• Journal of Korea Foundry Society
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• v.35 no.6
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• pp.178-184
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• 2015

Due to excellent abrasion resistance the high-chrome white irons are widely used in mining and mineral industries. Minor variation of carbon content in 28% chrome white iron resulted in difference in primarily solidified microstructure. Sub-eutectic (hypoeutectic) composition led to formation of primarily solidified dendrites. Formation of primarily solidified dendrites which were supersaturated with carbon and chrome also caused precipitation of fine secondary carbides that are different from relatively large plate type $M_7C_3$ carbides in the eutectic structure. Small portion of primarily solidified dendrite expected to contribute significantly to the improvement of abrasion resistance of the white iron because the dendrites provided mechanical support to carbides. The relative fraction of primary dendrite increased with reduction of carbon content from the eutectic composition. The increased fraction of primary dendrite increased hardness value of the white irons.

• Journal of Korea Foundry Society
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• v.33 no.1
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• pp.1-7
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• 2013

The effect of the Mo addition on the high temperature creep properties of the 9Cr-3W steel was also evaluated. Two experimental steels, (9Cr-3W and 9Cr-3W-0.5Mo), were prepared using a vacuum induction melting process, followed by hot rolling and heat treatment processes. Three types of precipitates, ($M_{23}C_6$, Nb-rich MX and V-rich MX) were observed in a typical tempered martensitic matrix. Significant effects of the Mo addition on the tensile properties were not observed. However, the creep properties at $650^{\circ}C$ under applied stresses of 140 and 150 MPa were considerably enhanced by the Mo addition. The microstructural observation after the creep test indicated that the addition of Mo could function to retain the recovery of the martensitic matrix, thus resulting in the enhanced creep properties of the 9Cr-3W-0.5Mo steel. Furthermore coarsening of the $M_{23}C_6$ carbides and formation of Laves phases were observed in both samples after the creep tests.

• Proceedings of the Korean Nuclear Society Conference
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• 1998.05b
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• pp.66-71
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• 1998

A study of treatment effects on laser surface melted Ni-base alloy 600, especially on precipitation behavior ad chemical composition changes on the grain boundary were conducted with microscopic equipments. Long-term aging treatment at 40$0^{\circ}C$ caused no considerable effects on the grain boundary properties. Cr-rich M$_2$$_3$C$_{6}$ and Cr$_{7}$C$_3$ carbides were precipitated and the resultant Cr depletion below 12 wt pct on some high angle grain boundaries was occurred by heat treatment at $600^{\circ}C$ for 24 hours. These results can imply that the resistance of intergranular stress corrosion cracking of heat treated alloy 600 might not be changed considerably in comparion with the as-LSM one.e.e.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2000.10a
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• pp.369-374
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• 2000

This study has been achieved on the characteristics of ultrasonic wave in 2.25Cr-1Mo steel to evaluate the feasibility of ultrasonic nondestructive technique on the assessment of aging degradation. The measured values were used find a relationship between the ultrasonic propagation properties and degradation such as coarsening of carbides and precipitates. The ultrasonic attenuation coefficient was mainly affected by the grain size of prior austenitic phase as well as degradation. In this results, degradation and grain size in 2.25Cr-1Mo steel was able to cope with the changes in ultrasonic wave properties by applying the nondestructive evaluation method

• Journal of the Korean institute of surface engineering
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• v.22 no.1
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• pp.26-42
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• 1989

It has between investigated that the optimum spaying conditions, such as, spraying distance, fusing temperature and fusing time, ect, in a Ni-cr base self fluxing alloy sprayed on the mild steel substrate by oxygen-acetylenc flame spraying. Sprayed specimens on various conditions were fuused in a vacuum furnace and the results were as follows. The optimum spraying condition for excellent coating layer are obtained under spraying distances, fusing temperature and fusing and time ; 180~240mm,1050~110$0^{\circ}C$and 15~30min, respectively. The adhesive strength and surface hurface hardness of the as sprayed specimens were very low by mechanical bonding becaus of the diffusion layer during process. The carbides and borides and formed in the sprayed coating layer and densification of the layer was resulted from the elimination of pores and oxides. The hardness of sprayed coating layer, particularly in the high temperature, was superior to ordinary tool steels.

• Journal of Power System Engineering
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• v.4 no.1
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• pp.74-80
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• 2000

This present study was investigated effect of Ni contents on the high temperature strength characteristic in 9Cr ferritic heat-resistant steel added 1.7%W in place of Mo in order to restraint laves phase formation. Precipitation amount of carbide, number of particle per unit area and particle size of carbide were decreased with increase of Ni content. In the steels, carbides of $M_{23}C_6$ type was mainly precipitated, but laves phases could not precipitated. Tensile and yield strength, creep strength and creep rupture time was decreased, but elongation were increased due to decreasing of particle number per unite area and carbide amount precipitated with increase of Ni content.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.314-319
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• 2001

