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화력 발전용 고압 로터강의 정하중 및 변동하중하의 고온 크립 균열전파 특성에 관한 연구
오세규(S. K. Oh),정순억(S. U. Jeong) 한국해양공학회 1991 韓國海洋工學會誌 Vol.5 No.2
The crack length measurements by electrical potential(EP) method for 1% Cr-Mo-V and 12%Cr steel of 0.5T-CT specimen were performed at 500℃, 600℃ and 700℃, and an applicability of stress intensity factor(K<SUB>I</SUB>), net section stress(σ<SUB>net</SUB>), C<SUP>*</SUP>-integral and C<SUB>t</SUB> parameter was studied to measure creep crack growth rate(da/dt) with side groove and without side groove under static and cyclic loading condition. The experimental result could be summarized as follows :<br/> 1) Crack measurement by EP method was available and coincided with the Johnson's analytical equation.<br/> 2) da/dt by K<SUB>I</SUB> and σ<SUB>net</SUB> was not adequate because of the wide scatter band according to load and temperature, but C<SUP>*</SUP>-integral, except for transition region, was adequate.<br/> 3) C<SUB>t</SUB> parameter showed the best fitted line through total creep region without relating with both temperature and load condition.<br/> 4) Under the cyclic loading condition, C<SUB>t</SUB> parameter was proper to estimate da/dt.<br/> And it was shown that da/dt for 1% Cr-Mo-V steel under the static condition(R=1) was 1.16 times faster than the case under cyclic loading(R=0), and for 12% Cr steel, 1.43 times.
화력 발전용 로터강의 초기 변형율이 CYCLIC 크리프 특성에 미치는 영향에 관한 연구
오세규(S. K Oh),정순억(S. U. Jeong),한상덕(S. D. Han) 한국해양공학회 1992 韓國海洋工學會誌 Vol.6 No.1
The creep behaviors of 1%Cr-Mo-V and 12%Cr steam turbine rotor steels under static or cyclic load were examined at 600 and 700℃. The relationship between these two kinds of phenomena was studied and the experimental results were summarized as follows :<br/> 1) It is confirmed that the cyclic creep strain dependent on time is more available for creep behavior analysis according to frequency change than that dependent on number of cycles, and the static creep, the special case of cyclic creep with stress ratio of 1 can be also more effectively analyzed by time-dependence.<br/> 2) The steady cyclic creep rate vs. the steady static creep rate, increases according to the increase of stress ratio, and this phenomena may occur on occasion of the decrease of the internal stress.<br/> 3) The initial strain affects on all the creep properties of the transient region, the steady state region and the rupture time in cyclic creep as well as static creep, and the quantitative relationships among them exist.
오세규(S.K. Oh),김민남(M.N.Kim) 한국해양공학회 1987 韓國海洋工學會誌 Vol.1 No.2
The feasibility for a practical use of underwater wet arc welding process is experimentally investigated by using low hydrogen and high oxide type electrodes and TMCP steel plates. Main results are summarized as follows :<br/> 1) The absorption speed of the coated low hydrogen and high titanium oxide type electrodes becomes constant after about 30 minutes in water, and more steeping time in water does not influnce welding arc behavior.<br/> 2) By bead appearance and X-ray inspection, the high titanium oxide type electrode is better than the low hydrogen type in underwater wet arc welding process.<br/> 3) The mechanical properties of underwater wet arc welds depend upon welding conditions more than those of in-air welds, and the optimum welding condition can be obtained.<br/> 4) Because of quenching effect by rapid cooling rate in underwater wet welding, the maximum hardness of HAZ is increased relatively higher in underwater wet welding process.
오세규(S.K. Oh),정순억(S.U. Jeong),전태언(T.E. Jeon) 한국해양공학회 1996 韓國海洋工學會誌 Vol.10 No.1
This paper deals with a study on improvement of long-time creep life prediction of steam turbine rotor steels by using initial strain method as a new approach at high temperatures of 500 to 700 ℃.<br/> The main result shows that the inital strain method could be reliably utilized to predict and evaluate the long-time creep life as well as creep rupture strength and that the predicting equation for long-time creep life under a certain creep stress at a certain high temperature could be empirically derived out from each initial instantaneous strain measured.