Fe-0.1C-(V, Nb) 제어압연강의 미세조직 및 기계적 특성

조경목 ( Kyung Mox Cho ),김수영 ( Su Young Kim ),박인애 ( In Ae Park ),이영중 ( Young Jung Lee ),강남현 ( Nam Hyun Kang ) 대한금속재료학회 ( 구 대한금속학회 ) 2007 대한금속·재료학회지 Vol.45 No.5

Following the trend of industrial high strength and toughness structural steel manufacturing, it is evolving and increasing needs of basic research and development efforts. One of the examples is, due to the high cost of vanadium, the replacement of Fe-V steel to Fe-Nb steel. However, there still exist difficulties for commercial production of Fe-Nb steel because of poor impact toughness of this steel comparing with Fe-V steel. In this study, a fundamental investigation was carried out to analyze the microstructure, tensile properties and impact toughness of Fe-Nb steel as a function of the rolling conditions with no post heat treatment. The steel samples were prepared with three different compositions, i.e., Fe-V steel (Fe-0.05V-0.001Nb), Fe-V-Nb steel (Fe-0.014V-0.03Nb), Fe-Nb steel(Fe-0.003V-0.033Nb). The steels were deformed with controlled rolling conditions, namely start rolling temperature(SRT) 1150℃ for the all experiment, but two different finish rolling temperature(FRT); 950℃ and 860℃. Ferrite grain size decreased and thus impact toughness was measured higher at FRT of 860℃ than at FRT 950℃ treated steels. Even though the impact toughness of Fe-Nb steel was quite low due to inhomogeneous distribution of ferrite grain size, Fe-V-Nb steel exhibited impact toughness improved with controlled rolling at FRT 860℃. Application of the controlled rolling process showed one of the possibilities to replace Fe-V steel with Fe-V-Nb and/or Fe-Nb steel.

Finite element simulation of unconstraint vibration treatment for fatigued copper film

Hai-Meng Zhang,De-Guang Shang,Shuai Lv,Xiao-Dong Liu,Yu Zhang 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.9

In this paper, in order to investigate the residual strain relief in the fatigued copper film with a thickness of 33 μm, an unconstraint vibration treatment process was simulated by finite element (FE) method. The experimental processes, including fatigue and unconstraint vibration processes, were simulated. The fatigue process for the original specimen and the vibration process for the damaged specimen were analyzed by the static and transient dynamic analysis, respectively. The simulation results showed that the unconstraint vibration treatment can lead to the residual strain of the fatigued copper film to be reduced and redistributed. The effect of the vibration parameters on the treatment effectiveness was analyzed by the different fatigue experiments and unconstraint vibration treatments, and the results showed that the FE simulation results are in agreement with the experimental observations.

분자 동역학 모사를 이용한 Fe(100) 표면의 스퍼터링 해석

김동호(Dong-Ho Kim) 한국표면공학회 2006 한국표면공학회지 Vol.39 No.2

Molecular dynamics simulations were carried out to investigate physical sputtering of Fe(100) substrate due to energetic ion bombardments. Repulsive interatomic potentials at short internuclear distances were determined with ab initio calculations using the density functional theory. Bohr potentials were fitted to the ab initio results on diatomic pairs (Ar-Fe, Fe-Fe) and used as repulsive screened Coulombic potentials in sputtering simulations. The fitted-Bohr potentials improve the accuracy of the sputtering yields predicted by molecular dynamics for sputtering of Fe(100), whereas Moliere and ZBL potentials were found to be too repulsive and gave relatively high sputtering yields. In spite of assumptions and limitations in this simulation work, the sputtering yields predicted by the molecular dynamics method were in fairly good accordance with the obtainable experimental data in absolute values as well as in manner of the variation according to the incident energy. Threshold energy for sputtering of Fe(100) substrate was found to be about 40 eV. Additionally, distributions of kinetic energies of sputtered atoms and their original depths could be obtained.

Reduction of Springback of Sheet Metals by Bottoming

Takayuki Ogawa,Atsushi Hirahara,Fusahito Yoshida 한국소성가공학회 2010 기타자료 Vol.2010 No.6

The effect of bottoming on the reduction of springback is investigated by performing V-air-bending experiment on a high strength steel sheet of TS590MPa and the corresponding FE simulation. From the experiment, it was found that the springback is drastically decreased with increasing bottoming force. This is mainly due to the reduction of bending moment by compressive load acting normally to the sheet. At an early stage of bottoming, springback is also influenced by the change of geometrical rigidity of the bent sheet due to the straightening of ridge line warp. Since bottoming is a process of reverse deformation of tension-compression, the Bauschinger effect of materials should be taken into account for its accurate numerical simulation. 3D FE simulation using Yoshida-Uemori kinematic hardening model predicts well the bottoming effect.

DV-Xα 클러스터 계산법에 의한 Fe₄N의 전자상태계산

송동원,이인섭,배동수,Song, Dong-Won,Lee, In-Seop,Bae, Dong-Su 한국재료학회 2002 한국재료학회지 Vol.12 No.1

DV(Discrete Variation)-X${\alpha}$ cluster calculation was employed to calculate the electronic states of ${\gamma}'- Fe_4N$ which was one of iron nitride phases synthesized from plasma ion nitriding to improve surface hardness and wear resistance. The result of calculated electron density of states for Fe was similar to the result of band calculation. The cluster used for calculation of electronic states of ${\gamma}'-Fe_4N$ was based on $Fe_{14}N$ cluster which comprises 15 atoms. Finally the electronic states of ${\gamma}'- Fe_4N$ such as net-charge, band order, energy level, electron wave-function, and contour map for electron density were derived by the calculation.

