TZM钼合金钨极氩弧焊工艺及焊接接头组织

针对TZM钼合金,研究了钨极氩弧(TIG)焊工艺中不同焊接电流对焊接品质的影响,分析了焊接接头的显微组织及性能。结果表明,当TIG焊焊接电流为210 A,焊接速度4 mm/s,氩气流量8～12 L/min时,可获得品质优良的焊缝。焊接接头组织主要由焊缝中心粗大的柱状晶及热影响区的等轴晶组成,取代了母材的片层状纤维织构,削弱了材料的强度,改善了材料的塑性。     

Mechanical properties and microstructure of pure nickel PAW and PAW-TIG welded joints

A plasma arc welding( PAW)-tungsten inert gas( TIG) hybrid welding process is proposed. And this paper investigated the microstructure and properties of pure nickel N6 joints by PAW-TIG hybrid welding. Compared with the conventional PAW method,the characteristic of PAW-TIG welding process is that there is no interaction between the two arcs.The addition of TIG can enhance the intrinsic high-efficiency peculiarity and the stability of the keyhole status of PAW. The joints made using PAW and PAW-TIG,respectively,were subjected to microstructural evaluations and tensile testing so as to analyze the effect of TIG arc energy on the microstructure and mechanical properties of these joints. The results of this investigation indicate that significant grain coarsening was observed in the weld metal( WM) and heat affected zone( HAZ)and it is found that the extent of grain coarsening increased with the addition of TIG arc. And the microstructure in hybrid joint,with wider weld width and the smooth surface,is coarser than in PAW joint. Furthermore,the microhardness and ultimate tensile strength( UTS) of hybrid joint is slightly lower than that of PAW joint. The fractograph observation shows that the fracturing mechanism of PAW joints ductile,while the hybrid welding joints exists as brittle-ductile fracture mode. The outcome of this work shows that in the condition of same deposited rate,TIG arc post-weld heat treatment can improve the welding efficiency and welding speed. The proposed PAW-TIG hybrid welding process is demonstrated to be suitable for welding nickel and its alloys in industry application.     

热处理对新型铸造模具钢焊接接头组织和性能的影响

对新型铸造模具钢进行焊接修复,研究焊后热处理对焊接接头组织和性能的影响。结果表明,焊后回火处理使模具钢完全淬火区组织由淬火马氏体转变成回火马氏体,不完全淬火区和回火区组织变化不明显。回火处理后淬火区和焊缝硬度明显降低,焊接接头抗拉强度增加。焊后回火处理对焊缝磨损率和平均摩擦系数影响不大。     

Effects of annealing on microstructure and properties of linear friction welded dissimilar titanium joints

Linear friction welds of Ti–6Al–4V (TC4, according to Chinese classification) to Ti–6·5Al–3·5Mo–1·5Zr–0·3Si (TC11, according to Chinese classification) were subject to post-weld heat treatment (PWHT) at 650°C×4 h (PWHT1) and at 950°C×1 h+530°C×4 h (PWHT2) under air cooling. In the as welded joint, TC4 had recrystallised sufficiently compared to TC11. After PWHT1, the α grains in the TC4 weld centre zone grew to some extent and many superfine equiaxed recrystallised α grains precipitated along β boundaries on the TC11 side. The grain growth along the weld line in the weld centre zone under PWHT2 was evident. PWHT2 reduced the joint tensile strength due to the coarsening of the microstructure. The joint microhardness decreased after PWHT.     

铝合金激光-MIG双面焊接接头组织和性能研究

针对16mm厚1561铝合金(俄罗斯牌号),采用不开坡口无间隙的双面激光-MIG复合焊接工艺,并研究焊接接头的拉伸性能、显微硬度和微观组织。结果表明,采用较大的激光功率使双面焊道交叉面积增大,有利于减少焊道根部缺陷,提高拉伸性能;接头中存在着基体相α-Al和第二相Fe(Mn Al)6,第二相经焊接热循环重熔后弥散分布,其中单独激光作用区弥散度最高;焊缝硬度在激光单独作用区相对于母材升高,而在激光-电弧复合作用区相对于母材降低,这与焊缝显微组织中的第二相数量和形态密切相关。     

