EFFECT OF FINAL ANNEALING ATMOSPHERE ON SECONDARY RECRYSTALLIZATION BEHAVIOR IN THIN GAUGE MEDIUM TEMPERATURE GRAIN ORIENTED SILICON STEEL
Gongtao LIU,Ping YANG(),Weimin MAO
School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
Cite this article:
Gongtao LIU,Ping YANG,Weimin MAO. EFFECT OF FINAL ANNEALING ATMOSPHERE ON SECONDARY RECRYSTALLIZATION BEHAVIOR IN THIN GAUGE MEDIUM TEMPERATURE GRAIN ORIENTED SILICON STEEL. Acta Metall Sin, 2016, 52(1): 25-32.
The development trend of grain oriented silicon steel is reducing the slab reheating temperature and the thickness of final product. Medium temperature slab reheating grain oriented silicon steel bearing copper was characterized by omitting hot band annealing and larger range of secondary cold rolling reduction which was suitable for the preparation of thin gauge product. But less research were reported about thin gauge grain oriented silicon steel produced by medium temperature reheat technique. It was well known that the sharpness of secondary recrystallization Goss texture is deteriorated by the preparation of 0.18 mm thin gauge grain oriented silicon steel, poor secondary recrystallization and deviated Goss grains occurs by the influence of Goss seeds decreasing and inhibitor decrease. So the key point of producing thin gauge grain oriented silicon steel was controlling the precipitations ageing behavior. In order to improve the sharpness of Goss texture and the magnetic flux density after secondary recrystallization, secondary recrystallization behavior was controlled by annealing atmosphere in this work. The microstructure and texture of interrupted annealing specimens were measured by EBSD system. The results show that the magnetic flux density of 0.18 mm gauge specimen was 1.95 T after final annealing in 90%N2 atmosphere. Due to the coarsening behavior of inhibitors was more strongly influenced by atmosphere in thin gauge silicon steel, the primary recrystallization grain size was smaller and secondary recrystallization duration was longer by improving volume fraction of N2 during final annealing. In this condition, deviated Goss grains were inhibited while Goss grains have enough time for abnormal growth. As a result, sharp Goss texture and stable secondary recrystallization were guaranteed and high magnetic flux density of thin gauge final product was obtained.
Fig.1 Process of secondary recrystallization annealing
Volume ratio
P1.7 / (Wkg-1)
B8 / T
N2∶H2=1∶3
2.07
1.51
N2∶H2=1∶1
1.08
1.40
N2∶H2=9∶1
1.66
1.95
Table1 Magnetic properties of samples in different atmospheres
Fig.2 EBSD orientation images of samples after hot rolling (a~c) and intermediate annealing (d~f)
(a, d) orientation distribution maps (ND—normal direction, RD—rolling direction)
(b, e) orientation distribution functions (ODFs) at j2=45° section
(c, f) {100} pole figures
Fig.3 EBSD orientation images of interrupted annealing samples in N2∶H2=9∶1 (a~e), 1∶1 (f~j) and 1∶3 (k~o) for soaking 0 h (a, f, k), 2 h (b, g, l ), 3 h (c, h, m), 5 h (d, i, n) and 10 h (e, j, o)
Fig.4 OM images (a, c) and grain orientations (b, d) of samples in N2∶H2=9∶1 (a, b) and N2∶H2=1∶3 (c, d) after 20 h final annealing
Fig.5 Orientations of secondary recrystallization grains in interrupted annealing samples in N2∶H2=9∶1 (a~d), N2∶H2=1∶1 (e, f) and N2∶H2=1∶3 (g, h) for soaking 2 h (a, e, g), 3 h (b, f, h), 5 h (c) and 10 h (d)
Fig.6 Average grain size (a) and area fraction of {111} texture (b) in interrupted annealing samples on soaking during final annealing in different atmospheres
Fig.7 Second phase distributions of samples in different atmospheres at 1050 ℃
(a) N2∶H2=9∶1
(b) N2∶H2=1∶1
(c) N2∶H2=1∶3
Fig.8 Schematic of orientation selectivity during grain growth of secondary recrystallization (F—critical driving force of secondary recrystallization with slow inhibitor dropping rate, F'—critical driving force of secondary recrystallization with quick inhibitor dropping rate, Δt—time difference of precise Goss and deviated Goss begin to secondary recrystallization with slow inhibitor dropping rate, Δt'—time difference of precise Goss and deviated Goss begin to secondary recrystallization with quick inhibitor dropping rate, solid line—slow inhibitor dropping rate and related critical driving force of secondary recrystallization, dash line—quick inhibitor dropping rate and related critical driving force of secondary recrystallization)
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