• 한국자동차공학회논문집
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• 제25권2호
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• pp.207-218
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• 2017

Improving fuel consumption, particularly that of commercial vehicles, has become a global concern. The reduction in logistics cost has been a key issue in efforts to improve fuel economy and efficiency of transportation equipment. Typical technologies for reducing reduce fuel usage include air resistance reduction technologies, tire rolling resistance technologies, and idle technologies among others. Air resistance technology is a highly effective method that can be easily applied in a short period. As with air resistance technology, several devices involving side skirt, boat tail and gap fairing have been developed based on an analytical 3-D modeling technique for reducing air resistance attributed to the vehicle configuration. The devices were on a 45 feet tractor-trailer and the emission test was done using PEMS equipment. Fuel economy was evaluated by introducing several devices to reduce outer air resistance. The test was conducted by changing the experimental method of SAE J1321 Joint TMC/SAE Fuel Consumption Test Procedure - Type II test. As a result, air resistance decreased by at least 15 % and fuel economy improved by at least 13 %. This study sought to reduce greenhouse gas and improve fuel economy by applying several devices to a test vehicle to lower air resistance.

• 한국분말재료학회지
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• 제27권4호
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• pp.311-317
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• 2020

In this study, the effects of Co content on the microstructure and Charpy impact properties of Fe-Cr-W ferritic/martensitic oxide dispersion strengthened (F/M ODS) steels are investigated. F/M ODS steels with 0-5 wt% Co are fabricated by mechanical alloying, followed by hot isostatic pressing, hot-rolling, and normalizing/tempering heat treatment. All the steels commonly exhibit two-phase microstructures consisting of ferrite and tempered martensite. The volume fraction of ferrite increases with the increase in the Co content, since the Co element considerably lowers the hardenability of the F/M ODS steel. Despite the lowest volume fraction of tempered martensite, the F/M ODS steel with 5 wt% Co shows the highest micro-Vickers hardness, owing to the solid solution-hardening effect of the alloyed Co. The high hardness of the steel improves the resistance to fracture initiation, thereby resulting in the enhanced fracture initiation energy in a Charpy impact test at - 40℃. Furthermore, the addition of Co suppresses the formation of coarse oxide inclusions in the F/M ODS steel, while simultaneously providing a high resistance to fracture propagation. Owing to these combined effects of Co, the Charpy impact energy of the F/M ODS steel increases gradually with the increase in the Co content.

• 동력기계공학회지
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• 제16권3호
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• pp.51-56
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• 2012

The effect of deformation induced martensite transformation on the mechanical properties in austenitic stainless steel with high Mn was studied. ${\alpha}$'-martensite was formed by deformation in austenitic stainless steel with high Mn. Deformation induced ${\alpha}$'-martensite was formed with surface relief by cold rolling. With the increase of deformation degree, volume fraction of deformation induced martensite was increased rapidly in early stage of deformation and then, increased slowly. With the increase of deformation degree, hardness and tensile strength were rapidly increased with linear relations, while elongation was rapidly decreased and then slowly decreased. Hardness, tensile strengths and elongation were influenced strongly by deformation induced martensite.

• 한국자동차공학회논문집
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• 제14권6호
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• pp.95-103
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• 2006

Wheel treads of E.M.U. are usually under a heavy thermal load by brake frictional heat between wheel and brake shoe and damaged by repeated thermal and mechanical loads. To examine the cause of wheel tread damage of E.M.U.'s in service running, a systematic approach has been used. This study is composed of three parts. Frictional heat analysis was conducted in the first part by finite element method. Two kinds of brake shoes in service were considered. In the second part, experimental study was carried out on a brake dynamometer. Temperatures were measured for the two brake shoes. And experimental study in service running E.M.U.'s was performed. Wheel and brake shoe temperatures were measured by using thermocouples and temperature indicating strips. Finally metallurgical characteristics were examined by a SEM/EDS and the cause of the wheel damage was analyzed. It seems that aggregated ferrous component is a main cause of the wheel tread damage.

• 대한조선학회논문집
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• 제44권1호
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• pp.1-7
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• 2007

Recently, researches to find rational mathematical model for prediction of capsizing have been progressed by ITTC. Lee(1997) developed a mathematical model which describes 6 DOF transient motions, such as capsizing, of a ship in regular waves. In this study a mathematical model for prediction of capsizing in following and quartering seas is developed based on Lee's model. And factors affecting prediction of capsizing are analyzed through comparing simulation results with experimental results. Present simulation results are compared with ITTC bench mark test results. In rolling tests with beam seas and tree runs with stern quartering seas, capsizing events are predicted well. But calculated roll angle is larger than experimental one. It is found that nonlinear manoeuvring coefficients don't affect the prediction of capsizing events.