Development of An Optimal Layout Design System in Multihole Blanking Process

Sun-Bong Lee,Dong-Hwan Kim,Byung-Min Kim 한국정밀공학회 2004 International Journal of Precision Engineering and Vol.5 No.1

The blanking of thin sheet metal using progressive dies is an important process on production of precision electronic machine parts such as IC leadframe. This paper summarizes the results of simulating the progressive blanking process by means of LS/DYNA. In order to verify the influence of blanking order on the final lead profile and deformed configuration, simulation technique has been proposed and analyzed using a commercial FEM code, LS/DYNA. The results of FE-simulations are in good agreement with the experimental result. After then, to construct rule base in progressive blanking process, FE-simulation has been performed using a simple model. Based on this result rule base is set up and then the blanking order of inner lead is rearranged. Consequently, from the results of FE-simulation using suggested method in this paper, it is possible to predict the shift of lead to manufacture high precision leadframe in progressive blanking process. The proposed method can give more systematic and economically feasible means for designing progressive blanking process.

Comparison of three-dimensional morphologies of abnormally growing grains between Monte Carlo simulations and experiments of Fe-3% Si steel

Na, Tae-Wook,Cho, Da-Hee,Park, Chang-Soo,Park, Jong-Tae,Han, Heung Nam,Hwang, Nong-Moon Elsevier 2018 Materials characterization Vol.144 No.-

<P><B>Abstract</B></P> <P>Three-dimensional (3-D) Monte Carlo simulations of grain growth with sub-boundaries in the presence of precipitates were performed based on the distribution of realistic grain boundary energy data. The simulated grains with sub-boundaries grew abnormally. The simulated and experimental morphologies of the abnormally growing grains in Fe-3%Si steel were compared. The experimental 3-D morphology was reconstructed from serially sectioned images. Both the simulated and experimental 3-D morphologies of abnormally growing grains have highly irregular and complicated shapes whereas both the simulated and experimental 3-D morphologies of normally growing grains have relatively regular and simple shapes. Growth by wetting is responsible for the highly irregular shape of the experimental abnormally growing grains of Fe-3%Si steel as well as for the highly irregular shape of the simulated abnormally growing grains.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Grains with sub-boundaries grew abnormally in the MC simulation with realistic grain boundary energy. </LI> <LI> The experimental 3-D morphology of Goss grain was reconstructed from serially sectioned images. </LI> <LI> 2-D sectioned microstructures of the MC simulation and experiment have highly irregular shape. </LI> <LI> Both simulated and experimental 3-D morphologies of AGG have similar complicated shapes. </LI> </UL> </P>

Identification of the bulk behavior of coatings by nano-indentation test and FE-analysis and its application to forming analysis of the coated steel sheet

Lee, J.M.,Ko, D.C.,Lee, K.S.,Kim, B.M Elsevier 2007 Journal of materials processing technology Vol. No.

<P><B>Abstract</B></P><P>In this study, nano-indentation tests, FE simulation and artificial neural network (ANN) technique were used to characterize the power law of the elasto-plastic stress–strain behavior of the coating layers of coated sheets. In addition, based on Oudin's work, two types of FE model were applied on the behavior of the coatings in FE simulations; one was a single-behavior model, which had only one stress–strain behavior and the other was a layer-behavior model, which consisted of separate coating layers and substrates. FE simulations of the cup drawing process were carried out for the two FE models, respectively. The results show that the layer-behavior model that considered the behavior of the coatings was most accurate at predicting of drawing loads.</P>

Improvement in Dimensional Accuracy of Roll-Die-Formed Clutch Hub Used in Automotive Transmission

고대훈,고대철,이상곤,권용남,김상우,김봉환,김병민 한국정밀공학회 2012 International Journal of Precision Engineering and Vol. No.

Roll die forming is investigated as a new process for manufacturing a clutch hub; in this process a tooth shape is formed by a deep drawing process using a die set with rotational rolls. Some problems are still encountered during roll die forming,such as a proper process design that takes into consideration the forming limit of sheet material, the improvement in the wear resistance of the punch and the rotational roll, and the control of dimensional accuracy. Particularly, the dimensional accuracy of the final product is affected by the clearance between the punch and the roll. Therefore, the objective of this study is to determine the optimal clearance between the punch and the roll for improving the dimensional accuracy during the roll die forming for a clutch hub. FE-simulation and the design of experiment method are employed to determine the optimal clearance required to produce a final product with satisfactory dimensional specifications. An experiment is performed under the same process conditions as the FE-simulation with an optimal clearance to validate the results obtained in this study. The results of the FE-simulation are in good agreement with the experimental ones within a maximum error of 5.55[%].

역 드로잉에 의한 74리터 알루미늄 라이너 성형 시 부분가열의 효과

이승윤(S. Y. Lee),강성훈(S. H. Kang),김준현(J. H. Kim),김병민(B. M. Kim) 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5

In the previous work, fracture generation according to blank holding force, drawing ratio, comer radius of punch and die was analyzed by experiments and FE simulation based on ductile fracture criterion. However, even though optimum die designs obtained from FE simulation were used in experiments, fracture still took place during reverse drawing process due to the lower drawability. Thus, in this work, partial heating on the end of the drawn cup obtained from the first drawing process was applied and its effect on the drawability was investigated by FE simulation. It was found from the simulation results that the drawability can be enhanced and the sound aluminum liner without fracture can be achieved due to the partial heating on the end of the first drawn cup.