304L奥氏体不锈钢搅拌摩擦焊与TIG焊接头的微观组织与性能

采用搅拌摩擦焊和钨极惰性气体保护电弧焊(TIG)分别对3 mm厚304L奥氏体不锈钢进行焊接,对比分析2种焊接方法下接头的微观组织和抗拉强度。304L不锈钢的搅拌摩擦焊焊接接头由焊核区、热力影响区、热影响区及轴肩变形区组成;焊核区组织为均匀细小的动态再结晶组织,热力影响区组织发生明显的塑性变形,而热影响区仅受到热的作用晶粒有所长大;TIG焊接头组织由呈胞状树枝奥氏体晶和呈蠕虫状或板条状铁素体组成。结果表明:2种焊接方法获得的接头强度相似,都略高于母材强度。     

CLAM-316L TIG焊接接头显微组织特征分析

采用309焊丝对中国低活化马氏体(CLAM)钢和316L不锈钢进行TIG焊,并利用光学显微镜、扫描电镜和维氏硬度仪分析对接接头的微观组织和显微硬度分布。结果表明,CLAM-316L TIG焊接头按照显微组织特征可分为六个区域,即CLAM钢母材、CLAM钢热影响区、CLAM钢熔合区、焊缝金属、316L热影响区、316L母材。CLAM钢熔合区显微组织为淬火马氏体;焊缝金属区为粗大的胞状枝晶组织;316L热影响区和母材均为奥氏体组织,热影响区晶粒尺寸有明显长大。焊态接头整体硬度分布均匀,只有CLAM钢熔合区硬度较高。     

CLAM钢TIG焊后的热处理工艺研究

为了解决利用钨极氩弧(TIG)焊方法焊接的CLAM钢在焊缝区存在的强度、硬度增加而韧性减弱的问题,从回火温度、回火时间以及重复回火等方面研究了回火对焊缝区硬度的影响,得到了回火温度选择为760℃、回火时间选择为2 h和在760℃保温1 h回火,重复进行两次的两种最佳热处理工艺.     

CLAM钢的钨极氩弧焊及焊接后的结构与性能

利用钨极氩弧焊(TIG)焊接方法对中国自行研制的低活化铁素体/马氏体(CLAM)钢进行焊接试验,分别采用了Y型坡口和双Y型坡口两种焊接工艺。对焊接件各部分的硬度和显微结构进行测试分析,利用透射电镜观测材料的微观形貌并进行析出物相分析,以此对CLAM钢的焊接性能进行初步评价。观察发现,焊缝区没有产生缩孔和裂纹;焊缝区和母材的微观形貌主要为板条马氏体,板条宽度约为600 nm,其析出物均为20~200 nm的M23C6型碳化物;经过焊后热处理,焊缝区、热影响区和母材的硬度之间的差别减小。     

重复焊接对304不锈钢热影响区组织与性能的影响

采用自动钨极氩弧焊接（GTAW）工艺设计刚性约束坡口,制备了304不锈钢1次焊接和1~5次试样。采用光学显微镜、X射线衍射（XRD）、扫描电子显微镜（SEM）与电子背散射衍射（EBSD）技术对重复焊接试样的热影响区（HAZ）显微组织进行观察分析,并开展室温拉伸性能测试,研究重复焊接对显微组织与力学性能的影响。结果表明,重复焊接试样的HAZ显微组织主要由奥氏体和条状δ铁素体组成,随着重复焊接次数增加,HAZ奥氏体晶粒尺寸呈长大趋势,δ铁素体含量先减少后增加,组织择优取向由<101>转变为<111>,局域取向差逐渐增大;晶粒尺寸是影响抗拉强度和延伸率变化的主要原因,加工硬化致使试样屈服强度逐渐增加。      

