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Nakashima J.,Process Technology Center | Toh T.,Mathematical Science and Technology Research Laboratory
Nippon Steel Technical Report

In order to achieve high quality slab production, to assess the cleanliness of the slab and the cleanliness of the molten steel in the tundish in continuous casting process, made it clear aggravating factor of cleanliness. To ensure the cleanliness of the continuously cast slabs, it is important to prevent the ladle slag outflow, tundish slag entrapment at the teeming point of tundish, and air oxidation. By the application of molten steel flow in mold control technology using electromagnetic force was developed by Nippon Steel Corporation (In-mold electromagnetic stirring and Level Magnetic Field), the slab can be manufactured with excellent internal cleanliness and surface cleanliness of slabs. Source

Yamamoto K.-I.,Process Technology Center | Toh T.,Mathematical Science and Technology Research Laboratory | Hamatani H.,Nagoya R and D Laboratory | Tsunenari K.,Plant Engineering and Facility Management Center | And 4 more authors.
Nippon Steel Technical Report

Tramp elements such as Cu cause a severe hot shortness. However, Cu is the useful alloying element for increasing hardness and improvement of the steel properties and Cu is often added to the steels. Therefore, by means of a steel surface melting technology, hot shortness should be suppressed by the addition of Ni only in the surface layer. After hotrolled, the sheets are sandblasted and checked for surface defects due to hot shortness. There are no defects and steel samples alloyed in the surface layer are very clean. Consequently, steel containing Cu alloyed Ni in the surface layer does not indicate hot shortness at the surface. Source

Iwasaki M.,Chiyoda Corporation | Matsuo M.,Process Technology Center
Nippon Steel Technical Report

Nippon Steel Corporation has endeavored to secure the world's topmost position in steelmaking technology over the last thirty years. The company has pursued technical innovation in the aspects of efficiency enhancement, quality improvement, labor saving and energy conservation in the operation of converters and continuous casting (CC) machines. In tandem with this, measures were taken to increase the production capacities of bottleneck processes in the vertically integrated production flow, as well as to rectify capacity imbalance while repairing furnaces and other periodic plant maintenance shutdowns. Nippon Steel has expended great efforts in developing new quality-enhancing technologies to differentiate itself with respect to surface and internal defects, especially for high-grade products. The material used for automotive steel sheets (for outer panels, in particular) has been changed to interstitial-free (IF) steels, as these products came to be manufactured through continuous annealing, but the problem with IF steels is that they are prone to surface defects due to slivers, scabs and blowholes. Source

Sasaki N.,Process Technology Center | Ogawa Y.,Process Technology Center | Mukawa S.,Nagoya RandD Laboratory | Miyamoto K.-I.,Muroran RandD Laboratory
Nippon Steel Technical Report

The converter-type hot metal pretreatment process which is developed and installed by NSC for all works is marked for improved productivity, heat balance and reduction of amount of slag without fluorine. The improvement is realized by lower basicity and higher oxygen potential. This report describes 1) the behavior of dephosphorization with lower basicity slag, 2) the evaluation and improvement of oxygen potential at the interface of slag and metal, 3) the improvement of dephosphorization reaction by using solid phase which is contain high phosphorous. The idea and feature of the MURC (Multi-Refining Converter) method and effects of implement of the converter- type hot metal pretreatment process are described. Source

Miyazaki M.,Process Technology Center | Isobe K.,Muroran RandD Laboratory | Murao T.,Process Technology Center
Nippon Steel Technical Report

Adequate understanding of the formation mechanism of centerline segregation is necessary for designing better equipment and determining the optimum operating conditions in order to improve the internal quality of the continuous cast steel. As a method for analyze the formation mechanism of centerline segregation, numerical simulation model analysis has recently been in practice concomitantly with the enhanced computational performance. The present report describes simulation models revealing the formation of the centerline segregation according to bulging between rolls, bridging in the portion of unevenness of solidification and molten steel fluidity at the tip of dendrite at the last stage of solidification. These models allowed us to better clarify the formation mechanism of the centerline segregation and to quantitatively estimate the effects on the centerline segregation caused by respective factors. Source

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