Microstructural Evolution on the T91 Dissimilar Metal Joints during Creep Rupture Tests

T91 steel is one of the new materials presently employed in power plant pipe components. The creep rupture strength and microstructure of the T91+10CrMo910 and T91+13CrMo44 welded joints were analyzed during creep rupture tests. Creep transgranular ductile rupture occurred at the 10CrMo910 matrix in the T91+10CrMo910 welded joints and creep intergranular brittle rupture occurred at the 13CrMo44 HAZ in the T91+13CrMo44 joints. Microhardness measurements showed high hardness at the heat affected zone (HAZ) of T91 and a sharply drop at the 13CrMo44 HAZ during creep rupture. The metallographic tests showed that no obvious microstructure degradation was observed in the 10CrMo910 HAZ and matrix, while creep cracks appeared at the 13CrMo44 HAZ. T91 steel had relatively high creep resistant strength in the welded joints tested. Recovery occurred in the T91 HAZ with the growth of subgrain size and the decrease of dislocation density during creep. It was concluded that the dissimilar joints of T91 and low alloy heat-resistant steel should have close creep strength matching to increase the service life of the overall joints at elevated temperature.

Research on the creep damage and interfacial failure of dissimilar metal welded joint between 10Cr9Mo1VNbN and 12Cr1MoV steel

The mechanical properties, creep damage, creep rupture strength and features of interfacial failures of welded joints between martensite (SA213T91) and pearlite steel (12Cr1MoV) have been investigated by means of argon tungsten pulsed arc welding, high temperature accelerated simulation, creep rupture, mechanical property tests and scanning electronic microscope (SEM). The research results indicate that the mechanical properties of overmatched and medium matched joint deteriorate obviously, and they are susceptible to creep damage and failure after accelerated simulation operation 500 h, in the condition of preheat 250℃, and post welding heat treatment 750℃×1 h. However, the mechanical properties of undermatched joint are the best, the interfacial failure tendency of undermatched welded joint is less than those of medium and overmatched welded joint. Therefore, it is reasonable that low alloy material TR31 is used as the filler metal of weld between SA213T91and 12Cr1MoV steel.

Numerical Simulation on Interfacial Creep Failure of Dissimilar Metal Welded Joint between HR3C and T91 Heat-Resistant Steel

The maximum principal stress, von Mises equivalent stress, equivalent creep strain, stress triaxiality in dissimilar metal welded joints between austenitic（HR3C） and martensitic heat-resistant steel（T91） are simulated by FEM at 873 K and under inner pressure of 42.26 MPa. The results show that the maximum principal stress and von Mises equivalent stress are quite high in the vicinity of weld/T91 interface, creep cavities are easy to form and expand in the weld/T91 interface. There are two peaks of equivalent creep strains in welded joint, and the maximum equivalent creep strain is in the place 27-32 mm away from the weld/T91 interface, and there exists creep constrain region in the vicinity of weld/T91 interface. The high stress triaxiality peak is located exactly at the weld/T91 interface. Accordingly, the weld/T91 interface is the weakest site of welded joint. Therefore, using stress triaxiality to describe creep cavity nucleation and expansion and crack development is reasonable for the dissimilar metal welded joint between austenitic and martensitic steel.

Influence of Creep Strength of Weld on Interfacial Creep Damage of Dissimilar Welded Joint between Martensitic and Bainitic Heat-Resistant Steel

The mechanical properties, creep rupture strength, creep damage and failure characteristics of dissimilar metal welded joint （DMWJ） between martensitic （SA213T91） and bainitic heat-resistant steel （12Cr2MoWVTiB（G102）） have been investigated by means of pulsed argon arc welding, high temperature accelerated simulation, mechanical and creep rupture test, and scanning electronic microscope （SEM）. The results show that there is a marked drop of mechanical properties of undermatching joint, and low ductility cracking along weld/G102 interface is induced due to creep damage. Creep rupture strength of overmatching joint is the least. The mechanical properties of medium matching joint are superior to those of overmatching and undermatching joint, and creep damage and failure tendency along the interface of weld/G102 are lower than those of overmatching and undermatching joint after accelerated simulation for 500 h, 1 000 h, 1 500 h, and the creep rupture strength of medium matching joint is the same as that of undermatching joint. Therefore, it is reasonable that the medium matching material is used for dissimilar welded joint between martensitic and bainitic steel.

