• Journal of Mechanical Science and Technology
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• 제19권2호
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• pp.496-504
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• 2005

The thermal and mechanical properties of an electro-slag cast steel of a similar chemical composition with an AISI-6F2 steel are investigated and compared with a forged AISI-6F2 steel. AISI-6F2 is a hot-working tool steel. Electro-slag casting (ESC) is a method of producing ingots in a water-cooled metal mold by the heat generated in an electrically conductive slag when current passes through a consumable electrode. The ESC method provides the possibility of producing material for the high quality hot-working tools and ingots directly into a desirable shape. In the present study, the thermal and mechanical properties of yield strength, tensile strength, hardness, impact toughness, wear resistance, thermal fatigue resistance, and thermal shock resistance for electro-slag cast and forged steel are experimentally measured for both annealed and quenched and tempered heat treatment conditions. It has been found that the electro-slag cast steel has comparable thermal and mechanical properties to the forged steel.

• 열처리공학회지
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• 제9권4호
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• pp.261-270
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• 1996

Boriding is one of the chemical methods to achieve the case hardening of steel as well as nitriding or carburizing. The surface layer of the borided steel shows higher hardness and exhibits better resistance to corrosion or fatigue than the nitrided or carburized steel. The great majority of previous studies were confined to mild steel or some alloy steel. To enlarge the application, ductile cast iron (DCI) as a material for boriding has been tried in this study. Thus, sliding wear test has conducted using a pin-on-disc machine to compare between borided DCI and mild steel in fluidized bed furnace. The results show that the wear resistance of borided DCI is improved. Especially it is more efficient in the case of occurence of the mechanical wear.

• Corrosion Science and Technology
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• 제13권2호
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• pp.48-55
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• 2014

Influence of annealing temperature on the microstructure and resistance to pitting corrosion of the hyper duplex stainless steel was investigated in acid and neutral chloride environments. The pitting corrosion resistance is strongly dependent on the microstructure, especially the presence of chromium nitrides ($Cr_2N$), elemental partitioning behavior and volume fraction of ferrite phase and austenite phase. Precipitation of deleterious chromium nitrides reduces the resistance to pitting corrosion due to the formation of Cr-depleted zone. The difference of PREN (Pitting Resistance Equivalent Number) values between the ferrite and austenite phases was the smallest when solution heat-treated at $1060^{\circ}C$. Based on the results of electrochemical tests and critical crevice temperature tests, the optimal annealing temperature is determined as $1060^{\circ}C$.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2340-2345
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• 2008

Cylindrical stainless-steel/sodium heat pipe for a high-temperature application was manufactured and tested for transient and steady-state operations. Two layers of Stainless-steel screen mesh wick was inserted as a capillary structure. The outer diameter of the heat pipe was 12.7 mm and the total length was 250 mm. As thermal transport conditions, the effective transport length, the heat flux, the tilt angle and the operating temperature were varied. The heat was supplied by an electric furnace up to 1 kW and the cooling was performed by forced convection of air. The effective thermal conductivity and the thermal resistance were investigated as a function of heat flux, heat transport length, and vapor temperature. Typical range of the total thermal resistance was as low as $0.036^{\circ}C/W$ at $175.8\;kW/m^2$ of heat flux and $700^{\circ}C$ of operating temperature.

• 한국기계가공학회지
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• 제9권6호
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• pp.7-15
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• 2010

Recently, with the high performance and efficiency of machine, there have been required the multi-functions in various machine parts, such as the heat resistance, the abrasion resistance and the stress resistance as well as the strength. Fatigue crack growth tests were carried out to investigate the fatigue characteristics of high carbon steel (SM53C) experienced by high-frequency induction treatment. The Cam nose part of the Automobile's Cam shaft is strongly bumped with rocker arm or valve-lift. Therefore abnormal wear such as unfair wear and early wear occur in the surface. This abnormal wear causes a defect that bad timing open and close actions of the engine valve happen in the combustion chamber so the fuel gas will be combustion imperfect. Therefore, the cam shaft demands high hardness and wear resistance. In this study, high frequency heat treatment has been accomplished while wear test for material SM53C.