• 열처리공학회지
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• 제6권2호
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• pp.89-97
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• 1993

An improvement in corrosion resistance of various types of Zn-coated steel sheets is thought to be possible with the addition of fine oxide powder to the coating. In this study the corrosion resistance of the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheet has been investigated and the results were as follows : The corrosion resistance of $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheets was improved by increasing the contents of Co and Cr ions, and also $Al_2O_3$ powders in the bath because of the increased amount of Co, Cr and $Al_2O_3$ in deposits. In the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steels sheet, the structure of deposits was changed from fine microstructure as observed in high Co containing deposits to coarse microstructure as in high Cr and $Al_2O_3$ containing deposits. By cold rolling of the $Al_2O_3$ dispersed Zn-Co-Cr electroplated steel sheets to about 2 percent, thr corrosion resistance was improved further.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1999년도 제3회 압연심포지엄 논문집 압연기술의 미래개척 (Exploitation of Future Rolling Technologies)
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• pp.37-46
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• 1999

Sheet pil VL 제조에 있어서 핵심적인 중요 기술은 압연 중 진행 소재가 좌우 휨이 없이 직진토록하여 치입 상에 문제가 없어야 하는 것이며, 또 하나는 압연 완료후 냉각 중에 있는 제품의 bending량을 최소로 하여 roller 교정기에서 1차 교정으로 교정이 완료되게 하는 것이다. 압연중 소재가 직진토록 하기 위해서 web와 flange 등의 caliber 협상에서 balance가 유지되어야 하므로, web와 flange의 reduction을 1:1 vs 1.0으로 web의 압하가 flange에 비해 10%정도 크게 하였고, 좌우 flange의 reduction이 변화하지 않도록 flange 온도 보존을 위하여 intermediated에서 2 pass를 생략하여 약 40초의 rolling time을 단축시켰고, 이는 7$0^{\circ}C$정도의 온도 drop를 방지하는 효과를 나타내었다. 이로 인한 roll force는 약 15%정도 down 되었다. 논리상으로 A3 변태점 이하에서 web(두꺼운 부분 24.3mm)나 flange(얇은부분 9.5mm)가 동시에 압연이 완료된다면 bending량은 휠씬 줄어든 것이나, 이 경우 roll force 증가에 따른 roll 절손 사고의 위험과 설비 trouble이 우려되기 때문에 web 온도를 약 95$0^{\circ}C$에서 flange 온도를 83.$0^{\circ}C$에서 압연 완료토록 함으로써 설비 안전을 도모하였고, 1차 교정을 위하여 냉각 주수 설비를 설치하여 공냉시켰을 때의 1400mm에서 700mm로 bending량을 감소시킴으로써 이를 가능토록하였다.

• Journal of Welding and Joining
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• 제32권5호
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• pp.21-25
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• 2014

Oil and gas fields were left unexploited which deemed too deep and sour. New developing markets are emerging in this part and pipe manufacturers need demanding requirements in the combination of sour service requirements with heavier wall thickness required to cope with increasing water depths. Whilst, the strength and fracture toughness needed to meet the strict requirements In order to deliver the optimum sour properties in the final pipe, attention needs to be paid to each stage throughout the process from steel making. The main key during steel making is strengthening, securing mechanical properties and suppression of center segregation by adding proper chemical elements and controlling water cooling and plate rolling. Additionally in welding, it is required to prevent HAZ softening by high heat input during welding of heavy thick pipes and hydrogen assisted cracking in high strength steels with hard phases. In this paper, we introduce markets of sour resistant linepipe steels and in response to this, have a look in the development trend of sour resistant linepipe steels and its sour characteristics in welded joints.

• 소성∙가공
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• 제19권6호
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• pp.329-336
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• 2010

Ring forging process is more appropriate for high-length and thin walled ring, because it utilizes the forging press and hence does not require heavy-duty ring rolling mill. Although ring forging process is very simple and economic for facilities, the process is not efficient because of multi-forging-step and low material utilization. An effective ring forging process is developed using a hollow ingot. When a hollow ingot is used with a workpiece, the ingot can be forged into a final ring without multi-stage pre-forging process, such as, cogging, upsetting, and piercing, etc.. Finally it has advantages of the material utilization and process improvement because a few reheating and forging process are not necessary to make workpiece for ring forging. The important design variables are the applied plastic deformation energy to eliminate cast structure and make uniform properties. In this study, the mechanical properties after forging of hollow cast ingot were investigated from the experiment using circumferential sectional model. Also, the effects of process variables were studied by FEM simulation on the basis of thermo-visco-plastic constitutive equation. Applied strain is different at each position in length direction because diameter of hollow ingot is different in length direction. The different strain distribution become into a narrow gap by additional plastic deformation during diameter extension process.

• 한국경영과학회:학술대회논문집
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• 대한산업공학회/한국경영과학회 2002년도 춘계공동학술대회
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• pp.109-113
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• 2002

Steel industry is the most capital intensive and the largest energy consuming industry, which operate huge and complex facilities to supply various steel products as the primary materials to almost every manufacturing industry Major steel products are hot-rolled and cold-rolled coils, plates, and wires that are produced through molten iron making, molten steel making, casting, and rolling. Each process runs in batch between setups and the specifications or bach are different with each other High energy consuming and heavy material handling require careful synchronization or processes, as well. Considering the synchronization or processes, the lot planning and scheduling problem in the integrated steelmaking process rovers the roll grouping with given casts. the sequencing or rolls over time, and the machine assignment and time scheduling or charges and casts. The problem is investigated by dividing it into two cases whether single or parallel machines at the molten steel making and the continuous casting processes. Problem descriptions and solution approaches or each instance are introduced. To test their performance and conformity, implementation or the algorithms and numerical experiments are carried out with real world and constructed data sets.