堆焊熔合区成分和组织分析

利用电子探针，透射电镜对不锈钢堆焊熔合区的成分和组织进行了分析和研究，发现无论焊态还是焊后热处理态，熔合区中都存在一个马氏体组织带，熔合区铬、镍呈线性分布且存在一人成分梯度，焊后热处理碳在熔合区中集聚，从而熔合区出现大量碳化物析出。     

一种热锻模具修复用堆焊焊条堆焊层的组织与硬度分析

对一种热锻模具修复用堆焊焊条的堆焊层成分、组织、硬度、热处理后的组织及硬度作了细致分析。焊芯采用H08A的5.0mm焊丝,并在焊条药皮中加入合金元素Ni、Cr和Mo,以向堆焊层中过渡合金元素Ni、Cr和Mo。试验中采用OLYMPUS GX71金相显微镜、Quanta600扫描电子显微镜及Genesis XM2 X射线能谱仪、Philips CM200透射电镜及Hanemann显微硬度计对堆焊层金属进行测试,结果表明,焊态下堆焊层显微组织为粒状贝氏体+少量铁素体,同时有白色马氏体组织存在,热处理后堆焊层显微组织为粒状贝氏体的回火组织+少量铁素体+碳化物。     

Fe-Cr-Ni-Co合金堆焊和重熔层的空蚀性能

将Fe-Cr-Ni-Co合金堆焊在304不锈钢表面,再对冷却后的堆焊层进行表面重熔,进行不同时间的空蚀实验.采用失重分析、扫描电镜(SEM)和X射线衍射仪分析空蚀后的合金层,与304不锈钢和堆焊层对比,研究了表面重熔对耐空蚀性能的影响.结果表明:堆焊层和重熔层的耐空蚀性能远高于304不锈钢,重熔后的合金层其耐蚀性优于堆...     

Cr-Ni-Mo双相不锈钢的空泡腐蚀行为

利用超声波空蚀实验装置对Cr-Ni-Mo奥氏体-铁素体不锈钢及其同质材料堆焊后的堆层金属在自来水溶液中的空蚀行为进行了研究.通过扫描电镜（SEM）、显微硬度计等检测设备研究了材料空蚀表面形貌和微观结构.结果表明：Cr-Ni-Mo双相不锈钢的抗空蚀性能明显优于经TIG（钨极惰性气体保护焊）表面堆焊后的堆层金属试样;双相不...     

ZAlSi7Mg合金壳体堆焊修复工艺的研究

应用钨极氩弧焊的方法对ZAlSi7Mg合金壳体进行了焊接堆焊修复工艺研究,通过对堆焊修复层的金相组织分析、X探伤检验和力学性能试验,证明堆焊修复层组织致密、无焊层剥离且基体焊接变形很小。该研究对修复ZAlSi7Mg合金零件在机械加工和铸造过程中造成的缺陷具有一定的参考价值。     

含稀土氧化物的WC-TiC-TaC-Co/CuZnNi复合耐磨堆焊材料

以WC-TiC-TaC—Co硬质合金、CuZnNi及氧化物La2O3为原料，研制出一种具有高耐磨性和良好抗冲击性能的堆焊材料，利用SEM、TEM、摩擦磨损试验分析了堆焊材料的组织及耐磨性，探讨了稀土氧化物对堆焊材料组织性能的影响．研究结果表明：硬质合金与Cu基合金通过元素扩散形成连接界面；堆焊层耐磨性随硬质合金含量的增加而增加，随载荷的增加而降低；加入La2O3后，基体组织细化，硬质合金与基体的界面上形成微晶过渡区，改善了界面结合强度，堆焊层耐磨性得到提高。     

两种冷却方式下双相钢2205堆焊层性能分析

采用药芯焊丝CO_2气保焊(FCAW)在低碳钢表面堆焊一层双相不锈钢表层,分析了水冷和空冷冷却方式对双相钢堆焊层的力学性能、耐腐蚀性能以及铁素体-奥氏体(α-γ)两相组织的影响。结果表明,水冷和空冷冷却方式对堆焊层的力学性能无显著影响;水冷时堆焊层铁素体含量为45.17%,比空冷更接近两相平衡,其显微组织为块状铁素体和沿晶界或亚晶界分布的针状奥氏体;水冷时堆焊层具有更优异的耐腐蚀性能,平均腐蚀速率为0.488 mm/a。     

