Method for manufacturing thermally treated steel sheets

Abstract

The present invention provides a heat treatment method and steel sheet for having a microstructure containing 0-100% of at least one phase selected from ferrite, martensite, bainite, pearlite, cementite, and austenite, within a heat treatment line, as well as a chemical steel composition. [Solution] A.1) A selection substep in which the chemical composition is compared with a predetermined list of products in order to select a product having a microstructure closest to the target and a thermal path to obtain it, and the microstructure includes a plurality of proportions of phases; 2) A calculation substep in which at least two thermal paths corresponding to the obtained microstructure are calculated based on the selected product and thermal paths in step A.1) and the target initial microstructure; 3) A preparation step in which one thermal path to reach the target is selected and the microstructure is selected to be close to the target; B. A heat treatment step in which T. is performed on the steel sheet.

Description

[Technical Field]

[0001] This invention relates to a microstructure in a heat treatment line that includes a chemical steel composition and at least one phase selected from ferrite, martensite, bainite, pearlite, cementite, and austenite, comprising 0-100% m target The present invention relates to a method for producing a thermally treated steel sheet having [a specific characteristic]. The present invention is particularly well suited for the manufacture of automobile vehicles. [Background technology]

[0002] It is known that coated or uncoated steel sheets are used in the manufacture of automobile vehicles. Numerous steel grades are used in the manufacture of vehicles. The selection of steel grade depends on the end use of the steel part. For example, IF (very low carbon) steel may be produced for exposed parts, TRIP (transformation-induced plasticity) steel may be produced for seats and floor cross members or A-pillars, and DP (duplex) steel may be produced for rear rails or roof cross members.

[0003] During the production of these steels, crucial treatments are performed on the steel to obtain the desired parts with the mechanical properties expected for a particular application. Such treatments may include, for example, continuous annealing or quenching and distribution treatments before the application of a metal coating. Typically, the treatment to be performed is selected from a list of known treatments, and this treatment is chosen according to the steel grade.

[0004] Patent application WO2010 / 049600 relates to a method using equipment for heat-treating a continuously moving steel strip, comprising, in particular, the steps of: selecting a cooling rate of the steel strip according to the metallurgical properties at the inlet and the required metallurgical properties at the outlet of the equipment; inputting the geometric properties of the band; calculating a power transfer profile along the path of the steel in light of the line speed; determining desired values ​​for the adjustment parameters of the cooling section and adjusting the power transfer of the cooling device of the cooling section according to the monitoring values.

[0005] However, this method is based solely on the selection and application of well-known cooling cycles. This means there is a significant risk that the same cooling cycle will be applied even if each grade of steel, such as TRIP steel, has its own unique properties, including chemical composition, microstructure, properties, and surface characteristics. Therefore, this method does not take into account the actual properties of the steel. This method allows for the undifferentiated heat treatment of numerous steel grades.

[0006] As a result, the heat treatment is not adapted to a particular steel, and therefore the desired properties are not obtained at the end of the process. Furthermore, after treatment, the steel may exhibit significant variations in its mechanical properties. Finally, even if a wide range of steel grades can be produced, the quality of the treated steel may be insufficient. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] International Publication No. 2010 / 049600 [Overview of the project] [Problems that the invention aims to solve]

[0008] Therefore, the object of the present invention is to achieve a specific chemical steel composition and a specific microstructure to be reached within a heat treatment line. target The objective is to solve the aforementioned drawbacks by providing a method for manufacturing a thermally treated steel sheet having [specific properties]. In particular, the objective is to perform a treatment tailored to each steel sheet, such a treatment calculated with great accuracy in the shortest possible computation time to provide a steel sheet having the expected properties, and such properties having the smallest possible variation. [Means for solving the problem]

[0009] This objective is achieved by providing the method according to claim 1. The method may also include any of the characteristics described in claims 2 to 18.

[0010] Another objective is achieved by providing the coil described in claim 19. The method may also include the properties described in claim 20 or 21.

[0011] Another objective is achieved by providing the thermal treatment line described in claim 22.

[0012] Finally, this objective is achieved by providing the computer program product described in claim 23.

[0013] Other features and advantages of the present invention will become apparent from the following embodiments for carrying out the invention.

