Improvement of hot bands for high-strength steel alloys

Abstract

Advanced high strength steel alloys are disclosed that provide a combination of toughness and directional toughness ratio (DTR). The combination of yield strength and tensile squareness ratio (TSR) can be achieved by hot band rolling at ambient or specified elevated temperatures.

Description

[Technical Field]

[0001] <Cross-reference of related applications> This application claims the interests of U.S. Provisional Patent Application No. 63 / 001,591, filed on 30 March 2020, and U.S. Provisional Patent Application No. 62 / 969,262, filed on 3 February 2020, both of which are incorporated herein by reference.

[0002] This application deals with a new class of advanced high-strength steel alloys that feature a combination of toughness and directional toughness ratio (DTR). The combination of yield strength and tensile squareness ratio (TSR) can be achieved by rolling a hot band at ambient temperature or a specified high temperature. [Background technology]

[0003] Toughness, or resistance to fracture, is crucial in many industrial applications. Automotive manufacturers seek materials with high toughness to absorb energy during collisions. Transportation industries, such as railways, require materials with high toughness to protect cargo during transit and in the event of collisions or derailments. In such applications, materials with high toughness are desired to provide and improve efficiency and safety for both the public and the cargo.

[0004] In simple terms, toughness as an engineering property can be thought of as the work energy required to cause fracture in a material. The more work required to cause fracture in a certain way, the higher the toughness of the material. Toughness in materials is becoming increasingly important in many fields, and high-toughness materials are increasingly being used to improve safety. In the automotive industry, high-toughness materials are used in so-called crumple zones to reduce the energy entering the vehicle during a collision. By using high-toughness materials, the gauge thickness can be reduced in areas where energy absorption is needed to protect occupants in a vehicle, improving fuel efficiency without compromising safety. These high-toughness materials can also be used in road barriers to absorb the energy of uncontrollable vehicles and bring them to a safe stop, preventing them from veering off the roadway or entering oncoming lanes. However, the automotive industry is not the only place where high-toughness materials are needed. In land transport by rail and water transport by ship, high-toughness materials can also improve the safety of cargo. In recent years, several accidents have occurred in which cargo ships have been damaged by collisions or derailments, resulting in significant losses of life, property, and cargo. New regulations have been introduced to mitigate the probability and impact of such accidents, and improving cargo storability using high-toughness materials is one option. By increasing the toughness of the materials used in such shipping containers, cargo can be retained within the container even if such an event occurs, reducing the environmental impact and loss of life and property that could result from cargo damage. Therefore, high-toughness materials offer many industries an opportunity to improve fuel and cargo efficiency while maintaining or enhancing safety.

[0005] In practical applications, uniform or isotropic toughness across multiple planes and orientations is crucial. While designers can plan specific impacts to best utilize anisotropic toughness in ideal cases, achieving this in uncontrolled events is difficult. Dynamic events such as collisions typically involve multiple impacts. The initial impact may initiate in a favorable manner, resulting in controlled material deformation. However, in complex events, subsequent impacts are likely to occur at different angles of incidence, potentially resulting in unfavorable orientations for the material being used. These events are more easily addressed in materials where toughness is similar or uniform across different orientations. If a material exhibits significant variation in toughness across different orientations, non-ideal impacts may prevent high toughness from being achieved in practical applications. For example, in layered or laminated structures, testing is conducted in favorable orientations, such as perpendicular to the layer planes, to achieve Charpy V-notch toughness exceeding 400 J. However, when tested in other orientations, toughness can be significantly impaired, often resulting in values ​​much lower than those in the preferred orientation (e.g., 1 / 5). In simple impact events, such as controlled experiments in the laboratory in the preferred orientation, these materials are expected to perform well. However, in real-world applications subjected to uncontrolled, unfavorable impact loads, effective toughness may be low or near zero. By using materials with more uniform toughness across multiple orientations, while toughness may be reduced compared to controlled experiments in non-ideal impact events, these materials are likely to be considerably more effective in terms of energy absorption than materials with non-uniform toughness.

[0006] Furthermore, multicomponent systems introduce potential complexity in achieving high toughness in real-world applications. The toughness of a multicomponent system is the sum of its energy absorption properties, and different parts of the system often have different toughness levels. Every multicomponent system inevitably has a weak point, and this weak point typically fails before the rest of the system. In the event of a failure, the other components in the system will deform and absorb energy until the system is compromised by the failure of the weak point. In these multicomponent systems, the individual parts will only experience partial strain, such as 10%, 20%, or 30% strain, until the system fails, and will not realize the full toughness of the material. Therefore, materials that achieve high toughness with high tensile elongation and moderate yield strength may not contribute adequately to energy absorption within the system during such events. This is because the majority of energy absorption in high-toughness, moderate-yield-strength materials is thought to occur at greater strains than the fracture strain (e.g., 10-30% strain range) of low-toughness or low-ductility materials. Furthermore, materials with comparable toughness but higher yield strength and ultimate tensile strength, and presumably lower elongation, are thought to contribute to greater energy absorption before the system fractures in the 10-30% strain range. Therefore, in multi-component systems, high yield strength and high ultimate tensile strength are preferable to achieve high energy absorption with low strain as a result of high loads before the system fractures at weak points. Materials with low yield strength and ultimate tensile strength but high tensile elongation can be improved to absorb more energy in the early stages of deformation by increasing yield strength and ultimate tensile strength through methods such as rolling at temperatures lower than the recrystallization and recovery temperatures, although these methods do not limit the materials. Through these methods, materials can be modified to meet the needs of multi-component systems. Advanced High Strength Steels (AHSS) are a class of materials with superior mechanical properties compared to conventional steels. Conventional mild steel has a relatively simple ferrite structure and typically has a low carbon content and few alloying elements, making it easy to form, and ductility is particularly desired.Mild steel, which is widely produced and used, is often used as a benchmark for comparison with other materials. Conventional low-to-high-strength steels include IF (extremely low carbon), BH (baking hardenable), and HSLA (high-strength low-alloy). These steels generally have a yield strength lower than 550 MPa, and their ductility decreases as their strength increases. High-strength steels are more composite and include types such as duplex steel (DP), polyplex steel (CP), and deformation-induced plastic steel (TRIP). High-strength steel is defined as steel exhibiting a tensile strength of 750 MPa or higher. Because high-strength steels above 750 MPa often have reduced ductility, cold workability, and toughness, the development of advanced high-strength steels is a challenge.

[0007] Fracture toughness is a material-specific parameter that quantifies a material's resistance to fracture under specific loading conditions. However, measuring fracture toughness is difficult for many engineering materials because tests for proper fracture must be performed without causing buckling or other undesirable plastic deformation. As a result, other methods that are more appropriate for the end application and simulate real-world fracture conditions are usually employed as ways to quantify toughness. One method is to calculate the area under the tensile stress-tensile strain curve, which provides an approximation of the energy required to fracture a specimen subjected to uniaxial tensile loading at a relatively constant strain rate. Dynamic impact testing is another method used to quantify toughness, in which rapid dynamic strain is applied to the material during the test. These tests accelerate fracture by limiting the time available for plastic deformation. The Charpy V-notch test is a commonly used technique to measure a material's fracture resistance by cracking it before the test. Drop impact tests can also be used to measure toughness, which measure a material's ability to withstand fracture caused by a moving mass without cracking. Unlike fracture toughness tests, toughness tests, not limited to the methods described above, do not provide material parameters; rather, they provide values ​​specific to the test, the material, and the loading conditions. The values ​​obtained in each test can be compared to other materials in the same test if necessary during material selection. Generally, steel grades with high ductility, measured as total elongation in tensile tests, exhibit high toughness in impact tests as well. However, high ductility can lead to a decrease in strength properties, including yield strength. [Overview of the project]

[0008] The present invention is a method for achieving a combination of properties, including toughness and directional toughness ratio (DTR), in a hot band made from a high-strength steel alloy. a. A metal alloy containing at least 65 atomic percent of Fe, Mn, Cr, Si, and C, and optionally Ni and / or Cu, is supplied; the alloy is melted; cooled at a rate of <250 K / s; and solidified to a thickness of 25.0 mm to 500 mm. b. A step of processing the alloy by heating the metal alloy of step (a) and rolling it in a selected direction to reduce its thickness, wherein a sheet having a thickness of 10.0 mm to 20.0 mm is formed, and optionally, the alloy sheet is exposed to a temperature range of 600°C to less than the melting point Tm of the alloy to produce an alloy sheet having a total elongation E1 of 30 to 75%, a yield strength Y1 at a 0.2% offset of 250 to 525 MPa, an ultimate tensile strength U1 of 750 to 1400 MPa, and a tensile square ratio TSR1 of 0.65 to 0.90, the step of processing the alloy, (1) The V-notch Charpy sample cut from the alloy sheet absorbs an impact energy of 150 J to 850 J, (2) The directional toughness ratio (DTR) is calculated by dividing the impact energy absorbed by a V-notch Charpy sample, which is a sample cut from the alloy sheet and has a notch formed perpendicular to the longitudinal plane of the sheet, by the impact energy absorbed by a V-notch Charpy sample, which is a sample cut from the alloy sheet and has a notch formed perpendicular to the width-longitudinal plane of the sheet, and the directional toughness ratio (DTR) is provided to be 0.8 to 1.5.

