발간논문

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Tensile properties and fracture toughness of AISI 4340 rolled steel have been measured as a function of test temperature, tempering temperature (-100℃ to 200℃) and tested direction, also fractographic observation was made by means of scanning electron microscope to find out the property difference between rolling and transverse directions, and ductile and brittle fracture toughness behavior. The tensile and yield strength decreased with increasing tempering temperature and increasing test temperature. while the specimens tempered at 550℃ and 650℃ showed higher elongation value at low temperature (-50℃ and -100℃) than at room temperature (25℃). The relation between KIC2/E and CVN values varried wih test direction and test temperature. The fracture toughness G1C values in rolling direction were in the range between l.5×l0(4) and 3.9×l0(4) J/m2 when the stretch zone size in front of fatigue pre-crack in compact tension specimens decreased with decreasing test temperature.

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The formability of 0.4mm and 0.6mm thick Al alloy 3003 sheet that had been double cold rolled and annealed was evaluated by analyzing its uniaxial tensile behavior, forming limit curve (F.L.C.), pole figure analysis, and earing behavior. The F.L.C. level of Al alloy 3003 sheet was considerably lower than those of the low carbon steels (Keeler-Goodwin Band). As the thickness of sheet increased, the F.L.C. level of Al alloy 3003 sheet became higher. The experimental strain ratio (R-value) was compared well with the theoretical R-value calculated by the Lee-Oh method, and the cup made an earing in the direction of the high R-value. It was found that the earing height decreased when the mixture of rolling and annealing textures developed.

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Effects of mechanical alloying process on the microstructure of Rapidly Solidified Al were studied by Varing the processing time. The mechanical alloying process can be divided into five stages; 1. The initial period. 2. The period of welding predominance. 3. The period of equiaxed particle formation. 4. The period of convolution of the lamellae. 5. Steady state. The establishment of steady state processing conditions characterized by microstructure and saturation hardness (120 HV) of composite is found to depend on the processing time. During the first 200 minutes of processing the microvickers hardness can be approximated by H = 60+ 0.33 t and strutural refinement rate of composite are as follows ε=(K/0.33)In(l+0.0055t)

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Effects of alloy composition on the transformation temperatures in Cu -14.5Zn-8.7Al, Cu-l4.1Zn-8.5Al, Cu-13.7Zn-8.2Al shape memory alloys were studied. The phase stability of electron compounds of β phase in Cu-Zn-Al shape memory alloys was analyzed in terms of electron concentration followed by Hume-Rothery theory. Orderning temperature TB2 and TDO3 were calculated using the formulae by Inden. It was founded that TB2 was relatively insensitive to concentration of Zn or Al, but TDO3 was founded to be greatly reduced with the increased Zn concentration (above about 10 atomic % Zn). Ms temperature of the SME alloys were found to be very sensitive to the Zn, Al concentration. The Ms temperatures of Cu-14.5Zn-8.7Al, Cu-14.1Zn-8.5Al, Cu-13.7Zn-8.2Al were found to be -120, -10, +120℃, respectively.

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Change of microstructure and pore shape during sintering was investigated in Fe-2.5% Si-l.4%C compacts. The compacts were sintered at 1140, 1150, 1160 and 1170℃ in Ar atmosphere for various sintering time. Slow and rapid cooling after sintering allowed to examine the behavior of inter-diffusion between elemental particles, change of microstructure and pore shape of sintered alloy. At early stage of sintering, as-quenched microstructure was fine pearlite and it changed to marten-site with succesive sintering upto 27 hr. This change of microstructure with sintering time seems closely related to the homogenization process of Si. Dissimilarly to the previous reports, two type of pores, surrounded by ferrite or pearlite, were observed in slowly cooled specimen after sintering 27 hr. This result suggests that the local content of carbon and silicon were slightly different due to the sluggish diffusion of Si.

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Experiments on characteristics of sintered stainless steel and bronze filters have been performed. The variables in this experiment are powder shape, particle size distribution, sintering temperature and atmosphere. The experimental data are presented to show permeability, maximum pore size, shear strength and corrosion resistance on various sintering conditions. The permeability is influenced to a greater extent by varying porosity than by varying the particle size which is only significant when the particle shape is spherical. The sintered bronze f1lter made of nearly spherical particle leads to an increment in permeability with larger sieve fraction even though it has almost same sintered porosity. However, the sintered stainless steel filter made of irregular particle shows negligible difference in permeability by varying particle size. The maximum mean pore size and permeability are significantly affected by powder shape; the filter made of spherical particle shows larger pore size and better permeability than that of irregular particle shape. The stainless steel filter sintered in N2, atmosphere shows higher shear strength than the filter sintered in H2 or Ar atmosphere, while the filter tends to show lower corrosion resistance.

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