급냉응고법에 의한 금속 섬유제조에 관한 연구

허성강,나형용,백남익 한국주조공학회 1989 한국주조공학회지 Vol.9 No.5

Metal fibers of Al and stainless steel were fabricated by the PDME method and the Taylor process. Tensile strength of metal fiber produced by both the PDME method and the Taylor process was much higher than that of conventionally solidified materials. Utilizing the PDME method, Al fiber with 100㎛ was fabricated under Ar gas atmosphere, and stainless steel fiber with 50㎛ was fabricated under 0.06 Torr vacuum. Continuous fiber of stainless steel was made by the Taylor process and the surface of this fiber was smother than that fabricated by the PDME method.

Mod.9Cr1Mo강에서 발생되는 일시적 취성현상

허성강,구지호,신기삼,신종호,Hur, Sung-Kang,Gu, Ji-Ho,Shin, Kee-Sam,He, Yincheng,Shin, Jong-Ho 한국재료학회 2011 한국재료학회지 Vol.21 No.11

It is well known that modified 9Cr-1Mo steel has a low thermal expansion and high thermal conductivity with excellent high temperature properties compared to austenitic stainless steel. For these advantages, the steel is very popular for the boiler tube of thermal power plants. Normalizing is commonly utilized to obtain martensite in this steel, which shows an unusual toughness for martensite. However, some accidents related to this steel have been reported recently, opening the necessity for further study. As a particular behavior of the steel, an abrupt drop of the impact value has been identified upon tempering at 750$^{\circ}C$ for about 1 hour. It is well known that $Fe_3C$ forms during autotempering and turns to $Cr_2C$ at an early stage and then transforms to $Cr_{23}C_6$. In this study, the cause of the abrupt drop of the impact value was investigated with an impact test, microstructural observation, nanodiffraction and phase analyses using instruments such as optical and transmission electron microscopes (TEM) with an extraction carbon replica of the carbides. The analyses revealed that the $M_2C$ that formed when retained for about 1 hour at 750$^{\circ}C$ causes a drastic decrease in the mechanical properties. The sharp drop in mechanical properties, however, disappeared as the $M_2C$ transformed into $M_{23}C_6$ with longer retention.

Mod.9Cr-1Mo강의 항온변태시 기계적 특성변화에 미치는 Cr탄화물의 영향

허성강,이재현,구지호,신기삼,신종호,Hur, Sung-Kang,Lee, Jae-Hyun,Gu, Ji-Ho,Shin, Kee-Sam,He, Yinsheng,Shin, Jong-Ho 한국재료학회 2012 한국재료학회지 Vol.22 No.1

In this study, mechanical tests and microstructural analyses including TEM analyses with EDX of precipitates in modified 9Cr-1Mo steel were carried out to determine the cause of embrittlement observed after heat-treatment, which limits the usage of the alloy for power plants. Mod. 9Cr-1Mo steel specimens at austenite temperature were quenched to the molten salt baths at $760^{\circ}C$ and $700^{\circ}C$, in which the specimens were kept for 10 min ~ 10 hr with subsequent air-cooling. Impact tests showed that the impact value dropped abruptly when the specimens were kept longer than 30 min at $\sim760^{\circ}C$ reaching to minima in about 1 hr, and then increasing at further retention. The tensile strength of the specimens reached the minimum value without much change afterward, whereas the values of elongation showed the same trend as that of the impact value. The isothermally heat-treated steel at $700^{\circ}C$ also showed a minimum impact value in about 1 hr. These results suggest that the isothermal heattreatment at 760 and $700^{\circ}C$ for about 1 hr induces temporal embrittlement in Mod. 9Cr-1Mo steel. The microstructural examination of all the specimens with extraction replica of the carbides revealed that the specimens with temporal embrittlement had $Cr_2C$, indicating that the cause of the embrittlement was the precipitation of the $Cr_2C$. In addition, TEM/EDX results showed that the Fe/Cr ratio was 0.033 to 0.055 for $Cr_2C$, whereas it was 0.48 to 0.75 for $Cr_{23}C_6$, making the distinction of the $Cr_2C$ and $Cr_{23}C_6$ possible even without direct electron diffraction analyses.