表面状态对铝合金激光焊接接头组织和性能的影响

采用激光焊焊接高强铝合金2524,研究三种表面状态——原始状态表面、去氧化膜表面、去包铝层表面对铝合金焊接接头组织和性能的影响。结果表明,三种表面状态下,去包铝层状态焊缝总裂纹长度最小,焊缝中心晶粒尺寸最大,接头抗拉强度368 MPa,达到母材强度的80.8%;原始状态接头抗拉强度最低331 MPa,比去包铝层状态低10.1%。     

热处理工艺对系泊链焊接接头组织与性能的影响

分析了不同热处理工艺对22MnCrNiMo钢系泊链的焊接接头的组织和力学性能的影响.结果表明,22MnCrNiiMo系泊链钢焊接接头经过930℃×30 min+620℃×30 min一次淬火回火后,强度和塑性明显改善;经过930℃×30min+930℃×30 min+620℃×30min二次循环淬火回火后,晶粒更加细小均匀,消除了大小晶粒不均匀的情况,力学性能尤其是塑性和冲击韧性得到进一步提高.     

Microstructure and mechanical properties of welded joints of NPP pipelines after long-term operation

The microstructure and mechanical properties of welded joints of cuts from Du 300 and Du 500 pipelines of the Leningradskaya and Novovoronezhskaya nuclear power plants are studied after 70 and 100 thousand hours of operation. The effects of thermal aging simulating operational impact on the microstructure and properties of welded joints of the cuts and of a model coil are determined. It is shown that long-term operation can be accompanied by embrittlement and decrease in the crack resistance of the metal of welds in Du 300 and Du 500 pipelines produced from steels 08Kh18N10T and 08Kh18N12T. The discovered changes in the microstructure can lead to deterioration of the mechanical properties of the metal of welded joints in operation of Du 300 and Du 500 pipelines. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 36–42, July, 2006.     

Evaluation of the effect of strength mismatch in undermatched joints on the static tensile strength of welded joints by considering microstructure

High-tensile strength 950 MPa steel, HT950, which is steel used in penstocks, was developed to provide two vital properties: fracture arrest to stop brittle fracture and high weldability. This steel has been already used for penstocks in some hydropower plants in Japan. To widely apply high-tensile strength steels in penstocks in the future, fewer restrictions against their welding conditions such as pre-heat and post-heat temperature controls are required. One proposed solution is to undermatch the strength of the filler metal to that of the base material. This allows less pre-heating, or no pre-heating at all, and the use of conventional rod and process management is easier. Previous studies have shown that there are softening conditions under which the strength of the joint can be considered as that of the base material. However, the shape and distribution of the soft region are assumed to be ideal. In this study, the method for calculating the change of the strength in heat-affected zone (HAZ) during the welding process is discussed. Then, the influence of the strength distribution of HAZ and welded zone to the strength of the joint is investigated by a wide plate test in both experiment and elastic–plastic analysis. Applicability of undermatched joints to penstock fabrication is considered by these discussions. As a result, it is concluded that the Vickers hardness distribution in the HAZ can be estimated by the method which is proposed in this study and the strength of the under-matched joints is high enough in both experiment and analysis in which the Vickers hardness distribution is considered. From these conclusions, the applicability of undermatched joints, of which the weld metal is the HT570 class, to penstock fabrication is conformed.     

焊接残余应力对20G管道焊接接头组织性能的影响

通过X射线衍射法研究管线用20G焊接残余应力的分布和焊后热处理对焊缝残余应力的影响,择优选取了焊后热处理条件。结果发现,在焊缝区存在较高的焊接残余应力。焊后热处理可以显著降低焊接残余应力,其中以620℃加热温度、1 h保温时间的处理工艺为宜。此外,热处理细化了焊缝区域晶粒,降低了焊缝区域硬度,改善了焊接接头抗H2S腐蚀的能力。     

保护气体对1.4003不锈钢焊接接头组织和疲劳性能的影响

CO2与O2作为MAG焊接时常用的活性气体,对1.4003不锈钢接头的金相组织与疲劳性能有不同的影响。通过金相组织分析和脉动拉伸疲劳试验,研究两种保护气氛下1.4003钢MAG焊接头的组织和疲劳性能。结果表明:两种接头焊缝组织的基体均为奥氏体,基体上分布δ铁素体;当保护气体为φ(Ar)95%+φ(CO2)5%时,中值疲劳强度为312.5 MPa;当保护气体为φ(Ar)97%+φ(O2)3%时,中值疲劳强度为302.5 MPa。两种保护气体的疲劳试件断裂位置主要集中在热影响区,均有明显的启裂源,扩展区疲劳纹清晰,终断区形态为韧窝型韧性断口。     

