乙二醇不锈钢蒸发器开裂原因分析

采用金相分析、断口微观分析以及腐蚀产物能谱分析等方法，对某石化公司乙二醇不锈钢蒸发器开裂原因进行了分析和研究。结果表明，由于材料在焊接过程中，焊接热影响区的组织受到敏化，铬的碳化物沿晶界呈网状析出，造成该区域贫铬，从而在应力与腐蚀介质的共同作用下，导致设备发生了晶问应力腐蚀开裂。     

油罐导油法兰焊缝热影响区开裂分析

油罐导油法兰仅服役三个月即在焊接热影响区产生断裂。采用宏、微观以及化学分析等方法对开裂原因进行了分析。认为，材料中的铬、镍、钛含量过低和焊接过程对法兰接口处热影响区的敏化作用，致使晶界区域由于析出碳化铬而贫铬，当与腐蚀介质接触后产生晶间腐蚀和应力腐蚀而开裂。     

304奥氏体不锈钢管焊接接头开裂原因

304奥氏体不锈钢管使用过程中在焊接接头附近发生开裂现象,通过宏观和微观观察、化学成分分析、能谱分析和金相检验等方法对不锈钢管焊接接头的开裂原因进行了分析。结果表明:不锈钢管焊接接头的开裂形式为晶间腐蚀导致的沿晶开裂,主要原因是一侧不锈钢管的成分不符合标准,碳含量偏高、铬含量偏低,在焊接加热的过程中发生了焊接敏化现象,降低了焊接接头的耐腐蚀性能,导致焊接接头的热影响区产生腐蚀裂纹,此外钢管中输送的自来水中氯离子较多,提供了腐蚀环境,进一步促进了裂纹的扩展。     

球罐应力腐蚀开裂研究与安全性分析

对球罐应力腐蚀开裂的原因和主要影响因素进行了分析.针对16MnR和SPV50Q球罐用钢,在分析湿硫化氢环境下应力腐蚀开裂形式的基础上,通过改进的WOL预裂纹试样的应力腐蚀开裂试验,对不同球罐用钢、不同硫化氢浓度、不同焊接状态条件下的应力腐蚀开裂进行了研究,并对设备的安全性能进行了分析,进而提出了防止应力腐蚀开裂的对策.     

原子力显微镜评价奥氏体不锈钢晶间腐蚀敏感性的研究

由13Cr可焊马氏体不锈钢(WMSGSS)制造的油气管线由于价格便宜,相对于昂贵的耐腐蚀合金来说是一个很有竞争力的选择。但是实验室试验和现场经历表明,13Cr马氏体不锈钢焊接接头热影响区发生了沿晶应力腐蚀开裂(IGSCC)。对于低等级的马氏体不锈钢来说,沿晶应力腐蚀开裂机理被认为是在晶界的碳化物附近存在贫铬区。对于中等级和高等级马氏体不锈钢来说,只在实验室试验发现有应力腐蚀开裂。它们的应力腐蚀开裂机理还没有明确,虽然最可能的应力腐蚀开裂机理也被认为和低等级马氏体不锈钢的应力腐蚀开裂机理类似。原子力显微镜(AFM)已开始广泛用于材料显微组织和环境敏感断裂的研究中。高等级马氏体不锈钢焊接接头对晶间腐蚀/应力腐蚀开裂敏感性很有希望由原子力显微镜检测到。在原子力显微镜技术应用于这项研究之前,用由304不锈钢准备的不同敏化度的试样来确定它的适用性是十分有益的。本文用原子力显微镜研究了不同敏化程度的304不锈钢的晶间腐蚀敏感性并和SEM和EDS结果进行了对比。     

焊接工艺对Q345R的硫化物应力腐蚀敏感性的影响

为了探讨和分析焊接工艺对Q345R的硫化物应力腐蚀敏感性影响成因,在饱和硫化氢NACE A溶液中对手工焊接和氩弧焊打底后手工焊接的Q345R材料进行硫化物应力腐蚀开裂敏感性测试评价,采用SEM和硬度计研究分析了2种焊接工艺Q345R组织和性能的变化.试验结果表明:焊接工艺对Q345R钢的硫化物应力腐蚀开裂敏感性的差异源...     

