• Proceedings of the KSME Conference
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• 2004.04a
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• pp.216-221
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• 2004

Linepipe steels with a low carbon acicular ferrite microstructure have been recently developed to accommodate the current transportation condition of the gas and oil industry, and they are finally applied to West- East pipeline project in China. By adopting acicular microstructure, both better formability and better toughness could be obtained due to low yield ratio and fine grained microstructure. Mechanical properties of pipe are not greatly different from those of base plates or hot coils with a microstructure of acicular ferrite. Merits of introducing higher strength steels are well known, i.e., reducing the gauge of pipe and the material cost, increasing the welding speed and decreasing construction cost because of reducing the construction period. Threfore, gas and oil industry has required higher strength steel than APIX70 grade steel. Under this background, API-X80 steel has been developed and shall be applied to the several projects. In this paper, developing stage of API-X80 steel is also presented and discussed.

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.248-249
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• 2003

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.278-280
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• 2003

• Journal of the Korean Society of Industry Convergence
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• v.24 no.5
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• pp.525-530
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• 2021

The purpose of this study was to investigate the effect of spherodizing heat treatment holding time on the microstructure and mechanical properties of the accelerated cooling-treated API X70 steel, which is mainly used as a structural material for line pipe steel for natural gas pipes. The accelerated cooling-treated API X70 steel was spherodizing treated at 700℃ for 12~48 h. The microstructure was observed using an OM and a FEG-SEM, and mechanical properties were obtained by tensile test. The microstructure of the API X70 steel was banded in the hot rolling direction, and the polygonal ferrite(PF) adjacent to pearlite(P) has mainly a fine size, and coarse PF and fine acicular ferrite were formed in the middle of P and P. As the spherodizing treatment time increased, the number of carbide particles decreased and its distribution interval increased, and the ferrite grain size was coarsened. The tensile strength decreased and the ductility increased with spherodizing treatment time, and the yield point elongation was disappeared in a stress-strain curve after the spherodizing treatment.

• Journal of the Korean Institute of Gas
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• v.16 no.3
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• pp.54-64
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• 2012

DWTT (Drop Weigh Tearing Test) is one critical method that can exhibit the fracture properties of line pipe steel, since it estimates the properties with real pipe steel. In this study, the ductile portion, inverse fracture ratio and absorbed energy of API X65 and X70 line pipe steels were estimated with temperature variation. Both steels showed that the ratio of ductile area and absorbed energy were decreased with respect to decreasing the test temperature. However, while the ductile fracture behavior exhibited until $-40^{\circ}C$ for the X70 steel, but it showed until $-30^{\circ}C$ for the X65 steel. The fracture properties were discussed with respect to test temperatures.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1292-1300
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• 1996

In-site X-ray diffraction measurements under electric field up to 20kV/ cm were carried out on PLZT (x/70/30) with x=7.5, 8.0, 8.5, and 10.5 All of PLZT belonged to cubic phases. At x=7.5, 8.0 and 8.5 PLZT behaved as an antiferroelectric under low electric fields up to 4-8 kV/cm. PLZT became ferroelectric at the higher electric fields. The high-temperature measurements on the dielectric constants of PLZT with x=7.5, 8.0 and 8.5 showed that they were similar to relaxor ferroelectrics and underwent a diffuse phase transition from antiferroelectrics to paraelectrics at 50-7$0^{\circ}C$. Their P-E hysteresis curves confirmed that they were antifer-roelectrics. The broad distribution of Curie points suggests that there is a significant disorder of cations and vacances in the crystal structure of those PLZT due to La-substitution. The variation of the lattice strain of PLZT(10.5/70/30) with electic field was very small and did not show any hysteresis confirming that it was paraelectric. The degree of the electric-induced strain variation decreased as La doping increased. In PLZT(7.5/70/30) the intensity of 110 reflection changes sensitively by applying electric field. Some domains with polarization parallel to [110] appeared to be developed in the field-induced ferroelectric phase of the PLZT.

• Journal of Hydrogen and New Energy
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• v.31 no.3
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• pp.284-292
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• 2020

In this study, hydrogen charging was conducted for API X70 steel by the electro-chemical hydrogen charging method. Right after hydrogen was diffused from the specimen surface to the inside of the X70, the small punch tests and hydrogen concentration analysis was conducted within 5 minutes. Hydrogen was analyzed by melting the whole specimen and detect the gas after melting. Mechanical properties were measured by the small punch (SP) testing. Fracture surface and specimen surface were observed using scanning electron microscope. Three tests were repeated for study sensitivity of the SP test results under a same charging condition. It was observed that the variation of the maximum load, SP displacement at failure, hydrogen concentration as the charging period was not much in the case of X70 as the other steel such as Inconel. It can be argued that X70 base metal may have high hydrogen damage resistance and hydrogen diffusion in the base metal would not cause much embrittlement. Limitations of the SP test with 0.5 mm thickness for hydrogen damage test for X70 were discussed.

• Proceedings of the Korean Society Of Semiconductor Equipment Technology
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• 2004.05a
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• pp.234-239
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• 2004

본 연구에서는 마이크로파용 유전재료로서 널리 사용되고 있는 BNT($BaO-Nd_{2}O_{3}-TiO_{2}$)계 세라믹스를 기본조성으로 하고, 저융점의 phoshpate계 유리 프릿의 첨가를 통해 LTCC(Low Temperature Cofired Ceramic)에 적용 가능한 유전율을 가진 조성을 개발 하고자, $70P_{2}O_{5}-5B_{2}O_{3}-(25-x)BaO-xNa_{2}O$ 유리를 제조 및 특성을 평가하였다. 또한, BNT계 세라믹스에 glass frit을 5 - 15 wt% 범위에서 첨가하고, $800 - 950^{\circ}C$의 온도범위에서 소결하여 제조된 유리-세라믹 복합체의 소결특성 및 유전특성을 조사하였다.

• Proceedings of the KOSOMBE Conference
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• v.1997 no.05
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• pp.27-30
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• 1997

As the fundamental study of designing x-ray dosimeter , we measured the voltage variation of CdS, II-VI group semiconductor compound, by mAs variation. We obtained data in the condition of 50, 70 kVp, by increasing the tube current as 1, 2, 2.5, 3.2, 4, 5, 10, 20, 32, 50 and 80 mAs. The output time of CdS was increased as mAs increased. We figured the slope value of 50kVp as 0.0088 and 0.0081 of 70 kVp. And by regression method, we obtained the standard deviation of time, Y axis, at 50 and 70kVp as 0.00268 and 0.00333. The result of this ssudy is so important to design x-ray dosimeter.

• Korean Journal of Mathematics
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• v.23 no.1
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• pp.153-161
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• 2015

In this work, we consider an elliptic system $$\left{\array {-{\Delta}u=au+bv+{\delta}_1u+-{\delta}_2u^-+f_1(x,u,v) && in\;{\Omega},\\-{\Delta}v=bu+cv+{\eta}_1v^+-{\eta}_2v^-+f_2(x,u,v) && in\;{\Omega},\\{\hfill{70}}u=v=0{\hfill{90}}on\;{\partial}{\Omega},}$$, where ${\Omega}{\subset}R^N$ be a bounded domain with smooth boundary. We prove that the system has at least two nontrivial solutions by applying linking theorem.