TIG焊对工业纯锆R60702接头腐蚀性能的影响

通过对工业纯锆(R60702)钨极惰性气体保护焊(TIG)保护效果和不平衡条件结晶的运用,制备焊接接头的显微组织试样及其焊接接头的腐蚀电位测定试样。观察接头在高倍金相显微镜下的显微组织特征,测定焊接接头极化曲线,研究R60702的显微第二相的分布及对接头组织腐蚀性能的影响。研究表明热影响区的耐腐蚀效果最差。     

压水堆核电厂主管道窄间隙自动焊焊丝研究

根据窄间隙自动焊工艺及主管道母材特点,在ER316L焊材基础上研究与主管道自动焊技术相匹配的专用焊材。通过模拟焊接试验和热裂纹试验验证了自动焊焊材的稳定性、可焊性,并对其焊缝疲劳寿命进行试验。研究结果证明新开发的自动焊焊材与主管道窄间隙自动焊工艺相匹配,焊缝接头综合性能良好。     

焊接接头非均匀力学性能对J积分和失效评定曲线的影响

由于焊缝填充金属的不同和焊接热循环的作用,焊接接头不同区域有着不同的力学性能。本文将焊接接头模化为由两种材料组成,即母材金属和焊缝金属,用弹塑性有限元分析法计算了焊接接头强度组配对Ｊ积分和失效评定曲线的影响。结果表明,焊接接头不均匀强度组配对裂纹驱动力－Ｊ积分和失效评定曲线的形状与位置有很大影响。对于一个特定的焊接接头,如果接头为低组配或等组配,则以母材金属的极限载荷作为无因次载荷而建立的安全评定     

Zr-Sn-Nb合金薄板焊后组织和力学性能研究

采用维氏硬度计和万能材料试验机进行了Zr-Sn-Nb合金薄板焊后的显微硬度、拉伸及循环变形试验,用金相显微镜和场发射扫描电镜分别分析了显微组织和断口特征。结果表明:焊缝熔合区(FZ)形成前β晶界包围的α′组织,热影响区(HAZ)基本为α+α′两相组织;FZ的硬度最高,HAZ硬度稍低,但均高于母材区(BM);FZ的抗拉强度要高于BM,但塑性降低;在高应变条件下,焊接试样的循环变形行为与母材差异明显。     

TC4钛合金焊后电子束局部热处理及焊接残余应力测试研究

针对TC4钛合金通过电子束焊后局部热处理工艺来改善接头的性能,采用X射线法对电子束局部热处理后焊接残余应力的分布趋势进行了测试研究.试验结果表明:经电子束局部热处理后,TC4钛合金焊缝区马氏体晶粒组织得到细化;同时上表面接头残余应力的分布得到改善.     

不锈钢堆焊层的晶间腐蚀

对反应堆压力容器的奥氏体不锈钢堆焊层所产生的晶间腐蚀现象作了研究。在很低的含碳量情况下堆焊层仍有产生晶间腐蚀的可能,其原因是显微组织中铁素体数量太少,确定了引起这种组织的工艺因素是焊后冷却速度过慢。还讨论了马氏体对晶间腐蚀的影响及富铬碳化物析出时的取向关系。     

Hastelloy C-276/316L脉冲激光异质焊接微观组织研究

为评价激光焊接AP1000部件工艺的可靠性,探究Hastelloy C-276与316L异质焊接焊缝的元素偏析及组织结构,利用Nd:YAG脉冲激光进行焊接,借助光学显微镜和电子探针X射线微区分析仪等分析测试仪器,对焊缝显微组织、元素成分及金相形貌进行分析。结果表明：焊缝组织晶粒细化,焊缝中部以细小等轴晶为主、边缘以柱状晶为主,且焊接接头两侧热影响区极窄;依据元素宏观分布,焊缝可分为3个区域,焊缝两侧元素成分急剧变化,中部均匀;元素存在微观偏析,晶界处Mo元素富集。焊缝组织以γ奥氏体为主,并未发现明显δ铁素体生成。     

Effect of heat treatment and precipitation state on toughness of heavy section Mn-Mo-Ni-steel for nuclear power plants components

