Method for hot rolling steel product

Abstract

A method for hot rolling a semi-finished steel product, comprising: estimating the composition of a molten steel to be cast, said molten steel being produced using copper-containing scrap; and calculating a melting temperature of a copper phase formed on the semi-finished product during casting to reheat the semi-finished product at the optimized reheating temperature.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for hot rolling a steel product, wherein the steel is produced using scrap. BACKGROUND

[0002] Steelmaking requires the use of ferrous materials, such as scrap, direct reduced iron (DRI) or pig iron. Today, scrap is commonly used in steelmaking processes for producing liquid steel. The scrap can be used at different stages of the steelmaking process and in different steelmaking tools. The converter, the basic oxygen furnace (BOF), the electric arc furnace (EAF), the smelting furnace (SF) are some tools that can be particularly used for steelmaking production.

[0003] In order to reduce the CO2 global footprint of the steelmaking process, there is a global trend to use more and more scrap in steel production. However, the scrap can have different types, in particular depending on its origin, and thus different characteristics in terms of shape, density, chemical composition and presence of impurities. Scrap contains residual elements, such as copper, chromium, molybdenum, nickel, tin, antimony, zinc and / or arsenic. Therefore, the use of scrap is not widely used for all steel grades, as these residual elements can have a detrimental effect on the properties of the steel.

[0004] When producing steel using direct reduced iron and / or pig iron, a small amount of residual elements inevitably remains in the molten metal. When using scrap, the amount of residual elements is much greater than in the case of pig iron or direct reduced iron from a blast furnace.

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

[0006] One of the impurities contained in scrap that is difficult to remove in the steelmaking process is copper. Copper is more noble than iron and it is enriched at the steel-oxide interface when iron is oxidized at high temperature. The copper-rich liquid phase thus formed, also called copper phase, eventually penetrates into the steel along the austenite grain boundaries, weakening the cohesion and inducing surface cracking during hot working. This cracking phenomenon is called hot shortness. SUMMARY

[0007] Therefore, there is a need for a method for producing hot rolled steel using scrap, wherein the risk of hot shortness is reduced and even suppressed.

[0008] This problem is solved by the method according to the invention, comprising the steps of: producing a liquid steel, comprising melting scrap containing copper; estimating the composition of the produced liquid steel, said estimation comprising the content of antimony, tin and sulfur; casting the produced liquid steel to produce a semi-finished product (5), the cast semi-finished product containing a copper phase; defining a reheating temperature of the semi-finished product ; calculating the melting temperature of the copper phase according to the following formula : where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, and %S is the weight percentage of sulfur, all as estimated in step B, where , , and are coefficients representative of the effect of antimony, tin, sulfur and remaining elements, respectively, on the melting temperature of the copper phase; if then calculating so that ; reheating the semi-finished product to an optimized reheating temperature ; and hot rolling the semi-finished product.

[0009] The method of the present application can also comprise the following optional features, taken individually or according to all possible combinations of techniques:

[0010] - the produced liquid steel comprises at least 0.1 wt% of copper,

[0011] - the produced liquid steel comprises from 0.1 wt% to 0.3 wt% of copper,

[0012] - in step B, the composition of the produced liquid steel is estimated using a model,

[0013] - the model uses as input data the composition of the raw materials melted in order to produce the liquid steel, the raw materials comprising scrap steel comprising copper,

[0014] - the estimation of the liquid steel composition is performed by analyzing a lollipop sample of said liquid steel,

[0015] - the production step comprises melting scrap together with molten iron and / or direct reduced iron,

[0016] - the semi-finished product is a slab,

[0017] - the produced liquid steel has the following composition, where %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%, the remainder being iron and unavoidable impurities, all amounts being expressed in weight percentage,

[0018] - , , and ,

[0019] The steps for estimating the composition of molten steel also include estimating the amounts of phosphorus, manganese, aluminum, arsenic, and boron, as well as the melting temperature. Calculate using the following formula: Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %As is the weight percentage of arsenic, and %B is the weight percentage of boron, all as estimated. , , , , , , , and It is a coefficient representing the influence of antimony, tin, nickel, phosphorus, sulfur, chromium, manganese, aluminum, silicon, arsenic and other elements on the melting temperature of the copper phase.

[0020] - , , , , , , , as well as ,

[0021] The steps for estimating the composition of molten steel also include estimating the amounts of silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium, and boron, as well as the melting temperature. Calculate using the following formula: Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %Ni is the weight percentage of nickel, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Cr is the weight percentage of chromium, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %Si is the weight percentage of silicon, %As is the weight percentage of arsenic, %Mo is the weight percentage of molybdenum, %C is the weight percentage of carbon, %Nb is the weight percentage of niobium, %Ti is the weight percentage of titanium, %V is the weight percentage of vanadium, and %B is the weight percentage of boron, all as estimated in step B. , , , , , , , , , , , , , , , and It is a coefficient representing the influence of antimony, tin, nickel, phosphorus, sulfur, chromium, manganese, aluminum, silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium, boron and other elements on the melting temperature of the copper phase.

