Papers by Keyword: API Grade

Abstract: The use of CSP^® thin slab casting followed by direct thermomechanical rolling is well placed for the production of low-carbon Nb microalloyed steels. In this process thin slabs of between 48 and 90 mm thickness are cast and directly hot rolled to hot strip typically between 1 and 12 mm thick. To obtain optimum strength and toughness property combinations in a direct rolling process, hot rolling has to compact the dendritic as-cast microstructure and to achieve a fine-grained microstructure. This affords a two-stage rolling strategy with start rolling above the recrystallization stop temperature and finish rolling in the non-recrystallization temperature range. Temperature and deformation in the first stand should be as high as possible in order to delete the initial as-cast microstructure by complete recrystallization. Based on these considerations, SMS Siemag further developed the CSP^® concept including features allowing isothermal rolling in the first stands of the finishing mill. The present contribution gives the results of a laboratory study of this innovative approach. The report concludes with resulting new plant configurations for improved high strength and API linepipe grade production.

Abstract: The use of thin slab casting and direct rolling is well suited for the production of niobium microalloyed low-carbon high strength linepipe grades. The slabs have excellent surface quality. Thermomechanical processing by controlling hot work hardening and softening processes of austenite and its polymorphic transformation into ferrite results in a powerful microstructure refinement. This is a sound basis for setting high strength, combined with excellent ductility and toughness.