프라즈마 소결법으로 제조된 NiCrAlY/PSZ 계 복합재의 물성에 관한 연구

허성강,권경재 대한금속재료학회(대한금속학회) 1998 대한금속·재료학회지 Vol.36 No.10

Physical properties were investigated in the NiCrAlY/PSZ composites with various NiCrAlY contents(0vol%, 20vol%. 40vol%. 60vol%, 80vol%, 100vol%). Samples of the NiCrAlY/PSZ composites were sintered in the temperature range of 1450 to 1200℃ by a Plasma Activated Sintering(PAS) process. SEM micrographs revealed that grain size of the PSZ, as a matrix in NiCrAlY/PSZ composites, decreased with increasing NiCrAlY content. Hardness values also decreased with increasing NiCrAlY contents. Sintering temperature was found to decrease with increasing NiCrAlY contents in hardness and density measurements. X-ray analysis revealed that the volume fraction of the tetragonal phases in PSZ, as a matrix in NiCrAlY/PSZ composites, increased gradually with increasing NiCrAlY contents and reached the maximum in the NiCrAlY content of 40vol%, and then decreased remarkably. Optical microscopy showed that the continuous phase in the NiCrAlY/PSZ composites changed from PSZ to NiCrAlY in the NiCrAlY content of 80vol%. On the other hand, fracture toughness values linearly increased with increasing NiCrAlY contents, reached the maximum in the NiCrAlY content. of 60vol%, and then decreased remarkably in the NiCrAlY content of 80vol%.

플라즈마 용사에 의한 ZrO2 (8wt% Y2O3) 코팅층의 미세조직과 마르텐사이트 상변태에 관한 연구

허성강,나형용,이주동,홍경태 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.12

The microstructures and effect of the residual stresses on the stress induced martensitic transformation in plasma-sprayed ZrO₂(8wt% Y₂O₃) coatings were discussed in this study. Acoustic counts and hardness decreased with an increase of compressive axial(or radial) residual stress since martensitic transformation was repressed. The critical stress for inducing phase transformation increased and was influenced greatly by the residual stress as the deposition rate decreased. This is because stress intensification decreases as well with decreasing the deposition rate. Transformable equilibrium tetragonal phase precipitated only at bundaries, which are believed to have small cooling rates due to a collision between solid/liquid interfaces, and was transformed readily by applied stress. It was revealed that the critical stress depended not on the effective stress of Von mises criterion but on the residual stress(σ_(xy) σ_y or σ_z). This implies that martensitic transformation occurs predominently at these boundaries.

1991년도 추계 학술강연 및 발표대회 개요 - 산학연협동 , 수상기념강연 ( 초청발표 182 ) : 석유화학공업에서의 Coking 및 침탄현상

허성강 대한금속재료학회 ( 구 대한금속학회 ) 1991 대한금속재료학회 학술대회 개요집 Vol.1991 No.1

1990년도 추계 학술강연 및 발표대회 개요 - 산학협동 ( 발표 69 ) : 파괴손상해석법과 해석례

허성강 대한금속재료학회 ( 구 대한금속학회 ) 1990 대한금속재료학회 학술대회 개요집 Vol.1990 No.1

연구논문 - Factors Related with Engineering Design - : CR - MO - V 강의 경년 열화 특성

허성강,홍경태,도정만 ( SUNG KANG HUR,KYUNG TAE HONG,JUNG MAN DO ) 대한금속재료학회 ( 구 대한금속학회 ) 1988 재료강도 심포지엄 Vol.- No.-

급속응고된 Al-Fe-(Mo, Si) 계 합금분말 압출재의 미세조직과 기계적 특성

허성강,나형용,백남익 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.8

A study has been made on the microstructure and mechanical properties of rapidly solidified Al-Fe-(Mo,Si) alloys. Examination of the extruded bar using TEM reveals the microstructure to be inhomogeneous along with the bimodal distribution of precipitates. It is believed that. such inhomogeneous microstructure is caused by the structural difference between zone A and zone B in the starting powder. The tensile testing shows an increase in tensile strength but a decrease in elogation as the content of iron in the alloy increases. It has been found that decrease in elongation can be prevented by the addition of Si to Al-8Fe-2Mo alloy. For the elevated temperature mechanical properties, all extruded specimens with 8% iron show tensile strength of 180-190㎫ at 573K, but their elongation values were decresed with incresing the test temperatures, reaching a minimum at around 423 K.

Al-Fe 합금의 열적안정성에 미치는 첨가원소의 영향

허성강,나형용,백남익 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.2

The effects of alloying elements on the thermal stability of rapidly solidified Al-Fe based alloys have been studied. Various specimens which were heattreated in the temperature range of 200-550℃ for one hour were observed by optical and transmission electron microscopes. Lattice parameter change and precipitated phases were investigated by X-ray diffraction. Zone A region decreased in the specimen temperature at 300℃, 450℃ and 500℃ for the Al-Fe, for the Al-Fe-Mo and Al-Fe-Si, and for the Al-Fe-Mo-Si respectively. After one hour annealing at 550℃, second phases were precipitated in the zone B ; they were identified as Al₃Fe for the Al-Fe and Al-Fe-Mo and as Al₃Fe and Silicide for the Al-Fe-Si and Al-Fe-Mo-Si. Precipitates in the Al-Fe-Mo-Si were fine and spherical shape. The hardness of Al-Fe-Mo-Si alloys is higher than that of the other Al-Fe based alloys. The change of the lattice parameter was not observed from all the specimens annealed at 550℃ for one hour.