발간논문

Home > KJMM 논문 > 발간논문

A bimetal was produced by a welding method. Its base metal was carbon steel containing 0.53 wt% C and the weld metal was pure copper containing 1 wt% Sn which was added as a deoxidizer. The yield strength and the ultimate tensile strength of the bimetal bonding were 6.8 ㎏/㎟ and 21.5 ㎏/㎟, respectively. The Charry V-notch impact absorption energy of the bimetal was 41.8 J/㎠ and the fracture was found to take place in copper near the interface indicating relatively high interface strength. The elastic-plastic fracture toughness value under static load, Jic, was 1.1 ㎏/㎜ and the mode of fracture was similar to that in the Charpy impact test, The wear resistance of the base metal was superior to that of SUS 304 stainless steel.

keyword :

A low temperature sintering in oxidizing atmosphere was employed to obtain high density UO₂pellets. The density of pellets sintered in CO₂ atmosphere followed by reduction treatment in H₂ atmosphere at 1100℃ for one hour was 10.66g/cc (i.e., 97.3% of theoretical density). The measured value is the same as those of pellets sintered at high temperatures above 1700℃ in H₂ atmosphere. When the sintering temperature was higher than 1100℃ (upto 1300℃), the sintered density decreased as either temperature or time increased.

keyword :

A low temperature sintering at 1000-1300℃ in CO₂atmosphere was adopted to control the density and microstructures of UO₂pellets for nuclear power plant applications. Effects of 4% to 12% U₃O_8 pellets, obtained by oxidation treatment of UO₂, sintering time and sintering temperature were investigated. As the amount of U₃O_8 increased, the sintered density and the number of large grains decreased, while quantity of pores increased. Increase either of sintering temperature above 1100℃ or of sintering time resulted in lower sintered density and reduction of the number of large pores.

keyword :

The magnetic properties of Nd_(15)(Fe_(1-x) Co_x)_(76)B_8Zry systems at low and high temperatures were investigated. When the composition of Co was 7.6 at%, 9.9 at% and 12.9 at% in Nd_(15)(Fe_(1-x) Co_x)_(76)B_8Zry, the decrease of saturation magnetization at low temperature was due to spin reorientation near -150℃. But the result like this did not appear at the composition of 15.2 at% Co. The remanent induction has minimum value at the composition of 12.9 at% Co, but the intrinsic coercivity has maximum value at 15.2 at% Co in Nd_(15)(Fe_(1-x) Co_x)_(76)B_8Zry systems. A temperature coefficient is low when the composition is 15.2 at% Co.

keyword :

Effects of intermittent rest period at 300℃, overload in tension and overload followed by rest period on fatigue crack growth in 4340 steel were investigated. The intermittent lest period stopped the growth of fatigue cracks completely near the threshold level of △K. The alleviation effect of rest period on the rate of crack growth was more distinct at the lower level of △K. The higher overload ratio was (i.e., OLR = 3), the more the alleviation effect. It is suggested that compressive residual stress at the ahead of crack tip was produced during overloading period, and it is enhanced roughness of the crack surface due to crack deflection after the overloading, which, in turn, ceased or retarded crack propagation during the subsequent cycling. The most retardation of fatigue crack growth was observed when overload and subsequent rest period were combined. The mechanisms are discussed.

keyword :

The manufacturing conditions for amorphous wire and its properties were studied in Fe-Nb, Mo)-Si-B alloy. The optimum manufacturing condition to get continuous amorphous wire was 70 psi of ejection pressure, 500-550 rpm in relating speed of drum and 1200℃ of melt temperature. Amorphous Fe_(75) Si_(10) B_(15) wire had larger residual induction and better squareness in hysteresis loop than those of ribbon. The tensile strength and elongation of amorphous wires were about 310-350 ㎏/㎟ and 2.1 - 2.7%, respectively.

keyword :

The dual phase steels of ferrite-martensite and ferrite-martensite-pearlite were prepared by two step cooling or isothermal holding after intercritical annealing. And this research investigated the effect of pearlite on the yielding and deformation behavior of these dual phase steels. It was observed that second phase particles with pearlite-martesite interfaces were distributed in the ferrite matrix. The structure of pearlite-martensite interface was also observed by using SEM. Continuous or discontinuous yielding apeared in the specimens of ferrite-martensite-pearlite. The lower yielding ratio and continuous yielding were shown in the specimens with more martensite content (≥5.8 vol%). The microstructure observed by TEM showed that the mobile dislocations causing continuous yielding and the pinned dislocations by solute atoms were distributed in the ferrite. The effect of pearlite on the variation of work hardening exponents during tensile deformation was also discussed in terms of the Modified Crussard-Jaoul analysis.

keyword :

keyword :