金属波纹管补偿器的应力腐蚀开裂分析

采用宏观及微观断口分析、金相检验与化学成分检测等方法,对某铬一镍奥氏体不锈钢波纹管补偿器的腐蚀开裂失效原因进行了分析。结果表明：由于该铬一镍奥氏体不锈钢波纹管在氯离子含量超标的环境中服役,并承受来自于波纹管自身加工变形过程中形成的残余应力、工作应力以及装配应力,最终导致波纹管补偿器发生了由表及里的应力腐蚀开裂。     

染缸热交换器焊缝开裂原因分析

某纺织公司染缸热交换器在检修过程中发现焊缝及筒体附近母材出现裂纹。通过宏观分析、化学成分分析、硬度测试、金相检验和氯离子检测等方法对热交换器焊缝开裂的原因进行了分析。结果表明:该热交换器焊缝及筒体附近母材的开裂模式为应力腐蚀开裂。由于蒸汽冷凝水中氯离子质量浓度过高,在焊接残余应力和工作应力的共同作用下,焊缝发生应力腐蚀开裂。     

WP304WX管道泄漏原因分析

不锈钢管道使用5a(年)后出现泄漏事故。采用化学成分分析、硬度测试、金相检验、晶间腐蚀与断口扫描电镜分析方法,对泄漏原因进行了分析。结果表明:焊接过程中造成的贫铬及残余应力的存在导致了管道的开裂。建议对管道所有焊缝热影响区进行探伤,查找腐蚀裂纹,对发现的裂纹进行打磨和补焊处理,并进行消除残余应力处理。     

矩形脉动真空灭菌器内腔开裂原因

某医院矩形脉动真空灭菌器内腔发生开裂事故,通过宏观分析、金相检验和光谱分析等方法,结合工作介质,对内腔开裂的原因进行了分析。结果表明:灭菌器内腔与加强筋不连续焊接处存在焊接残余应力,且靠近内腔弯折处存在局部应力集中现象;灭菌器内腔的工作介质中含有氯离子,而氯离子水溶液是300系列不锈钢发生应力腐蚀开裂的敏感介质。灭菌器内腔在焊接残余应力、含氯离子介质等因素的综合作用下发生起始于靠近内腔弯折的焊接起始处的应力腐蚀开裂。     

Failure investigation of a convection line elbow

Failure investigation was carried out on a cracked 5″ 304L stainless steel elbow tube for the convection line of an ethylene furnace. The crack was observed in the heat-affected zone (HAZ) at the end leading to the elbow parent material. The crack was along the circumference and was about 12″ in length. The crack started from the toe of the weld to the parent metal on the elbow side. The failure investigation revealed that the HAZ of the elbow tube suffered from stress corrosion cracking and mild grain boundary carbide precipitation during welding. The carbide precipitation was possibly due to improper welding practices such as high heat input and/or extended welding time. The tube thickness, which is relatively thick, was a contributing factor in making proper welding more difficult.     

HMn58-2铜制冷却器开裂失效分析

某HMn58-2铜制冷却器在库房存放4a后开裂,采用光学显微镜、力学性能试验机和布氏硬度计对开裂冷却器进行了检验和分析。结果表明:由于焊接工艺或者焊接操作不当造成的热影响区晶粒粗大和α-Cu相自β相晶界大量析出形成魏氏组织形态,降低了材料的韧性、塑性和强度;此外,冷却器铜板冷卷后没有及时进行退火处理,使得材料内部存在较大的内应力;两方面共同作用导致冷却器在存放过程中于焊缝处萌生裂纹并不断扩展最终造成开裂失效。     

Single pass laser joining of Inconel 718 superalloy with filler

Abstract

Microstructure and mechanical property of CO₂ laser beam welded IN 718 superalloy were studied by electron microscopy and hardness testing. The use of a welding filler wire produced a sound fusion zone with no cracking but grain boundary microfissuring occurred in the heat affected zone (HAZ) and was observed to be significantly influenced by pre-weld heat treatment and laser welding speed. Crack-free weld was produced by a pre-weld heat treatment that minimised non-equilibirum grain boundary boron segregation and inhibited grain growth. While post-weld heat treatment (PWHT) reduced the difference between the hardness values of the base alloy, HAZ and the fusion zone, it resulted in increased HAZ cracking, which was likely aided by pre-existing cracks. The PWHT cracking was, however, avoided by subjecting pre-weld material to the heat treatment condition that produces crack-free weld during welding process.     

Mechanism of intergranular reheating crack in butt-welded joint of 12Cr1MoV tube served for 40,000 hours

Cracking failure of butt-welded joint of 12Cr1MoV tube was comprehensively studied. Results show that both of initiation and propagation of the primary crack were circumferentially intergranular in the coarse-grained heat affect zone (CGHAZ). Many isolated and intergranular micro-cracks and cavities were observed near the primary crack．Neither oxide or corrosion products were observed in the isolated cavities or micro-cracks. According to the microstructure, location, propagation mode and morphology of the crack,the primary crack in butt-welded joint is concluded to be the intergranular reheating cracking (IRC). The crack failure is mainly due to poor welding quality, characterised by high residual stress and coarsened grain size. Mechanisms on the IRC based on previous laboratory research were studied on the failed tube sample, and results showed that the IRC is accumulation of high-stress induced creep damage, such as cavities along prior austenite grain boundaries (PAGBs). Neither segregation of alloys elements nor trace impurities were detected.     

