Hot rolling with residual elements

Abstract

1. A method for producing hot rolled steel sheet, wherein the annual rolled steel sheet product has a composition, in weight percent, of: 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 remainder consisting of Fe, one or more residual elements and unavoidable impurities, the method comprising the steps of: i. Initial target manganese content Mn t,i obtaining an initial target composition having ii. Melting steel scrap containing residual elements; iii. Estimating the content of Mn0, Mo0, Sn0, Sb0 or As0; iv. Adjusted manganese content Mn t,a determining an adjusted target composition having Mn t,a =Mn t,l -Mn RES and Mn RES is an adjustment term combining the correction terms respectively associated with the residual elements; v. Mn0+Mn ADD =Mn t,a adding elements to the steel melt so that Mn ADD represents the content of added manganese, vi. Casting semi-finished products; vii. hot rolling said semi-finished product.

Description

[Technical Field]

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

[0002] Steelmaking requires the use of iron-containing materials such as steel scrap, direct reduced iron, or pig iron. To reduce the carbon footprint of the steel industry, the use of steel scrap is seen as key. However, steel scrap contains residual 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 because the residual elements can have a detrimental effect on steel properties.

[0003] During the refining of steel with direct reduced iron and / or pig iron, small amounts of residual elements inevitably remain in the molten steel. When steel scrap is used, the amount of residual elements is much higher compared to pig iron derived from blast furnaces or direct reduced iron.

[0004] The present inventors have recently observed that the production of steel using significant amounts of steel scrap is causing problems during some manufacturing steps, such as hot rolling. Summary of the Invention

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

[0006] The present invention relates to a method for producing a hot rolled steel sheet, wherein the hot rolled product has a composition, in weight percent, of 0.002≦C≦0.8, 0.1≦Mn≦12.0, Si≦2, Al≦2, Cr≦0.5, Nb≦0.08, Ti≦0.1, with the balance consisting of Fe, one or more residual elements and unavoidable impurities, wherein the one or more residual elements include one or more of Mo, Sn, Sb, and As, the method comprising the steps of: i. Initial target manganese content Mn t,i obtaining an initial target composition that identifies ii. melting steel scrap comprising at least one of the one or more residual elements and optionally hot metal and / or direct reduced iron to form a steel melt; iii. estimating an estimated content of manganese in the steel produced in step ii., MnO, and estimating, for each of one or more residual elements, an estimated residual content of MoO, SnO, SbO, or AsO in the steel melt produced in step ii.; iv. Adjusted target manganese content Mn t,a determining an adjusted target composition that identifies Mn t,a =Mn t,l -Mn RES and Mn RES is an adjustment term combining one or more correction terms respectively associated with one or more residual elements, the higher the estimated residual content of the residual element being considered, the higher the correction term, and each correction term is at least equal to the estimated residual content of the residual element being considered, Mo0, Sn0, Sb0 or As0; v. Mn0+Mn ADD =Mn t,a adding elements to the steel melt so that Mn ADD represents the content of added manganese, vi. casting a semi-finished product using the molten steel; vii. hot rolling said semi-finished product. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hot rolling allows the thickness of the slab to be reduced to obtain the desired shape, which involves the skilled person determining the optimum rolling pattern (i.e., number of passes, reduction) while taking into account metallurgical constraints (i.e., steel temperature) and equipment constraints (i.e., bonding, speed, force, applicable stress).

[0008] These parameters therefore make it possible to establish a preset setting of the rolling stands for each rolling pass. For example, it is possible to define the reduction to be applied in each rolling stand, which applies an average flow stress to the product. The average flow stress is determined by the strain ε α Strain ε β It is equal to the area under the stress-strain curve up to

[0009] However, in the prior art, the content of residual elements from the steel scrap is not taken into account when establishing the rolling pattern and therefore the pre-settings.

[0010] It has also been surprisingly found that the presence of certain residual elements, namely Mo, Sn, Sb and As, originating from the steel scrap leads to deviations from the theoretical stress-strain curve, since the latter is defined without taking into account said residual elements, which deviations lead to changes in the mean flow stress resulting from the necessary deformation applied during hot rolling to achieve the target reduction.

[0011] All hot rolling parameters are defined using adapted presets so that when applying a target reduction during hot rolling of steel processed from steel scrap containing said residual elements, the applied mean flow stress deviates from the theoretical mean flow stress in order to achieve the target strain rate.

[0012] This deviation can lead to workability problems and possibly to accelerated deterioration of the rolling cylinders, since the actual stresses exerted by the hot rolling stand are higher than those expected and may exceed the maximum stress allowed on the rolling cylinders.