[0014] To illustrate the present invention, various non-limiting embodiments and trials will be described with particular reference to the following figures. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of the method according to the present invention. [Figure 2] This figure shows an example of continuous annealing of a steel sheet, including a heating step, a soaking step, a cooling step, and an overaging step. [Figure 3] This figure shows a preferred embodiment of the present invention. [Figure 4] This figure shows an example according to the present invention in which continuous annealing is performed on a steel sheet before the coating is applied by melting. [Figure 5] This figure shows an example of how quenching and distribution treatment are performed on a steel plate. [Modes for carrying out the invention]

[0016] The following terms are defined: - CC: Chemical composition in weight percent, - m target : Target value of microstructure, - m standard : Microstructure of the selected product, - P target : Target value of mechanical properties, - m i : Initial microstructure of the steel plate, - X: Phase fraction in weight percent, - T: Temperature in degrees Celsius (°C), - t: Time (s), - s: Second, - UTS: Ultimate tensile strength (MPa), - YS: Yield stress (MPa), - A zinc-based metal coating means a metal coating containing more than 50% zinc, - An aluminum-based metal coating means a metal coating containing more than 50% aluminum, and - Thermal path, TP standard 、TP target 、TP x 及びTP xint includes at least one rate selected from time, the temperature of the heat treatment, and the cooling rate, isothermal rate, or heating rate. The isothermal rate has a constant temperature.

[0017] The term "steel" or "steel plate" means a steel plate, coil, or plate having a composition that enables the component to achieve a tensile strength of up to 2500 MPa, more preferably up to 2000 MPa. For example, the tensile strength is 500 MPa or more, preferably 1000 MPa or more, and advantageously 1500 MPa or more. Since the method according to the invention is applicable to any type of steel, a wide range of chemical compositions is included.

[0018] The present invention is a method for manufacturing a heat-treated steel plate having a chemical steel composition and a microstructure m target containing at least one phase selected from 0 to 100% of ferrite, martensite, bainite, pearlite, cementite, and austenite in a heat treatment line, A. 1)m target The microstructure closest to m standard Products and m standard A predetermined heat path TP to obtain standard To select, chemical composition and m target However, it is compared with a predetermined list of products, and the microstructure is selected if it includes predetermined phases and predetermined proportions of phases, 2) TP x The microtissue obtained at the end x TP corresponding to each x at least two heat paths TP x However, the selected product and TP in step A.1) standard and m target m to reach i Calculation substeps calculated based on, 3)m target One heat path TP to reach target Cutting edge, TP target , TP x Selected from, and m x ga m target Select the substep that is closest to it. Preparation steps, B.TP target A heat treatment step performed on the steel plate. This includes methods.

[0019] While we do not wish to be limited by any theory, when the method according to the present invention is applied, it appears possible to obtain individualized heat treatment for each steel sheet to be processed in a short computation time. In fact, the method according to the present invention is m target , more precisely, the proportion of all phases along the process and m iThis allows for precise, specific heat treatments that take into account (including variations in the microstructure along the steel sheet). In fact, the method according to the present invention considers, for calculation purposes, thermodynamically stable phases, namely ferrite, austenite, cementite, and pearlite, as well as thermodynamically metastable phases, namely bainite and martensite. Thus, a steel sheet with the expected properties and the smallest possible variation is obtained.

[0020] Preferably, the microstructure to be reached m target teeth, - 100% austenite, - 5-95% martensite, 4-65% bainite, the remainder being ferrite. - 8-30% retained austenite, 0.6-1.5% carbon in the solid solution, the remainder being ferrite, martensite, bainite, pearlite and / or cementite. - 1% to 30% ferrite and 1% to 30% bainite, 5% to 25% austenite, the remainder being martensite. - 5-20% retained austenite, the remainder being martensite. - Ferrite and retained austenite, - Retained austenite and intermetallic phases, - 80-100% martensite and 0-20% retained austenite - 100% martensite, - 5-100% perlite and 0-95% ferrite, - At least 75% isometric ferrite, 5-20% martensite, and 10% or less bainite. Includes.

