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In Al-1.1wt%Mg-0.68wt%Si alloy the effect of Cr and Ti additions on precipitation behavior of the homogenized and/or aged specimens has been investigated homogenizing. Ephase(Al, Mg, Cr₂) is preferentially precipitated around Mg₂Si and distributed unevenly near a cored dendrite structure. With the addition of Cr and Ti the aged microstructure has indicated that the coarsening of needle-shaped G. P. zone and rod-shaped intermediate phase(β`) is delayed, and transition from needle-shaped G. P. zone to β` phase is, thus, delayed. This in turn, caused deceleration of the hardness decrease rate during overaging.

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The effect of addition of boron on the anneal-induced enthalpy relaxation, the change in Curie temperature(T_c) and the atomic parking density for metal-metal type Fe-(Ni, Co)-Zr amorphous alloys has been investigated. As boron content increased, the magnitude of enthalpy relaxation, which was evaluated with that of endothermic reaction, increased for (Fe_(0.5)Co_(0.5))_(90)Zr_(10-x)B_x(x=0-3) and (Fe_(0.85)Ni_(0.15))_(90-x)Zr_(10)B_x(x=0.4) amorphous alloys. Moreover, the atomic packing density decreased with increasing boron content for (Fe_(0.5)Co_(0.5))_(90)Zr_(10-x)B_x alloys. The large enthalpy relaxation for boron -auditioned alloys was ascribed to the low atomic packing density. Additionally we concluded that the structure of the metal-metal type amorphous alloys is comparative1y stab1e against the low∼temperature enthalpy retaxation because of their high atomic packing. The annealing response of T for (Fe_(0.85)Ni_(0.15))_(90-x)Zr_(10)B_x alloys suggested that boron stabilizes the topological structure of the metal-metal type amorphous alloys.

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Using a twin-roller type melt-quenching technique, we investigated the effects of Cr alloying element on the microstructure and mechanical properties of rapidly to solidified high manganese steel strip(0.5㎜ thick). We confirmed the possibility of manufacturing a high Mn alloy steel plate without hot-rolling by this method. In melt-quenched, the transformation from austenite to ferrite was suppressed resulting in only austenite phase. Its solidification mode is similar to the typical structure of the rapidly solidified metals. The dendrite structure region without directionality increased with increasing Cr alloying element. The 0.2% yield stress of the alloy with Cr was higher than the standard high manganese steel. The strengthening effect of Cr after heat treatment cannot be explained by its small solution hardening effect alone and is rather considered to be mainly attributable to gram refining due to the rapid solidification and the addition of carbide forming element, Cr.

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The fracture properties obtained in austempered ductile iron castings are dependent on metallurgical process variables, including chemical composition and heat treatment conditions. In the present work alloyed ductile irons of 0.27%Mo-1.08%Ni and of 0.24%Mo-0.57%Cu were studied for their response to austempering. The alloys were austenitized for 1.5 hrs at 850-1000℃ and austempered for 2 hrs in salt at 385℃. The optimum mechanical properties and fracture toughness were obtained when the alloys were austenitized at 900-950℃.

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The microstructure and fracture toughness of weld heat affected zone of ductile cast iron have been investigated by using thermal cycle simulator on the assumption of practical welding process. The matrix structure of heat-affected zone was transformed to martensite, martensity ＋ pearlite, pearlite and pearlite including small amount of ferrite, by turns, with increasing the cooling time from 800℃ to 500℃. The use of a proper preheat temperatures prevented the formation of martensite. The instrumented charpy impact test has been carried out on a welded ductile cast iron. Result showed that dynamic fracture touhghness, k_(Id) was increased slightly with preheat temperature and heat input In this work, it was shown that apparent impact energy includes contributions other than that of the true deflection of specimen. We found that a compliance energy correction was always needed to determine the true specimen energy. For this purpose, elastic compliance value of testing machine was measured dynamically by the low blow test to correct the apparent impact energy. From this result, true specimen energy was nearly 62 percent of apparent of apparent impact energy value, Therefore, machine compliance corrections must be adapted to load-deflection curves in instrumented impact testing.

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A straight-forward method for simultaneously optimizing thermodynamic functions and phase diagrams from experimental data of both is described. The method introduces the flags in a subprogram which allow us to calculate several thermodynamic functions. The functions may be derived from phase diagram analysis. In order to test the validity and the applicability of the present method, the Ag-Cu system is chosen because of its variety of phase boundaries including a miscibility gap. The experimental data are found to be excellently reproduced by the optimized expressions.

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The influence of plastic strain amplitude and gaseous environment on the low cycle fatigue properties has been studied in a Nb-bearing HSLA steel. The cyclic response under plastic-strain controlled loading is determined. Neither the cyclic stress-strain curve (CSSC) shows a plateau nor persistent slip bunds (PSB`s) have been observed in the bulk. The cyclic plastic strain energy (ΔW) and the accumulated plastic strain energy (W) have been calculated as a function of plastic strain amplitude (Δ_(εΡ)/2) in the form of Κ(Δ_(εp)/2)＾N. The computed values of ΔW and W are in good agreement with the experimental data. The vacuum environment enhances fatigue crack initiation life, fatigue life and W. The environmental effect becomes more severe as the plastic strain amplitude decreases. Tensile properties, cyclic stress response and ΔW are not affected by the gaseous environment.

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In order to concentrate of pyrrhotite ore by collectorless flotation in acidic solution, the relation between floatability and formation of elemental sulphur by oxidation of pyrrhotite, galena and sphalerite was investigated. Perfect floatability of pyrrhotite through aeration was obtained by formation of elementary sulphur of pyrrhotite surface in pH values lower than 2.0. Galena and Sphalerite, however, can be floated by using oxidation agent such as H₂O₂in this range. It was confirmed in the batch flotation that collectorless flotation of pyrrhotite with frother and dispersing agent in acid solution was appreciable process to grade up of pyrrhotite ore.

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The effect of welding heat input on the HAZ toughness was systematically investigated through crack tip opening displacement (CTOD) test for two different offshore structural steels of TMCP type API 2H Gr. 50 and normalized BS 4360 Gr. 50D steel. The heat input levels of 15,50 and 70KJ/㎛ were applied in this study. Test results showed that the HAZ toughness of normalized steel deteriorates with increasing heat input, while that of TMCP steel shows the opposite trend. These trend it atlributable to the fact that increasing heat input decreases the amount of the brittle M-A constituent in the HAZ of TMCP steel but has little effect on that of normalized steel in the heat input range between 15 and 70 KJ/㎝. Such the difference in the effect of heat input on the amount of M-A constituent formed in the HAZ can be explained in terms of compositional difference between the two steels. As the result of this study, it can be claimed that the maximum welding heat input level can be raised up to 70kJ/㎝ for TMCP steel.

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The purpose of this study is to investigate the effect of thermo-mechanical treatment (TMT) on the low cycle fatigue behavior an 7050 Al alloy. During low cycle fatigue tests, the conventional T6 and T74 treated specimens showed cyclic softening, where as the TMT resulted in cyclic hardening behavior. At strain amplitude of 1.1%, conventionally heat-treated specimens showed longer fatigue life than the TMT ones At total strain amplitude less than 0.9%, however, the TMT showed longer fatigue life than the T6 and T74 treatments due to the reduction of mean free path of dislocations. The reduction of mean free path could be ascribed to an interaction between matrix precipitates and dislocations introduced during the TMT process, strengthening due to precipitate free zone (PFZ) and the formation of grain boundary steps.

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