• 한국기계가공학회지
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• 제16권4호
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• pp.76-82
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• 2017

The cylinder liner of a diesel engine is commonly made of gray cast iron. However, this cylinder liner can be damaged by the cavitation phenomenon in wet conditions. This cavitation has remained an unsolved problem until now. In this study, the cause of cavitation corrosion due to antifreeze solution was examined using a scanning electron microscope (SEM) and a 3D microscope. The necessary data to prevent the damage caused by cavitation erosion and the corrosion of gray cast iron cylinder liner was obtained. Analysis determined that the gray iron structure consists of an ${\alpha}-matrix$, flake graphite, and steadite. Cavitation erosion was initiated in the coarse flake graphite and propagated into the steadite with pitting. Under repetitive reaction conditions, the ${\alpha}-matrix$ was partially separated from the gray cast iron. This study is expected to be used as the basic data for the prevention of gray cast iron cavitation erosion and corrosion by controlling the graphite and steadite phases.

• 한국주조공학회지
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• 제42권3호
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• pp.191-197
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• 2022

This study aims to improve the machinability of gray cast irons in high speed cutting by using nonmetallic inclusions. In this research, small quantities of AL and Mg were added to conventional gray cast irons without influencing their mechanical characteristics and castability to investigate the effects of these nonmetallic inclusions in the gray cast irons on tool wear in high speed cutting. During the high speed turning of gray cast iron containing Al and Mg using a cermet tool, protective layers consisting of Al, Mg, Si, Mn, S and O were detected on the flank face and rake face of the tool, and flank and crater wear were significantly reduced compared to the turning of conventional gray cast iron and gray cast iron added with Al. The effect of inclusions on tool wear increased with increasing cutting speed, and flank and crater wear was the smallest at the cutting speed of 700m/min. Moreover, in face milling, the addition of Al and Mg drastically decreased the wear rate, and wear hardly progressed even in prolonged cutting length after initial wear. The amount of adhesion on tool faces increased as the cutting speed increased. This increase in cutting speed resulted in the formation of a thick protective layer and the reduction of tool wear. Furthermore, the addition of small amounts of Al and Mg prevented thermal cracks in the face milling of gray cast irons.

• Corrosion Science and Technology
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• 제20권3호
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• pp.143-151
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• 2021

In this study, optimal shot peening process conditions were investigated for improving the cavitation erosion resistance of gray cast iron under a marine environment. Shot peening was performed with variables of injection pressure and injection time. The durability was then evaluated through cavitation erosion test which was conducted according to the modified ASTM G-32 standard. The tendency of cavitation erosion damage according to shot peening process condition was investigated through weight loss rate, surface and cross-sectional analysis of the specimen before and after the test. As a result, the shot peening process condition that could minimize cavitation erosion was when the injection pressure was the lowest and when the injection time was the shortest. This was because the flake graphite exposed on the gray cast iron surface could be easily removed under such condition. Therefore, the notch effect can be prevented by surface modification. In addition, the cavitation erosion damage mechanism of gray cast iron was discussed in detail.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 제35회 춘계학술대회
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• pp.235-239
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• 2002

The objective of the experiment is to investigate the effect of microstructures of gray cast iron oil wear characteristics of automotive disc brakes. Six different gray cast iron rotors were manufactured by changing carbon equivalent and cooling rate. The change of DTV (disc thickness variation) before and after wear tests was measured to examine the wear properties according to the microstructures of gray iron discs since the DTV generation is caused by the circumferential uneven wear. Experimental results showed that the morphology of graphite flake and hardness in gray cast iron were crucially associated with the change of DTV. In particular, the DTV changes of rotor decrease when the length and area fraction of graphite flake in brake rotors increase and hardness of brake discs reduces.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제30회 추계학술대회
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• pp.57-61
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• 1999

The effect of the microstructure of gray cast iron on friction properties was investigated by using a pad-on-disk type friction tester. Cast iron samples used in this investigation were obtained from "step block" castings, which were designed to produce microstructure with different graphite flake morphologies from different cooling rate and solidification rate. Results of this work showed that the gray cast iron disks with long graphite flakes showed less fading. The rotors containing smaller amounts of ferrite showed higher friction coefficient and better fade resistance than others.an others.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.114-116
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• 2005

