Hot rolling with residual elements
By adjusting the manganese content in steel composition to counteract the effects of residual elements, the processability and mechanical properties of hot-rolled steel are improved, addressing deviations in the stress-strain curve and preventing mill roll failure.
Patent Information
- Authority / Receiving Office
- RU · RU
- Patent Type
- Patents
- Current Assignee / Owner
- ARCELORMITTAL SA
- Filing Date
- 2023-12-01
- Publication Date
- 2026-07-06
AI Technical Summary
The presence of trace elements such as molybdenum, tin, antimony, and arsenic in steel scrap negatively impacts the processability and mechanical properties of hot-rolled steel products, leading to deviations in the stress-strain curve and potential mill roll failure during hot rolling.
Adjust the manganese content in the steel composition by accounting for the residual elements' influence on the average flow stress, using a correction term (Mn RES) to maintain consistent mechanical properties and prevent mill roll failure.
The adjusted manganese content compensates for the stress deviation caused by residual elements, ensuring consistent average flow stress and improved machinability of hot-rolled steel products.
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Abstract
Description
[0001] This invention relates to a method for producing hot rolling steel, in which the steel is produced using steel scrap.
[0002] Steel production requires the use of iron-containing materials such as steel scrap, direct reduced iron, or pig iron. The use of steel scrap is considered key to reducing the carbon footprint of the steel industry. However, steel scrap contains trace elements such as copper, chromium, molybdenum, nickel, tin, antimony, zinc, and / or arsenic. Therefore, the use of steel scrap is not widespread for all steel grades, as these trace elements can negatively impact the steel's properties.
[0003] During steelmaking using direct-reduced iron and / or pig iron, small amounts of residual elements inevitably remain in the liquid steel. When using steel scrap, the amount of residual elements is much greater than with blast furnace pig iron or direct-reduced iron.
[0004] Recently, the present inventors noticed that the production of steel using a significant amount of scrap steel causes problems in some production stages, such as hot rolling.
[0005] The objective of the present invention is to improve the processability of hot rolling a semi-finished steel product manufactured, at least in part, from steel scrap containing the following residual elements: molybdenum, tin, antimony, and arsenic. This is achieved by the method according to any one of claims 1 to 8.
[0006] The present invention relates to a method for producing a hot rolled steel product having a composition in mass percent: 0.002 ≤ C ≤ 0.8, 0.1 ≤ Mn ≤ 12.0, Si ≤ 2, Al ≤ 2, Cr ≤ 0.5, Nb≤ 0.08, Ti ≤ 0.1 and a residue consisting of Fe, one or more residual elements and inevitable impurities, wherein said one or more residual elements include one or more elements of Mo, Sn, Sb, As, and said method includes the steps of:
[0007] i. obtaining the initial target composition, which determines the initial target content of manganese Mn t,i ,
[0008] ii. melting steel scrap including at least one of the said one or more residual elements and optionally pig iron and / or direct reduced iron, to form a steel melt
[0009] iii. an estimate of the expected manganese content Mn0 in the steel obtained in step ii, and for each of one or more residual elements: an estimate of the expected residual content of Mo0, Sn0, Sb0 or As0 in the melt of the steel obtained in step ii.,
[0010] iv. Determination of the adjusted target composition, which determines the adjusted target content of manganese Mn t,a , where Mn t,a = Mn t,I - Mn RES with Mn RES as a correction term that combines one or more correction terms respectively associated with one or more residual elements, the higher the expected residual content for the residual element in question, the higher the correction term, each correction term being at least equal to the expected residual content for the residual element in question Mo0, Sn0, Sb0 or As0.
[0011] v. adding elements to the steel melt so that Mn0+ Mn ADD = Mn t,a , where Mn ADD represents the content of added manganese,
[0012] vi. casting a semi-finished product from the specified liquid steel,
[0013] vii. hot rolling of the said semi-finished product.
[0014] Hot rolling allows for slab thickness reduction to achieve the desired geometry. This requires a specialist in the field to determine the optimal rolling pattern (i.e., number of rolling passes, rolling reduction), taking into account metallurgical (i.e., steel temperature) and equipment limitations (i.e., roll pairs, speed, force, applied voltage).
[0015] These parameters allow you to set preset rolling stand settings for each rolling pass. For example, you can define the degree of reduction applied at each rolling stand, which applies an average flow stress to the product. The average flow stress is equal to the area under the stress-strain curve ε. α before deformation ε β .
[0016] However, in the current state, the residual element content of steel scrap is not taken into account when establishing the rolling pattern and therefore the preliminary settings.
