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Effect of decarburization annealing process on microstructure and texture of bismuth-containing Hi-B steel

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  The carbon content and texture of the bismuth-containing Hi-B steel after different decarburization annealing treatments were studied by means of infrared carbon and sulfur analysis and EBSD technology.
  Cold-rolled oriented silicon steel is a ferrosilicon soft magnetic material with {110}<001> texture (Goss texture). Its production equipment is complex and the production process is strict. It is known as the ”artwork“ in steel materials. In recent years, researchers at home and abroad have been working to explore new low temperature solid solution inhibitors. Studies have shown that nanoscale Nb(C,N) precipitates formed in Nb-oriented silicon steel not only have lower solid solution temperature and stability, but also can effectively inhibit austenite when used as an inhibitor. Crystallization and growth of primary recrystallized grains are consistent with the trend toward the production of oriented silicon steel towards low temperature slab heating and thin gauge orientation.
  On the other hand, the carbon content in oriented silicon steel is closely related to its magnetic properties. In order to ensure the proper microstructure evolution of oriented silicon steel during hot rolling, cold rolling and annealing, and to obtain the best texture and magnetic properties, the carbon content of the steel before decarburization annealing needs to be maintained at 0.04%-0.07%. At the same time, in order to ensure that the oriented silicon steel finished sheet is organized into a single ferrite phase to eliminate the magnetic aging phenomenon, the carbon content in the steel sheet after the decarburization annealing treatment generally does not exceed 50×10-6~60×10-6. A cold-rolled steel strip (typically within 0.3 mm thick) undergoes a recrystallization after decarburization annealing. {111}<112> and {111}<110> oriented grains in oriented silicon steel can promote the abnormal growth of Goss nucleus and improve its magnetic properties. Rotating copper type {112}<110> and {001} oriented grains This is not conducive to the occurrence of secondary recrystallization. Therefore, the number and distribution of these oriented grains after primary recrystallization have a great influence on the secondary recrystallization of oriented silicon steel. However, at present, there is still a lack of systematic and in-depth research on the decarburization process parameters and the evolution of texture after primary recrystallization in bismuth-containing Hi-B steel.
  Based on this, Hi-B steel with Nb content of 0.028% was studied. The effects of decarburization annealing conditions on carbon content, primary recrystallization texture and grain size of steel were investigated and analyzed. Orientation relationship between grains such as <112> and {111}<110> and Goss grains.
  (1) Under the condition that the protective atmosphere is 33% H2+67%N2 (volume fraction) and the dew point of the atmosphere is 45 °C, it is annealed at a temperature of 850 °C for 180s, and the decarburization effect of bismuth-containing Hi-B steel is the best. The medium carbon content is about 0.0037%.
  (2) After decarburization annealing, the yttrium-containing Hi-B steel samples have been recrystallized completely, and the texture is composed of strong {411}<148>, {111}<112> and {111}<110> textures. Composition, a small amount of Goss grains are scattered between {111}<112> or {411}<148> grains.
  (3) When the annealing time is 180s, as the decarburization temperature is increased from 830 °C to 850 °C, the number of grain boundaries of Σ9 and Σ13b which are favorable for Goss grain growth in yttrium-containing Hi-B steel samples increases first. After the large reduction, the maximum value appeared after annealing at 840 °C; when the decarburization temperature was 850 °C, the number of grain boundaries of Σ9 and Σ13b increased with the increase of holding time.