W-250 maraging강에서 Ti 함량과 열처리가 기계적 성질, 미세조직 및 시효거동에 미치는 영향 The effects of Ti and heat treatment on mechanical properties, microstructure, and aging behavior in W-250 maraging steels원문보기
The effects of Ti-content (0.65-1.48 Ti) on tensile properties and impact toughness in Fe-18.5 Ni-4.5 W- Ti- 0.05 Al with varying heat treatments were investigated. Heat treatment temperatures varied from $750\,^\circ\!C$ to $950\,^\circ\!C$ for solution treatments and from $375\,^\circ\!C$ to $650\...
The effects of Ti-content (0.65-1.48 Ti) on tensile properties and impact toughness in Fe-18.5 Ni-4.5 W- Ti- 0.05 Al with varying heat treatments were investigated. Heat treatment temperatures varied from $750\,^\circ\!C$ to $950\,^\circ\!C$ for solution treatments and from $375\,^\circ\!C$ to $650\,^\circ\!C$ for aging treatments. The optimum condition of high yield strength (250 ksi) and good toughness was obtained in the alloy composition of Fe- 18.5 Ni- 4.5 W-1.35-1.4 Ti -0.05 Al after the solution treatment at $900\,^\circ\!C$ and aging at $500\,^\circ\!C$ for 3 hrs. It was found that impact energy adn tensile properties were sensitivie to the Ti content, under a standard aging treatment ($500\,^\circ\!C$/3hrs); the tensile strength increased from 1400 MPa to 1900 MPa and the impact energy decreased from 54 J to 12 J as the Ti content increased from 0.65 to 1.48 Ti. Overaging condition was designed to simulate the condition of HAZ during welding cycles. The retainedaustenite formed during the overaging treatment did not offer any advantage in impact energy compared with maraged state of the same level with fully martensite structure. As aging temperature increased from $550\,^\circ\!C$ to $650\,^\circ\!C$ with varying aging time, the amounts of retained austenite were studied by X-ray diffraction analysis. By varying aging temperatures from $375\,^\circ\!C$ to $550^\circ\!C$, the aging kinetics were studied by hardness measurements. At low temperature aging treatment, the exponent of JohnsonMehl equation(n) was about 0.6. By the value of time to reach the maximum hardness, apparent activation energy estimated was about 295 KJ/mole. Thsi value was about the same as the activation energy for volume diffusion of W in bcc-iron, 29dKJ/mole reported. The precipitates formed during aging treatment were identified by transmission electron microscopy. The major strengthening precipitates formed during the aging treatment of Co-free W-bearing maaging steel was hexagonal 7-$Ni_3Ti$ and orthorhomibc $Ni_3W$. The orientation relationships of the precipitates and matrix were identified by electron diffraction spot pattern analysis. The orientation relationships of n-$Ni_3Ti$ was $(110)_{\alpha'}$//(0001)_\eta$ and $_{\alpha'} // [2\overline{1} \overline{1}0]_{\eta}$, while those of $Ni_3W$ was $(110)_{\alpha'}// (010)$ and $_{\alpha'}// [100]$
The effects of Ti-content (0.65-1.48 Ti) on tensile properties and impact toughness in Fe-18.5 Ni-4.5 W- Ti- 0.05 Al with varying heat treatments were investigated. Heat treatment temperatures varied from $750\,^\circ\!C$ to $950\,^\circ\!C$ for solution treatments and from $375\,^\circ\!C$ to $650\,^\circ\!C$ for aging treatments. The optimum condition of high yield strength (250 ksi) and good toughness was obtained in the alloy composition of Fe- 18.5 Ni- 4.5 W-1.35-1.4 Ti -0.05 Al after the solution treatment at $900\,^\circ\!C$ and aging at $500\,^\circ\!C$ for 3 hrs. It was found that impact energy adn tensile properties were sensitivie to the Ti content, under a standard aging treatment ($500\,^\circ\!C$/3hrs); the tensile strength increased from 1400 MPa to 1900 MPa and the impact energy decreased from 54 J to 12 J as the Ti content increased from 0.65 to 1.48 Ti. Overaging condition was designed to simulate the condition of HAZ during welding cycles. The retainedaustenite formed during the overaging treatment did not offer any advantage in impact energy compared with maraged state of the same level with fully martensite structure. As aging temperature increased from $550\,^\circ\!C$ to $650\,^\circ\!C$ with varying aging time, the amounts of retained austenite were studied by X-ray diffraction analysis. By varying aging temperatures from $375\,^\circ\!C$ to $550^\circ\!C$, the aging kinetics were studied by hardness measurements. At low temperature aging treatment, the exponent of JohnsonMehl equation(n) was about 0.6. By the value of time to reach the maximum hardness, apparent activation energy estimated was about 295 KJ/mole. Thsi value was about the same as the activation energy for volume diffusion of W in bcc-iron, 29dKJ/mole reported. The precipitates formed during aging treatment were identified by transmission electron microscopy. The major strengthening precipitates formed during the aging treatment of Co-free W-bearing maaging steel was hexagonal 7-$Ni_3Ti$ and orthorhomibc $Ni_3W$. The orientation relationships of the precipitates and matrix were identified by electron diffraction spot pattern analysis. The orientation relationships of n-$Ni_3Ti$ was $(110)_{\alpha'}$//(0001)_\eta$ and $_{\alpha'} // [2\overline{1} \overline{1}0]_{\eta}$, while those of $Ni_3W$ was $(110)_{\alpha'}// (010)$ and $_{\alpha'}// [100]$
주제어
#MetalsHeat treatment Microstructure Aging MetalsMechanical properties 마르에이징강 열 처리 기계적 성질 미세 구조 시효
학위논문 정보
저자
Jung, Jae-Young
학위수여기관
한국과학기술원
학위구분
국내석사
학과
재료공학과
발행연도
1988
총페이지
[iii], 65 p.
키워드
MetalsHeat treatment Microstructure Aging MetalsMechanical properties 마르에이징강 열 처리 기계적 성질 미세 구조 시효
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