[0009] Furthermore, a method for achieving a combination of properties, including yield strength and tensile square ratio (TSR), in a hot band made from a steel alloy, a. A metal alloy containing at least 65 atomic percent of Fe, Mn, Cr, Si, and C, and optionally Ni and / or Cu is supplied, the alloy is melted, cooled at a rate of <250 K / s, and solidified to a thickness of 25.0 mm to 500 mm. b. Processing the alloy by heating the alloy and reducing the thickness to form a sheet having a thickness of 10.0 mm to 20.0 mm, and optionally exposing the alloy sheet to a temperature of 600 °C to less than Tm to produce an alloy sheet having an elongation E1 of 30 to 75%, a yield strength Y1 at 0.2% offset of 250 to 525 MPa, an ultimate tensile strength U1 of 750 to 1400 MPa, and a tensile rectangular ratio TSR1 of 0.65 to 0.90. c. Rolling the alloy sheet, comprising: (1) reducing the thickness of the sheet in step (b) by 1 to 10% in a first temperature range T1 of 15 °C to <50 °C, or (2) reducing the thickness of the sheet in step (b) by 10 to 40% in a second temperature range of 50 °C to ≦600 °C to produce an alloy sheet having a yield strength Y2≧Y1 and a tensile rectangular ratio TSR2>TSR1.

Brief Description of the Drawings

[0010] [Figure 1] Figure 1 shows an overview of the steps for the present alloy to achieve a novel combination of properties including toughness and direction toughness ratio.

[0011] [Figure 2] Figure 2 shows an overview of the steps for the present alloy to achieve a novel combination of properties including yield strength and tensile rectangular ratio.

[0012] [Figure 3] Figure 3 is an example of an engineering stress-strain curve, representing the energy absorption throughout the tensile test, and the areas under the curves are equal (SA = SB). Note that the behaviors of Material 1 and Material 2 are different during the test, and Material 2 has a greater energy absorption at initial strain than Material 1.

[0013] [Figure 4]Figure 4 shows an example of an engineering stress-strain curve, illustrating two regions: A) the ductility region calculated based on the product of UTS and strain at UTS (lightly shaded rectangular area), and B) the ductility region calculated based on the area below the curve up to UTS (darkly shaded area). The Tensile Squareness Ratio (TSR) is defined as the area ratio of B / A.

[0014] [Figure 5] Figure 5 is a schematic diagram illustrating the orientation of V-notch Charpy samples taken from an alloy sheet to determine the directional toughness ratio (DTR). The directional toughness ratio (DTR) is calculated by dividing the impact energy absorbed by a V-notch Charpy sample, which is a sample cut from the alloy sheet and has a notch formed perpendicular to the longitudinal-normal plane of the sheet, by the impact energy absorbed by a V-notch Charpy sample, which is a sample cut from the alloy sheet and has a notch formed perpendicular to the transverse-longitudinal plane of the sheet.

[0015] [Figure 6] Figure 6 is a schematic diagram of a Charpy V-notch sample, and the units of measurement are in millimeters unless otherwise specified.

[0016] [Figure 7] Figure 7 shows images of the orientation of the LN in unbroken samples after Charpy testing for 80 alloy samples.

[0017] [Figure 8] Figure 8 shows SEM images of the fracture surfaces of 66 alloy samples in the orientation of the LN after Charpy testing.

[0018] [Figure 9]Figure 9 shows SEM images of the fracture surfaces of alloy 66 samples in the LT orientation after Charpy testing.

[0019] [Figure 10] Figure 10 shows SEM images of the fracture surface of alloy 80 samples in the LT orientation after Charpy testing.

[0020] [Figure 11] Figure 11 shows SEM images of the fracture surfaces of alloy 84 samples in the orientation of the LN after Charpy testing.

[0021] [Figure 12] Figure 12 shows SEM images of the fracture surfaces of alloy 84 samples in the LT orientation after Charpy testing.

[0022] [Figure 13] Figure 13 is an SEM micrograph of the fracture surface of the hot band of alloy 2 before annealing.

[0023] [Figure 14] Figure 14 is an SEM micrograph of the fracture surface of the hot band of alloy 2 after annealing at 600°C for 10 minutes.

[0024] [Figure 15] Figure 15 is an SEM micrograph of the fracture surface of the hot band of alloy 3 before annealing.

[0025] [Figure 16] Figure 16 is an SEM micrograph of the fracture surface of the hot band of alloy 3 after annealing at 600°C for 10 minutes.

[0026] [Figure 17] Figure 17 shows the types of fracture behavior of materials in instrumented Charpy tests, a) Type I, b) Type II, c) Type III, and d) Type IV.

[0027] [Figure 18] Figure 18 shows the force-displacement curve of alloy 18, which exhibits type IV behavior.

[0028] [Figure 19] Figure 19 shows the force-displacement curve for alloy 32, which exhibits type IV behavior.

[0029] [Figure 20] Figure 20 shows the force-displacement curve for alloy 37, which exhibits type IV behavior.

[0030] [Figure 21] Figure 21 shows the force-displacement curve for alloy 44, which exhibits type IV behavior.

[0031] [Figure 22] Figure 22 shows the yield strength of the hot band of alloy 66 during rolling at ambient temperature as a function of reduction.

[0032] [Figure 23] Figure 23 shows the yield strength of the hot band of alloy 80 as a function of reduction ratio when rolled at ambient temperature.

[0033] [Figure 24] Figure 24 shows the yield strength of the hot band of alloy 84 as a function of reduction ratio when rolled at ambient temperature.

[0034] [Figure 25] Figure 25 shows the tensile rectangle ratio of the hot band of alloy 66 as a function of the reduction ratio during rolling at ambient temperature.

[0035] [Figure 26] Figure 26 shows the tensile rectangle ratio of the hot band of alloy 80 as a function of the reduction ratio during rolling at ambient temperature.

[0036] [Figure 27] Figure 25 shows the tensile rectangle ratio of the hot band of alloy 84 as a function of the reduction ratio during rolling at ambient temperature.

[0037] [Figure 28] Figure 28 shows the yield strength of the hot band of alloy 66 as a function of reduction ratio when rolled at 550°C.

[0038] [Figure 29] Figure 29 shows the yield strength of the hot band of alloy 80 as a function of reduction ratio when rolled at 600°C.

[0039] [Figure 30] Figure 30 shows the yield strength of alloy 84 as a function of temperature when the hot band is rolled with a reduction ratio of 10%.

[0040] [Figure 31] Figure 31 shows the tensile rectangle ratio of the hot band of alloy 66 as a function of the reduction ratio when rolled at 550°C.

[0041] [Figure 32] Figure 32 shows the tensile rectangle ratio of the hot band of alloy 80 as a function of the reduction ratio when rolled at 600°C.

[0042] [Figure 33] Figure 33 shows the tensile square ratio of the hot band of alloy 84 as a function of temperature during rolling with a reduction ratio of 10%.

[0043] [Figure 34] Figure 34 shows the force-displacement curve of a hot band of alloy 88 with a thickness of 11.9 mm, exhibiting type IV behavior.

[0044] [Figure 35]Figure 35 shows the force-displacement curve of the hot band after rolling alloy 88 at ambient temperature with a reduction ratio of 3%, exhibiting Type IV behavior.

[0045] [Figure 36] Figure 36 shows the force-displacement curve of the hot band after rolling alloy 88 at ambient temperature with a reduction ratio of 9%, exhibiting Type IV behavior.

[0046] [Figure 37] Figure 37 shows the force-displacement curve of a 17.5 mm thick hot band of alloy 88, exhibiting type IV behavior.

[0047] [Figure 38] Figure 38 shows the force-displacement curve of the hot band after rolling alloy 88 at 550°C with a reduction ratio of 20%, exhibiting Type IV behavior.

[0048] [Figure 39] Figure 39 shows the force-displacement curve of the hot band after rolling alloy 88 at 550°C with a reduction ratio of 40%, exhibiting type IV behavior. [Modes for carrying out the invention]

[0049] <Detailed description of a preferred embodiment> This alloy can be manufactured in sheet or plate form by various casting methods, including, but not limited to, continuous casting, thin-walled slab casting, thick-walled slab casting, and bloom casting, and subsequent hot rolling and optional heat treatment can achieve combinations of advanced properties. Further applications include rolling at ambient temperature or at an identified elevated temperature. Figures 1 and 2 outline the steps by which this alloy achieves novel combinations of properties, including toughness, yield strength, tensile square ratio (TSR), and directional toughness ratio (DTR), in hot bands with thicknesses from 2 mm to 20 mm.

[0050] Figure 1 outlines the steps for achieving a novel combination of properties, including toughness and directional toughness ratio (DTR), in high-strength steel. High-strength steel refers to steel exhibiting a tensile strength of 750 MPa or higher. Furthermore, the method is applied to hot bands, which can be understood as sheets of steel that have been hot-rolled to reduce their thickness.

[0051] Therefore, in step 1 of Figure 1, the starting condition is to supply a metal alloy containing at least one element selected from Fe, Mn, Cr, Si, and C, as well as Ni and Cu. The alloy chemistry is melted, cooled at a rate of <250 K / s, and solidified to a thickness of 25 mm to 500 mm. The casting process can be carried out in a wide variety of ways, such as ingot casting, bloom casting, continuous casting, thin-walled slab casting, thick-walled slab casting, and belt casting. The preferred method is continuous casting in the form of sheets or plates by thin-walled or thick-walled slab casting.

