Hot rolling with residual elements

Abstract

A method of manufacturing a hot-rolled steel product having the following composition in percentage by weight: 0.002 < = C < = 0.8, 0.1 < = Mn < = 12.0, Si < = 2, Al < = 2, Cr < = 0.5, Nb < = 0.08, Ti < = 0.1, and the balance consisting of Fe, residual elements and unavoidable impurities, the method comprising the steps of i. Obtaining an initial target composition having a manganese content Mnt, i, ii. Melting scrap steel comprising the residual elements, the present invention relates to a method for producing a hot-rolled semi-finished product comprising the steps of: i. Providing a hot-rolled semi-finished product, iii. Estimating a content Mn0, Mo0, Sn0, Sb0 or As0, iv. Determining an adjusted target composition having an adjusted manganese content Mnt, a, where Mnt, a = Mnt, i-MnRES, where the adjustment terms MnRES combine correction terms relating to residual elements, v. Adding elements to the molten steel such that Mn0 + Mn addition = Mnt, a, where Mn addition represents the content of added manganese, vi. Casting the semi-finished product, vii. Hot-rolling the semi-finished product.

Description

Field of the Invention

[0001] The present invention relates to a method for processing steel to be hot-rolled, wherein the steel is processed using scrap steel. Background Art

[0002] Steelmaking requires the use of iron-containing materials such as scrap steel, direct reduced iron or pig iron. To reduce the carbon footprint of the steel industry, the use of scrap steel is considered crucial. However, scrap steel contains residual elements such as copper, chromium, molybdenum, nickel, tin, antimony, zinc and / or arsenic. Therefore, the use of scrap steel has not been widely extended to all steel grades because those residual elements may have an adverse effect on steel properties.

[0003] During the steel processing by direct reduced iron and / or pig iron, a small amount of residual elements inevitably remain in the molten steel. When using scrap steel, the amount of residual elements is much larger compared to pig iron or direct reduced iron from the blast furnace.

[0004] Recently, the present inventors have observed that producing steel using a significant amount of scrap steel causes problems during some manufacturing steps such as hot rolling. Summary of the Invention

[0005] Therefore, the object of the present invention is to improve the hot rolling processability of semi-finished steel products made at least in part from scrap steel containing the following residual elements: molybdenum, tin, antimony, arsenic. This is achieved by a method according to any one of claims 1 to 8. Detailed Description

[0006] The present invention relates to a method for manufacturing a hot-rolled steel product having the following composition by weight percentage: 0.002 ≤ C ≤ 0.8, 0.1 ≤ Mn ≤ 12.0, Si ≤ 2, Al ≤ 2, Cr ≤ 0.5, Nb ≤ 0.08, Ti ≤ 0.1, and the balance consisting of Fe, one or more residual elements and inevitable impurities, wherein the one or more residual elements include one or more of Mo, Sn, Sb, As, and wherein the method comprises the following steps:

[0007] i. Obtaining an initial target composition with a specified initial target content Mn of manganese t,i thereof,

[0008] ii. Melting scrap steel containing at least one of the one or more residual elements and optionally hot metal and / or direct reduced iron to form a steel melt,

[0009] iii. Estimating an estimated content Mn0 of manganese in the steel produced in step ii, and for each of the one or more residual elements: estimating an estimated residual content Mo0, Sn0, Sb0 or As0 of the steel melt produced in step ii.

[0010] iv. Determine the adjusted target content of the specified manganese, Mn t,a of the adjusted target composition, where Mn t,a = Mn t,I - Mn RES , where the adjustment term Mn RES combines one or more correction terms respectively related to one or more residual elements. The higher the estimated residual content of the considered residual element, the higher the correction term, and each correction term is at least equal to the estimated residual content Mo0, Sn0, Sb0 or As0 of the considered residual element.

[0011] v. Add elements to the molten steel such that Mn0 + Mn 添加 = Mn t,a , where Mn 添加 represents the content of the added manganese.