[0021] Advantageously, during selection substep A.1), the chemical composition and m targetHowever, it is compared against a predetermined list of products. The predetermined products can be any type of steel grade. For example, the predetermined products include duplex DP, transformation-induced plasticity (TRIP), quenched and distributed steel (Q&P), twinning-induced plasticity (TWIP), carbide-free bainite (CFB), press-hardened steel (PHS), TRIPLEX, DUPLEX, and high-ductility duplex (DP HD).

[0022] The chemical composition depends on the type of steel sheet. For example, the chemical composition of DP steel may include the following: 0.05 <C<0.3%、 0.5 ≤ Mn < 3.0%, S ≤ 0.008%, P ≤ 0.080%, N ≤ 0.1%, Si ≤ 1.0%, The remainder of the composition, consisting of iron and unavoidable impurities resulting from growth.

[0023] Each predetermined product comprises a microstructure containing a predetermined phase and a predetermined proportion of the phase. Preferably, the predetermined phase in step A.1) is defined by at least one element selected from size, shape and chemical composition. Therefore, m standard This includes a predetermined proportion of phases, in addition to a predetermined phase. For advantage, mi, m x , m target It includes a phase defined by at least one element selected from size, shape, and chemical composition. According to the present invention, m target The microstructure closest to m standard A predetermined product having m standard The heat path TP to reach standard Selected together with m standard is, m target It includes the same phase as m. Preferably, standard Also, m target It includes the same phase ratio.

[0024] Figure 1 shows an example according to the present invention in which the steel sheet to be treated has the following CC by weight: 0.2% C, 1.7% Mn, 1.2% Si, and 0.04% Al. target It contains 15% retained austenite, 40% bainite, and 45% ferrite, and 1.2% carbon from the solid solution in the austenite phase. According to the present invention, CC and m target The selected product is compared to a predetermined list of products chosen from products 1-4. CC and m target This corresponds to product 3 or 4, and such products are TRIP steel.

[0025] Product 3 has the following CC3 by weight: 0.25% C, 2.2% Mn, 1.5% Si, and 0.04% Al. CC3 contains 12% retained austenite, 68% ferrite, and 20% bainite, with 1.3% carbon from the solid solution in the austenite phase.

[0026] Product 4 has the following CC4 by weight: 0.19% C, 1.8% Mn, 1.2% Si, and 0.04% Al. CC4 contains 12% retained austenite, 45% bainite, and 43% ferrite, with 1.1% carbon in the solid solution within the austenite phase.

[0027] Product 4 is m target It has the closest microstructure to m, and the reason is that product 4 is m target This is because they share the same phases in the same proportions.

[0028] As shown in Figure 1, two predetermined products can have the same chemical composition CC and different microstructures. In fact, product 1 and product 1’ Both are DP600 steel (duplex with a UTS of 600 MPa). One difference is that product 1 has microstructure m1, and product 1’ Different microstructures 1’ The other difference is that product 1 has a YS of 360 MPa, and product 1’This means that it has a YS of 420 MPa. Therefore, it is possible to obtain steel sheets with different compromise UTS / YS for a single steel grade.

[0029] During calculation substep A.2), at least two heat paths TP x However, the selected product and m in step A.1) target m to reach i It is calculated based on TP. x This calculation takes into account both the thermal and metallurgical behavior of the steel plate, compared to conventional methods that only consider thermal behavior. In the example in Figure 1, m4 is m target Product 4 is selected because it is the closest, TP4 is selected, and m4 and TP4 are respectively m standard and TP standard It corresponds to.

[0030] Figure 2 shows the continuous annealing of a steel sheet, including a heating step, a soaking step, a cooling step, and an overaging step. As shown only for the heating step in Figure 2, m target A large number of TP x This is calculated. In this example, TP x However, this is calculated along all continuous annealing processes (not shown).

[0031] Preferably, at least 10 TP X This is calculated, more preferably at least 50, favorably at least 100, and more preferably at least 1000 TP X The following is calculated: For example, the calculated TP x The number is between 2 and 10,000, preferably between 100 and 10,000, and more preferably between 1,000 and 10,000.

[0032] In step A.3), m target One heat path TP to reach target This is selected. TP target is, m X ga m target TP X It is selected from. Therefore, in Figure 1, TPtarget , a large number of TP x Selected from. Preferably, m target and m x The difference in the proportion of each phase present is ±3%.

