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Chen J.Q.,Shanghai JiaoTong University | Yu C.,Shanghai JiaoTong University | Chen J.M.,Shanghai JiaoTong University | Lu H.,Shanghai JiaoTong University | Zhang M.L.,Shanghai Electrical Nuclear Power Equipment Co.
Science and Technology of Welding and Joining | Year: 2012

Alloy 690 is a Ni-Cr-Fe type alloy with a widespread application in nuclear power plants. However, the companion filler metal 52M (FM-52M) is susceptible to ductility dip cracking (DDC), which seriously affects safety and life extension in nuclear application. To provide a better understanding of DDC formation in the varestraint test, local strain is adopted to assess materials resistance of DDC instead of average bending strain. In this work, spot varestraint tests of FM52M were performed with an average strain (0·25-7%). Then, a thermomechanical simulation of the spot varestraint tests was modelled based on the experiment. The simulation obtained preferential propagation orientation of DDC and accumulated strain increment during a susceptible temperature range. Simulated local strain caused at an elevated temperature is much larger than the average strain. Besides, prediction of DDC distribution agrees well with experimental results. The finite element model presents a clear local strain distribution and provides an extra understanding of DDC formation. © 2012 Institute of Materials, Minerals and Mining.


Ou P.,Shanghai JiaoTong University | Sun J.,Shanghai JiaoTong University | Zhang M.-L.,Shanghai Electrical Nuclear Power Equipment Co. | Wei Y.,Shanghai Nuclear Power Office
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2013

SA508Gr.3 Cl.2/316L dissimilar steel welding joints were produced by tungsten inert gas (TIG) welding using ERNiCr-7 (Inconel52M) welding wires. Microstructure and hardness of the welding joints were investigated by optical microscope, transmission electron microscopy and microhardness test. The results show that the weld metal are composed of coarse dendritic solidification structure, M23C6 carbides precipitated along grain boundaries and a small amount double layer inclusions, which are generated by coupling growth of Ti(C, N) carbon nitrides and Al2MgO4 compounds inside grains. There exists a heat affected zone (HAZ) of about 3 mm wide granular bainite in SA508Gr.3C1.2 low-alloy steel of the welding joints, of which the microhardness is higher than that of the upper bainite in SA508Gr.3C1.2 matrix. No obvious HAZ is observed in the 316L austenitic stainless steel of the welding joints, of which the microhardness almost does not change.


Chen J.Q.,Shanghai JiaoTong University | Lu H.,Shanghai JiaoTong University | Yu C.,Shanghai JiaoTong University | Chen J.M.,Shanghai JiaoTong University | Zhang M.L.,Shanghai Electrical Nuclear Power Equipment Co.
Science and Technology of Welding and Joining | Year: 2013

Inconel 690 and the companion filler metal 52M (FM-52M) have susceptibility of ductility dip cracking (DDC) in welding procedure. According to test results, DDC was not only preferential to propagate on grain boundaries vertical to loading direction but also related to grain boundary structure. To reveal the relation of grain boundary angle and cracking, a three-dimensional polycrystalline model was constructed to simulate the formation of DDC. In this work, the initiation and propagation of DDC were studied based on extended Read-Shockley formula. The results indicate that grain boundaries with approximate 45 ° disorientation are most prone to cracking, and the simulated DDC morphology shows agreement with experimental results. The study provides an extra method to predict DDC propagation and helps to evaluate DDC susceptibility in grain level. © 2013 Institute of Materials, Minerals and Mining.


Wei X.,Shanghai JiaoTong University | Xu M.,Shanghai JiaoTong University | Wang Q.,Shanghai JiaoTong University | Zhang M.,Shanghai JiaoTong University | And 7 more authors.
Materials and Design | Year: 2016

The multi-pass ERNiCrFe-7A overlay depositions, produced by cold wire feed (CWF) or hot wire feed (HWF) gas tungsten arc welding (GTAW) process with typical parameters, were employed to investigate the effects of different micro-characteristics on ductility-dip cracking (DDC) susceptibility. The results show that, the HWF-produced deposit exhibited the texture with larger quantity of 〈001〉 oriented grains in the pass region (away from the fusion line), while the CWF-produced deposit was weakly textured with increased crystallographic misorientation for the higher heat input per unit volume. Crystal misorientation also increased in the interpass region (near the fusion line) of both the overlays. Results of strain-to-fracture (STF) tests indicated that the overall DDC resistance in the deposit CWF was lower than that in the deposit HWF. And the interpass region exhibited higher DDC susceptibility than the pass region. The intergranular cracking is found to be triggered by the strain accumulation between differently oriented grains. Meanwhile, both the over 30° misorientation angle and melting of Cr-rich M23C6 carbides reduced the grain boundary (GB) strength and promoted the cracking. Therefore, the DDC resistance would be increased by decreasing the GBs those have misorientation angles over 30°, as well as the carbides distributed on the GBs. © 2016


