• Journal of Technologic Dentistry
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• v.31 no.3
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• pp.9-14
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• 2009

This study evaluated the mechanical properties of Ti-Cu alloys with the hope of developing an alloy for dental casting with better mechanical properties than unalloyed titanium. Ti-Cu alloys with four concentrations of Cu(2,5,10wt%) were made in an argon-arc melting furnace. The microstructure and micro-Vickers hardness were determined. X-ray diffraction pattern test was performed on the polished specimens. The microstructure of 2%Cu and 5%Cu alloys are shown acicular ${\alpha}Ti$ phase formed on the surfaces of previously formed $\beta$grains. The 10%Cu alloys has essentially a eutectoid structure; this structure includes lamella of ${\alpha}Ti$ and $Ti_2Cu$ phase that transformed from ${\alpha}Ti$ at the eutectoid temperature. The micro-Vickers hardness of CP Ti specimens was significantly(p<0.05) lower than that of any of the other alloys. Among the Ti-Cu alloys, the 10%Cu alloys exhibited a significantly(p<0.05) higher hardness value. but lower than that of Ti-6%Al-4%V alloy. From these results, it was concluded that new alloys for dental castings should be designed as Ti-Cu based alloys if other properties necessary for dental castings were obtained.

• Journal of Korea Foundry Society
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• v.39 no.4
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• pp.61-74
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• 2019

The effects of Sr and (Ti-B) additives on the impact and fatigue properties of recycled (35% scrap content) AC4A aluminum alloy are investigated here. The acicular morphology of the eutectic Si phase of as-cast specimens was converted to the fibrous one with Sr additives. The grain size of the α-solid solution decreased by the addition of (Ti-B) additives. The crack initiation energy (E_i) of the impact absorption energy decreased due to the incorporation of an oxide film and inclusions depending on the scrap used. The modification of the eutectic Si morphology by Sr additives is considered as the main factor of the increase of the average impact absorption energy (E_t). The addition of (Ti-B) additives contributed to an increase in the occurrence of crack deflections due to the refining of α-Al grains, resulting in improved fatigue properties.

• Proceedings of the KWS Conference
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• 2010.05a
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• pp.71-71
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• 2010

SBD (Strain-based design) of pipe lines have gained world-wide attention in recent years. The present research aims to evaluate the fracture characteristics of API (America Petroleum Institute) SBD X100 girth weldment that typically applied for cold climate and deep water offshore, with the focus on the influence of heat input changing with 6kJ/cm and 10kJ/cm from GMAW (Gas Metal Arc Welding). At a low heat input at 6kJ/cm, the weld metal had Multi-phase matrix (Acicular ferrite + Banite + Martensite) that could fill up both fracture toughness and strength as reported previously. Also, the weld metal exhibited 859MPa YS (Yield strength), 108J impact toughness at $-40^{\circ}C$ and 0.52mm CTOD (Crack Tip Open Displacement) at $-10^{\circ}C$. These results can be satisfied with the requirement of API SBD X100 girth weldment and Alaska pipe line project.

• Journal of Welding and Joining
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• v.32 no.5
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• pp.7-12
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• 2014

In this study, API-X100 steel pipes were welded with various kinds of welding wires in the laser-arc hybrid welding process. 10kW fiber laser source was combined to MIG arc welding process. API X-100 steel of base metal was of 16.9mm thickness, and butt welding applied. After welding, full penetration weld was acquired by 1-pass welding. A root porosity and the lack of fusion was observed in some welding conditions. By the mixing the melted wire, acicular ferrite, polygonal ferrite, pro-eutectoid, aligned side plate, and bainite structures were observed at the weld metal. From the observation of hybrid weld, unmixed zone had more Ni and Cr. The unmixed zone was a 1/3 area of the weld metal. As the mechanical test of the hybrid welding, tensile test and impact test applied. From the tensile test, all of the welding except SM70S was fractured at the base metal. The result of the impact test at -30 degree C led 60J~320J of the absorbed energy. The result of the low-absorbed energy might be from the coarse equiaxed structures of the weld metal.

• Journal of Korea Foundry Society
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• v.12 no.3
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• pp.230-237
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• 1992

The purpose of present investigation is to obtain ductile cast iron with ferrite-bainite matrix by pearlite-bainite transformation treatment. Ductile cast irons having three kinds of Mn ampunt had been manufactured. Mn increased pearlite volume fraction iin as-cast ductile cast iron. Ductile cast irons of different pearlite fraction were austenitized at $875\;^{\circ}C$ for 230-350 sec or $925\;^{\circ}C$ for 130-170 sec followed by austempering at $300\;^{\circ}C$ or $400\;^{\circ}C$ for the various periods of time from 5 to 30 min. When specimen was austenitixed for 130 sec at $925\;^{\circ}C$ and for 230 sec at $875\;^{\circ}C$, pearlite was transformed into austenite. Bainite around graphite was found at $925^{\circ}C$ for 170 sec. Bainite in grain boundary of ferrite was happened at $875^{\circ}C$ for 350 sec. During the austempering process, acicular bainite was precipitated at $300^{\circ}C$ and lath bainite was precipitated at $400^{\circ}C$. Increment in manganese content restrained bainitic transformation. Retained austenie was of little quantity.