• Corrosion Science and Technology
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• 제7권6호
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• pp.319-323
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• 2008

The polarization resistance of mild steel in 0.5M hydrochloric acid has been evaluated by using impedance (Z) and linear polarization (LPR) techniques and compared to the noise resistance obtained from electrochemical noise data. The degree of localization of this general corrosion has also been discussed by evaluating localization index and power spectral density. Polarization resistance obtained by LPR technique ($28\Omega$) was higher than that obtained by impedance technique ($15\Omega$). Noise resistance ($11\Omega$) was much lower than polarization resistance measured by both of above techniques. Higher polarization resistance obtained by LPR technique is generally caused by passivation effect in the presence of scales or deposits which can introduce an increased resistance as can low conductivity electrolytes. The reason why noise resistance is lower than polarization resistance is the effect of background noise detected by using three platinum electrodes cell in 0.5M hydrochloric acid. Slope($-\beta$) of power spectral density (PSD) obtained from analysis of noise data ($-\beta$ = 3.3) was much higher than 2 which indicates mild steel corroded uniformly. Localization index (LI) calculated from statistical analysis (LI=0.08) is much lower than 1 which indicates that mild steel did not corroded locally. However, LI value is still higher than $1x10^{-3}$ and this indicates that mild steel corroded locally in microscopic point of view.

• 한국해양공학회지
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• 제25권6호
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• pp.56-59
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• 2011

The demand for cold rolled steel (CR) for structural members is gradually increasing. If no surface treatment (coating for corrosion resistance) for CR is conducted, its use is very limited because CR is vulnerable to corrosion. Therefore, we need to develop a coating solution to provide high corrosion resistance for CR. In this study, an organic/inorganic coating solution with Si and Ti (Si polysilicate 7 wt.% + Urethane 13 wt.% + Ti amorphous 0.5 wt.%; LR-0727(1)) was used to evaluate the corrosion resistance of CR under a salt spray test. The specimens with the LR-0727(1) coating were heat treated in a drying oven at $120{\sim}210^{\circ}C$for 5 min. The corrosion resistance was investigated using a salt spray test of 7 h. In addition, an adhesive test was conducted. Rust showed under a heat treatment of $150^{\circ}C$, but no vestiges were found over $160^{\circ}C$. The specimens with heat treatment at $160^{\circ}C$ or more did not experience delamination. From these results, it is considered that the temperature limit for optimum heat treatment is $160^{\circ}C$ considering energy efficiency.

• 국제초고층학회논문집
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• 제13권1호
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• pp.85-95
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• 2024

A composite member made of concrete-filled steel tubes (CFT columns) has been recognized for its fire resistance due to the thermal mass effect of concrete inside the steel tube, as shown in various studies. In this study, the fire resistance performance of reinforced CFT columns under constant axial load was evaluated using finite element analysis with ABAQUS. For this purpose, the variables including cross-section size, steel tube thickness, and concrete cover thickness were set, and the temperature distribution in the column cross-section exposed to a standard fire was investigated using heat transfer analysis. Ultimately, a P-M interaction curve was obtained by evaluating the overall residual strength of columns, and the fire resistance time was determined by evaluating axial displacement-time responses due to the reduction in load capacity during fire through stress analysis.

• Corrosion Science and Technology
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• 제3권4호
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• pp.154-160
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• 2004

The Sulfide Stress Corrosion Cracking (SSCC) resistance of structural steels is one of the critical concerns for the operators, material designers, and fabricators of oil-field equipment, especially treating sour gas (H2S) containing fluids. As far as its fabricators concerned, the systematic care of welding parameters should be taken to obtain comparable SSCC resistance of their weldment to that of its base material. In this respect, every different type of welding joint design for this use should be verified to be SSCC-proof with relevant test procedures. In this study, the welding parameters to secure a proper SSCC resistance of steel pipe's weldments were reviewed on the Welding Procedure Qualification Records (WPQR), which had been employed for actual fabrication of an offshore structure for oil and gas production. Based on this review, a guideline of welding parameters, such as, heat input, welding consumable for Y.S. 65 ksi class steel pipe material is proposed in terms of the NACE criteria for SSCC resistance.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2000년도 춘계학술대회논문집
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• pp.75-78
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• 2000

There are several effective factors to influence die life in the warm forging process. For instance process design die design and die materials etc This study presented heat treatment method which could improve toughness and wear resistance simultaneously in high temperature to apply high speed tool steels like SKH51 to die material for warm forging process. To verify the feasibility of application of heat treatment method mentioned above wear test was performed under the condition of constant time in 40$0^{\circ}C$ Wear coefficient was examined to search a relation between wear amount and time for each material and heat treatment method in 30, 60, and 130 minutes. To quantify the toughness-behavior between room and high temperature impact test was performed and heat fatigue test also fulfilled to compare with the resistance of heat check in room, 200, 400, and $600^{\circ}C$ temperature. On the basis of experimental results mentioned above high speed tool steel was applied to verify appropriateness of newly proposed heat treatment method for die of rotor pole used in automobile alternator. As a result die life of high speed tool steel applied newly proposed heat treatment is longer than that of STD61.