验选用B1500HS快冷淬火后的超高强钢薄板,通过德国NIMAK点焊机器人进行电阻点焊,制备焊接构件,并通过X射线衍射法测量点焊构件焊核区、热影响区、母材区表面处的残余应力,分别从电极直径、焊接电流、锻压力方面考察不同工艺对超强钢点焊构件残余应力的影响. 结果表明,残余应力以焊核为中心基本呈对称分布,从焊核到母材,数值先增大后减小,在热影响区处达到最大值且为拉应力,远离焊核区降低为压应力,且拉应力最大值明显高于压应力最大值;残余应力随电极直径增大而增大;残余应力随着电流增大其最大值先增大后减小;锻压力可以降低残余应力峰值.     

Dissimilar spot welding of dual phase steel/ferritic stainless steel: phase transformations

Phase transformations in dissimilar resistance spot welds of dual phase steel and ferritic stainless steel are analysed. In contrast to a full martensitic microstructure predicted by the Schaeffler and Balmforth diagrams, a ferrite–martensite microstructure was observed in the fusion zone. The formation of ferrite phase in the fusion zone can be attributed to the rapid cooling rate of resistance spot welding, which suppresses the post-solidification ferrite–austenite transformation. The grain growth and martensite formation were main metallurgical features of the heat affected zone of ferritic stainless steel side. Microstructure gradient of heat affected zone in dual phase steel side was dictated by martensitic transformation. The effect of weld thermal cycle on the mechanical performance of the joint is discussed.     

X80M管线钢铜衬垫外根焊接头冷裂敏感性分析

开展了不同装配条件下大厚度、大管径X80M管线钢铜衬垫外根焊接头的冷裂敏感性分析. 采用碳当量法和应力场模拟等方法,研究了不同装配条件对接头冷裂倾向的影响. 结果表明,接头顶部盖面层的热影响区和底部根焊层是X80M管线钢焊接接头的最薄弱区域,冷裂倾向最大. 对口间隙从0 ~ 0.5 mm增大至0.6 ~ 1 mm后,焊缝区根焊层的相对碳当量提高16.6%,增大了冷裂倾向. 错边量提高使得接头盖面层热影响区淬硬性增大,冷裂敏感性增大. 错边量和对口间隙增加均会导致焊后残余拉应力的进一步增大,错边量增大也会导致接头错边区域存在应力集中,错边量从0 mm增加为3 mm,其焊缝区根焊层凹角处残余应力峰值增加52.4%. 因此,X80M管线钢电弧焊接过程需尽量减小对口间隙和错边量以降低冷裂倾向.     

拉剪载荷下超高强度钢点焊残余应力试验

点焊后焊接残余应力叠加工作载荷后,内部应力会重新分配.文中选用B1500HS超高强度钢薄板,制备焊接构件,并通过X射线衍射法测量焊核区、热影响区及母材区的表面残余应力.在施加拉剪载荷的情况下,分别从电极端面直径、焊接电流两方面考察点焊构件在施加拉剪载荷前后残余应力的分布情况.结果表明,点焊时电流变化对试件的残余应力有一定影响;电极端面直径增加使得焊核区的残余应力增大.施加拉剪载荷后,残余应力在焊核与热影响区有所释放,远离焊核区的释放较小.     

焊后热处理对输送H_2S介质压力管道维修焊接接头组织性能的影响

采用手工钨极氩弧焊(TIG焊)打底,焊条电弧焊(SMAW)填充、盖面的焊接工艺对输送H_2S介质压力管道(20钢)进行维修焊接,并对其焊接接头进行720～750℃下保温1h的焊后热处理.对热处理前、后焊接接头组织和性能进行分析研究,结果表明:720～750℃×1h热处理使焊缝区与热影响区成针状分布的魏氏组织铁索体晶粒得到细化,并使其呈退化形态;焊缝区、热影响区与母材的显微硬度整体呈下降趋势;焊接接头抗拉强度大幅度提高,断裂均处在远离焊缝的母材上.焊后热处理有效地降低了焊接接头的残余应力,改变了残余应力的分布特征,使其分布趋于"均匀",拉应力大幅度降低.