[0017] Furthermore, it was unexpectedly discovered that the presence of certain residual elements from steel scrap, namely Mo, Sn, Sb, and As, leads to a deviation from the theoretical stress-strain curve, as the theoretical stress-strain curve is determined without taking these residual elements into account. This deviation leads to a change in the average flow stress resulting from the required deformation applied during hot rolling to achieve the target reduction ratio.
[0018] Since all hot rolling parameters are determined using the adapted presetting, when applying the target reduction ratio during hot rolling of steel made from steel scrap containing the specified residual elements, the average applied flow stress deviates from the theoretical average flow stress to achieve the target deformation ratio.
[0019] This deviation may cause processability problem and possibly accelerated failure of the mill roll because the actual stress applied by the hot rolling stand is higher than expected and may exceed the maximum allowable stress for the mill rolls.
[0020] To counteract this unexpected effect of residual elements, the inventors proposed to adjust the composition of the final product by determining the equivalent content of manganese Mn RES , which has the same effect as the content of the said residual elements on the increase in the average flow stress resulting from the deformation applied during the hot rolling pass. Preferably during the last pass of said hot rolling. Mn RES represents an adjustment term that combines one or more adjustment terms, respectively associated with the residual elements.
[0021] Therefore, the manganese content added during composition adjustment and thus the manganese content of the final product is lower due to the equivalent content of manganese Mn RES , taking into account the influence of residual impurities.
[0022] This counteracts the deviation in average flow stress caused by the deformation applied during hot rolling due to the presence of the specified residual elements. In other words, this allows for the production of steel with an adjusted manganese content and residual impurities that has the same average flow stress as steel with the initial manganese content and no residual impurities. The initial manganese content represents the content developed by a person skilled in the art to obtain the desired steel properties, assuming that residual impurities have no effect on these properties. The desired properties are performance properties, such as mechanical properties or surface properties.
[0023] This invention improves the machinability of steel by influencing its composition rather than the hot rolling process parameters. However, the purpose of this invention can be combined with changing the hot rolling process parameters due to the presence of residual elements, such as the hot rolling temperature. Since steel becomes more ductile with increasing temperature, increasing the hot rolling temperature can improve the machinability of the steel without significantly changing its composition.
[0024] The composition in mass percent represents the composition of the hot rolled steel product, where Mn t,a = Mn0+ Mn ADD = Mn t,i - Mn RES .
[0025] Mn t,a represents the adjusted target manganese content, which represents the actual manganese content in the final product.
[0026] Mn t,irepresents the initial target manganese content, which is the theoretical manganese content developed by a person skilled in the art to obtain the desired properties of the steel without taking into account the effect of residual impurities or assuming that residual impurities are absent.
[0027] Mn0 represents the manganese content obtained in step ii., in which steel scrap containing at least one of the said residual elements and, optionally, cast iron and / or direct reduced iron, form a steel melt.
[0028] Mn RES represents an adjustment term which represents the equivalent manganese content having the same effect as the content of the specified residual elements on the increase in mean flow stress resulting from the deformation applied during the hot rolling pass.
[0029] Mn ADDrepresents the content of manganese added at stage v., i.e. at the stage of composition adjustment.
[0030] Preferably, the hot-rolled steel product comprises 0.1 to 3.0 mass percent manganese. Alternatively, the hot-rolled steel product comprises 3.0 to 12.0 mass percent manganese.
[0031] In step ii., a steel melt is obtained by melting steel scrap including at least one of the following elements: Mo, Sn, Sb and As and optionally cast iron and / or direct reduced iron to form a steel melt.
[0032] For example, the steel scrap that can be used is called amortization scrap (E1 or E3), scrap metal from current production (E8), crushed cleaned scrap (E40) or crushed scrap (E46) in the EU-21 steel scrap specification.
[0033] This melting step, step ii., may be carried out in any manner deemed suitable by one skilled in the art.
[0034] It is preferably carried out in an electric arc furnace. More preferably, 10 to 100% by weight of steel scrap is charged into this electric arc furnace, the rest is direct reduced iron and / or cast iron and / or any iron-containing material. More preferably, 30 to 90% by weight of steel scrap is charged into this electric arc furnace, the rest is direct reduced iron and / or cast iron and / or any iron-containing material.
[0035] It is preferably performed in a converter. More preferably, said converter is a basic oxygen converter. More preferably, said converter is loaded with 50-500 kg of scrap per ton of pig iron, and even more preferably, 50-300 kg of scrap per ton of pig iron.
[0036] It is preferably performed in an open-hearth furnace. More preferably, 50-500 kg of scrap per ton of pig iron is loaded into said furnace, and even more preferably, 50-300 kg of scrap per ton of pig iron.
[0037] In step iii., the contents of Mo0, Sn0, Sb0, As0 and Mn0 are estimated and / or determined before adding manganese element in step v.
