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Research paper : Toward the integrated optimization of steel plate production process (K. Nishioka et al.)−97−Synthesiology - English edition Vol.5 No.2 (2012) line, and rolled to become steel plate products. Steel plates are produced based on orders received and on elaborate production planning. Each plate weighs about 3 tons and is manufactured from a large lot of 300 – 400 tons per one converter vessel by dividing them into small tonnage for each plate. Steel plates as products are used widely as important components of various structures including ships, buildings, bridges, construction/ industrial machinery, offshore structures for drilling offshore oil/ liquefied natural gas, etc., and they must comply with a huge variety of standards. They have characteristics that differ from other steel products. For example, their places of use are rigorously specified and each one of them is delivered in a particular specified size.Steel plates are manufactured based on orders received and the orders are diversified and small in each lot, which explains why their manufacturing processes are complicated. First of all, in the rolling processes, plates of various sizes are manufactured, and during these processes, their metallurgical microstructure is controlled to meet varieties of specifications in their material properties. After rolling, in the finishing processes, various works are conducted including the correction of defects occurring in the upstream processes and supplementary treatments (heat treatment, coating, etc.).By incorporating material quality (Tsukurikomi) during the rolling process, the thermo-mechanical control process (TMCP) was developed in Japan during the 1980s and for the 30 years that followed, TMCP played the role of one of the state-of-the-art core technologies for manufacturing high quality steel plates in Japan. The schematic illustration of the steel plate rolling processes is illustrated in Fig. 3.TMCP enables the production of as-required steels of whichever microstructure and property by controlling the Fig. 3 Microstructure control of steel plates and TMCP technology[3]02040608010012014060 Hr20052001Lead Time (required process time), Hr 20052001JapanKimitsuGrowth rate of production 0.80.91.01.11.21.31.41.51.6Further toughness by combining rolling and coolingCoolingTransformationElongationRecrystallizationCurbing grain growthFinish rollingRough rollingHeatingCHANGE OF METAL STRUCTURESCHANGE OF TEMPERATURESPROCESSCLC: online water cooling processHot levelerFinishing millRoughingmillReheating furnaceFlattening by hot levelerMulti-pass rolling controlHeating tempcontrolCasting conditioncontrolStructure control by online water coolingPlate Intensive cooling:martensiteMedium cooling:bainiteMild cooling:ferrite/ perlite800 N/mm2<500~600 N/mm2class600~800 N/mm2classCCFig. 1 Shorter production lead time in the Plate Mill of Kimitsu WorksFig. 2 Comparison of production growth rates of plate mills in Japan(Source: Monthly Steel Statistics Report of Secured Orders of Steel Products (ordinary and specialty steel products), The Japan Iron and Steel Federation)

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