Li G.,Shanghai Key Laboratory for Engineering Materials Evaluation | Fang K.,Shanghai Key Laboratory for Engineering Materials Evaluation | Peng J.,Shanghai Key Laboratory for Engineering Materials Evaluation | Yang W.,Shanghai Key Laboratory for Engineering Materials Evaluation | And 2 more authors.
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2011

The stress corrosion cracking (SCC) behavior of advanced dissimilar metal weld A508/52M/316L in simulated primary water environments of pressurized water reactor (PWR) at 290 _ was investigated by means of slow strain rate testing (SSRT). The tests were performed at various applied electrode potentials which correspond to the electrochemical conditions of the weld in various water environments, from low potentials with ideal water chemistry to high potentials with oxygen-contaminated water chemistry. The weld exhibits complicated microstructure and chemical composition distributions, especially, significant changes appear around the A508/52M interface and the 52M/316L interface. For tensile specimens in SSRT, sharp notches were machined at important and typical places, i. e., at the two interfaces and in the bulk parts of the low alloy steel, Ni base weld metal and stainless steel of the weld. Results showed that the specimens always failed in bulk zone of the Ni base weld metal with ductile appearances when tested in the potential range from -780 mV to -300 mV (vs SHE). When electrode potential was raised into the range from -200 mV to +200 mV which corresponds to oxygen-contaminated water chemistry, the weld exhibits significant SCC. The area around the A508/52M interface is the weakest place, transgranular stress corrosion cracking (TGSCC) happened both along the interface and in A508 heat affected zone (HAZ), intergranular stress corrosion cracking (IGSCC) occurred in the Ni base weld metal close to the interface. The cracking mechanism and the engineering practical significance were discussed. © Copyright.


Ding J.,CAS Shenyang Institute of Metal Research | Zhang Z.,CAS Shenyang Institute of Metal Research | Wang J.,CAS Shenyang Institute of Metal Research | Han E.-H.,CAS Shenyang Institute of Metal Research | And 6 more authors.
Jinshu Xuebao/Acta Metallurgica Sinica | Year: 2015

The dissimilar metal weld joint (DMWJ) in primary water system of pressurized water reactors (PWRs) has been proven to be a vulnerable component owing to its proneness to different type of flaws. Thus, maintaining integrity of such joint in case of defect presence is of great importance to the design and safe management of nuclear power plants (NPPs). For a reliable integrity analysis of DMWJ, it is essential to understand the microscopic characteristics in all regions of the joint. In this work, OM, TEM, SEM, durometer, AFM, MFM and SKPFM were utilized to investigate the microstructure, micro-hardness and the distribution of main elements, grain boundary characteristic and residual strain in the A508/52M/316L DMWJ that used for connecting the pipe safeend and the nozzle of reactor pressure vessel in PWRs, and a comparative analysis about the microstructure and property along the radical direction of the DMWJ was obtained. The results showed that there was no region that differed from the other part of the weldment in terms of the microstructure and micro-hardness dramatically. A layer of fine grain resulting from unmelted filler metal was found in the backing weld part of the joint. The residual strain in the heat affected zone (HAZ) of 316L was higher than that in other regions. Meanwhile, drastic variations in the microstructure, chemical composition distribution and grain boundary character distribution (GBCD) in both the 316L/52Mw and the 52Mb/A508 interface regions were observed. The analyses using TEM and MFM test showed that a large number of chromium and molybdenum-rich precipitates particles distributed both along the grain boundaries and inside grains in the 316L base metal, which were identified to be precipitates with complex elementary composition rather than the normal string delta ferrite in 316L austenitic stainless steel. The SKPFM test result indicated that these precipitates were more prone to be corroded than the base metal. Therefore, further investigation about the cause of deformation and the impacts to the corrosion resistance, particularly the stress corrosion cracking (SCC) sensitivity of the precipitates needs to be carried out. © Copyright.

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