• Journal of Korea Foundry Society
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• v.23 no.4
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• pp.204-211
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• 2003

Ti-3wt.%Nb(${\alpha}$type), Ti-20wt.%Nb(${\alpha}+{\beta}$,type) and Ti-40wt.%Nb(${\beta}$type) alloys were melted by vacuum are remelting. The specimens were homogenized at 1050$^{\circ}C$ for 24 hr and were then hot rolled to 50% reduction. Each alloys were solution heat treated at ${\beta}$ zone and ${\alpha}+{\beta}$, zone after homogenization, and then aged. The microstructural and hardness changes in Ti-Nb alloys with Nb contents were investigated by SEM, XRD and hardness tester. The microstructural change from equiaxied to acicular and the increase of ${\beta}$ phase in Ti-Nb alloys were obtained when the Nb content increased. The higher hardness value of ${\alpha}+{\beta}$type alloy was obtained compared to the other alloys.

• Journal of Welding and Joining
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• v.28 no.2
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• pp.79-83
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• 2010

In this study, newly developed welding consumables for EGW were welded in EH 36 TM steel plates and their welded joints were evaluated in point of mechanical properties and microstructures compared with imported consumables. Newly developed welding consumables were evaluated as good arc stability and slag fluidity, substantially the same with imported products. The tensile strength of all welded joints were sufficient to meet the requirements specified in a ship’s classification(490~640MPa) and all areas of fracture were heat affected zone(HAZ). Charpy absorbed energy values of all EG welded metals were sufficient to meet the requirements of classification(min. 34J) and those of newly developed wires were evaluated to be better than those of imported wires. As a result observing microstructures of single and tandem EG welded metals through optical and scanning electron microscope (OM&SEM), no grain boundary ferrite(PF(G)) were created in a prior austenite grain boundary and a volume fraction of a fine acicular ferrite were observed very high.

• Journal of Welding and Joining
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• v.28 no.1
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• pp.60-65
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• 2010

This paper is concerned with effects of Al, Mn and Si contents on spatter, fume, microstructure and mechanical property with 490MPa Grade Flux Core Wire(FCW). Ten kinds of FCW were fabricated by varying Mn, Si and Al contents and each FCW was weld for check the amount of spatter and fume generations, microstructures and mechanical property. Amount of spatter and fume generations was decreased with the increasing Si contents and decreasing by Al contents in FCW. And, their microstructure of weld metal were changed by Mn, Al and Si contents in FCW. With increasing of Al and Si, acicular ferrite was fine and volume fraction of acicula ferrite was increased. Thereby leading to improvement of Charpy impact property and strength.

• Journal of the Korean Society of Industry Convergence
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• v.23 no.4_1
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• pp.531-539
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• 2020

When injection mold is repeatedly used for mass production, fatigue phenomenon due to cyclic stress may occur. The surface and interior of structure might be damaged due to cyclic stress or strain. The objective of this study was to analyze failure of SCM435 high-tension bolts connecting upper and lower parts of a three-stage injection molding machine. These bolts have to undergo an accurate heat treatment to prevent the formation of chromium carbide and the action of dynamic stresses. Bolts were fractured by cyclic bending stress in the observation of ratchet marks and beach marks. Damaged specimen showed an acicular microstructure. Impurity was observed. Chromium carbide was observed near the crack origin. Both shape parameters of the Vickers hardness were similar. However, the scale parameter of the damaged specimen was about 20% smaller than that of the as-received specimen. Much degradation occurred in the damaged specimen. Bolts should undergo an accurate heat treatment to prevent the formation of chromium carbide. They must prevent the action of dynamic stresses. Bolts need accurate tightening and accuracy of heat treatment and screws need compression residual stress due to peening.

• Journal of Welding and Joining
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• v.23 no.4
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• pp.27-33
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• 2005

Quantitative evaluation was performed on the microstructure of flux-cored arc(FCA) weld metal using a method blown as IIW scheme. It was mainly intended to figure out any practical difficulties in applying this method and also to provide the consumable makers with basic guide line in developing FCA welding consumables far better properties. Assessment of the experimental results showed IIW scheme was quite reliable in the low heat input range where the acicular ferrite was a major constituent. However, in the high heat input range, some scatter was noticed as the other phases like grain boundary ferrite and Widmansttaten ferrite become dominant. It implies that the accuracy of IIW scheme depends on the faction of microstructural constituents and it become worse as the fraction of latter two phases increases. This tendency was discussed in terms of the characteristics of those two phases. In addition, base line microstructure of rutile type FCA weld metal was addressed for developing new FCA welding consumables intended for higher heat input welding.