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Thermal stability of Fe-P-C-B-Al-Ga glassy alloys with effect of additional elements(Al, Ga) were investigated. The dissolution of 5 at% Al and 2 at% Ga for the Fe_(79-x-y)P_(11)C_6B₄Al_xGa_y alloy was found to be effective for the extension of the supercooled liquid region defined by the difference in the glass transition temperature(T_g) and crystallization temperature (T_x), ΔT_x(=T_x-T_g). The ΔT_x value is 30 K for the Fe-P-C-B alloy and is increased to 61 K for 5% Al and 2% Ga. The effectiveness of addition Al and Ga is presumably due to the combination effects of ; (1) the difficulty of atomic rearrangements for the precipitation of the Fe-metalloid compounds caused by the generation of Al-metalloid pairs with strongly attractive bonding nature, and (2) the decrease in the preferential precipitation tendency of Fe-B, Fe-C compounds by the dissolution of Ga which is immiscible to B and C and soluble to Fe.

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In order to investigate the effect of Mo addition on the mechanical properties of 13Cr-0.2C martensitic stainless steel, tensile test and Charpy V-notch test were performed after tempering at the temperature range of 200∼700℃ following austenitizing at 1100℃. The yield strength and hardness of the steel were increased with the increase of Mo content at all tempering conditions, because Mo causes retardation of precipitation and coarsening of carbides and solid solution strengthening of matrix. Except 500℃ of tempering temperature. the Charpy impact energy was significantly increased with Mo content and showed the highest value at 1.5 wt.% addition. The increase of impact energy of the steel containing Mo is thought to be caused by δ-ferrite formed in the tempered martensitic matrix. At 500℃ tempering, Charpy impact energy was decreased drastically due to temper embrittlement and it was not possible to prevent it even though Mo was added up to 1.5 wt.%.

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The effect of special austempering treatments on the microstructures and mechanical properties of Mo-Cu, Mo-Cu-Ni and Mo-Ni added ADIs(Austempering ductile cast irons) has been investigated. The microstructures of alloys prior to austempering treatment can be changed by introducing the pre-quenched(PQ), pre-heated(PH) or step heated(ST) treatments. The mechanical properties of the Mo-Cu ADI which was austenitized at 900℃ for 2 hours, followed by tempering at 350℃ for 2 hours were superior to those of the Mo-Ni ADI, Mo-Cu-Ni ADIs, and unalloyed ADI. Before austempering treatment, the mechanical properties of ADI can be improved by the control of various prior structures of DCI using a special heat treatment, such as pre-quenched(PQ), pre-heated(PH) or step heated(ST) austempering treatments. The mechanical properties of Mo-Cu ADI were improved by PQ, PH austempering treatment compare to those of other ADIs, therefore PQ Mo-Cu ADI and PH Mo-Cu ADI are expected as promising materials to produce automobile parts in the future.

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During pipe forming, the pipe-wall fibres undergo different deformation patterns, resulting in a stress gradient through the wall. The cold flattening and subsequent tensile-testing operation leads to additional tension-tension and compression-tension cycles on the inner and outermost fibres of the pipe wall, respectively. The compressive strains on outer surface reduce the yield strength due to the Bauschinger effect, while the additional cold work in the other surface increase the yield strength. Therefore, the yield strength of the ERW pipe becomes much different from that of the original material. Such phenomenon should be considered in designing forming condition for high strength pipes. In this study, the relation between work hardening and the Bauschinger effect is experimentally obtained and discussed in order to evaluate final yield strength of pipes. For the ferrite-pearlite Line pipe steels used, the following conclusions are reached. The Nb+Ti+V and Nb+Mo steels(API-X70 grade) were predicted a significant reduction in yield strength, averaging about 4.2 ㎏/㎟ in 4% prestrain. Much less difference in the reduction of yield strength was predicted in the Nb+Ti+V and Nb+Mo steels. API-X65 and X52 grade steels showed 2.3 ㎏/㎟ yield strength loss in 4% prestrain.

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The texture evolution in AA1050 sheet metals during deep drawing process was experimentally investigated. The measured textures varied with the initial crystal orientations and strain path. In the specimen parallel to RD, the grains oriented at the D component rotated toward the Cu component and the grains having orientations along the fibre rotated toward the G {110}<001> and P{110}<111> during deep drawing. In the specimen parallel to 45° with respect to RD, the initial crystal orientations between the G and RG also rotated toward the G and P during deep drawing. In the specimen parallel to TD, the initial crystal orientations between the B{110}<112> and RG {110}<110> rotated toward the P{110}<111> during sleep drawing. The deviation from the plane strain state in the flange area gave rise to a decrease in the orientation density around P.