[0012] vi. Cast a semi-finished product with the molten steel.

[0013] vii. Hot-roll the semi-finished product.

[0014] Hot rolling allows reducing the thickness of the slab to obtain the desired geometry. This will require a person skilled in the art to determine the optimal rolling mode (i.e., the number of rolling passes, the rolling reduction) while considering metallurgical constraints (i.e., the steel temperature) and equipment constraints (i.e., the couple, speed, force, applicable stress).

[0015] Therefore, these parameters allow establishing a preset for the rolling mill stand for each rolling pass. For example, the reduction ratio applied at each rolling mill stand that applies an average flow stress to the product can be defined. The average flow stress is equal to the area under the stress-strain curve from strain ε α to strain ε β .

[0016] However, in the prior art, when establishing the rolling mode and thus the preset, the content of the residual elements from the scrap steel is not considered.

[0017] Furthermore, it has unexpectedly been found that since the theoretical stress-strain curve is defined without considering specific residual elements (i.e., Mo, Sn, Sb, and As) from the scrap steel, the presence of these residual elements causes a deviation from the theoretical stress-strain curve. This deviation results in a change in the average flow stress generated by the necessary deformation applied during hot rolling to achieve the target reduction ratio.

[0018] Since all hot rolling parameters are defined using suitable presets, when applying the target reduction ratio during the hot rolling of steel processed from scrap steel containing these residual elements, the applied average flow stress deviates from the theoretical average flow stress to achieve the target strain rate.

[0019] Since the actual stress applied through the hot rolling mill is higher than the expected stress and may exceed the maximum stress allowed for the rolling cylinder, such deviation may cause workability problems and may lead to accelerated deterioration of the roll.

[0020] To counteract this unexpected effect of the residual elements, the present inventors propose to adjust the composition of the final product by defining an equivalent content of manganese Mn RES which has the same effect on the increase in the average flow stress generated by the deformation applied during the hot rolling passes as the content of the residual elements. Preferably, during the last pass of the hot rolling. Mn RES is an adjustment term that combines one or more correction terms respectively related to the residual elements. RES

[0021] Therefore, taking into account the effect of the residues, the manganese content added during the composition adjustment and thus the manganese content in the final product is lower due to the equivalent content of manganese Mn RES

[0022] It allows to counteract the deviation of the average flow stress generated by the deformation applied during hot rolling due to the presence of the residual elements. In other words, it allows to obtain a steel having a regulated manganese content and having residues, which has the same average flow stress as a steel having an initial manganese content and no residues. The initial manganese content is the content designed by a person skilled in the art to obtain the desired properties of the steel (assuming that the residues have no effect on said properties). The desired properties are the properties in use, such as mechanical properties or surface properties.

[0023] The present invention allows to improve the workability of the steel by acting on its composition rather than on the hot rolling process parameters. However, due to the presence of the residual elements, the object of the present invention can be combined with the modification of the hot rolling process parameters (such as the hot rolling temperature). Since the steel is more ductile as the temperature increases, increasing the hot rolling temperature can improve the workability of the steel without changing the composition too much.

[0024] The composition by weight percentage is the composition of the hot rolled steel product, where Mn t,a = Mn0 + Mn 添加 = Mn t,i - Mn RES

[0025] Mn t,a is the regulated target content of manganese, which represents the actual manganese content in the final product.

[0026] Mn t,i ​​​Mn0 is the initial target content of manganese, which represents the theoretical manganese content designed by a person skilled in the art to obtain the desired properties of the steel without considering the influence of residues or assuming the absence of residues.

[0027] Mn0 is the content of manganese produced in step ii., during which scrap steel containing at least one of the residual elements and optionally hot iron and / or direct reduced iron are used to form a molten steel.

[0028] Mn RES Mn is an adjustment term, which represents the equivalent content of manganese that has the same effect on the increase in the average flow stress generated by the deformation applied during the hot rolling pass as the content of the residual element.

[0029] Mn 添加 Mn is the content of molybdenum added in step v. (i.e., during the composition adjustment step).

