Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co.

Shanghai, China

Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co.

Shanghai, China
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Wang X.,Shanghai JiaoTong University | Shao C.,Shanghai JiaoTong University | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | Lu F.,Shanghai JiaoTong University
Journal of Materials Science and Technology | Year: 2017

This work focused on the low-cycle fatigue (LCF) behavior of modified 9Cr/CrMoV dissimilar welded joint at elevated temperature. Narrow gap submerged arc welding (NG-SAW) process via multi-pass and multi-layer techniques was employed to fabricate the welded joint. LCF tests at different strain amplitude range from 0.22% to 0.75% were performed at strain ratio R = -1. The two-slope behavior based on fracture location shift was presented both on the cyclic stress-strain (CSS) curve and Manson-Coffin (M-C) curve, which could be applied to predict the fatigue life more precisely especially at relatively low strain amplitude. The results indicated that the joint failed in CrMoV-base metal (BM) at relatively low strain amplitude below 0.4% while failure shifted to CrMoV-over tempered zone (OTZ) at higher strain amplitude above 0.4%. Fatigue failure occurred in CrMoV-BM at low strain amplitude could be attributed to temperature softening effect in CrMoV-BM combined with cyclic strengthening in CrMoV-OTZ. While CrMoV-OTZ with a comparable number of grain boundaries and much lower hardness than that of CrMoV-BM was deemed to be the weakest zone across the welded joint at higher strain amplitude. EBSD investigations also revealed that CrMoV-BM experienced more fatigue damage at relatively low strain amplitude, while CrMoV-OTZ accumulated more plastic strain at higher strain amplitude. © 2017.


Xu H.,Shanghai JiaoTong University | Liu W.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Wang P.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | Ding Y.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co.
Materials Characterization | Year: 2017

The carbides evolution affected by heating will have great effect on the mechanical property of welded components. The paper focused on the microstructure characterization and carbides evolution under different thermal cycle in narrow-gap tungsten inert gas welding (NG-TIG) on Alloy 617B. The carbides were characterized to be M23C6 by TEM in 617B base metal (BM), which distribute along the grain boundaries and within the grains in roughly similar size and characteristics. However, many kinds of multi-carbides and various characteristics were found in heat affected zone (HAZ) with different distance to fusion line, which contributed to different heating peak temperatures (Tp). As the Tp reaches the solvus temperature of M23C6 carbides, M23C6 carbides show partial dissolution and M6C will form at the interface γ/M23C6 due to the segregation of element Mo. Upon the eutectic temperature, the surviving M23C6 carbides react with the surrounding γ matrix and then it leads to the formation of liquid film. Some phases with lamellar structure composed of M6C and M23C6 multi-carbides and islands of γ-austenite will occur as the temperature decreases. In addition, a large number of fine granular Cr-rich second phases like texturing morphology, scattered around each new kind of multi-carbide after the post weld heat treatment (PWHT). Basing on the analysis result, it can be seen that the evolution behavior of carbides is determined by the thermal input during NG-TIG welding process. No adverse effects, such as liquation cracking, have been brought into the welded joint due to the low thermal input, proving that NG-TIG is a suitable welding method to join Alloy 617B. © 2017 Elsevier Inc.


Wu Q.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Cui H.,Shanghai JiaoTong University | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | And 2 more authors.
Materials and Design | Year: 2014

The present work aims at studying the role of butter layer (BL) in low-cycle fatigue (LCF) behavior of modified 9Cr steel and CrMoV steel dissimilar welded joint. The significant difference of the chemical composition of base metals (BMs) makes it a challenge to achieve sound welded joint. Therefore, buttering was considered to obtain a transition layer between the dissimilar steels. The LCF tests of two kinds of specimens without and with butter layer were performed applying strain-controlled cyclic load with different axial strain amplitudes. The test results indicated that the number of cycles at higher strain amplitudes of welded joint without butter layer was greatly higher than that of the joint with butter layer, while the fatigue lifetime to crack initiation (2. Nf) became closer to each other at low and middle strain amplitudes. The failure was in the tempered heat affected zone (HAZ) at the CrMoV side for specimens without BL, while the fracture occurred at the tempered HAZ in the BL for specimens with BL. The microstructure details of BM, BL, HAZ and weld metals (WMs) were revealed by optical microscopy (OM). It was found that the tempered martensite was major microstructure for welded joint and much more carbides were observed in tempered HAZ than other parts due to the repeated tempering. Microhardness test indicated a softest zone existing tempered HAZ of BL and also there was a softer zone in tempered HAZ at the CrMoV side due to repeated tempering during welding and post weld heat treatment (PWHT). And scanning electron microscopy (SEM) was applied to observe the fractography. It was indicated that the fatigue crack initiation occurred from the specimen surface and all specimens were ductile-brittle mixed fractures. It is deemed that the softening behavior in BL caused by twice tempering correspondingly decreased the LCF lifetime at higher strain amplitudes. So suitable welding parameters and heat treatment processes became a key measure to ensure LCF property without losing other properties for welded joint with BL. © 2014 Elsevier Ltd.


