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The susceptibility to intergranular stress-corrosion cracking of type 321 stainless steel weldments with the effect of various post-weld heat treatments was investigated measuring the degree of sensitization by using the double loop EPR(electrochemical potentiokinetic reactivation) test and the oxalic acid etch test. The effects of post-weld heat treatments on the increase in resistance to sensitization of weldments were simulated by heat-treating as-received samples with a furnace in the laboratory. In addition to heat-treatment simulation tests, the weldments fabricated same as done in the field were tested in order to elucidate the effects of post weld heat treatments on sensitization and intergranular stress-corrosion cracking. The relationship between the resistance to polythionic acid stress-corrosion cracking (PA SCC) and the sensitization of weldments was also investigated by conducting bending SCC tests as well as slow strain-rate tensile tests. The results showed that type 321 stainless steels with than Ti/C>10 have very little chance for PA SCC in the vicinity of the weldment.

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Microstructural observations revealed that increase in volume fraction of SiC particles lower the coefficients of thermal expansion (CTE) of the composites, and the CTE of metal matrix composites is proportionally changed with the size of Si phase. To analyze the thermal expansion behavior of aluminium composites, a new model for the CTE of monodispersed binary composites on the basis of Ashelby`s cutting and welding approach was introduced. In this theoretical model, it was considered that during cooling relaxation of residual stresses can create elastoplastic deformation zone around a SiC or Al₂O₃ particle in the matrix. Size of reinforced particles and other metallurgical factors of matrix alloy and composites were also considered. In this model, the interacting effect between the reinforced hard particle and soft matrix is considered by introducing the influence of the elastoplastic deformation zone around a particle, which is distinguished from the Kerner`s model. It was revealed that the CTEs of composites are influenced by particle volume fraction, elastic modulus and Poisson`s ratio as well as elastoplastic deformation zone size and particle size.

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The kinetic experiments have been made on iron oxidation in slag by oxidizing gases at 1387∼1500℃. The effect of temperature, FeO content and oxygen potential of gas on the reaction rate have been examined. The iron oxidizing rate is considerably increased with increasing temperature and FeO content in slag. It was also found that the rate controlling step of reaction have been depended on the temperature, FeO content in slag and (P_(co₂)/P_(co) as an oxygen potential at gas/slag interface. The dependence of the overall reaction rate constant on temperature and initial FeO content in slag at 1450℃ could be expressed as follows; log k_(overall) = -0.36-10,820/T[㏖/㎠·sec·atm] k_(overall) = 1.04×10^(-7)(wt%FeO)^(0.75)[㏖/㎠·sec·atm] In condition of high oxygen potential such as high FeO content and (P_(co₂)/P_(co)), the chemical reaction at interface between slag and gas might play a important role as a rate controlling step of overall reaction, which is controlled by the dissociation of CO₂ at slag/gas interface. But in case of low (P_(co₂)/P_(co)), mass transfer and chemical reaction at interface between slag and iron become important as a rate controlling step. The reaction mechanism of iron oxidization in slag by gas have been discussed in terms of rate constant for elementary reactions.

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A study on the longitudinal reduction behaviors of iron ore pellets in the fixed bed was carried out by hydrogen gas at 690∼800℃. Reduction of iron ore pellets from Fe₂O₃ to Fe in the fixed bed was a non-isothermal reaction which temperature of the charging bed dropped rapidly in intial reduction stage on account of the endothermic reaction between hydrogen gas and iron ore pellets. Gas utilization degree in the fixed bed reduction was 12∼18% and was depended on the reaction temperature. When an average reduction degree of the charging bed reached 50%, a partial reduction degree at the height of 20, 40 and 60 ㎝ from the hearth were 80, 30 and 10%, respectively. Calculated reduction curves obtained from unreacted core model were well accorded with experiments. Chemical reaction rate constant.(Kc) and effective diffusivity(De) were varied with reduction temperature and charging conditions like volume, voidage in the fixed bed.

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The unreacted-core model has been extensively used for the analysis of the gaseous reduction rate of the iron oxide because of its simplicity and relatively a good agreement of the experimental result with the calculated reduction curve. However, the rate parameters in the model are known to be affected by many factors such as the reactivity, the diffusivity in the reactant zone and through the product layer, and the size- and shape of the solid particle, so that it is criticized that the applicability of this model is rather restricted. In this study, the applicability of the unreacted-core model was reviewed based on the intermediate model. It was found that the unreacted-core model showed a good applicability when Thiele`s modulus was higher than 20 and effective diffusivity through the product layer was larger than 10 times of that in the reactant zone. However, it showed worser applicability when the effective diffusivity through the product layer becomes closer to that in the reactant zone even in case of a higher Thiele`s modulus than 20.

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In order to improve manganese yield by smelting reduction of manganese ore in less slag blowing at BOF, the reduction kinetics of manganese oxide in CaO-SiO₂-MgO_(sat)-FeO-MnO slag was investigated under experimental scale. The effects of temperature, slag composition and addition of CaF₂ on the reduction rate of MnO in slag were examined. From the assumption that the reduction of (MnO) is controlled by the equilibrium manganese distribution and mass transfer through the metal and slag boundary layers at the metal/slag interface, the rate equation was obtained. The kinetic model suggested in the present study showed good agreement between calculated and observed values of 〔Mn〕 and (MnO) and the reduction behaviour of (MnO) in slag can be described by the present model.

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The thermodynamic behavior of copper in molten Fe-C-S alloy at high temperature was investigated by chemical equilibrating technique. The effects of copper, carbon, sulfur content and temperature on the activity coefficient of copper in molten pure iron and carbon saturated were was determined by measuring the distribution ratio between silver and Fe-C-S-Cu alloy. The activity coefficient of copper in molteniren and carbon saturated iron at infinite dilution of copper were measured 11.02 and 28.50 at 1823K respectively. The interaction parameter between copper and copper, sulfur and carbon in molten iron at 1823K, was estimated as follows; ε^(Cu)_(Cu) = -4.80, ε^S_(Cu) = -2.544, ε^C_(Cu) = -4.60 The dependence of the activity coefficient in molten Fe-C alloy on temperature was determined as follows; For molten pure iron : lnγ^(oFe)_(Cu) = 4370/T For Fe-2wt%C : lnγ^(oFe-2wt%C)_(Cu) = 0.72 + 3840/T For carbon saturated iron : lnγ^(oFe_C)_(Cu) = 1.11 + 4100/T Combining the effect of temperature and the alloying component, the activity coefficient of copper could be expressed as follows ; lnγ^(Fe-C-S)_(Cu) = 4370/T·(1-X_(Cu))² + (2.15 + 4600/T)·2.54·X_s The possibility of removal of copper from steel by slag refing and evaporating technique was discussed.

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An attempt has been performed to separate Co(II) and Ni(II) in the sulfate solution by supported liquid membrane containing 2-ethylhexyl phosphoric acid mono-2-ethylhexyl ester(HEH(EHP)) as a carrier. The mathematical model for the supported liquid membrane(SLM) of flat type was developed to predict the permeations of metal ions in terms of diffusion at the aqueous boundary layer and organic membrane phase, and the reaction at the aqueous-organic interface. The mathematical model developed for flat SLM showed good agreement with the experimental results.

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