[0052] Step 2 in Figure 1 corresponds to a sheet or plate of hot band made from the alloy, with a thickness of 10.0 to 20.0 mm. To manufacture this alloy in hot band form, hot rolling in a selected direction is applied to the cast product (slab, bloom, etc.). One example is thick-walled slab casting as one process route to a hot band product. The alloy is cast through a water-cooled mold to a thickness typically ranging from 150 to 350 mm, then typically processed into a transfer bar slab with a thickness of 25 to 150 mm via hot rolling on a roughing mill, and finally processed into a hot band with a thickness of 10.0 to 20.0 mm via a finish rolling mill. More preferably, the thickness of the alloy in step 2 may be 10.0 mm to 15.0 mm, and even more preferably, the thickness of the alloy may be 10.0 mm, 11.0 mm, 12.0 mm, 13.0 mm, 14.0 mm, 15.0 mm, 16.0 mm, 17.0 mm, 18.0 mm, 19.0 mm, or 20.0 mm.

[0053] Another example would preferably involve processing the casting material via a thin-walled slab casting process. In this case, after casting typically to a thickness of 25–150 mm by passing through a water-cooled mold, the newly formed slab is directly hot-rolled, and the strip is rolled into a hot-band coil, typically 10.0–20.0 mm thick. Bloom casting is similar to the above example, but is typically cast to a thicker thickness, typically 200–500 mm, so it should be noted that an initial fracture step will be required to reduce the initial casting thickness so that hot rolling can be performed. Thin-walled slab casting is another process route that can obtain hot-band products with a thickness of 10.0–20.0 mm. By heating and reducing the thickness to 10.0–20.0 mm, a relatively ductile structure with a total elongation of 30–75% is formed, exhibiting a microvoid coalescene mechanism at fracture. Microvoid coalescence is a ductile fracture mechanism involving the nucleation, growth, and coalescence of microvoids, and is preferred over other brittle fracture modes such as intergranular fracture and intragranular cleavage. Optionally, the hot-band product can be exposed to a temperature range of 600°C to less than Tm (where Tm is the melting point of the alloy) by annealing. Preferably, the hot-band of the alloy has a total elongation of 30-75% (E1), a yield strength of 250-525 MPa (Y1), and a tensile strength of 750-1400 MPa (U1).

[0054] Among the methods for evaluating the toughness of a material, the tensile test is the most widely used method for evaluating mechanical properties. Generally, this involves applying a tensile load to a sample with a thickness reduction using a moving crosshead until the sample fractures. Since the displacement rate of the crosshead in a tensile test is generally kept constant or nearly constant, the range of strain rates during the test is narrow. The tensile test can provide a measure of toughness by calculating the integral of the engineering stress-engineering strain curve (area under the curve), which corresponds to the work required to break the sample in tension (Figure 3). The material behavior during the tensile test in step 2 of Figure 1 corresponds to material 1 in Figure 3, which is the ultimate tensile strength multiplied by the total elongation (strength-ductility product), and in the case of this alloy, it was determined to vary in the range of 25,000 to 80,000 MPa%. The material was reduced to 10% (S1 0.1 The area under the stress-strain curve corresponding to the work required to deform it to ) is 4,500-8,500 MPa%, and 20% (S1 0.2 The area that can be deformed up to 10,500-18,500 MPa% is 30% (S1 0.3 The area that can be deformed to this extent is 17,500 to 27,000 MPa%.

[0055] Another method for evaluating toughness is to look only at the uniform elongation (before necking). In Figure 4, this is shown as region A, which is enclosed by a rectangle and a dotted line, and is defined as the product of UTS and the strain at UTS. For this alloy, the toughness value in region A is 20,000 to 65,000 MPa%. In Figure 4, the region below the UTS point of the stress-strain curve is represented as region B. The ratio B / A is defined as the tensile rectangle ratio (TSR), and provides a measure of the material toughness achieved based on the potential of the material. Therefore, the closer the TSR is to 1.0, the higher the toughness achieved in the material is compared to its potential value. The calculated tensile rectangle ratio (TSR1) for this alloy was in the range of 0.65 to 0.90.

[0056] The alloy sheet produced in step (2) can be arranged as all or part of a storage tank, freight car, railway tank car, vehicle frame, vehicle chassis, vehicle panel, and / or the alloy sheet can be used in a battery exo-skeleton (i.e., an external skeleton that protects a battery from external damage), a battery tray (i.e., a protective structure consisting of an upper and lower half that prevents water or other corrosive agents from coming into contact with the battery and improves thermal management), or a battery cage (i.e., a structure designed to enclose and protect individual or multiple batteries). Thus, the alloy sheet can be configured and utilized as all or part of any one of these aforementioned applications. Furthermore, the impact energy in the range of 150J to 850J absorbed by the V-notch of the sheet is the same impact energy that would occur in such an alloy sheet when arranged and utilized in these applications.

[0057] In step 3 of Figure 1, the hot band of the alloy is subjected to impact until fracture occurs in one or more stages, and the amount of energy absorbed (J) is recorded. The toughness of the alloy hot band can be evaluated by a Charpy V-notch impact test. The Charpy impact test is performed by applying a dynamic load to the specimen with a swing hammer, starting from a known height and distance from the center of rotation. Both ends of the specimen are free in the Charpy impact test, and the load on the specimen is the same as in the three-point bending test. The total energy of the moving hammer is known, and the energy lost in impact with the specimen can be measured by the angle of rotation of the hammer after impact. In the Charpy V-notch test, the specimen has a pre-machined stress concentration point at the tip of the V-notch, which promotes crack nucleation. In this test, the hammer strikes the face opposite the machined notch. The Charpy V-notch impact test measures the work required to plastically deform the specimen and the nucleation and propagation of cracks. The uniformity of toughness in a sheet or plate of this alloy can be determined by the directional toughness ratio (DTR). As can be understood, the alloy sheet of the present invention may also be described as having a longitudinal-normal plane, as shown in Figure 5, otherwise this plane is a plane defining the stretched edge portion of the sheet, as illustrated. The longitudinal direction coincides with the rolling direction of the sheet. Furthermore, the sheet may include a width-longitudinal plane, which is a plane defining the top or bottom surface of the sheet, as illustrated. Next, a sample may be cut from the sheet, a notch perpendicular to the longitudinal-normal plane of the sheet may be formed, and the Charpy impact strength of such first sample may be measured (LN). Next, a sample may be cut from the sheet, a notch perpendicular to the width-longitudinal plane of the sheet may be formed, and the Charpy impact strength of such second sample may be measured (LT). The DTR value is then determined by dividing the Charpy impact result (LN) of the first sample by the Charpy impact result (LT) of the second sample.In Figure 5, it should be noted that the LN and LT portions were identified from samples taken from the sheet alloy of the present invention having a thickness of 10.0 mm to 20.0 mm. DTR The closer this value is to 1.0, the more uniform the toughness achieved in the alloy. The hot band from this alloy has a directional toughness ratio (DTR) of 0.8 to 1.5. Preferably, the hot band from this alloy has a Charpy V-notch toughness (J1) of 150 J to 850 J.

[0058] Figure 2 outlines the steps for achieving a novel combination of properties, including yield strength and tensile square ratio (TSR), after rolling the hot band of the alloy at ambient or intermediate temperatures. Steps 1 and 2 are the same as in Figure 1. In step 3 of Figure 2, the hot band of the alloy is rolled in a first or second temperature range (as specified herein), and the sheet passes through a set of rolls to further reduce the sheet thickness. Rolling can be carried out by many means using numerous forms of rolling mills, including, but not limited to, reversing mills, tandem mills, and senzimir mills. This process reduces the thickness of the hot band by plastically deforming the material by utilizing the deformation mechanisms available to the material in the first or second temperature range, which alters the properties and behavior of the material. Preferably, the rolling of the hot band of the alloy results in a thickness reduction of 1 to 10% at a first ambient temperature (T1) of 15°C to less than 50°C, or a thickness reduction of 10 to 40% at a second high temperature range (T2) of 50 to 600°C. In all cases, a metal alloy sheet with increased yield strength is formed, Y2 > Y1, and the tensile square ratio is TSR2 > TSR1. TSR2 is calculated to be in the range of 0.75 to 0.95 for this alloy. The material behavior during the tensile test in step 3 of Figure 2 corresponds to material 2 in Figure 3. To further define the shape of the stress-strain curve and the toughness at intermediate temperatures, three applied strain levels were defined and shown in Figure 3 at 10%, 20%, and 30% strain levels. 0.1 >S1 0.1The area under the stress-strain curve for the work required to distort up to 0.2 >S1 0.2 5,500 - 10,500 MPa% and the area for distortion up to 20% (S2 0.3 >S1 0.3 ) is 13,000 - 21,000 MPa%, and the area for distortion up to 30% (S2

[0059] The alloy sheet produced in step (3) can be arranged as all or part of a storage tank, freight car, railroad tank car, vehicle frame, vehicle chassis, vehicle panel, and / or the alloy sheet can be used as all or part of a battery exoskeleton, battery tray, or battery cage. Therefore, this alloy sheet can be configured and utilized as all or part of any one of these aforementioned uses.

[0060] {Main body} <Alloy> The chemical composition of this alloy is shown in Table 1, and preferred atomic ratios are indicated.

