http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
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.
오스테나이트계 스테인리스강 레이저 용접부의 응고균열 거동 (Part 2)
천은준(Eun-Joon Chun),이수진(Su-Jin Lee),서정(Jeong Suh),강남현(Namhyun Kang),Kazuyoshi Saida 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.5
A numerical simulation of the solid/liquid coexistence temperature range, using solidification segregation model linked with the Kurz-Giovanola-Trivedi model, explained the mechanism of the BTR shrinkage (with an increase in welding speed) in type 310 stainless steel welds by reduction of the solid/liquid coexistence temperature range of the weld metal due to the inhibited solidification segregation of solute elements and promoted dendrite tip supercooling attributed to rapid solidification of laser beam welding. The reason why the BTR enlarged in type 316 series stainless welds could be clarified by the enhanced solidification segregation of impurity elements (S and P), corresponding to the decrement in δ-ferrite crystallization amount at the solidification completion stage in the laser welds. Furthermore, the greater increase in BTR with type 316-B steel was determined to be due to a larger decrease in δ-ferrite amount during welding solidification than with type 316-A steel. This, in turn, greatly increases the segregation of impurities, which is responsible for the greater temperature range of solid/liquid coexistence when using type 316-B steel.
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℃.
후열처리에 따른 Cu-NiCrBSi 이종 레이저 클래드부의 미세조직 및 기계적 성질 변화
김경민,정예선,심아진,박원아,박창규,천은준,Kim, Kyeong-Min,Jeong, Ye-Seon,Sim, Ahjin,Park, Wonah,Park, Changkyoo,Chun, Eun-Joon 한국재료학회 2020 한국재료학회지 Vol.30 No.9
For surface hardening of a continuous casting mold component, a fundamental metallurgical investigation on dissimilar laser clads (Cu-NiCrBSi) is performed. In particular, variation behavior of microstructures and mechanical properties (hardness and wear resistance) of dissimilar clads during long-term service is clarified by performing high-temperature post-clad heat treatment (temperature range: 500 ~ 1,000 ℃ and isothermal holding time: 20 ~ 500 min). The microstructures of clad metals (as-clads) consist of fine dendrite morphologies and severe microsegregations of the alloying elements (Cr and Si); substrate material (Cu) is clearly confirmed. During the post-clad heat treatment, the microsegregations are totally homogenized, and secondary phases (Cr-based borides and carbides) precipitated during the short-term heat treatment are also almost dissolved, especially at the heat treatment conditions of 950 ℃ for 500 min. Owing to these microstructural homogenization behaviors, an opposite tendency of the surface mechanical properties can be confirmed. In other words, the wear resistance (wear rate) improves from 4.1 × 10<sup>-2</sup> ㎣/Nm (as-clad condition) to 1.4 × 10<sup>-2</sup> ㎣/Nm (heat-treated at 950 ℃ for 500 min), whereas the hardness decreases from 453 HV (as-clad condition) to 142 HV (heat-treated at 950 ℃ for 500 min).
핫스탬핑강의 너트 프로젝션 용접시 너트 재질이 용접부 파단모드 변화에 미치는 영향
임성상(Sung-Sang Lim),김영태(Young-Tae Kim),천은준(Eun-Joon Chun),남기성(Ki-Sung Nam),박영환(Young-Wan Park),김재완(Jae-Wan Kim),이선영(Sun-Young Lee),최일동(Il-dong Choi),박영도(Yeong-Do Park) 대한용접·접합학회 2016 대한용접·접합학회지 Vol.34 No.2
The use of materials for modern lightweight auto-bodies is becoming more complex than hitherto assemblies. The high strength materials nowadays frequently used for more specific fields such as the front and rear sub frames, seat belts and seats are mounted to the assembled body structure using bolt joints. It is desirable to use nuts attached to the assembled sheets by projection welding to decrease the number of loose parts which improves the quality. In this study, nut projection welding was carried out between a nut of both boron steel and carbon steel and ultra-high strength hot-stamped steel sheets. Then, the joints were characterized by optical and scanning electron microscope. The mechanical properties of the joints were evaluated by microhardness measurements and pullout tests. An indigenously designed sample fixture set-up was used for the pull-out tests to induce a tensile load in the weld. The fractography analysis revealed the dominant interfacial fracture between boron steel nut weld which is related to the shrinkage cavity and small size fusion zone. A non-interfacial fracture was observed in carbon steel nut weld, the lower hardness of HAZ caused the initiation of failure and allowed the pull-out failure which have higher in tensile strengths and superior weldability. Hence, the fracture load and failure mode characteristics can be considered as an indication of the weldability of materials in nut projection welding.