[0013] To counter this surprising effect of residual elements, we have determined that the equivalent manganese content, Mn RES It is proposed to adjust the composition of the final product by defining the manganese equivalent content Mn RES has the same effect as the content of said residual elements on the increase in mean flow stress resulting from the deformation applied during the hot rolling passes. Preferably, during the last pass of said hot rolling, Mn RES is an adjustment term that combines one or more correction terms each associated with a residual element.

[0014] Consequently, the manganese content added during composition adjustment, and therefore the manganese content in the final product, is determined by taking into account the influence of the residues, and the equivalent manganese content Mn RES Lower due to.

[0015] It makes it possible to counteract deviations in the mean flow stress resulting from the deformations applied during hot rolling due to the presence of said residual elements. In other words, it makes it possible to obtain a steel with a regulated manganese content and a residual, said steel having the same mean flow stress as a steel with an initial manganese content and no residual. The initial manganese content is a content designed by a person skilled in the art to obtain the desired properties of the steel, assuming that the residual does not affect said properties. The desired properties are properties during use, such as mechanical properties or surface properties.

[0016] The present invention makes it possible to improve the workability of steel by acting on its composition rather than on the hot rolling process parameters. However, the object of the present invention can be combined with modifying hot rolling process parameters such as the hot rolling temperature due to the presence of residual elements. Increasing the hot rolling temperature can improve the workability of steel without significantly changing the composition, since steel is more ductile with increasing temperature.

[0017] Compositions in weight percent are those of hot rolled steel products, Mn t,a =Mn0+Mn ADD =Mnt,1 -Mn RES is.

[0018] Mn t,a is the adjusted target content in manganese, which represents the actual manganese content in the final product.

[0019] Mn t,i is the initial target content in manganese, which represents the theoretical manganese content designed by a person skilled in the art to obtain the desired properties of the steel without taking into account the effect of the residuals or assuming there are no residuals.

[0020] Mn0 is the manganese content resulting from step ii., during which the steel scrap comprises at least one of said residual elements and optionally hot metal and / or direct reduced iron to form a steel melt.

[0021] Mn RES is an adjustment term representing the equivalent content of manganese which has the same effect as the contents of the residual elements on the increase in mean flow stress due to the deformation applied during the hot rolling pass.

[0022] Mn ADD is the content of molybdenum added in step v, i.e., during the composition adjustment step.

[0023] Preferably, the hot rolled steel product contains 0.1 to 3.0 weight percent manganese, alternatively, the hot rolled steel product contains 3.0 to 12.0 weight percent manganese.

[0024] In step ii., a steel melt is obtained by melting steel scrap containing at least one of the following elements: Mo, Sn, Sb and As and optionally hot metal and / or direct reduced iron to form a steel melt.

[0025] For example, steel scrap that may be used is referred to in the EU-21 steel scrap specification as old scrap (E1 or E3), new scrap (E8), shredded scrap (E40) or fragmented scrap (E46).

[0026] This melting step, step ii., can be carried out by any means deemed suitable by one skilled in the art.

[0027] Preferably, the process is carried out in an electric arc furnace. More preferably, the electric arc furnace is fed with 10% to 100% by weight of steel scrap, the remainder being direct reduced iron and / or hot metal and / or any iron-bearing material. More preferably, the electric arc furnace is fed with 30% to 90% by weight of steel scrap, the remainder being direct reduced iron and / or hot metal and / or any iron-bearing material.

[0028] Preferably, the process is carried out by a converter. More preferably, the converter is an oxygen converter. More preferably, the converter is charged with 50 to 500 kg of scrap per tonne of hot metal, and even more preferably, 50 to 300 kg of scrap per tonne of hot metal.

[0029] Preferably, the process is carried out in an open hearth furnace, more preferably the furnace is charged with 50 to 500 kg of scrap per tonne of hot metal, even more preferably 50 to 300 kg of scrap per tonne of hot metal.

[0030] In step iii., the contents of Mo0, Sn0, Sb0, As0, and Mn0 are estimated and / or measured before the addition of the manganese-containing element in step v.

[0031] Preferably, this estimation is done by sampling and / or calculation using a model. Sampling can be done before, during and after each step of ladle metallurgy.

[0032] Step v. may also include an operation of deoxidizing the steel melt obtained in step ii. and may make it possible to meet the required specifications in terms of composition, inclusion cleanliness, gas content (hydrogen, nitrogen) and temperature.

[0033] Step v. can be carried out by any means deemed appropriate by one skilled in the art.

