Development of mathematical models for the design of annealing cycles of high-strength steels through laboratory tests and subsequent industrial validation

Batch annealing in bell furnace is one of the most common and widespread technology to thermally treat aluminium killed low carbon manganese steels. This paper focus on the recovery annealing of cold rolled Al-killed steels. The tensile properties evolution due to recovery annealing has been studied through i) the crystalline grain measurement; ii) micro-hardness measurement iii) by means of x-ray diffraction techniques analysing the diffraction peaks in correspondence with the planes (200) and (220). To reach this purpose a simulator of the recovery kinetics has been designed, tested and validated. The metallurgical model was created starting from the equation proposed by Verdier, Brechet and Guyot for AlMg alloys, adapting it for carbon steels. The model, valid only for isothermal annealing, has been extended to the more general case of non-isothermal annealing applying the Scheil's additivity rule. The so obtained simulator, tested and validated on an industrial scale, was subsequently used within the Marcegaglia plant in Ravenna.