Method for hot rolling steel product

Abstract

The invention relates to a method for hot-rolling a semi-finished steel product, comprising the following steps: producing a molten steel, said production step comprising melting scrap steel comprising copper; estimating the amount% Cuest of copper, and optionally the amount% Sest of tin, the amount% Sest of antimony, and the amount% Sest of sulfur in the produced molten steel; casting the molten steel to produce a semi-finished product; the semi-finished product is reheated to a reheating temperature TR and the reheated semi-finished product is hot-rolled. The method further includes calculating optimized amounts of tin, antimony, and sulfur.

Description

Technical Field

[0001] This invention relates to a method for hot rolling steel products, wherein the steel is produced using scrap steel. Background Technology

[0002] Steelmaking requires ferrous materials such as scrap steel, direct reduced iron (DRI), or pig iron. Today, scrap steel is commonly used in the steelmaking process to produce molten steel. This scrap can be used at different stages of the steelmaking process and in various steelmaking tools. Converters, basic oxygen converters (BOF), electric arc furnaces (EAF), and smelting furnaces (SF) are some of the tools specifically suited for steelmaking production.

[0003] To reduce the global CO2 footprint of steelmaking processes, a global trend is towards the increasing use of scrap in steel production. However, this scrap can vary greatly, depending particularly on its source, and therefore exhibits different characteristics in terms of shape, density, chemical composition, and the presence of impurities. Scrap steel contains residual elements such as copper, chromium, molybdenum, nickel, tin, antimony, zinc, and / or arsenic. Therefore, the use of scrap steel is not widespread for all steel grades, as these residual elements can adversely affect the steel's properties.

[0004] When steel is produced using direct reduced iron and / or pig iron, small amounts of residual elements inevitably remain in the molten metal. When scrap steel is used, the amount of residual elements is far greater than that from pig iron or direct reduced iron from the blast furnace.

[0005] Recently, the inventors have observed that using large quantities of scrap steel in steel production can cause problems during certain manufacturing steps, such as hot rolling.

[0006] One of the most difficult impurities to remove from scrap steel during the steelmaking process is copper. Copper is more inert than iron, and when iron is oxidized at high temperatures, it accumulates at the steel-oxide interface. The resulting copper-rich liquid phase (also known as the copper phase) eventually penetrates into the steel along the austenite grain boundaries, weakening the bond and inducing surface cracking during hot working. This cracking phenomenon is known as hot brittleness. Summary of the Invention

[0007] Therefore, there is a need for methods to produce hot-rolled steel using scrap steel, in which the risk of hot brittleness is reduced or even suppressed.

[0008] i) This problem is solved by the method according to the invention, the method comprising the steps of: producing molten steel, the production step including melting copper-containing scrap steel; estimating the amount of copper (%Cu) in the produced molten steel. est ; Cast the molten steel to produce a semi-finished product; Reheat the semi-finished product to a reheating temperature T RThe reheated semi-finished product is hot-rolled, wherein between the estimation step and the casting step, the calculated and optimized amount of tin (%Sn) is performed. Opt Antimony content %Sb Opt And the amount of sulfur %S Opt The optimized quantity satisfies the equation in the following steps. ,in , , It represents tin, antimony, and sulfur according to the reheating temperature T. R The coefficients of their respective effects on the solubility of copper, and It represents the reheating temperature T. R The coefficients affecting the solubility of copper; and the final amounts of tin, antimony, and sulfur in the molten steel are adjusted to achieve the optimized amounts calculated for the molten steel.

[0009] The method of the present invention may also include the following optional features, either individually or according to all possible combinations of techniques:

[0010] - The produced molten steel contains at least 0.1% by weight of copper.

[0011] - In the production process, scrap is melted together with molten iron and / or direct reduced iron.

[0012] - The estimation steps include estimating the amount of tin (%Sn), antimony (%Sb), and sulfur (%S) in the produced molten steel.

[0013] The produced molten steel has the following composition, wherein %Sb ≤ 0.01%, %As ≤ 0.1%, %Sn ≤ 0.05%, %Si ≤ 0.9%, %Ni ≤ 4.5%, %P ≤ 0.46%, %S ≤ 0.008%, %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%, with the remainder being iron and unavoidable impurities. All quantities are expressed as a percentage by weight.

[0014] - The amount of copper in the molten steel is 0.1% to 0.3% by weight.

[0015] - Reheating temperature T R The temperature ranges from 1100°C to 1350°C.

[0016] - The semi-finished product is a slab.

[0017] - , , as well as .