Wu Q.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Lu F.,Shanghai Key Laboratory of Modem Metallurgy and Materials Processing | Cui H.,Shanghai JiaoTong University | And 3 more authors.
Materials Science and Engineering A | Year: 2014

Advanced 9% Cr and CrMoV steels chosen as candidate materials are first welded by narrow-gap submerged arc welding (NG-SAW) to fabricate the heavy section rotor. The present work focuses on studying the high-cycle fatigue (HCF) behavior of advanced 9% Cr/CrMoV dissimilarly welded joint at different temperatures. Conditional fatigue strength of this dissimilarly welded joint was obtained by HCF tests at room temperature (RT), 400°C and 470°C. It was observed that the failure occurred at the side of CrMoV base metal (BM), weld metal (WM) and heat affected zone (HAZ) of CrMoV side over 5×107 cycles for the specimens tested at RT, 400°C and 470°C. The detailed microstructures of BMs, WMs and HAZs as well as fracture appearance were observed by optical microscopy (OM) and scanning electron microscopy (SEM). Precipitation and aggregation of carbides along the grain boundaries were clearly detected with the increase of temperature, which brought a negative effect on the fatigue properties. It is interesting to note that the inclusion size leading to crack initiation became smaller for the HCF test at higher temperature. Therefore, reduction in the inclusion size in a welded joint helps to improve the HCF performance at high temperature. © 2014 Elsevier B.V.


Ren W.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Yang R.,Shanghai Turbine Works Company | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | Li Z.,Shanghai JiaoTong University
Journal of Materials Processing Technology | Year: 2015

Abstract Liquation cracking in the fiber laser welding Inconel 617 joint under different heat input and preheating conditions was systemically investigated. Liquation cracking is prevalent in the necking region of the welded fusion zone. The liquation of the grain boundaries (GBs) is mainly caused by the constitutional liquation of M23(C,B)6 carbides. The continuous (Cr, Mo)-rich phase is re-solidified due to the continuous liquid film along GBs during the solidification. The continuous (Cr, Mo)-rich phase decreases as the heat input and preheating temperature increases. The presence of the GB resolidified phase around liquation cracking is one of the features in the formation of liquation cracking. As well as, liquation cracking in heat affected zone (HAZ) would also decrease with increasing heat input and preheating temperature in the fiber laser welding of Inconel 617. © 2015 Elsevier B.V.


Guo Q.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Cui H.,Shanghai JiaoTong University | Yang R.,Shanghai Turbine Works Company | And 2 more authors.
Journal of Materials Processing Technology | Year: 2015

Crack propagation behavior in different zones of advanced 9Cr/CrMoV dissimilar steel welded joint was simulated by ABAQUS software. The Gurson-Tvergaard-Needleman (GTN) damage model and brittle cracking model were introduced to analyze the crack propagation behavior for ductile and brittle region on the dissimilar steel welded joint, respectively. It is found that the numerically calculated J-Δa resistance curves for the ductile regions i.e., the CrMoV base metal (CrMoV-BM), the heat affected zone of CrMoV (CrMoV-HAZ) and weld metal (WM) matched the experimental results, implying the reliability of the model developed in the present study. Three cases with different initial crack length (a0) were simulated to probe into the effect of a0 on the crack propagation resistance. The simulated results revealed that higher equivalent plastic strain and stress triaxiality occurred on the right ahead of the crack tip for longer initial crack length, which induces the lower crack propagation resistance. The brittle crack propagation behavior in 9Cr base metal (9Cr-BM) and heat affected zone of 9Cr (9Cr-HAZ) was well simulated by the brittle cracking model. The local stress distribution around the crack tip before crack destabilization could be obtained from the established model for BM and HAZ of 9Cr steel. © 2015 Elsevier B.V. All rights reserved.


