高張力鋼의 熔接低溫龜裂感受性에 미치는 入熱量, 豫熱溫度와 組成의 影響

鄭潾相,朴景采 慶北大學校 1988 論文集 Vol.45 No.-

It is well known that cold cracking occurrence in the JIS-y cracking test of high strength steels is attributed to microstructure of heat affected zone (HAZ), residual hydrogen content of HAZ at 100℃ and intensity of restraint. The effects of heat input, preheating temperature and carbon equivalent on weld cold crack susceptibility in the JIS-y cracking test of the three different steels have been studied. Much heat input, high preheating temperature and low carbon equivalent in steels lead to relatively low cold cracking and low hardness in bond area. Root cracking initiated at the root near the bond and propagated in HAZ and then propagated into weld metal. The failure of HAZ occurred by a mixed mode of microvoid coalescence and ductile tearing. The calculated t_100^*and T_0^* values from several weld cold crack susceptibilities have good relationships with the experimental ones.

Ti을 첨가한 Cu-Al-Ni 형상기억합금의 열처리에 따른 조직과 성질 변화

鄭潾相,姜成泰 慶北大學校 1988 論文集 Vol.46 No.-

In order to improve mechanical properties of a Cu-Al-Ni shape memory alloy, grain refinement by Ti and heat treatment were applicated. By addition of 0.05wt% Ti and controlled solution treatment, the grain of martensite was significantly refined as small as 50㎛, and fracture strength and fracture strain of the alloy were also remarkably increased, and shape memory effect of the alloy are not deteriorated on thermal cycling 273K-523K than those of the untreated alloy. The optimum heat treatment condition for the alloy was solution treating at 1123K and subsquent aging at 47K.

Cu-Zn-Al形狀記憶合金의 擬彈性 變形擧動

鄭潾相,朴景采,黃永根 慶北大學校 1986 論文集 Vol.41 No.-

It is generally recognized that both phenomena of the shape memory and pseudoelasticity effects in Cu-based alloys are associated with order structure in parent phase and thermoelastic martensitic transformation. The pseudoelasticity effects is a phenomenon, by which strain is attained through a stress-induced martensitic transformation and such strain is completely recoverable upon unloading, due to the reversible nature of the transformation. In the present work, pseudoelasticity in a Cu-20.80 wt%Zn-6.36 wt% Al shape memory alloy(A_s=252K) has been extensively studied as a function of deformation temperature, grain constraints, cyclic loading and heat treatment, by tensile test and optical microscopy. The results obtained are as follows; At temperature above A,, the stress-induced martensites were formed and the stress needed to induce the martensitic transformation increased with increasing deformation temperature. An important of the grain constraint effect is the grain size/thickness ratio(gs/t), a relaxation of the grain constraints is associated with a decrease in the critical stress needed to induce the martensitic transformation. The critical stress for martensitic transformation decreased with number of cycles in loading-unloading. After 10 cycles, extened cycling did not result in additional changes on stress-strain curve. After low temperature heat treatment (423-573K) in a quenched alloy, the stress needed to induce the martensitic transformation increased due to the stabilization of parent phase.

6063 Al 合金의 熱間變形에 미치는 溫度 및 變形速度의 影響

鄭潾相,尹秉河 경북대학교 공과대학 1974 工大硏究誌 Vol.3 No.-

The dependence of the flow stress of a 6063 Al alloy on temperature and strain rate was studied by conducting tensile test at 400°-500℃ and 10^-4-10^-2 sec^-1 of strain rate. The principal results are as follows. 1) The strain hardening exponent, n, which is more affected by temperature than strain rate, is 0.28-0.16 at 400˚-500℃ and 10^-4-10^-2 sec^-1. 2) The strain rate sensitivities, m, determined from the linear relationship of log σ_max-logε`curves are 0.120, 0.127 and 0.150 at 400℃, 450℃ and 500℃, respectively. These are linearly increased by an increase in temperature and smaller than those of pure Aluminum. 3) The strain rate showes the Arrehnius type temperature dependence. The activation energy decreases as stress increases and its value is about 36 kcal/mole on low stress, and it is close to the activation energy for self-diffusion, for high temperature creep, or for shearing of grain boundary of Al, and for diffusion of Mg and Si in Aluminum. 4) The fracture strain increaseses with temperature, but because of nonuniform deformation after necking, it decreases as strain increases.