[0022] - , , , , , , , , , , , , , , , as well as . Attached Figure Description

[0023] 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:

[0024] - Figure 1 The facility for producing hot-rolled steel sheets is shown.

[0025] The elements in the accompanying drawings are schematic and may not be drawn to scale. Detailed Implementation

[0026] 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. 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 convert 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] In the method according to the invention, the composition of the produced molten steel is estimated, including the contents of antimony, tin and sulfur.

[0031] The steel composition of molten steel 1 can be estimated at the end of the smelting step and before the casting step begins. 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.

[0032] 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.

[0033] In this patent, residual elements are undesirable elements derived from scrap steel. Unavoidable impurities arise from the refining process, such as oxides and nitrides.

[0034] 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 reheating furnace 7.

[0035] Due to the use of copper-containing scrap, a copper phase is present on the surface of the semi-finished product. The copper phase refers to a phase containing more than 75% copper by weight, with the remainder primarily consisting of iron and other alloying elements and residual elements present in the molten steel. It is this copper phase that diffuses into the steel along the austenite grain boundaries and causes hot brittleness.

[0036] Typically, the semi-finished product to be rolled is charged at the inlet of reheating furnace 7, in which 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. Reheating furnace 7 is preferably a continuous reheating furnace, such as a pusher furnace, walking beam furnace, or walking beam furnace.

[0037] In the method according to the present invention, the temperature of the semi-finished product at the outlet of the reheating furnace is first defined according to the prior art, also known as the reheating temperature. In particular, considering the chemical composition, metallurgical constraints and / or rolling process requirements of semi-finished product 5, which depend on rolling speed, semi-finished product size, steel composition and heat loss.

[0038] 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.

[0039] Then, the melting temperature of the copper phase is calculated according to the following formula (1). :

[0040] (Formula 1) ,

[0041] Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, and %S is the weight percentage of sulfur, all as estimated in step B, and , , and These are coefficients representing the effects of antimony, tin, sulfur, and the remaining elements on the melting temperature of the copper phase. Indeed, the inventors have discovered that tin, antimony, and sulfur are the elements that have the greatest influence on the melting temperature of the copper phase by increasing or decreasing it.

[0042] "Equal to" means equal to + / - 10%, or even + / - 5% or even + / - 2%.

[0043] In another embodiment of the method according to the invention, in step B, the amounts of phosphorus (%P), manganese (%Mn), aluminum (%Al), boron (%B), and arsenic (%As) are further estimated, and the melting temperature of the copper phase is calculated according to the following formula (2). :

[0044] (Formula 2) ,

[0045] Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %B is the weight percentage of boron, and %As is the weight percentage of arsenic, all as estimated in step B. , , , , , , , and It is a coefficient representing the influence of antimony, tin, phosphorus, sulfur, manganese, aluminum, arsenic, boron and other elements on the melting temperature of the copper phase.

[0046] In another embodiment of the method according to the invention, in step B, the amounts of silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium and boron are further estimated, and the melting temperature of the copper phase is calculated according to the following formula (3). :

[0047] (Formula 3)

[0048] ,

[0049] Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %Ni is the weight percentage of nickel, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Cr is the weight percentage of chromium, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %Si is the weight percentage of silicon, %As is the weight percentage of arsenic, %Mo is the weight percentage of molybdenum, %C is the weight percentage of carbon, %Nb is the weight percentage of niobium, %Ti is the weight percentage of titanium, %V is the weight percentage of vanadium, and %B is the weight percentage of boron, all as estimated in step B. , , , , , , , , , , , , , , , and It is a coefficient representing the influence of antimony, tin, nickel, phosphorus, sulfur, chromium, manganese, aluminum, silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium, boron and other elements on the melting temperature of the copper phase.

[0050] Then the predefined reheat temperature With the calculated melting temperature of copper Compare, and if the predefined reheat temperature Greater than or equal to the melting temperature of copper Then calculate the offset temperature. Make The offset temperature is calculated taking into account the sensitivity of temperature control in the reheating furnace. The sensitivity depends on the technology of the reheating furnace; some furnaces have a sensitivity of a few degrees, while others have a sensitivity control of about 10°C.

[0051] Finally, the semi-finished product 5 is reheated to the optimized reheating temperature. And then it was hot-rolled.

[0052] If the optimized reheating temperature is obtained in this way If the temperature is too low to meet the target of the hot rolling step, some compensation can be performed to provide additional heat outside the reheating furnace, such as by using induction heating devices, and / or adjusting the hot rolling process parameters. For example, if the distance between the reheating furnace outlet and the mill inlet is too long, the semi-finished product may no longer have the required temperature by the time it reaches the first rolling pass, and additional short-term heating may be required.

[0053] Examples of coefficients for each formula are given in Table 1 below.

