High-strength hot-rolled steel strip with a high hole expansion rate, its production method and component produced from it.

Abstract

HOT-ROLLED HIGH-STRENGTH STEEL STRIP WITH HIGH HOLE EXPANSION RATE. The present invention relates to a high-strength steel with a careful selection of the normal alloying elements C, Mn, Si, and Al, along with the addition of microelements. This high-strength steel with a high hole expansion rate can be produced. The invention also relates to the method of producing this high-strength steel.

Description

High-strength hot-rolled steel strip with a high hole expansion rate, its method OF PRODUCTION AND COMPONENT PRODUCED FROM THE SAME

[0001] The present invention relates to a hot-rolled steel strip with high strength and a high hole expansion rate.

[0002] High-strength steels are used in the automotive industry to improve in-service performance and / or to reduce the weight and fuel consumption of cars. However, high strength alone, for example, to improve in-service performance is not sufficient for relatively complex automotive components, such as those found in automotive chassis and suspensions. The value of using high-strength steels for automotive chassis components, for example, may be to increase resistance to collapse to maintain the integrity of the component in the event of an accident. However, the higher the strength of the steel, the more difficult it is to shape the steel into an automotive component without the steel cracking at the sheared or perforated edges of a blank from which a component is formed.The reason for this is that the increase in strength in most cases is obtained by the presence of low-temperature transformation products in the microstructure through transformation hardening. However, this leads to increased hardness differences in the final microstructure, which, in turn, comes at the cost of detrimental stretch flangability. Thus, the application of high-strength multiphase steels, such as DP and TRIP steels, but to some extent also CP multiphase steel, is limited by the formability of these steel types for specific automotive applications such as chassis and suspension components in highly intricate, complex shapes.

[0003] In addition, to reduce the weight of the components, the approach Petition 870250081836, dated 11 / 09 / 2025, page 7 / 138 A common practice is to use high-strength steel and reduce the thickness of the steel sheet used to reduce weight. However, this can lead to a loss of stiffness, which is crucial for some applications in car bodies, chassis and suspension, and / or automotive seats and interiors. For example, for automotive chassis components, stiffness is a key performance parameter, as a lack of stiffness impairs car handling and passenger safety. The intrinsic loss of stiffness from reducing the thickness of the steel used to manufacture automotive chassis components can be recovered by optimizing the component geometry – for example – by creating deeper flanges and / or flanges with a greater degree of stretch and / or bend.To enable automotive engineers to strive to increase component stiffness through geometry optimization, the high-strength steel used needs to have excellent formability in terms of good elasticity (or tensile elongation) and excellent stretch flangability (or hole expansion capacity).

[0004] In recent years, steel suppliers have developed high-strength steel types that have both a reasonable maximum tensile strength Rm and a reasonable total elongation A50 or A80. These mechanical properties provide information about the strength and tensile capacity of the steel type.

[0005] However, for certain applications of high-strength steel in the automotive industry, it is also a requirement that the steel have good stretch flangability. Stretch flangability is an indication of the formability at the flange of a sheet, but also at the edge of an opening in the sheet. Stretch flangability is normally measured by the expansion of a circular drilled hole in a sheet, and is indicated by the hole expansion rate λ. The hole expansion rate λ is often determined according to Petition 870250081836, dated 11 / 09 / 2025, page 8 / 138 3 / 54 conforms to the Japan Iron and Steel Federation's JFS T 1001 standard. This standard will be attached below.

[0006] It is an object of the invention to provide a high-strength hot-rolled steel with a high hole expansion rate.

[0007] It is also an objective of the invention to provide a high-strength steel with good elongation and a high rate of expansion of the holes.

[0008] It is a further object of the invention to provide a high-strength steel with a tensile strength of at least 760 MPa and a hole expansion rate of at least 50%.

[0009] Another object of the invention is to provide a high-strength steel having a tensile strength of at least 960 MPa and a hole expansion rate of at least 40%.

[0010] Furthermore, it is an objective of the invention to provide such high-strength steel, which also has a total elongation A50 or A80 of at least 9 ± 1%.

