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Jiankun Xiong,Haibo Zhang,Fuheng Nie,Fen He,Jianping Yang,Zhan Hu,Zhongbo Wen,Haiyan Zhao,Xinjian Yuan 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7
The formation mechanisms for two carbides with co-existence and increasing stacking faults nearby the carbides duringsurfacing welding were investigated in this study. The results indicated that the surfacing layer had a two-phase structure ofa matrix phase and a second phase, the density of the second phase was relatively small and the second phase was discontinuous,by contrast with the as-received welding wire. Relatively uniform microstructure of surfacing layer and the weldinginterface without melting of base metal were obtained, resulting in an inapparent change in the microhardness. A few carbideswith blocky shape were identified in the surfacing layer. The mechanisms for (Cr,Co)23C6 of face-centered cubic crystalstructure co-existing with (Cr,Co)7C3 of hexagonal close-packed crystal structure and (Cr,Co)23C6 subsequently forming closeto the pre-formed (Cr,Co)7C3 during the cooling process were discussed in alloying element, calculated equilibrium phasediagram, Gibbs energy, etc. The relatively higher density of the stacking fault present around the carbides was understoodfrom forming energy of stacking faults.
Ting Li,Xinjian Yuan,Rui Li,Jiankun Xiong,Shiwei Tao,Kanglong Wu 한국정밀공학회 2021 International Journal of Precision Engineering and Vol.22 No.6
Dissimilar 9% Cr heat-resistant steels (G115 and CB2) with good creep properties for ultra-supercritical steam turbines were butt-joined by tungsten inert gas welding. The microstructure of welded metal (WM) was quenched martensite without carbide precipitates and lath packets existed inside prior austenite grains (PAGs), which leaded to higher hardness of WM. Partially melted zone at G115 side was composed of untempered martensite within equiaxed PAGs. The lowest hardness occurred in both G115 and CB2 steels which was attributed to tempered martensite with many M 23 C 6 precipitates. The heat-affected zone consisted of three sub-grains and their microstructure was detailly analyzed in current work. As current increased from 130 to 150 A, both the tensile strength at room temperature and 650°C increased while strength had no obvious change with further increasing current. The values of 673 MPa and 309 MPa corresponded to the tensile stress with 150 A at room temperature and 650°C, respectively. The fracture mode of joints at room temperature was cleavage and ductile failure at 130 and 150 A, respectively. The high-temperature fracture surface at 150 A was composed of deep and fi ne dimples.