발간논문

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In order to develop an arctic line-pipe of X70 type HSLA steel strip with high toughness and good weldability, additions of several micro-alloying elements and applications of different post-rolling treatments were attempted. On a basic composition of Fe-0.05C-1.0Mn-0.3Si, several micro alloying elements such as Nb, V, Mo and Ni were added. The applied post-rolling treatments were water-spray cooling followed by either furnace cooling or air cooling to room temperature after the final controlled rolling at 800℃. It was found that the steel composition of Fe-0.05C-1.0Mn-0.35Si-0.03Nb-0.05V-0.1 Ni exhibited optimum combination of high strength (Y.S. 75 ksi) and excellent impact toughness 250 joules at -20℃) after the water-spraying to 600℃ followed by a furnace cooling to room temperature. The applied post-rolling treatment was the condition simulating hot strip production. This paper highlights the effects of the micro-alloying elements and the post-rolling treatments on structure and mechanical properties in a low Carbon-Manganese steel.

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The thermodynamic data of the Al-Zr, Al-V and Zr-V systems have been obtained from their phase diagram data using the tie line variation method. The binary thermodynamic data have subsequently been used to calculate the binary phase diagrams which are in good agreement with the measured phase diagrams. The calculated binary thermodynamic data and some measured ternary data have been used to calculate isothermal ternary phase diagrams of the Al-Zr-V system at 750 and 1800k.

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High temperature tensile behavior and heat resistant strength of a C/V graphite cast iron produced by a reduced-Mg method have been studied. The maximum true tensile strength of 41.5 ㎏/㎟ was obtained when it was tested at room temperature with a strain rate of 10^(-1)sec^(-1)and that of 10.4㎏/㎟ was acquired with it was tested at 600℃ with a strain rate of 10^(-4) sec^(-1). The combined effects of temperature and strain rate on the strength could be expressed by the following equation in the temperature range of 400 and 500℃; ε˙=0.18 exp (0.4lσ-20,000/RT), where ε˙ is a strain rate and σ is a maximum true tensile strength. From the results of stress-rupture tests and the Larson-Miller parameter. the 10＾5 hr rupture stresses of C/V graphite cast iron were 16 ㎏/㎟ 9.2 ㎏/㎟, 5.5 ㎏/㎟ and 1.9 ㎏/㎟ at 300℃, 400℃, 400℃, and 600℃, respectively.

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Dual phase steels are characterized by a microstructure consisting of a dispersion of about 20 percent of hard martensite particles in a soft, ductile ferrite matrix and their mechanical properties are controlled by martensite and ferrite matrix In this experiment the effects of the volume fraction of the martensite phase and martensite distribution on the hydrogen embrittlement of the dual phase steel were investigate. As the volume fraction of the martensite phase increased and the intermartensite distance decreased, higher degree of the hydrogen embrittlement was observed. The hydrogen was found to increase the decohesion of ferrite/martensite interface.

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Characteristics of several Co-base alloy thin films were studied in relationship with sputtering parameters. Thicknessuniformity of the films on 10 inch substrate were investigated by changing the distance between substrate and target. It was found that deposition rate increased with increasing input power, and decreased with increasing the substrate temperature and the distance between substrate and target. Substrate temperature increased with increasing input power and time. The solute concentration of film linearly increased with increasing the area ratio of solute metal on a Co target. The relative solute concentration of film to area ratio of target decreased in the order of Mo, Nb, Zr and V. The relative differences were discussed in terms of sputter yield.

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The effects of coiling temperature on the carbide precipitation and the texture development in At-killed low carbon sheet steel for deep drawing quality were investigated. To simulate coiling effect, commercial hot-bands with three different microstructures in size, morphology and distribution of carbide particles were cold-rolled and annealed at various conditions, and optical microstructures of overawed state were examined Cold-rolling textures were nearly unvaried, independent of initial structure, but the specimen with coarse carbide particles showed the strongest {111} component in recrystallization texture. Plastic strain ratio (γ￣) was maximum in the specimen with coarse carbides annealed at 850℃ Initial pearlites in the hot band remained even after over-aging treatment and the number of carbide particles after over-aging treatment was the smallest in the coarse-carbide specimen.

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Physical effects resulting from strain-path changes from cold rolling to uniaxial tension were studied on two sheet steels; a aluminum-killed steel and a normalized aluminum-killed steel. Cold rolling caused a unusually large decrease in uniform strain and in total strain to failure in all orientations in subsequent tension. The prestrained sheets showed three stages of deformation; initial rapid work hardening, work softening and low-work hardening stage.

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The thermal stability and crystallization process of amorphous Fe_(80)Si_xP_(20-x) alloys were studied by DSC and x-ray diffractometer. The crystallizations of the amorphous Fe_(80)Si_xP_(20-x) occurred in one step when 2≤x ≤4 as amorphous → α-Fe (b.c.e) + Fe₃P (b.c.t). However, when 6≤x≤10 the crystallization was completed in two stage as amorphous → amorphous + Fe₃P (b.c.t) → Fe₃P (b.c.t) + Fe₂P (h.c.p). Then, Fe₃P + Fe₂P transformed into Fe₃P (b.c.t) + α-Fe. The activation energy for crystallization was about 115㎉/㏖ for x≥4 at % and the activation energy for 1st step, about 20 ㎉/mole larger than that of 2nd step.

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