[0033] To be advantageous, in step A.2), m i and m target The thermal enthalpy H released or consumed during this period is

number

[0034] While we do not wish to be limited by any theory, H represents the energy released or consumed along all heat pathways when a phase transformation takes place. Some phase transformations are considered exothermic, while others are endothermic. For example, the transformation from ferrite to austenite in the heating pathway is endothermic, while the transformation from austenite to pearlite in the cooling pathway is exothermic.

[0035] In a preferred embodiment, in step A.2), all thermal cycle TP x but,

[0036]

number

[0037] Preferably, in step A.2), the intermediate heat path TP xintAt least one intermediate steel microstructure m corresponding thereto xint and the thermal enthalpy H xint are calculated. In this case, TP x is calculated by the calculation of a number of TPs xint . Therefore, preferably, TP x is the sum of all TPs xint , and H x is the sum of all Hs xint . In this preferred embodiment, TP xint is calculated periodically. For example, CP xint is calculated every 0.5 seconds, preferably every 0.1 seconds or less.

[0038] FIG. 3 shows a preferred embodiment in which, in step A.2), m xint1 and m xint2 corresponding to TP int1 and TP int2 respectively, as well as H xint1 and H xint2 are calculated. H x in all heat paths is determined to calculate TP x .

[0039] In a preferred embodiment, before step A.1), at least one target mechanical property P target selected from yield stress YS, maximum tensile strength UTS, elongation, hole expansion property, formability is selected. In this embodiment, preferably, m target is calculated based on P target .

[0040] Although it is not desired to be limited by any theory, it is considered that the properties of the steel sheet are defined by the process parameters applied during steel production. Therefore, advantageously, in step A.2), the process parameters that the steel sheet undergoes before entering the heat treatment line are considered to calculate TP x . For example, the process parameters include at least one element selected from final rolling temperature, run-out table cooling path, coiling temperature, coil cooling rate, and cold rolling reduction rate.

[0041] In another embodiment, the process parameters of the heat treatment line through which the steel sheet passes are TP x This is considered when calculating the process parameters. For example, process parameters include at least one element selected from line speed, a specific hot steel sheet temperature to be reached, heating capacity of the heating section, heating temperature and soaking temperature, cooling capacity of the cooling section, cooling temperature, and overaging temperature.

[0042] Preferably, a heat path, TP x , TP xint , TP standard or TP target This includes at least one treatment selected from heat treatment, isothermal treatment, or cooling treatment. For example, the thermal path may be recrystallization annealing, press hardening, recovery, two-phase annealing, or fully austenitic annealing, tempering, or distribution, isothermal, or quenching.

[0043] Preferably, recrystallization annealing is performed. Recrystallization annealing optionally includes a preheating step, a heating step, a soaking step, a cooling step, and optionally a homogenization step. In this case, recrystallization annealing is performed in a continuous annealing furnace which optionally includes a preheating section, a heating section, a soaking section, a cooling section, and optionally a homogenization section. Although we do not wish to be limited by any theory, recrystallization annealing is considered a more difficult thermal path to handle because it involves many steps to consider, including the cooling and heating steps.

[0044] Preferably, each time a new steel sheet enters the heat treatment line, a new calculation step A.2) is automatically performed based on the previously performed selection step A.1). In fact, since the actual properties of each steel often differ, the method according to the present invention allows for the calculation of the heat path TP even when the same steel grade enters the heat treatment line. target This is adapted to each steel plate. New steel plates can be detected, their new properties measured, and pre-selected. For example, the detector can detect a weld between two coils.

[0045] In this preferred embodiment, to prevent large changes in the process, thermal path adaptation is performed on the first few meters of the steel sheet when it enters the heat treatment line.

[0046] Figure 4 shows an example according to the present invention in which continuous annealing is performed on the steel sheet before the coating is attached by melting. By the method according to the present invention, m target After selecting a predetermined product (not shown) that has a microstructure similar to TP, x However, m i , selected products and m target It is calculated based on m. In this example, m xint1 ~m xint6 TP corresponding to each xint1 ~TP xint6 Intermediate heat pathway and H xint1 ~H xint6 This is calculated. TP x To obtain H x This is determined. In this diagram, TP target Many TP x Selected from.