Effect of heat treatment temperature on dissimilar welded joint

The dissimilar metals 1Crl8Ni9 and 16MnR are welded by shielded metal arc welding process using electrode A312. The corrosion experiments are carried out on welded joint samples, which is as-welded and post-weld heat treatment at 650 ℃, 750 ℃ and 850 ℃, for 2 h in 70% sodium hydroxide solution. EDS and X-ray diffraction analysis are carried out on the samples after corrosion. Average corrosion rate calculation and microhardness measurement are conducted on both as- welded and post-weld heat treatment samples. The results indicate that average corrosion rate of as-welded joint metal is smaller than that of post-weld heat treatment joint metal. Compared with that of post-weld heat treatment at 750 ℃ and 850 ℃ for 2 h, the average corrosion rate of welded joint after post-weld heat treatment at 650 ℃ for 2 h increases greatly.

Effect of joining temperature on microstructure and properties of diffusion bonded Mg/Al joints

The joining of AZ31B Mg alloy to 6061 Al alloy was investigated at different joining temperatures by vacuum diffusion bonding method. The microstructures of Mg/Al dissimilar joints were studied by means of optical microscopy （OM）, scanning electron microscopy （SEM） and energy dispersive X-ray （EDX）. The results show that the thickness of each layer in the diffusion zone increases with the increase of joining temperature, and the microstructure changes obviously. At joining temperature of 440 °C, the diffusion zone is composed of Mg2Al3 layer and Mg17Al12 layer. At joining temperatures of 460 and 480 °C, the diffusion zone is composed of Mg2Al3 layer, Mg17Al12 layer, eutectic layer of Mg17Al12 and Mg-based solid solution. The width of high-hardness zone in the joint increases with increasing joining temperature, and the micro-hardnesses at different locations in the diffusion zone are significantly different. The joining temperature of 440 °C offers the highest tensile strength of 37 MPa, and the corresponding joint exhibits brittle fracture at the intermetallic compound layer of Mg17Al12.

激光功率对铝/铜激光熔钎焊接头组织及性能的影响

采用激光熔钎焊方法对5052铝合金和T2紫铜进行对接试验,研究了激光功率(2000,2200,2400,2600,2800 W)对接头显微组织和力学性能的影响。结果表明:不同激光功率下接头铜侧钎焊区组织均以柱状晶为主,随着激光功率的增加,焊缝区树枝晶由细针状转变为雪花状;铜侧钎焊区由界面层和金属间化合物层组成,2000,2600 W激光功率下的界面层主要为AlCu相,金属间化合物层主要为Al_(4)Cu_(9)相,2400 W激光功率下的界面层主要由AlCu相和CuZn相组成,金属间化合物层主要为CuZn_(5)相;焊缝区主要由Al_(4.2)Cu_(3.2) Zn_(0.7)和Al_(0.71)Zn_(0.29)相组成。随着激光功率的增加,金属间化合物层厚度增加。激光功率对铜侧钎焊区的显微硬度影响较大,各接头的最高显微硬度均出现在铜侧钎焊区。随着激光功率的增加,接头最高硬度增加,抗拉强度先增大后减小;当激光功率为2400 W时,接头的抗拉强度最大,达到铝合金母材的92%,此时接头在靠近铝合金母材处断裂,而其他激光功率下制备的接头均在铜侧钎焊区和焊缝区处断裂。

海洋平台支撑板异种金属焊接试验研究

目的结合Q245R/Q690D 2种材料的优势研究其焊接接头性能,获得最优的焊接和后热处理工艺参数。方法以某海洋平台建造为背景,选用E50-6焊丝、J形坡口设计对Q245R/Q690D中厚板多道次焊接进行试验研究。在8、12、16、20 kJ/cm热输入下,对接头进行力学性能测试和微观组织观察;为细化接头组织、提高综合力学性能,对最佳热输入下的接头进行不同温度的后热处理,后热处理温度分别为250、350、580℃并保温2 h,进一步观察接头的性能和微观组织。结果焊态下拉伸断裂均发生在Q245R母材侧,在12 kJ/cm热输入下,焊缝表面硬度在338HV左右,焊缝冲击功为172 J;在20 kJ/cm热输入下,冲击功下降至82.7 J,组织粗大且呈板条状。在250、350℃回火能够降低表面硬度,同时焊缝冲击功较焊态的略有上升,最大增加了21 J;在580℃回火后,内部晶粒粗大,焊缝表面硬度增大,最大为448HV,较焊态的提高了32.5%,同时冲击功显著下降,下降至80 J,下降约53.5%。结论Q245R/Q690D中厚板多道次焊接热输入采用12 kJ/cm为宜,同时焊后对接头进行250~350℃回火并保温2 h为推荐后热处理方式。

