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980 MPa급 열연강의 권취온도와 탄화물 거동에 따른 신장플랜지성
천은준 ( Eun Joon Chun ),이주승 ( Ju Seung Lee ),도형협 ( Hyeong Hyeop Do ),김성주 ( Seong Ju Kim ),최윤석 ( Yoon Suk Choi ),박용호 ( Yong Ho Park ),강남현 ( Nam Hyun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2012 대한금속·재료학회지 Vol.50 No.7
To analyze the factors on stretch-flangeability for 980 MPa-grade hot-rolled steels, two types of steels (Fe-Cr and Fe-Mo) were manufactured by hot-rolling. Manufactured steels at the low coiling temperature, such as 400 and 500℃, had poor stretch-flangeability due to un-uniformly distributed carbides and a large deviation of interphase hardness. However, when the coiling temperature was set at 650℃ with Fe-Cr steel, 998 MPa of ultimate tensile strength, 19% of total elongation and 65% of the hole expanding ratio were achieved by microstructural constituents of polygonal ferrite (PF) and granular ferrite (GF) dispersed with fine carbides (<50 nm). Therefore, the material to attain 980 MPa with superior formability was the Fe- Cr steel that was precipitation-hardened in polygonal ferrite and granular ferrite at the coiling temperature 650℃.
천은준,이주승,도형협,김성주,박용호,강남현,Chun, Eun-Joon,Lee, Ju-Seung,Do, Hyeong-Hyeop,Kim, Seong-Ju,Park, Yong-Ho,Kang, Nam-Hyun 한국재료학회 2012 한국재료학회지 Vol.22 No.1
Research into the development of high strength (1 GPa) and superior formability, such as total elongation (10%), and stretch-flangeability (50%) in hot-rolled steel was conducted with a thermomechanically controlled hot-rolling process. To improve the overall mechanical properties simultaneously, low-carbon steel using precipitation hardening of Ti-Nb-V multimicroalloying elements was employed. And, ideal microstructural characteristics for the realization of balanced mechanical properties were determined using SEM, EBSD, and TEM analyses. The developed steel, 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V), consisted of ferrite as the matrix phase and second phase of granular bainite with fine carbides (20-50 nm) in both phases. The significant factor of the microstructural characteristics that affect stretch-flangeability was found to be the microstructural homogeneity. The microstructural homogeneity, manifest in such characteristics as low localization of plastic strain and internally stored energy, was identified by grain average misorientation method, analyzed by electron backscattered diffraction (EBSD) and hardness deviation between the phases. In summar, a hot-rolled steel having a composition 0.06C-2.0Mn-0.5Cr-0.2(Ti + Nb + V) demonstrated a tensile strength of 998 MPa, a total elongation of 19%, and a hole expansion ratio of 65%. The most important factors to satisfy the mechanical property were the presence of fine carbides and the microstructural homogeneity, which provided low hardness deviation between the phases.
유사한 전자상태를 가지는 타이타늄 합금의 영률에 베타 안정화 원소 함량이 미치는 영향
유가영 ( Ga Young Yoo ),박찬희 ( Chan Hee Park ),홍재근 ( Jae Keun Hong ),김승언 ( Seong Eun Kim ),강남현 ( Seong Eun Kim ),염종택 ( Jong Taek Yeom ) 대한금속재료학회(구 대한금속학회) 2013 대한금속·재료학회지 Vol.51 No.4
Previously, Gum Metal (Ti-24(Nb + Ta + V)-(Zr, Hf)-O (at%)) exhibiting an ultralow Young`s modulus, ultrahigh strength and super elasticity was developed by Saito et al., who proposed that three electronic magic numbers, an average electron/atom (e/a) ratio of 4.24, an average bond order (Bo) of about 2.87, and an average “d” electron-orbital energy level (Md) of about 2.45 eV, should be satisfied simultaneously to obtain such “super” properties. The purpose of this study was to find new alloy systems possessing those properties and to examine the effect of beta equivalent content ([Mo]eq) on Young`s moduli of new alloys having the same three electronic numbers mentioned above. It was found that not only three electronic numbers but also [Mo]eq should be considered to obtain a similar Young`s modulus and hardness with respect to the Gum Metal.