제품개발에 있어 금속재료의 선정 -특허권취득과 관련하여-

맹선재 한국발명진흥회 1978 特協 Vol.3 No.4

응력에 따른 초소성 7475 Al 합금의 변형거동

맹선재,신동혁,주연준,조종원,이동헌 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.7

Superplastic properties of 7475 Al alloy were evaluated at 516℃ over the strain-rate range of 6.3×10^(-5) to 2.1×10^(-2)s^(-1). The strain-rate sensitivity(m) was determined either from the true stresses and the true strain rates at the points of maximum load, or from change in strain rates. The latter method shows clear distinction between Region I(low stress region) and Region II (superplastic region). Observation of 7475 Al alloy after superplastic deformation was done by optical, scanning electron and transmission electron microscopy. Optical micrographs revealed that at low stress($lt;2 MPa) dispersoidfree zones(DFZ) formed at grain boundaries, primarily normal to the tensile direction. This result demonstrates the importance of diffusional flow at low stress. Also, scanning electron micrographs revealed that cavitation was reduced in the DFZ. Finally, transmission electron micrographs showed that dispersoid particles were accumulated at grain boundaries during the superplastic deformation. This result suggested that the deformation behavior at low stress was most likely a consequence of the existence of a thershold stress.

열작용과 변형을 받은 아연단결정의 전위구조

맹선재 대한금속재료학회(대한금속학회) 1964 대한금속·재료학회지 Vol.2 No.1

Dislocation etch pits of zinc single crystals grown by modified Bridgman method were studied using etchants of Gilman. The effects of deformation and heat treatment on the substructure of etch pits were also investigated. Elongated cell structures, which were observed by Kratochvil and Sichovla were not found from the as grown crystals. But nonelongated cell structures were detected occasionally. The secondary substructures following homogenization of segregated impurities were not found. Annealed samples have shown grown subgrains and also secondary substructures. Some samples were deformed (bending) at 100℃ or 180℃ during the slow cooling following annealing, and proceeded further slow cooling until it reached room temperature. The substructures which were induced through deformation, were found but not the secondary substructures. With the samples, which were annealed at about 300℃ after deformation, deformation-induced substructures were not found mostly. But greatly grown secondary substructures were found. With the deformed crystals the growth of secondary substructures through heating were more enhanced than undeformed ones.

7075 Al 합금의 초소성 변형시 공동형성에 관한 연구

맹선재,신동혁,최능열,주연준 대한금속재료학회(대한금속학회) 1997 대한금속·재료학회지 Vol.35 No.9

Cavitation during superplastic flow was investigated for 7075 Al alloy strained under uni-axial tension at 516℃. The 7075 Al alloy was thermomechanically processed to develop fine grain sizes of Bum and 12㎛, respectively. Cavitation and superplastic elongations between specimens with 8㎛ and 12㎛ were observed to be different. In the 8㎛ microstructure, the cavity stringers were formed along the tensile direction, whereas in the 12㎛ microstructure, the stringers were always oriented along the rolling direction, regardless of the tensile direction. The difference in the formation of cavity stringers seems to be mainly due to the distribution of the second phase particles in the matrix.

저탄소 Ni-Cr-Mo-V 강의 Bainite 변태조직에 관한 연구

맹선재,강찬형,현도빈 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.4

低炭素鋼, 0.13C-1.8Ni-1.6Cr-0.5Mo-0.07V의 bainite變態組織을 電子顯徵鏡으로 調査하였다. Bainite變態組織은 試片을 austenite化溫度에서 부터 400℃, 450℃ 및 500℃로 유지되고 있는 鹽浴 속에 넣어 等溫處理시켜 줌으로서 얻었다. Bainite變態는, 試片이 austenite化溫度에서부터 等溫變態處理溫度로 冷却되는 過程에서 이미 일어났는데, 이와같이 初期 冷却過程中에 이미 生成된 變態組織과, 一定한 溫度에서 等溫變態시킬 때 形成되는 變態組織等을 調査하였다. 450℃및 500℃ 等溫變態의 경우에는 初期 冷却過程에서 粗大한 bainitic ferrite lath가 形成된다. 450℃및 500℃에서 等熊變態시킨 組織은 bainitic ferrite의 retained austenite의 混合組織으로 이루어지며, 變態處理時間의 經過에 따라 retained austenite는 점차 微細한 bainitic ferrite lath로 變態하고, 初期에 形成된 粗大한 bainitic ferrite內部에는 carbide가 析出한다. 400℃에서 變態處理시킨 경우에는 이들과는 다른 形態의 微細組織, 즉 이른바 granular bainite의 形態로 나타난다. Bainitic transformation structure in a low carbon alloy steel, 0.13C-1.8Ni-1.6Cr-0.5Mo-0.07V, has been studied by electron microscopy. Bainitic structure was obtained by isothermal transformation in the salt bath holding at 400℃, 450℃ and 500℃, Bainitic transformation has already begun at the initial cooling stage, from the austenitizing temperature to the respective transformation temperature. In the case of isothermal treatment at 450℃ and 500℃, mixed structure of coarse bainitic ferrite lath and retained austenite was observed in the specimens of short transformation time, for example, 200 sec. As the isothermal transformation time increased, the region of retained austenite was replaced gradually by finer bainitic ferrite lath, and carbide was precipitated in the revious coarse bainitic ferrite lath. Detailed microstructural features of the bainitic structure, produced at the initial cooling stage and at the later isothermal treatment stage, were studied, respectively. At the transformation temperature of 400℃, somewhat different microstructure, so-called granular type bainite, was developed.

