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Vol.57, No.7, 422 ~ 430, 2019
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| Title |
| Effect of Carbides Formed in 9Cr-1Mo-V-Nb Weld Metals on Elevated Temperature Tensile Strength |
| 문병록 Byungrok Moon , 이정훈 Junghoon Lee , 강남현 Namhyun Kang , 이태호 Taeho Lee , 정우상 Woosang Jung , 박철규 Chulgyu Park , 조경목 Kyungmox Cho |
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| Abstract |
| Alloy design of 9Cr-1Mo-V-Nb weld metals was carried out through thermodynamic simulation, and elevated temperature tensile testing was performed on the designed alloy. Based on the thermodynamic simulation of the 9Cr-1Mo-V-Nb weld metal, 0.09 to 0.10 wt% C was added to increase Cr-rich M23C6. Nitrogen was reduced from 0.04 to 0.02 wt% to suppress the formation of the Z-phase. Elevated tensile tests at 600 ℃ showed that the 0.10C specimen, in which a large amount of Cr-rich M23C6 was formed, produced a higher tensile strength and elongation than the 0.09C specimen. Below the fracture surfaces after the elevated temperature tensile test, the microvoids located in the 0.10C specimen were smaller than those in the 0.09C specimen. In the 0.10C and 0.09C specimens, the microvoids generated by oxide inclusions were mostly located in the grain boundaries. Cr-rich M23C6 precipitates in the weld metal were mainly located on the grain boundaries, and the (V, Nb)-rich MX precipitates were located in the grains. In the 0.10C weld metal, a large amount of Cr-rich M23C6 precipitates, which were coherent with the grain, were distributed at the grain boundaries. The coherent Cr-rich M23C6 precipitated along the grain boundary probably inhibited the mobility of dislocations and grain boundaries, and the propagation of microvoids generated by oxide inclusions, therefore increasing the high temperature strength and elongation.
(Received April 8, 2019; Accepted May 24, 2019) |
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| Key Words |
| 9Cr-1Mo-V-Nb steel, weld metal, thermodynamic simulation, elevated temperature tensile properties, Crrich M23C6 precipitates |
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