With regard to the mechanical properties of heavy forgings, made from steel grade 508 ASTM Class 3 (20 MnMoNi 5 5) the influence of the cooling intensity during hardening was investigated and the possibilities and limits of accelerating the cooling rate were studied. The importance of the transformation heat is discussed. It can be concluded from this, that it is impossible to avoid the formation of upper bainite as a typical microstructure of heavy forgings from this steel type.To obtain high impact energy the annealing condition must be conform with this type of microstructure. The reason for impact decrease by over-annealing is related to Mo₂C precipitation in the bainitic ferrite.Finally, experiences with intercritical heat treatment of this steel type are described and the special behaviour of the microstructure obtained is demonstrated.     

Thermal stress prediction in divertor cooling finger using the local heat transfer distribution

An approach that combines computational fluid dynamics (CFD) and structural mechanics simulation is used for evaluating stresses in a divertor cooling finger. Local distributions of heat transfer coefficient (HTC) between the helium and inner surface of the thimble are used as a boundary condition for the structural mechanics analysis. Stresses calculated with a realistic non-homogeneous HTC distribution are compared with the results where averaged HTC values in three representative zones of inner thimble surface are used. The obtained maximum stresses are considerably higher in the case of realistic non-homogeneous HTC boundary condition. The highest thermal stresses in the tile–thimble assembly are obtained on the thimble inner surface, in the region where the highest thermal gradients due to jet cooling can be observed. The results also show that tetrahedral based finite element model underestimate the computed stresses, especially when a coarse mesh is used.     

Measurement and analysis of SHCCT diagram for CLAM steel

China Low Activation Martensitic (CLAM) steel is a leading candidate material for construction of the Chinese fusion reactor Test Blanket Module. The Simulated HAZ Continuous Cooling Transformation (SHCCT) diagram is developed via physical simulation, and the effects of thermal history on the microstructure and mechanical properties of the weld coarse-grain heat-affected zone (CGHAZ) in CLAM steel are evaluated. The results of thermal cycle simulation show that grain size increases and hardness decreases gradually with increasing heat input. Under certain conditions, especially when cooling times from 800 °C to 500 °C (T8/5) are larger than 136 s, delta ferrite may form which is deleterious for the TBM application. The amounts of delta ferrite are given under different T8/5. A SHCCT diagram of CLAM steel is developed using dilatometry and it predicts the AC1, AC3 and the Ms temperatures. With decreased cooling rate (larger T8/5), martensite laths widen and carbide precipitates grow. The results indicate that welding heat input should be taken into consideration and controlled in practical CLAM steel welding process applications.     

Effect of the ITER FW Manufacturing Process on the Microstructure and Properties of a CuCrZr Alloy

The first wall(FW) is one of the core components in ITER. As the heat sink material,the CuCrZr alloy shall be properly jointed with beryllium and stainless steel. At present, the grains of CuCrZr are prone to coarsen seriously in the thermal cycle process of FW manufacturing, which has become a critical issue for ITER parties. To investigate the mirostructure and mechanical properties of the optimized CuCrZr alloy in the first wall fabricating thermal cycle, simulative experiments have been done in this study. The alloy ingot was forged and hot rolled into plates,and then solid solution annealed, cold rolled and aged for strengthening. Several heat treatments were done to the CuCrZr samples, and the changes of microstructure, micro-hardness and tensile strength were investigated. The results indicated that the original elongated grains had changed into equiaxed ones, and the vickers hardness had declined to about 60 after experiencing the process of CuCrZr/316L(N) bi-metallic plate manufacturing, either by hot isostatic pressing at a higher temperature or by explosion welding followed by solution annealing. Joining Be/CuCrZr by hot isostatic pressing acts as an aging process for CuCrZr, so after the simulated heat treatment,the hardness of the alloy increased to about 110 HV and the tensile yield strength at 250?C rose to about 170 MPa. Meanwhile, the average grain size was controlled below 200 μm.     