저온가공열처리한 H13 강의 강도와 조직

맹선재,강찬형 대한금속재료학회(대한금속학회) 1981 대한금속·재료학회지 Vol.19 No.12

Mechanical properties and microstructures in the ausextruded AISI H13 steel have been studied. Carbon extraction replicas were examined to find the evidence for a fine carbide dispersion after ausfoming. The carbides in as-ausformed specimens were observed to be about 0.05㎛ of average size, whereas those in conventionally as-quenched ones were 0.22㎛. The ausformed specimens showed higher hardness and bending strength than the conventional ones. Upon tempering, the ausformed specimens maintained the same strength level with increasing temperature up to 500℃, in spite of the marked increase in carbide size. This result is interpreted as being attributed to the formation of cell substructures, which has been verified by thin film transmission electron microscope.

중탄소 (0.25C) Ni-Cr-Mo-V 강의 변태조직과 기계적 성질

맹선재,강찬형 대한금속재료학회(대한금속학회) 1980 대한금속·재료학회지 Vol.18 No.2

中炭素低合金鎬(0.25C-2.5Ni-2.5Cr-0.5Mo-0.1V)의 變態組織과 機械的性質을 硏究하였다. 즉 martensite, 50% martensite+50%下部 bainite의 混合組織 및 下部 bainite의 세 組織에 대하여 引張性質과 衝擊靭性을 調査하고, 透過電子顯微鏡으로 微細組織을 觀察하였다. 230℃ 및 350℃에서 tempering한 경우 混合組織의 引張强度와 降伏强度가 martensite 또는 下部 bainite 各 單一組織의 그 값들보다 높았다. Tempering溫度의 增加에 따라, martensite와 混合組織에서는 引張强度 및 降伏强度가 점차 減少하였으나 下部 bainite의 경우는 別 變化가 없다가 대략 400℃ 이상의 tempering 溫度로부터 減少했다. 이들 세 組織을 450℃에서 40分 동안 tempering하여 引張强度를 145㎏/㎟ 水準으로 同一하게 한 후 衝擊靭性을 試驗 比校한 바 martensite 組織의 靭性이 가장 優秀했다. 引張試驗 및 衝擊靭性에 대한 試驗結果를 電子顯微鏡으로 觀察한 微細組織과 관련시켜 檢討하였다. Tensile properties and impact toughness of 0.25C-2.5Ni-2.5Cr-0.5Mo-0.1V steel have been studied in relation to three different transformation structures of martensite, mixed structure of 50% martensite+50% lower bainite, and lower bainite. Mixed structure has shown higher tensile and yield strength than any of the single structure of martensite or lower bainite, when they have been tempered at 230℃ and 350℃. As the tempering temperature increases, strength of the martensite and that of the mixed structure have decreased gradually. But lower bainite structure has shown the decrease of strength only by increasing the tempering temperature above about 400℃. Impact toughness of the three structures has been tested after tempering at 450℃ for 40 min to the same ultimate tensile strength level of 145㎏/㎟ . Martensite structure has shown the highest impact toughness. Test resultes of tensile properties and impact toughness are discussed in connection with electron microscopic structure.

초소성 7475Al 합금의 고온 변형 특성

맹선재,신동혁,주연준,하종신 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.2

The superplastic properties of fine-grained 7475 Al alloy were investigated at 516℃ over the strain-rate range of 2.8 × 10^(-4)s : to 1.7 × 10^(-2)s^(-1). A significant improvement in superplastic elongation was achieved by adopting two-stage strain-rate deformation compared to a usual single strain-rate test. The initially higher strain-rate deformation in the first stage caused rapid microstructural changes including the conversion of subboundaries to high angle grain boundaries, The optimum stain-rate in the first stage was found to be 8.3 × 10^(-3)s^(-1). The specimens tested at lower strain-rates, revealed the dispersoid-free zones(DFZs) near grain boundaries normal to the stress axis. When a higher strain-rate was applied to the specimens with DFZs, the grain refining was not observed. This absence of grain refining was due to the concentration of plastic deformation in the weak DFZs.

재료시험과 특허에 관한 고찰

맹선재 한국발명진흥회 1977 特協 Vol.2 No.3

상이한 초기조직에서 얻은 이상조직강의 열처리에 따른 인장변형 및 파괴거동

맹선재,신동혁,김일영 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.6

The different starting structures of the present study were ferrite + coarse pearlite (F+ P₁), ferrit + fine pearlite(F+P₂) and martensite(M). True stress vs. true strain curves were analysed before and after tempering. When compared the work hardening rate before tempering, the DP steel with the M-starting structure has shown the highest value. Uniform true strain was decreased with increasing tempering temperatures up to 400℃, and then increased above 400℃. Void formation behavior beneath the fracture surfaces of the tensile specimens has been studied. Preferred sites of void formation are the ferrite-martensite interfaces, the elongated martensite ends and the precipitate particles. Voids are also formed by splitting of martensite phases in the case of tempering.