[0061] [[ID=2​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​As shown in Table 1, preferably, the alloy provides an elemental composition in which Fe is present in greater than 65 atomic percent, and one or two elements from the group consisting of Mn, Cr, Si, and C, and Ni and Cu, totaling 100 atomic percent. More preferably, the alloy may be described as containing, or being essentially composed of, the elements Fe (65.0-80.0 atomic percent), Mn (9.5-17.5 atomic percent), Cr (1.0-10.0 atomic percent), Si (1.0-5.5 atomic percent), and C (0.5-1.5 atomic percent), and optionally Ni (0.2-4.0 atomic percent) and Cu (0.1-2.5 atomic percent), in the indicated atomic percent (when present), or being essentially composed of, or being composed of, the elements. The total amount of impurities of other elements is in the range of 0-5,000 ppm. Therefore, for individual elements defined as impurities, the total amount of a particular element is <1,000 ppm. The content of all such selected elements may be such that, in combination of elements, they account for 5,000 ppm of impurities, but the total amount of all elements present (selected elements and impurities) is 100 atomic percent.

[0066] This alloy was processed into laboratory sheets by treating laboratory slabs. The processing of the laboratory alloy simulates industrial sheet manufacturing through continuous casting and hot rolling. Annealing may also be applied depending on the desired properties.

[0067] <Laboratory Slab Casting> Using commercially available ferroadditive powders and base steel raw materials with known chemical composition, alloys were weighed into 3,000–3,400 g charges according to the atomic ratios in Table 1. Impurities can be present at varying levels depending on the raw materials used. Commonly present impurity elements are Co, Al, N, P, Ti, W, Mo, Nb, V, Ga, Ge, Sb, Zr, O, Sn, Ca, B, and S, and, if present, are in the range of 0–5,000 ppm (parts per million) (0–0.5 wt%) at the expense of the desirable elements mentioned above. Preferably, the level of impurities is controlled to fall within the range of 0–3,000 ppm (0.3 wt%).

[0068] The above quantities were placed in a zirconia-coated silica crucible and then placed in an Indutherm VTC800V vacuum inclined casting machine. Next, to prevent oxidation of the molten material, the casting chamber and melting chamber of the casting machine were evacuated and flushed twice with argon to atmospheric pressure before casting. The molten material was heated for approximately 5-7 minutes using a 14kHz RF induction coil until completely dissolved, depending on the alloy composition and the weight of the charge. After confirming the dissolution of the last solid, it was heated for a further 30-45 seconds to ensure the homogeneity of the molten material. Next, the chamber of the casting machine was evacuated, the crucible was tilted, and the molten material was poured into a water-cooled copper die. After the molten material was cooled under vacuum for 200 seconds, the chamber was filled with argon and brought to atmospheric pressure.

[0069] <Material properties of cast alloys> Samples of 50–150 mg were taken from each alloy in the as-cast state. These samples were heated at a rate of 40°C / min to an initial ramp temperature between 900°C and 1300°C, depending on the alloy's chemical properties. The temperature was then increased at a rate of 10°C / min, depending on the alloy's chemical properties, to a maximum temperature between 1425°C and 1510°C (the maximum temperature limit of the DSC instrument used). Once this maximum temperature was reached, the sample was cooled at a rate of 10°C / min back to the initial ramp temperature, and then reheated to the maximum temperature at 10°C / min. Differential scanning calorimeter (DSC) measurements were performed throughout all four stages of the experiment using a Netzsch Pegasus 404 DSC, and this data was used to determine the solidus and liquidus temperatures of each alloy. These temperatures range from 1369–1469°C, as shown in Table 2. In preferred embodiments of this alloy, the solidus temperature is 1350°C to 1450°C, the liquidus temperature is 1400°C to 1500°C, and the gap between the liquidus and solidus is 40°C to 100°C. Thermal analysis provides information on the maximum temperature of the hot rolling process, which varies depending on the chemical properties of the alloy.

[0070] [Table 2-1]

[0071] [Table 2-2]

[0072] [Table 2-3]

[0073] [Table 2-4]

[0074] The density of this alloy was measured using the Archimedes method with a balance specially configured to weigh in both air and distilled water, by measuring samples from hot-rolled material. The densities of each alloy are shown in Table 3, ranging from 7.74 to 7.91 g / cm³. 3 It was found to be within this range. The accuracy of this technology is ±0.01 g / cm². 3 That is the case.

[0075] [Table 3-1]

[0076] [Table 3-2]

[0077] <Processed into hot bands for tensile testing by hot rolling in the laboratory> Due to the limitations of the load cell, tensile testing of 10 mm thick samples was not possible. Therefore, to measure the tensile properties of the material, it was hot-rolled to a thinner gauge. Slabs of alloys 1 to 44 in Table 1 were hot-rolled to a final thickness of approximately 4 mm. Laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace before hot-rolling. The furnace temperature was set to 1100°C to 1250°C depending on the melting point of the alloy and the temperature of the hot-rolling process. The initial temperature was set high to easily obtain a large reduction, and the subsequent temperature was set low to minimize surface oxidation of the hot band. To ensure that the slab reached the target temperature, it was soaked for 40 minutes before hot-rolling, and then removed from the tunnel furnace and fed into a Fenn Model 061 two-stage rolling mill. 50 mm castings were hot-rolled by passing through the rolling mill 5 to 10 times, and then air-cooled. The final thickness after hot rolling is 3.89–4.24 mm. While the tensile tests in this study were conducted at these final thicknesses due to load limitations, the microstructure of the hot band is sufficiently homogenized in the 10.0 mm–20.0 mm range. Therefore, it is reasonable to conclude that these tensile properties exist within this range.

[0078] Tensile samples were cut from laboratory hot bands using wire EDM (Electrical Discharge Machining). Tensile properties were measured on an Instron Model 3369 mechanical test frame equipped with hydraulic grips, using Instron's Bluehill control and analysis software. The load limit of the 3369 test frame was 150kN, and the hydraulic grips were limited to a load of 120kN. Due to the high strength of the alloys, considering the load limitations, the maximum thickness of the sample that could be subjected to tensile testing until failure was 7mm. To obtain tensile data, 4mm thick hot bands were subsequently prepared, and the results for 4mm thick hot band samples (3-4 samples for each alloy), including the area under the stress-strain curve, are shown in Table 4. The ultimate tensile strength of sheets annealed with this alloy is 784–1218 MPa, the yield strength at a 0.2% offset is 257–391 MPa, the recorded total elongation is 36.6–72.1%, and the area under the tensile stress-strain curve ranges from 29,272–61,055 MPa%.

[0079] The strength-ductility product is calculated by multiplying the UTS by the total tensile elongation and is in the range of 41,800 to 73,600 MPa%. The tensile square ratio (TSR) (Figure 4) is determined by dividing the area under the stress-strain curve up to the UTS by the product of the UTS and the strain at the UTS, and the calculated value is in the range of 0.70 to 0.85. Table 5 shows the area under the tensile curve for this alloy after being subjected to 10%, 20%, and 30% strain. 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 4,791 to 5,973 MPa%, and 20% (S1 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 10,949 to 13,556 MPa%, and 30% (S1 0.3 The area under the stress-strain curve corresponding to the work required to cause deformation is in the range of 17,933 to 23,256 MPa%. Note that the characteristics in Tables 4 and 5 correspond to Step 2 in Figures 1 and 2.

[0080] Table 4-1

[0081] Table 4-2

[0082] Table 4-3

[0083] Table 4-4

[0084] Table 4-5

[0085] Table 4-6

[0086] Table 4-7

[0087] Table 5-1

[0088] Table 5-2

[0089] Table 5-3

[0090] Table 5-4

[0091] [Table 5-5]

[0092] [Table 5-6]

[0093] [Table 5-7]

[0094] The slabs of alloys 45 to 88 shown in Table 1 were hot-rolled to a final thickness of approximately 2.5 mm. Before hot-rolling, the laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace. The furnace temperature was varied between 1100°C and 1250°C depending on the melting point of the alloy and the temperature of the hot-rolling process. The initial temperature was set high to easily obtain a large reduction, and the subsequent temperature was set low to minimize surface oxidation of the hot band. To ensure that the slabs reached the target temperature, they were soaked for 40 minutes before hot-rolling, and then removed from the tunnel furnace and fed into a Fenn Model 061 two-stage rolling mill. The 50 mm castings were hot-rolled by passing through the rolling mill 5 to 10 times, and then air-cooled. The final thickness after hot-rolling was 2.37 to 2.60 mm. Hot bands in this thickness range are thought to have similar properties to those in the 10-20 mm thickness range, but these reduced-thickness hot bands were much faster to cut into tensile samples by wire EDM.

[0095] Tensile properties were measured on an Instron mechanical test frame (Model 3369) equipped with hydraulic grips, using Instron's Bluehill control and analysis software. The load limit of the 3369 test frame was 150 kN, and the hydraulic grips were limited to a load of 120 kN. Due to the high strength of these alloys, considering the load limit, the maximum thickness of the sample that could be subjected to tensile testing until failure was 7 mm. The tensile test results of a 2.5 mm thick hot band are shown in Table 6, including the area under the stress-strain curve. The ultimate tensile strength of sheets from this alloy was 902–1383 MPa, the yield strength at a 0.2% offset (determined by drawing parallel lines with a 0.2% offset on the initial stress-strain curve and recording the resulting intersection) was 267–504 MPa, the recorded total elongation was 34.7–65.3%, and the area under the tensile stress-strain curve ranged from 30,497–64,399 MPa%. The product of strength and ductility is calculated by multiplying UTS by total tensile elongation and is in the range of 41,755 to 79,325 MPa%. The tensile square ratio (TSR) (Figure 4) is determined as the area under the stress-strain curve up to UTS divided by the product of UTS and the strain at UTS, and the calculated value is in the range of 0.66 to 0.89. Table 7 shows the area under the tensile curve for this alloy after being subjected to 10%, 20%, and 30% strain. 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 5,521 to 6,861 MPa%, and 20% (S1 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 13,676 to 15,310 MPa%, and 30% (S1 0.3 The area under the stress-strain curve corresponding to the work required to deform the material is in the range of 22,332 to 25,777 MPa%. Note that the characteristics in Tables 6 and 7 correspond to Step 2 in Figures 1 and 2.

