• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1997년도 특별강연 및 추계학술발표 개요집
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• pp.36-39
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• 1997

• 한국산학기술학회논문지
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• 제9권6호
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• pp.1555-1559
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• 2008

$5{\sim}150{\mu}m$의 오스테나이트계 304(Fe-18%Cr-12%Ni) 및 316L(Fe-18%Cr-13%Ni-2.4%Mo)미립 분말을 사용하여 소결 특성을 평가한 결과, 다음과 같은 결론을 얻었다 (1) 3.6ks의 소결 시간으로는 어느 경우에 있어서나 소결조건에 관계없이 소결체의 상대밀도는 $95{\sim}98%$에서 포화하여 완전 치밀화된 소결체를 얻을 수 없었다. (2) $5{\mu}m$분말을 진공소결 하였을 경우, ts=57.6ks에서 거의 완전 치밀화된 소결체가 얻어졌다. (3) 소결 분위기에 상관없이 304 및 316L소결체에는 $0.5{\sim}0.6%$정도의 산소가 잔류하였다. (4) 진공 소결의 경우, 탄소분 첨가에 의해 소결체의 잔류 산소량은 무첨가 소결체에 비하여 0.375이상 감소하였고, 조직적으로도 산화물은 거의 관찰되지 않았다. 또한 탄소 첨가는 소결체의 밀도 향상 효과로 작용하여 목적하는 완전 치밀화된 고성능 소결체를 제조하는 것이 가능하게 되었다.

• 대한금속재료학회지
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• 제47권9호
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• pp.533-541
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• 2009

Materials used for a reactor pressure vessel(RPV) are required high strength and toughness, which determine the safety margin and life of a reactor. Ni-Mo-Cr low alloy steel shows better mechanical properties than existing RPV steels due to higher Ni and Cr contents compared to the existing RPV steels. The present study focuses on effects of Ni, Cr contents on the cleavage fracture toughness of Ni-Mo-Cr low alloy steels in the transition temperature region. The fracture toughness was characterized by a 3-point bend test of precracked Charpy V-notch(PCVN) specimens based on ASTM E1921-08. The test results indicated that the fracture toughness was considerably improved with an increase of Ni and Cr contents. Especially, control of Cr content was more effective in improving fracture toughness than manipulating Ni content, though Charpy impact toughness was changed more extensively by adjusting Ni content. These differences between changes in the fracture toughness and that in the impact toughness were derived from microstructural features, such as martensite lath size and carbide precipitation behavior.

• 열처리공학회지
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• 제9권3호
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• pp.205-211
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• 1996

Structural studies have been performed on precipitation hardening discovered in $Ll_2$-ordered $Ni_3$(Al,Cr) containing 0.2 and 0.5 mol% of carbon in terms of transmission electron microscopy(TEM). By aging at temperatures around 1073 K after solution treatment at 1423 K, fine polyhedral precipitates appear firstly on the dislocations and then in the matrix. The selected area electron diffraction (SAED) studies revealed that these particles are a $M_{23}C_6$ type carbide which has the cube-cube orientation relationship with the matrix lattice. Weak-beam electron microscopy observations of deformation induced dislocations suggested that the dislocations bypass the carbide particles during deformation.

• Journal of Welding and Joining
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• 제28권5호
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• pp.45-50
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• 2010

The fatigue crack growth characteristics of base metal and weld joint of 9% Ni steel for LNG storage tank was carried out using CT specimen at room temperature and $-162^{\circ}C$. Fatigue crack growth rate of base and weld metals at RT and $-162^{\circ}C$ was coincided with a single line independent of the change of stress ratio and temperature. In the region of lower stress intensity factor range, fatigue crack growth rate at $-162^{\circ}C$ was slower than that at RT, and the slop of fatigue crack growth rate at $-162^{\circ}C$ increased sharply with propagating of fatigue crack, fatigue crack growth rate at RT and $-162^{\circ}C$ was intersected near the region of $2{\times}10-4\;mm$/cycle, and after the intersection region, fatigue crack growth rate at $-162^{\circ}C$ was faster than that at RT. The micro-fracture mechanism using SEM shows the ductile striation in the stable crack growth region. Also the defects of weld specimen after fatigue testing were detected using the A scan of ultrasonic apparatus.

