• 대한금속재료학회지
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• 제48권3호
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• pp.187-193
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• 2010

The solute carbon content in ferrite is one of the important factors to obtain good formability in low carbon steels. Although most of the carbons are consumed by the formation of grain boundary cementite during coiling after hot-rolling, the carbon content after coiling is normally observed much more than that of equilibrium. In this study, a classical nucleation and growth model is used to simulate the precipitation kinetics of the grain boundary cementite from coiling temperature (CT) to room temperature (RT). The predicted precipitation behaviors depending on the initial carbon content and the cooling rate are compared with the reported. As a result, the lateral growth of thickening of cementite is a major factor for the sluggish reaction of grain boundary cementite. The reduction of solute carbon content after coiling is divided into three regions: a) increase due to no cementite precipitation, b) decrease due to the fast length-wise growth of cementite, c) increase due to the slow thickness-wise growth of cementite.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권3호
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• pp.376-391
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• 2013

Brackets in ships and offshore structures are added structures that can endure stress concentrations. In this study, a concurrent engineering solution was proposed, and a high strength low carbon cast steel alloy applicable to offshore structures was designed and developed. The yield strength and ultimate tensile strength of the designed steel were 480 and 600 MPa, respectively. The carbon equivalent of the steel was 0.446 with a weld crack susceptibility index of 0.219. The optimal structural design of the brackets for offshore structures was evaluated using ANSYS commercial software. The possibility of replacing an assembly of conventional built-up brackets with a single casting bulb bracket was verified. The casting process was simulated using MAGMAsoft commercial software, and a casting fabrication process was designed. For the proposed bulb bracket, it was possible to reduce the size and weight by approximately 30% and 50%, respectively, compared to the conventional type of bracket.

• 한국건축시공학회지
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• 제13권3호
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• pp.218-226
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• 2013

건설재료 중 시멘트 및 철강은 대표적으로 탄산가스를 발생시키는 재료산업이다. 건설 산업에서의 탄소 배출량 감소를 위해서는 이러한 재료의 사용을 감소시키는 것이 가장 효과적이라고 할 수 있다. 본 연구에서는 시멘트의 사용량을 감소시킨 저발열형 혼합시멘트의 개발을 목적으로 하고 있다. 시멘트 혼합 비율을 10 %로 낮춘 저탄소 배출형 저발열 혼합시멘트의 수화 특성 및 콘크리트의 온도상승 특성을 검토하였다. 시험 결과, 혼화재의 반응 활성화를 위해서는 CaO 및 $SO_3$의 공급원 필요하며, 석고 및 생석회를 적정 배합비율 적용할 경우 초기에는 강도 발현이 다소 지연되지만 장기재령에서는 기존의 저발열 혼합시멘트와 유사한 성능을 확보 가능한 것으로 나타났다. 특히 저탄소 저발열 혼합시멘트의 경우 콘크리트의 수화열도 기존 저발열 혼합시멘트에 비해 감소시킬 수 있는 것으로 나타났다.

• 열처리공학회지
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• 제21권2호
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• pp.79-86
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• 2008

As a basic research for developing 600 MPa yield strength reinforcing steel bars, the strengthening of 0.25 wt.% carbon steel by vanadium addition was studied. The changes of microstructure and mechanical properties were investigated for the specimen V0 (0.00 wt.% V), V1 (0.03 wt.% V) and V2 (0.06 wt.% V) processed by various heat treatments. To set the heat treatment conditions, the continuous cooling transformation (CCT) curves were drawn for austenitizing temperatures of $900^{\circ}C$ and $1100^{\circ}C$. For specimens tempered at $600^{\circ}C$ after quenching from $900^{\circ}C$ and $1100^{\circ}C$, yield strength was increased by 19 MPa and 21 MPa for 0.01 wt % V addition, and tensile strength was increased by 25 MPa and 28 MPa for 0.01 wt % V addition, respectively. Also, for 0.06 wt.% V added specimens tempered after quenching and normalized, tensile strength was increased by 50 MPa and 30 MPa for increasing austenitizing temperature of $100^{\circ}C$, respectively.

• Advances in materials Research
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• 제4권1호
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• pp.1-12
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• 2015

Low carbon steel of composition 0.05C - 0.18 Mn - 0.012 Si is intercritically annealed at temperatures $750^{\circ}C$, $775^{\circ}C$ and $800^{\circ}C$. The equilibrated alloys of different amounts of austenite with varying carbon contents are quenched in iced water. The same alloys are subcritically annealed at $675^{\circ}C$ and $700^{\circ}C$ for varying periods of times; the subcritically annealed alloy samples are quenched in iced water. Optical, scanning electron and transmission electron microscopy are carried out for all the samples. The dislocation structure, its distribution and density present in the above prepared duplex ferrite martensite steels are studied. The martensites are found to be highly dislocated due to lattice invariant deformation. At the same time ferrite adjoining the martensite areas also exhibits quite a high dislocation density. The high dislocation density is favorable for strain ageing and hence bakes hardenability. EDS analyses were carried out for both martensite and ferrite phases; it is found that the degree of supersaturation in ferrite together with carbon content in martensite varies with the process parameters. The microhardness test results show that the hardness values of different phases differ appreciably with process parameters. The microstructures and the corresponding microanalyses reveal that differently processed steels contain phases of varying compositions and different distribution.

