• Journal of Welding and Joining
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• v.15 no.1
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• pp.101-108
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• 1997

In repaired weldment of ASTM A-470 class 8 high pressure stream turbine rotor steel, creep rupture life was studied in relation with carbide morphology. Carbides were identified using carbide extraction replica method. A retired rotor has molybdenum rich carbide $M_2C$, lndacochea vanadium rich carbide $M_4C_3$, and chromium rich carbides $M_{23}C_6$and $M_7C_3$. Weldments ruptured at ICHAZ showed that some of carbides have been transformed into spherical types of coarsened carbides at ruptured area. Those carbides were revealed as molybdenum rich $M_6C$ carbide and they provided cavitation sites due to molybdenum depletion around $(M_6C)$ carbide. However coarsened $M_6C$ and $M_{23}C_6$ carbides were observed at ruptured area in case of ruptured at CGHAZ.

• Bulletin of the Korean Chemical Society
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• v.15 no.3
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• pp.245-249
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• 1994

NaMg[$Cr(C_2O_4)_3]{\cdot}10H_2O$ crystallizes in the trigonal space group P$\bar{3}$c1, with a=b= 16.969(3), c=12.521(3) ${\AA}$, ${\alpha}={\beta}=90^{\circ},\;{\gamma}=120^{\circ},\;{\rho}=1.734 \;gcm^{-3},\;{\mu}=6.46\;cm^{-1}$, Z=6. Intensities for 1062 unique reflections were measured on a four-circle diffractometer with Mo K${\alpha}$ radiation (${\lambda}=0.71069\;{\AA}$). The structure was solved by direct methods and refined to a final ${\omega}$R value of 0.084. X-ray crystal structure showed that magnesium ion appears to be occupied over two sites with the occupancy ratio of 2:1. The crystal possesses 10 water molecules instead of previously estimated 9 water molecules.

• Journal of the Korean Society for Heat Treatment
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• v.12 no.1
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• pp.31-39
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• 1999

In the present study, oxidation behavior of 304 and 316 stainless steels was investigated. After solution treatment, specimens were polished up to $1{\mu}m$ $Al_2O_3$ grade and then subjected to oxidation treatment in dry air. The range of temperature was used for oxidation treatment at $300^{\circ}C{\sim}500^{\circ}C$ and TEM was used for analyzing the components and structure of oxide film. Also, these results were compared with the results of ESCA and TG. According to the results of TEM analysis, it was found that Cr oxide film was formed on top of the surface after room temperature oxidation but amorphous Fe oxide was formed on top of the surface and polycrystalline $(Cr,Fe)_2O_3$ was formed below the amorphous Fe oxide layer after $500^{\circ}C$ oxidation treatment. The oxidized specimens at $500^{\circ}C$ showed that 316 stainless steel resists more strongly to grain and grain boundary oxidation than 304 stainless steel. These results suggested that Mo component resolved in 316 stainless steel matrix suppressed the formation of Cr carbide which may results in local Cr deplete area.

• Journal of Welding and Joining
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• v.20 no.6
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• pp.99-99
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• 2002

In order to evaluate the proper fracture strength of microstructures in a steel weldment, smaller size loading ball than used for a conventional small punch(CSP) testing is required due to regional limitation on constitutive structures. In this study, the minimized loading ball(φ 1.5mm) and bore diameter of lower die(φ 3mm) were designed for an advanced small punch(ASP) test. The results obtained from the ASP test were compared with those from a CSP testing for a X20CrMoV121 steel weldment. It was found that the ASP test clearly showed the microstructural dependance on fracture strength and ductile-brittle transition behavior of the weldment. In the ASP test, especially, the cracks tend to initiate for various directions within hemispherical indentation region of an objective structure in SP test. This indicates that the evaluation of more proper fracture strength for F.L+CGHAZ, FGHAZ and ICHAZ can be performed by means of the ASP test in a steel weldment.

• Journal of Welding and Joining
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• v.20 no.6
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• pp.823-829
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• 2002

In order to evaluate the proper fracture strength of microstructures in a steel weldment, smaller size loading ball than used for a conventional small punch(CSP) testing is required due to regional limitation on constitutive structures. In this study, the minimized loading ball(${\varphi}1.5mm$) and bore diameter of lower die(${\varphi}3mm$) were designed for an advanced small punch(ASP) test. The results obtained from the ASP test were compared with those from a CSP testing for a X20CrMoV121 steel weldment. It was found that the ASP test clearly showed the microstructural dependance on fracture strength and ductile-brittle transition behavior of the weldment. In the ASP test, especially, the cracks tend to initiate for various directions within hemispherical indentation region of an objective structure in SP test. This indicates that the evaluation of more proper fracture strength for F.L+CGHAZ, FGHAZ and ICHAZ can be performed by means of the ASP test in a steel weldment.