[0034] Preferably, this composition adjustment step, step v., is performed by ladle metallurgy, which may use one or more of the following devices: a ladle furnace, a stirring station, a vacuum tank degassing station, and a desulfurization station.

[0035] Preferably, the manganese content is adjusted by the addition of ferromanganese and / or manganese ore and / or manganese metal.

[0036] In step i., an initial target composition is obtained. This composition has an initial target manganese content, Mn t,i and the initial content amounts of other elements desired in the final product. The content of each remaining element in the initial target composition is equal to 0 or is negligible. It should be understood that when the content of each remaining element is said equal, it is equal to more or less than 10% of its value, preferably more or less than 5% of its value, and more preferably more or less than 2% of its value.

[0037] In step iv, the manganese content Mn0 and the contents of the remaining elements Mo0, Sb0, Sn0, and As0 in the steel melt obtained in step ii are estimated, and then an adjusted target composition is determined. This adjusted target composition is the adjusted target manganese content Mn t,a is identified, which is represented by the following formula Mn t,a =Mn t,i -Mn RESThe adjusted target composition takes into account the fact that some residues will be present in the steel melt, although this is undesirable. For this reason, in the adjusted target composition, the residual contents are Mo0, Sb0, Sn0, or As0. For the other elements, their contents are equal to their contents in the initial target composition.

[0038] Mn RES is a combination of one or more correction terms respectively associated with one or more residual elements, the higher the estimated residual content of the residual element being considered, the higher the correction term, each correction term being at least equal to the estimated residual content MoO, SbO, SnO or AsO of the residual element being considered, or even equal to at least twice the estimated residual content MoO, SbO, SnO or AsO of the residual element being considered.

[0039] Preferably, Mn RES combines one or more correction terms by adding them together.

[0040] Preferably, each of the one or more correction terms is equal to an adjustment factor associated with the residual element considered multiplied by the estimated residual content Mo0, Sn0, Sb0, or As0 of the residual element considered.

[0041] Preferably, Mn RES is the sum of one or more of a*Mo0, b*Sn0, c*Sb0, and d*As0, where the adjustment coefficient a is 2.25 to 3.38, the adjustment coefficient b is 4.09 to 6.14, the adjustment coefficient c is 17.08 to 25.62, and the adjustment coefficient d is 9.83 to 14.75.

[0042] Preferably, Mn RES is expressed as a function of the molybdenum, tin, antimony and arsenic content. Even more preferably, Mn RES teeth, Mn RES =a*[Mo]+b*[Sn]+c*[Sb]+d*[As] where [Mo] is the molybdenum content in weight percent, [Sn] is the tin content in weight percent, [Sb] is the antimony content in weight percent, and [As] is the arsenic content in weight percent.

[0043] Even more preferably, a=2.82, b=5.12, c=21.35, and d=12.29.

[0044] Mn RES To calculate the flow stress of a steel without residuals, the first step involves using a physical model to calculate the flow stress of the steel without residuals, then defining the content of each residual element in another steel, and using the same physical model to calculate the Mn content that allows the other steel to have the same flow stress as the steel without residuals. The physical model and calculation can be performed using the software JMatPro published by Sente Software. The use of this software to calculate the flow stress of a material is described, for example, in Guo et al., paragraph 2.3, "Introduction of materials modeling into metal forming simulation," and Farah et al., paragraph 3.1, "Deformation behavior and plastic instability of ultra-high strength low alloy steel over a wide temperature and velocity range." Calculations can also be performed using the physical model described in Perlade et al., "A model to predict the austenite evolution during hot strip rolling of conventional and Nb microalloyed steels."

[0045] The calculations are repeated to obtain a database with Mn contents for different residual element contents. This database is then used to establish a formula to calculate Mn as a function of one or more contents of one or more residual elements. RES Get the value of [Example]

[0046] -Experimental results- The following section deals with simulations that demonstrate the effectiveness of the present invention.

[0047] For each simulation, the initial target composition of the steel is as follows: C 0.1 wt.%, Mn (Mn) 1.9 wt.%, Si 0.2 wt.%, Al 0.02 wt.%, and the balance Fe.

[0048] The contents of Mn and residual elements at the end of step ii. are listed in Table 1.

[0049] For example, steel melt D has, in final step ii., 0.10 weight percent molybdenum, 0.05 weight percent tin, 0.03 weight percent antimony, 0.04 weight percent arsenic and 0.2 weight percent manganese MnO.