• Corrosion Science and Technology
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• 제14권3호
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• pp.127-131
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• 2015

Model alloys Fe-9Cr, Fe-20Cr and Fe-20Cr-20Ni (wt. %) with 0.1 and 0.2 % Si were exposed to $Ar-20CO_2-20H_2O$ gas at $818^{\circ}C$. The undoped alloys formed a thick iron-rich oxide scale. The additions of Si reduced scaling rates of Fe-9Cr to some extent but significantly suppressed the formation of iron oxide scales on Fe-20Cr and Fe-20Cr-20Ni. Carburisation also occurred in all undoped alloys, but not in Si-containing Fe-20Cr and Fe-20Cr-20Ni. Protection against carburisation was a result of the formation of an inner scale layer of silica.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.167-172
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• 2008

This study is to evaluate the fatigue crack growth characteristics for base metals and welded metal of 9% Ni steels. Since this material has very excellent fracture toughness at low temperature, it has been widely used for inner walls of LNG storage tank. These materials to compare fatigue crack growth (FCG) behaviour are treated with heat by the method of quenching and tempering (QT), and quenching, lamellarizing and tempering (QLT). FCG tests using compact temsion (CT) specimen under stress ratio R=0.1, 0.5, and constant load are carried out. K-increasing tests are conducted by the standard test method described in ASTM E 647. To investigate the effect of welded metal on the crack growth rate, the locations of notch tip were chosen at the center of welded metal and heat affected zone (HAZ). Form the results, FCG rate has almost same tendency according to stress ratio, base and welded metal, the locations of welded metal. FCG rate of welded metal is somewhat faster than base metal. Also scanning electron microscope (SEM) is used to observe the striation of the fractured surface after fatigue crack tests.

• 한국해양공학회지
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• 제25권4호
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• pp.12-17
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• 2011

Little design data is available for the creep life prediction of 9% Ni alloy in elevated temperatures. Therefore, in this study, a series of creep tests under 16 combined conditions with 4 kinds of stresses and 4 temperatures was performed to obtain creep design and life prediction data for 9% Ni alloy, with the following results. The stress exponents decreased as the test temperature increased. The creep activation energy gradually decreased as the stresses became larger. The Larson-Miller parameter (LMP) constant for this alloy was estimated to be about 2.

• Corrosion Science and Technology
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• 제20권6호
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• pp.373-383
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• 2021

The effect of Cr addition to high Mn steel on flow-accelerated corrosion (FAC) behavior in a neutral aqueous environment was evaluated. For comparison, two types of conventional ferritic steels (API X70 steel and 9% Ni steel) were used. A range of experiments (electrochemical polarization and impedance tests, weight loss measurement, and metallographic observation of corrosion scale) were conducted. This study showed that high Mn steel with 3% Cr exhibited the highest resistance to FAC presumably due to the formation of a bi-layer scale structure composed of an inner Cr enriched Fe oxide and an outer Mn substituted partially with Fe oxide on the surface. Although the high Mn steels had the lowest corrosion resistance at the initial corrosion stage due to rapid dissolution kinetics of Mn elements on their surface, the kinetics of inner scale (i.e. Cr enriched Fe oxide) formation on Cr-bearing high Mn steel was faster in dynamic flowing condition compared to stagnant condition. On the other hand, the corrosion scales formed on API X70 and 9% Ni steels did not provide sufficient anti-corrosion function during the prolonged exposure to dynamic flowing conditions.

• Nuclear Engineering and Technology
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• 제54권11호
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• pp.4072-4083
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• 2022

Ultrasonic impact treatment (UIT) is carried out on the Ni-based alloy stainless steel pipe gas tungsten arc welding (GTAW) girth weld, the differences of microstructure, microhardness and shear strength distribution of the joint before and after ultrasonic shock are studied by microhardness test and shear punch test. The results show that after UIT, the plastic deformation layer is formed on the outside surface of the Ni-based alloy overlayer, single-phase austenite and γ type precipitates are formed in the overlayer, and a large number of columnar crystals are formed on the bottom side of the overlayer. The average microhardness of the overlayer increased from 221 H V to 254 H V by 14.9%, the shear strength increased from 696 MPa to 882 MPa with an increase of 26.7% and the transverse average residual stress decreased from 102.71 MPa (tensile stress) to -18.33 MPa (compressive stress), the longitudinal average residual stress decreased from 114.87 MPa (tensile stress) to -84.64 MPa (compressive stress). The fracture surface has been appeared obvious shear lip marks and a few dimples. The element migrates at the fusion boundary between the Ni-based alloy overlayer and the austenitic stainless steel joint, which is leaded to form a local martensite zone and appear hot cracks. The welded joint is cooled by FA solidification mode, which is forming a large number of late and skeleton ferrite phase with an average microhardness of 190 H V and no obvious change in shear strength. The base metal is all austenitic phase with an average microhardness of 206 H V and shear strength of 696 MPa.