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An investigation was made on the metallurgical factors responsible for the separations in Charpy V-notch impact specimens of HSLA steels with different cooling process after controlled telling. As compared with air cooling, accelerated cooling increased separations whilst more rapid cooling decreased them. Lowering the finishing temperature of accelerated cooling decreased separations in acicular ferrite type Nb-Mo steels but increased in polygonal ferrite type Nb-V steels. Major factors governing the variation of separation with cooling process were banded structures, martensite-austenite constituents and structural fineness.

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The mechanism of damping in cold worked-30.wt% Cu alloy has been investigated by using X-ray diffraction, microscopy, tortional pendulum and magnetic susceptibility measurements. The tetragonality and the antiferromagnetism formed by aging disappeared by cold working and the specific damping capacity (SDC) decreased drastical1y. But the tetragonality and antiferromagnetism are restored by subsequent re-aging and the SDC increases much higher. It can be thought that the SDC of cold worked and re-aged alloys are higher than that of normal1y aged alloys because of dislocations formed by cold working.

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The effect of heating rate and holding temperature during annealing on texture and deep drawability of rephosphorized cold rolled steel sheet was studied using tensile test for r-value and x-ray diffraction technique. Low carbon steel used in this study had 0.056% phosphorus The principal results are as follows: The peak r-value appears at a heating rate near 50℃/hr. So does (222) x-ray integrated intensity. But (200) intensity and (110) intensity show lowest values at this heating rate. As annealing temperature increases, (222) intensity increases and (200) intensity shows the lowest value at this heating rate. As annealing temperature increases, (222) intensity increases and (200) intensity, (110) intensity decrease, so r-value increases . As a result of recrystallization during annealing, the preferred orientation becomes (111) [112] which showes good deep drawability.

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In order to investigate the relation between the pitting corrosion and precipitated carbides, the heat treatment of specimens was carried out in two ways: Solution treatment and carbides precipitation treatment. The experiment was focused on the polarization curves of specimens immersed in HCl solution and on the microscopic analysis of the corroded specimens through a potentiodynamic method. It was Found out that the intergranular and pitting corrosion occurred remarkably in 0.1N and 1N HCl solution when carbides were precipitated around the grain boundary of the 304 stainless steel. The intergranular corrosion was noticed in the region of passivation and the pitting was prominent in the region of passivation break-down. The distribution of pits on solution treated 304 stainless steel was random, while that of pits on carbides precipitated specimen was concentrated around the grainboundary in 0.1N and 1n HCl solution. It was ascertained that the pitting resistance of the solution treated 304 stainless steel was better than that of carbidds precipitated specimen.

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In the aspects of economical design, it is very important to weld carbon steel and stainless steel for many industrial plants. But because of many differences between these two materials, it is very difficult to select not only proper welding conditions but also optimized conditions of post heat treatment for improvement of mechanical properties of welds. In this study, to find those conditions, submerged are welding were performed and three conditions of post weld heat treatment (PHHT) were adopted, i.e. at 650℃, 1,000℃, for 1.5 hrs respectively and then measured the variation of mechanical properties of welds The results obtained are as follows: 1. Weldability of carbon steel and stainless is good, because there are no fractures and cracks at the weld deposit and the interfaces between weld deposits and base metals under the tensile stress. 2. Tensile strength of the welds heat treated at 850℃ is higher than those of others. 3. The impact energy of HAZ of carbon steel shows highest value when heat treated at 850℃, whereas weld deposit metal and HAZ of stainless steel show the highest impact values when heat treated at 1000℃ and as welded, respectively.

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There are many problems to be solved for more wide practical applications of near-equiatomic TiNi shape memory alloys. In this point of view, a study has been made of the effect of isothermal heat treatment in the temperature range of 450℃ to 750℃ on the transition temperatures, especially M_s and A_f, and on the mechanical properties and the effect of thermal cycling on the electric resistivity curve. For this investigation, a Ti-rich TiNi shape memory alloy containing 52.36 at.% Ti was prepared. Thermal cycling caused the electric resistivity peak and the decrease of M_s. but did not affect T_R, the temperature at which electric resistivity started increasing. Both M_s and A_f increased with the temperature of isothermal heat-treatment above 450℃. when the increasing rate of M_s was higher than that of A_f. Elongation and tensile strength were highly increased by long-time (100 hr) isothermal heat-treatment and these were dependent on the holding time rather than the temperature. There also existed the variation in the fracture mode about 550℃.

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Effects of the heat treatment on transformation temperatures and shape memory abilities in Cu-l5.66 wt.% Zn-6.34 wt.% Al alloy have been investigated. The normally reversible transformations are prevented in the quenched specimens If the quenched specimens, however, are heated to temperature above 853 K for 5 minutes, the stabilized transformation temperatures can be obtained. The specimens heated in the temperature range of 653-853 K are harder than quenched and high temperature aged ones X-ray diffraction stadies indicate that quenched and high temperature (above 853 K) aged specimens have the same M18R martensitic structures but hardened ones hove the mixed structures of bcc(β) and fcc(α). Shape memory effect and reversible shape memory effect developed by the $quot;training$quot; and the $quot;constraint heating$quot; in the high temperature aged specimens are apparently higher than that in the quenched and lower temperature aged ones.

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