[0050] Mn RES is an adjustment term representing the equivalent content of manganese which has the same effect as the contents of said 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: Mn RES =2.82*[Mo%]+5.12*[Sn%]+21.35*[Sb%]+12.29*[As%] =2.82*0.10+5.12*0.05+21.35*0.03+12.29*0.04=1.67

[0051] Therefore, the following formula Mn t,a =Mn0+Mn ADD =Mn t,1 -Mn RESUsing this, one skilled in the art can determine Mn ADD =Mn t,1 -Mn0-Mn RES leads to.

[0052] Therefore, Mn ADD = 1.9 - 0.2 - 1.67 = 0.03. Those skilled in the art can adjust the element contents to reach the composition defined above and ADD Manganese is added in an amount such that is 0.03 weight percent of the composition.

[0053] The semi-finished product is then cast and then hot rolled.

[0054] Considering the target composition and rolling parameters in the final hot rolling stand listed in Table 1, the average flow stress for the last active rolling stand is 173 MPa, if the influence of residual elements is not taken into account.

[0055] However, residual elements are taken into consideration and the manganese content is adjusted to Mn ADD =Mn t,1 If the presence of residual elements is not taken into account, such as -Mn0, the average flow stress is 196 MPa for the last active rolling stand. In other words, the residual elements result in an increase in the average flow stress of 23 MPa.

[0056] However, as explained above, residuals are taken into account and Mn ADD =Mn t,1 -Mn0-Mn RES If so, then a reduced amount of manganese is added during the adjustment composition step, thereby offsetting the increase in mean flow stress due to the residual elements.

[0057] As a result, the average flow stress required in the last active rolling stand is the same as the average flow stress of the composition in the absence of the residual elements.

[0058] [Table 1]

Claims

1. 1. A method for producing a hot rolled steel product, comprising:

1. A method of manufacturing a hot rolled steel product having a composition, in weight percent, of: 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 unavoidable impurities, said one or more residual elements comprising one or more of Mo, Sn, Sb, As, said method comprising the steps of: i. Initial target manganese content Mn ｔ，ｉ obtaining an initial target composition that identifies ii. Melting steel scrap comprising at least one of the one or more residual elements and optionally hot metal and / or direct reduced iron to form a steel melt; iii. Estimated manganese content Mn in the steel produced in step ii. ０ and for each of one or more residual elements, estimate the estimated residual content Mo of the steel melt produced in step ii. ０ , Sn ０ , Sb ０ Or As ０ estimating the iv. Adjusted target manganese content Mn ｔ，ａ determining an adjusted target composition specifying Mn ｔ，ａ = Mn ｔ，ｌ -Mn ＲＥＳ and Mn ＲＥＳ is an adjustment term that combines one or more correction terms associated with one or more residual elements, respectively, and the higher the estimated residual content of the considered residual element, the higher the correction term. Each correction term is a sum of the estimated residual content Mo ０ , Sn ０ , Sb ０ Or As ０ a process at least equal to v. Mn ０ +Mn ＡＤＤ = Mn ｔ，ａ adding elements to the steel melt so that Mn ＡＤＤ represents the content of added manganese, vi. Casting a semi-finished product using the molten steel; vii. Hot rolling the semi-finished product.

2. 2. The method of claim 1, wherein step ii. is carried out using at least an electric arc furnace.

3. Mn ＲＥＳ Each corrected content of the residual element under consideration is the estimated residual content Mo ０ , Sn ０ , Sb ０ Or As ０ 3. The method of claim 1 or 2, wherein the .alpha.-methyl-.beta ...

4. Mn ＲＥＳ The method according to any one of claims 1 to 3, wherein one or more correction terms are combined by adding together one or more correction terms.

5. 5. The method of claim 1, wherein each of the one or more correction terms is equal to: - adjustment coefficient Mo associated with the residual element considered ０ , Sn ０ , Sb ０ Or As ０ , - Estimated residual content of the residual element to be considered Mo ０ , Sn ０ , Sb ０ Or As ０ It is multiplied by .

6. Mn ＲＥＳ But a*Mo ０ , b*Sn ０ , c*Sb ０ , d*As ０ is the sum of one or more of the adjustment coefficient a is between 2.25 and 3.38, the adjustment coefficient b is between 4.09 and 6.14, the adjustment coefficient c is between 17.08 and 25.62, the adjustment factor d is between 9.83 and 14.75; 6. The method according to claim 4 or 5.

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

8. Mn ＲＥＳ is calculated to represent the content of manganese that has the same effect as the estimated content of one or more of the one or more residual elements on the increase in mean flow stress resulting from the deformation applied during the hot rolling pass.

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