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Stress corrosion cracking behaviors of RS/PM Al-9Zn-2.5Mg-1Cu alloys with the addition of 2%Fe, 2%Mn, and 1%Fe+1%Ni, respectively, were examined in the present study. Each alloy was exposed to 3.5% NaCl aqueous solution under an applied stress of 200MPa for 5 and 20 days, respectively, and tensile tested in air. The alloys containing Fe+Ni and Mn showed a significant reduction in ductility after exposure for 20 days. SEM fractographic studies indicated that the size and depth of dimples, as well as the sign of plastic deformation around dimples, were greatly reduced after exposure for those alloys susceptible to stress corrosion cracking. The present study strongly suggested that hydrogen played an important role in stress corrosion cracking behaviors of Al-9Zn-2.5Mg-1Cu alloys with the addition of 2%Mn and 1%Fe+1%Ni, respectively.

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Three-dimensional numerical analyses were performed to simulate the transport phenomena far the heat transfer and fluid flow in the molten pool formed by a bifurcated round submerged entry nozzle(SEN) in twin roll strip casting process. From the point of skull formation at the free surface, or meniscus, the submerged depth of 80 ㎜ was preferred to that of 150 ㎜. The skull formation in the vicinity of edge dam and around the nozzle could be minimized when the outlet of the nozzle was declined at 16 degrees with the nozzle submerged by 80 ㎜. The region up to about 200 ㎜ from the nip remained in mushy state : the cooler melt was being squeezed upwards from the nip while the hotter melt from the nozzle could not reach down to that region. In the vicinity of edge dam, the squeezing was more severe than in the center of the width, and the hotter melt from the nozzle was pushed upwards. This kind of flow pattern could promote the skull formation near the edge dam. Solidified shell thickness was thinner in the edge dam regions than any other regions, but was thicker near the nozzle close to free surface. Nonuniformities of solidified shell thickness which were formed at the initial stage of solidification remained during the solidifying process.

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The sludge in Zn-Ni electroplating on steel is a major source of various surface defects and low productivity. We investigated the electrolyte and sludge with ICP. EPMA, TEM, and XRD. Generally the sludge was formed of Fe-rich yellow brown phase and Si rich dark gray one and had various colors. We notified that the dissolved impurity ion(Fe, Si and Al) played an important role in the sludge formation and suggested an effective removal process of those impurity ions by controlling the pH of the electrolyte before and after filtering process. Based on the results, it was possible to propose an electrolyte cleaning system for electro-galvanizing line of POSCO.

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The codeposition of Cr and Al into Ni substrate has been achieved using the single-step pack cementation process. The effect of activators, temperature and the activity of Cr and Al in the Cr-Al masteralloys on the formation of Ni-Cr-Al coatings and concentration control of Cr and Al was investigated in an argon atmosphere at 1273K and 1373K. The coatings consisted of an outward-grown β-NiAl layer in which Cr was dissolved except for the coating formed by 5wt%Al-1273K coating condition where Cr and Al dissolved in Ni substrate. Aluminide coatings grown outwards in pack powders were embedded with Al₂O₃ and masteralloy particles and Kirkendall voids were formed in Ni beneath the coating-substrate interface. A masteralloy of high Cr/Al activity ratio, low coating temperature and less stable activator are essential for codeposition of Cr-Al and provision of microstructures and composition which promise good oxidation/corrosion resistance to Ni-Cr-Al coatings.

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The present work is aimed at proposing the measures how to impede the galvanic corrosion occurring between Pd outer-layer and Alloy42 lead frame matrix and at the same time the formation of microcracks by hydrogen absorption into Pd layer electrodeposited on the Alloy42 lead frame. For this purpose, charge-transfer resistance, surface morphology, surface chemical composition and electrochemical characteristics of various electrodeposited layers were investigated by using ac-impedance spectroscopy. SEM, EDS and cyclic voltammetry, respectively. From the analysis of ac-impedance spectra, it is found that introduction of the intermediate electrodeposited layers between Pd outer layer and Alloy42 lead frame improves the galvanic corrosion resistance and Alloy42/Cu/Ni/Pd-Ni/Pd structure shows the highest corrosion resistance of all structures. As the hydrogen-charging potential decreases below the β-PdH formation potential, the formation rate of microcrack on the surface of the electrodeposited outer layer remarkably increases. This is attributed to the molar volume expansion by 10% developed due to the formation of the β-PdH phase. It is suggested that the formation of microcracks in the electrodeposited Pd outer layer is hindered by employing the Pd-Ni or Pd-Au alloy as outer layer instead of the pure Pd outer layer and/or by introducing the Cu/Ni intermediate electrodeposited layer between the Alloy42 lead frame substrate and Pd outer layer.

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