[0054]

[0055] Table 1

[0056] These coefficients are given by way of example and have been determined using Thermocalc® software, along with the Ssol4 database for antimony and arsenic and the TCFe12 database for other elements, based on a composition range in which the produced molten steel has the following composition, wherein %Sb is less than or equal to 0.01%, %As is less than or equal to 0.1%, %Sn is less than or equal to 0.05%, %Si is less than or equal to 0.9%, %Ni is less than or equal to 4.5%, %P is less than or equal to 0.46%, %S is less than or equal to 0.005%, %Mo is less than or equal to 2.2%, %Cr is less than or equal to 4.5%, %Mn is less than or equal to 2.5%, %Al is less than or equal to 0.6%, %C is less than or equal to 0.21%, %Nb is less than or equal to 0.21%, %Ti is less than or equal to 0.21%, %V is less than or equal to 0.21%, and %B is less than or equal to 0.002%, with the remainder being iron and unavoidable impurities. All amounts are expressed as a percentage by weight.

[0057] Of course, other software and / or other components can be used, which will result in slight modifications to the coefficients.

[0058] The tests were performed using two steel samples, S1 and S2, with compositions defined as shown in Table 2, the remainder being iron and unavoidable impurities. Those solid samples were reheated at a predefined temperature of 1235°C. 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.

[0059] According to the present invention, the melting temperature of the copper phase The calculation is performed according to Formula 1, and the results are shown in Table 2.

[0060] Samples S1bis and S2bis, which have compositions similar to those of samples S1 and S2 respectively, are then subjected to an optimized reheating temperature. 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.

[0061] N means no penetration was observed, while Y means that copper phase penetration was observed in the steel matrix.

[0062]

[0063] Table 2

[0064] In the method of the present invention, reheating is performed at a temperature below the melting temperature of the copper phase, thereby preventing or at least limiting the penetration of the copper phase into the steel along the austenite grain boundaries and causing hot brittleness.

Claims

1. A method for hot rolling a steel semi-finished product (5), comprising the following steps: A. Producing molten steel (1), the production step comprising melting copper-containing scrap steel, B. Estimate the composition of the produced molten steel (1), the estimation including the content of antimony, tin, and sulfur. C. The produced molten steel (1) is cast to produce a semi-finished product (5), the cast semi-finished product containing a copper phase. D. Limiting the reheating temperature of the semi-finished product. , E. Calculate the melting temperature of the copper phase using the following formula. : ， Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, and %S is the weight percentage of sulfur, all of which are estimated in step B. in , , and These are coefficients representing the effects of antimony, tin, sulfur, and the remaining elements on the melting temperature of the copper phase. F. If Then calculate Make , G. Reheat the semi-finished product (5) to the optimized reheating temperature. , H. The semi-finished product is hot-rolled.

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 claim 2, wherein the produced molten steel (1) contains 0.1% to 0.3% by weight of copper.

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 semi-finished product (5) is a slab.

6. The method according to any one of claims 1 to 8, wherein the produced molten steel (1) 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 the remainder is iron and unavoidable impurities, all amounts expressed as weight percentages.

7. The method of claim 6, wherein , , as well as .

8. The method according to any one of claims 1 to 7, wherein step B, which estimates the composition of the molten steel, further includes estimating the amounts of phosphorus, manganese, aluminum, arsenic, and boron, and the melting temperature. Calculate using the following formula: ， Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %As is the weight percentage of arsenic, and %B is the weight percentage of boron, all of which are estimated in step B. , , , , , , , and It is a coefficient representing the influence of antimony, tin, nickel, phosphorus, sulfur, chromium, manganese, aluminum, silicon, arsenic and other elements on the melting temperature of the copper phase.

9. The method according to claim 8, wherein , , , , , , , as well as .

10. The method according to any one of claims 1 to 6, wherein step B, which estimates the composition of the molten steel, further includes estimating the amounts of silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium, and boron, as well as the melting temperature. Calculate using the following formula: Where %Sb is the weight percentage of antimony, %Sn is the weight percentage of tin, %Ni is the weight percentage of nickel, %P is the weight percentage of phosphorus, %S is the weight percentage of sulfur, %Cr is the weight percentage of chromium, %Mn is the weight percentage of manganese, %Al is the weight percentage of aluminum, %Si is the weight percentage of silicon, %As is the weight percentage of arsenic, %Mo is the weight percentage of molybdenum, %C is the weight percentage of carbon, %Nb is the weight percentage of niobium, %Ti is the weight percentage of titanium, %V is the weight percentage of vanadium, and %B is the weight percentage of boron, all of which are estimated in step B. , , , , , , , , , , , , , , , and It is a coefficient representing the influence of antimony, tin, nickel, phosphorus, sulfur, chromium, manganese, aluminum, silicon, arsenic, molybdenum, carbon, niobium, titanium, vanadium, boron and other elements on the melting temperature of the copper phase.

11. The method of claim 10, wherein , , , , , , , , , , , , , , , as well as .

12. The method according to any one of claims 1 to 11, wherein in step B, the estimation of the composition of the produced molten steel (1) is performed using a model.

13. The method of claim 11, 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.

14. The method according to any one of claims 1 to 13, 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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