焊后热处理对海洋平台用钢焊缝低温断裂韧性的影响北大核心

分别采用焊条电弧焊(2G,3G)、CO2气体保护焊(2G,3G)与埋弧焊(2.0 k J/mm,3.5 k J/mm)工艺得到板厚分别为80 mm,80 mm,100 mm焊接接头。将试样均分为两组,根据英国BSI 7448—2005《断裂韧性试验标准》,分别进行焊态和热处理态低温断裂韧性(CTOD)测试。结果表明,相同热处理工艺对不同焊接方法焊缝中心线CTOD值影响不同。FCAW接头的低温韧性对热处理敏感性较低,热处理前后2G与3G位置的CTOD值都基本不变;埋弧焊接头断裂韧性提升幅度较小,低热输入下CTOD约提高5%,高热输入下约提高32%;焊条电弧焊2G和3G位置CTOD值分别提高14.15倍和1.5倍。试验结果为评价这几种焊接方法和相应板厚焊接接头的免除热处理提供了一定依据。     

焊后热处理对DH36钢焊接接头断裂韧性的影响

文中对DH36钢埋弧焊焊接接头进行了焊后热处理,并根据BS7448标准对焊缝和热影响区进行裂纹尖端张开位移CTOD测试,研究焊后热处理对断裂韧性的影响.结果表明,焊后热处理对焊缝断裂韧性的影响并不一定是好的效果,热处理后,焊缝δ值有的升高有的降低;焊后热处理对热影响区粗晶区的断裂韧性有不利影响,热处理后,热影响区粗晶区的δ值均有所下降.经过焊后热处理,90 mm厚焊缝试样的δ值略有下降,60mm厚焊缝试样的δ值明显升高;90mm厚热影响区试样的δ值明显下降,60mm厚热影响区试样的δ值略有下降.     

100 mm厚S420高强钢的热处理工艺及焊接性能

采用低C低Si、Ni+Cr+Mo+Cu复合强化的理念设计了100 mm厚的S420高强钢,对钢板焊接前后的微观组织、力学性能和裂纹尖端张开位移CTOD进行了观察和测试.试验结果表明:经过900℃淬火+580℃回火后,钢板的综合性能达到最佳,屈服强度为478 MPa,抗拉强度为581 MPa,伸长率为28.4％;钢板焊后...     

X70海底管线低温断裂韧性试验研究

根据BS7448断裂韧性试验标准,对国内自主研发的X70海底管线钢管管体及焊接接头的低温(0℃)裂纹尖端张开位移(CTOD)进行断裂韧性试验,并对其阻力曲线及断口形貌进行了研究分析.结果表明:0℃下管体的CTOD值大于焊接接头,且管体横向略大于管体纵向;熔合线+5 mm位置试样的CTOD值接近管体横向;焊缝、熔合线及熔合线+2mm位置试样的CTOD值相对较低,易产生突进或失稳现象,是断裂韧性最薄弱的部位.     

钢箱梁焊接接头的断裂韧度评定

采用冲击试验评定钢箱梁焊接工艺存在局限性,指出用裂纹尖端张开位移(CTOD)试验评定钢箱梁焊接工艺的优越性.介绍了焊接工艺CTOD断裂韧度评定的方法.针对港深西部通道香港段后海湾大桥钢箱梁焊接建造,运用英国标准BS7448对两项拟用焊接工艺进行CTOD试验评定.结果表明,埋弧自动焊工艺焊接接头的CTOD断裂韧度较高,该工艺可以直接用于钢箱梁焊接施工;而焊条电弧焊工艺焊接接头的CTOD断裂韧度较低,经扫描电子显微镜断口分析和X射线分析,发现其原因是焊缝中心存在气泡、微裂纹、夹杂物和硫等有害元素.试验评定结果为港深西部通道香港段后海湾大桥钢箱梁焊接质量控制提供了依据.     

X65管线钢焊接接头CTOD断裂韧度

根据BS74 4 8断裂韧度试验标准 ,对X6 5管线钢焊接接头的低温 (0℃ )裂纹尖端张开位移 (CTOD)进行了测试。取尺寸为B× 2B(B为试样厚度 )、缺口方向为NP的试样进行三点弯曲试验 ,然后由所得到的 0℃下母材、焊缝和热影响区 (HAZ)的P -V曲线来计算CTOD值 ,并对试验结果进行了讨论和总结。对显微组织的分析表明 ,共有3个HAZ试件不满足裂纹尖端不超过熔合线 0 .5mm且落在粗晶区内的要求。该结果恰好与P -V曲线和所得的CTOD值相一致 ,从而解决了试验值分散性大的问题 ,同时为ECA评估提供了重要依据 ,验证了BS74 4 8标准的合理性并体现了它的优越性。     

超超临界锅炉水冷壁T23/12Cr1MoV异种钢焊接接头焊后热处理裂纹分析

分析了T23/12Cr1MoV异种钢焊接接头焊后热处理裂纹的宏观和微观特征、断口形貌及接头的显微组织,测试了接头的硬度分布,在此基础上讨论了裂纹的性质及形成原因,并提出了防止裂纹的措施。结果表明,裂纹启裂于T23钢侧焊趾部位,沿粗晶粒热影响区(CGHAZ)晶界扩展,为典型的再热裂纹。焊后热处理明显降低了异种钢焊接接头两侧热影响区的硬度,T23钢侧CGHAZ产生再热裂纹与其在焊后热处理过程中晶界析出碳化物有关,其析出促进了孔洞的形成。在焊后热处理前,对异种钢焊接接头进行一次550 ℃×1 h的中间热处理有利于抑制再热裂纹的产生。     