核用SA508-4N钢粗晶区再热裂纹敏感性评价

采用等温恒速拉伸方法评价了核用SA508-4N钢焊接粗晶区(CGHAZ)的再热裂纹敏感性。使用激光共聚焦、扫描电镜和透射电镜观测和分析粗晶区和断口处的组织、裂纹以及断口形貌,结果表明：SA508-4N钢的母材为回火马氏体,较高含量的碳和铬影响碳化物的大小和分布状态,粗晶区马氏体的形成不利于抑制再热裂纹的产生。碳化物的析出使晶内和晶界的强度不同,当晶内强度大于晶界强度时形成沿晶脆性断裂;当晶内和晶界强度的差距较小时断裂形式包括穿晶和沿晶断裂。SA508-4N钢粗晶区对再热裂纹不敏感,成分A粗晶区的抗再热裂纹能力比成分B的高。在实际生产中,优选的工艺参数为：成分A、焊接t_8/5为25 s、焊后热处理温度580℃。     

微量Sc对Al-Zn-Mg合金焊接接头组织和性能的影响

使用光学显微镜、扫描电镜和透射电镜分析了Al-Zn-Mg合金和含微量钪的Al-Zn-Mg合金钨极氩弧焊接头的微观组织,并对其力学性能和耐应力腐蚀性能进行了对比。结果表明：在传统Al-Zn-Mg合金板材熔合线附近的热影响区出现再结晶和晶粒异常长大,而含钪Al-Zn-Mg合金基体中热稳定性优良的纳米Al₃(Sc, Zr, Ti)相在焊接过程中能阻碍晶界迁移,抑制再结晶晶粒的形核和长大,进而细化熔合线附近的组织。同时,含微量钪的Al-Zn-Mg合金焊接接头的强度明显比传统合金的高,其强化效果主要来源于熔合线附近区域的细晶强化和二次Al₃(Sc, Zr, Ti)相的弥散强化。     

On preventing HAZ cracking in laser welded DS Rene 80 superalloy

Abstract

The heat affected zone (HAZ) cracking behaviour in a laser beam directionally solidified (DS) Rene 80 nickel based superalloy subjected to preweld heat treatments was studied. The HAZ cracks in the alloy are grain boundary liquation cracks caused by liquation reaction of both non-equilibrium secondary solidification product, MC carbides and equilibrium solid state reaction product, γ′ precipitates. In contrast to theoretical prediction based a preweld heat treatment that reduced grain boundary liquid film thickness did not result in a lower HAZ cracking, which can be related to concomitant reduction in the ability of the base alloy to relax welding stress. In addition, formation of intergranular M₅B₃ boride particles in preweld alloy appeared to have aided cracking susceptibility by lowering grain boundary liquation temperature and widening the brittle temperature range in the HAZ during cooling. Based on the analysis of the results, application of a new preweld heat treatment that prevents the formation of the intergranular borides and induces moderate base alloy hardness resulted in a nearly crack free HAZ in laser welded DS Rene 80 superalloy.     

Effect of minor Sc addition on microstructure and stress corrosion cracking behavior of medium strength Al–Zn–Mg alloy

Influence of Sc content on microstructure and stress corrosion cracking behavior of medium strength Al–Zn–Mg alloy have been investigated by optical microscopy, scanning electron microscopy, electron backscatter diffraction, transmission electron microscopy and slow strain rate test. The results indicate that the addition of Sc results in the formation of the quaternary coherent Al_3(Sc, Zr, Ti) dispersoids during homogenization treatment, which will inhibit the dynamic recrystallization behavior. The number density of Al_3(Sc, Zr, Ti) particles increases with the increase of Sc content, and thus the recrystallization fraction of hot-extruded alloy is reduced and the peak strength in two-stage artificial aging sample is enhanced. At the same time, the wide of precipitation free zone is reduced, and the content of Zn and Mg in grain boundary particles and precipitation free zone is increased with the increase of Sc content. In peak-aged state, the 0.06 wt% Sc added alloy shows the better stress corrosion cracking resistance than the Sc-free alloy because of the reduction of recrystallization fraction and the interrupted distribution of grain boundary precipitates along grain boundary. However, the further addition of Sc to 0.11 wt% will result in the deterioration of stress corrosion cracking resistance due to the increase of electrochemical activity of grain boundary particles and precipitation free zone as well as hydrogen embrittlement.