Flexible Manufacturing Technologies Of 345MPa～460MPa Grade High Strength And Low-alloy Steel Plates

With the development of modern science and technology and economy, the steel industry, which is a pillar of country economy, realizes the large scale production. Its typical characteristic is large-scale, continuous and intensive, that is, tons of thousands of steel are produced at one time of casting. But, the user's demands to the steel productions tend to be more and more diversified, personalized and highly quality, such as, the actual supply of steel plate is only a few dozen tons. A bigger contradiction exists between market demands and production technology or management. This contradiction becomes more prominent due to the relationships of supply and demand transformed from seller's market to buyer's one. And the duty for resolving it increasingly transfers to the steel producer's, which make the research and development of flexible manufacturing technology (FMT) be so necessary. FMT refers to the rolling technology with a more flexible and adaptable process, that is, the process of modern metal producing maximally carries out according to the user's demands to solve the contradiction between large-scale production and personalized needs.In this paper, based on the production line of the Third Steel Plate of Jinan Steel Co., selected 345MPa and 460MPa low alloy high strength steels as the research object, through optimizing the steel's chemical composition, molten technology and TMCP, the FMTS to produce the steel plates from 345MPa to 460MPa have been developed by means of different rolling and cooling processes to make the number of smelted steels decrease to several ones. And the corresponding composition design, smelting and rolling plans have been also determined clearly to provide the technical safeguard for mass production.The results of studied in the paper show as follows.(1) For the 345MPa level test plate, its yield strength significantly increases with the cooling speed accelerating, and impact toughness decreases basically with the finishing rolling temperature raising and the cooling speed accelerating. Slowing cooling speed is beneficial to toughness. Coexistence of grain boundary and strengthening phases as well as their comprehensive effect basically result in the changes of the steel plate's properties.(2) For the 460MPa level test board, its strength increases and toughness decreases with the finishing rolling temperature raising, and when the cooling speed accelerates and the final cooling temperature reduces, its strength increases and toughness hardly changes. The effects of acicular ferrite and bainite on strengthening and toughness weakening as well as the influence of polygonal ferrite with fine grains on toughening jointly cause the changes of the plate's performances.(3) The flexible manufacturing technologies with the combination of different finishing temperatures and cooling conditions can form different microstructures and the corresponding matches of strength and toughness, which meet the requirements to the performances of different quality grade steel plates from 345MPa to 460MPa with same ingredients.The development and application of the FMTS reduce the difficulties of production arrangement and steelmaking process, and better solve the contradiction between the user's personalized demands and the characteristic of large-scale, continuous and intensive in steel plate production so that they become the important measure of cost decrease and benefit increase in Jinan Steel Co.