표제지
목차
Nomenclature 6
Ⅰ. 서론 15
1.1. 연구배경 15
1.2. 연구 동향 19
1.3. 연구목적 및 내용 25
Ⅱ. 이론적 배경 28
2.1. 증기터빈 블레이드의 주요 손상 기구 28
2.2. 강의 취성화(Embrittlement of Steel) 39
2.3. 전자 회절 이론 45
2.3.1. Bragg's equation 45
2.3.2. 역격자의 정의 49
2.3.3. 파동의 수학적 표현 56
Ⅲ. 재료 및 시험 방법 62
3.1. 재료 및 시험편 62
3.2. 시험 방법 64
3.2.1. 화학성분 및 기계적 특성 시험 64
3.2.2. 파면 및 미세조직 관찰 68
3.3. 모사 열처리 효과 시험 68
Ⅳ. 결과 및 고찰 71
4.1. 12Cr강 블레이드 파손 원인 연구 71
4.1.1. 화학성분 및 기계적 물성 시험결과 71
4.1.2. 파면과 미세조직 분석결과 73
4.1.3. 모사 열처리 효과 시험결과 88
4.2. 템퍼링 조건에 따른 12Cr강 재질 취성화 특성 93
4.2.1. 12Cr강 재질취성에 관한 이론적 고찰 93
4.2.2. 재질 취성화 요인 분석 97
Ⅴ. 결론 133
참고문헌 136
ABSTRACT 150
Table 2.1. Procedures for hardening and tempering wrought martensitic stainless steels to specific strength and hardness levels 43
Table 2.2. {hkl} crystal planes where diffraction intensity is obtained in lattice with lattice point 55
Table 3.1. Chemical compositions of blade 62
Table 3.2. Mechanical properties of blade 62
Table 3.3. Conditions of simulated heat treatment 69
Table 4.1. Chemical analysis results of alloying elements in blade 72
Table 4.2. Mechanical properties test results of blade 72
Table 4.3. Changes of impact energy for the difference of HT condition 88
Table 4.4. Changes of mechanical properties for the difference of HT condition 90
Table 4.5. Relationship between Charpy impact energy and mechanical properties of 12Cr Martensitic stainless steel 98
Table 4.6. Fracture characteristics of Charpy impact energy 104
Fig. 1.1. Blade root structure used in steam turbine and multi-finger pinned root 18
Fig. 1.2. Fractured low pressure last stage blade 18
Fig. 2.1. Creep damage in high pressure turbine rotor 29
Fig. 2.2. Fatigue damage in blades 31
Fig. 2.3. Damaged stationary blade by solid particle erosion 32
Fig. 2.4. Locations on rotating blades/buckets of an low pressure turbine affected by localized corrosion and corrosion fatigue 35
Fig. 2.5. Corrosion fatigue in an L-1 blade. crack initiation can be seen in the first hook(serration) of the blade root 35
Fig. 2.6. Outline of stress corrosion cracking 36
Fig. 2.7. Schematic representation of the development of liquid droplet erosion in steam turbine blades 37
Fig. 2.8. Effect of temper embrittlement on notch toughness. Variation in Charpy V-notch impact energy with temperature for 5140 steel... 40
Fig. 2.9. Room-temperature Charpy V-notch impact energy versus tempering temperature for 4130, 4140 and 4150 steels austenitized at 900℃... 41
Fig. 2.10. Effect of austenizing temperature on as quenched hardness. Specimens were wrought martensitic stainless steels containing 0.15%... 43
Fig. 2.11. Examples of waves obtained when two waves of the same wavelength are combined. (a) wave I which has wavelength and... 46
Fig. 2.12. Scattering of X-ray beam from a single crystal plane placed on the surface 47
Fig. 2.13. Scattering of X-ray beams on crystal planes with a constant crystal plane spacing 48
Fig. 2.14. Lattice unit vector a₁→, a₂→, a₃→ and reciprocal lattice unit vector b₃→ in the real crystal unit cell[이미지참조] 50
Fig. 2.15. The lattice points and crystal planes existing on the (001) crystal plane of simple cubic and the reciprocal lattice points and... 52
Fig. 2.16. (001) reciprocal crystal plane of simple cubic with lattice constant (a) a=0.1 nm, (b) a=0.2 nm 53
Fig. 2.17. (100) reciprocal crystal plane of (a) simple cubic, (b) face centered cubic, (c) body centered cubic with lattice constant a=0.2 nm 55
Fig. 2.18. Five waves with various path difference 57
Fig. 2.19. Ewald sphere, incident beam direction and diffraction beam direction at reciprocal lattice space 59
Fig. 2.20. Diffraction condition on Ewald sphere 61
Fig. 2.21. Relationship between diffraction angle 2θ and reciprocal vector in reciprocal space 61
Fig. 3.1. Heat treatment process of blade 63
Fig. 3.2. Position for specimens 63
