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二相 混合 組織을 가진 球狀黑鉛鑄鐵의 靭性에 미치는 熱處理의 影響
尹義博,李相鶴 成均館大學校 1981 論文集 Vol.29 No.-
本 論文은 Ferrite 球狀黑鉛鑄鐵을 利用하여 第二相의 上部 Bainite와 下部 Bainite 等의 混合量을 廣範圍하게 變化시켜 鑄鐵의 機械的 特性을 向上시키는 데 그 目的이 있다. ① 0.2% 耐力, 引張强度 및 硬度는 第二相 變態量의 增加와 더불어 上昇하였으나 直線的으로는 上昇하지 않았다. 또한 第二相이 强하면 强할수록 引張强度는 더욱 높았다. ② 伸率 및 흡수에너지는 變態量이 20∼30%정도 까지는 急激하게 低下하지만 그 以上에서는 완만하게 低下함을 알았다. ③ 球狀黑鉛鑄鐵의 勒性은 Ferrite地 組織에 적절한 第二相을 적당량 混合함으로써 改善됨을 알았다. The object of this paper is to improve the mechanical properties spheroidal graphite cast iron by duplex matrix which is used in steel alloys. Ferrite spheroidal graphite case iron is heat-treated to produce the following duplex matrices with various proportions; Ferrite-upper bainite, Ferrite-low bainite etc. 0.2% proof stress, tensile strength and hardness increase with volume fraction of the second phase, but are no linearly shown as the law of mixture. The harder the second phase is, the higher the strength becomes. The elongation value and absorbed energy decrease rapidly with in 20-30% of volume fraction of the second phase, but decrease slowly in above 20-30% of volume fraction of the second phase. The toughness of spheroidal graphite case lron can be improved by proper volume fraction of the proper second phase in ferrite structure.
Al-7%Si-0.3%Mg 合金의 衝擊靭性에 미치는 Zn添加의 影響에 관한 硏究
尹義博,金永稷 成均館大學校 1981 論文集 Vol.29 No.-
熱處理, Sb添加條件, Zn含量이 機械的 性質에 미치는 영향에 대해 조사하였다. 共晶Si의 크기와 형태는 적절한 熱處理에 依해 微細·球狀化하였다. 760℃에서 Al-7%Si合金에 0.15%Sb를 添加함으로써 共晶Si의 改良處理가 되었으며, 그 後 0.3%Mg를 添加시키면 强度와 伸率은 向上되었다. 356合金에 Zn이 0.2%에서 2.0%까지 添加되면 引張强度, 降伏强度는 增加하나 伸率은 오히려 減少하는 데, 이것은 Mg_2Si및 Zn_2Mg相이 粒界 및 粒內에 석출되기 때문이라고 생각된다. 또, 흡수에너지는 1.3%Zn까지는 급격히 減少하나, 그 以上에서는 거의 一定하게 되었다. Effects of heat treatment, addition of Sb, and Zn contents on the mechanical properties were examined. The size and shape of eutectic-Si particles is refined and spherodized by the optimum heat treatment. Adding of 0.15% Sb to the Al-7% Si alloy at 760℃, it is obtained modification of eutectic-Si particles, and moreover addition of 0.3% Mg contributes to promote strength and ductility. When the Zn content in increases up to 2% in Al-7%Si-0.3%Mg alloy, ultimate and yield strength increases, while ductility decreases because of precipitation of Mg_2Si, Zn_2Mg in matrix and between grain boundaries. The toughness (absorbed energy) decreases rapidly up 1.3% Zn, but become-nearly constant above 1.3% Zn.
