http://chineseinput.net/에서 pinyin(병음)방식으로 중국어를 변환할 수 있습니다.
변환된 중국어를 복사하여 사용하시면 됩니다.
12% Cr강의 고온 확산계수의 응력의존성과 조직의 특성에 관한 연구
장윤석(Yun Souk Chang),김태형(Tae Hyung Kim) 한국해양공학회 1997 韓國海洋工學會誌 Vol.11 No.2
Creep rate at the elevated temperature is known to be controlled by the softening process of microstructure especially in the solid solution alloys such as 12% Cr rotor steel. The change of structure is a decreasing process of the free energy of the state including stress, diffusivity of the material, and temperature.<br/> This study shows that the diffusion coefficient, D of 12% Cr rotor steel at 953K with 74.8 ㎫ is 1.084~3.140*10<SUP>-15</SUP>㎟ sec<SUP>-1</SUP> compared to 1.658*10<SUP>-24</SUP>㎟sec<SUP>-1</SUP>at 953K without stress.<br/> During creep, the growth of martensite laths accelerates the diffusion coefficient under stress due to incoherency of interface between carbides and matrix.
蔣允石(Yun-Souk Chang),吳世旭(Sae-Wook Oh) 한국해양공학회 1989 韓國海洋工學會誌 Vol.3 No.2
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. Microstrures of the samples are examined and reviewed. The results can be summarized as follows.<br/> 1) Fracture appearance transition temperatures are 80℃ at the center part and 60℃ near surface of 12% Cr rotor, and 8℃ near surface of 1% Cr-Mo-V rotor.<br/> 2) Comparative rapid softening occurs at higher temperatures above 600℃ for 12% Cr steel and 550℃ for 1% Cr-Mo-V steel in tension tests.<br/> 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.<br/> 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.<br/> 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.
은옥기,장윤석 ( Ok Ki Eun,Yun Souk Chang ) 한국주조공학회 1990 한국주조공학회지 Vol.10 No.6
N/A In order to reduce segregation in 12%Cr steel ingots of 60-100tons, numerical analysis by computer was applied to simulate solidification profiles and the profiles of liguid-solid coexisting zone in accordance with the ratios of H(Height) /D(diameter) of 100-ton ingot. The result is that the ratio of L(vertical length) /D(diameter) of liquid-solid coexisting zone was reduced in proportion to the decrease of H/D ratio. With the reduced H/D ratio(0.92) of ingot, the segregation in 60-ton ingot of 12% Cr steel can be much reduced and recovery was also improved by reducing ingot weight.
吳世旭(Sea-Wook Oh),蔣允石(Yun-Souk Chang) 한국해양공학회 1990 韓國海洋工學會誌 Vol.4 No.2
In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following :<br/> 1) Creep rates calculated by ?=pbv show 10~15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel.<br/> 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of 10±5㎏f/㎟ and increase with the increase of temperature.<br/> 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design.<br/> 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.
오세욱(Sae-Wook Oh),이치우(Chi-Woo Lee),장윤석(Yun-Souk Chang),정순호(Soon-Ho Chung) 한국해양공학회 1987 韓國海洋工學會誌 Vol.1 No.2
In order to estimate the running life of turbine rotors, fatigue crack propagation law, da/dN=C(ΔK)<SUP>m</SUP>, proposed by Paris et al. has been widely applied.<br/> In this study, fatigue crack propagation rates for 16 samples of 1% Cr-Mo-V rotor steel were measured and statistical characteristics of m and C values in above equation were reviewed.<br/> The results are summarized as follows.<br/> 1. C and m follow a log-normal distribution and normal distribution, respectively. And the relation of C and m shows a strong negative correlation.<br/> 2. Fatigue crack propagation equation can be expressed as da/dN=4.11×10<SUP>-4</SUP>(ΔK/153.8)<SUP>m</SUP>, introducing the relationship C=CoKo<SUP>-m</SUP>.<br/> In this case, contribution of Co distribution to the distribution of log C shows very small compared to degrees of contribution by m.
정순억(Soon-Uk Chung),정순호(Soon-Ho Chung),장윤석(Yun-Souk Chang),이현우(Hyun-Woo Lee) 한국해양공학회 1988 韓國海洋工學會誌 Vol.2 No.1
The increasing size of steam turbines during recent years has resulted in corresponding increase in diameters of rotors. These larger rotor diameters lead to higher thermal stress in the rotor during start up. So the development of system for rotor life evaluation methodology becomes quite important. This system performs a computer program analysis for the remaining life evaluation of Y-Fossil turbine rotor as a sample.<br/> Stress and thermal analyses were carried out by FEM (finite element method). In the case of the most severe starting condition(115% over speed), the maximum allowable non-metallic inclusion size was calculated through linear elastic fracture mechanics. And, regard of operating conditions(cold, warm, hot start), life consumption ratios were obtained by low cycle fatigue and creep theory.<br/> FEM program ROTEMP(analysis of rotor temperature) was developed to calculate temperature distribution of the rotor by heat transfer from hot steam. And, stress and life evaluation analyses were calculated by the programs such as ROSTRS (analysis of rotor stress) and ROLIFE (analysis of rotor life), respectively. FEM codes used axi-symmetric, quadrilateral (or triangle) element.