[0047] According to the present invention, m target This can be the expected microstructure at any point in the heat treatment. In other words, m target This could be the expected microstructure at the end of the heat treatment shown in Figure 4 or at the exact moment of the heat treatment shown in Figure 5. In fact, for example, for Q&P steel sheets, the important point of the quenching and distribution treatment is T, which corresponds to T'4 in Figure 5. q This is the quenching temperature. Therefore, the microstructure to be considered is m' target This is possible. In this case, TP' target After applying it to the steel plate, it is possible to apply a predetermined treatment.

[0048] The method according to the present invention makes it possible to obtain coils made of steel sheets including the predetermined product types, such as DP, TRIP, Q&P, TWIP, CFB, PHS, TRIPLEX, DUPLEX, and DP HD, and such coils have a standard deviation of mechanical properties of 25 MPa or less, preferably 15 MPa or less, and more preferably 9 MPa or less, between any two points along the coil. In fact, although we do not wish to be limited by any theory, the method including calculation step B.1) is considered to take into account the variation in the microstructure of the steel sheet along the coil. Therefore, the TP applied to the steel sheet in step B) target This enables homogenization of microstructure and mechanical properties.

[0049] Preferably, the mechanical properties are selected from YS, UTS, and elongation. A low standard deviation value is TP. target This is due to the accuracy of the system.

[0050] Preferably, the coil is covered with a metal coating based on zinc or aluminum.

[0051] Preferably, in industrial production, the standard deviation of the continuously measured mechanical properties between two coils made of steel sheets, including the predetermined product types such as DP, TRIP, Q&P, TWIP, CFB, PHS, TRIPLEX, DUPLEX, and DP HD, produced on the same line, is 25 MPa or less, preferably 15 MPa or less, and more preferably 9 MPa or less.

[0052] A thermal treatment line for carrying out the method according to the present invention is TP target These are used to carry out the following. For example, thermal treatment lines include continuous annealing furnaces, press hardening furnaces, batch annealing, or quenching lines.

[0053] Finally, the present invention is TP targetThe present invention relates to a computer program product comprising at least a metallurgical module, an optimization module, and a thermal module that cooperate with each other to determine a method according to the present invention, wherein such modules include software instructions that, when executed by a computer, perform a method according to the present invention.

[0054] The metallurgical module is a microstructure (metastable phase: bainite and martensite and stable phase: ferrite, austenite, cementite and pearlite). x , m target ), or more precisely, predict the proportion of each phase throughout the entire process and predict the rate of phase transformation.

[0055] The thermal module predicts the steel sheet temperature based on the equipment used for heat treatment, such as a continuous annealing furnace, process parameters including the geometric properties of the band, cooling capacity, heating capacity, or isothermal capacity, and the thermal enthalpy H released or consumed along all heat paths when the phase transformation is performed.

[0056] The optimization module is performed according to the method of the present invention using a metallurgical module and a thermal module, m target The best heat path to reach, i.e., TP target To decide.

[0057] The present invention is described here in terms of trials conducted for informational purposes only. These trials are not limiting. [Examples]

[0058] In this example, DP780GI having the following chemical composition was selected:

[0059] [Table 1]

[0060] To obtain a thickness of 1 mm, the reduction ratio during cold rolling was 50%.

[0061] m to reach target The following P target It contained 13% martensite, 45% ferrite, and 42% bainite, corresponding to YS at 500 MPa and UTS at 780 MPa. A cooling temperature of 460°C was used for hot-dip galvanizing with a zinc bath. cooling It also had to reach this temperature. To ensure good coverage within the Zn bath, this temperature had to be reached with an accuracy of + / - 2°C.

