발간논문

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Wear resistance properties of pearlite cast iron have been studied when nitrided at 650℃ with C-H-N-O type nitrogen gas forming agent. The results found are W_c (㎎/㎠)=0.675×[applied load (㎏/㎠)] for non-nitrided cast iron W_c (㎎/㎠)=0.225×[applied load (㎏/㎠)] for nitrified specimen. Where W_c is wear loss per unit area, under the conditions of applied load if 4㎏/㎠, speed 1 m/sec and distance 400㎞-1,400㎞. And also it is found that the sear rate are 6.0 ㎍/㎠·㎏ and 0.67㎍/㎠·㎞ for non-nitrided and nitrided specimens respectively.

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The diffusivities of hydrogen in Zr-0.5, 1.05, 1.5 and 2.3 at.% Ni alloys were respectively measured over 900-1080℃ by the gravimetric technique. The diffusion activation energies for hydrogen increased linearly as Ni concentration increased and expressed by the equation. Q_D=(8297±221)+(3366±148)×(at.%Ni) ㎈/mole H₂ while the hydrogen diffusivities decreased, Ni concentration is increased, The diffusivity data at each alloy composition are presented.

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Intergranular cracking properties of 304 austenitic stainless steel, particularly its welding region, have been evaluated by exposing C-ring specimen to polythionic acid. Effects of stress relief annealing temperature, cooling rate, and applied stress have been closely investigated. The results obtained are as follows. The stress corrosion cracking of 304 austenitic stainless steel is preferred at intergranular boundary and normal to the direction of tensile stress. The cracking of welding region happens in heat affected zone where grain is coarsened. When stress relief annealing is carried out, the efficiency is significant at 1050℃ furnace cooling or water quenching, at 850℃ furnace cooling. Preventing SCC in polythionic acid, furnace cooling is better than air cooling in all heat treatment. As the applied stress has higher value, the incubation period is shorter, so one must design and heattreat to lessen applied streess and residual stress. Plotting applied stress against log time-to-failure, knee of the plot appears. The stress of this point is similar to the stress which is shown by boiling 42% MgCl₂ Solution.

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We have numerically calculated the hydrogen distribution in Zircaloy-2 in one dimensional and two dimensional systems for α-Zircaloy-2 and linear temperature gradients by using continuous system modeling program (CSMP) in IBM 360/50 computer. When the hydrogen concentration is below terminal solubility only α phase is present. Redistribution of hydrogen are described in terms of temperature and distance. For higher concentration, both α and δ phases are present. The calculation is extended for two phase region in one dimensional system. Where applicable, our results are compared with previous work.

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Fe-Ni-C alloys with Ms temperature of -28℃ were prepared by a high frequency induction furnace. Carbon content ranged from zero to 0.33 wt. % and nickel content was varied in accord with the above Ms temperature. Then the effects of deformation degree and carbon content on austenite stabilization of these alloys were investigated. When the austenite structures of Fe-Ni-C alloys were subjected to deformation at room temperature, the retained austenite content in martensite structure transformed from the austenite was increased with increasing deformation degree, and the increase in retained austenite content, at the same levels of deformation degree, became greater with increasing carbon content. In martensites obtained from reverted austenites of these alloy, prior martensites of which were subjected to deformation at room temperature, the retained austenite content was also increased with increasing deformation degree but the increase in retained austenite content at the same levels of deformation degree showed a same value, independent of carbon content. From the comparison between the above two results, it could be concluded that the reverted austenite transformed from deformed martensite is more stabilized in subsequent martensite transformation than the deformed normal austenite, at all deformation degrees.

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