Estudo da precipitação de MnS, AIN e CuS no aço 3%Si, em uma laminação com acabamento reversível

Abstract

For good performance of electrical steels it is necessary a high magnetic induction and a low power loss when submitted to cyclic magnetization. For that it is fundamental a high degree of preferential orientation, obtained through secondary recrystallization during the manufacturing process. For such, it is required a good dispersion of inhibitors (particles of second phases, such as manganese sulphide (MnS), copper sulphide (CuS/Cu2S) and aluminium nitride (AlN) or their combination) whichdelay the normal grain growth during primary recrystallization, causing preferential growth grain with Goss orientation during secondary recrystallization. The crucial point for grain oriented silicon steel production using AlN as inhibitor is to secure that AlN is precipitated finely in the hot rolling process and hot band annealing. In this work compression test by Gleeble simulator was used to verify the inhibitors precipitation kinetic during hot conformation simulating the hot rolling thermal cycle in reversible finishing rolling, as via Steckel mill. The samples were heated to 1350 °C to dissolve the precipitates and cooled down to the temperatures of: 900 °C, 1000 °C, 1100 °C and 1200 °C; at these temperatures two deformation of 40% were applied, with soaking between deformations for: 1 s, 10 s, 100 s and 1000s. The samples were analyzed using the optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). For TEM observation extraction replica and thin foils were used. In addition, precipitate extraction by dissolution methods and inductively coupled plasma optical emission spectrometry (ICP-OES) were used to measure the percentages of Al, Mn and Cu inthe precipitates. With the results obtained from this work it was possible to draw the precipitation-time-temperature (PTT) diagrams for the precipitation ofsulphides and nitrate in silicon steel high permeability grain oriented (HGO).