발간논문

Home > KJMM 논문 > 발간논문

keyword :

In the spheroidal graphite cast iron, the effects of carbon-content and cooling velocity on the matrix structure were examined quantitatively by differentiating the carbon content and the diameter of sample at constant silicon content. The important results of this study are as follows; 1. With 0.1% increase of carbon content, the amount of the pearlite matrix showed 4.5% decrease in hypoeutectic and 1.7% decrease in hypereutectic. 2. With 0.1% increase of carbon content, the amount of the ferrite showed 3.8% and 1.1% increase in Hypoeutectic and Hypereutectic respectively. 3. The effects of carbon content are larger than that of cooling velocity on the matrix structure.

keyword :

For the purpose of investigating the mechanism of deoxidation cf stainless steel, the oxidation reaction rates of 17Cr, 18Cr-8Ni stainless steels and electrolytic iron being in the solid state were measured by means of T. G. -D. T. A. technique. And the behaviors of oxides and inclusion in the melt were studied by the X-ray methods. From this experiment, the following conclusion can be drawn. 1) With the heat-reaction curves the endothermic reactions were shown in electrclytic iron and stainless steels (AISI 430, 304 type) above 500℃ and 800℃, respectively. This is seemed to be the heat decomposition of ferric oxides to ferrous oxides accompaning with the increase in the weight rapidly. 2) Being heated from room temperature to 1100℃, electrolytic iron and 17Cr stainless steel represented parabolic-linear curves resulting in the increase in weight, and 18Cr-8Ni stainless steel was depicted parabolic curve with the increase in weight. 3) Chromium oxides, formed in the 17Cr and 18Cr-8Ni stainless steels at the heating stage, were observed as FeO·Cr₂O₃·in the slag and, on the other hand, as Cr₂O₃and Fe₃O, in the inclusions in the as cast state. And FeO, SiO₂ or MnO could not be identified by the X-ray diffraction method.

keyword :

The phenomenon of decreasing chromium content, the effect of deoxidation by adding silicon and the floating mechamism of slags, the crystal structre of inclusions for 18Cr-8Ni and 17Cr stainless steel respectively have been investigated. The scraps are melted by a high frequency induction furnace. The results are as follows; (1) The chromium content in 17Cr stainless steel exhibits a remarkable decrease more than 1 hr. is required for melting the scrap. The chromium content in 18 Cr-8 Ni stainless steel exhibits a small decrease, as 1.67% until holding for 2 hrs. The required melting time is 1 hr. 2) The floating rate of spheroidal inclusions is greater than the floating rate of dispersed inclusions from molten bath. 3) The slags of 17 Cr stainless steel before deoxidation and after deoxidation by adding silicon are FeO·Cr₂O₃and SiO₂, the slag of 18 Cr-8 Ni stainless steel is FeO·Cr₂O₃, which can be seen by X-ray diffraction. 4) The inclusions in 18Cr-8Ni and 17Cr stainless steel (containing less than 0.8% Si and less than 1.0% Mn, as cast) are Cr₂O₃and Fe₃O₄ as can be seen by X-ray diffraction.

keyword :

A series of study using Argon/CO₂ gas mixture in shielded gas welding was carried out to overcome some difficulties in CO₂-arcwelding or MIG-welding. In this paper, single bead was performed on mild steel and low alloy steel pipes using bare electrode and CO₂ and Argon, singly or mixed, as shielding gas. The mode of metal transfer, bead shape, blow holes, chemical composition and non-metallic inclusions of weld metal, further, V-Charpy impact value of weld metal were investigated on these metal. The results obtained are as follow: 1) With increasing Argon content, the mode of metal transfer was observed to be of Spray transfer type. In the range of Ar 40% per CO₂60%-Ar 60% per CO₂ 40%, the mode of transfer is observed to be a combination of spray and globular types. 2) The penetration depth with increasing Argon content decreases and the bead shape factor (W/P) increases. The flank angle (θ) decreases a little with increasing CO₂ content. 3) If the welding is performed with appropriate shielding gas under appropriate welding conditions, the welding defects (mainly blow holes) hardly occurs. 4) The carbon content of deposited metal is not affected by change in Ar/CO₂ composition of shelding gas, but the contents of silicon and manganese decrease with increasing CO₂. The Chromium and molybdenum contents hardly depend on the composition of shelding gas in the case of low alloy steel. 5) The non-metallic inclusions hardly depend on the composition of shielding gas. 6) The V-Charpy Impact value is practically not affected by the shielding gas composition for mild steel but decreases a little with increasing Argon content in the case of low allay steel.

keyword :

The kinetics of the reaction of hydrogen with titanium and Ti-Fe alloys were studied in the temperature range of 890℃-1030℃ at 8-19 torr hydrogen pressure by the thermogravimetic method. The experimental data indicate that the rate controlling step of both reactions are hydrogen diffusion in diffusion metals. The temperature dependence of diffusion coefficients of hydrogen in pure Ti and Ti-7 at.% Fe alloy are D=1.62×10^(-3)exp(­6650±410/RT)㎠/sec D=1.58×10^(-3)exp(­7450±300/RT)㎠/sec respectively. It is found that the iron decreases markedly the diffision coefficient of hydrogen. It is believed that the Fe in Ti decrease the interstitial site of titanium lattice.

keyword :

Chlorination of titaniferous magnetite was investigated by means of batch-boat-weighing technique at elevated temperatures. The chlorination of titaniferous magnetite was characterized by the chlorination of magnetite at the initial stage of reaction, followed by that of ilmenite. It is also interesting to note that the chlorination of ilmenite was affected by two-step process: chlorination of ferrous oxide at the initial stage of reaction, followed by that of ferric oxide. Results were interpreted in terms of rate equations as well as chlorination mechanisms.

keyword :

Relation between the magnetic characteristics and the microstructure of nitrided iron wire has been studied. The compound and diffusion zones in iron wire are obtained by the nitriding. The compound zone consists of ε(F_(2-3)N), γ`(Fe₄N) and α〃(Fe_8N) nitrides from the surface. But the α〃 translated to γ` when the nitriding time was longer than 60 min. In nitrided iron, saturation magnetization and coercive force are increased from 1714 Gauss to 1740 Gauss and from 75 Oe, to 99 Oe, respectively for 60 min of nitriding time. The measured magnetic characteristics are determined by the mean value of magnetic moments of the constituent phased.

keyword :

keyword :

keyword :