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Vol.43, No.12, 874 ~ 882, 2005
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| Title |
| Special Edition : Symposium on Mechanical Behavior of Materials(2) ; Effects of Alloying Elements and Tempering Conditions on Mechanical Properties of Copper Bearing 9 to 12% Cr Ferritic Heat Resistant Steels |
| 유석현 Seog Hyeon Ryu , 김민수 Min Soo Kim , 이연수 Yeon Soo Lee , 김정태 Jeong Tae Kim , 유진 Jin Yu |
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| Abstract |
| Effects of alloying elements and tempering conditions on mechanical properties in Cu bearing 9 to 12% Cr ferritic heat resistant steels have been studied by the tensile tests, the Charpy impact test, the creep rupture test, and the microstructural analysis of crept specimen. Alloys studied met sufficiently the minimum requirements for tensile strength (TS) of 800 MPa and FATT50 of 60℃ of high pressure turbine rotor steel using up to 593℃. Yield strength (YS) was more than the minimum criterion of 700 MPa by a slim margin. It was difficult to meet the Charpy energy requirements of minimum 3 kgf-m in alloys containing about 3.5% W or 1.8% Mo equivalent. Strength and toughness were improved simultaneously by additions of C, N, Cu, Ni, and V elements. TS and YS of BCu alloy had the relationships with Larson-Miller parameter (LMP) by TS (±14.0 MPa) = 2637-0.07606*LMP and YS (±12.5 MPa) = 2359-0.05917*LMP, respectively. Cu element in alloys studied caused the precipitation of fine Cu-rich precipitates of nanometer size acting on a nucleation site for Laves phase and M23C6 carbide. In Cu bearing alloys, the needle type Laves phase existing simultaneously with the globular type Laves phase contributed to the improvement of creep rupture strength (CRS) of alloys studied. The CRS at 650℃ were similar to one another regardless of minor modifications of Mo, Cr, and Cu contents in Cu bearing alloys. Tempering treatments at higher temperatures were more advantageous for the long-term CRS due to the formation of the more stable microstructure. |
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| Key Words |
| 9-12Cr heat resistant steels, Creep rupture strength, Tensile properties, Toughness, Tempering, Turbine rotor |
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