[0018] - The estimation step also includes estimating the amount of carbon (%C). est Boron content %B est Aluminum content (%Al) est %V of vanadium est ,

[0019] - The calculation steps include calculating the optimized amount of carbon (%C). Opt Aluminum content (%Al) Opt Boron content %B Opt %V of vanadium Opt The optimized quantity satisfies the equation

[0020] in , , , , , , These are coefficients representing the effects of tin, carbon, antimony, sulfur, aluminum, vanadium, and boron on the solubility of copper according to reheating temperature, and... This is a coefficient representing the effect of reheating temperature on the solubility of copper.

[0021] - , , , , , , as well as

[0022] - The estimation step also includes estimating the amount of nickel (%Ni). est Molybdenum content (%) est Manganese content (%Mn) est % of silicon est Chromium content (%Cr) est Arsenic content (%As) est Phosphorus content %P est %Nb est And the amount of titanium %Ti est ,

[0023] - The calculation steps include calculating the optimized amount of tin %Sn Opt Nickel content (%) Opt Molybdenum content (%) Opt Manganese content (%Mn) Opt %C of carbon Opt Antimony content %Sb Opt %Si of silicon OptSulfur content %S Opt Chromium content (%Cr) Opt Aluminum content (%Al) Opt vanadium content %V Opt Arsenic content (%As) Opt Phosphorus content %P Opt %Nb Opt %Ti of titanium Opt Boron content %B Opt The optimized quantity satisfies the following equation:

[0024]

[0025] in , , , , , , , , , , , , , , , These are coefficients representing the effects of tin, nickel, molybdenum, manganese, carbon, antimony, silicon, sulfur, chromium, aluminum, vanadium, arsenic, phosphorus, niobium, titanium, and boron on the solubility of copper according to reheating temperature, and... It is a coefficient representing the effect of reheating temperature on the solubility of copper.

[0026] - , , , , , , , , , , , , , , , as well as ,

[0027] - In step B, the composition of the produced molten steel is estimated using a model.

[0028] - This model uses the composition of the raw materials melted to produce molten steel as input data, including scrap steel containing copper.

[0029] - The estimation of the composition of the molten steel is performed by analyzing a lollipop sample of the molten steel. Attached Figure Description

[0030] Other features and advantages of the invention will become apparent from the following description, which is exemplary and in no way limiting, with reference to the accompanying drawings, wherein:

[0031] - Figure 1 The facility for producing hot-rolled steel sheets is shown.

[0032] The elements in the accompanying drawings are schematic and may not be drawn to scale. Detailed Implementation

[0033] Figure 1 A facility for producing hot-rolled steel products is shown. Molten steel 1, contained in ladle 2, is poured into tundish 3, which then allows the molten steel to flow through a nozzle into a crystallizer. The molten steel begins to solidify along continuous casting machine 4 until it is completely solidified and cut to form semi-finished product 5. The semi-finished product 5 is typically cooled at ambient temperature and stored in a slab warehouse before being sent to hot rolling mill 6. Hot rolling mill 6 includes a reheating furnace 7, in which the semi-finished product 5 is reheated and then transferred to mill 8, where the semi-finished product is rolled and converted into steel product, which is then coiled to form hot-rolled steel coil 9.

[0034] Figure 1 An embodiment of a facility for producing hot-rolled steel sheets is shown, but the method according to the invention can be performed in other facilities that allow molten steel to be transformed into semi-finished products such as billets, slabs, bars, ingots, slabs or large billets, and to transform such semi-finished products into steel products 9 in a hot rolling mill 6, which includes a reheating furnace 7 suitable for reheating the semi-finished products 5.

[0035] In another embodiment of the facility for producing hot-rolled steel products (not shown here), the semi-finished product 5 after casting is directly fed to a hot rolling mill, where it undergoes a heating step before being rolled. This heating step can be performed in a tunnel furnace. This facility is referred to as a continuous facility or a direct casting and rolling facility.

[0036] In the method according to the invention, the production of molten steel 1 includes melting copper-containing scrap steel. Different production routes can be used; the scrap can optionally be melted in an electric arc furnace (EAF) together with pig iron and direct reduced iron (DRI) to obtain molten steel, which undergoes refining steps before being poured into a tundish. Alternatively, the scrap can be melted in a smelting furnace (SF) together with pig iron and / or DRI, and the resulting molten metal is sent to a converter or BOF for decarburization and conversion into molten steel. This molten steel can then undergo refining steps such as dephosphorization and / or desulfurization steps and / or secondary metallurgical steps. The scrap can also be charged into a BOF.