Most parts of facilities in domestic petroleum plants and power plants are needed to be abandoned, repaired or replaced, because in Korea they were built in the 1960s and, they have been used under severe conditions and exposed corrosive environments. 2.25Cr- lMo steels have excellent high-temperature mechanical properties. Therefore, the material have been widely used as heat exchanger tubes, boiler headers and its tubes in such industries. But, those microstructural evolutions in high temperature such as precipitation and carbide coarsening give a reason to degrade the material. Especially, in case of this material, carbides induced embrittlement(CIE) is the primary reason for degrading mechanical properties at over 50$0^{\circ}C$. In this paper, we introduce a electrochemical polarization method for detecting CIE quantitatively.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.125-137
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Journal of Ocean Engineering and Technology
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• v.3 no.2
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• pp.625-625
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• 1989

To check technical improvement in the soundness and strength of 12% Cr steel rotor, a 25 tons of rotor with 65 tons of ingot was made in real size and was cut to pieces to take test samples, and the various mechanical tests such as impact, tensile, creep, and fatigue were carried out. The strengths are compared with those of 1% Cr-Mo-V rotor of same size. Microstructures of the samples are examined and reviewed. The results can be summarized as follows. 1) Fracture appearance transition temperatures are 80.deg. C at the center part and 60.deg. C near surface of 12% Cr rotor, and 8.deg. C near surface of 1% Cr-Mo-V rotor. 2) Comparative rapid softening occurs at higher temperatures above 600.deg. C for 12% Cr steel and 550.deg. C for 1% Cr-Mo-V steel in tension tests. 3) Fatigue crack propagation rate of 12% Cr steel is almost same as that of 1% Cr-Mo-V steel at the same corresponding surface part of the rotors. The crack growth rate of center part of 12% Cr rotor is faster than near surface part of the rotor, and the crack growth rate at the load condition of R=0.04 is slower than that of the load condition of R=0.5 for both 12% Cr steel and 1% Cr-Mo-V steel. 4) Crack growth rate of radial direction near surface of 12% Cr rotor is faster than that of transverse direction at the same part because of the difference in residual stresses. 5) Both creep and fatigue strengths of 12% Cr steel are superior to those of 1% Cr-Mo-V steel and the difference is thought the effect of climb and glide controlled creep by solid solution of alloying elements and dispersion of carbides.

• Journal of Technologic Dentistry
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• v.32 no.3
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• pp.195-207
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• 2010

Purpose: The purpose of this study was to observe the microstructural changes of surface in the specimens, performing the shear bond strength testing. The currently most used non-precious alloys are nickel-chromium based alloys with or without beryllium. However, their biocompatibility has been questioned concerning possible damages to the health of the patient and professionals involved in the fabrication of prosthesis caused by long exposure to Ni and Be. An option to nickel-chromium alloys is the cobalt-chromium alloy, an alternative that does not sacrifice the physical properties of the metal porcelain systems. Studies in the animals substantially show that the cobalt-chromium alloys are relatively well tolerated, being therefore more biocompatible than the nickel-chromium alloys. Methods: Non-addition Be to nickel-chromium based alloy(Bellabond plus) and cobalt-chromium alloy which has been widely used(Wirobond C) fused with ZEO light porcelain classified control group and cobalt-chromium alloy which is developing alloy of Alphadent company in Korea(Alphadent alloy) fused with ZEO light porcelain classified experimental group. The specimens of $4mm{\times}4mm{\times}0.5mm$ were prepared as-cast and as-opaque to cast body to analyze the mechanical characteristic change, the microstructure of alloy surface. The phase change was used to observe through XRD analysis and OM/SEM was used to observe the surface of specimens as-cast and as-opaque to cast body. Chemical formation of their elements was measured with EDS. Then hardness was measured with Micro Vicker's hardness tester. Shear bond strength test thirty specimens of $10mm{\times}10mm{\times}2mm$ was prepared, veneered, 3mm high and 3mm in diameter, over the alloy specimens. The shear bond strength test was performed in a universal testing machine(UTM) with a cross head speed of 0.5mm/min. Ultimate shear bond strength data were analyzed with one-way ANOVA and the Scheffe's test (P<0.05). Within the limits of this study, the following conclusions were drawn: The X-ray diffraction analysis results for the as-cast and as-opaque specimens showed that the major relative intensity of Bellabond plus alloy were changed smaller than Wirobond C and Alphadent Co-Cr based alloys. Results: Microstructural analysis results for the opaque specimens showed all the alloys increased carbides and precipitation(PPT). Alphadent Co-Cr based alloy showed the carbides of lamellar type. The Vickers hardness results for the opaque specimens showed Wirobond C and Alphadent Co-Cr based alloys were increaser than before ascast, but Bellabond plus alloy relatively decreased. The mean shear bond strengths (MPa) were: 33.11 for Wirobond C/ZEO light; 25.00 for Alphadent Co-Cr alloy/ZEO light; 18.02 for Bellabond plus/ZEO light. Conclusion: The mean shear bond strengths for Co-Cr and Ni-Cr based alloy were significantly different. But the all groups showed metal-metal oxide modes in shear bond strengths test at the interface.