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극저온 시험장치의 제작과 AISI 300계열 스테인리스강의 극저온 인장변형거동
이해무,남승훈,허용학,이주진,방건웅 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.11
For practical application of cryogenic engineering, development and characterization of structural materials for use at low temperatures are essential. For these purposes, a system for mechanical testing at liquid helium temperature was developed and it was shown that the precision and accuracy of the system met the requirements of standards for materials testing machines. Using this system, tensile deformation behavior of AISI 304, 316 and 310S austenitic stainless steels at cryogenic temperatures was investigated. Tests were conducted on round, tensile specimens having a 6.25㎜ diameter at 4, 77, and 295 K and loading rate was 0.5㎜/min. Serrations were observed in all alloys at 4 K. The stress-displacement curves at 77 and 4 K showed different tendency from those at 298 K. As the testing temperature decreased, ultimate strengths of 304 and 316 were largely increased compared to the increase of yield strengths, but the increase of ultimate strength of 310S was almost the same to that of yield strength. Type 310S had the highest yield strength and the lowest tensile strength at all temperatures. These tensile characteristics were considered to be strongly affected by austenite stability.
AISI 300 계열 스테인리스강의 극저온 하중제어 인장특성
이해무,김시천,방건웅 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.4
In case of cryogenic structures such as superconducting magnets and pressure vessels, the structural material experiences unrestricted force. It is, therefore, desirable to characterize the load-controlled tensile properties at cryogenic temperatures to simulate operating condition. At 4 K, however, discontinuous yielding occurs, which arises mainly from low specific heat and thermal conductivity of the materials at low temperatures, and it affects the load-displacement or stress-strain curves. In this study, load-controlled tensile tests were conducted at 77 ad 4K on AISI 300 series stainless steels. The load rate was varied from 5 to 5000 N/s. The effect of load rate and testing temperature on tensile properties of 300 series stainless steels were observed. A model which correlate discontinuous yielding and ultimate tensile strength was proposed.
이해무,윤기봉,남승훈,소철호 ( H . M . Lee,K . B . Yoon,S . H . Nahm,C . H . Soh ) 한국열처리공학회 1994 熱處理工學會誌 Vol.7 No.3
As Cr-Mo-V steels have excellent mechanical and creep properties at elevated temperatures, they are extensively used in power plants. However, the steam turbine components are supposed to have suffered material degradation during long-term service at elevated tenperatures. Many efforts have been made to assess the safety and residual life of these components by means of non-destructive methods such as plastic replication, hardness and electric resistance techniques. Recently, a parameter correlating hardness changes during long-term heating to those during creep was introduced and it was named `G parameter`. The electric resistivity as well as hardness are affected by damage accumulation, but there have been no efforts to correlate G parameter to resistivity changes. In this study, relationship between G parameter and changes in electric resistivity was investigated using artificially aged Cr-Mo-V steel. It is well understood that G parameter can be applied to electric resistance techmique.
이해무,윤기봉,신규인,최현창,박재학 한국산업안전학회 1997 한국안전학회지 Vol.12 No.2
Fracture behavior of ex-serviced 1Cr-0.5Mo steel was measured at room(24℃) and elevated(538℃) temperature and compared with that measured with virgin 1Cr-0.5Mo steel. Compact C(T) specimens were machined from the base and welded test materials. In case of the C(T) specimens of the weld, fatigue precrack was introduced along the fusion line so that following crack growth should occurs along the region of heat affected zone. It was observed that the J-R curve of the serviced material was significantly lower than that of the virgin material at room temperature. Brittle fracture was observed in the serviced material. On the other hand, at elevated temperature no noticeable difference was found between the J-R curves of the virgin and the serviced material. The measured J-R curves were also compared with those of the 1.25Cr-0.5Mo steel obtained from the other literatures. Optical microscopy and SEM examination of the serviced material reveal the carbide in/along the grain boundary which shows material degradation due to long-term usage. An example of application of the measured J-R curves is shown.