Ren W.,Shanghai JiaoTong University | Lu F.,Shanghai JiaoTong University | Yang R.,Shanghai Turbine Works Company | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | And 2 more authors.
Materials and Design | Year: 2015

A comparative study on the influence of fiber laser welding (FLW) and CO2 laser welding (CLW) on the weld bead geometry and the microstructure of fusion zone (FZ) of Inconel 617 was investigated. In CLW joints, the weld bead geometry is Y-type shape. In FLW joints, the weld bead geometry transforms from Y-type to I-type with the decrease of the heat input. The minimum heat input required to achieve the full penetration of the weldment in FLW is lower than the CLW. The melting efficiency in FLW is higher than that in CLW. From the top to the root regions, the secondary dendrite arm spacing (SDAS) in fiber laser welded FZ undergoes a smaller change than that in CO2 laser welded FZ. The elements of Ti, Mo, Cr and Co segregate into the interdendritic regions both in FLW and CLW process. The second phases in CLW with the highest input of 360J/mm are much larger and more than ones in FLW with the highest heat input of 210.5J/mm. © 2015 Elsevier Ltd.


Wei Y.,Shanghai JiaoTong University | Wei Y.,Collaborative Innovation Center for Advanced Ship and Deep Sea Exploration | Qiao S.,Shanghai JiaoTong University | Qiao S.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | And 4 more authors.
Materials and Design | Year: 2016

Creep rupture behavior and microstructure evolution of modified casting 9Cr-1.5Mo-1Co steel welded joint were systematically investigated in this paper. Based on a series of creep rupture tests at 620 °C under 110-170 MPa, a curve of stress versus rupture time was achieved to evaluate the service life of welded joint. The results indicated that creep rupture is considered to occur in over tempered zone (OTZ) under relatively high stress above 130 MPa while failure transferred to weld metal (WM) under lower stress below 130 MPa. The ruptured specimens showed less ductility and necking with the decrease of stress. Microstructure characterization revealed OTZ with less grain boundaries than WM and relatively lower hardness than BM was more possible to deform in short-term creep rupture accompanied by the coarsening of M23C6. Besides, formation of Laves phase and deterioration of martensite lath structure were detected during long-term creep exposure. Mo segregation near M23C6 provided the condition for Laves phase to form adjacent to M23C6. The difference of plastic deformation resistance in each zones of welded joint and nucleation and coarsening of Laves phase in WM are considered as the main factors to result in the failure transition. © 2016 Elsevier Ltd.


Wu W.,Key Safety Systems | Zhu M.-L.,Key Safety Systems | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | Xuan F.-Z.,Key Safety Systems
Fatigue and Fracture of Engineering Materials and Structures | Year: 2016

Axially push-pull fatigue tests of a low-strength Cr-Ni-Mo-V steel welded joint were conducted up to very high cycle fatigue regime at room temperature and 370°C. The S-N curve at room temperature shows a duplex shape, while the S-N curve at 370°C is continuously decreasing with lower fatigue strength. The welds at 370°C undergoes dynamic strain ageing and has an enhanced load-defects interaction, leading to equal distribution of failures among different parts of the welds. The Z parameter model, with micro-defect location incorporated, having sound physical representation, is life-controlling of the welds at high temperature. © 2016 Wiley Publishing Ltd.


Du Y.-N.,East China University of Science and Technology | Zhu M.-L.,East China University of Science and Technology | Liu X.,Shanghai Turbine Plant of Shanghai Electrical Power Generation Equipment Co. | Xuan F.-Z.,East China University of Science and Technology
Journal of Materials Processing Technology | Year: 2015

Effect of thermal aging at 350 °C for 3000 h on near-threshold fatigue crack growth (FCG) behavior of a Ni-Cr-Mo-V steel welded joint was investigated at various load ratios, R. FCG resistance of base metal after long-term aging was decreased and found to be dominated by microstructure influence; whilst FCG was controlled by R in weld metal due to microstructure homogeneity. Degradation of FCG threshold was assessed using a quantitative parameter. A microscopic interpretation of FCG threshold showed the predominant role of characteristic microstructure size. A model for fatigue threshold prediction involving the long-term aging effect was developed, and able to evaluate the stability of near-threshold FCG resistance of the welds in case of long-term service exposure. © 2015 Elsevier B.V. All rights reserved.

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