Manufacturing Process Flow Of Cold Rolled Grain-oriented Silicon Steel

09 May 2024
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(1) Demanganization, smelting, vacuum treatment and mold casting (or continuous casting) of molten iron. When the manganese content of the molten iron in the blast furnace is greater than 0.35%, add Fe0, etc. to the molten iron ladle to reduce the manganese content to less than 0.35%, and blow argon to stir. Smelted in a top-blown or top-bottom-blown converter, control C<0.06%, P<0.01%, s<0.03% and Mn<0.07%. During tapping, aluminum is added to the ladle for deoxidation, ferrosilicon is added for alloying, and argon is blown to make the temperature and composition uniform and the oxide inclusions to float up. Vacuum processing fine-tunes ingredients. In the past, mold casting was used, but now continuous casting is mostly used.

(2) Hot rolling. The billet is put into a heat preservation pit and slowly cooled. When the billet temperature is greater than 250°C, it is put into a heating furnace and heated at a high temperature of 1350 to 1400°C to make the coarse MnS and AlN in the billet dissolve into solid solution. During the hot rolling process, MnS is regenerated. Precipitates in fine dispersion (less than 50nm). Therefore, heating and hot rolling are also heat treatment processes for MnS solid solution and precipitation. The thickness of rough rolled slab is 30~40mm. Control the temperature before finishing rolling to be in the range of 1160 ~ 1200°C, because MnS precipitates again during the finishing rolling process. Minimize the amount of AlN precipitation during hot rolling of Hi-B steel. The final rolling temperature is 950~1050℃. After hot rolling, it is sprayed with water and cooled to about 550℃ for coiling. The thickness of the hot rolled strip is 2.2~2.5mm.

(3) High temperature normalization, cold rolling, decarburization annealing and coating with release agent. The Hi-B steel hot-rolled strip is subjected to (1100~1120℃) × (3~5min) normalization treatment in nitrogen, and is air-cooled to 900℃ and sprayed with water to precipitate fine AlN. After hot rolling or normalization, pickle and keep at 50~60℃ for cold rolling. G.0. After the steel is cold rolled at a reduction rate of 60% to 70%, it is subjected to (850~950℃) Eliminates work hardening and partial decarburization. After secondary cold rolling at a reduction rate of 50% to 70% to the finished thickness. Hi-B steel adopts the cold rolling method with the next largest reduction rate (82% to 90%). During the cold rolling process, aging treatment at 150 to 300°C increases the amount of solid solution carbon and nitrogen in the steel, hindering the movement of dislocations and promoting the formation of more deformation bands and secondary crystal nuclei. The cold-rolled plate is decarburized and annealed in a continuous furnace in wet 20% H2+N2 at (835~850°C) Develop perfect secondary recrystallization in the single-a phase and eliminate the magnetic aging phenomenon of the product; second, obtain fine and uniform primary recrystallized grains and primary recrystallization that is conducive to the preferential growth of (110)[001] secondary crystal nuclei. Recrystallization texture; the third is to form a uniform and dense SiO2 film on the surface. After decarburization and annealing, wet-coat MgO (isolating agent) to prevent adhesion during roll high-temperature annealing and form a bottom layer of magnesium silicate glass film (.Mg2SiO4) with surface SiO2.

(4) High temperature annealing, flat stretch annealing and insulating film coating. MgO-coated steel coils are annealed at high temperature in a bell-type furnace or a continuous annular furnace. The purpose is to complete the secondary recrystallization and obtain the (110)[001] texture (G0 steel at 850~950℃, Hi-B steel at 980 ~1030℃); forming magnesium silicate bottom layer (1000~1100℃); removing sulfur and nitrogen in steel (1180~1200℃). First raise it to 600°C in nitrogen and keep it for 1 hour to remove the combined water in MgO, then slowly raise it to about 1150°C in 75% H2+N2 at 15-20°C/h, and then change to pure dryness with a dew point of -60°C. The hydrogen was raised to 1200°C, kept warm for 20 hours, then replaced with 75% H2+N2 furnace and cooled to 700°C, then replaced with nitrogen to continue cooling. After high temperature annealing, it is flattened, stretched and annealed and coated with an insulating film. The steel strip is first scrubbed with water and dilute pickling to remove residual MgO, coated with a stress coating based on colloidal SiO2 and phosphate, and then processed in a continuous furnace nitrogen at 800°C × 5 minutes and appropriate tension to make the steel strip smooth. and sintered insulating film. The thermal expansion coefficient of the stress coating (about 4×10-6/℃) is different from that of silicon steel (about 13×10-6/℃). During tensile annealing and cooling, a tensile stress of about 4.9N/mm2 is generated in the steel plate, making 180 . Domain refinement and iron loss reduction. In order to further reduce the iron loss, it can be processed by laser irradiation, toothed roller processing or plasma spraying in the transverse direction.

Cold rolled grain oriented steel

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