[0096] [Table 6-1]

[0097] [Table 6-2]

[0098] Table 6-3

[0099] Table 6-4

[0100] Table 6-5

[0101] Table 6-6

[0102] Table 6-7

[0103] Table 7-1

[0104] Table 7-2

[0105] Table 7-3

[0106] Table 7-4

[0107] Table 7-5

[0108] [Table 7-6]

[0109] [Table 7-7]

[0110] <Processed into hot bands for toughness testing by hot rolling in the laboratory> The laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace before hot rolling. The furnace temperature was set between 1100°C and 1250°C, depending on the melting point of the alloy and the temperature of the hot rolling process. The initial temperature was set high to easily obtain a large reduction, and the subsequent temperature was set low to minimize surface oxidation of the hot band. To ensure that the slabs reached the target temperature, they were soaked for 40 minutes before hot rolling, and then removed from the tunnel furnace and fed into a Fenn Model 061 two-stage rolling mill. The 50mm castings were hot-rolled by passing through the mill 5 to 10 times, and then air-cooled. The final thickness after hot rolling was approximately 12mm.

[0111] The toughness of the material was measured by a Charpy V notch test. Charpy V notch samples were cut from hot-rolled sheets using wire EDM. As shown in Figure 5, the Charpy V notch samples were cut in the direction of LT (sample length in the rolling direction, notch in the transverse direction) and LN (sample length in the rolling direction, notch in the normal direction relative to the rolling surface).

[0112] The Charpy V-notch specimen was cut to a thickness of (10 mm × 55 mm × 10 mm) in accordance with ASTM E23-12c, with a central 45° V-notch having a radius of 0.25 mm and a depth of 2 mm, and the surface finish Ra of the notch and impact surface being less than 2.0 μm. An example of a Charpy V-notch specimen before testing and its schematic diagram are shown in Figure 6. The Charpy V-notch specimen was placed using self-centering tongs to ensure it was centered on the anvil. The test was performed using a Satec Systems S1-1K3 pendulum impact tester. The impact tester's arm was set to the high-latch position, and a 66.6-pound weight was configured to indicate approximately 400 J, the maximum reading on the dial. After releasing the latch and making contact with the specimen, the energy absorbed by the specimen was recorded in joules.

[0113] The test results are shown in Table 8. The absorbed energy values ​​of this alloy during the Charpy V-notch test range from 154 to 407 J under hot band conditions. The directional toughness ratio (DTR) was calculated based on the test results. The directional toughness ratio (DTR) was calculated by dividing the impact energy absorbed by a V-notch sample cut from an alloy sheet with a notch perpendicular to the longitudinal-normal plane of the alloy sheet by the impact energy absorbed by a V-notch sample cut from an alloy sheet with a notch perpendicular to the width-longitudinal plane of the alloy sheet. The DTR (LN / LT) of this alloy ranges from 0.93 to 1.44. The properties in Table 8 correspond to step 3 in Figure 1.

[0114] [Table 8-1]

[0115] [Table 8-2]

[0116] [Table 8-3]

[0117] [Table 8-4]

[0118] {Case Study} <Case Study #1: Uniformity of Hot Band Toughness> For impact toughness testing, hot bands of alloys 66, 80, and 84 with thicknesses exceeding 10 mm were used. Laboratory slabs with a thickness of 80 mm were cast from alloys with atomic ratios shown in Table 1 and processed in the laboratory by hot rolling as described in the "Main Body" section of this application until they reached a thickness of approximately 12 mm.

[0119] V-notch Charpy samples were cut from laboratory-prepared hot bands using an EDM in different orientations, as shown in Figure 5. The V-notch Charpy samples used for impact testing were cut from hot-rolled sheets. Impact testing was performed using an Instron SI-1B Charpy impact testing machine. The V-notch Charpy impact energy was... 246 The value was ~372J, and the results are shown in Table 9. Based on the test results, two types of directional toughness ratios (DTR) were calculated as the ratio of the toughness in the direction of the Charpy impact normal to the hot band surface to the toughness in the direction of the Charpy impact width. For samples oriented in the longitudinal direction, the DTR (LN / LT) varied from 1.09 to 1.18. Note that the characteristics in Table 9 correspond to step 3 in Figure 1.

[0120] Fracture samples of each alloy in each direction were placed on a Zeiss MA-10 scanning electron microscope (SEM) to examine the fractured surface. Note that the alloy 80 sample in the LN direction did not fracture during the test and is shown in Figure 7. Microscopic images of the fracture surfaces are shown in Figures 8 and 9 for the alloy 66 sample, in Figure 10 for the alloy 80 sample, and in Figures 11 and 12 for the alloy 84 sample. Microvoid coalescence was observed in all samples, exhibiting ductile fracture in all four directions.

[0121] [Table 9]

[0122] This case demonstrates that the hot band of this alloy exhibits similar impact toughness in different orientations, with a directional toughness ratio (DTR) of 1.09–1.18. Ductility fracture, exhibiting microvoid coalescence, occurred in each orientation.

[0123] <Case Study #2: Improvement of Hot Band Toughness through Annealing> Charpy specimens were cut by wire EDM from hot-rolled material of the selected alloys listed in Table 10. The specimens were cut in two orientations (LN and LT) as shown in Figure 5. The specimens were then wrapped in foil and placed in a preheated furnace at 600°C. Argon gas was injected into the furnace during the annealing process. After 10 minutes, the specimens were removed from the furnace and cooled under a fan. The specimens were then cleaned with a Scotch-Brite pad and wire brush before starting the test.

[0124] The test results are shown in Table 10. The absorbed energy values ​​of this alloy during the Charpy V-notch test range from 258 to 407 J for the hot-rolled sheet after annealing. Based on the test results, the directional toughness ratio (DTR) (Figure 5) was calculated as the ratio of the toughness in the direction of the Charpy impact normal to the hot band surface to the toughness in the direction of the Charpy impact width. The DTR (LN / LT) of the alloy ranges from 0.91 to 1.28. Note that the properties in Table 10 correspond to step 3 in Figure 1.

[0125] [Table 10-1]

[0126] [Table 10-2]

[0127] [Table 10-3]

[0128] In this case, the Charpy V-notch toughness of the hot band from this alloy was improved by annealing, demonstrating a high toughness of 258-407 J and a directional toughness ratio (DTR) of 0.91-1.28.

[0129] <Case Study #3: Analysis of fracture surfaces after Charpy test (before and after annealing)> To evaluate the impact toughness of the hot-banded material, the fracture surfaces of Charpy samples were observed using a scanning electron microscope (SEM). V-notch Charpy samples were cut from hot-banded alloys 2 and 3 using an EDM (Electronic Deposition Modeling) machine. Half of the samples were annealed at 600°C for 10 minutes. Charpy tests were performed on samples before and after heat treatment. SEM analysis of the fracture surfaces was performed using a scanning electron microscope (SEM) EVO-MA10 manufactured by Carl Zeiss SMT Inc. Figures 13 to 16 show the fracture surfaces of the hot-banded samples before and after heat treatment for alloys 2 and 3.

[0130] Figure 19 shows the fracture surface of a V-notch Charpy specimen of alloy 2 before annealing. The fracture surface shows ductile fracture characteristic of microvoid coalescence. The fracture after annealing at 600°C for 10 minutes also exhibits ductile characteristics (Figure 17). Although fracture toughness is improved after annealing, ductile fracture is dominant in both cases. This is because energy absorption is greater after heat treatment, which may be due to microstructural relaxation caused by annealing, but no clear difference is observed in the fracture surface. For alloy 3, Figure 15 shows the fracture surface before annealing, and Figure 16 shows the fracture surface after annealing. Similar to alloy 2, ductile fracture is observed in alloy 3 both before and after annealing.

[0131] This case demonstrates that the fracture of hot-band materials exhibits ductile properties, specifically a microvoid coalescence fracture mechanism.

[0132] <Case Study #4: Instrumented Charpy Test> For the instrumented Charpy test, hot bands of alloy 18, alloy 32, alloy 37, and alloy 44 with a thickness of approximately 10 mm were used. A laboratory slab with a thickness of 80 mm was cast from alloys with atomic ratios shown in Table 1 and processed to a thickness of approximately 10 mm by laboratory hot rolling as described in the "Main Body" section of this application.