[0062] First, m target The microstructure closest to m standard To obtain a selected product having the following characteristics, steel plates were compared with a predetermined list of products. The selected product was DP780GI, which had the following chemical composition:

[0063] [Table 2]

[0064] The microstructure of DP780GI, i.e., m standard It contains 10% martensite, 50% ferrite, and 40% bainite. Corresponding thermal path TP standard This includes: - Preheating step: The steel plate is heated from ambient temperature to 680°C for 35 seconds. - Heating step in which the steel plate is heated from 680°C to 780°C for 38 seconds. - The steel plate is heated to a uniform temperature of 780°C T soaking Heat for 22 seconds, soaking step, - The steel plate is as follows HN x Cooling step: Cooled by 11 cooling jets that spray the solution:

[0065] [Table 3]

[0066] - Hot-dip plating in a zinc bath at 460℃, - Cooling of the steel sheet to the top roll at 300°C for 24.6 seconds and - Cooling of the steel plate at ambient temperature.

[0067] Next, numerous heat paths TP x The selected products are DP780 and TP standard and m target To reach m i It was calculated based on [the following].

[0068] TP x After the calculation, m target One heat path TP to reach target Select TP target , TP x Choose from, and m x ga m target I selected the one that was closest to it. TP target This includes: - Preheating step: The steel plate is heated from ambient temperature to 680°C for 35 seconds. - Heating step in which the steel plate is heated from 680°C to 780°C for 38 seconds, - The steel plate is heated to a uniform temperature of 780°C T soaking Heat for 22 seconds, soaking step, - The steel plate is as follows HN x Cooling step: Cooled by 11 cooling jets that spray the solution:

[0069] [Table 4]

[0070] - Hot-dip plating in a zinc bath at 460℃, - Cooling of the steel sheet to the top roll at 300°C for 24.6 seconds and - Cooling of the steel plate to ambient temperature.

[0071] Table 1 shows the TP for steel plates. standard and TP target The properties obtained are shown below:

[0072] [Table 5]

[0073] Table 1 shows the thermal path TP by the method according to the present invention. target This demonstrates that because it is adapted to each steel sheet, it is possible to obtain a steel sheet with the desired expected properties. On the other hand, the conventional thermal path TP standard Applying this will not yield the expected properties.

Claims

1. Within the heat treatment line, the chemical steel composition and the microstructure containing 0-100% of at least one phase selected from ferrite, martensite, bainite, pearlite, cementite, and austenite are determined. ｔａｒｇｅｔ A method for producing a thermally treated steel sheet having, A. 1) m ｔａｒｇｅｔ The microstructure closest to m ｓｔａｎｄａｒｄ Products having and m ｓｔａｎｄａｒｄ A predetermined heat path TP to obtain ｓｔａｎｄａｒｄ To select, chemical composition and m ｔａｒｇｅｔ However, it is compared with a predetermined list of products, and the microstructure is selected if it includes a predetermined number of phases and predetermined proportions of those phases, 2) TP ｘ The microstructure m obtained at the end of ｘ Each corresponding TP ｘ At least two heat paths TP ｘ Are the selected product and TP of step A.1) ｓｔａｎｄａｒｄ And m ｔａｒｇｅｔ The initial microstructure m of the steel sheet to reach ｉ Calculated based on, calculation sub-step 3) m ｔａｒｇｅｔ One heat path TP to reach ｔａｒｇｅｔ Selected, TP ｔａｒｇｅｔ , TP ｘ Selected from, and m ｘ ga m ｔａｒｇｅｔ Select the substep that is closest to it. Preparation steps, B. TP ｔａｒｇｅｔ A heat treatment step is performed on the steel plate. Methods that include...

2. The method according to claim 1, wherein the plurality of phases predetermined in step A. 1) are defined by at least one element selected from size, shape and chemical composition.

3. The aforementioned microstructure m ｔａｒｇｅｔ but, - 100% austenite, - 5-95% martensite, 4-65% bainite, the remainder being ferrite. - 8-30% retained austenite, 0.6-1.5% carbon in the solid solution, the remainder being ferrite, martensite, bainite, pearlite and / or cementite. - 1% to 30% ferrite and 1% to 30% bainite, 5% to 25% austenite, the remainder being martensite. - 5-20% retained austenite, the remainder being martensite. - Ferrite and retained austenite, - Retained austenite and intermetallic phases, - 80-100% martensite and 0-20% retained austenite - 100% martensite, - 5-100% perlite and 0-95% ferrite, - At least 75% equiaxed ferrite, 5-20% martensite, and 10% or less bainite. The method according to claim 1 or 2, including the method described in claim 1 or 2.