Effect of cooling rate on the microstructure of electron beam welded joints of two-phase TiAl-based alloy

The analysis of the microstructural characterization and phase composition of electron beam welded joint zones of Ti- 43Al-9V-O. 3Y alloy has been done in this study. The welded seam is mainly composed of B2 phase, the partial γ ＋ α2 twophase lamellar structure and granular γm phase. And the lanthanon Y existed as YAl2 phase and served as grain refined. The impact of different cooling rates on joint microstructure, fracture characteristic and tensile strength were investigated. The high cooling rate restrained the structural transformation and resulted in the ordering structure. The fracture of the joint was brittle cleavage fracture because the ordering structure went against restraining the crack propagation. With the decrease of cooling rate, the transformation amounts of lamellar structure increased, and the fracture presented the layered and crosslayered characteristic.     

YG30硬质合金与45#钢TIG焊接头组织及抗弯强度的研究

选用Ni-Fe合金和Ni-Fe-C合金作为填充金属对YG30硬质合金与45^#钢进行了TIG焊试验。运用扫描电镜、X射线衍射、弯曲力学性能试验等方法对焊接接头的组织形态、物相及抗弯强度进行了研究。结果表明，分布于YG30／焊缝界面区域的η相为M6C型的Fe3W3Cη1相的存在是焊接接头抗弯强度低下的原因。选择适当碳含量的Ni-Fe-C合金作为填充金属，能够提高焊接接头的抗弯强度。     

超声冲击处理对TA15钛合金焊接接头组织和性能的影响

采用光纤激光焊对TA15钛合金进行无间隙对接焊,选取6组不同的超声冲击处理时间对焊接接头显微组织、力学性能、晶粒尺寸、应力分布和粗糙度进行研究,确定较优的超声冲击处理时间。结果表明,当冲击电流为1. 2 A、振动频率为20 k Hz、超声冲击处理时间为75 min时,可获得50μm厚的致密强化层,103. 4 nm的晶粒尺寸,其粗糙度为34. 13μm。经过超声冲击处理后,减少了气孔、缩松等缺陷,使得拉应力转变为压应力,接头的应力集中得到极大地改善,对钛合金材料组织和性能的提高有积极的促进作用。     

焊接速度对微合金钢激光焊接接头组织性能的影响

研究了激光焊接速度对800 MPa级Nb-Ti-Mo微合金钢焊接接头的组织和性能的影响。通过体式显微镜、扫描电镜和透射电镜观察其形貌组织,硬度、拉伸试验测试其力学性能。结果表明,焊接接头宽度随着焊接速度(0.78~1.8 m/min)增大而逐渐减小,低焊速(0.78 m/min)下接头下塌严重。焊缝区组织主要为板条马氏体,并且在低焊速(0.78~1.2 m/min)情况下会形成少量贝氏体和铁素体。粗晶区组织为板条马氏体,并随着焊接速度增大,原始奥氏体晶粒尺寸逐渐减小。细晶区和混晶区组织均为铁素体和M-A组元,但是细晶区的组织更为细小,而混晶区的组织均匀性不佳。焊接接头峰值硬度出现在粗晶区,且随着焊接速度增大而减小。高焊速(1.5~1.8 m/min)下的接头拉伸断裂位置均出现在母材区,抗拉强度达835 MPa。     

Asymmetric microstructure and fracture behaviour of friction stir welded joints of 2024 aluminium alloy under cyclical load

In this study, the effect of asymmetric microstructure on fracture behaviour of friction stir welded joints of 2024-O aluminium alloy under cyclical load was investigated via optical microscopes, electron backscattering diffraction, microhardness and infrared thermography, and digital imaging correlation (DIC). The results demonstrate that the thermo-mechanical affected zone (TMAZ) at retreating side possesses a relatively higher fraction of low-angle grain boundaries and coincidence site lattice boundaries in comparison to that at the advancing side (AS), which results in the strain localisation and fracture path along the region between nugget zone and TMAZ at the AS under cyclical load. The profile of microhardness presents the asymmetric characteristic as well. The temperature evolution of the joint obtained by infrared camera is in good agreement with strain distribution measured by DIC. The thermography proves to be generally sufficient to predict the fracture path before failure under cyclical load.