STS304강의 단시간 크리프 파단특성 평가

김선진,공유식 한국해양공학회 2007 韓國海洋工學會誌 Vol.21 No.4

The objective of this paper is to investigate the relationship between the short-term creep rupture time and the creep rupture properties at three different elevated temperatures in STS304 stainless steel. Uniaxial constant stress creep rupture tests were performed on the steel to observe the creep rupture behaviors at the elevated temperatures of 600, 650 and 700, according to the testing matrix. It is very important to predict creep life in practical creep design problems. As one of the series of studies on the statistical modelling of probabilistic creep rupture time and the development of creep life prediction techniques, the relationship between applied stress and creep rupture behaviors, such as creep strain rate and rupture time, were investigated. In addition, the Monkman-Grant relationship was observed between the steady-state creep rate and the creep rupture time. The creep rupture surfaces observed by SEM showed up dimple phenomenon at all conditions.1. 서 론크리프(Creep)란 일정 하중 또는 일정 응력하에서 시간의 경과와 더불어 변위 혹은 변형률이 증가하는 현상을 말한다. 상온에서 탄소성거동을 보이는 재료라 하더라도 고온하에서는 일정 하중 또는 응력하에서 시간에 따라 변형률이 증가하는 것이 일반적이다. 이와 같이 시간에 의존하는 변형을 크리프 현상이라 하며, 경험에 의하면 이 현상은 온도와 아주 밀접한 관계가 있고, 또한 크리프 속도는 온도의 상승과 더불어 급격히 증가하는 것으로 알려져 있다(Hult, 1966).현재 선박이나 해양구조물 등의 열기관, 자동차나 항공기 등의 엔진, 발전소 보일러, 터빈, 원자로 부품 등의 여러 가지 고온 분위기하에서의 사용 기회가 증가하고 있을 뿐 아니라 효율 면에서도 이들의 사용 온도가 높아지는 추세이다. 이러한 고온 분위기하에서 사용되는 내열강 또는 내열합금의 개발과 더불어 이들 재료에 대한 고온 강도, 특히 크리프 강도 특성에 관한 연구가 중요하다. 이와 같은 재료는 고온에서 장시간 사용되므로 고온 파괴, 즉 크리프 손상에 의한 고장 및 파손으로 경제적 손실은 물론 인명 피해까지도 발생할 수 있다. 그러므로 이러한 강재의 장시간 고온 크리프 특성을 비교적 단시간 크리프 실험을 통하여 파악하고 크리프 안전 강 와 수명을 예측함으로써 고장이나 파손을 방지하는 하는 것은 고온재료의 사용에 있어서 중요한 요소라 할 수 있다(이상국 등, 교신저자 공유식: 부산광역시 남구 용당동 산 100051-620-1623 kongys@pknu.ac.kr 2000; Kim et al., 2001).

다양한 온도에서의 응력 파단 시험 결과 분석을 통한 크리프 수명 예측 방법에 관한 연구

이정민,송현우,윤정한,박수,석창성 대한기계학회 2019 大韓機械學會論文集A Vol.43 No.5

발전시스템의 고효율화가 추진됨에 따라 발전시스템의 가동온도가 높아졌으며, 그에 따라 고온 환경에서 핵심부품의 내구성 확보가 중요시되고 있다. 고온 환경에서 내구성을 확보하기 위하여 초내열합금이 적용되고 있으며, 그중 니켈기 초내열합금이 고온강도, 크리프 및 피로 저항성, 내산화성이 우수하여 터빈 블레이드 소재로 널리 사용되고 있다. 터빈 블레이드는 고온 환경에 노출될 뿐만 아니라 고속회전에 의한 원심력을 받으며, 이로 인하여 크리프 변형이 발생한다. 따라서 블레이드 설계시 크리프 파단 수명이 반드시 고려되어야 한다. 본 연구에서는 상용 가스터빈 블레이드 소재로 사용되는 IN738LC에 대한 크리프 특성을 분석하기 위하여 여러 온도조건에서의 크리프 파단 시험 결과를 확보하였으며, 이로부터 IN738LC의 크리프 수명을 예측하기 위한 방법에 대한 연구를 수행하였다. As the efficiency of power-generation systems has improved, their operating temperature has increased. Accordingly, it is important to secure the durability of the core parts in a high-temperature environment. To ensure this durability, super heat-resistant alloys have been applied. Among them, nickel-based alloys have been widely used as turbine-blade materials because of their high-temperature strength, and creep, fatigue, and oxidation resistance. The turbine blades are not only exposed to high-temperature environments, but also to centrifugal force, due to the high-speed rotation, which causes creep deformation. Therefore, the creep-rupture life must be considered when designing the blade. In this study, the creep rupture was tested at various temperature conditions, and a study on the creep-life prediction method was conducted by analyzing the creep characteristics of the IN738LC superalloy, which is used as a commercial gas-turbine blade material.