[0037] For example, usable scrap steel is referred to as old scrap (E1 or E3), new scrap (E8), shredded scrap 20 (E40), or fragmented scrap (E46) in the EU-21 scrap steel specification.

[0038] In the method according to the invention, estimating the composition of the produced molten steel includes estimating the amount of copper (%Cu). est And the preferred amount of tin (%Sn) est Antimony content %Sb est And the amount of sulfur %S est In a preferred embodiment, the estimation also includes estimating the amount of carbon (%C). est Boron content %B est Aluminum content (%Al) est %V of vanadium est In the most preferred embodiment, the estimate further includes estimating the amount of nickel (%Ni). est Molybdenum content (%) est Manganese content (%Mn) est Chromium content (%Cr) est %Si of silicon est Arsenic content (%As) est Phosphorus content %P est %Nb est And the amount of titanium %Ti est All percentages are expressed as weight percentages.

[0039] The steel composition of the molten steel can be estimated at the end of the refining step and before the casting step. The estimation of the steel composition is preferably performed by analyzing a lollipop sample from a hot metal ladle 2 used to fill the casting tundish 3 or ingot mold to obtain a semi-finished product. This estimation can also be performed using a model.

[0040] Preferably, in step A of producing molten steel, 100 kg to 1000 kg of scrap steel is used per ton of molten iron. Preferably, in step A, 100 kg to 950 kg of scrap steel is used per ton of molten iron. Preferably, in step A, 100 kg to 900 kg of scrap steel is used per ton of molten iron. Preferably, in step A, 100 kg to 800 kg of scrap steel is used per ton of molten iron. Preferably, in step A, 100 kg to 600 kg of scrap steel is used per ton of molten iron. Preferably, in step A, 100 kg to 500 kg of scrap steel is used per ton of molten iron. Even more preferably, in step A, 200 kg to 400 kg of scrap steel is used per ton of molten iron.

[0041] In this patent, residual elements are undesirable elements derived from scrap steel. Unavoidable impurities arise from the refining process, such as oxides and nitrides.

[0042] After refining, the molten steel is poured into a tundish 3 and then cast in a continuous casting machine 4 to produce a semi-finished product 5. As previously mentioned, this semi-finished product 5 is typically cooled at ambient temperature and stored in a warehouse before being sent to a hot rolling mill 6. The semi-finished product 5 is then sent to a reheat furnace 7.

[0043] Due to the use of copper-containing scrap, a copper-rich phase exists on the surface of the semi-finished product. Copper-rich, or copper phase, refers to a phase containing more than 75% copper by weight, with the remainder mainly consisting of iron and other alloying elements and residual elements present in the molten steel. It is this copper-rich phase that diffuses into the steel along the austenite grain boundaries and causes hot brittleness problems.

[0044] Typically, the semi-finished product to be rolled is charged at the inlet of reheating furnace 7, where it is advanced forward on the furnace bed by means of a pusher. The semi-finished product is usually preheated, heated, and homogenized as it passes through the preheating zone, heating zone, and homogenizing zone of the reheating furnace. At the end of the homogenizing zone, the semi-finished product is discharged from the furnace by an ejector for subsequent rolling in a rolling mill. The temperature T of the semi-finished product upon discharge is... R Depending on several factors, and it can vary in the range of 1100°C to 1350°C. The reheating furnace 7 is preferably a continuous reheating furnace, such as a pusher furnace, a walking beam furnace, or a walking beam furnace.

[0045] If the production facility is a continuous facility or a direct casting and rolling facility, then the reheating temperature T R This must be understood as the temperature of the semi-finished product 5 at the outlet of the heating step before rolling.

[0046] In the method according to the invention, the optimized amount of tin (%Sn) is calculated before casting. Opt Antimony content %Sb opt And the amount of sulfur %S opt To satisfy the following equation:

[0047] (Formula 1)

[0048] in , , These are coefficients representing the effects of tin, antimony, and sulfur on the solubility of copper according to reheating temperature, and... It is a coefficient representing the effect of reheating temperature on the solubility of copper.

[0049] "Equal to" means equal to + / - 10%, or even + / - 5% or even + / - 2%.

[0050] In another embodiment of the method according to the invention, the optimized amount of tin %Sn is calculated. Opt %C of carbon Opt Antimony content %Sb Opt Sulfur content %S Opt Aluminum content (%Al) Opt vanadium content %V Opt and the amount of boron %B opt To satisfy the following equation:

[0051] (Formula 2)

[0052]

[0053] in , , , , , , It is a coefficient representing the effect of tin, carbon, antimony, sulfur, aluminum, vanadium, and boron on the solubility of copper according to reheating temperature.