4. The method according to any one of claims 1 to 3, wherein the predetermined product type includes two phases, transformation-induced plasticity, quenched and distributed steel, twinning-induced plasticity, carbide-free bainite, press-hardened steel, TRIPLEX, DUPLEX, and high-ductility two phases.

5. I understand ｔａｒｇｅｔ and m Ｘ The method according to any one of claims 1 to 4, wherein the difference between the proportions of the phases present is ±3%.

6. Step A. 2) In m ｉ and m ｔａｒｇｅｔ The thermal enthalpy H released or consumed during this period is [Math 1] (X is the phase fraction.) The method according to any one of claims 1 to 5, which is calculated as follows.

7. Step A. 2) All thermal cycle TP ｘ but, [Math 2] (In the formula, Cpe: specific heat of the phase (J·kg)) －１ ・K －１ ), ρ: density of steel (g.m³) －３ ), Ep: thickness of the steel (m), φ: heat flux (convection + radiation, W), H ｘ (J.Kg －１ ), T: temperature (°C) and t: time (s). ) The method according to claim 6, which is calculated as follows.

8. Step A. 2) Intermediate heat path TP ｘｉｎｔ at least one intermediate steel microstructure corresponding to m ｘｉｎｔ and thermal enthalpy H ｘｉｎｔ The method according to claim 6 or 7, wherein the following is calculated.

9. Step A. 2) TP ｘ However, all TP ｘｉｎｔ It is the sum of H ｘ However, all H ｘｉｎｔ The method according to claim 8, which is the sum of the two.

10. Step A. Before step 1), select at least one target mechanical property P from among yield strength YS, maximum tensile strength UTS, elongation, hole expandability, and formability. ｔａｒｇｅｔ The method according to any one of claims 1 to 9, wherein is selected.

11. I understand ｔａｒｇｅｔ However, P ｔａｒｇｅｔ The method according to claim 10, calculated based on the following:

12. Step A. 2) The process parameter that the steel sheet goes through before entering the heat treatment line is TP ｘ A method according to any one of claims 1 to 11, which is considered for calculating the following:

13. The method according to claim 12, wherein the process parameters include at least one element selected from cold rolling reduction ratio, winding temperature, runout table cooling path, cooling temperature, and coil cooling rate.

14. The process parameters of the heat treatment line through which the steel plate passes are TP ｘ A method according to any one of claims 1 to 13, which is considered for calculating the following:

15. The method according to claim 14, wherein the process parameters include at least one element selected from a specific hot steel sheet temperature to be achieved, line speed, cooling capacity of the cooling section, heating capacity of the heating section, overaging temperature, cooling temperature, heating temperature, and soaking temperature.

16. Heat pathway, TP ｘ , TP ｘｉｎｔ , TP ｓｔａｎｄａｒｄ or TP ｔａｒｇｅｔ The method according to any one of claims 1 to 15, wherein the method comprises at least one treatment selected from heat treatment, isothermal treatment, or cooling treatment.

17. The method according to any one of claims 1 to 16, wherein each time a new steel sheet enters the heat treatment line, a new calculation step A. 2) is automatically performed based on a previously performed selection step A. 1).

18. The method according to claim 17, wherein when the steel sheet enters the heat treatment line, the thermal path adaptation is performed on the first few meters of the steel sheet.

19. A coil made of a steel sheet, comprising the predetermined product types including DP, TRIP, Q&P, TWIP, CFB, PHS, TRIPLEX, DUPLEX, and DP HD, which can be obtained by the method according to any one of claims 1 to 18, wherein the coil has a standard deviation of mechanical properties of 25 MPa or less between any two points along the coil.

20. The coil according to claim 19, wherein the standard deviation between any two points along the coil is 15 MPa or less.

21. The coil according to claim 20, wherein the standard deviation between any two points along the coil is 9 MPa or less.

22. A thermal treatment line for carrying out the method according to any one of claims 1 to 18.

23. TP ｔａｒｇｅｔ A computer program product comprising at least a metallurgical module, an optimization module, and a thermal module that cooperate with each other to determine, wherein such modules include software instructions that, when executed by a computer, perform the methods described in claims 1 to 18.

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