Al합금의 크리프 파단수명에 관한 연구

배춘익,진도훈 한국기계기술학회 2011 한국기계기술학회지 Vol.13 No.4

Technological mode progress demands the use of materials at high temperature and pressure. Constant load creep tests have been carried out over the range of stresses at high temperatures. One of the most critical factors in considering such applications as the most critical one is the creep behavior. In order to investigate the creep behavior in this study, the stress exponents during creep were determined over the temperature range of 275℃ to 325℃ and the stress range of 36MPa to 72MPa. The applicability of modified Monkman-Grant relationship was also discussed.

티타늄합금(Ti-6Al-4V)의 정적인 크리프 거동

황경충(Kyungchoong Hwang),윤종호(Jongho Yoon) 한국자동차공학회 2004 한국자동차공학회 춘 추계 학술대회 논문집 Vol.- No.-

Titanium 6AI-4V alloy has been used as the part materials of aerospace and automobile industry because they have many benefits. The light weight of them is attractive because it makes the energy savings. They have high specific strength, excellent corrosion resistance, but its machinability is very poor. In this study, a series of static creep tests for the titanium 6AI-4V alloy under the 16 temperature and stress conditions had been performed. And then the study of stress dependence, activation energy, creep life prediction and fractography have been followed. The life prediction constant of Larson-Miller parameter is calculated as about 6.2 and the ductile fracture was primarily observed by intergranular fracture.

응력과 온도에 따른 폴리카보네이트(PC)의 크리프특성

강석춘(Suk Choon Kang),이용원(Young Won Lee) Korean Society for Precision Engineering 2010 한국정밀공학회지 Vol.27 No.9

응력과 온도에 따른 ABS 의 크리프특성에 관한 연구

강석춘(Suk Choon Kang) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.10

응력과 온도에 따른 아크릴(PMMA)의 크리프특성

강석춘(Suk Choon Kang) Korean Society for Precision Engineering 2011 한국정밀공학회지 Vol.28 No.12

2상 스테인리스강(STS 329J1)의 크리프 특성

황경충,권종완,윤종호 한국공작기계학회 2005 한국생산제조학회지 Vol.14 No.2

Micro duplex stainless steel is used to denote a fine scale two-phase micro structure consisting austenite and ferrite. The development of this structure was done by proper thermo-mechanical processing. The objective of present investigation is to study creep characteristics of this alloy. Since we have little design data about the crap behaviors of the alloy. An apparatus has been designed and built for conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of micro duplex stainless steel products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become higher. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated as about 5. Last, the fractographs at the creep rupture show both the ductile and brittle fracture modes according to the creep conditions.

크리프 파단 데이터의 변동성에 대한 새로운 고찰

김선진(Seon-Jin Kim),정원택(Won-Taek),공유식(Yu-Sik Kong) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5

This paper deals with the variability analysis of short term creep rupture test data based on the previous creep rupture tests and the possibility of the creep life prediction. From creep tests performed by constant uniaxial stresses at 600, 650 and 700℃ elevated temperature, in order to investigate the variability of short-term creep rupture data, the creep curves were analyzed for normalized creep strain divided by initial strain. There are some variability in the 'creep rupture data. And, the difference between general creep curves and normalized creep curves were obtained. The effects of the creep rupture time and state steady creep rate on the Weibull distribution parameters were investigated. There were good relation between normal Weibull parameters and normalized Weibull parameters. Finally, the predicted creep life were compared with the Monkman-Grant model.

안경테소재 합금(Ti-6AI-4V)의 크리프 특성

황경충,윤종호 한국공작기계학회 2003 한국공작기계학회 추계학술대회논문집 Vol.2003 No.-

Titanium alloy has widely been used as glasses rim material because it has high specific strength and also is light, harmless to men. But, we have little design data about the creep behaviors of the alloy. Therefore, in this study, an apparatus has been designed and built for conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of titanium products and we have gotten the following results. First, the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy gradually decreases as the stresses become bigger. Thirdly, the constant of Larson-Miller parameters on this alloy is estimated about 13. And last, the fractographs at the creep rupture show both the ductile and the brittle fracture according to the creep conditions.