[0030] Preferably, the hot-rolled steel product contains 0.1 wt% to 3.0 wt% of manganese. Alternatively, the hot-rolled steel product contains 3.0 wt% to 12.0 wt% of manganese.

[0031] In step ii., the molten steel is obtained by melting scrap steel containing at least one of the following elements and optionally hot iron and / or direct reduced iron to form a molten steel: Mo, Sn, Sb, and As.

[0032] For example, the scrap steel that can be used is called old scrap (E1 or E3), new scrap (E8), shredded scrap (E40), or fragmented scrap (E46) in the EU-21 scrap steel specification.

[0033] This melting step (step ii.) can be completed by any means considered suitable by a person skilled in the art.

[0034] Preferably, it is carried out in an electric arc furnace. More preferably, the electric arc furnace is fed with 10 wt% to 100 wt% of scrap steel, and the remaining part is direct reduced iron and / or hot iron and / or any iron-containing material. More preferably, the electric arc furnace is fed with 30 wt% to 90 wt% of scrap steel, and the remaining part is direct reduced iron and / or hot iron and / or any iron-containing material.

[0035] Preferably, it is carried out in a converter. More preferably, the converter is an oxygen converter. More preferably, the converter is charged with 50 kg to 500 kg of scrap steel per ton of hot iron, and even more preferably, 50 kg to 300 kg of scrap steel per ton of hot iron.

[0036] Preferably, it is carried out in an open-hearth furnace. More preferably, the furnace is charged with 50 kg to 500 kg of scrap per ton of hot molten iron, and even more preferably, with 50 kg to 300 kg of scrap per ton of hot molten iron.

[0037] In step iii., before the addition of the manganese-containing element in step v., the contents Mo0, Sn0, Sb0, As0 and Mn0 are estimated and / or measured.

[0038] Preferably, such estimation is done by sampling and / or by calculation using a model. Sampling can be done before, during and after each step of ladle metallurgy.

[0039] Step v. may also include an operation of deoxidizing the molten steel obtained in step ii. and may also allow the required specifications to be met in terms of composition, inclusion cleanliness, gas content (hydrogen, nitrogen) and temperature.

[0040] Step v. can be completed in any manner considered appropriate by those skilled in the art.

[0041] Preferably, this composition adjustment step (step v.) is carried out by ladle metallurgy. Ladle metallurgy can use one or more of the following equipment: ladle furnace, stirring station, vacuum degassing station, desulfurization station.

[0042] Preferably, the manganese content is adjusted by adding ferromanganese and / or manganese ore and / or metallic manganese.

[0043] In step i., an initial target composition is obtained. This composition specifies the initial target content Mn of manganese t,i and the initial contents of other elements desired in the final product. The content of each residual element in the initial target composition is equal to 0 or negligible. When it is said to be equal, it should be understood that it is equal to within 10% of that value, preferably within 5% of that value, and more preferably within 2% of that value.

[0044] In step iv., after estimating the content Mn0 of manganese and the content of each of the residual elements Mo0, Sb0, Sn0, As0 in the molten steel obtained in step ii., the adjusted target composition is determined. This adjusted target composition specifies the adjusted target content Mn of manganese t,a , which is calculated using the following formula: Mn t,a = Mn t,i - Mn RES . The adjusted target composition takes into account the fact that, although not desired, some residues are found to be present in the molten steel; for this reason, in the adjusted target composition, the residual contents are set to Mo0, Sn0, Sb0 or As0. For the other elements, their contents are equal to the contents in the initial target composition.

[0045] Mn RES combines one or more correction terms respectively associated with one or more residual elements, the higher the estimated residual content of the considered residual element, the higher the correction term, and each correction term is at least equal to the estimated residual content Mo0, Sn0, Sb0 or As0 of the considered residual element, or even at least equal to twice the estimated residual content Mo0, Sn0, Sb0 or As0 of the considered residual element.

