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Vol.43, No.1, 23 ~ 31, 2005
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| Title |
| Deformation behavior of Flame-hardened Surface Layer of 12Cr Steel by Supersonic Water Drop Impacts |
| 김광호 Gwang Ho Kim , 이민구 Min Ku Lee , 김경호 Kyeong Ho Kim , 김흥회 Whung Whoe Kim , 김길무 Gil Mu Kim |
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| Abstract |
| Water drop impact erosion properties of the 12Cr steel, currently used as nuclear steam turbine blade material, surface-hardened by the flame hardening process have been characterized. For this, variations of both the maximum erosion depth de,,,,ax and volume loss V with the cumulative impacts n at the supersonic impact velocity (~350 m/s) have been investigated for the as-received and flame-hardened 12Cr steels with different hardnesses. Typically all the samples showed an erosion-time characteristic involving the incubation period initially followed by the steady state period. It is also found that the d_(e,max) increases stepwise-like with the number of impacts n, which results from a sudden formation of craters by crack propagation. Compared to those for the as-received 12Cr steel, the flame-hardened ones showed an excellent resistance to water drop impact erosion with 2.2~2.8 times higher incubation time n, and 115~1/8 times lower erosion rate a. In the incubation period the as-received 12Cr steel was damaged by ductile depression and ploughing, while the flame-hardened 12Cr steel by fatigue cracks and brittle platelet deformation. Erosion in the steady state period was developed by the cleavage fracture commonly. (Received July 22, 2004) |
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| Key Words |
| 12Cr steel, Flame hardening, Water drop impact, Erosion, Surface heat treatment |
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