METHOD FOR DETERMINING THE OPTIMUM SILICON CONTENT IN LIQUID STEEL

Claims

1. Method for determining the optimized silicon content %Si opt , which must be obtained in liquid steel (1) before casting, wherein said liquid steel (1) is obtained by melting steel scrap containing copper, the method includes: a. obtaining the reheating temperature T R , determined for reheating the semi-finished products (5) obtained by casting the said liquid steel, wherein said reheating precedes hot rolling, b. determination of the optimized silicon content %Si opt in such a way that the following condition is met , where σ(%Si opt ), ρ(%Si opt ) and β(%Si opt ) predetermined coefficients that do not depend on the reheating temperature T R , and where Δ is a constant threshold value independent of T R and %Si opt .

2. The method according to paragraph 1, in which the value represents the ratio of the content of liquid fayalite eutectic FeO-Fe2SiO4 formed during reheating to the total amount of oxides formed during reheating.

3. The method according to claim 1 or 2, wherein the obtained liquid steel (1) contains at least 0.1 wt.% copper.

4. The method according to any of paragraphs. 1 to 3, wherein the liquid steel (1) has a composition in which Sb ≤ 0.01%, As ≤ 0.1%, Sn ≤ 0.05%, 0.004% ≤ Si ≤ 6%, Ni ≤ 4.5%, P ≤ 0.46%, S ≤ 0.005%, Mo ≤ 2.2%, Cr ≤ 4.5%, Mn ≤ 2.5%, Al ≤ 0.6%, C ≤ 0.21%, Nb ≤ 0.21%, Ti ≤ 0.21%, V ≤ 0.21%, B ≤ 0.002% and Cu ≥ 0.1%, the remainder being iron and unavoidable impurities, all contents are expressed as mass percent.

5. The method according to any one of paragraphs 1-4, in which the copper content in the liquid steel (1) is 0.1-0.3 wt.%.

6. The method according to any one of paragraphs 1-5, in which the reheating temperature T R is 1100-1350°C.

7. The method according to any one of paragraphs 1-6, further comprising a preliminary step of obtaining or calculating an estimated silicon content %Si est , present in liquid steel (1).

8. The method according to item 7, in which the set of coefficients σ(%Si opt ), ρ(%Si opt ) and β(%Si opt ), used to determine the optimized silicon content %Si opt , are selected from various sets of coefficients depending on the estimated silicon content %Si est in liquid steel.

9. The method according to claim 7 or 8, wherein, when the estimated silicon content in the liquid steel is %Si est is 0.004-0.38 mass percent, then σ(%Si opt ) = 9.96-6% Si opt + 1.8233e-8, ρ(%Si opt ) = - (2.364e-2·%Si opt + 4.518e-5), β(%Si opt ) = 14.1511% Si opt + 0.028104 and Δ=0.

03.

10. The method according to claim 7 or 8, wherein, when the estimated silicon content in the liquid steel is %Si estis 0.39 - 4.0 mass percent, then σ(%Si opt ) = -1.3157e-6%Si opt ² + 1.3656e-5%Si opt – 8.0137e-7, ρ(%Si opt ) = 3.1971e-3%Si opt ² - 3.2969e-2%Si opt + 2.0283e-3), β(%Si opt ) = -1.9492% Si opt ² + 20.04% Si opt - 1.2828 and Δ=0.

03.

11. The method according to claim 7 or 8, wherein, when the estimated silicon content in the liquid steel is %Si est is 4.1-6 wt.%, then σ(%Si opt ) = 5.8849E-6%Si opt ² - 6.3844E-5%Si opt + 1.9346E-4, ρ(%Si opt ) = -1.4669E-2%Si opt ² + 0.15942% Si opt -0.48037, β(%Si opt ) = 9.1268% Si opt ² - 99.283% Si opt + 297.99 and Δ=0.

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12. A method for hot rolling a steel semi-finished product (5), comprising the following stages: A. obtaining liquid steel (1), wherein said obtaining stage includes melting steel scrap containing copper, B. Estimation of silicon content %Si est in the resulting liquid steel, C. pouring liquid steel (1) to obtain a semi-finished product (5), D. reheating the semi-finished product (5) to the reheating temperature T R , E. hot rolling of reheated semi-finished product, in this case, between stages B and C the following stages are performed: i) determination of the optimized silicon content %Si opt in accordance with the method according to any of paragraphs 1-11, ii) adjusting the silicon content of liquid steel to achieve the calculated optimized silicon content %Si opt .

13. The method according to claim 12, wherein at the stage of obtaining Al, the scrap is melted with hot metal and / or direct reduced iron.

14. The method according to claim 12 or 13, wherein the semi-finished product is a slab.

15. The method according to any one of paragraphs 12-14, in which the determination of silicon content is carried out by analyzing samples in the form of a disk sample from the obtained liquid steel (1).

16. The method according to any one of paragraphs 12-14, in which the determination of silicon content is carried out using a model.