[0038] This assessment is preferably performed by sampling and / or model-based calculations. Sampling can be performed before, during, and after each stage of ladle metallurgy.
[0039] Stage v. may also include the operation of deoxidizing the steel melt obtained in stage ii., and may also allow the required characteristics to be met in terms of composition, inclusion purity, gas content (hydrogen, nitrogen) and temperature.
[0040] Stage v. may be accomplished by any means deemed appropriate by a person skilled in the art.
[0041] This composition adjustment stage, stage v., is preferably performed by ladle metallurgy. Ladle metallurgy may use one or more of the following devices: a ladle furnace, a stirring device, a vacuum tank degassing device, and a desulfurization device.
[0042] The manganese content is preferably adjusted by adding ferromanganese and / or manganese ore and / or metallic manganese.
[0043] In step i, an initial target composition is obtained. This composition determines the initial target manganese content Mn t,i and the initial content of other target elements in the final product. The content of each residual element in the initial target composition is 0 or negligible. When we say "equal," we mean greater than or less than 10% of the value, preferably greater than or less than 5% of the value, and more preferably greater than or less than 2% of the value.
[0044] In step iv, after estimating the manganese content Mn0 and the content of each of the residual elements Mo0, Sb0, Sn0, As0 in the steel melt obtained in step ii, the adjusted target composition is determined. This adjusted target composition determines the adjusted target manganese content Mn 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 undesirable, some residual elements are present in the steel melt; for this purpose, the adjusted target composition sets the residual element contents at Mo0, Sn0, Sb0, or As0. For other elements, their contents are equal to those in the original target composition.
[0045] Mn REScombines one or more adjustment terms, respectively associated with one or more residual elements, the higher the estimated residual content for the residual element in question, the higher the adjustment term, each adjustment term is at least equal to the estimated residual content for the residual element in question Mo0, Sn0, Sb0 or As0, or even at least equal to twice the estimated residual content for the residual element in question Mo0, Sn0, Sb0 or As0.
[0046] Preferred, Mn RES combines one or more adjustment terms by adding one or more adjustment terms together.
[0047] Preferably, each of the one or more correction terms is equal to a correction factor associated with the residual element in question multiplied by the calculated residual content for the residual element in question of Mo0, Sn0, Sb0, or As0.
[0048] Preferably Mn RES is the sum of one or more of a*Mo0, b*Sn0, c*Sb0, d*As0, where the correction factor a is 2.25 - 3.38, the correction factor b is 4.09 - 6.14, the correction factor c is 17.08 - 25.62, the correction factor d is 9.83 - 14.75.
[0049] Preferably Mn RES expressed as a function of the content of molybdenum, tin, antimony, and arsenic. More preferably, Mn RES is expressed as equal to:
[0050] Mn RES =a*[Mo] + b*[Sn] + c*[Sb] + d*[As] ,
[0051] where [Mo] represents the molybdenum content in mass percent, [Sn] represents the tin content in mass percent, [Sb] represents the antimony content in mass percent, and [As] represents the arsenic content in mass percent.
[0052] Even more preferable, a=2.82, b=5.12, c=21.35, d=12.29.
[0053] When calculating Mn RESThe first step is to use a physical model to calculate the flow stress of steel without residual elements, then determine the content of each residual element in another steel and calculate, using the same physical model, the Mn content that allows the other steel to have the same flow stress as the steel without residual elements. The physical model and calculations can be performed using the JMatPro software published by Sente Software. The use of software to calculate the flow stress of a material is described in "Introduction to Modeling of Metal Forming" by Guo et al., section 2.3, and "Deformation Behavior and Plastic Instability of Ultra-High-Strength Low-Alloy Steel over a Wide Range of Temperatures and Speeds" by Farah et al., section 3.1, for example.Calculations can also be performed using the physical model described in "A Model for Predicting Austenite Evolution during Hot Strip Rolling of Plain and Microalloyed Nb Steels" by Perlade et al.
[0054] The calculations are repeated to obtain a database of Mn contents for various trace element contents. A formula is then established using this database to obtain the Mn value. RES as functions of one or more contents of one or more residual elements.
[0055] Experimental results
[0056] The following section discusses simulations showing the result of the present invention.
[0057] In each simulation, the initial target composition of the steel is: 0.1 mass% C, 1.9 mass% Mn (Mn), 0.2 mass% Si, 0.02 mass% Al, and the remainder 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, the steel melt D contains 0.10 mass percent molybdenum, 0.05 mass percent tin, 0.03 mass percent antimony, 0.04 mass percent arsenic and 0.2 mass percent manganese Mn0at the end of stage ii.
