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The effect of welding condition on mechanical properties and Hydrogen Induced Stress Corrosion Cracking (HISCC) resistance of Heat Affected Zone (HAZ) in high strength steel weldment was studied. Multi-pass Submerged Arc Welding of A5l6 Grade 70 steel plate with different heat input of 30, 40, 50 KJ/㎝ were carried out, which were followed by Post Weld Heat Treatment (PWHT) for 2 hrs at 630 ℃. As the heat input during welding was increased, the impact energy and hardness at HAZ were decreased, on the other hand, the hardness was decreased and both the impact energy and the resistance of HISCC were increased. With proper selection of welding heat input and PWHT, better results of the resistance of HISCC and Charpy V notch impact energy of HAZ can be obtained.

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Hydrogenated amorphous carbon(a-C H) films prepared by plasma-assisted chemical vapor deposition of C₃H_8-Ar are studied by thermal analysis by using gas chromatography (GC) and differential scanning calorimetry(DSC) at constant heating rate and Ar atmosphere. Hydrogen evolution is detected by GC above 380℃ and the evolution rate increases with temperature up to 700 ℃. Corresponding to the hydrogen evolution exothermic reaction appears in the DSC curve followed by a sudden conversion into endothermic reaction at higher temperature. The starting points of endothermic reactions on the DSC curves are raised by the temperature and time of the prior heat treatments. It Is considered that during heating the overall structural changes, including C-H bond breaking, H₂formation, C = C double bond formation and network distortion etc., occur consecutively, irreversibly and endothermically and the initial exothermic reaction is due to the evolution of hydrogen weakly bound during cooling or the structural relaxation.

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Quench and tempering heat treatment was evaluated for alleviating the brittle characteristics of the weld zone of flash butt welded Ni-Cr-Mo steel. From the study of the effects of transformed microstructure on the impact properties and fracture toughness of the weld zone, it was concluded that the microstrueture of quenched and tempered weld zone and that of the base metal were similar, and the fine ferrite and cementite structure produced by high temperature tempering improved charry V-notched impact strength and fracture toughness The finer prior austenite grain produced by low temperature austenitizing was found to contribute to superiority of these properties. However, as followed by low temperature tempering at which retained austenite existed, the coarser prior austenite existed, the coarser prior austenite grain produced by high temperature austenitizing was found to contribute superior fracture toughness compared to the finer one. A high temperature austenitizing followed by 350℃ tempering was found to show tempered martensite embrittlement in both K_IC and charpy V-notched impact strength.

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The fracture properties of ductile cast iron (DCI) can be significantly improved by austempering, isothermal transformation in the temperature range from Ar$quot; to Ar` point following austenitization. According to the results of experiment, when a 0.27%Mo-1.08%Ni alloyed DCI was austenitized for 1.5hr at 900 ℃ and austempered for 2hr at temperature range from 280 to 415℃, as the austempering temperature was increased, strength and hardness decreased, while ductility increased. Also, the fracture toughness values K_IC obtained were over about 80 MPa m＾(½) when yield strength, elongation and hardness were the ranges of 750 to 850 MPa, 5 to 8% and 270 to 330 H_B respectively. The homogeneous bainitic microstructure of the austempered ductile iron (ADI) was obtained by the austempering temperature range of 340 to 385 ℃, and its SEM fractography showed a fibrous structure of dimple pattern, and it had the high fracture toughness.

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The magnetic properties and the grain structure of 6.5 wt%Si-Fe alloy made by the twin roller method were measured after the various annealing temperature. When the annealing temperature was around 700℃, the primary recrystallization was formed near the middle part of the sheet thickness and the grain size increased with increasing temperature. When the sheets were annealed at 1200℃, the grains with the (100) planes were paralled to the sheet surface, The magnetic properties are improved by furnace cooling after annealing at 1200℃ for 1hr at the air pressure of 10^(-4) Torr.