[0046] Preferably, Mn RES combines one or more correction terms by adding them together.

[0047] Preferably, each of the one or more correction terms is equal to the adjustment coefficient associated with the considered residual element multiplied by the estimated residual content Mo0, Sn0, Sb0 or As0 of the considered residual element.

[0048] Preferably, Mn RES is the sum of one or more of a*Mo0, b*Sn0, c*Sb0, d*As0, where the adjustment coefficient a is from 2.25 to 3.38, the adjustment coefficient b is from 4.09 to 6.14, the adjustment coefficient c is from 17.08 to 25.62, and the adjustment coefficient d is from 9.83 to 14.75.

[0049] Preferably, Mn RES is expressed as a function of the contents of molybdenum, tin, antimony and arsenic. Even more preferably, Mn RES is expressed as equal to:

[0050] Mn RES = a*[Mo] + b*[Sn] + c*[Sb] + d*[As]

[0051] where [Mo] is the molybdenum content by weight percentage, [Sn] is the tin content by weight percentage, [Sb] is the antimony content by weight percentage, and [As] is the arsenic content by weight percentage.

[0052] Even more preferably, a = 2.82, b = 5.12, c = 21.35, d = 12.29.

[0053] For calculating Mn RES, the first step includes using a physical model to calculate the flow stress of residue-free steel, then defining the content of each residual element in additional steel and using the same physical model to calculate the Mn content, where the Mn content allows the additional steel to have the same flow stress as the residue-free steel. The physical model and calculations can be done using the software JMatPro released by Sente Software. The use of software for calculating the flow stress of materials is described in, for example, Section 2.3 of "Introduction of materials modelling into metal forming simulation" by Guo et al. and Section 3.1 of "Deformation behavior and plastic instability of ultra-highstrength low alloy steel over wide temperature and velocity range" by Farah et al. The calculations can also be done using the physical model described in "A model to predict the austenite evolution during hot strip rolling of conventional and Nb microalloyed steels" by Perlade et al.

[0054] The calculations are repeated to obtain a database of Mn contents for different residual element contents. Then, an equation is established using this database to obtain Mn as a function of one or more of the contents of one or more residual elements. RES value.

[0055] ——Experimental Results——

[0056] The following part relates to simulations showing the effects of the present invention.

[0057] In each simulation, the initial target composition of the steel is: 0.1 wt% C, 1.9 wt% Mn (Mn), 0.2 wt% Si, 0.02 wt% Al, and the balance consisting of Fe.

[0058] The contents of Mn and residual elements at the end of step ii. are listed in Table 1.

[0059] For example, at the end of step ii., the molten steel D has 0.10 wt% molybdenum, 0.05 wt% tin, 0.03 wt% antimony, 0.04 wt% arsenic, and 0.2 wt% manganese Mn0.

[0060] Adjustment item MnRES (It represents the equivalent content of manganese that has the same effect on the increase in the average flow stress generated by the deformation applied during the final hot rolling pass) can be calculated using the following formula:

[0061] Mn RES = 2.82 * [Mo%] + 5.12 * [Sn%] + 21.35 * [Sb%] + 12.29 * [As%]

[0062] = 2.82 * 0.10 + 5.12 * 0.05 + 21.35 * 0.03 + 12.29 * 0.04 = 1.67

[0063] Therefore, using the formula: Mn t,a = Mn0 + Mn 添加 = Mn t,i - Mn RES , those skilled in the art derived: Mn 添加 = Mn t,i - Mn0 - Mn RES .

[0064] Therefore, Mn 添加 = 1.9 - 0.2 - 1.67 = 0.03. Those skilled in the art adjust the element content to achieve the composition defined above and add a certain amount of manganese such that Mn 添加 is 0.03 weight percentage of the composition.

[0065] Then the semi-finished product is cast and then hot rolled.

[0066] Considering the target composition listed in Table 1 and the rolling parameters at the final hot rolling stand, when not considering the influence of residual elements, the average flow stress of the final active rolling stand is 173 MPa.

