발간논문

Home > KJMM 논문 > 발간논문

By development of a new process combining plasma nitriding process and MO-PACVD process, plasma nitrided+Ti(NCO) composite coating was formed on SKD11 tool steel. Using established process parameters obtained from previous research, the composite coating with superior mechanical and electrochemical properties was produced at relatively low deposition temperature of around 500℃ without softening and distortion of SKD11 substrate. The characteristics of the composite coating such as adhesion strength, microhardness, friction coefficient, wear and corrosion resistance were investigated. The hardness of composite coating was H_v2150. The corrosion potential of composite coating increased from -0.2V to -0.08V and the corrosion current decreased about 100 times in comparison with that of nitrided layer. Adhesion strength of composite coating determined by scratch adhesion test was over 100N which was roughly twice of that of Ti(NCO) coating.

keyword :

The corrosion resistances of the Fe-Ti alloys fabricated by an ion-beam sputter and an arc-melting process were examined in acid solutions. XPS analysis has been used to compare the passive films formed on the alloys. The sputtered Fe-Ti alloys have an amorphous structure while the arc-melted Fe-Ti alloys have a crystalline with a dendritic structure. The corrosion rate of the sputtered Fe-Ti alloys in 3 M HCl decreased with increasing the titanium fraction in the alloys. For the arc-melted Fe-Ti alloys which contain more than 57 at% Ti, the corrosion rate decreases with increasing the titanium fraction in the alloys. However, the corrosion rate of the sputtered Fe-Ti alloys is about ten times lower than that of the arc-melted alloys. The sputtered Fe-Ti alloys passivate anodically in 1 M H₂SO₄, and HCl, and exhibit higher corrosion resistance since the passive films formed on the alloys contain high chemical resistant oxides.

keyword :

Martensitic Stainless Steel has high strength and hardness in comparison with other stainless steels. But the toughness and corrosion resistance is lower. So lots of researches have been done in order to improve these properties. In the previous study the alloying element of Mo resulted in increasing the toughness at tempered condition of the steel. It has been investigated in this work how the Mo addition and tempering condition influence on the various types of corrosion behavior of 13% Cr martensitic stainless steel. Corrosion resistance was hardly changed by the tempering up to temperature of 500℃, but decreased at 600℃ due to the formation of Cr carbide on the prior austenite boundary. However, the corrosion resistance increased again at 700℃, because Cr carbides were resolved and redistributed. Both general corrosion resistance and intergranular corrosion resistance of tempered steel are significantly improved with Mo content.

keyword :

Much of improvement in efficiency and in reduction of energy consumption in the steel industry has resulted from the application of high speed continuous casting technology. The thermal behavior of the guide roll and pinch roll in the continuous casting process have been computed to estimate the thermal characteristics of a high speed casting roll. To calculate the thermal deformation of guide roll and pinch roll according to roll types in high speed casting process, the solidification analysis of slab is performed with one dimension finite element method. The both temperature distribution of pinch roll and guide roll is also calculated by using of two dimensional finite element method. The roll size with new shape was proposed to high speed continuous casting.

keyword :

A driven roll measuring system has been developed to diagnose strand deformation and bulging during continuous casting and their effect on slab qualities has been discussed. In-cast roll gap profile in the casting direction could be predicted by driven roll displacement monitoring and was discussed regarding the frequency of transversal corner crack. Unsteady bulging, which is generally accompanied by steel level variation within mold and casting speed variation, has a tendency to occur for the steels with 0.09-0.12% C and to increase along downstream side. Frequency analysis which was performed on unsteady bulging showed that high frequency of 0.2-0.25 ㎐ as well as roll rotation and roll pitch frequencies occurred. These particular frequencies were discussed regarding the relation of unevenness of solidified shell. A mathematical model has been developed to simulate the unsteady bulging phenomena based on FEM analysis on the case of periodical casting speed change. Finally, the effect of unsteady bulging on slab qualities also has been discussed.

keyword :

In this study, an attempt was made to develop an in-situ processing method of Sn-Ag composite solders for the ball grid array in electronic packaging applications. The reinforcing phase(Cu_6Sn_5) was produced by the reaction between Sn in the matrix and Cu powders added. It was found that the shape and size of the phase formed are affected by the processing parameters such as holding time very sensitively. The mechanical properties and the thermal stability of the composite solders were proved to be superior to those of Sn-3.5 %Ag solder.

keyword :

To quantify and standardize the burden distribution method for high pulverized coal injection operation, various tests in the operating blast furnace and 1/10 model of blast furnace are done, the results are summarized as follows; (1) to control the central gas flow, the alternation of center charging amount of large sized coke; (2) to control the middle gas flow, the alternation of mixing ratio between large sized ore and small sized coke; (3) to control the circumferential gas flow, the alternation of the rotating time of distributing chute in the 1_(st) notch of coke and the total rotating time of distributing chute for charging large sized ore as well as the average notch number for charging small sized ore. As results, stable gas flow distribution has been maintained with high pulverized coal injection operation as well as high productivity.

keyword :

To investigate the softening and melting characteristics of the blast furnace pellets and sinter, reduction and softening under load tests and hot test at the commercial plant, Kwangyang No. 4 blast furnace, have been carried out, using commercial sinter and pellets. The results of tests are as follows: (1) Indirect reduction area has been reduced by pellet, because of its lower softening and melting temperature than that of sinter. And since direct reduction has been sharply taken place just before melting, peak pressure drop was very high. (2) In case of pellet with high basicity and MgO content, its softening and melting behavior was better than that with lower one. (3) When pellet ratio was increased by 1%, productivity was increased by 7 ㎏/D.㎥.

keyword :

In order to improve manganese yield by smelting reduction of manganese ore in less slag blowing at BOF, the reduction kinetics of manganese oxide in CaO-SiO₂-MgO_(sat.)-FeO-Mn0 slag was investigated under experimental scale. The optimum initial carbon content in metal to the reduction of MnO is about 1.9%. The existence of Si in metal can accelerate the reduction of MnO in slag, and the initial Mn content has no influence on the reduction rate. From the assumption that the reduction of (MnO) is controlled by the equilibrium manganese distribution and mass transfer through the metal and slag boundary layers at the metal/slag interface, the rate equation was obtained. The kinetic model suggested in the present study showed good agreement between calculated and observed values of [Mn] and the reduction behaviour of (MnO) in slag can be described by the present model.

keyword :

A Li_(1.05)CoO₂ powder has been prepared by the solid state reaction of Li₂CO₃ and Co₃O₄ at 1000℃. Li_(1.05)CoO₂ powder was characterized a layered structure with space group of R3￣m by XRD analysis. But Li_(1.05)CoO₂ has a shorter c-axis than LiCoO₂ because, in the former case, a coulombic interaction is more dominent than elastic strain energy effect. In this experiment, electrochemical properties about porous Li_(1.05)CoO₂ were investigated by galvanostatic, CV(Cyclic Voltammetry) and GITT(Galvanostatic Intermittent Transient Technique) method.

keyword :