[0060] Mn RES is a correction term which represents the equivalent manganese content having the same effect as the content of the specified residual elements on the increase in mean flow stress resulting from the deformation applied during the last hot rolling pass, and 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 following formula: Mn t,a = Mn0+ Mn ADD = Mn t,i - MnRES , any specialist in this field of technology will receive that: Mn ADD = Mn t,i - Mn0- Mn RES .
[0064] Thus, Mn ADD = 1.9 - 0.2 - 1.67 = 0.03. A person skilled in the art will adjust the content of the elements to achieve the composition determined above and add the amount of manganese so that Mn ADD amounted to 0.03 mass percent of the composition.
[0065] Then the semi-finished product is cast and then subjected to hot rolling.
[0066] Considering the target composition and rolling parameters of the last hot rolling stand, which are listed in Table 1, the average flow stress is 173 MPa for the last active rolling stand when the influence of residual elements is not taken into account.
[0067] However, when residual elements are taken into account, and if the adjustment of manganese content does not take into account the presence of residual elements, so that Mn ADD = Mn t,i- Mn0, then the average flow stress is 196 MPa for the last active rolling stand. In other words, residual elements lead to an increase in the average flow stress of 23 MPa.
[0068] But, as explained above, when the residual elements are taken into account, so that Mn ADD = Mn t,i - Mn0- Mn RES , then a reduced amount of manganese is added during the composition adjustment stage. As a result, the increase in average flow stress due to residual elements can be compensated for.
[0069] Therefore, the required average flow stress for the last active rolling stand is the same as that of the compositions containing no residual elements.
[0070]
Claims
1. A method for producing a hot-rolled steel product having a composition in mass percent: 0.002 ≤ C ≤ 0.8, 0.1 ≤ Mn ≤ 12.0, Si ≤ 2, Al ≤ 2, Cr ≤ 0.5, Nb ≤ 0.08, Ti ≤ 0.1 and a residue consisting of Fe, one or more residual elements and unavoidable impurities, wherein said one or more residual elements include one or more elements from Mo, Sn, Sb, As, and said method includes the steps of: i. obtaining the initial target composition, which determines the initial target content of manganese Mn t,i , ii. melting steel scrap including at least one of the said one or more residual elements to form molten steel, iii. an estimate of the expected manganese content Mn0 in the steel obtained in step ii, and for each of one or more residual elements: an estimate of the expected residual content of Mo0, Sn0, Sb0 or As0 in the steel melt obtained in step ii., iv. determination of the adjusted target composition, which determines the adjusted target content of manganese Mn t,a , where Mn t,a = Mn t,i - Mn RES , where Mn RES is a correction term that combines one or more correction terms respectively associated with one or more residual elements, wherein the higher the estimated residual content for the residual element in question, the higher the correction term, and each correction term is at least equal to the estimated residual content for the residual element in question Mo0, Sn0, Sb0 or As0, v. adding elements to the steel melt so that Mn0+ Mn ADD = Mn t,a , where Mn ADD represents the content of added manganese, vi. casting a semi-finished product with the specified liquid steel, vii. hot rolling of the said semi-finished product.
2. The method according to claim 1, wherein at stage ii of melting the steel scrap to form the steel melt, cast iron and / or direct reduced iron are also used.
3. The method according to claim 1 or 2, wherein said step ii. is carried out by means of at least an electric arc furnace.
4. The method according to any one of paragraphs 1-3, in which each corrective Mn content RES at least equal to twice the calculated residual content for the residual element in question, Mo0, Sn0, Sb0, or As0.
5. The method according to any one of paragraphs 1-4, in which Mn RES combines one or more adjustment terms by adding one or more adjustment terms together.
6. The method according to any one of paragraphs 1-5, wherein each of the one or more adjustment terms is equal to: - a correction factor associated with the residual element in question Mo0, Sn0, Sb0 or As0, - multiplied by the calculated residual content for the residual element in question Mo0, Sn0, Sb0 or As0, 7. The method according to claim 5 or 6, wherein Mn RES is the sum of one or more of a * Mo0, b * Sn0, c * Sb0, d * As0, in which: - the correction factor a is 2.25-3.38, - the correction factor b is 4.09-6.14, - the correction factor c is 17.08-25.62, - the correction factor d is 9.83-14.75, 8. The method according to claim 7, in which Mn RES calculated using the formula: Mn RES = a*[Mo]+b*[Sn]+c*[Sb]+d*[As], where [Mo] represents the molybdenum content in mass percent, [Sn] represents the tin content in mass percent, [Sb] represents the antimony content in mass percent, and [As] represents the arsenic content in mass percent.
9. The method according to any one of paragraphs 1-8, in which Mn REScalculated to represent the manganese content having the same effect as one or more estimated contents of one or more residual elements on the increase in mean flow stress resulting from the deformation applied during the hot rolling pass.