• International Journal of Korean Welding Society
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• v.3 no.2
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• pp.46-52
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• 2003

The refinement of microstructure and phase transformation near the interface of pure copper/carbon steel dissimilar metals joints with various friction welding parameters have been studied in this paper. The microstructure of copper and carbon steel joints were changed to be a finer grain compared to those of the base metals due to the frictional heat and plastic deformation. The microstructure of copper side experienced wide range of deformed region from the weld interface and divided into very fine equaxied grains and elongated grains. Especially, the microstructures near the interface on carbon steel were transformed from ferrite and pearlite dual structure to fine ferrite, grain boundary pearlite and martensite due to the welding thermal cycle and rapid cooling rate after welding. These microstructures were varied with each friction welding parameters. The recrystallization on copper side is reason for softening in copper side and martensite transformation could explain the remarkable hardening region in carbon steel side.

• Korean Journal of Materials Research
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• v.30 no.6
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• pp.292-300
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• 2020

In this study, the effect of tempering on the stretch-flangeability is investigated in 980 MPa grade dual-phase steel consisting of ferrite and martensite phases. During tempering at 300 ℃, the strength of ferrite increases due to the pinning of dislocations by carbon atoms released from martensite, while martensite is softened as a consequence of a reduction in its carbon super-saturation. This strength variation results in a considerable increase in yield strength of the steel, without loss of tensile strength. The hole expansion test shows that steel tempered for 20 min (T20 steel) exhibits a higher hole expansion ratio than that of steel without tempering (T0 steel). In T0 steel, severe plastic localization in ferrite causes easy pore formation at the ferrite-martensite interface and subsequent brittle crack propagation through the highly deformed ferrite area during hole expansion testing; this propagation is mainly attributed to the large difference in hardness between ferrite and martensite. When the difference in hardness is not so large (T20 steel), on the other hand, tempered martensite can be considerably deformed together with ferrite, thereby delaying pore formation and hindering crack propagation by crack blunting. Eventually, these different deformation and fracture behaviors contribute to the superior stretch-flangeability of T20 steel.

• Journal of Ocean Engineering and Technology
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• v.9 no.2
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• pp.141-148
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• 1995

Fatigue tests were carried out by a rotary bending testing machine of cantilever type. M.E.F.(ferrite encapsulated islands of martensite) materials were made by a series of heat treatment from a low carbon steel(SM 20 C). The fatigue tests were conducted at stress levels of 302 MPa and with frequencies of 25Hz, 2.5 Hz and 0.5 Hz in 3% NaCl solution. The fatigue strength increased with frequency got higher. The microcracks and corrosion pits were generated at the boundary between the matrix and the 2nd phase. The cracks generated by the corrosion pits were coalesced with the pits around the notch and became the initial crack. The $N_i/N_f$ ratio increased as the frequency and stress level decreased. The interference phenomenon increased with stress level and frequency gots higher. The crack propagation rate was delayed as the stress level lowers and the frequency gets higher, however, the range of the stress intensity factor depended only on a stress level.

• Corrosion Science and Technology
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• v.19 no.3
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• pp.146-155
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• 2020

To elucidate the effect of heat inputs on phase transformation and resistance to intergranular corrosion of F316 austenitic stainless steel (ASS), thermodynamic calculations of each phase and time-temperature-transformation diagram were conducted using JMaPro simulation software, oxalic acid etch test, double-loop electrochemical potentiokinetic reactivation test (DL-EPR), field emission scanning electron microscopy with energy dispersive spectroscopy, and transmission electron microscopy analyses of Cr carbide (Cr₂₃C₆), austenite phase and ferrite phase. F316 ASS containing a relatively low C content of 0.043 wt% showed a slightly sensitized microstructure (acceptably dual structure) due to a small amount of Cr carbide precipitated at heat affected zone irrespective of heat inputs. Based on results of DL-EPR test, although heat input was increased, the ratio of I_r to I_a was only increased very slightly due to a slight sensitization. Therefore, heat inputs have little influences on resistance to intergranular corrosion of F316 austenitic stainless steel containing 0.043 wt% C.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2008.10a
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• pp.30-30
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• 2008

• Journal of Power System Engineering
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• v.5 no.1
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• pp.97-103
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• 2001

The present study was investigated changes of precipitation behaviour of laves phase in ferrite single phase and ferrite-martensite dual phase and the mechanical properties of 10%Cr ferritic alloys. In the ferrite phase, laves phase was mainly precipitated, whereas in the martensite phase, carbide was preferentially formed during the initial stage of aging and with increasing aging time. Laves phase and carbide were simultaneously precipitated by precipitation of laves phase at around carbide. Strength and toughness were lowered by the disk-type precipitator in the initial stage of aging and toughness was recovered with increasing of aging time and then, decreasing by precipitation of laves phase.

• Transactions of the Korean Society of Mechanical Engineers
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• v.7 no.4
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• pp.372-378
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• 1983

Use of dual phase steel are growing for its high strength and light weight in automobiles. The effect of the martensite volume fraction with various impact velocities on the strength, ductility and absorbed energy of dual phase (ferrite-martensite) steels were investigated in low carbon 1.5% Mn steels which were soaked at 700.deg. C, 730.deg. C, 780.deg. C, and brine quenched. Both the yield load and the maximum impact load increased when the martensite volume fraction increased, the loading time and the absorbed energy of the specimen decreased when the martensite volume fraction increased.

• Steel and Composite Structures
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• v.35 no.3
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• pp.343-351
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• 2020

The present research deals with the multi-dual-phase-lags thermoelasticity theory for thermoelastic behavior of transversely isotropic thermoelastic thin circular plate The Laplace and Hankel transform techniques have been used to find the solution of the problem. The displacement components, stress components, and conductive temperature distribution are computed in the transformed domain with the radial distance and further determined in the physical domain using numerical inversion techniques. The effect of rotation and two temperature are depicted graphically on the resulting quantities.

• Transactions of Materials Processing
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• v.24 no.3
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• pp.194-198
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• 2015

Microstructure based FE simulations were conducted to investigate the micro-mechanical properties of ferrite-martensite dual-phase steels. The FE model was built based on real microstructure images which were characterized by optical microscopy through the thickness direction. Serial sectioned 2D images were converted into semi-2D representative volume elements (RVEs) model. Each RVE model was subjected to a non-proportional loading condition and the mechanical response was analyzed on both the macroscopic and microscopic levels. Macroscopically, stress-strain curves were described under tension-compression and tension-orthogonal tension conditions and the Bauschinger effect was well captured for both loading paths. In addition, micromechanical properties were investigated in the view of stress-strain partitioning and strain localization during monotonic tension.

• Transactions of the Korean Society of Mechanical Engineers
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• v.10 no.4
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• pp.477-486
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• 1986

본 연구에서는 SM20C를 모재로 하여 입경의 크기가 다른 3종의 복합조직강을 제작 동일한 분위기에서 저 및 고사이클 전영역에 걸쳐 피로특성을 검토하고져 한다. 제일보는 그 중 저사이클특성에 대한 보고이다. 일반적으로 저사이클 피로현상은 재 료가 탄소성 상태하에서 전위, 미소크랙, 보이드(void) 등의 인자가 복합적으로 작용 하여 발생함으로 변형률속도, 제어파형, 온도, 시험방법 및 분위기에 따라 많은 영향 을 받는다. 따라서 본 연구에서는 두가지 실험방법을 사용, 응력-변형율거동을 검토 복합조직강의 피로특성과 입경크기가 피로거동 및 강도에 미치는 영향을 비교 고찰하 였다.