显微CT在早期釉砂研究中的应用:以西周倗国出土釉砂珠为例

利用同步辐射显微CT、XRD和EDXRF对西周倗国墓地出土的一枚釉砂开展无损分析,探讨该枚釉砂的制作工艺。结果表明,此釉砂珠的石英胎质较为致密,胎料为研磨很细的石英颗粒,与西方釉砂的内部结构相差较大,暗示该样品不是从西方输入。此釉砂珠的制作工艺为,首先围绕圆柱形内芯制作石英胎,然后施釉,烧制后去除内芯;这种工艺可能受当时青铜器铸造工艺和原始瓷制作工艺的影响。显微CT无损分析釉砂的内部结构的优越性,显示其在釉砂研究中有着广阔的应用前景。     

Study of Titanizing the Surface of Copper Substrates by the Double Glow Discharge Plasma Surface Alloying Technique

This paper discusses a study in which Ti surface alloying has been performed on copper substrates by means of a double glow discharge plasma surface alloying technique. The micro-structure, the phase structure, the micro-hardness and the distribution of Ti concentration of alloying layer were investigated in detail by XRD, SEM and so on. The effect of process parameters on the alloying layer was studied. The experimental results show that a Ti solid solution with the precipitation Cu4Ti alloying layer has been formed on the copper surface. The thickness of the alloying layer is about 120 μm and the surface titanium concentration gradually decreases from ω （Ti） = 87% to ω （Ti） = 4%. The micro-hardness of the alloying layer is between 300 HV-800 HV. Source sputtering, surface absorption, ion bombarding and high temperature diffusion are the major factors that affect the alloying layer.     

Quantification of the toughness distribution in a heavy section submerged arc multilayer reactor pressure vessel weldment

In a working procedure qualification test weld representing a heavy section circumferential reactor pressure vessel (RPV) weld tested in 1968, lower toughness values were observed in the top layer region compared to those found in the filler region. Gleeble simulation, extensive microscopic evaluation, diligent Charpy V-notch testing and modelling of the bead sequence and distribution of alloying elements was applied to explain this effect. It could be revealed that the microstructure of the weld metal is the most important factor influencing the toughness. When an ‘as welded’ microstructure is partly or fully reaustenitised by the adjacent multilayer beads, the microstructure transforms and the toughness increases. In the filler region, 85% of the cross-section consists from transformed microstructure, whereas in the top layer only 20% are transformed. It is quite evident that, accidentally, the notch tip of Charpy samples in 1968 were placed in untransformed microstructures. When the top layer on the inner surface of the RPV is weld cladded by austenitic stainless steel, full transformation occurs and the toughness representing the filler region can be taken into account for safety evaluations.     

Reduction method for residual stress of welded joint using harmonic vibrational load

Welding is widely used for construction of many structures. Since welding is a process using locally given heat, residual stress is generated near the bead. Tensile residual stress degrades fatigue strength. Some reduction methods of residual stress have been presented and, for example, heat treatment and shot peening are practically used. However, those methods need special tools and are time consuming. In this paper, a new method for reduction of residual stress using harmonic vibrational load during welding is proposed. The proposed method is examined experimentally for some conditions. Two thin plates are supported on the supporting device and butt-welded using an automatic CO₂ gas shielded arc welding machine. Residual stress in the direction of the bead is measured by using a paralleled beam X-ray diffractometer with scintillation counter after removing quenched scale chemically. First, the welding of rolled steel for general structure for some excitation frequencies is examined. Specimens are welded along the groove on both sides. For all frequencies, tensile residual stress near the bead is significantly reduced. Second, welding of the specimen made of high tensile strength steel is examined. In this case, tensile residual stress near the bead is also reduced. Finally, the proposed method is examined by an analytical method. An analytical model which consists of mass and preloaded springs with elasto-plastic characteristic is used. Reduction of residual stress is demonstrated using this model.