(α+β)二相 黃銅의 變形에 대한 結晶粒界效果

鄭潾相,河泰琪,李淳麟 慶北大學校 産業開發硏究所 1985 硏究報告 Vol.13 No.-

Grain boundaries in policrystalline alloys play an important role on the deformation and its strength. It is necessary that a complete understanding of the effect of grain boundary on the deformation, in order to put these alloys into the best utilization. The purpose of this study is to investigate the effects of grain boundaries on the deformation of (α+β) two phase brass polycrystalline. For this study, grains of specimens were coarsened to simplify the complicate grain boundary. After tensile deformation, slip line analysis near grain boundary was accomplished. Schmid factor, stress delivering factor and strain incompatibility were introduced in the explanation of present results. The activation of slip system which was affected by the grain boundary itself were explained by the combination of these factors. Also, it was introduced that the properties of strain incompatibility depend on the condition of grain boundaries and tensile axis.

ABS AH 32鋼의 熔接金屬에서 低溫 龜裂 感受性에 미치는 豫熱效果

鄭潾相,朴景采,金庚周 경북대학교 공과대학 1987 工大硏究誌 Vol.16 No.-

It is known that the occurrence of cold cracking in welded materials is influenced by restraint, diffusible hydrogen and microstructure of weldments. The purpose of this work is to investigate effects of preheating in the same humidity of electrode as well as influences of diffusible hydrogen content. The results of obtained are as follows : Thermal cycles in welments were changed by preheating temperatures and particularly, t_8/5(cooling time from 800℃ to 500℃) and t_100(colling time from solidification to 100℃) were increased according to increase of predeating temperture. First of all. in the same humidity of dried electrode, when specimens we welded at ambient temperature, weld cracking percentages for surface and root were 100%, but when 150℃, no cracking was occurred. In the view of hardness distribution, hardness of HAZ were higher than those of base metal and weld metal and were in inverse proportion to preheating temperature and thickness of HAZ. Secondly, in the same preheating temperature, when specimens were welded in the various humidity of electrode, regardless of humidity of electrode, surface cracks were not occurred. With increasing diffusible hydrogen content, root cracking percentages increased slightly, but hardness distribution and thickness of HAZ were not changed.

인장축에 평행한 결정입계를 가진 아연삼결정의 변형응력

鄭潾相,朴景采 慶北大學校 1982 論文集 Vol.34 No.-

In order to investigate of grain boundary effect on flow stress, zinc tricrystal with two boundaries parallel to tensile axis is tested in tension-at room temperature. The flow stress of tricrystal, at a given elongation, could be estimated from the rule of mixtures which depend on the flow stress and the volume fraction of component crystal consist of it. Increase in flow stress, as result, compare to be estimated flow stress have been observed in the all tricrystal. Since there is are only a grain boundary variable, this strengthening is due entirely to two grain boundaries in each crystal. The two reason which could explain these results are discussed. Finally macro and microscoscopic strain incompatibility, which is arised at grain boundary, for compatible deformation generate large back stress on the primary slip system and increase the flow stress of tricrystal.

경화 육성 용접부의 경도에 미치는 용접변수의 영향

鄭潾相,李鍾燮,朴景采 경북대학교 산업기술연구소 1990 産業技術硏究誌 Vol.18 No.-

Abrasive wear occurs when material is removed from a surface by the cutting or gouging action of hard particles. The rate of wear depends on the degree of penetration of the surface by the abrasive and is therfore related to the surface hardness of the material. The inherent high hardness of the surface minimizes penetration by the abrasive and consequently reduces wear rate. Wear of haedfacing alloys may be caused by a number of factors including abrasion, impact, erosion, heat and corrosion any of which may act alone or in combination. In this study, the following conclusions are drawn from the experimental results about the effect of wear resistance of hardfaced weld deposit. The abrasive wear resistance of hardfaced weld deposit is increased with increasing hardness. The hardness of hardfaced weld deposit is proportional to the welding current and voltage, but not to the welding speed. The effect of torch angle on the hardness is relatively small, but the effect of stick-out, wire setting position and interpass temperature are significant.

Cu 및 α-황동의 결정입도에 따른 변형거동

鄭潾相,朴權熙 慶北大學校 1983 論文集 Vol.35 No.-

The gram size dependence of the stress-strain behavior of annealed pure Cu and a-brass (10%, 20%, 30%Zn) was investigated at room temperature in tensile test. The strain hardening coefficient(n) was increased with grain size. Hall-Petch slope(k_ε) was increased with plastic strain and saturated at 5% in Cu, 10% in Cu-10%Zn and Cu-20% Zn and 20% in Cu-30% Zn. At higher strain, k_ε decreased due to the formation of a cell structure in the grain interior. The slope of Hall-Petch relation of the grain boundary including twin boundary showed low value. The initiation stress and strain of deformation twin are also grain size dependent.

주사전자현미경의 기초

정린상 대한금속재료학회(대한금속학회) 1982 대한금속·재료학회지 Vol.20 No.4