Achieving High‑Quality Aluminum to Copper Dissimilar Metals Joint via Friction Stir Double‑Riveting Welding

In order to achieve a high-quality joining of aluminum(Al)and copper(Cu)dissimilar metals,a new friction stir doubleriveting welding(FSDRW)with a Cu rod as the rivet was proposed,and the rotating tool with a large concave angle shoulder was specially designed.The results showed that under the thermal–mechanical effect of rotating tool,the Cu rod was deformed to be a double riveting heads structure with a Cu anchor at the upper surface of Al plate and an Al anchor above the lap interface of joint,and these two anchors greatly enhanced the mechanical interlocking of Al/Cu joint.The effective bonding interfaces were formed among the double riveting heads structure,the upper Al plate and the lower Cu plate,which contained the Cu/Cu interface and the Al/Cu interface.The Cu/Cu interface without the kissing bond and the Al/Cu interface with the rationally thin AlCu and Al_(2)Cu intermetallic compounds(IMCs)layers were beneficial to heightening the joint tensile shear strength.The maximum tensile shear load of the FSDRW joint achieved 5.52 kN,and the joint under different plunging depths of rotating tool presented a mixed mode of ductile fracture and brittle fracture.This novel FSDRW technique owns the advantages of strong mechanical interlocking and superb metallurgical bonding,and provides a new approach to acquiring a high-quality Al/Cu dissimilar metals joint.

焊接速度对铝合金/铜激光熔钎焊接头组织及性能的影响

采用激光熔钎焊在不同焊接速度(4,5,6,7,8 mm·s^(-1))下对5052铝合金和T2铜进行对接焊,研究了焊接速度对接头宏观形貌、显微组织、显微硬度、抗拉强度及拉伸断裂机理的影响。结果表明:随着焊接速度增加,激光熔钎焊接头的焊缝成形先变优后变差,当焊接速度为6 mm·s^(-1)时焊缝成形最佳;随着焊接速度增加,接头中树枝状Al-Cu共晶组织变少,Zn-Al共晶组织变多,当焊接速度为6 mm·s^(-1)时接头铜侧界面反应区出现Al_(4)Cu_(9)和Al_(2)Cu金属间化合物,熔焊区由α-Al固溶体、η-Zn固溶体、Al-Cu共晶组织和Zn-Al共晶组织组成;随着焊接速度增加,铝合金/铜激光熔钎焊接头熔焊区硬度变化不大,铜侧界面反应区硬度下降,接头抗拉强度先增大后减小,拉伸断裂模式按照解理断裂、准解理断裂、韧性断裂、准解理断裂顺序依次变化,当焊接速度为6 mm·s^(-1)时抗拉强度(212 MPa)最大,接头发生韧性断裂。

反应堆压力容器接管安全端焊接残余应力模拟及其焊接参数优化研究

目的针对反应堆压力容器接管安全端焊接残余应力较大易导致应力腐蚀开裂的问题,探究焊接工艺参数对焊接残余应力的影响,并寻找最佳工艺参数。方法利用有限元参数化建模方法建立反应堆压力容器接管安全端的三维热-力耦合模型,模拟其焊接过程,研究焊接残余应力的变化情况。采用正交试验设计法分析了焊接电流、焊接速度及层间冷却时间对焊后最大等效应力的影响,建立了焊后最大等效应力与焊接电流、焊接速度及层间冷却时间的二次回归模型,基于该模型利用遗传算法寻优焊接参数。结果焊接残余应力峰值靠近熔合区位置,残余应力较高,超过了材料的屈服应力;各参数按对焊后等效残余应力峰值的影响由大到小的顺序依次为焊接速度、焊接电流、层间冷却时间。正交试验所得最佳工艺参数如下:焊接电流为610 A,焊接速度为20 mm/s,层间冷却时间为400 s,经遗传算法进一步优化后所得的最佳参数如下:焊接电流为610 A,焊接速度为23 mm/s,层间冷却时间为427 s。通过仿真验证遗传算法优化结果,得到焊接残余应力的峰值为373 MPa,比未优化前减小了44 MPa。结论优化后的工艺参数有效降低了焊接残余应力,提高了反应堆压力容器接管安全端服役过程中的安全性,该研究方法可为实际焊接生产提供一定的参考。

