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오스테나이트계 내식강 튜브 소재의 손상진단에 관한 연구
조종춘,김영석,김학민,정형조,Jo, Jong-Chun,Kim, Yeong-Seok,Kim, Hak-Min,Jeong, Hyeong-Jo 한국기계연구원 1989 기계연구원소보 Vol.19 No.-
Material damage of Unifiner Change Heater: Tube used for nearly 20 years was evaluated and Mechanical tests such as tensile tests and creep-rupture tests were conducted to predict the residual life. After the investigation, any major damage or degradation was not found except the welded zone. Microstructural observation showed that most of delta-ferrite was transformed. to sigma-phase and consequently, the ductility was very much reduced. A KLA(Knife-Line Attack) crack with 60mm in length and 2.8mm in depth was found just near the welded zone, which is believed to be caused by intergranular corrosion. Creep-rupture tests, which are very essential to predict the residual life, showed that both used base and weld metals have similar results with the reference data.
Fe-Aluminide합금의 미세조직과 기계적 특성에 관한 연구
조종춘,이도인,이성재,최병학,김학민,Jo, Jong-Chun,Lee, Do-In,Lee, Seong-Jae,Choe, Byeong-Hak,Kim, Hak-Min 한국기계연구원 1992 硏究論文集 Vol.22 No.-
Mechanical properties and microstructure were investigated on vacuum induction melted $Fe_3A1$base alloys of $DO_3$ structure. Specal emphasis were put on the effect of alloy chemistry, grain size and process(rolling, directional solidification) on mechanical properties of Fe-22.5-39at.%Al at elevated temperature between room temperature and $800^{\circ}C$. grain size of as-cast alloys is refined by rolling from 1mm to $80\mum$. Tensile strength of Fe-24.lat.%AI was about 404MPa at the critical ordering temperature, and the fracture strain of the alloy was 1-2% at room temperature. An inverse temperature dependence of the strength is noticed as-cast $Fe_3A1$. The presence of Cr and Zr do not affect the room temperature ductility and high temperature strength. Fracture strain of directionally solidified(DS) $Fe_3A1$ is about 1%at room temperature, but is about 60%at. $T_C$(550^{\circ}C)$. Tensile strength of DS alloy is lower than that of as-cast alloy at $530^{\circ}C$ and $430^{\circ}C$. Failure mode at room temperature varies from transgranular fracture to intergranular fracture with the addition of Al. the failure mode also varies from mixed(transgranular+ intergranular) mode between room temperature and $500^{\circ}C$ to intergranular mode above $550^{\circ}C$
조종춘,Jo, Jong-Chun,Werner Osterler 한국기계연구원 1986 기계연구원소보 Vol.16 No.-
Several heat treatment were applied to on HSLA steel of type StE47 (German standard) to produce five ferrite microstructures of different strength and at least two different grain sizes respectively. Whereas the ferrite microstructure had a strong influence on yield strength the effect of grain size was negligible. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbide particles, and their mutual interaction. Specimens tranformed at $600^{\circ}C$ showed the highest strength levels. In this case precipitation has occured after the $\gamma$- $\alpha$ transformation. Very small VC particles are arranged mostly along dislocation lines. Increasing both, grain size and pearlite volume fraction leads to a remarkable shift of transition temperature which was further enhanced by increasing ferrite strength.
스테인레스강용접 열영향부의 KLA거동 및 기계적 특성에 관한 연구
조종춘,김영석,김학민 대한용접접합학회 1990 대한용접·접합학회지 Vol.8 No.4
Integranular corrosion behaviors of KAL (Knife Line Attack) and mechanical properties such as tensile and creep rupture were investigated for the tube material used for nearly 20 years under the condition of 463.deg. C and 28 $kg/cm^2$. Based and weld metal were austenitic stainless steel AISI 321 containing Ti, AISI 347 containing Nb, respectively. KLA is a kind of the intergranular corrosion which often occurs just near the HAZ (heat affected zone) of AISI 321 and AISI 347 stainless steel due to the grain boundary sensitization. In KLA zone, intergranular corrosion crack has propagated outwards from the inner surface and carbides of white and narrow band type assuming as (Cr, Fe) carbide were confirmed. All the delta-ferrite formed in the weld metal during weld solidification has been transformed into sigma-phase since delta-ferrte was exposed for 20 years at 463.deg. C. Elongation was very low at the range from room temperature to 600.deg. C and it was confirmed that creep-rupture properties were not consideralbly affected.
Fe-Al 금속간 화합물의 조직과 기계적성질에 관한 연구
허보영,이도인,조종춘 慶尙大學校 1991 論文集 Vol.30 No.2
The intermetallic compound materials has various merits such as high temperature strengh, good resistance oxidation, etc. However, it is not available for use because of its room temperature brittleness and low ductility. This study was carried out through high temperature tensile test, heat treatment, OM, TEM, SEM, EDS for the purpose of improving mechanical prorerties. The results are as follows. 1. Grain size and homegenization effect decreased by homegenization heat treatment. 2. When Fe-23%Al alloy was solidified unidirectionally, elongation was increased and yield strength was decreased as compared with commercial solidification. 3. After tensile strength tested in polycrystals alloys, the fractographys were grain boundary and intergranular cleavage frature type, but it were transgranular and intergranular cleavage type at the unidirectionally solidified samples.