• 한국해양공학회지
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• 제12권1호
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• pp.32-38
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• 1998

This paper is to investigate of microhardness, adhesive strength, tensile strength, and fatigue strength of ceramic sprayed steel. Rotary bending fatigue tests have been conducted at room temperature in air and 3% NaCl solution using specimens of carbon steel(S45C) with sprayed coating layers of Ni-4.5% Al(under coating) and $TiO_2$ (top coating). The microhardness has been improved at $800^{\circ}C$ heat treatment and 150mm spraying distance. Tensile strength of the sprayed steel is dependent on the substrate strength. The fatigue strength of the sprayed steel is larger than that of substrate due to blasting and constraint surface of plastic deformation effect. In low stress level, the corrosion fatigue strength of the sprayed steel were lower than that of fatigue strength in air by corrosion.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.802-806
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• 2001

Chrome-molybden steel or chrome steel for machine structural use been shown to excellent hardenability adding boron of a small amount at low carbon steel. In the country boron steel has been used widely high strength volt and wear resistant components of construction equipment. SEM results showed classical fatigue fractures, consistent with surface crack initiation. The speciments were cycled using under load controlled rotary bending fatigue tests. In this study, the fatigue crack initiation as well as the fatigue crack growth behavior and the fracture mechanism were investigated through observations of fracture surface boron steel(AISI 51B20).

• KSTLE International Journal
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• 제9권1_2호
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• pp.31-35
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• 2008

DLC (Diamond Like Carbon) films have predominant tribological properties like a high hardness, low friction and high chemical resistance; therefore, DLC films are applied in a wide range of industrial fields. This paper evaluated the characteristics of DLC films deposited on bearing steel with different hardness by RF-PECVD (Radio Frequency - Plasma Enhanced Chemical Vapor Deposition) method. Si-interlayer was deposited on bearing steel to improve adhesion strength by RF-Sputtering method. The DLC film structures were analyzed with Raman spectra and Gaussian function. Adhesion strength of DLC films was measured with a scratch tester. Friction and wear test were carried out with a ball-on -disc type to investigate the tribological characteristics. Experimental results showed that DLC films deposited on bearing steel under same deposition condition have typical structure DLC films regardless of hardness of bearing steel. Adhesion strength of DLC film is increased with a hardness of bearing steel. Friction coefficient of DLC film showed lower at the high hardness of bearing steel.

• 한국정밀공학회지
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• 제18권11호
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• pp.174-178
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• 2001

Chrome-molybden steel or chrome steel for machine structures has been shown to excellent hardenability adding boron of a small amount at low carbon steel. These days, boron steel has been used high strength bolt and wear resistant components of construction equipment. SEM results showed classical fatigue fractures, consist with surface crack initiation. The specimens were tested repeatedly(9 times) under controlled load rotary bending fatigue tests. In the study, the fatigue crack initiation as well as fatigue crack growth behavior and the fracture mechanism were investigated through observations of fracture of boron steel surface(AISI 51B20).

• 한국강구조학회 논문집
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• 제15권3호
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• pp.331-339
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• 2003

Thermo Mechanical Control Process(TMCP) 강재는 열간압연시에 압연 온도를 제어하면서 경우에 따라 압연직후 냉각, 열처리하여 안정된 조직으로 압연, 제조된 강재이다. 본 연구에서는 극후판 TMCP강재의 소재특성과 건축구조용 강재로서의 적합성과 특성을 밝히기 위하여 화학성분 및 조직특성, 내력 및 기계적 특성, 사용성 및 인성, 등으로 분류하여 소재특성과 용접특성을 분석하였다. 실험결과, 대상강재는 극후판에서도 설계기준강도를 만족하고 낮은 탄소당량 ($C_{eq}$) 및 용접갈라짐 감수성조성($P_cm$)과 저항복비 등이 확보되었다. 또한, 기준온도(${\pm}0^{\circ}C$)는 물론 $-60^{\circ}C$의 극저온에서도 충분한 충격흡수에너지값으로 양호한 인성의 소재특성을 나타냈고, 용접부에서도 경화현상이 저감되고, 용접부의 인성 및 내력이 충분한 것으로 나타났다.