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Hydriding rate data of FeTi with minimum heat effect, which had been obtained by applying thermal ballast in a Cu tube reactor, were analysed by both the rate equations developed under the assumption of continuous moving boundary and the Johnson-Mehl-Avrami equation. The rate was directly proportional to (pH₂-Peq) at high temperature and low reacted fraction, and to (√pH₂√Peq) at low temperature and high reacted fraction, which illustrates the change of the rate controlling step from a surface reaction to a reaction in the bulk, the diffusion or the interface reaction, as the temperature is decreased and as the reaction proceeds. The dependence of the rate on the reacted fraction showed the characteristic feature of the nucleation and growth process. A model which relates the surface reaction and the nucleation and growth process is proposed. The apparent activation energy of the surface reaction is estimated to be about 1500㎈/mole, and that of the reaction in the bulk about 8000㎈/mole.

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The phenomenon of strain burst is observed in Cu-25Ni alloy subjected to cyclic creep at intermediate temperature (0.45-0.55 Tm) and high stress however in static creep under the same condition, strain burst is never occurred. The purpose of this work is to study the tendency and mechanism of the strain burst. Strain bursts occur frequently as the temperature and stress are increased, but at low stresses or high temperatures the strain burst is not observed. The strain burst can be seemingly explained as follows: in cyclic creep the localized dislocation network spacing growth is occurred by recovery during cyclic unloading, on reloading instantaneous large increase in mobile dislocation density caused by destruction of grown dislocation network spacing results in strain burst.

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Stress corrosion cracking (SCC) testing on Fe-Mn-Al alloys has been carried out in the boiling 42% MgCl₂ solution, and the effects of phase difference or of some chemical contents on SCC sensitivity have been studied. Comparing with the austenitic 18-8 stainless steel, Fe-Mn-Al alloy of austenitic structure has shown much higher resistivity to SCC. By increasing the ferrite phase in the dual phase (γ+α) Fe-Mn-Al alloys, SCC sensitivity was increased. Under the studied condition, pitting occurred more easily at ferrite phase than at austenite phase. These pittings acted as the crack initiation sites, resulting in increased SCC sensitivity. Silicon-added austenitic Fe-Mn-Al alloy has shown increased SCC sensitivity than without it. Increased carbon content of the similar dual phase alloys, resulted in the higher SCC sensitivity.

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This investigation was undertaken to deters me the feasibility and consistency of obtaining desirable compacted vermicular graphite cast iron from co1d pig iron obtained from blast furnaces. The molten iron after treatment to convert it to C.V graphite was cast into large sections that would provide solidification conditions similar to those prevailing in large ingot molds. Three types of treatment of the molten iron were employed: Mg treatment plus the addition of denodularizing elements such as Ti & Al; deliberate undertreatment with Mg; and the addition of rare earth silicides. The best method of producing a C.V. graphite in large sectioned castings for ingot mold purposes is the treatment with a Mg bearing alloy such as 5% MgFeSi plus a denodularizing element such as Al. A mostly ferritic matrix can be obtained in C.V. graphite cast iron made from cold pig iron in heavy sections with silicon contents in the range of at least 1.9% and manganese contents under 0.6%.

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The low cycle fatigue test of ductile cast iron was studied for the purpose of promoting the qualitative confidence for its importance. The main results obtained are as follows: 1. The stabilization of stress amplitude under the cyclic strain was faster when the strain level was higher or the strain rate was slower. 2. The cyclic strain grave rise to hardening in ferritic matrix but did not cause hardening or softening in pearlitic matrix. And the cyclic stress-strain curves obtained from companion specimens were in accord with that from incremental step test results. 3. The fatigue lives of the materials depended on Ce and Ke according to matrices, and depended on Cp and Kp according to strain rates when its matrix was same. Especially, Cp dependence of fatigue life was much greater than Kp. Here Ce and Ke are the coefficient and the exponent of cyclic elastic strain, and Cp and Kp are the coefficient and the exponent of cyclic plastic strain. 4. The equations for the fatigue life of the material were as follows. ⅰ) When its strain rate was 10＾(-2)/sec ε_ta = (0.239-0.263)/_Nf (0.653-0.698) + (0.003 -0.005)/_Nf (0.036 -0.073) ⅱ) When its strain rate was 17＾(-3)/sec ε_ta = (0.166 -0.172)_Nf (0.626-0.674) + (0.003 -0006)/_Nf (0.057-0.097) 5. Cyclic hardending exponent, n` of the annealed specimens ranged from 0.059 to 0.118, and the normalized specimens, 0.116 to 0.183. 6. Calculated fatigue strength was in fair agreement with experimental points within low cycle range. 7. Under the static stress, the crack initiation of ferritic matrix was caused by closing and linking up between nodules by plastic deformation in the stress direction, and the crack initiation of normalized specimens was attributed to the stress concentration in soft ferritic shell around the nodule due to a hard pearlitic matrix. And fatigue cracks were mainly due to notch effect of nodules.

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A W-surface-alloyed layer was obtained on alloy tool steel by the irradiation of CO₂ laser in order to improve wear-resistance and heat-resistance. Beneath the W-alloyed layer a solid-state transformed layer was formed and then was followed by matrix. W-concentration was homogeneous throughout the alloyed layer by well-interdiffusion of components. Behind the interface of liquid/solid, however, the solid-state diffusion of W was neglected. As the laser scanning speed was decreased normal grains were obtained near the laser-irradiated surface, and meanwhile dendritic structures were formed around the alloyed zone by rapid cooling. Many fine carbides were precipitated in grains, but they were not found in dendritic grains. But by increasing scanning speed fine dendritic structures were produced throughout the alloyed zone due to rapid cooling. As long as W-particles became larger, they were not completely dissolved and at the same time the size of retained W-particles became larger. As the laser energy density was increased and scanning speed was decreased, the width and depth of the surface-alloyed layer became wider and deeper. However, as the size of W-particles was increased, the width became wider but the depth was decreased. When the size of W-particles was small, the battiness of alloyed layer was almost constant due to the thorough dissolution of W-particles and the intermixing of components. As the size of W-particles became larger, the hardness was increased and resulted irregular in alloyed layer due to retained W-particles. As the W-particle size was increased and laser scanning speed was decreased, the hardness of solid-state transformed martensitic region increased. However, as laser scanning speed was decreased further below a certain threshold level, the hardness was decreased by tempering effect of martensitic structure due to the passage of heat in the liquid region.

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A study on the leaching of pyrrhotite was carried out in the presence of oxygen and sulfuric acid. The effects of various reaction factors such as a concentration of leachant, temperature and partial pressure of oxygen were discussed. The results are as follows. 1. The rate of the hydrolysis reaction of ferric ion and the oxidation reaction of ferrous ion into ferricion increases with the increase of temperature and partial pressure of oxygen. 2. The phase of precipitate which is the product of the hydrolysis of ferric ion is changed with the increase of temperature 110℃, 130℃, 150℃ as follows. Fe₂(SO₄)₃ → Fe₃(SO₄)₂(OH)_5 2H₂O → 3Fe₂O₃4SO₃ → αFe₂O₃ 3. The sulfur in the pyrrhotite can be removed as elemental state. The elemental sulfur can be easily oxidized. 4. The reactivity of hexagonal pyrrhotite is greater than the mono type pyrrhotite.

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