Precipitation Reactions in a Copper – Bearing GOES

Abstract

The paper deals with minor phase evolution in a Cu – bearing grain oriented electrical steel during the following production steps of the AlN + Cu industrial processing route: hot rolling of slabs, the 1^st cold rolling + decarburization annealing and the 2^nd cold rolling + slow laboratory heating to the temperature of primary recrystalization. Thermocalc calculations were used for prediction of the effect of copper additions on equilibrium phases in the temperature interval 450 – 850 °C. Minor phase evolution was studied by using transmission electron microscopy. Hot rolling was accompanied by dissolution of copper rich sulfides. Slow cooling of coils after hot rolling resulted in precipitation of Fe₃C along ferrite grain boundaries. Decarburization annealing after the 1^st cold rolling was accompanied by dissolution of Fe₃C, re-precipitation of fine Cu₂S, (Mn,Cu)S and very intensive precipitation of nitrides (AlN and Si₃N₄). Slow laboratory heating after the 2^nd cold rolling to the onset of primary recrystallization (620 °C) did not cause precipitation of any other minor phase. No copper rich metallic particles (ɛ - Cu) formed during the production steps investigated. Most fine particles of inhibition phases formed during decarburization annealing.