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A study on the leaching of the molybdenite from the soda roasted ore obtained by the oxidizing roasting of the mixtures of molybdenite and bismuthinite has been made. To determine the oxidizing roasting temperature of mixed sulphide ore and the soda roast ing temperature of oxidizing roasted ore, and also to identify those compounds, the differential thermal analysis and X-ray diffraction analysis have been performed. The results obtained are as follows. The suitable soda roasting temperature of oxidizing roasted ore was in the range from 500℃ to 700℃ and the oxidizing roasted ore has been found to be composed of γ-Bi₂O₃, MoO₃and Bi₂MoO_6. The leaching rate of the soda roasted ore mixed with caustic soda has shown to be greater by more than 8% as comparted to that of the soda roasted ore mixed with the soda ash. The recovery of soda roasted ore mixed with caustic soda has been determined to be 93% at the soda roasting temperature of 700℃. The concentrated leaching residues have been found consisting of γ-Bi₂O₃and Bi₂MoO_6.

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The growth kinetics of the intermediate nitride, the γ´-phase (Fe₄N), in the iron-nitrogen binary system was observed by assuming the diffusion control in multiphase diffusion. The observed growth rate of the γ´-phase was given by dX_(III)/dt=(M/ρ)Fe₄N·5/4·D_(III)ΔC_(III)/X_(III) (1) and the depth of the γ´-phase layer by X_(III)=[10/4(M/ρ)Fe₄N·D_(III)ΔC_(III)]^½·t½ (2) On the other hand, the diffusion coefficient of nitrogen obtained from the quantity of nitrogen diffused into the cylindrical sample of pure iron and the saturation value of the nitrogen in the temperature range of 650℃-900℃ was given by D=1.3×10^(-2)exp[-28300/RT]㎠/sec (3) The diffusion coefficient obtained by substituting the depth of γ´-phase generated in the sample in to Eq. (2) was D=2.9×10^(-2)exp[-27700/RT]㎠/sec (4) from which we may notice a good agreement with Eq. (3). However, the result obtained by treating the diffusion of nitrogen in a single phase was D=1.6×10^(-4)exp[-18600/RT]㎠/sec (5) showing discrepancy with the above results.

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The effect of aluminium contents on the mechanical properties and dendritic morphology in Zn-Al-2% Cu casting alloys has been investigated experimentally. The results obtained from this study are summarized as follow. 1. Tensile strength is decreased from 33㎏/㎟ to 29㎏/㎟ with the addition of 16, 19, 22% Al and increased from 29㎏/㎟ to 37㎏/㎟ with the addition of 22, 25, 28% Al. 2. Work hardening index (n´) is 2.05 in 22% Al and is increased slightly as the Al content increase or decrease from 22% Al. 3. The primary arm length of dendrite is increased with the addition of 13-22% Al and the other contents of Al constrain primary arm length growth of dendrite. 4. Tensile strength is increased with the secondary arm length increasing of dendrite

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The effect of silicon addition and graphite dispersion in cast aluminum alloys on the wear characteristics was investigated. The graphite particles were initially coated with copper by cementation process, and then dispersed into the alloy melt by vortex method. The wear rate was measured on pin-on-disk type wear test machine without any lubricant. The wear rate decreased as the graphite content increased. At the higher contact pressure the increase in wear resistance of graphite dispersed aluminum alloy became more apparent. At the sliding speed near 1m/sec, high wear rate due to the abrasive wear mechanism was observed. At the higher sliding speed than 8m/sec lower friction and wear rate were observed. The reduced friction and wear rate were attributed to adhesive surface wear mechanism. The reduction of wear by graphite dispersion was more effective at the slow sliding speed less than 1m/sec.

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Stress corrosion behavior of type-304 austenitic stainless steel in 45.5wt.% MgCl₂ solution was studied with U-bend specimen between 125℃ to 155℃ solution temperature. Maximum crack depth increased logarithmically with the increase of time exposed to solution at various temperatures. From maximum crack depth measurement, induction period before cracking and crack propagation period were evaluated. The result indicated that these periods decreased with the increasing corrosive solution temperature. Apparent activation energy obtained from Arrhenius equation showed that the apparent activation energy for induction period was larger than that for crack propagation period. This study emphasizes the importance of corrosive solution temperature in constant strain.

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The mechanical Properties and grain size of the coldrolled Al-11%Zn base alloys contained Ti or Mn metal have been investigated. The results obtained for the specimens heated at different temperature for various time periods are as follows; 1) The grain refinement effect of Ti was observed at high temperature when Ti content was small (0.29wt % Ti) 2) In general, the elongation of annealed and air cooled alloys containing Ti or Mn was observed greater than that of water-quenched same alloys. 3) The small addition of Ti caused the elongation to increase, approximately, up to 44%, but didn`t effect the large change in tensile strength. 4) The age hardenability of the alloy due to the addition of Ti or Mn is not likely to exist. 5) The improvement of mechanical properties of the alloy seems to be better for the case of Ti addition than that of Mn.

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An austenitic high manganese heat resisting alloy was newly designed. Effects of phosphorus addition and two step solution treatment on the microstructure of the alloy were investigated in order to improve creep rupture properties. A small addition of phosphorus resulted in the uniform dispersion of fine carbide precipitates in the matrix and the narrowing the width of the precipitate free zone along grain boundaries. Two step heat treatment brought out the serration of grain bourdary which was very effective in the prevention of the formation and the growth of cracks or cavities at the grain boundaries. It was found that the grain size was closely related to the rupture life, i. e., the maximum rupture life was achieved at the optimum grain size. As the result of combined effects of phosphorus addition and grain boundary strengthening by the serration, the rupture life was improved remarkably up to ten times at 600℃ and 26 ㎏/㎟.

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In the present work, mechanical properties (strength and toughness, etc) of medium carbon silicon steel according to the prior austenite grain size and the change of structures tempered at various temperatures were studied, using primarily electron microscopy. As-quenched martensitic structure consits mainly of packets of laths, and auto-tempered precipitate (ε-carbide) could be also observed within some of laths. ε-carbide was precipitated within laths when tempered at below 300℃, while cementite begins to form first along lath boundaries tempered at 400℃ and develop in spheroidized shape at higher tempering temperature. Packet size was related to yield stress and toughness. And it was apparent for silicon to retard the softening of tempered carbon steel. Tempered martensite embrittlement occurred at around 400℃ tempering and resulted in interlath cleavage of fracture mode. Such a considerable decrease in toughness is thought to be attributed to the formation of cementite in interlath boundaries, since retained austenite in lath boundaries is thermally unstable with respect to tempering temperature.

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In order to study the effect of carbide behavior on mechanical properties in bearing steel, the responses of two different microstructure to subsequent heat treatment were investigated. One microstructure was a fine lamellae pearlite prepared by the isothermal transformation at the nose temperature, and the other microstructure was that of a commercial bearing steel, ie, coarse spheroidized carbide dispersed in ferrite matrix. The results obtained in this experiment were summarized as follolws. 1. The fine lamellae pearlite structure showed faster carbide dissolving rate than the spheroidized carbide in the commercial steel. 2. The fine lamellae pearlite structure resulted in finer and smallor amount of undissolved carbide in the martensite matrix than the spheroidized carbide. 3. The fine lamellae pearlite structure showed higher flow stress and work hardening exponent after subsequent austenitizing for hardening. 4. The martensite with retained austenite showed higher tensile strength than the one without it because of better ductility.

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