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Crystallization of Fe_(81)B_(13.5)Si_(3.5)C₂metallic glass has been studied by differential thermal analysis, differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. The crystallization temperatures are 490℃, 515℃ and 588℃ at the heating rate 5℃/min. In the first crystallization stage α-(Fe, Si) dendrites (bcc) are formed from the amorphous matrix, and in the second crystallization stave Fe₃B compounds (bct) are formed from the remaining amorphous matrix. In the last crystallization stage the metastable Fe₃B transforms into the stable Fe₂B compounds (bct), and Fe₃C compounds (orthorhombic) are formed. The exponent n in Johnson-Mehl-Avrami equation determined by Ozawa method is about 2.4 for the α-(Fe, Si) formation. This means that the nucleation rate of the α-(Fe, Si) phase is constant regardless of time. On the other hand, the exponent n for Fe₃B formation shows about 2.8, which suggests that the nucleation rate is supposed to be increased with increasing time.

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Among many metals the magnesium has excellent hydrogen-storage characteristics except that its hydriding and dehydriding rates are low Many works have been carried but in order to improve the reaction rates of magnesium with hydrogen. But their processes for the sample preparation were energy-consuming and complicated. In this work, to simplify the process of sample preparation, magnesium powder and cobalt powder were mixed in a 2 : 1 atomic ratio and pressed under 5 kbar to cylindrical pellet. The activation of the mixture was completed after about 15 hydriding-dehydriding cycles at about 700K and 25 barH₂The activated mixture absorbed hydrogen of about 2.8 weight percent at about 700K and 25 barH₂. The hydrogen storage capacity did not change until the 50th hydriding-dehydriding cycle. Equilibrium plateau pressures appeared at two different pressures, for example at 698K, 9 bar and about 14.5 bar. Under hydrogen pressures of relatively small deviations from the equilibrium plateau pressure, the hydriding reaction rates were controlled by the nucleation. After nucleation they were controlled by Knudsen flow and ordinary gaseous diffusion. Dehydriding reaction rates were controlled by the transformation of hydide into hydrogen and α-solid solution of Mg and Co.

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The glass forming range, saturation magnetization, coercive force, Curie and crystallization temperatures have been studied for Co-Zr-Nb thin film alloys made by sputtering. The glass forming range it expanded in the middle ratio of Zr and Nb. The relationship of magnetic moment to solute concentration in Cn-Zr, Co-Nb and Co Zr-Nb systems could be correctly interpreted by Friedel`s theory. Coercive force of Co-Zr and Co-Nb alloys correspond to the magnitude of magnetostriction in amorphous region. With increasing solute concentration, the crystallization temperature is increased and the Curie temperature is decreased. The solute concentration which the crystallization temperature is higher than the Curie temperature is about 17 at.%.

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The effect of low temperature magnetic field annealing on the soft magnetic properties of Fe_(81-x)Co_xB_(14)C₁Si₄(x=0-12) amorphous alloys have been investigated. The crystallization and Curie temperature are not changed with the Co content. By low temperature magnetic field annealing, the magnetic flux density increases and the coercive force and magnetostriction decreases. These effects are discussed in terms of the structural relaxation and the unidirectional induced magnetic anisotropy. The maximum permeability has a inverse relation with magnetostriction. The best magnetic property are obtained by the magnetic field annealing at 375℃ for 2 hours in Fe_(69)Co_(12)B_(14)C₁Si₄amorphous alloy.

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In order to provide some basic data on the mechanical properties of Ni-activated sintered W-powder compact, hardness and strength of this material were measured at the room temperature as well as the high temperature. The measured high temperature tensile strength was ranged from 11.25 ㎏/㎟ at 1000 ℃ to 4.3 ㎏/㎟ at 1400 ℃, which was lower than that of the pure W-specimen given in literature by a factor of two to three. The high temperature hardness was 240 to 55㎏/㎟, depending on the testing temperature between 600℃ and 1200 ℃. This value is somewhat higher than that of the normal sintered pure W-specimen. The transverse rupture strength of the Ni-activated sintered W-specimen was also lower then that of the normal sintered W, being 440 MPa, but the hardness of the former was comparable to that of the latter at room temperature.

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