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제출문
List of Figure
List of Table
칼라
목차
제1장 서론 13
제1절 연구개요 13
제2절 Ti-6Al-4V 합금의 특성 16
제3절 Ti-6Al-4V 합금의 기계적 열적 처리 17
1. 단조(Forging) 18
2. 압연(Rolling) 20
3. 열처리(Heat Treatment) 21
제2장 실험 23
제1절 실험장치 23
제2절 실험재료 23
제3절 실험방법 24
1. 버튼로를 이용한 예비실험 24
2. 60Al-40V 모합금(master alloy)의 제조 24
3. 소모성 전극의 제조 25
4. 1차용해 25
5. 2차용해 27
6. 단조(Forging) 27
7. 압연(Rolling) 29
8. 열처리(Heat treatment) 29
제3장 실험결과 및 고찰 32
제1절 버튼로를 이용한 예비실험 32
제2절 1차용해 실험 35
1. 용해전류와 잉고트 품질의 관계 35
2. 1차 잉고트내의 합금원소 분포 37
3. 1차 잉고트의 특성조사 39
제3절 2차용해 실험 44
1. 컴퓨터 프로그램에 의한 용해전류의 제어 44
2. 2차 잉고트의 특성 49
3. 2차 잉고트내의 합금원소 분포 53
제4절 합금의 열처리 실험 56
1. 열처리조건에 따른 미세구조 56
2. 인장시험 60
3. 기계적성질에 미치는 가스 불순물의 영향 62
제4장 결론 69
참고문헌 72
2차년도 연구결과 보유 73
[초록 (국문)](제목없음) 77
[초록 (영문)](제목없음) 78
연구실적 79
Table 1. Chemical compositions and mechanical properties of unalloyed titanium and Ti-6Al-4V alloys. 17
Table 2. Typical rolling temperatures for Ti-6Al-4V alloy (℃). 20
Table 3. Conditions for solution treating and aging (STA) of Ti-6Al-4V alloy. 22
Table 4. Chemical composition of sponge titanium. 23
Table 5. Chemical composition of aluminum. 24
Table 6. Chemical composition of 60Al-40V master alloy. 25
Table 7. Rolling schedule adopted in the current experiment. 29
Table 8. Chemical composition of the 60Al-40V master alloy. 34
Table 9. Chemical composition of the Ti-6Al-4V alloy melted with a button furnace. 35
Table 10. Average chemical composition of the first-melt ingots. 38
Table 11. Mechanical properties of Ti-6Al-4V alloys after various heat treatment. 61
Fig. 1. Strength to weight ratios of various structural alloys. 14
Fig. 2. Schematic diagram of a conventional forging and subsequent heat treatment sequence for producing alpha-beta structure. 18
Fig. 3. The effects of the proportion of equated(equiaxed) alpha in the microstructure on the ductility and notch sensitivity of forged Ti-6Al-4V alloy. 19
Fig. 4. The consumable electrodes for the first and the second melting. The top electrode is made of the 6 of the bottom electrode. 26
Fig. 5. The actual forging schedule adopted in the current experiment. 28
Fig. 6. Specifications of the subsized tension specimens used in the experiment. 31
Fig. 7. The photograph of the tension specimens. 31
Fig. 8. Comparison between the Al concentrations before and after arc melting. 33
Fig. 9. XRD patterns of Al-V master alloys with variation of Al/V the ratio. 34
Fig. 10. The defects observed in the first-melt ingots. 36
Fig. 11. Chemical composition of the various spots in the longitudinal cross section of a first-melt ingot. 38
Fig. 12. Micrographs of the specimens from a first-melt ingot; (a) as-cast structure, (b) hot rolled at 940℃. 41
Fig. 13. Micrographs of the specimens rolled and heat treated below β transus ; (a) 940℃ 1h + water quenching, (b) ditto + 485℃ 8h + air cooling. 42
Fig. 14. Micrographs of the specimens rolled and heat treated above(ablve) β transus ; (a) 1100℃ 1h + water quenching, (b) ditto + 485℃ 8h + air cooling. 43
Fig. 15. Pre-programmed current schedule for the second melting. 44
Fig. 16. The chart record showing the beginning part of the 2nd melting; the current and the arc voltage follow the pre-programmed melting schedule. 46
Fig. 17. The chart record showing a part of the steady state melting stage; the current and arc voltage are held constant. 47
Fig. 18. The chart record showing the last part of the 2nd melting; the melting current is lowered slowly to prevent shrinkage holes and pipes. 48
Fig. 19. The first and the second ingots of the Ti-6Al-4V alloy; the second ingot is obtained by melting the first ingots as a consumable electrode. 49
Fig. 20. Overview of the 2nd-melt ingot; (a) before machining, (b) after machining. 51
Fig. 21. Transverse cross section of the ingot shown in the Fig. 20. (a) top part, (b) bottom part. 52
Fig. 22. Longitudinal cross section of the ingot shown in the Fig. 20. 53
Fig. 23. Chemical composition of the various spots in the longitudinal cross section of a second-melt ingot. 54
Fig. 24. Micrographs of the specimens after various heat treatments. (a) F13 (b) F13M (c) F13S (d) F13R (e) F13RM (f) F13RS 57
Fig. 25. SEM micrographs showing the fracture(frature) surface. (a) F13 (b) F13S 63
Fig. 26. Relationship between Brinell Hardness and Ultimate tensile strength. 64
Fig. 27. The amounts of oxygen and nitrogen in tensile test samples after various heat treatments. 66
Fig. 28. Relationship(Relatioship) between Brinell Hardness and oxygen equivalent. 67