Thyssenkrupp Acciai Speciali Terni S.p.a.

Claudia Rocchi

Stefano Fortunati

Giuseppe Abbruzzese

Stefano Cicale'

Stefano Cicale′

In the production of electrical steel strips, a special islab-reheating treatment before hot rolling is carried out so that the maximum temperature within the furnace is reached by the slab well before its extraction from the furnace. During the heating stage and performance at the highest temperatures of the thermal cycle, second phase particles are dissolved and segregated elements are distributed in the metallic matrix, while during cooling and temperature equalising steps of the slab in the furnace a controlled amount of small second phases particles are more homogeneously re-precipitated from the metallic matrix. Differently from all the conventional processes for the production of electrical steels, the slab reheating furnace become a site in which it is performed the precipitation of a controlled amount of second phases particles for the necessary grain growth control during the successive process steps.

Process for the control of inhibitors distribution in the production of grain oriented electrical steel strips

Process for the production of oriented grain electrical steel strips, in which a silicon steel, comprising at least 30 ppm of S, is directly cast as strip 1.5-4.5 mm thick and cold rolled to a final thickness of between 1.0 and 0.15 mm; characterised by the following staged: Cooling and deformation of the solidified strip to obtain a second phases distribution in which 600 cm&#x3c;Iz&#x3c;1500 cmand Iy=1.9 Fv/r (cm), Fv being the volume fraction of second phases stable at temperatures of less than 800&#xb0; C., and r being the precipitates mean radius, in cm; Hot rolling between solidification and coiling of the strip at a temperature of not less than 750&#xb0; C., with a reduction ratio of between 15 and 60%; Cold rolling with reduction ratio of 60-92%; Cold rolled strip annealing at 750-1100&#xb0; C., with increase of the nitrogen content of at least 30 ppm with respect to the initial composition at the strip core, in nitriding atmosphere.

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Claudia Rocchi