[0133] Standard V-notch Charpy test specimens were cut with a wire EDM, tested, and the absorbed energy was recorded. The results are shown in Table 11. The absorbed energy values ​​in the Charpy V-notch test of this alloy ranged from 262 to 424 J, and the directional toughness ratio (DTR) was 0.98 to 1.14. The characteristics in Table 11 correspond to step 3 in Figure 1. The Charpy machine used was equipped with a small force sensor to record the load and an encoder to record the hammer speed. Based on the material's response to impact, its fracture behavior can be represented by four types of fracture behavior (Figure 17). Type I behavior is characterized by only a linear elastic response. Type II behavior is elastoplastic, showing unstable cleavage fracture but without crack propagation. Type III fracture behavior is elastoplastic, showing stable crack propagation followed by unstable cleavage fracture. Type IV is elastoplastic, showing stable crack propagation. Type IV is the most ductile fracture mode, characterized by ductile fracture due to microvoid coalescence. In addition to the total absorbed energy, force-displacement data was obtained, and the corresponding curves are shown in Figures 18 to 21 for each alloy tested. Dynamic fracture toughness (J 0.2 The values ​​are calculated based on the test results and are shown in Table 11, ranging from 120 to 274 J / cm². 2 There is some variability. Note that the reported fracture toughness values ​​are for notched Charpy specimens. The final fracture toughness value is reported with the number "0.2," which indicates that the ultimately recommended fracture toughness value is J at a crack expansion of 0.2 mm. Idn This indicates the value is as follows. The letters "Idn" indicate a dynamic test under Mode I loading, and that a notch was used to initiate the crack. This fracture toughness value is the size requirement J for E1820. Idn <J max=B σ0 It does not satisfy the condition / 10 and should be considered an estimate.

[0134] [Table 11]

[0135] In this case, the hot band of this alloy exhibits ductile type IV behavior, regardless of whether annealing occurs, demonstrating high toughness in the range of 262–424 J and a directional toughness ratio (DTR) of 0.98–1.14.

[0136] <Case Study #5: Toughness of the Hot Band of Alloy 88> A laboratory slab with a thickness of 80 mm was cast from alloy 88 with the atomic ratio shown in Table 1 and processed by hot rolling in the laboratory as described in the "Main Body" section of this application. Before and after cold rolling, Charpy V-notch test specimens were cut from the hot band using wire EDM and tested according to the procedure described in the "Main Body" section of this application. The results are shown in Table 12. The absorbed energy value of this alloy during the Charpy V-notch test was in the range of 249 to 298 J, and the directional toughness ratio (DTR) was 1.08.

[0137] Hot-rolled hot bands with a final thickness of approximately 11.9 mm were further cold-rolled by 3% and 9%. Before and after cold rolling, Charpy V-notch test specimens were cut from the hot bands using wire EDM and tested according to the procedure described in the "Main Body" section of this application. The results are shown in Table 12. The absorbed energy values ​​of this alloy during the Charpy V-notch test ranged from 96 to 158 J, and the directional toughness ratio (DTR) was 0.91 to 0.96.

[0138] A hot band approximately 17.5 mm thick was further rolled at 550°C by 20% and 40% to form an intermediate band. Before and after cold rolling, Charpy V-notch test specimens were cut from the hot band using a wire EDM and tested according to the procedure described in the "Main Body" section of this application. The results are shown in Table 12. The absorbed energy values ​​of this alloy during the Charpy V-notch test ranged from 89 to 171 J, and the directional toughness ratio (DTR) was 0.94 to 1.20.

[0139] [Table 12-1]

[0140] [Table 12-2]

[0141] This case demonstrates that the hot band of this alloy maintains uniform toughness and has a directional toughness ratio (DTR) of 0.91 to 1.20 when rolled at ambient and intermediate temperatures.

[0142] <Case Study #6: Tensile Properties After Hot Rolling for Large Thicknesses> Alloy 66 was processed into laboratory hot bands by hot-rolling laboratory-cast slabs at high temperatures. The laboratory alloy processing was developed to simulate the production of hot bands from slabs produced by continuous casting. Industrial hot rolling is performed by heating the slab to a target temperature in a tunnel furnace and then passing it through either a reversing mill, a multi-stand mill, or both until it reaches a target gauge. In either rolling mill, the temperature of the slab gradually decreases due to heat dissipation to the atmosphere or rolls, so the final hot band that is formed is at a lower temperature. In the laboratory, this is simulated by heating in a tunnel furnace to 1100°C to 1250°C and then performing hot rolling. Laboratory rolling mills operate at a slower speed than industrial rolling mills, and heat loss is greater as the slab passes through each hot-rolling section. Therefore, the slab is reheated for 4 minutes after each hot-rolling section to minimize the temperature drop. As a result, the final temperature on the target gauge when the slab leaves the laboratory rolling mill is typically in the range of 800°C to 1000°C, depending on the furnace temperature and final thickness.

[0143] Before hot rolling, the laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace. The furnace temperature was varied between 1100°C and 1250°C depending on the melting point of the alloy and the temperature of the hot rolling process. The initial temperature was set high to easily obtain a large reduction, and the subsequent temperature was set low to minimize surface oxidation of the hot band. To ensure that the slabs reached the target temperature, they were soaked for 40 minutes before hot rolling, and then removed from the tunnel furnace and fed into a Fenn Model 061 two-stage rolling mill. The 50mm castings were hot-rolled by passing them through the mill 5 to 10 times, and then air-cooled. The final thickness after hot rolling was 11.9 to 17.0 mm.

[0144] Tensile test specimens were cut from laboratory hot bands using a wire EDM. Because the laboratory tensile testing machine could not test specimens thicker than 10 mm, thick hot band specimens were "sliced" into multiple specimens approximately 1.6 mm thick. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. The tensile test results are shown in Table 13, representing the characteristics of the thick-walled hot bands. The ultimate tensile strength of the thick-walled hot bands was 914–1060 MPa, the yield strength with a 0.2% offset was 276–340 MPa, the recorded total elongation was 30.4–46.4%, and the area under the tensile stress-strain curve was 20,149–35,535 MPa%. The product of strength and ductility was calculated by multiplying the UTS by the total tensile elongation, resulting in 27,959–49,174 MPa%. The tensile square ratio (TSR) (Figure 4) is determined by dividing the area of ​​the stress-strain curve up to the stress-strain point (UTS) by the product of UTS and the strain at UTS. The calculated value is in the range of 0.71 to 0.73. Note that the characteristics in Table 13 correspond to step 2 in Figures 1 and 2.

[0145] [Table 13-1]

[0146] [Table 13-2]

[0147] [Table 13-3]

[0148] This case demonstrates that the tensile properties of the hot band of this alloy with a thickness exceeding 10 mm have a tensile square ratio (TSR) in the range of 0.71 to 0.73.

[0149] <Case Study #7: The effect of rolling at ambient temperature on the yield strength of hot bands> Slabs of alloys 66, 80, and 84 were cast to a thickness of 80 mm with the elemental compositions shown in Table 1. These slabs were heated at 1250°C for 40 minutes, then hot-rolled to a thickness of 18 mm by passing through a hot-rolling mill seven times. These slabs were reheated to 1100°C, rolled to a thickness of 12 mm in a single pass, and cooled to room temperature. Due to the large thickness of the hot band, it was sliced ​​to a thickness of approximately 1.6 mm for tensile property testing. Ten tensile test specimens were cut from the hot band using wire EDM. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software.

[0150] Tensile test specimens were cut from the laboratory hot band using a wire EDM. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. The tensile test results are shown in Table 14 (hot-rolled state). The yield strength at 0.2% offset was determined to be 307–320 MPa, and the tensile square ratio (TSR) was determined to be in the range of 0.72–0.82. The material was subjected to 10% (S1 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 4,936 to 8,446 MPa%, and 20% (S1 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 11,618 to 18,193 MPa%, and 30% (S1 0.3 The area under the stress-strain curve corresponding to the work required to deform the material is in the range of 20,015 to 26,899 MPa%.

[0151] The hot bands of each alloy were rolled at ambient temperature with a reduction ratio of 2-9%. Although no external heating was used, there was some temperature rise depending on the reduction amount and the time required to pass through the rolling mill, with a temperature range of 15-50°C. Due to the large thickness of the cold-rolled material, it was sliced ​​to a thickness of approximately 1.6 mm for tensile property testing. 10-12 tensile test samples were cut from each cold-rolled plate using wire EDM, and tested according to the procedure described above. Table 14 shows the average values ​​of the 0.2% offset yield strength and tensile rectangle ratio measured under each condition. Both yield strength and tensile rectangle ratio increase with increasing cold-rolling reduction ratio. The average yield strength (Y2) ranges from 403 to 562 MPa, with Y2 > Y1. The average tensile rectangle ratio (TSR2) ranges from 0.78 to 0.92, with TSR2 > TSR1. The material was then subjected to 10% (S2 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 5,918 to 8,510 MPa%, and 20% (S2 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 13,159 to 18,721 MPa%, and 30% (S2 0.3 The area under the stress-strain curve corresponding to the work required to deform the material is in the range of 21,310 to 30,015 MPa%.

[0152] The yield strength (Y2) as a function of reduction ratio at ambient temperature is shown in Figures 22, 23, and 24 for alloy 66, alloy 80, and alloy 84, respectively. The tensile square ratio (TSR2) as a function of reduction ratio is shown in Figures 25, 26, and 27 for alloy 66, alloy 80, and alloy 84, respectively. Note that this data in Table 14 corresponds to step 3 in Figure 2.

[0153] [Table 14-1]

[0154] [Table 14-2]

[0155] [Table 14-3]

[0156] This case demonstrates that the yield strength of the hot band of this alloy increases as a function of the reduction ratio at ambient temperature, forming an alloy with yield strength Y2 > Y1 and tensile squareness ratio TSR2 > TSR1. Y1 and TSR1 are the yield strength and tensile squareness ratio of the hot band before rolling.