Creep Rupture of Mismatched Welded Joints of Steels with Dissimil ar Creep Strengths

The finite element analysis of mismatched welded jo ints with a 30°groove angle was performed to study the mechanical behavior of D MWJs (dissimilar metal welded joints). It is concluded that the distribution of stress triaxiality in the DMWJs is uneven, especially near the fusion lines. The degree of creep strength mismatch has remarkable effect on the distribution. Th e higher the level of mismatch is, the more uneven the distribution is and the e asier for premature failure to occur in the joint.

核反应堆压力容器低合金钢与奥氏体不锈钢异种金属焊接研究现状

核电反应堆压力容器是核电站的核心设备之一,其安全性和可靠性对核电站的运行至关重要。在压力容器的制造中,涉及到低合金钢与奥氏体不锈钢的异种金属焊接。针对该异种金属焊接接头存在的组织不均匀性、元素扩散、应力腐蚀裂纹等问题,从焊接填充材料的选择和优化、可能应用的焊接方法、焊后热处理及工艺控制等方向探讨了解决措施与发展方向。为提高此类接头质量和可靠性的研究提供参考,从而确保核电站的安全运行。

铜/钛热辅助超声波焊接接头组织和性能分析

为实现铜与钛异种金属的可靠连接,探索了一种热辅助超声波焊接的工艺方法。以MCGS触摸屏作为上位机,陶瓷加热片作为辅助加热热源,搭建了热辅助超声波焊接成套装置。通过MCGS软件开发的人机界面及控制程序,实现了热辅助超声波焊接工艺过程的实时控制。通过对不同加热温度下Cu/Ti超声波焊接接头力学性能和微观组织的分析,建立了热辅助超声焊接过程界面反应模型,以此阐释了Cu/Ti热辅助超声波焊接接头的形成机理。试验结果表明,辅助加热不仅提高了焊接区峰值温度,还促进了界面元素的相互扩散,使反应区的宽度和有效连接面积显著增加,机械嵌合作用明显增强,是Cu/Ti接头抗剪切强度显著提高的主要原因。

不同铆接速度下板材搭接顺序对钢/铝异种金属铆接接头性能的影响

采用自冲铆接实现了钢/铝异种金属的有效连接。通过改变铆接速度,对比研究了钢上铝下和铝上钢下两种搭接顺序下的接头的成形性能、断裂力和断裂方式。研究结果显示,随着铆接速度的增大,接头头高和底切量不断减小,互锁值不断增大。钢上铝下搭接顺序下的接头的成形情况较为稳定,缺陷较少。钢上铝下搭接顺序下的拉剪接头的断裂力明显高于铝上钢下搭接顺序下的拉剪接头的,而铝上钢下搭接顺序下的十字拉伸接头的断裂力明显高于钢上铝下搭接顺序下的十字拉伸接头的。铆钉变形时受力方向的不同导致拉剪接头的断裂力明显高于十字拉伸接头的。铆接速度为250~325 mm/s时,可以实现两种搭接顺序下的接头成形性能和断裂力的良好匹配。

超声振动辅助铝/钢激光–MIG熔钎焊外观成形、组织以及拉伸性能研究

目的利用超声振动改善铝/钢对接接头界面的微观结构,降低气孔缺陷并提高接头力学性能。方法通过超声振动辅助激光–MIG焊接方法实现铝/钢异种金属连接,采用光学显微镜观察焊缝形貌,采用金相显微镜和扫描电子显微镜观察焊缝和界面微观结构,利用拉伸试验机测试接头的拉伸强度。结果超声振动的施加提高了熔融金属的润湿铺展性能,减少了焊缝中的气孔缺陷,并降低了界面层金属间化合物的厚度。带有余高和去除余高的接头拉伸强度由未加超声的175 MPa和154 MPa分别提高到189 MPa和172 MPa。结论利用超声振动的声流、空化效应有效改善了熔融金属的润湿铺展性能和界面微观结构,并在一定程度上消除了气孔缺陷,进而提高了接头的力学性能。