耐磨堆焊板焊接冷却方式对其机械性能的影响

耐磨堆焊板焊接过程中有水冷和空冷两种方式，水冷设备使母材温度降低，大规范焊接使母材稀释率增大，虽获得了较高的熔敷速度和较小的焊后变形，但堆焊板的熔合区合金元素多，含碳量较高，在焊接骤冷后机械性能降低，造成堆焊层受冲击时产生局部脱落，进而影响耐磨板使用寿命。空冷设备堆焊板焊后变形较大，焊接熔敷速度稍低，但母材稀释率较低，熔合区合金元素较少，耐磨板的机械性能优于水冷堆焊设备耐磨板。     

超级双相不锈钢2507焊接工艺研究现状

主要梳理和综述了超级双相不锈钢2507焊接方面的研究工作,从而对超级双相不锈钢2507焊接工艺进行指导。从超级双相不锈钢2507焊接工艺、焊接接头两相比例调节两个维度进行综述,其中,超级双相不锈钢2507焊接工艺部分从钨极氩弧焊、埋弧焊、等离子弧焊、激光焊、电子束焊、激光-电弧复合焊这6种焊接工艺开展评述,焊接接头两相比例调节部分从调整焊接热输入、焊后热处理、添加合金元素镍或氮3个方面进行评述。结合国内外研究现状,探讨了超级双相不锈钢焊接如何控制接头两相比例这一关键问题。研究现状表明:钨极氩弧焊、等离子弧焊和激光焊可以较好地实现超级双相不锈钢优质焊接;添加合金元素镍或氮是调控焊接接头两相比例的重要手段。开展超级双相不锈钢2507焊接工艺研究现状的综述具有重要意义,向熔池过渡合金元素的高能量密度焊接工艺可能是超级双相不锈钢焊接的优选技术。     

15CrMoR(H)+SUS321不锈复合钢板的焊接

对15CrMoR(H)+SUS321不锈复合钢板的基层和堆焊层焊接性进行了分析,选择手工电弧焊+埋弧焊的方法,制定合理的焊接工艺,对焊前预热、层间温度、焊后消氢进行控制,完成了15CrMoR(H)+SUS321的焊接。     

焊后热处理对奥氏体／珠光体钢接头熔合区断裂形态的影响

利用扫描电镜对比观察了不同碳含量母材的奥氏体（Ａ）／珠光体（Ｐ）异种钢焊接接头熔使区在焊态和焊后热处理后的断口形态与对应的金相组织。发现焊态接头熔合区的断裂形态由滑移变形、浅纫窝和准解理小面组成，崦焊后的热处理接头熔合区的断裂形态为碳化物带＋放射状解理混合花样。在溶合区两侧可看到明显的边界线和脆－韧转变特征，初步讨论了熔合区粘口的形成机理和焊后热处理对它的影响。     

Effect of postweld heat treatment on development of interfacial structures in nickel-based transition joints

Abstract

The interfacial structures between 2·25Cr–1Mo steel and Inconel 182 weld metal have been studied after post-weld heat treatments (PWHTs) at 700°C and subsequent aging at 630°C. This aging temperature accelerates the changes in interfacial structure that occur during power-station operation, and thus provides a method of studying the effects of the initial PWHT. The paper shows that during PWHT for ≤8 h at 700°C, arrays of carbide particles develop in the ferritic steel, parallel and very close to the weld metal interface, and that these arrays continue to grow during aging at 630°C for 6000 h. However, the precipitate sizes after PWHT are small compared with those developed during the subsequent aging. For longer heat treatments, up to 100 h at 700°C, the I interfacial precipitates develop to significant sizes, but growth then ceases because of the limited carbon migration from the 2·25Cr–1Mo steel. Aging at 630°C then causes carbon redistribution in the heat-affected zone, resulting in an incubation period before further interfacial precipitate growth can occur. The net result is that after aging for ≥500 h at 630°C, PWHTs of 2–100 h at 700°C have negligible effects on the interfacial-precipitate sizes and distributions, compared with those found in similarly aged as-welded specimens.

MST/119     

On the weldability of grey cast iron using nickel based filler metal

Shielded metal arc welding process using nickel based filler metal was used to join grey cast iron. The effect of post weld heat treatment (PWHT) on the microstructure and hardness was studied. PWHT included heating up to 870 °C, holding for 1 h at 870 °C and then furnace cooling. By using nickel based filler metal, formation of hard brittle phase (e.g. carbides and martensite) in the fusion zone is prevented. Before PWHT, heat affected zone exhibited martensitic structure and partially melted zone exhibited white cast iron structure plus martensite. Applied PWHT resulted in the dissolution of martensite in heat affected zone and graphitization and in turn the reduction of partially melted zone hardness. Results showed that welding of grey cast iron with nickel based filler metal and applying PWHT can serve as a solution for cast iron welding problems.     