[0157] <Case Study #8: Effect of rolling at intermediate temperatures on the yield strength of hot bands> Slabs of alloys 66, 80, and 84 with the elemental compositions shown in Table 1 were cast to a thickness of 80 mm. These slabs were heated at 1250°C for 40 minutes, then hot-rolled to a thickness of 25 mm by passing them through a rolling mill six times. After reheating these slabs to 1100°C, they were rolled to a thickness of 18 mm in a single pass through the rolling mill and cooled to room temperature. Due to the large thickness of the hot bands, they were sliced ​​to a thickness of approximately 1.6 mm for tensile property testing. Sixteen tensile test specimens were cut from the hot bands using wire EDM. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software.

[0158] Hot band material of alloy 66 was heated at 550°C for 40 minutes, then rolled at reduction ratios of approximately 10%, 20%, 30%, and 40%. The thickness was sliced ​​to approximately 1.6 mm for tensile property testing. Ten to twelve tensile test specimens with reduced thickness were cut by wire EDM for each rolling condition, and tested according to the procedure described above. Hot band material of alloy 80 was heated at 600°C for 40 minutes, then rolled at reduction ratios of approximately 10%, 20%, 30%, and 40%. The thickness was sliced ​​to approximately 1.6 mm for tensile property testing. Ten to twelve tensile test specimens with reduced thickness were cut by wire EDM for each rolling condition, and tested according to the procedure described above. Hot band material of alloy 84 was rolled at four intermediate temperatures (50, 150, 250, and 350°C) at a reduction ratio of approximately 10%. The material was sliced ​​to approximately 1.6 mm in thickness for tensile property testing. Ten to twelve tensile test specimens with reduced thickness were cut by wire EDM for each condition and tested according to the procedure described above. The average values ​​of the 0.2% offset yield strength and tensile rectangle ratio measured for each condition are shown in Tables 15 and 16.

[0159] The yield strength at a 0.2% offset in the hot-rolled state (Y1) was 319-331 MPa, and the tensile square ratio (TSR) was determined to be in the range of 0.70-0.83. 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 4,882 to 4,998 MPa%, and 20% (S1 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 11,518 to 11,701 MPa%, and 30% (S1 0.3 The area under the stress-strain curve corresponding to the work required to cause the deformation is in the range of 19,194 to 19,831 MPa%.

[0160] Both yield strength and tensile square ratio increase with increasing rolling reduction ratio. The average yield strength (Y2) is in the range of 393 to 7462 MPa, with Y2 > Y1. The average tensile square ratio (TSR2) is 0.78 to 0.91, with TSR2 > TSR1. The material is 10% (S2 0.1The area under the stress-strain curve corresponding to the work required to deform is in the range of 6,466 to 10,007 MPa%, and 20% (S2 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 14,754 to 20,762 MPa%, and 30% (S2 0.3 The area under the stress-strain curve corresponding to the work required to cause deformation is in the range of 23,962 to 32,102 MPa%. Note that the data in Table 15 corresponds to step 3 in Figure 2.

[0161] [Table 15]

[0162] [Table 16]

[0163] The yield strength (Y2) as a function of the rolling reduction ratio is shown in Figures 28 and 29 for alloy 66 and alloy 80, respectively. The yield strength (Y2) as a function of the rolling temperature is shown in Figure 30 for alloy 84. The tensile square ratio (TSR2) as a function of the rolling reduction is shown in Figures 31 and 32 for alloy 66 and alloy 80, respectively. The tensile square ratio (TSR2) as a function of the rolling temperature is shown in Figure 33 for alloy 84.

[0164] This case demonstrates that the yield strength of the hot band of this alloy increases as a function of the reduction ratio during rolling at an intermediate temperature, forming an alloy with a yield strength Y2 ≥ Y1 and a tensile squareness ratio TSR2 > TSR1. Y1 and TSR1 are the yield strength and tensile squareness ratio of the hot band before rolling.

[0165] <Case Study #9: Effect of Rolling on the Hot Band Properties of Alloy 88> Laboratory slabs with a thickness of 80 mm were cast from alloy 88 with the atomic ratios shown in Table 1 and processed in the laboratory by hot rolling as described in the main body section of this application. Furthermore, slices approximately 1.6 mm thick were prepared for tensile property testing. Tensile test specimens were cut by wire EDM for each rolling condition and tested according to the procedure described above. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. The tensile properties are shown in Table 17. In the hot band state, the yield strength at a 0.2% offset (Y2) was 268-319 MPa, and the tensile square ratio (TSR2) (Figure 4), determined as the area of ​​the stress-strain curve up to UTS divided by the product of UTS and the strain at UTS, was in the range of 0.77-0.82. 0.1 The area under the stress-strain curve corresponding to the work required to deform is in the range of 4,835 to 4,969 MPa%, and 20% (S1 0.2 The area under the stress-strain curve corresponding to the work required to deform is in the range of 11,499 to 11,787 MPa%, and 30% (S1 0.3 The area under the stress-strain curve corresponding to the work required to deform the material is in the range of 19,439 to 19,880 MPa%.

[0166] The final hot-rolled hot band, approximately 11.9 mm thick, was further rolled at ambient temperature with reduction ratios of 3% and 9%. It was also sliced ​​to a thickness of approximately 1.6 mm for tensile property testing. Tensile test specimens were cut using a wire EDM for each rolling condition and tested according to the procedure described above. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron Bluehill control and analysis software. The tensile properties are shown in Table 17. For the material rolled at ambient temperature, the yield strength at a 0.2% offset (Y2) was 327–801 MPa, and the tensile square ratio (TSR2) (Figure 4), determined as the area of ​​the stress-strain curve up to UTS divided by the product of UTS and the strain at UTS, was in the range of 0.82–0.93. 0.1) The area under the stress-strain curve corresponding to the work required to distort is in the range of 6,068 - 9,349 MPa%, 20% (S1 0.2 ) The area under the stress-strain curve corresponding to the work required to distort is in the range of 13,891 - 19,555 MPa%, 30% (S1 0.3 ) The area under the stress-strain curve corresponding to the work required to distort is in the range of 22,782 - 30,305 MPa%.

[0167] A hot band with a thickness of about 17.5 mm was further processed into an intermediate band by rolling at 550 °C with 20% and 40% reduction. Also, it was sliced to a thickness of about 1.6 mm for the tensile property test. Tensile test specimens were cut by wire EDM for each rolling condition and tested according to the above-described procedure. Tensile properties were measured on an Instron mechanical test frame (Model 3369) using Instron's Bluehill control and analysis software. Tensile properties are shown in Table 17. For the material after rolling at intermediate temperature, the yield strength at 0.2% offset (Y2) is 529 - 840 MPa, and the tensile rectangular ratio (TSR2) (Figure 4), determined as the value obtained by dividing the area up to the UTS of the stress-strain curve by the product of the UTS and the strain at the UTS, is in the range of 0.89 - 0.94. The material was 10% (S2 0.1 ) The area under the stress-strain curve corresponding to the work required to distort is in the range of 7,624 - 8,174 MPa%, 20% (S1 0.2 ) The area under the stress-strain curve corresponding to the work required to distort is in the range of 16,575 - 17,647 MPa%, 30% (S1 0.3 ) The area under the stress-strain curve corresponding to the work required to distort is in the range of 26,179 - 27,767 MPa%.

[0168]

Table 17-1

[0169]

Table 17-2

[0170] [Table 17-3]

[0171] Standard V-notch Charpy samples (Figure 6) were cut with a wire EDM, and instrumented Charpy impact tests were performed on the hot band before and after rolling at ambient and intermediate temperatures. The Charpy machine used was an instrumented device equipped with a small force sensor to record the load and an encoder to record the hammer speed. The results are shown in Table 18. Based on the material's response to impact, its fracture behavior was represented by four types, with type IV being the most ductile (Figure 17). In addition to the total energy absorbed, force-displacement data was acquired, and the corresponding curves are shown in Figures 34 to 39. The measured V-notch Charpy impact energy of the material under hot-rolled conditions was 293–319 J, and after rolling at ambient or intermediate temperatures, it was 105–160 J. Dynamic fracture toughness (J) 0.2 The fracture toughness values ​​were calculated based on the test results and are shown in Table 18. The reported fracture toughness values ​​are for notched Charpy test specimens. The final fracture toughness value is reported with the subscript "0.2", and the final recommended fracture toughness value is J at a crack propagation of 0.2 mm. Idn This indicates the value is as follows. The subscript "Idn" indicates that the crack was initiated using mode I loading, dynamic testing, and notching. The fracture toughness value is as per the E1820 size requirement J. Idn <J max The condition Bσ0 / 10 is not satisfied, and therefore the values ​​should be considered estimates. Note that the data in Tables 17 and 18 correspond to Figure 2.

[0172] [Table 18]

[0173] This case demonstrates that the hot band of the 88 alloy exhibits type IV ductility behavior in its initial state, similar to that after rolling at ambient or intermediate temperatures. Both ambient and intermediate temperature rolling result in alloys with yield strength Y2 ≥ Y1 and tensile squareness ratio TSR2 > TSR1. Y1 and TSR1 are the yield strength and tensile squareness ratio of the hot band before rolling, respectively.