Microstructure and intergranular stress corrosion cracking susceptibility of a SA508-52M-316L dissimilar metal weld joint in primary water

Correlation of microstructure and intergranular stress corrosion cracking （IGSCC） susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain rate tension test following a microstructure characterization. The susceptibility to IGSCC in var- ious regions of the dissimilar metal weld joint was observed to follow the order of Alloy 52 Mb〉 the heat affected zone of 316L〉 the dilution zone of Alloy 52 Mw〉 Alloy 52 Mw weld metal. The chromium- depletion at the grain boundary is the dominant factor causing the high IGSCC susceptibility of Alloy 52 Mh. However, IGSCC initiation in the heat affected zone of 316L is attributed to the increase of resid- ual strain adjacent to the grain boundary. In addition, the decrease of chromium content and increase of residual strain adjacent to the grain boundary increase the IGSCC susceptibility of the dilution zone of Alloy 52 Mw.

铜/钨异种金属冷焊接头组织与力学性能研究

随着对金属材料强度的要求越来越高,单一金属材料的性能具有巨大的局限性,已难以满足人们日益增长的使用需要。近年来,Cu/W异种金属的连接在焊接领域发挥着日益重要的作用。本文采用冷焊技术制备出了钨/铜异种金属焊接搭接头,研究表明冷焊焊接电流对接头的成形有显著的影响,160 A时,界面处存在许多孔洞、未焊合缺陷,断裂发生在界面结合处;170 A时发生咬边,且焊缝中靠近熔合线处出现气孔聚集,断裂发生在此处;180 A时焊缝成形较均匀,界面结合较致密,Cu、W的扩散程度最大,接头强度最高,断口在钨上;190 A时,焊点之间交叠、间隔,连接面积变化大,界面及焊缝处均存在很大气孔,焊件质量不稳定。接头剪切强度随电流升高呈先增大后减小的变化趋势,180 A时达到峰值77.78 MPa,焊接接头质量最好。焊后钨侧硬度与焊前相差不大,焊缝处硬度极低,热影响区的硬度介于铜母材与焊缝之间,界面处的硬度随电流的增大而减小。除170 A外,其他电流参数下接头都无明显的软化区。

Microstructure and stress corrosion cracking of a SA508-309L/308L-316L dissimilar metal weld joint in primary pressurized water reactor environment

Stress corrosion cracking(SCC) of an SA508-309 L/308 L–316 L dissimilar metal weld joint in primary pressurized water reactor environment was investigated by the interrupted slow strain rate tension tests following a microstructure characterization. The 308 L weld metal shows a higher content of δ ferrite than the 309 L weld metal. In addition, no obvious Cr-depletion but carbides precipitation at δ phase boundaries was observed in both 308 L and 309 L weld metals. The slow strain rate tension tests showed that the SCC susceptibility of the base and weld metals of the dissimilar metal weld joint follows the order of SA508 < 308 L weld metal < the heat affected zone of 316 L base metal < 309 L weld metal.The higher SCC susceptibility of 309 L weld metal than that of 308 L weld metal is likely due to the lower content of δ ferrite. In addition, a preferential SCC initiation in the 309 L weld metal adjacent to 308 L weld metal is attributed to few carbides in this region.

铝合金/钢异种金属激光熔钎焊技术研究进展

铝合金/钢异种金属激光熔钎焊技术具有能量密度高、升温和冷却速度快、熔化位置控制精确、焊后变形小、自动化程度高等优势,特别适用于汽车制造行业。从铝合金与钢界面润湿铺展、界面微观调控、熔钎焊接头性能评价三个方面对国内外铝合金/钢异种金属激光熔钎焊技术的研究成果进行了综述,重点介绍了金属镀层、钎剂、母材热场对铝合金与钢激光熔钎焊过程中的界面润湿铺展的影响,归纳了界面热场、辅助能场、坡口面角度、合金元素对铝合金与钢激光熔钎焊过程中的界面微观调控作用,总结了铝合金与钢激光熔钎焊接头性能的评价方法。并指出优质、高效、高可靠的铝合金/钢异种金属激光熔钎焊技术仍需要解决以下四方面的问题:钢母材表面钎料润湿铺展的精准可控;铝合金/钢激光熔钎焊界面反应的精确可调;铝合金/钢激光熔钎焊接头的高强韧设计;铝合金/钢熔钎焊接头性能的可靠性评价。