Effect of initial ferrite content on phase transformations in niobium stabilized austenitic clad metals

Austenitic stainless steel welds which normally contain some ferrite may be exposed to high temperatures either during stress relief or service exposure. Ferrite being an unstable phase is transformed to various secondary phases during high temperature exposure. Data on the affect of temperature and time at temperature on the transformation products of austenitic stainless steel welds are meagre, also few reports are available on the affect of initial ferrite content on phase transformations.The present study included cladding on low carbon steel with two niobium-stabilized austenitic stainless strips using submerged arc welding to obtain clads with two ferrite contents, low (4 FN) and high (12 FN). Clads were PWHT at 600, 800, 1000 ° C for 1, 10 and 100 h. Ferrite was measured using a ferritescope. Electrochemical dissolution in 10%HCl-CH₃OH solution was done to separate out secondary phases which were analysed using the X-ray diffraction powder technique.The results of the study indicated that the as-weld samples contained both M23C6 and NbC. The PWHT samples were found to contain M23C6, NbC and sigma phases. NbC was found in all the PWHT samples. Both 4 FN and 12 FN samples showed M23C6 after PWHT at 600 °C. After 800 °C PWHT 4 FN samples did not show M23C6, while 12 FN samples showed weak M23C6 lines. After 1000 °C PWHT, was absent in both cases.Sigma was absent in the 4 FN sample PWHT at 600 °C, while it was present in the 800 °C PWHT samples. In contrast, samples containing 12 FN samples showed sigma both after 600 and 800 °C PWHT. Sigma was absent in samples PWHT at 1000 °C.The interesting observation of the study was the effect of initial ferrite content on sigma phase formation. It was observed that ferrite transformed to sigma at 600 °C itself when ferrite content is relatively high (12 FN) and not when it is less (4 FN). This behaviour suggests that sigma formation is not only a function of temperature but also initial ferrite content and readily forms even at lower temperatures like 600 °C when initial ferrite content is high. This in contrast to the earlier studies where it was noticed that short time exposures at temperatures up to 700 °C did not show sigma formation.The observations based on percentage ferrite transformed indicated that the kinetics of sigma at 600 and 800 °C are very fast. Also, ferrite dissolution is faster at 1000 °C when the ferrite content is lower.     

Characterisation of dissimilar P91 and P92 steel welds joint

In the present study, dissimilar weld joint was prepared using the P91 and P92 steel plate of 8-mm thickness, using the multi-pass gas tungsten arc (GTA) welding with filler (weld 1) and autogenous tungsten inert gas welding (A-TIG) process (weld 2). Evolution of δ-ferrite patches was studied in weld zone and heat affected zone (HAZ) for both weld 1 and weld 2. Effect of varying post weld heat treatment (PWHT) duration was also studied on δ-ferrite patches and mechanical properties of the dissimilar weld joint. PWHT was carried out at 760°C. For weld 2, weld zone showed poor impact toughness and higher peak hardness as compared to weld 1. After the PWHT, a considerable reduction in hardness was obtained for both weld 1 and weld 2,while impact toughness of weld zone showed a continuous increment with PWHT duration. For weldments characterisation, optical microscope, scanning electron microscope (SEM) and microhardness tester were utilised.     

Effect of heat treatment on tensile properties of friction stir welded joints of 2219-T6 aluminium alloy

Abstract

The effect of post-weld heat treatment (PWHT) on the tensile properties of friction stir welded (FSW) joints of 2219-T6 aluminium alloy was investigated. The PWHT was carried out at aging temperature of 165°C for 18 h. The mechanical properties of the joints were evaluated using tensile tests. The experimental results indicate that the PWHT significantly influences the tensile properties of the FSW joints. After the heat treatment, the tensile strength of the joints increases and the elongation at fracture of the joints decreases. The maximum tensile strength of the joints is equivalent to 89% of that of the base material. The fracture location characteristics of the heat treated joints are similar to those of the as welded joints. The defect free joints fracture in the heat affected zone on the retreating side and the joints with a void defect fracture in the weld zone on the advancing side. All of the experimental results can be explained by the hardness profiles and welding defects in the joints.     

