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Nickel-based superalloy is the most widely used material for piping tubes of nuclear power plants, aircraft engines, and turbine disks. It has excellent strength and creep resistance under conditions of high temperature and high stress by using solid solution and precipitation hardening. In particular, it is known as a relatively inexpensive material because it contains a large amount of Fe. As the demand for large-sized parts increases, research is needed to achieve high efficiency in harsh environments.
Inconel 718 alloy has been actively studied for property improvement by controlling the components of Nb, Al, and Ti alloy elements that affect various heat treatment conditions and precipitation strengthening. In the case of δ phase, there is a study result that, when properly precipitated at the grain boundary, it inhibits grain growth and forms a sawtooth-shaped grain boundary to limit grain boundary sliding, thereby improving fatigue and creep resistance. However, in the case of a material that has undergone an intermediate heat treatment process, the formation of a large amount of δ phase prevents the precipitation of the main reinforcing phase and causes a decrease in high-temperature strength. It is necessary to derive the optimized heat treatment conditions for satisfy the mechanical properties
Many parts made of super heat-resistant alloy are manufactured through hot forming such as forging. In order to obtain a desired microstructure, it is necessary to control the microstructure that varies depending on various process variables. In particular, for super heat-resistant alloys, microstructure change due to dynamic recrystallization and grain growth during high-temperature forming is directly related to mechanical properties, so microstructure control according to forming is essential. Research on prediction is steadily continuing.
In this study, Inconel 718 alloy was used for forging and rolling ingots manufactured using the triple melting method of VIM-ESR-VAR. In order to derive the optimal heat treatment conditions, the grain size, precipitation phase, and high-temperature mechanical properties of alloys according to solution heat treatment and various aging heat treatments were analyzed. In addition, the hot forging process design of the blade, a component used in an actual aircraft engine, was carried out, and a finite element analysis applied with microstructure prediction modeling was conducted. To verify the microstructure prediction modeling, the microstructure of the actual hot forged product was comparatively analyzed, and the microstructure and mechanical properties of the hot forged product were analyzed according to solution heat treatment and aging heat treatment.
Inconel 718 alloy has been actively studied for property improvement by controlling the components of Nb, Al, and Ti alloy elements that affect various heat treatment conditions and precipitation strengthening. In the case of δ phase, there is a study result that, when properly precipitated at the grain boundary, it inhibits grain growth and forms a sawtooth-shaped grain boundary to limit grain boundary sliding, thereby improving fatigue and creep resistance. However, in the case of a material that has undergone an intermediate heat treatment process, the formation of a large amount of δ phase prevents the precipitation of the main reinforcing phase and causes a decrease in high-temperature strength. It is necessary to derive the optimized heat treatment conditions for satisfy the mechanical properties
Many parts made of super heat-resistant alloy are manufactured through hot forming such as forging. In order to obtain a desired microstructure, it is necessary to control the microstructure that varies depending on various process variables. In particular, for super heat-resistant alloys, microstructure change due to dynamic recrystallization and grain growth during high-temperature forming is directly related to mechanical properties, so microstructure control according to forming is essential. Research on prediction is steadily continuing.
In this study, Inconel 718 alloy was used for forging and rolling ingots manufactured using the triple melting method of VIM-ESR-VAR. In order to derive the optimal heat treatment conditions, the grain size, precipitation phase, and high-temperature mechanical properties of alloys according to solution heat treatment and various aging heat treatments were analyzed. In addition, the hot forging process design of the blade, a component used in an actual aircraft engine, was carried out, and a finite element analysis applied with microstructure prediction modeling was conducted. To verify the microstructure prediction modeling, the microstructure of the actual hot forged product was comparatively analyzed, and the microstructure and mechanical properties of the hot forged product were analyzed according to solution heat treatment and aging heat treatment.
목차
- 제 1 장 서 론 1제 2 장 연구 목적 3제 3 장 연구 배경 4제 3.1 절 니켈기 초내열 합금 43.1.1 니켈기 초내열 합금의 개발 43.1.2 니켈기 초내열 합금의 제조 공정 73.1.3 니켈기 초내열 합금의 응력 파단 특성 10제 3.2 절 Inconel 718 합금 123.2.1 Inconel 718 합금의 구성 원소 123.2.2 Inconel 718 합금의 강화기구 143.2.3 단련용 Inconel 718 합금 193.2.4 Inconel 718 합금의 열처리 21제 3.3 절 Inconel 718 합금의 단조 공정 23제 3.4 절 동적재료모델(Dynamic materials model) 25제 3.5 절 고온변형기구 및 미세조직 예측 모델 29제 4 장 연구 방법 32제 4.1 절 Inconel 718 합금의 미세조직 분석 32제 4.2 절 고온압축시험 33제 4.3 절 유한요소해석 33제 4.4 절 열처리 실험 방법 34제 4.5 절 기계적 특성 분석 354.5.1 상온인장시험 354.5.2 고온인장시험 354.5.3 응력파단시험 36제 5 장 연구 결과 및 고찰 38제 5.1 절 Inconel 718 합금 미세조직 및 기계적 특성 분석 385.1.1 Inconel 718 합금 원소재 미세조직 분석 385.1.2 Inconel 718 합금의 용체화 열처리에 따른 미세조직 분석 405.1.3 Inconel 718 합금의 시효 열처리에 따른 미세조직 분석 425.1.4 Inconel 718 합금의 열처리 조건에 따른 기계적 특성 분석 495.1.4.1 상온인장시험 결과 495.1.4.2 고온인장시험 결과 495.1.4.3 응력파단시험 결과 52제 5.2 절 Inconel 718 블레이드 열간 형단조 공정 유한요소해석 545.2.1 Inconel 718 합금의 고온압축시험 결과 545.2.2 조직예측모델 및 재료상수 결정 615.2.2.1 동적 재결정 모델링식 655.2.3 열간 형단조 공정 유한요소해석 결과 68제 5.3 절 블레이드 형단조품 미세조직 및 기계적 특성 분석 745.3.1 블레이드 단조품 미세조직 및 유한요소해석 값 비교분석 745.3.2 블레이드 단조품 기계적 특성 분석 785.3.2.1 고온인장시험 결과 785.3.2.2 응력파단시험 결과 78제 6 장 결론 82참고문헌 83
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