• Transactions of Materials Processing
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• v.24 no.1
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• pp.44-51
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• 2015

The current study seeks to examine the effects of V and C additions on the mechanical and low thermal expansion properties of a high strength invar base alloy. The base alloy (Fe-36%Ni-0.9%Co-2.75%Mo-0.7Cr-0.23Mn-0.17Si-0.3%C, wt.%) contains $Mo_2C$ carbides, which form as the main precipitate. In contrast, alloys with additions of 0.4%V+0.3%C (alloy A) or 0.4%V+0.45%C (alloy B) contain $Mo_2C$+[V, Mo]C carbides. The average thermal expansion coefficients of these high strength invar based alloys were measured in the range of $5.16{\sim}5.43{\mu}m/m{\cdot}^{\circ}C$ for temperatures of $15{\sim}230^{\circ}C$. Moreover, alloy B showed lower thermal expansion coefficient than the other alloys in this temperature range. For the mechanical properties, the [V, Mo]C improved hardness and strengths(Y.S. and T.S.) of the high strength invar base alloy. T.S.(tensile strength) and Y.S.(yield strength) of hot forged alloy B specimen were measured at 844.6MPa and 518.0MPa, respectively. The tensile fractography of alloy B exhibited a ductile transgranular fracture mode and voids were initiated between the [V, Mo]C particles and the matrix. Superior properties of high strength and low thermal expansion coefficient can be obtained by [V, Mo]C precipitation in alloy B with the addition of 0.4%V and 0.45%C.

• Journal of Welding and Joining
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• v.5 no.1
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• pp.73-80
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• 1987

During PWHT, it is well known that residual stress in weld HAZ is one of the reasons for PWHT embitterment. In case of static loading, it was experimentally found that fracture toughness of weld HAZ was dependant upon PWHT conditions. However, the effects of PWHT on fatigue behavior are not clearly verified. Therefore, in this paper, the effects of heating rate PWHT conditions and residual stress simulated in weld HAZ of Cr-Mo steel on fatigue crack propagation behavior were evaluated by fatigue Testing and SEM observation. The obtained results are summarized as follows; 1. Applied stress($10 Kgf/mm^2$) in weld HAZ during PWHT tneded to decrease fatigue strength and to increase fatigue crack growth rate. 2. Applied stress and slow heating rate of 60.deg. C/hr during PWHT contributed to precipitin of impurity elements as well as carbide, which promoted the fatigue crack growth. 3. Fatigue crack growth rate decreased at the heating rate of 220.deg. C/hr in contrast with 600.deg. C/hr and 60.deg. C/hr.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.1
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• pp.89-98
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• 2003

Titanium requires special ceramic system for veneering. Low fusing dental ceramics with coefficients of thermal expansion matching that of titanium have been developed. The purpose of this study was determine the bond strengths between cast and noncast pure titanium and two commercial titanium porcelains, and to compare the results with a conventional nickel-chromium alloy-ceramic system. The bond strengths were determined using a 3-point flexure test. Three-point flexure specimens $25{\times}3{\times}0.5mm$ were prepared After removal of ${\alpha}-case$ layer, they were veneered with $8{\times}3{\times}1mm$ of ceramics at the center of the bar. Specimens were tested in a universal testing machine. Within the limits of this study, the following conclusions were drawn: 1. The bond strengths between pure titanium and two commercial porcelains exceeded th lower limit of the bonding strength value in ISO 9693(25MPa). 2. There was no significant difference between cast and noncast titanium-porcelain bonds. 3. There was no significant difference between two commercial titanium porcelains. 4. The bond strengths of the titanium-porcelain systems ranged from 73% to 79% of that of the Ni-Cr-conventional porcelain system.

• Corrosion Science and Technology
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• v.21 no.6
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• pp.454-465
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• 2022

The objective of this study was to determine effects of temperatures and pH of sodium chloride solution with MgCl₂ ions on corrosion resistance of duplex stainless-steel X2CrNiMoN22-5-3 (DSS) and Ti 6Al 2Nb1Ta1Mo (Ti). Effects of sodium chloride concentration on corrosion resistance were also studied. Corrosion behavior and pitting morphology of duplex stainless steel (DSS) and Ti alloys were evaluated through potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM). It was found that a decrease in pH significantly reduced the corrosion resistance of both alloys. Changes in chloride concentration and temperature had more substantial impact on corrosion behavior of DSS than on Ti alloys. Pitting corrosion was formed on DSS samples under all conditions, whereas crevice corrosion was developed on Ti samples with the presence of magnesium chloride at 90 ℃. In conclusion, magnesium chloride ions in an exceedingly strong acidity solution appear to interact with re-passivation process at the surface of these alloys and influence the resulting surface topography.

• Journal of the Korean Society of Radiology
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• v.6 no.2
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• pp.121-127
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• 2012

Of this study, it was found that there were 250 mammographic units in total installed and used in the areas for this study, and 36 units were used in general hospitals, 53 units in hospitals and 116 units in clinics. That is, the units in clinics accounted for 50% out of the whole units. As for the image acquisition method, it was found there were 131 units using F/S, 67 units using CR and 7 units using DR respectively. At present, F/S system was mainly used in the areas. As for the materials of target/filter, it was found that Mo/Mo was mostly used (66%), followed by Mo/Rh (25%). As for the size of focus, both 0.1 mm for small focus and 0.3 mm for large focus were mainly used for the units.