Fig. 3.3. Equipment for analysis of chemical components. (a) ICP-Optical Emission Spectrometer (b) Emission spectrometer analysis(QSN750) 65
Fig. 3.4. Dimensions for tension test specimen and Photo of tension test machine 66
Fig. 3.5. Dimensions for Charpy impact test specimen and Photo of Impact test machine 67
Fig. 3.6. Heat treatment process of Case 1 69
Fig. 3.7. Heat treatment process of Case 2 70
Fig. 3.8. Heat treatment process of Case 3 70
Fig. 4.1. Relationship between Charpy impact energy and hardness of 12Cr steel 72
Fig. 4.2. Photos of fracture surface 74
Fig. 4.3. SEM fractographs of crack initiation area for No. 4 finger (x75, x300) 75
Fig. 4.4. SEM fractograph of final area for No.1 finger (x500) 75
Fig. 4.5. SEM fractographs of tensile test for fractured blade 76
Fig. 4.6. SEM fractographs of tensile test for sound blade 77
Fig. 4.7. SEM fractography of impact test for fractured(left) and sound(right) blade 78
Fig. 4.8. Results of EDS analysis for deposits on fracture surface 79
Fig. 4.9. Microstructures of fractured blade 81
Fig. 4.10. Microstructures of sound blade 82
Fig. 4.11. TEM micrographs of (a) Fractured blade and (b) Sound blade 83
Fig. 4.12. TEM micrographs of Cr-rich carbides : (a) Fractured blade, (b) Sound blade 84
Fig. 4.13. Diffraction pattern of (a) Cementite and (b) Cr-rich carbides 85
Fig. 4.14. TEM microstructure and diffraction of fractured blade 87
Fig. 4.15. Crack appearance of cross section(x200) 87
Fig. 4.16. Results of Charpy impact test for Case 1 90
Fig. 4.17. Results of Charpy impact test for Case 2 91
Fig. 4.18. Results of Charpy impact test for Case 3 91
Fig. 4.19. Results of Charpy impact test for Case 4 92
Fig. 4.20. Tempering temperature effects on Charpy V-notch of 12 Cr Stainless steels 94
Fig. 4.21. Tempering temperature effects on mechanical properties of 12 Cr stainless steels 95
Fig. 4.22. Effect of tempering temperature on the stress corrosion characteristics of two wrought martensitic stainless steels at high... 96
Fig. 4.23. Distribution of Charpy impact energy of 363 blades 98
Fig. 4.24. Schematic fracture appearance of a Charpy impact test specimen after breakage and definition of percent brittle fracture and... 100
Fig. 4.25. Fracture surface of low Charpy impact energy 10 J 101
Fig. 4.26. Fracture surface of medium Charpy impact energy 53 J 102
Fig. 4.27. Fracture surface of high Charpy impact energy 173 J 103
Fig. 4.28. Optical microscope micrographs of (a) embrittled and (b) sound blade 107
Fig. 4.29. SEM micrographs of the (a) embrittled and (b) sound blade 109
Fig. 4.30. TEM micrographs at z=〈113〉 of Ti-39Nb-6Zr heat treated 400℃/1h : ⒜ modulated structure, ⒝ spot streaks, ⒞ bright field... 111
Fig. 4.31. TEM micrographs at z=〈113〉 of Ti-39Nb-6Zr heat treated 400℃/1h : ⒜, (c) HRTEM image, (b), (d) diffraction patterns 111
Fig. 4.32. TEM micrographs at z=〈110〉 of fractured blade : ⒜, (c) microstructures, (b), (d) diffraction patterns (Charpy impact energy : 25 J) 114
Fig. 4.33. TEM micrographs at z=〈113〉 of oil quenched 12Cr steel : ⒜ microstructure, (b) HRTEM of B area, (c),(d) diffraction patterns of A, B area 117
Fig. 4.34. TEM microstructure and diffraction pattern of 975℃/1h quenched and 545℃/1h tempering specimen (Case 2 #4, Charpy impact energy : 10J) 120
Fig. 4.35. Results of EDS analysis for matrix and tweed structure 121
Fig. 4.36. TEM microstructure and diffraction pattern of 600℃/6h tempering specimen (Case 1 #2, Charpy impact energy : 55 J) 123
Fig. 4.37. TEM microstructure and diffraction pattern of 600℃/6h tempering specimen : (a) HRTEM of rod appearance (b~f) diffraction... 125
Fig. 4.38. Phase transformation of β→α"→ω for a β-Ti alloy[87] (IC ω : Incommensurate omega phase, C ω : commensurate omega phase) 131
Fig. 4.39. TEM microstructure and diffraction pattern at z=〈113〉 of embrittled blade 132