There are some problems when weld gray cast iron which is used well in automobile industry with auto MIG welding. the problems are followed like this 1) Occurrence of porosity and hardening organization. 2) Occurrence of crack due to lower elongation of gray cast iron when restraint stress works on. 3) Occurrence of porosity and unstable bead shape due to unstable arc under low current MIG welding.. especially there is a restraint on chemical composition of weld metal because the weldment demands more than 570Hv hardness. so it is hard to use Fe-Ni wire to prevent cracks occured on weldment and new welding method is needed to resolve that problems. This study shows how to prevent porosity and cracks occurring when weld gray cast iron trimming die and shows a new welding method for press die of gray cast iron

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1999년도 제29회 춘계학술대회
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• pp.240-246
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• 1999

The effect of microstructure of gray cast iron disk was investigated by using a pad-on-disk type friction tester. Three different rotors with different microstructures were studied in this work. They showed a pearlitic matrix, a ferritic matrix, and a martensitic structure, respectively. All of them have graphite flakes in common. Drag tests at different pressure and speed conditions were carried out to study friction stability, temperature rise during drags. The rotor containing pearlitic matrix showed lower values of friction coefficient, small amount of temperature rise, and less fading. The results showed that gray cast iron disk containing pearlitic matrix has good friction characteristics.

• 한국주조공학회지
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• 제3권2호
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• pp.92-99
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• 1983

This study has been carried out to investigate into the difference of rolling life and rolling wear characteristics for various gray cast iron under unlubricated dry rolling condition by amsler type wear test with 9.09% sliding.The results obtained from this study are summerized as follows: 1) It has been found that the amount of rolling wear id decreased when tensile strength and hardness are low, and then the rolling life up to generation of abnormal wear is conspicuously increased. 2) At the given condition the amount of rolling wear has been found to decrease as carbon equivalent of gray cast iron increases and resistance of crack propagation is an important factor on improvement of wear characteristics. 3) The amount of rolling wear is increased with increasing rolling revolution and wear of gray cast iron under dry rolling condition is characterized by three modes; initial wear, stationary wear and abnormal wear. 4) It has been found that the amount of rolling wear is increased with increasing maximum compressive stress and extremely increased when maximum compressive stress is over 59.1kg.f/mm.

• 소성∙가공
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• 제27권6호
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• pp.339-346
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• 2018

This study investigated the microstructure and wear properties of extruded hyper-eutectic Al-Si (15wt.%) alloy in an engine oil environment. The wear mechanism of the material was also analyzed and compared to conventional gray cast iron. In microstructural observation results of Al-15wt.%Si alloy, primary Si phase ($45.3{\mu}m$) and eutectic Si phase ($3.1{\mu}m$) were found in the matrix, and the precipitations of $Mg_2Si({\beta}^{\prime})$, $Al_2Cu({\theta}^{\prime})$ and $Al_6(Mn,Fe)$ were also detected. In the case of gray cast iron, ferrite and pearlite were observed. It was also observed that flake graphite ($20-130{\mu}m$) were randomly distributed. Wear rates were lower in the Al-Si alloy as compared to those of gray cast iron in all load conditions, confirming the outstanding wear resistance of Al-15wt.%Si alloy in engine oil environment. In the $4kg_f$ condition, the wear rate of gray cast iron was $6.0{\times}10^{-5}$ and that of Al-Si measured $0.8{\times}10^{-5}$. The microstructures after wear of the two materials were analyzed using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The primary Si and eutectic Si of Al-Si alloy effectively mitigated the abrasive wear, and the Al matrix effectively endured to accept a significant amount of plastic deformation caused by wear.

• 한국주조공학회지
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• 제2권2호
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• pp.10-17
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• 1982

This study has been carried out to determine the change of mechanical properties and microstructures by the heattreatment to relieve the residual stresses for gray cast irons. The results have been obtained from the experiment as follows; 1) The annealing above $600^{\circ}C$ for the stress relieving of gray cast iron decrease the tensile strength and hardness 2) The decrease reates of tensile strength and hardness of gray cast iron after annealing above $600^{\circ}C$ are increased with increasing the holding time. 3) The gray cast iron containing the elements of Mn, Cr has increased the heating temperature for the decrease of tensile strength and hardness. 4) The decrease of mechanical properties by annealing are assumed that the formation of ferrite takes placed from the decomposition of eutectoid cementite in the matrix.