발간논문

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TiC films, through A.R.E. (Activated Reactive Evaporation), were deposited on 304 stainless steel substrate. The structure and properties of TiC films were analyzed according to the substrate temperatures and the partial pressures of the reactive gas (C₂H₂). Coated surfaces and cross sections were examined by S.E.M., and the pole intensity were measured by x-ray diffraction. Hardness was measured by a Micro Vickers Hardness Tester with 10 gr load. Surface structure was of micro-dome structure at low temperature (＝0.23 T_m) and the micro-dome structure changed to smooth dome-structure at 650℃ (＝0.28 T_m). The intergrated pole intensities of (200) and (220) increased with temperature, but that of (111) were strong at all temperatures. Hardness decreased from 3000 to 1875 ㎏/㎟ and C/M ratio decreased from 0.701 to 0.667, with decreasing temperature and partial pressure.

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Rapidly solidifed Al-Cr-Zr alloy specimen was made by atomization and splats quenching method. The calculated cooling rate ranges from 10^6 K/s to 10^7 K/s, and as-quenched microstructure consisted of a very fine dendritic or cellular zone, and interdendritic segregation was not suppressed for Al-Cr alloys. We obtained a grain size of 1-5㎛. The Al-Cr-Zr alloy evidently shows an age hardening response and peak hardness was observed at the specimen which held at 450℃ for 1 hr. Agglomeration of precipitates having a agglomeration size of 0.5-2㎛ and a precipitate size of 300-800Å was observed for the first time. In this study we also studied the precipitation behavior during isochronal aging by TEM and X-ray diffractometer.

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In order to produce CV-cast iron easily and accurately, small amount of Cu were added after spheroidizing treatment by Mg, And then mechanical and physical properties were investigated with graphite form and variation of matrix. The results obtained from this study are as follows: 1) In case of 2.0% Cu addition without holding time, CV graphite cast iron could be obtained with satisfaction. 2) With increasing Cu addition and holding time, the graphite length increased, but the graphite width decreased. 3) Impact properties and tensile strengths of CV graphite cast iron were in the range of 0.8-0.9 ㎏f.m and 40-45㎏f/㎟, respectively. 4) Thermal diffusitivity of CV graphite cast iron was 6.66×10^(-6) ㎡/sec at room temperature.

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The kinetics of arsenic cementation with iron was studied by use of rotating disc geometry and using iron powder. The rate of arsenic cementation with iron was very slow owing to the formation of nonconductive thin film of arsenic on the iron disc surface. However, the addition of Cu ions to the system as an activate reagent increased the reaction rate remarkably. The kinetics showed two steps first order reaction, and the initial rate constant was proportional to the square root of agitation speed as suggested from Levich equation, k＝0.62D^(⅔)ν^(-1/6)ω^(½). Above 55℃, the activation energy of initial stage was 3.4 ㎉ while that below 55℃ was 20.9㎉. In the enhanced region, however, the activation energy was 4.1㎉ above and 10.9㎉ below 55℃ respectively. Therefore, the reaction mechanism both in the initial and final stages considered to be changed from diffusion through a boundary layer above 55℃ to surface chemical control below 55℃. The deposit composed of a Cu-As compound and armorpous arsenic was found by the X-ray analysis. In the case of using iron powder the rate can be described in terms of the Fro¨ssling equation, Sh＝2＋0.4Re_p^(½)Sc^(⅓).

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The effect of normalizing of commercial 3% single grain oriented Si steel on the cold rolling and secondary recrystallization have been studied by observation of microstructured texture coefficient. The variables of normalizing are temperature, holding time and cooling rate. As the temperature of normalizing is raised, texture coefficients of (200) and (222) increased in the second cold rolling and that of (110) was very strong in the secondary recrystallization. The optimum conditions for normalizing treatment are thought to be 950℃ 3 min, and air cooling.

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Rotating bending fatigue behavior of the smooth and pitted specimens of STS 316 stainless steel has been examined at room temperature, 538℃, 593℃ and 650℃. The experimental results are as follows: The endurance fatigue limits of the smooth and the pitted specimens are clearly appeared at all experimental temperature below 10^7 cycles. Particularly, the knees of S-N curves at 650℃ appear at about 10⁴cycles. As temperature increases, endurance fatigue limits of the pitted specimens decrease more than those of the smooth ones. Cracks on the smooth specimens initiate in overall sites of the smooth specimens and those on the pitted ones initiate on the pit. Cracks propagate in brittle fracture, ductile striation and dimple fracture successively, in transgranular fracture modes. On the well defined ductile striation stage of the pitted specimens, ductile striation spacings are 1-3㎛. These striation spacings in this range are expressed as a function of σ_max√(πa). (Received May 28, 1984)

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Casting thickness influences mechanical property and graphite shape in ductile cast iron and the results from this study are as follows: 1) The strength and the hardness were decreased rectilinearly as the casting size increased from Ø25㎜ to Ø100㎜ and were nearly same at the size of Ø100㎜ and 150㎜. 2) The strength and the hardness were appeared homogeneous in every step bar of the same thickness. 3) The best ductility was obtained at Ø50㎜. 4) The maximum diameter of huge graphite nodule was 130㎛.

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