발간논문

Home > KJMM 논문 > 발간논문

The effect of cold rolling on the magnetic properties of nonoriented electrical steel sheet containing 3% silicon was examined by the observation of microstructure and texture analysis. Grain size of each specimen was maximum when the reduction rate of 2nd cold rolling was 5% and it gradually reduced as the rate increased. It was thought that grain growth of 2nd cold rolled specimen was occurred by random, abnormal grain growth. In view of the texture of final product, specimens processed by single cold rolling method had (222) texture, which is unfavorable to magnetic properties, but the ones processed by double cold rolling method had nearly random texture. Specimen with 2nd cold reduction of 5%, thus, had the minimum iron-core loss.

keyword :

In order to clarify the shape control mechanism of nonmetallic inclusions in molten steel, the morphology changes of oxide and sulfide inclusions were investigated by Ca treatment in Al-deoxidized steel at 1600℃. The Ca addition of suitableamount into Al-deoxidized steel considerably improved the degree of steel cleanliness because the alumina cluster formed after Al-deoxidization changed to liquid phase calcium-aluminates which float out rapidly from steel bath. And also, when total oxygen content in molten steel was less than about 20ppm, MnS sulfide and Al₂O₃oxide were modified to C type inclusions such as (Ca, Al, Mn) O-(Ca, Mn) S or CaO-Al₂O₃-CaS

keyword :

Oxidation reaction of molybdenum sulfides has been studied by thermodynamic analysis of the diagrams of Molybdenum-Sulfur-Oxygen System. The results obtained in this investigation are as follows; 1) Partial pressure diagrams of Mo-S-O system were represented by thermodynamic calculations between 673˚K and 923˚K. 2) The followings are feasible reactions among the oxidation reactions of molybdenite. MoS₂＋3O₂= MoO₂＋2SO₂ MoO₂＋0.5O₂= MoO₃ MoS₂＋6boO₃= 7MoO₂＋2SO₂ 3) During the roasting of molybdenite in air, the oxidation reaction occurs through the following steps. MoS₂→MoO₂→MoO₃

keyword :

Oxidation roasting of molybdenite pellets was carried out to study the effect of temperature and oxygen concentration on the oxidation rate. The effect of heat transfer between pellet and surroundings on the reaction rate was also studied by measuring the temperature of pellet during reaction. The result obtained in this experiments are as follows; 1) The effect of heat transfer on the reaction rate was significant at the beginning of the oxidation processes. 2) The temperature difference between pellet and surroundings was increased with increasing the reaction temperature and the oxygen concentration. And the larger the difference of the temperature, the more the effect of heat transfer on the reaction rate. 3) The activation energies calculated from these experimental conditions were of the order of 34㎉/㏖ and 11㎉/㏖ for the non-isothermal and isothermal periods, respectively. And the oxidation rate of the molybdenite was mainly depended on diffusion rate.

keyword :

The variations of microstructure, interphase spacing and mechanical properties in Al-Fe and Al-Fe-Ni eutectic alloys have been investigated over a range of solidification rate from 1.2 to 38㎜/min under the thermal gradient of approximately 80℃/㎝. The results obtained are summarized as follows; 1. The coupled growth condition of aligned FeNiAl_9 phase was improved by Ni addition. 2. Increasing the solidification rate caused the transverse structure of Al-1.8% Fe-1.0% Ni alloy change gradually from non-cellular to elongated, square-cellular structure. 3. The relationship between the interphase spacing and the solidification rate was Rλ²＝1.24×10^(-8)㎤/min. 4. The fracture occurred approximately on 45˚directions to the tensile axis.

keyword :

To investigate the effects of hard eye structure on the mechanical properties of BMC (black heart malleable cast iron), a harder second phase was formed around the temper carbon by carbon diffusion. (rapid heating) Index, n, in the rate equation for the austenitization (Johnson-Mehl equation) was 1.4. It was found that, althouth the hardness increased considerably, the impact strength of BMC having a pearlitic structure surrounding the temper carbon has inferior to that of BMC having not hard eye structure, but the decrease in the impact strength was not as large as when the tempered martensitic structure was formed. Also BMC showed a change from ductile to a brittle mode of fracture with increasing the volume fraction of hard eye structure.

keyword :

keyword :

keyword :