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P122강 열화재의 소형펀치 크리프 평가 및 미세조직 분석
김범준 ( Bum Joon Kim ),김문기 ( Moon K Kim ),임병수 ( Byeong Soo Lim ),Hoang Tien Dung 대한금속·재료학회 2010 대한금속·재료학회지 Vol.48 No.1
This paper investigates the influence of aging time on creep properties via a small punch creep test and evaluates the microstructural change of P122 steel at 600℃. The area fraction of precipitates was quantitatively analyzed to identify the relationship between the creep rupture life and precipitates. The coarsening behavior of precipitates along the grain boundaries was also investigated for various aging times. It is found that this coarsening behavior led to a loss of solution hardening and resulted in a hardness drop and a reduction of creep life.
논문 : AISI 316L스테인리스강의 소형펀치 크리프 거동에 미치는 마찰계수의 영향
김범준 ( Bum Joon Kim ),조남혁 ( Nam Hyuck Cho ),김문기 ( Moon K. Kim ),임병수 ( Byeong Soo Lim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.7
Small punch creep testing has received attention due to the convenience of using smaller specimens than those of conventional uniaxial creep tests, which enables creep testing on developing or currently operational components. However, precedent studies have shown that it is necessary to consider friction between the punch and specimen when computing uniaxial equivalent stress from a finite element model. In this study, small punch creep behaviors of AISI 316L stainless steel, which is widely used in high temperature-high pressure machineries, have been compared for the two different ceramic balls such as Si3N4 and Al2O3. The optimal range of the friction coefficient is 0.4~0.5 at 650℃ for the best fit between experimental and simulation data of AISI 316 L stainless steel. The higher the friction coefficient, the longer the creep rupture time is. Therefore, the type of ceramic ball used must be specified for standardization of small punch creep testing.
임지우 ( Ji Woo Im ),김범준 ( Bum Joon Kim ),김문기 ( Moon K Kim ),임병수 ( Byeong Soo Lim ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 대한금속·재료학회지 Vol.48 No.11
The small punch creep (SPC) test has recently received much attention as a new alternative to the conventional uniaxial creep test because it needs only a miniature-sized specimen directly detached from an operating system or component without any serious sampling damages. However, it is difficult to obtain the equivalent uniaxial creep data directly from the SPC data. As a specimen is deformed by a punch in the SPC test, the test result is sensitive to the friction between them. Finite element analyses with various friction coefficients was performed and showed a tendency of increased SPC life with an increased friction coefficient. The necking position predicted by the SPC simulation with a proper friction coefficient showed good agreement with that observed from the real SPC test. Finally, a noble method to convert the SPC load and displacement rate into the equivalent uniaxial creep stress and strain rate, respectively, was established in this study.