[0054] as well as It is a coefficient representing the effect of reheating temperature on the solubility of copper.

[0055] In another embodiment of the method according to the invention, the optimized amount of tin %Sn is calculated. Opt Nickel content (%) Opt Molybdenum content (%) Opt Manganese content (%Mn) Opt %C of carbon Opt Antimony content %Sb Opt %Si of silicon Opt Sulfur content %S Opt Chromium content (%Cr) Opt Aluminum content (%Al) Opt vanadium content %V Opt Arsenic content (%As)Opt Phosphorus content %P Opt %Nb Opt %Ti of titanium Opt and the amount of boron %B Opt To satisfy the following equation,

[0056] (Formula 3)

[0057]

[0058] in , , , , , , , , , , , , , , , It is a coefficient representing the effect of tin, nickel, molybdenum, manganese, carbon, antimony, silicon, sulfur, chromium, aluminum, vanadium, arsenic, phosphorus, niobium, titanium, and boron on the solubility of copper according to reheating temperature.

[0059] as well as It is a coefficient representing the effect of reheating temperature on the solubility of copper.

[0060] Examples of coefficients for each formula are given in Table 1 below. Throughout the text, the symbol “E” must be understood as “×10”. n For example, 9.96E-6 must be understood as 9.96 × 10 -6 Or 0.00000996.

[0061]

[0062] Table 1

[0063] These coefficients are given by way of example and have been determined using Thermocalc® software with the Ssol4 database for antimony and arsenic and TCFe12 for other elements, based on the compositional ranges defined below. Of course, other software and / or other compositions may be used, which would result in slight modifications to the coefficients.

[0064] After calculating those optimized quantities, the composition of the molten steel is adjusted accordingly, and then the molten steel with the adjusted composition is cast to produce a semi-finished product.

[0065] This compositional adjustment can be accomplished by removing or adding tin, antimony, and / or sulfur, or by maintaining appropriate amounts of one or more of these species if these species are already present in calculated optimized quantities. Addition can be accomplished by charging material (preferably in wire form) into the molten metal. Removal can be accomplished using suitable techniques known to those skilled in the art. For example, iron can be added to the molten pool in the form of molten iron, pig iron, or direct reduced iron to dilute other components of the molten steel. Sulfur can be removed by adding limestone or other Ca-containing materials. The composition of the slag can also be altered to capture tin and / or antimony. Other processes can also be used, such as NH3 injection for tin removal.

[0066] The produced molten steel preferably has the following composition, wherein %Sb ≤ 0.01%, %As ≤ 0.1%, %Sn ≤ 0.05%, %Si ≤ 0.9%, %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%, with the remainder being iron and unavoidable impurities. All amounts are expressed as a percentage by weight. The amount of copper is preferably from 0.1% to 0.3% by weight.

[0067] In the method of the present invention, the composition of the molten steel is adjusted such that the copper content at the steel surface is below the copper solubility limit, thereby preventing or at least limiting copper from penetrating into the steel along the austenite grain boundaries and causing hot brittleness.

[0068] The tests were performed using three steel samples S1 to S2 with compositions defined as shown in Table 2, the remainder being iron and unavoidable impurities. The solid samples were heated at a temperature of 1235°C. R The steel was subjected to a heating step to simulate the reheating process of industrial equipment, and microscopic observation was used to determine whether infiltration was present in the steel body. The results are also included in Table 2.

[0069] N indicates that no penetration was observed, while Y indicates that copper-rich phase penetration was observed in the steel matrix.

[0070] Then, according to the present invention, the optimized amounts of tin, sulfur, and antimony are calculated using Formula 1 and the coefficients shown in Table 1. The composition of the molten steel is then adjusted and new samples named S1bis and S2bis are cast, respectively, and the new samples are subjected to the same heating steps and observations as previously described.

[0071]

[0072] Table 2

[0073] It can be observed that permeation was observed for samples S1 and S2 that were not produced according to the invention, while no permeation was observed for samples S1bis and S2bis that had been calculated and implemented with optimized composition and thus produced using the method according to the invention.

