MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A NEW CORROSION-RESISTING NICKEL-BASED ALLOY AND 625 ALLOY DISSIMILAR METAL WELDING JOINT
ZHAO Xia1,2, ZHA Xiangdong2, LIU Yang3, ZHANG Long2, LIANG Tian2, MA Yingche2(), CHENG Leming3
1 School of Materials and Metallurgy, Northeastern University, Shenyang 110819 2 Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 3 ENN Science & Technology Development Co. Ltd., Langfang 065001
Cite this article:
ZHAO Xia, ZHA Xiangdong, LIU Yang, ZHANG Long, LIANG Tian, MA Yingche, CHENG Leming. MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A NEW CORROSION-RESISTING NICKEL-BASED ALLOY AND 625 ALLOY DISSIMILAR METAL WELDING JOINT. Acta Metall Sin, 2015, 51(2): 249-256.
With the fast development of industry, pollution becomes a very serious problem. The industrial and life wastewater are discharged and cause the environment pollution. Supercritical water oxidation (SCWO) becomes the most effective method to treat the wastewater. But the material used in the equipment plays a key role in restricting the application of the SCWO process. Currently, during the SCWO wastewater treatment process, 304 austenitic stainless steel, Alloy 625, P91 and P92 steels are the main preheater and reactor materials. In order to reduce the serious corrosion and improve economic efficiency of the materials for this process, a new corrosion resistant Ni-based alloy X-2# alloy has been developed with an aim of replacing the previous ones. In particular, it is highly important to the related behavior of this new alloy welding with the original SCWO. Therefore, the microstructure and mechanical properties of the welding joint of the new alloy and alloy 625 with manual argon arc welding were investigated. The microstructure and fracture morphologies of the welding joint were analyzed by OM, SEM and EDX. The micro-hardness, tensile strength and other mechanical properties were tested and analyzed. The results indicated that more isometric crystals in remelting zone to improve the welding seam strength and the microstructure in fusion zone of X-2# side did not show welding defects. However, some NbC and Laves phases formed near the fusion zone of 625 alloy sides, which affected the mechanical properties of material. Due to the influence of two thermal cycles near the remelting zone, the grains of heat affected zone (HAZ) were easy to grow. But the thermal stability of X-2# side HAZ could reach excellent level. Fine grains of 625 parent material led to grain growth seriously in HAZ, which reduced its Vickers hardness. Because of the tensile strength of welding joints of room temperature and 500 ℃ was lower than the parent materials, the welding seam could be the weakest link. The tesile fracture of X-2#/625 dissimilar metal welding joint was dimple morphology。
Fig.1 Schematic of positions of welding joint for micro-hardness test
Fig.2 Schematic of the tensile specimen (unit: mm)
Fig.3 Microstructures of parent material of X-2#/625 dissimilar metal welding joint
(a) X-2# alloy (b) 625 alloy
Fig.4 Microstructures of welding seam (a) and welding remelting zone (b) of X-2#/625 dissimilar metal welding joint
Fig.5 OM images of fusion zone on X-2# (a) and 625 (b) sides and SEM image of precipitates of 625 side fusion zone (c) of X-2#/625 dissimilar metal welding joint
Fig.6 SEM images (a, b) and EDS analysis (c, d) of NbC (a, c) and Laves phases (b, d) on 625 side fusion zone
Fig.7 Microstructure of heat affected zone (HAZ) on X-2# (a) and 625 (b) sides of X-2#/625 dissimilar metal welding joint
Fig.8 Distribution of micro-hardness of X-2#/625 dissimilar metal welding joints
Temperature ℃
Rm / MPa
η %
X-2#
625
X-2#/625
20
715
818
671
93.8
300
637
741
605
95.0
400
615
722
577
93.8
500
597
703
535
89.7
600
560
700
498
88.9
700
557
614
475
85.4
Table 2 Mechanical properties of X-2#/625 dissimilar metal welding joints after tensile test at different temperatures
Fig.9 Macro-morphologies of X-2#/625 dissimilar metal welding joints after tensile test at different temperatures
Fig.10 Fracture morphologies of X-2#/625 dissimilar metal welding joints after tensile test at 20 ℃ (a) and 500 ℃ (b)
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