Investigation of fracture for friction welded joint between pure nickel and pure aluminium with post-weld heat treatment

The present paper described the investigation of the fracture of friction welded joint between pure nickel (Ni) and pure aluminium (Al) with post-weld heat treatment (PWHT). Most of joints autogenously fractured from the adjacent portion of the intermediate layer (interlayer) consisting of intermetallic compound (IMC) on the weld interface due to growing of that after long heating time during the cooling process after PWHT. The IMC interlayer was composed with mainly NiAl, and that grew at the weld interface with PWHT. The joint fracture temperature increased with increasing width of the IMC interlayer in the axial direction of the joint. That is, the fracture of the joint occurred at the interface between NiAl layer and Al base metal. The fractured surface was covered with a little Ni₂Al₃ and/or NiAl₃, and that was like as disbonding. Furthermore, when the width of the IMC interlayer was smaller than approximately 40 μm, the joint fracture temperature of the joint was under about 470 K. However, when the width of the IMC interlayer exceeded 50 μm, the joint fracture temperature drastically increased up to about 800 K. Hence, it was able to be estimate that the joint fracture temperature increased with increasing width of the IMC interlayer. Therefore, one of the main reasons for the fracture of the joint could be concluded as remarkable decreasing of the bonding strength between NiAl layer and Al base metal, which was produced with PWHT.     

Effect of post-weld heat treatment on the microstructure and plastic deformation behavior of friction stir welded 2024

To improve the plasticity of friction stir welded joints for plastic processing applications, post-weld heat treatment (PWHT) of 2024-O aluminum alloy friction stir welding joints was carried out at annealing temperatures from 250 °C to 450 °C with an interval of 50 °C for 2 h, followed by cooling to 200 °C in the furnace. The effect of PWHT on the microstructure and plastic deformation behavior of the joints was investigated. It was found that the fine-equiaxed grains are stable and retained in the nugget of the joints even after annealing at 450 °C for 2 h. However, the grains in the thermo-mechanically affected zone (TMAZ) of the joints become coarse and equiaxed as annealing temperature increases. The plastic deformation of as-welded joint is very heterogeneous. In contrast, the plastic deformation of PWHT joint is relatively homogeneous by both the nugget and the base material showing large deformation. The decrease in elongation of as-welded joints is completely recovered by PWHT. The high ductility of the joint is mainly attributed to the retention of the fine-equiaxed grains in the nugget during PWHT.     

Microstructures and mechanical properties of welded joints of novel 3Cr pipeline steel using an inhouse and two commercial welding wires

The welded joints of the novel 3Cr pipeline steel were fabricated via the gas tungsten arc welding (GTAW) technique using an inhouse welding wire labeled as R01 and two kinds of commercial wires (H08Cr3MoMnA and TGS-2CML). Microhardness, impact toughness and tensile properties of the joints were measured, and microstructure characteristics were observed by scanning electron microscopy (SEM). The results show that under selected welding procedure, the joints of R01 can achieve quite good mechanical properties without preheating and post weld heat treatment (PWHT). After thermal refining, elongation (15.2%) doubled and met the DNV-OS-F101 standard. For low carbon or super low carbon pipeline steels such as 3Cr steel, the revised formula with the carbon applicable coefficient (A(c)) was quite good for predicting the maximum hardness in heat affected zone (HAZ). Compared with these two selected commercial wires, the inhouse welding wire R01 can provide the highest cost-performance ratio.     

Correlation between microstructure and creep performance of martensitic/austenitic transition weldment in dependence of its post-weld heat treatment

This paper deals with the influence of post-weld heat treatment (PWHT) of T92/TP316H martensitic/austenitic transition weldment on the resulting microstructure and creep characteristics. Experimental weldments were fabricated by gas tungsten arc welding using a nickel-based weld metal (Ni WM). After the welding, two individual series of produced weldments were heat-treated according to two different PWHT procedures. The first “conventional PWHT” was carried out via subcritical tempering (i.e. bellow Ac₁ temperature of T92 steel), whereas the other one, the so-called “full PWHT” consisted of a complete reaustenitization of the weldments followed by water-quenching and final tempering. The use of “conventional PWHT” preserved microstructural gradient of T92 steel heat-affected zone (HAZ), consisting of its typical coarse-grained and fine-grained subregions with tempered martensitic and recrystallized ferritic–carbidic microstructures respectively. In contrast, the “full PWHT” led to the complete elimination of the original HAZ via transformation processes involved, i.e. the reaustenitization and back on-cooling martensite formation. The observed microstructural changes depending on the initial PWHT conditions were further manifested by corresponding differences in the weldments’ creep performance and their failure mode. The weldments in “conventional PWHT” state ruptured after long-term creep tests by premature “type IV failure” within their recrystallized intercritical HAZs. On the contrary, the long-term creep behavior of the weldments processed by “full PWHT” was characterized by their remarkable creep life extension but also by the occurrence of unfavorable “decohesion failure” along T92/Ni WM interface.