[0067] However, when considering the residual elements and if the adjustment of the manganese content does not consider the presence of residual elements such that Mn 添加 = Mn t,i - Mn0, then the average flow stress of the final active rolling stand is 196 MPa. In other words, the residual elements cause an increase in the average flow stress of 23 MPa.

[0068] But as described above, when considering the residue such that Mn 添加 = Mn t,i - Mn0 - Mn RES , then a reduced amount of manganese is added during the composition adjustment step. Therefore, the increase in the average flow stress caused by the residual elements can be offset.

[0069] Thus, the average flow stress required for the final active rolling stand is the same as the average flow stress of the composition in the absence of residual elements.

[0070]

[0071] Table 1

Claims

1. A method for manufacturing a hot-rolled steel product, the hot-rolled steel product having the following composition by weight percentage: 0.002 ≤ C ≤ 0.8, 0.1 ≤ Mn ≤ 12.0, Si ≤ 2, Al ≤ 2, Cr ≤ 0.5, Nb ≤ 0.08, Ti ≤ 0.1, and the balance consisting of Fe, one or more residual elements, and inevitable impurities, where the one or more residual elements include one or more of Mo, Sn, Sb, As, and where the method comprises the following steps: i. Obtain the initial target content Mn of the specified manganese t,i with the initial target composition, ii. melting scrap steel containing at least one of the one or more residual elements and optionally hot iron and / or direct reduced iron to form a molten steel; iii. estimating an estimated content Mn0 of manganese in the steel produced in step ii, and for each of the one or more residual elements: estimating an estimated residual content Mo0, Sn0, Sb0, or As0 of the molten steel produced in step ii; iv. Determine the adjusted target content of the specified manganese, Mn t,a of the adjusted target composition, where Mn t,a = Mn t,I - Mn RES , where the adjustment term Mn RES combines one or more correction terms respectively related to the one or more residual elements. The higher the estimated residual content of the considered residual element, the higher the correction term. Each correction term is at least equal to the estimated residual content Mo0, Sn0, Sb0 or As0 of the considered residual element v. Add elements to the molten steel such that Mn0 + Mn 添加 = Mn t,a , where Mn 添加 represents the content of added manganese vi. casting a semi-finished product with the molten steel; vii. hot rolling the semi-finished product.

2. The method according to claim 1, wherein step ii is carried out by at least an electric arc furnace.

3. The method according to any one of the preceding claims, wherein each calibration content of Mn RES is at least twice the estimated residual content Mo0, Sn0, Sb0 or As0 of the residual element under consideration.

4. The method according to any one of the preceding claims, wherein Mn RES combining the one or more correction terms by adding the one or more correction terms together.

5. The method according to any one of the preceding claims, wherein each of the one or more correction terms is equal to: - an adjustment coefficient associated with the residual element Mo0, Sn0, Sb0, or As0 under consideration; - multiplied by the estimated residual content Mo0, Sn0, Sb0, or As0 of the residual element under consideration.

6. The method according to claims 4 and 5, wherein Mn RES is the sum of one or more of a*Mo0, b*Sn0, c*Sb0, d*As0, wherein: - The adjustment coefficient a is from 2.25 to 3.38; - The adjustment coefficient b is from 4.09 to 6.14; - The adjustment coefficient c is from 17.08 to 25.62; - The adjustment coefficient d is from 9.83 to 14.

75.

7. The method according to claim 6, wherein Mn RES is calculated according to the following formula: Mn RES = a * [Mo] + b * [Sn] + c * [Sb] + d * [As], where [Mo] is the molybdenum content by weight percentage, [Sn] is the tin content by weight percentage, [Sb] is the antimony content by weight percentage, and [As] is the arsenic content by weight percentage.

8. The method according to any one of the preceding claims, wherein Mn RES is calculated to represent a manganese content having the same effect on the increase in the average flow stress generated by the deformation applied during the hot rolling pass as the one or more estimated contents of the one or more residual elements.

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