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노광섭,최용,김병훈,이창순 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.9
Sulfide stress corrosion cracking (SSCC) behavior of X65 line-pipe steels was studied by a constant elongation rate test method to understand the sulfide stress corrosion mechanism. The SSCC test was carried out in aqueous acetic acid solution containing chloride ion in the strain rate range of 5×10^5∼5×10^7 sec^(-1). The corrosion potential and the corrosion rate in the aqueous solution were -580 mV_(SHI) and 4.2×10³ Acm^(-2), respectively. Degradation of the mechanical properties such as yield strength and ultimate tensile strength was observed during SSCC test. The SSCC resistance expressed by relative fracture energy ratio decreased from 55% to 13.5% at an open circuit potential of -580 mV_(SHI) as the strain rate decreased from 5×10^5 to 5×10^(-7)/sec. Anodic or cathodic polarization at about 100 mV resulted in reducing the SSCC resistance, which was explained by a model related to anodic dissolution and hydrogen embrittlement. The brittle fracture surface with intergranular and transgranular cracking was observed. The corrosion products on the failed surface were the mixture of iron oxide and sulfide.
석유수송용강의 수소유기균열감수성에 미치는 열간압연 및 권취온도의 영향
노광섭,강기봉 대한금속재료학회(대한금속학회) 1988 대한금속·재료학회지 Vol.26 No.7
The effect of hot rolling condition on the mechanical properties, microstructure, find HIC susceptibility was investigated for microal1oyed steels which were prtpared in the mill lines as well as in the la bo ratory. The results are as follows. (1) The microstructure of hot-rolled steels was hardly affected by the change of the finishing temperature. But by lowering the coiling temperature, the polygonal ferritic and pearlitic structures were changed to the bainitic stucture. (2) With lowering the coiling temperature, the tensile and yield strengths were increased by more than 10 ㎏.f/㎟, while total elongation was decreased by 10%. However, the effect of the coiling temperature on the impact tou ghness was very little. (3) The most important factor affecting the initiation of HIC was the morphology of non-metallic inclusions. Elongated MnS inclusions as well as large and/or clustered oxides rendered the steels very crack sensitive. (4) Cracks propagated along the pearlitic bands or low temperature transformed phases developed in the center-segregated regions of C.C.slabs. HIC susceptibility was decreased to some extent as center-segregation was decreased. (5) The propagation of HIC was reduced when the formation of the low temperature transformed structure and/or the growth of the lamellar pearlite was supressed by proper cooling control.
최종술,노광섭 대한금속재료학회(대한금속학회) 1985 대한금속·재료학회지 Vol.23 No.10
The effect of cooling rate on the morphology of the martensite and the mechanical properties of Fe-20% Ni martensitic alloy has been studied. The alloy was cooled from the austenite state at 1000℃ by the various practical cooling precesses iced brine, water, oil, air and furnace cooling Fe-20% Ni alloy is fully transformed to lath martensite even at very slow cooling rate such as 0.8℃/min. The size of block in the lath martensite structure increases with decreasing cooling rate. The mechanical properties such as hardness, tensile strength, elongation and reduction of area show nearly constant values, independent of cooling process However, although the impact energy shows a high and almost same vague at iced brine, water, oil and air cooling process, only the furnace cooling process shows a very low impact energy. Impact energy of the ail-cooled specimen, which was furnace-cooled again from a temperature just above M_s points is nearly same as or a little higher than that of the as-air cooled specimen. Hence, the reason that the furnace-cooled specimen shows a very low impact energy is considered to be due to packet/packet boundary segregation formed with assistance of movable dislocations during martensitic transformation between M_s and M_f temperature.