尹義博 成均館大學校 1980 論文集 Vol.27 No.-
Primary and secondary dendrite arm spacing increases with decreasing average cooling velocity. But primary arm spacing increases with Cu content, while secondary arm spacing does not change appreciably with Cu content over the composition range investigated. The relationships between these were obtained as follows; λ_1=0.87√Co/Va, λ_2=177Va^-1/3 wehre, λ_1 is the primary arm spacing (mm), Co is the Cu content (%), Va the average cooling velocity (℃/min) and λ_2 the secondary arm spacing (μ). As the solidification rate increases, the size and mean free path of the θ phase show an appreciable decrease. And mean free path between θ-partcles is similar to the order of the secondary dendrite arm spacing. With decreasing distance from the chill face (that is, increasing solidification rate), the amount of θ phase decreases over the range of solidification conditions investigated in this paper. As distance from chill becomes smaller, lattice constant decreases, and the Cu-content in α-matrix increased. From these results. The behavior of second phase in unidirectionally soildified Al-Cu alloys could be confirmed quantitatively.
윤의박,김기배,조순형,김경민,김헌주 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.11
In order to investigate the interface phenomena, namely wettability, interface reaction, interfacial bonding, between Al₂O₃, and various Al alloys, wettability with the addition of alloying elements was measured by the dip coverage method, and the distribution of alloying elements and interfacial compounds at the interface were examined by using SEM-EDAX, Auger electron spectroscope and X-ray diffractometer. The interfacial bonding strength was also estimated by the indentation method. Wettability of Al was considerably improved by addition of Mg, Cu, Ni or Si. Among the four elements, Mg was the most effective. Mg was segregated at the interface of AC8A/Al₂O₃-20%SiO₂;the segregated Mg formed MgAl₂O₄, an interfacial compound. In pure Al/Al₂O₃ the inierface bonding strength was not affected by the concentration of SiO₂ in A1₂O₃ but in AC8A/Al₂O₃ the interface bonding strength increased with SiO₂ concentration and was 6.05 kgf/㎟ at 20%SiO₂.
윤의박,조순형 대한금속재료학회(대한금속학회) 1987 대한금속·재료학회지 Vol.25 No.12
The microstructure of rapidly solidified Al-Cr alloys was investigated by scanning transmission electron microscopy (STEM), X-ray diffraction and micro-Victors hardness test. The temperature mariation during rapid solidification was studied to interpret the results. From the thermal analysis, the relationship between the cooling rate and the dendritic cell size was found to correspond to a previous theory which was obtained from an extrapolation of the measurements at slow cooling rate. The relatinship between the growth rate and the dendritic ceil size, however, was shown to be lower than those of general Al alloys, because the rate of the primary phase formation was suppressed by the increased fooling rate. By detailed composition measurements, the possible solubilily range of the complete supersaturation was found to be 3.43 wt% Cr. Above this concentration, the microstructure changed to a cellular structure by recoalescence in the last stage of solidification.
침적 피복법에 의한 Al2O3 와 Al 과의 젖음성에 미치는 Al2O3 에 첨가된 SiO2 의 영향
윤의박,김기배,조순형,김경민,김헌주 대한금속재료학회(대한금속학회) 1991 대한금속·재료학회지 Vol.29 No.11
In this study wettability between Al₂O₃ and Al to the variation of SiO₂ concentration in Al₂O₄ was investigated. Alumina specimens containing from 0 Lo 20wt%SiO₂ were prepared by using the coventional ceramic processing techniques. Wettability was measured by using the dip coverage method and was compared with wettability measured by using the sessile drop method. Also the distributions of Al and Si element around the interface were investigated. As the results of these investigation, wetting process in the dip coverage method was shorter than that of the sessile drop method, and the equation of reaction rate for wetting process between alumina and aluminium was almost agreed with the following equation. Qn[ 1/(1- α)]=K_0(t-τ²) Both the started time and the completed time of wetting became short with SiO₂ concentration and this tendency bacame severe with higher melt temperature. The Si content around the interface did not change.
윤의박,김기철 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.7
Dynamic fracture toughness of simulated HAZ of a structural steel (equivalent to KS D3503) was investigated by instrumented impact testing technique. According to the validity criteria of this testing method, the measured fracture toughness values of this steel were evaluated to be valid when tested at temperatures lower than -40℃ for fine grained HAZ and lower than -l0℃ for coarse grained HAZ, respectively Even though the coarse grained HAZ fails in brittle manner at fairly low temperatures, the specimens must be fatigue precracked to obtained valid results.