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Martensite 체적분률에 따른 복합조직강의 인장강도 및 Void형성과 성장에 관한 연구
吳澤烈,金斗英 慶熙大學校 材料科學技術硏究所 1991 材料科學技術硏究論集 Vol.4 No.-
The mechanical properties of ferrite-martensite dual phase steel are affected by the microstuctural factors such as the martensite volume fraction, grain size of ferrite, strength ratio of ferrite-martensite, connectivity and chemical components, etc. Therefore, by means of the heat treatment of low carbon steel (SM20C), this study deals with the tensile strength and void formation, growth for martensite volume fraction of dual phase steel. The results obtained could be summarized as follow : ⅰ) The tensile strength increased by increasing martensite volume fraction in dual phase steel. And experimental strength made a differerence in theorectical strength in low martensite volume fractionm, but it accorded with that in high martensite volume fraction. ⅱ) The void formation, growth in dual phase steel occured in the onset of plastic deformation. Voids were observed more at martensite/martensite than at ferrite/martensite interface. The longest void was observed near at noting surface, the rate of increase for the longest void is much larger than that for average void size. According to strain, the number of voids increase in low strain, and then decrease in high strain(0.4 over) because of void coalescence. ⅲ) Under martensite volume fraction 60%, fraction mode of dual phase steel showed ductile fracture. Over martensite volume fraction 60%, there was shear fracture mode which had the rate of fast crack propagation. Therefore, beyond martensite volume fraction 60%, dual phase steel is not good for the use of Engineering.
吳澤烈 慶熙大學校 材料科學技術硏究所 1988 材料科學技術硏究論集 Vol.1 No.-
Mechanical properties of dual phase steel is affected by microstructural factors. Microstructural factors are composed of martensite volume fraction, grain size, hardness ratio, connectivity and chemical composition etc. In this study, connectivity of low Mn steel specimen on which other microstructural factors were made be constant has been changed by treatment process. This ferrite - Martensite dual phase specimen had given impact bending load, thereby impact strength, impact loading time and absorbed energy etc. of specimen was investigated. Some important results in this study can be summerized as follows. 1. The more connectivity increase, the more impact strength increase. Impact strength was increased according to the increase on impact velocity. 2. Based upon the velocity to cause fracture, impact load time curve shape devided into two.
Dual phase steel의 衝擊破壞特性에 關한 硏究
吳澤烈 慶熙大學校 1982 論文集 Vol.11 No.-
In this report strength, ductility, formability, energy absorption and deformed angle of dual phage being accompanied martensite volume fraction under the dynamic Impact bending load, is present. The reciprocal relations of thess factor which are studied in connection with variation impact velocity are as follows. (1) Impact maximum load is increased linearly in proportion to Martensite volume fraction increase rate. (2) Imapat maximum load is rapidly increased until fraction on the other hand, is slowly increased after fraction. (3) Loading time is nearly decreased linearly because ferrite volume decrease rate is constant. (4) Due to ferrite volume, energy absorption is decreased in proportion to martensite volume increase rate. (5) Reformed angle condition is similar until impact velocity reach 2.71 m/sec.
吳澤烈 慶熙大學校 1986 論文集 Vol.15 No.-
A study has made of the tensile characteristics of dual phase(martensite plus ferrite) steels produced when a low carbon steel is quenched from either the austenite of austenite plus ferrite phase fields. The results can be summarized as follows; 1. The hardness ratio of second phase martensite to ferrite phase and reduction of area are decreased with increasing the martensite volume fraction when dual phase structures are made of a steel having the same composition. 2. Ductile fracture decreases when the intercritical temperature is increased and martensite hardness is decreased, because of the composite hardness increasing with increasing the intercritical temperature. 3. Tensile and yield strength of dual phase steel are function of martensite volume fraction, and the yield ratio showed relative low values. 4. The morphology of martensite in a low carbon steel through the step quenching is a lath type, and the true uniform strain is decreased according to the increase of martensite volume fraction, but it is higher than HSLA steel in the same strength level.
오택열,함영삼 경희대학교 산학협력기술연구원 2005 산학협력기술연구논문집 Vol.11 No.3
For the safety of railway, it should be evaluated for the running safety by measuring the derailment coefficient. Although railway has run the fixed and maintained rail, some of railway is derailed. This report shows the results that performed the static load test, wheelset manufacturing for test, main line running test on the basis of the derailment theory and experience. It is executed main line test into more than 80km/h for estimating the curving performance and running safety of Gwangju EMU. As the test results, could confirm the curving performance and running safety of Gwangju EMU from the results of the wheel unloading, lateral force, derailment coefficient etc. Derailment coefficient was less than 0.8, and lateral force allowance limit and wheel load reduction ratio were enough safe.
오택열,김웅찬,김석환,곽대순 경희대학교 산학협력기술연구원 2004 산학협력기술연구논문집 Vol.10 No.1
In this paper, we studied low cycle fatigue behavior of laser welded sheet metal that used automobile body panel. Specimens were manufactured as laser welding speed 5.5m/sec, power 4KW for 0.8mm and 1.2mm sheet metal. In order to understand mechanical properties, micro Vicker's hardness test was performed of specimens. But, we can’t confirm mechanical properties of weld bead and heat affected zone because laser weld makes very narrow weld bead and heat affected zone than other welding method. Therefore, we performed low cycle fatigue test with similar weldment, dissimilar weldment, similar thickness and dissimilar weldment, and dissimilar thickness and dissimilar weldment for fatigue properties of thickness and welding direction. As well, we analysis stress distribution of base metal, weld bead, and heat affected zone according to strain load using finite element method.