[0174] Finally, it should be noted that another application of this alloy, where the combination of relatively uniform or isotropic toughness and relatively high yield strength and ultimate tensile strength is important, is for battery protection in plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs). These vehicles share the commonality of utilizing batteries or battery packs to store energy for subsequent propulsion. Protecting the battery from all conceivable stresses and external impacts is one important application, and alloy sheets manufactured in step (2) of Figure 1 or step (3) of Figure 2 would be utilized. There are countless potential designs for exoskeletons, battery trays, battery cages, etc., to protect the battery from impact, penetration, and damage from external contact and fracture.

Claims

1. A method for achieving a combination of properties including toughness and directional toughness ratio (DTR) in a hot band of a high-strength steel alloy, wherein the method is: (a) A step of supplying a metal raw material, melting the metal raw material, cooling it at a rate of less than 250 K / s and solidifying it to produce an alloy with a thickness of 25.0 mm to 500 mm and a composition consisting of 65 to 80 atomic percent Fe, 9.5 to 17.5 atomic percent Mn, 1.0 to 10.0 atomic percent Cr, 1.0 to 5.5 atomic percent Si, 0.5 to 1.5 atomic percent C, and 0 to 5,000 ppm of other elements contained as impurities, (b) A step of producing an alloy sheet, comprising heating the alloy produced in step (a) and rolling it in a selected direction to reduce the thickness, thereby forming an alloy sheet having a thickness of 10.0 mm to 20.0 mm, (1) The alloy sheet produced in step (b) has a total elongation E1 of 30 to 75%, a yield strength Y1 at a 0.2% offset of 250 to 525 MPa, an ultimate tensile strength U1 of 750 to 1400 MPa, and a tensile squareness ratio TSR1 of 0.65 to 0.

90. (2) The V-notch Charpy sample cut from the alloy sheet prepared in step (b) absorbs an impact energy of 150 J to 850 J, (3) A method wherein the directional toughness ratio (DTR) is defined as the ratio obtained by dividing the impact energy absorbed by a V-notch Charpy specimen cut from the alloy sheet produced in step (b) and having a notch formed perpendicular to the longitudinal-normal plane of the alloy sheet by the impact energy absorbed by a V-notch Charpy specimen cut from the alloy sheet and having a notch formed perpendicular to the width-longitudinal plane of the alloy sheet, and the directional toughness ratio (DTR) is 0.8 to 1.

5.

2. The method according to claim 1, wherein the composition of the alloy in step (a) comprises 0.2 to 4.0 atomic percent of Ni and / or 0.1 to 2.5 atomic percent of Cu.

3. The method according to claim 1 or 2, wherein step (b) comprises rolling the alloy and then exposing the alloy sheet to a temperature range of 600°C to less than the melting point Tm of the alloy.

4. The method according to any one of claims 1 to 3, wherein the other element includes at least one selected from the group consisting of Co, Al, N, P, Ti, W, Mo, Nb, V, Ga, Ge, Sb, Zr, O, Sn, Ca, B, and S.

5. The method according to any one of claims 1 to 3, wherein the alloy produced in step (a) has a solidus temperature of 1350°C to 1450°C, a liquidus temperature of 1400°C to 1500°C, and a liquidus-solidus gap of 40°C to 100°C.

6. The alloy sheet produced in step (b) above has a density of 7.7 g / cm³. ３ ~8.0 g / cm ３ The method according to any one of claims 1 to 3, having the density of

7. The alloy sheet produced in step (b) above has an area under the stress-strain curve of S1 ０．１ The pressure is 4,500 to 8,500 MPa%, S1 ０．２ The pressure is 10,500 to 18,500 MPa%, S1 ０．３ The pressure is 17,500 to 27,000 MPa%, S1 ０．１ S1 is the stress required to deform a tensile test specimen by 10%. ０．２ S1 is the stress required to deform a tensile test specimen by 20%. ０．３ The method according to any one of claims 1 to 3, wherein is the stress required to deform a tensile test specimen by 30%.

8. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) has a product of ultimate tensile strength and total elongation of 25,000 to 80,000 MPa%.

9. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) has an area obtained by multiplying the ultimate tensile strength by the strain at the ultimate tensile strength that is 20,000 to 65,000 MPa%.

10. The method according to any one of claims 1 to 3, wherein the V-notch Charpy sample is subjected to impact in both the direction of the normal and the direction of the width.

11. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) is arranged as all or part of a storage tank, a freight car, or a railway tank car.

12. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) is arranged as all or part of a storage tank, a freight car, or a railway tank car, and the arranged alloy sheet absorbs impact energy.

13. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) is arranged as all or part of a vehicle frame, vehicle chassis, vehicle panel, battery exoskeleton, battery tray, or battery cage.

14. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) is arranged as all or part of a vehicle frame, vehicle chassis, vehicle panel, battery exoskeleton, battery tray, or battery cage, and the arranged alloy sheet absorbs impact energy.

15. The method according to any one of claims 1 to 3, wherein the alloy sheet produced in step (b) exhibits ductile fracture upon fracture.

16. A method for achieving a novel combination of properties, including yield strength and tensile square ratio (TSR), in a hot band of a high-strength steel alloy, wherein the method is: (a) A step of supplying a metallic material, melting the metallic material, cooling it at a rate of less than 250 K / s and solidifying it to produce an alloy with a thickness of 25.0 mm to 500 mm and a composition consisting of 65 to 80 atomic percent Fe, 9.5 to 17.5 atomic percent Mn, 1.0 to 10.0 atomic percent Cr, 1.0 to 5.5 atomic percent Si, 0.5 to 1.5 atomic percent C, and 0 to 5,000 ppm of other elements as impurities, (b) A step of producing a first alloy sheet, comprising heating the alloy produced in step (a) and rolling the alloy to reduce its thickness, thereby forming an alloy sheet having a thickness of 10.0 mm to 20.0 mm, (c) A step of producing a second alloy sheet, comprising rolling the first alloy sheet produced in step (b) in a first temperature range T1 of 15°C to less than 50°C to reduce the thickness of the first alloy sheet by 1 to 10%, or rolling it in a second temperature range T2 of 50°C to less than 600°C to reduce the thickness of the first alloy sheet by 10 to 40%, thereby producing a second alloy sheet. (1) The first alloy sheet produced in step (b) has a total elongation E1 of 30 to 75%, a yield strength Y1 at a 0.2% offset of 250 to 525 MPa, an ultimate tensile strength U1 of 750 to 1400 MPa, and a tensile square ratio TSR1 of 0.65 to 0.

90. (2) The V-notch Charpy sample cut from the first alloy sheet prepared in step (b) absorbs an impact energy of 150 J to 850 J, (3) When the directional toughness ratio (DTR) is obtained by dividing the impact energy absorbed by a V-notch Charpy sample cut from the first alloy sheet produced in step (b) and having a notch formed perpendicular to the longitudinal-normal plane of the alloy sheet by the impact energy absorbed by a V-notch Charpy sample cut from the alloy sheet and having a notch formed perpendicular to the width-longitudinal plane of the alloy sheet, the directional toughness ratio (DTR) is 0.8 to 1.5, (4) The method wherein the second alloy sheet produced in step (c) has an average yield strength of Y2, Y2 ≥ Y1, and an average tensile rectangle ratio of TSR2, TSR2 > TSR1.

17. The method according to claim 16, wherein the composition of the alloy in step (a) comprises 0.2 to 4.0 atomic percent of Ni and / or 0.1 to 2.5 atomic percent of Cu.

18. The method according to claim 16 or 17, wherein step (b) comprises rolling the alloy and then exposing the alloy sheet to a temperature range of 600°C to less than Tm, which is the melting point of the alloy.

19. The method according to any one of claims 16 to 18, wherein the other element includes at least one selected from the group consisting of Co, Al, N, P, Ti, W, Mo, Nb, V, Ga, Ge, Sb, Zr, O, Sn, Ca, B, and S.

20. The method according to any one of claims 16 to 18, wherein the alloy produced in step (a) has a solidus temperature of 1350°C to 1450°C, a liquidus temperature of 1400°C to 1500°C, and a liquidus-solidus gap of 40°C to 100°C.

21. The first alloy sheet produced in the step (b) has a density of 7.7 g / cm ３ to 8.0 g / cm ３ The method according to any one of claims 16 to 18.

22. The first alloy sheet produced in step (b) has an area under the stress-strain curve of S1 ０．１ The pressure is 4,500 to 8,500 MPa%, S1 ０．２ The pressure is 10,500 to 18,500 MPa%, S1 ０．３ The pressure is 17,500 to 27,000 MPa%, S1 ０．１ S1 is the stress required to deform a tensile test specimen by 10%. ０．２ S1 is the stress required to deform a tensile test specimen by 20%. ０．３ The method according to any one of claims 16 to 18, wherein is the stress required to deform a tensile test specimen by 30%.

23. The method according to any one of claims 16 to 18, wherein the second alloy sheet produced in step (c) shows Y2 > Y1.

24. The method according to any one of claims 16 to 18, wherein the second alloy sheet produced in step (c) has an average yield strength Y2 of 300 to 850 MPa.

25. The method according to any one of claims 16 to 18, wherein the second alloy sheet produced in step (c) has an average tensile square ratio TSR2 of 0.75 to 0.

95.

26. The method according to any one of claims 16 to 18, wherein the second alloy sheet produced in step (c) is placed in all or part of a storage tank, a freight car, or a railway tank car.

27. The method according to any one of claims 16 to 18, wherein the second alloy sheet produced in step (c) is placed in a vehicle frame, vehicle chassis, vehicle panel, battery exoskeleton, battery tray, or battery cage.

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