How to utilize the thin slab continuous casting and rolling process to produce high-grade non-oriented silicon steel, thereby giving full play to the advantages of the thin slab continuous casting and rolling process, is a technical problem that needs to be solved in the existing technology.
The chemical composition of the non-oriented silicon steel of the present invention is, in terms of mass percentage:
Si: 2.5～3.5％, Al: 0.10～1.5％, Mn: 0.10～1.5％, [S+O+C+N+Ti]≤80ppm, rare earth elements (La and/or Ce and/or Nd): 0.001～0.01％, the balance being Fe and other impurity elements.
The method for producing non-oriented silicon steel by thin slab continuous casting and rolling process of the present invention comprises the following steps: Step A: smelting; Step B: continuous casting; Step C: heating; Step D: hot rolling; Step E: pickling; Step F: cold rolling; Step G: recrystallization annealing.
As a further improvement of the present invention, in step A smelting process, converter smelting is first carried out, and then RH refining treatment is carried out. The final chemical composition of the molten steel after treatment is, in terms of mass percentage:
Si: 2.5～3.5％, Al: 0.10～1.5％, Mn: 0.10～1.5％, [S+O+C+N+Ti]≤80ppm, rare earth elements (La and/or Ce and/or Nd): 0.001～0.01％, the balance being Fe and other impurity elements;
The rare earth elements are added within 1～2 minutes after the alloying of RH refining is completed. After adding the rare earth elements, stirring is carried out, and the stirring time is ≥3 minutes.
As a further improvement of the present invention, in step B continuous casting process, the pulling speed is controlled at 2.8～4.6 meters/minute, and the thickness of the continuously cast billet is 30～70 mm.
As a further improvement of the present invention, in step C heating process, the billet is sent to a tunnel furnace for heating. The billet inlet temperature is ＞800℃, the heating temperature is 950～1150℃, and the homogenization time is ＜30 minutes.
As a further improvement of the present invention, in step D hot rolling process, 7-stand hot rolling is carried out. The rolling temperature is controlled at 950～1100℃, the final rolling temperature is controlled at 900～920℃, the coiling temperature is controlled at 600～700℃, and the target thickness of the hot-rolled plate is controlled at 0.8～1.0 mm.
As a further improvement of the present invention, in step F cold rolling process, the thickness is cold rolled to 0.5 mm.
As a further improvement of the present invention, in step G recrystallization annealing process, the annealing temperature is controlled at 1000～1200℃, and the holding time is controlled at 1～3 minutes.
As a further improvement of the present invention, in step B continuous casting process, the intermediate tundish superheat is controlled at ≤0℃, and the equiaxed crystal ratio is ensured to be ≥80％; in step D hot rolling process, the reduction rate of the last pass is controlled to be greater than 50％; in step F cold rolling process, the reduction rate is controlled to be ≤50％.
As a further improvement of the present invention, a single-stand reversible cold rolling mill or a cold tandem rolling mill is used in step F cold rolling process; and pure hydrogen atmosphere is used in step G recrystallization annealing process.
Beneficial Effects
Compared with the existing technology, the technical scheme provided by the present invention has the following remarkable effects:
(1) The process for producing low-grade non-oriented silicon steel by thin slab continuous casting and rolling is basically mature in the existing technology. However, for high-grade non-oriented silicon steel, especially when the silicon content is greater than 2.5％, there are obvious product defects. In view of the above problems, the method for producing non-oriented silicon steel by thin slab continuous casting and rolling process of the present invention combines the various process parameters of steps A to G to produce qualified high-grade non-oriented silicon steel by thin slab continuous casting and rolling process, thereby giving full play to the advantages of thin slab continuous casting and rolling process.
(2) The method for producing non-oriented silicon steel by thin slab continuous casting and rolling process of the present invention produces high-grade high-efficiency non-oriented silicon steel with a silicon content of ＞2.5％ on the thin slab continuous casting and rolling process through reasonable setting of composition and process, without electromagnetic stirring and without homogenization process. The final product has high magnetic induction and low iron loss, and solves the corrugated defects that are easy to appear in the production of high-grade non-oriented silicon steel by the existing thin slab continuous casting and rolling process. Its main technical characteristics are: it requires that [S+O+C+N+Ti]≤80ppm in the molten steel, which is ultra-clean molten steel; adding rare earth elements, firstly, to deeply purify the molten steel, reduce inclusions, and improve magnetic properties, and secondly, to use rare earth sulfides as nucleation points to refine the columnar crystals of the billet and eliminate corrugations; negative superheat is used in the casting process to make the equiaxed crystal ratio greater than 80％ and eliminate corrugations; the reduction rate of the last pass in the hot rolling process is controlled to be greater than 50％, low-temperature large reduction, reducing the banded structure in the core of the hot-rolled plate, improving the hot-rolled structure, and eliminating corrugations; optimizing the thickness of the hot-rolled plate, controlling the reduction rate of the cold rolling process to ≤50％, medium reduction rate, reducing (111) texture, increasing (100) texture, and improving magnetic properties.
Wechat