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The stress corrosion cracking (SCC) of Al-Zn-Mg welds in an aqueous solution of 3.5 wt.% NaCI (PH = 1) at 20±2℃ was studied with specimens under constant load, relative to heat input rate of the welding process and postweld heat treatment. Dendrite arm spacing determined by heat input rate was a major factor in the reduction of yield strength of welds. The failure time of welds was dependent on both heat input rate and postweld heat treatment: Electrochemical corrosion due to galvanic effect was influenced by the heat input rate. Heat input rate dependence of failure time showed that the higher the susceptibility to galvanic corrosion of welds, the lower the susceptibility to SCC of welds in the case of weld specimens, postweld-heat-treated under the same conditions (temperature and time). Weld specimens, postweld-heat-treated at 120℃ for 24 hrs showed the highest susceptibility to SCC followed by the specimen at 80℃ for 48 hrs and then that at 150℃ for 16 hrs. The postweld heat treatment effect on SCC was explained in terms of the ageing stage-SCC relation.

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Taking notice of the accelerating effect of oxygen on sintering of UO₂, this study was undertaken to investigate effects on sintering characteristics of slightly oxidizing atmospheres with use of CO₂/CO mixed gas and other sintering conditions. When the sintering atmosphere for UO₂powder is made slightly oxidizing by adjusting the CO₂/CO ratio of the mixed gas, the sintering temperature can be lowered as much as 600℃ or more in comparison with sintering under the conventional reducing atmosphere. Sintered pellets having the O/U ratio of 2.01 can be readily obtained by reducing at 1100℃ for one hour pellets sintered under a slightly oxidizing atmosphere. Sintered pellets having the density of 96% of the theoretical density can be readily obtained by sintering for a short period under a slightly oxidizing atmosphere followed by a reducing treatment.

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A study has been made of the distribution equilibria of sulfur between liquid iron and stags of Fe_tO-MgO, Fe_tO-SiO₂-MgO and Fe_tO-SiO₂-CaO-MgO systems saturated with MgO. 1) The distribution ratio of sulfur, Ls, in Fe_tO-SiO₂-MgO(sat) slags increases as Fe_tO content increases, as a result of the corresponding decrease in the amount of (SiO₂＋MgO) content. 2) In Fe_tO-SiO₂-CaO-MgO(sat) slags, the values of Ls increase with the molar ratio of bases to acid, and as Fe_tO content increases, the values of Ls increase progressively at the higher basicity than about 2.0, but less basic stags result in a increases of Ls. 3) It is considered that Fe_tO contributes to the increase of oxygen potential rather than a_(o 2)- in the higher basic range, while Fe_tO contributes to the increase of a_(o 2)-in the less basic range. 4) The sulfur equilibrium in Fe_tO-MgO(sat) slags is expressed by the equation of Log{(%S)·[a_o]/[a_s] } = -4,560/T＋2.22, and the value of ΔH˚is estimated to 21 ㎉/㏖. But due to the compensation of endothermic effect by the corresponding increase with temperature in [a_o] , the values of Ls are found to be nearly independent of temperature in the experimental range. 5) The sulfide capacity, Cs, decreases considerably as SiO₂content increases, and is fairly correlated with the modified base concentration, N`_(Base) (= N_(cao)＋0.8N_(FeO) ＋0.5N_(MgO)), regardless of slag systems and compositions. The order of desulfurizating power is CaO > FeO > MgO.

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An investigation was carried out on the effect of cyclic heat treatment on the strength and toughness of Cr-Mo low alloy steel. Specimens were soaked at 820℃, just above the region of austenite for 1∼3½minutes and the number of cycling was 1∼4 cycles. Alternate cyclic heat treatment in the region of austenite and (austenite＋ferrite) was also applied. Experimental results showed that the yield strength, tensile strength and impact toughness were remarkably improved by refining prior sustenite grain size from ASTM #6 to #9. But the rate of improvement in the mechanical properties was reduced with increasing number of cycle. In the condition of alternate cyclic heat treatment, the impact toughness was remarkably increased as high as 12㎏·m/㎠. The improvements in the strength and toughness by cyclic heat treatment were attributed to the grain refinement, fine carbide precipitation and the increase of lath martensite in the matrix due to carbide precipitation at lath boundary.

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The effects of Aluminum and Copper addition to the cast iron in hypoeutectic composition range were studied on the shape of graphite, the structure of matrix and the mechanical properties. The results obtained are as follows: 1) When the addition was in the form of Al-Cu (50 to 50) alloy, the shape of graphite was uniformed flake graphite (A Type on A.S.T.M). The tendency of such phenomena was more distinct at the 2.0 wt.% addition of Al-Cu alloy. 2) The addition of Aluminum and copper strengthened the matrix structure. 3) The tensile strength and hardness were increased by the addition of either Al or Cu and Al-Cu alloy. In the case of Al-Cu alloy addition, the tensile strength was increased by 20% and 7% compared with that when either Al or Cu was added, respectively.

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Unidirectional solidification experiments were conducted on Al-Cu-Mg ternary eutectic alloys to investigate the effects of the growth rate and (Cu＋Mg)/(Al＋Cu＋Mg) ratio on the composites structure and the mechanical properties at temperature gradient 80℃/㎝ in the range of crystal growth rate from 0.1 to 1.2 ㎜/min. The results indicated that lamellar composite structure and colony structure are formed in the range of growth rate 0,1∼0.3 ㎜/min. and 0.6∼1.2 ㎜/min., respectively. The scale of phases varies as the growth rate to the negative one-half power and λ²R was 8.5 ×10^(-6) ㎣/min. The faster growth and he higher (Cu＋Mg) wt.% in the range below 40.3 wt.% cause the higher mechanical strength. Failure in tension of these alloys initiates from crack formed by loading and is describable by Griffith brittle-fracture theory.

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A study has been made of the computer calculation of ternary phase diagrams using binary thermodynamic data. Binary data were expressed in analytical formula of Redlich-Kilter equation or Legendre polynomials. A path dependent equation and a path independent equation developed from a regular solution equation were used to the calculation of ternary free energies of mixing. In order to determine the phase boundaries or tie lines, minimization of free energies in two-phase regions was adopted, which was achieved by the simplex and the hill-climbing methods. The calculated phase diagrams of the Bi-Al-Pb system at 1173˚K and Fe-Cr-Ni system at 1573˚K were in good agreement with the measured phase diagrams.

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