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INFLUENCE OF FINISHING ROLLING TEMPERATURE ON RECRYSTALLIZATION OF ELECTRICAL STEELS

INFLUENCE OF FINISHING ROLLING TEMPERATURE ON RECRYSTALLIZATION OF ELECTRICAL STEELS C. Capdevila , J.P. Ferrer and C. García de Andrés Solid-Solid Phase Transformations Group (MATERALIA) Department of Physical Metallurgy Centro Nacional de Investigaciones Metalúrgicas (CENIM)

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INFLUENCE OF FINISHING ROLLING TEMPERATURE ON RECRYSTALLIZATION OF ELECTRICAL STEELS

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  1. INFLUENCE OF FINISHING ROLLING TEMPERATURE ON RECRYSTALLIZATION OF ELECTRICAL STEELS C. Capdevila, J.P. Ferrer and C. García de Andrés Solid-Solid Phase Transformations Group (MATERALIA) Department of Physical Metallurgy Centro Nacional de Investigaciones Metalúrgicas (CENIM) Consejo Superior de Investigaciones Científicas (CSIC) Avda. Gregorio del Amo, 8 E-28040 Madrid, Spain www.cenim.csic.es

  2. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) What is a electrical steel? • Electrical steels (Fe-Si) belong to the group of soft magnetic materials, which are generally used to increase and to conduct magnetic flux inside electromagnetic components. • There are two basic types of electrical steels: non grain- and grain-oriented electrical steels. • The grain-oriented electrical steel (Goss texture) present a high anisotropy of the magnetic properties. For that reason the grain-oriented electrical steels are basically used in magnetic cores of transformers, where the magnetic flux is mainly following one direction. • The non grain-oriented electrical steels (Cube texture) may be used in any application with varying direction of the magnetic flux like motors, generators, etc. In this work we are dealing with non grain-oriented electrical steel

  3. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Main aim of the work: Improve texture of the final product by controlling hot rolling Processing route (thickness  0.7 mm) CT  800 – 950 ºC CT  800 – 950 ºC 700 – 800 ºC Ar3 10 ºC/s FRT FRT 50 ºC/s 760 ºC Cold rolling  40 – 80 %

  4. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Processing route to be study (thickness  0.7 mm) Nuleation at grain boundaries decreases after cold rolling + annealing (high energy nucelation) Coarse grains obtained during coiling Formation of deformation bands during cold rolling is enhanced Nucleation sites for desirable grains (low energy nucleation) ReX grains with {111} texture ReX grains with {001} texture

  5. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Table I. Silicon levels and finishes rolling temperatures.

  6. 20 mm 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Starting microstructure before coiling FRT=840 ºC FRT=900 ºC Deformation texture is more intense in material with low FRT

  7. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Recrystallisation during coiling High FRT induce coarser ReX grains after coiling ReX grain size decreases as CT is increased

  8. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels AlN Recrystallisation during coiling: why these differences in grain size? The more likely nucleation mechanims is rotation of subgrains. AlN particles pin subgrain boundaries difficulting nucleation of ReX. ES1-B FRT=900 ºC Annealed at 850 ºC t=1.5 h

  9. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Recrystalisation Mechanism: Low FRT  Nucleation + Growth ReX High FRT  Continuous ReX Alfa (green) and gamma (red) fibres Grain Boundaries 2º5º10º 15º Low angle boundaries reveal the existence of subgrains

  10. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels ES1B (high FRT) t=10 s CT=850 ºC t=100 s t=3000 s ES1C (low FRT)

  11. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Electrical steels Evolution of ReX and AlN precipitation At low FRT, the material ReX first, and then AlN precipitation takes place At high FRT, ReX and AlN precipitation takes place simultenously

  12. 30th of May, PTM 2005 – Phoenix (USA) Solid-Solid Phase Transformation Group (MATERALIA) – CENIM (CSIC) Conclusions Because of the interaction between recovery and AlN precipitation on subgrain boundaries, material with high FRT recrystallizes by continuous recrystallization. The final microstructure presents a large grain size. However, in material with low FRT, continuous recrystallization is replaced by ‘discontinuous recrystallization’. The final grain size is lower in this case.

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