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The special alloy steel which is widely used for the bearing and structural parts for a car and construction equipment etc.has great needs for improving the function and quality, because it affects the processing characteristic and heat treatability at machining and decides the reliability and durability of the final products.Therefore, various countermeasures have been taken for improving surface quality and internal quality of bloom (ex.surface and internal crack, inclusions, center segregation) in the continuous caster for a long time.NIPPON STEEL & SUMIKIN ENGINEERING CO., Ltd.(NSENGI) has developed many innovative technologies for improving the quality of the large section bloom caster from 1970 s and put them into commercial use,such as NS plasma heater in tundish, NS M-EMS (In-Mold Electro-Magnetic Stirrer), NS Soft reduction.Moreover, NSENGI aimed at no internal defects in the special bar quality and co-developed the large reduction technology for bloom continuous caster (NS bloom large reduction) with a special steel maker.So, NSENGI succeeded in reducing center porosity of cast bloom.In addition, NSENGI firstly succeeded in putting it into commercial use in the world and have contributed to improving the yield ratio at the various steel grades.In the development, NSENGI did the numerical analysis and a rolling mill test by using the casting piece processed the artificial porosity in it, and gained a better understanding of the reduction characteristic of the bloom.Finally, NSENGI realized the compact equipment which could reduce center porosity by high efficient bloom reduction and be installed into a little space of multi-strand bloom continuous caster.In this paper, the principle, the solved technological problems, the improved quality effect and the feature of bloom large reduction equipment are stated.