This paper focuses on the evolution of the microstructure in a grain-oriented electrical steel (GOES) thin strip after casting. After solidification, the microstructure consisted of delta-ferrite. A small fraction of austenite was formed during the cooling of the thin strip in the two-phase region (gamma+delta). Fine Cr2CuS4 particles precipitated in the ferrite and along the delta/gamma interfaces. Laths of primary Widmanstätten austenite (WA) nucleated directly on the high-angle delta-ferrite grain boundaries. The formation of WA laths in both adjacent ferritic grains resulted in a zig-zag shape of delta-ferrite grain boundaries due to their local rotation during austenite nucleation. Based on the EBSD results, a mechanism of the formation of the zig-zag grain boundaries has been proposed. Besides the Widmanstätten morphology, austenite also formed as films along the delta-ferrite grain boundaries. Sulfide precipitation along the delta/gamma interfaces made it possible to prove that austenite decomposition upon a drop in temperature was initiated by the formation of epitaxial ferrite. Further cooling brought the decay of austenite to either pearlite or a mixture of plate martensite and some retained austenite.

This paper deals with the formation of sulphides in as-cast grain-oriented electrical steel (GOES) thin strip during solidification and subsequent cooling through the (δ + γ) field. Chemical composition of the strip was as follows, in mass %: 0.034 C, 2.81 Si, 0.06 Mn, 0.024 S, 0.20 Cr, 0.15 Cu, 0.055 Ni, 0.0011 Ti, 0.0056 N and 0.002 Al. It was found out that chemical composition of coarse sulphides, formed in the area of final solidification, was very different from the composition of fine sulphides precipitated in the two-phase region. Coarse sulphides were rich in iron. Fine complex sulphides were identified as the Cr2CuS4 phase. The effect of fine sulphides on the austenite decomposition at the end of the (δ + γ) field was studied.

In austenitic steels, the tetragonal Z-phase (NbCrN) has frequently been credited with beneficial strengthening effects during dislocation creep. In the modified Z-phase, niobium is partially substituted by vanadium. The basic objective of this contribution is a detailed characterization of the modified Z-phase in vanadium bearing austenitic AISI 316LN+Nb+V and HR3C steels. Experimental activities were focused on crystallography, thermodynamic and dimensional stability, kinetics of precipitation (TTP diagram) and solvus temperature of the modified Z-phase in the steels examined. Thermodynamic modelling was used for prediction of stable minor phases and solvus temperature of the modified Z-phase. Kinetics of precipitation of the (Nb,V)CrN phase in the AISI 316LN+Nb+V steel was experimentally investigated in the temperature interval of 550–1250 °C. The kinetics of precipitation of the modified Z-phase in austenitic matrix was fast. Results of diffraction studies on particles of the modified Z-phase confirmed the existence of the tetragonal unit cell already after short-term annealing. The solvus temperature of the modified Z-phase in austenitic steels was determined to be lower than that for the NbCrN phase. The decrease in the solvus temperature is dependent on the vanadium content in austenitic steels. Both thermodynamic calculations and experimental results proved that the thermodynamical stability of the modified Z-phase in austenite was high. More data are needed for evaluation of long-term dimensional stability of the (Nb,V)CrN phase in austenitic steels at temperatures for their engineering applications.

Twin -roll strip casting is an advanced technology for production of thin strips with the thickness of several millimetres. Recent progress in twin -roll strip casting makes it possible to apply this technology for the production of grain oriented electrical steels (GOES). Optimization of technological processing of GOES using this revolutionary technology requires the detailed knowledge about microstructure evolution.Cooling of GOES thin strips in the  +  phase field is accompanied by the formation of austenite in the form of Widmanstätten laths. This paper summarises basic knowledge about the formation and subsequent decomposition of Widmanstätten austenite in GOES thin strips. Attention is paid to nucleation of Widmanstätten austenite, its growth in the matrix of -ferrite, pinning of austenite/ferrite interfaces by sulphides, the formation of epitaxial ferrite, partitioning of carbon and finally to the decomposition of Widmanstätten austenite either to pearlite or plate martensite. Phase transformations were studied by a combination of light microscopy, XRD, SEM + EBSD and TEM.

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