9Ni钢焊接接头裂纹尖端张开位移试验研究

通过CTOD试验测试了液化天然气(LNG)储罐用9Ni钢埋弧焊(SAW焊)和TIP-TIG焊(简称TT焊)焊接接头的断裂韧性,分析了接头组织对断裂性能的影响。结果表明：SAW焊和TT焊接头CTOD值均能够满足相关工程标准要求,焊接接头达到失稳破坏时,TT焊接头需要更大的力,接头强度更高;SAW焊焊缝金属以长条状的胞状树枝晶为主,其间胞状晶,TT焊焊缝金属为细小均匀分布的胞状晶构成,细小均匀分布的胞状晶能够增加裂纹扩展抗力,利于提高焊缝金属韧性;TT焊应用于LNG储罐立焊缝,不仅可以去除打磨清根环节,还具有与SAW焊相当的焊接效率和焊接质量,自动化程度高,因此,具有很高的发展潜力。     

全焊接管线球阀抵抗地质灾害能力研究

为研究全焊接管线球阀在地质灾害下的安全性,参照《建筑抗震设计规范》,从PEER数据库选取两条天然地震波,用Simqke gr软件合成一条人工地震波作为地震载荷,然后利用时程分析法计算阀门的地震响应;针对地陷灾害,查阅相关文献及规范,提出适用于不同管径、不同埋深的地陷载荷计算公式,并计算阀门在该载荷下的安全性。结果表明：阀门在地震及地陷载荷下,危险位置均出现在左、右阀体与管道连接位置,与实际相符。然后利用JB 4732—1995《钢制压力容器分析设计标准》进行评价,阀门安全裕度较大,在地震及地陷载荷下安全。研究方法为同类阀门设计提供了参数依据,同时为天然气管道设备及构件抵抗地质灾害能力提供了参考。     

海底管线用钢低温断裂韧度的试验研究和数值模拟

根据BS7448断裂韧度试验标准,对X65管线钢焊接接头的低温(-15℃)裂纹尖端张开位移(CTOD)进行了测试并对其进行了三维有限元数值模拟.试验取标准三点弯曲试样,然后根据试验得到的p-V曲线来计算CTOD值,并对试验结果进行了讨论和总结.尤其是对试验后试样的断面分析,验证了试验结果的有效性,从而解释了试验值分散性大的问题.通过有限元分析得到了计算的p-V曲线,该p-V曲线落在试验测得的p-V曲线区间内,说明有限元分析的正确性.因此,在没有其它方法可获得的情况下,能够用有限元数值模拟进行分析计算.     

Effects of Post-Weld Heat Treatment on Microstructure and Mechanical Properties of Al-12.7Si-0.7Mg Alloy Welded Joints by GMAW

In this study, 3-mm-thick hot-extruded plates of A1-12.7Si-0.7Mg alloy were used to fabricate the joints welded by gas metal arc welding. Effects of the post-weld heat treatment include solid solution treatment, water quenching, and artificial aging treatment on the microstructure, and mechanical properties of the weld joints have been investigated. Results showed that the welded joints after solid solution and artificial aging exhibited the increases in yield strength of 166 MPa and ultimate tensile strength of 148 MPa, respectively. Based on the microstructural observations, the associated mechanisms were discussed.     

Weldability and toughness evaluation of pressure vessel quality steel using the shielded metal arc welding (SMAW) process

The present study was carried out to assess the weldability properties of ASTM A 537 Cl. 1 pressure-vessel quality steel using the shielded metal arc welding (SMAW) process. Implant and elastic restraint cracking (ERC) tests were conducted under different welding conditions to determine the cold cracking susceptibility of the steel. The static fatigue limit values determined for the implant test indicate adequate resistance to cold cracking even with unbaked electrodes. The ERC test, however, established the necessity to rebake the electrodes before use. Lamellar tearing tests carried out using full-thickness plates under three welding conditions showed no incidence of lamellar tearing upon visual examination, ultrasonic inspection, and four-section macroexamination. Lamellar tearing tests were repeated using machined plates, such that the central segregated band located at the midthickness of the plate corresponded to the heat-affected zone (HAZ) of the weld. Only in one (no rebake, heat input: 14.2 kj cm^-1, weld restraint load: 42 kg mm^-2) of the eight samples tested was lamellar tearing observed. This was probably accentuated due to the combined effects of the presence of localized pockets of a hard phase (bainite) and a high hydrogen level (unbaked electrodes) in the weld joint. Optimal welding conditions were formulated based on the above tests. The weld joint was subjected to extensive tests and found to exhibit excellent strength (tensile strength: 56.8 kg mm^-2, or 557 MPa), and low temperature impact toughness (7.4 and 4.5 kg-m at-20 °C for weld metal, WM, and HAZ) properties. Crack tip opening displacement tests carried out for the WM and HAZ resulted in δ_m values 0.36 and 0.27 mm, respectively, which indicates adequate resistance to brittle fracture.