• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.20 no.5
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• pp.646-652
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• 2011

Recently, lots of automobile part manufacturers try to increase glass fiber content of their plastic parts to improve strength and impact-resistance. For this reason, injection mold requires high hardness and wear-resistant. Laser surface treatment is used to improve characteristics of wear and to enhance the fatigue resistance for injection mold. In this paper, high carbon steel (HP4MA) for injection mold material was heat-treated to harden surface by using high power diode laser (HPDL). To find the process parameters for laser surface treatment of HP4MA, many experiments are carried out as changing the parameters of surface temperature and travel speed of laser. From the results of the experiments, it has been shown that the maximum average hardness is approximately 711~739 Hv when the temperature and the travel of laser are $1,050^{\circ}C$ and 2 mm/sec.

• Journal of Korea Foundry Society
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• v.42 no.6
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• pp.392-397
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• 2022

In order to compliant the stringent exhaust emission regulations, higher fuel efficiency and cleaner exhaust gas in combustion engines have been required. To improve combustion efficiency, an exhaust gas temperature is increasing, therefore higher temperature resistance is required for components in exhaust system, especially turbine wheel in turbocharger. IN100 looks quite attractive candidate as it has high temperature properties with low density, however it has low castability due to poor ductility at high temperature. In this study, the balance of Al and Ti composition was optimized from the base alloy IN100 to improve the high temperature ductility by expanding the γ single phase region below the solidification temperature, while obtaining the high temperature strength by maintaining the volume fraction of γ' phase equivalent to IN100 around 1000℃. Furthermore, the high temperature creep rupture life increased by adding a small amount of Ta. The alloy developed in this study has high castability, low density and high specific strength at high temperature.

• Fire Science and Engineering
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• v.28 no.5
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• pp.52-57
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• 2014

When structural elements of steel framed structures are exposed to fire situations, the structural stability begins to decrease due to dislocation of substantial. The increase of the beam length causes an additional stress and deflection. These can be serious factors to cause a severe failure of structures. To improve the fire resistance of beams, prevention of the heat from a fire by coating with fire protection material is essential for beams. The FR 490 was developed to enhance fire resistance compared with SM 490 steel. However, the fire resistance of FR 490 H-beams has not been evaluated by analysis method since it was developed. In this paper, materials properties in high temperature and a heat transfer and thermal stress theory were used in the evaluation of the fire resistance of FR490 H-beams. The fire resistance of FR490 steel beams was compared with that of SM490 beams. The comparison verified that the structural stability of FR490 beams at high temperature was superior to that of SM490 beams.

• Journal of the Korean Society for Heat Treatment
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• v.23 no.4
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• pp.198-204
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• 2010

Modified 9Cr-1Mo steels possess excellent high-temperature mechanical properties and are widely used in energy conversion industries. However, in-service materials degradation, such as softening, carbide-induced embrittlement, temper embrittlement, etc., can take place during long-term operation. Evolution of microstructure due to service exposure to high temperature has a strong effect on the performance of heat resistant steels. In case of modified 9Cr-1Mo steels, precipitation of $Fe_2Mo$-type laves phases and coarsening of $M_{23}C_6$-type carbides are the primary cause of degradation of mechanical properties such as toughness, hardness, tensile strength and creep resistance. This study was aimed at finding reliable parameter for assessing the integrity of modified 9Cr-1Mo steels. Characteristic parameters were attained between mechanical and ultrasonic properties.

• Journal of Welding and Joining
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• v.34 no.6
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• pp.1-10
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• 2016

Flux Cored Wire is the most widely used welding material for Flux Cored Arc Welding these days. This paper introduces the technical aspects of manufacturing FCW and the development trend of FCW for each type of steel and metal. The studies are ongoing to lower the production cost of seamless-type FCW since it has not been generally used in welding shops so far because of it high cost even though the seamless-type FCW has various advantages than folded-type FCW in terms of manufacturing technology. Meanwhile, a technical research has been carried out to develop a rutile type of FCW products which satisfies high toughness after post heat treatment. In addition, for high-speed fillet welding, there has been a development of welding materials which can be welded in Single Auto-Carriage 100 cpm or more and up to Twin Tandem 200 cpm without occurring any welding defect in order to improve the welding productivity. As Zn coated steel is being used recently to improve the corrosion resistance of the automotive parts, a research and development for Metal Cored Wire has been conducted to reduce the Si island produced in welding operation than those produced when using the former solid wires. A development of welding material that guarantees CTOD performance beyond $-40^{\circ}C$ CTOD to $-60^{\circ}C$ is underway by different steel grades, and FCW for super austenitic stainless steel is being developed as the corrosion resistant steel has been upgraded.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.6
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• pp.70-77
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• 2000

In this paper, the effect of solution and age heat treatment to the corrosion behavior for the Ti-6Al-4V alloy were studied by cyclic polarization methods. Ti-6Al-4V was solution heat treated at $1,066^{\circ}C$ and $966^{\circ}C$ for 5 hours, and followed by age heat treated at $650^{\circ}C$, $600^{\circ}C$ and $550^{\circ}C$ with 1, 2, 4, 8 and 16 hours under vacuum environment. Test solution was 3.5% NaCl with temperature $25^{\circ}C$. The obtained results were as follows: 1. Base metal was exhibited higher electrical charge than that of solution and aged material. With decrease of solution-treatment temperature from 1066 to $966^{\circ}C$, the electrical charge was increased due to softening of micro structure. 2. The corrosion resistance of specimen that solution treated at $966^{\circ}C$ for 5 hours and age heat treated at 650, 660 and $550^{\circ}C$ were increased with increase of aging time to 4, 8 and 16 hours respectively, and then decreased. 3. In case of 316L stainless steel, measured charge and corrosion potential was 0.0627 coulomb and -614 mV respectively. Corrosion resistance of Ti-6Al-4V was higher than that of 316L.