Claims

1. A method for hot rolling a steel semi-finished product, comprising the following steps: A. Producing molten steel (1), the production step comprising melting copper-containing scrap steel, B. Estimate the amount of copper (%Cu) in the produced molten steel (1). est , C. Cast the molten steel (1) to produce a semi-finished product (5). D. Reheat the semi-finished product (5) to the reheating temperature T. R , E. Hot rolling of the reheated semi-finished product. Between steps B and C, the following steps are performed: ii) Calculate the optimized amount of tin %Sn Opt Antimony content %Sb opt And the amount of sulfur %S opt The optimized quantity satisfies the following equation: in , , It represents tin, antimony, and sulfur according to the reheating temperature T. R The coefficients representing the effects of each factor on the solubility of copper. as well as This represents the reheating temperature T. R The coefficient of influence on the solubility of copper. iii) Adjust the final amounts of tin, antimony and sulfur in the molten steel so that the molten steel matches the calculated optimized amounts.

2. The method according to claim 1, wherein the produced molten steel (1) contains at least 0.1% by weight of copper.

3. The method according to any one of claims 1 or 2, wherein step B further comprises estimating the amount of tin (%Sn) in the produced molten steel (1). est Antimony content %Sb est And the amount of sulfur %S est .

4. The method according to any one of claims 1 to 3, wherein in the production step A, the scrap is melted together with molten iron and / or direct reduced iron.

5. The method according to any one of claims 1 to 4, wherein the produced molten steel has the following composition, wherein %Sb ≤ 0.01%, %As ≤ 0.1%, %Sn ≤ 0.05%, %Si ≤ 0.9%, %Ni ≤ 4.5%, %P ≤ 0.46%, %S ≤ 0.008%, %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%, with the remainder being iron and unavoidable impurities, all amounts expressed as weight percentages.

6. The method according to any one of claims 1 to 5, wherein the amount of copper in the molten steel is from 0.1% to 0.3% by weight.

7. The method according to any one of claims 1 to 6, wherein the reheating temperature T R The temperature ranges from 1100°C to 1350°C.

8. The method according to any one of claims 1 to 7, wherein the semi-finished product is a slab.

9. The method according to any one of claims 1 to 8, wherein , , as well as .

10. The method according to any one of claims 1 to 9, wherein the calculation step Ei) comprises calculating the optimized amount of carbon %C. Opt Aluminum content (%Al) Opt Boron content %B Opt %V of vanadium Opt The optimized quantity satisfies the following equation: in , , , , , , These are coefficients representing the effects of tin, carbon, antimony, sulfur, aluminum, vanadium, and boron on the solubility of copper according to the reheating temperature. as well as It is a coefficient representing the effect of the reheating temperature on the solubility of copper.

11. The method of claim 10, wherein the estimation step B further comprises estimating the amount of carbon %C. est Boron content %B est Aluminum content (%Al) est %V of vanadium est .

12. The method according to claim 10 or 11, wherein , , , , , , as well as .

13. The method according to any one of claims 10 to 12, wherein the calculation step Ei) comprises calculating the optimized amount of tin %Sn Opt Nickel content (%) Opt Molybdenum content (%) Opt Manganese content (%Mn) Opt %C of carbon Opt Antimony content %Sb Opt %Si of silicon Opt Sulfur content %S Opt Chromium content (%Cr) Opt Aluminum content (%Al) Opt vanadium content %V Opt Arsenic content (%As) Opt Phosphorus content %P Opt %Nb Opt %Ti of titanium Opt Boron content %B Opt The optimized quantity satisfies the following equation: in , , , , , , , , , , , , , , , These are coefficients representing the effects of tin, nickel, molybdenum, manganese, carbon, antimony, silicon, sulfur, chromium, aluminum, vanadium, arsenic, phosphorus, niobium, titanium, and boron on the solubility of copper according to the reheating temperature. as well as It is a coefficient representing the effect of the reheating temperature on the solubility of copper.

14. The method of claim 13, wherein the estimation step B further comprises estimating the amount of nickel (%Ni). est Molybdenum content (%) est Manganese content (%Mn) est %Si of silicon est Chromium content (%Cr) est Arsenic content (%As) est Phosphorus content %P est %Nb est And the amount of titanium %Ti est .

15. The method according to claim 13 or 14, wherein , , , , , , , , , , , , , , , as well as .

16. The method according to any one of claims 1 to 15, wherein, In step B, the composition of the produced molten steel (1) is estimated using a model.

17. The method of claim 16, wherein the model uses the composition of the raw materials melted for the production of the molten steel (1) as input data, the raw materials including scrap steel containing copper.

18. The method according to any one of claims 1 to 15, wherein the estimation of the composition of the molten steel is performed by analyzing a lollipop sample of the molten steel (1).

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