• Journal of the Korean Recycled Construction Resources Institute
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• v.5 no.2
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• pp.83-90
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• 2010

As a reinforced fabric, asbestos has been utilized as a fire-resistant material as it has a superior flexural stiffness and heat resistance up to $1500^{\circ}C$. However, due to its harmfulness, its use has been prohibited recently and the even the installed asbestos materials are being repaired or supplemented if there is a concern about flying. Asbestos is mainly used for construction panels as a reinforced fabric and coating materials to ensure the fire-resistance of steel frames. Asbestos was used as fire-resistant materials for steel frames until 1991 and then prohibited as Act on Industrial Safety and Health limits the concentration of asbestos in the air. Classified as a designated waste according to Act on Waste Control, asbestos must be buried if there is no possibility of flying (panel-type materials) or cement-solidified and then buried if there is a possibility of flying (spray coating material) In general, it is required that a new waste landfill include a certain landfill facility for designated waste, but in reality there is an absolute storage of landfill facilities for designated waste as they only install facilities of the size required by the regulations. This could result in the 2nd environmental pollution as they cannot process asbestos wastes which will be generated in large volume in the future. This study explores a method that melts asbestos wastes at $700^{\circ}C$ rather than cement-solidifying the waste asbestos from construction sites, especially asbestos-containing spray coating. The study results showed that there was no change in the composition and shape even though asbestos wastes was melted at $1300^{\circ}C$, but there was a change for the specimen which was process in advance for low temperature melting and then melt at $900^{\circ}C$.

• Computers and Concrete
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• v.19 no.6
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• pp.711-716
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• 2017

This paper presents a method using artificial neural networks (ANNs) to predict the residual moment capacity of thermally insulated reinforced concrete (RC) beams exposed to fire. The use of heat resistant insulation material protects concrete beams against the harmful effects of fire. If it is desired to calculate the residual moment capacity of the beams in this state, the determination of the moment capacity of thermally insulated beams exposed to fire involves several consecutive calculations, which is significantly easier when ANNs are used. Beam width, beam effective depth, fire duration, concrete compressive and steel tensile strength, steel area, thermal conductivity of insulation material can influence behavior of RC beams exposed to high temperatures. In this study, a finite difference method was used to calculate the temperature distribution in a cross section of the beam, and temperature distribution, reduction mechanical properties of concrete and reinforcing steel and moment capacity were calculated using existing relations in literature. Data was generated for 336 beams with different beam width ($b_w$), beam account height (h), fire duration (t), mechanical properties of concrete ($f_{cd}$) and reinforcing steel ($f_{yd}$), steel area ($A_s$), insulation material thermal conductivity (kinsulation). Five input parameters ($b_w$, h, $f_{cd}$, $f_{yd}$, $A_s$ and $k_{insulation}$) were used in the ANN to estimate the moment capacity ($M_r$). The trained model allowed the investigation of the effects on the moment capacity of the insulation material and the results indicated that the use of insulation materials with the smallest value of the thermal conductivities used in calculations is effective in protecting the RC beam against fire.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.21 no.3
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• pp.12-21
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• 2022

Directed energy deposition (DED) was adopted as a metal additive manufacturing method to develop a mold for the hot stamping process. The test piece was machined from Heatvar laminate material, and results were obtained through microstructure and defect observations, as well as hardness, tensile strength, and joint strength tests. 1) Spherical pores and irregular-shaped cavities were observed as lamination defects, and columnar dendrites formed in the structure, which tended to become coarse upon heat treatment. 2) The hardness of the heat-treated material (480HV) was slightly lower than that of the non-heat-treated material (500HV). 3) In the tensile test, the maximum tensile stress and strain of the heat-treated material were 1392 MPa and 15%, respectively, which were slightly higher than the values of 1381 MPa and 13%, respectively, for the non-heat-treated material. 4) In the case of the early final fracture in the tensile test, in most cases, pores or irregularly shaped cavities were observed at the fracture surface or near the surface. 5) In the joint strength test, most of the specimens finally fractured in the laminated metal area, and the fracture surface was intragranular. In addition, dimples formed over the entire area on the fracture surface of the fractured specimen after sufficient elongation.

• Journal of Korea Foundry Society
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• v.26 no.5
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• pp.222-226
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• 2006

Steel making slag has gained a considerable attraction as one candidate of eco-materials in research fields for recycling resources. Thus, many researches have been performed but were limited to development of substitute for cement being used in the construction field. A little research work also has been done on development of higher value-added materials, including heat resistant and sound absorbing materials. For this reason, the present study were focused on macrostructure characterization of fabricated slag fibers which are applicable to heat resistant materials. The slag fibers were fabricated through a modified melt extraction method. The processing variables employed were the wheel speed and molten slag temperature. The synthesized fibers were characterized by optical microscope and scanning electron microscopy. It was found that the wheel speed of 1400 rpm generated better quality of mineral fibers in terms of the relative amount of shot, diameter and length. This was attributed to the relative extent of contact width between the flowing melt and the rotating wheel. The thickness of the slag fibers also were decreased with increasing the slag melt temperature due mainly to significant decrease in the viscosity of the slag melt. In addition, the lower melt temperature caused an increase in number of shots plus the mineral fibers.