[0011] According to the invention, a high-strength hot-rolled steel strip is provided, consisting of: • 0.02 - 0.13% by weight of C; • 1.20 - 3.50% by weight of Mn; • 0.10 - 1.00% by weight of Si; • 0.01 - 0.10% by weight of Al_tot; • 0.04 - 0.25% by weight of Ti; • 0 - 0.010% by weight of N; • 0 - 0.10% by weight of P; • 0 - 0.01% by weight of S; optionally 0 - 0.005% by weight of B, preferably 0.0005 0.005% by weight of B; optionally one or more of the following: • 0 - 1.5% by weight of Cu; Petition 870250081836, dated 11 / 09 / 2025, page 9 / 138 4 / 54 • 0 - 1.0% Cr by weight; • 0 - 1.0% by weight of Mo; • 0 - 0.50% by weight of Ni; • 0 - 0.30% by weight of V; • 0 - 0.10% by weight of Nb; • where Ti + Nb < 0.25% by weight, • where Cr + Mo < 1.0% by weight, the remainder being iron and the inevitable impurities, the steel having a microstructure consisting of (in % by volume): - at least 85% bainite, - a maximum of 10% martensite plus retained austenite, - more than 0% and at most 5% cementite, - unavoidable amounts of inclusions, totaling 100% by volume, in which the steel strip has the following mechanical properties: - a tensile strength of at least 760 and at most 960 MPa, - a total elongation (A50) of at least 10%, - a hole expansion ratio (λ) of at least 50%, or where the steel strip has the following mechanical properties: - a tensile strength of at least 960 and at most 1380 MPa, - a total lengthening (A50) of at least 9%, - a hole expansion rate (λ) of at least 40%.

[0012] By using this composition with this microstructure for a hot-rolled steel, it is possible to supply a steel with a high Petition 870250081836, dated 11 / 09 / 2025, p. 10 / 138 5 / 54 resistance, that is, a resistance above 760 MPa and a high hole expansion rate λ. As always, the higher the resistance, the lower the formability. This also applies to the hole expansion rate. When the hot-rolled steel according to the invention has a high average tensile strength, for example between 760 and 960 MPa, the hole expansion rate can be at least 50%. For a higher strength steel, for example, with a tensile strength between 960 and 1380 MPa, the hole expansion rate can be lower, for example, 40% or more.

[0013] The use of the composition according to the invention provides a microstructure consisting almost entirely of bainite. Preferably, no martensite and retained austenite is present. However, due to the hot rolling and coiling conditions, some cementite will be present, but in an amount below 5%. In addition, small amounts of carbides, precipitates and unavoidable inclusions may be present in the steel.

[0014] The high strength and high formability, especially the high expansion rate of the holes, result from the careful selection of the normal alloying elements C, Mn, Si and Al, together with the addition of microelements. The elements used in the composition according to the invention are discussed below.

[0015] Carbon is present in an amount between 0.02 and 0.13% by weight. C is a bainite-forming element and, as such, an essential element for achieving a final microstructure that provides sufficient strength and formability in terms of tensile elongation and hole expansion capacity. To achieve sufficient strength, a suitable minimum C content is 0.02% by weight, or in a preferred embodiment at least 0.03% by weight. A low C content, in a preferred embodiment, is at most 0.12% by weight, preferably 0.09% by weight, or more. Petition 870250081836, dated 11 / 09 / 2025, page 11 / 138 6 / 54, preferably 0.06% by weight, is beneficial for suppressing the effect of cooling rate dependence on the homogeneity of the final microstructure and for promoting a high expansion capacity of the holes. Furthermore, C is an essential element for achieving precipitation strengthening in combination with carbide-forming microalloying elements such as titanium, niobium, or vanadium, and for expelling C as much as possible to suppress the amount of cementite in the final microstructure. By optimizing other alloying elements, including Ti, Nb, and / or V, it is possible to obtain a nearly uniform bainitic / bainitic-ferritic microstructure with very little cementite.

[0016] Manganese is present in an amount of 1.20–3.50% by weight. Mn provides hardening of solid solutions and, in addition, is an essential element for promoting low-carbon bainitic microstructures. Mn stabilizes austenite and retards the bainitic transformation at a given temperature, thus ensuring good hardenability. A disadvantage of very high Mn content is the increased segregation of continuously cast steel slabs and poor surface quality. Thus, preferably the Mn content is a maximum of 2.20% by weight.

[0017] Silicon is present in an amount of 0.10 - 1.00% by weight to improve the strength of steel through solid solution hardening. In addition, Si is beneficial for suppressing cementite formation. However, when using higher amounts of Si, the weldability and coating capacity of the steel deteriorate, so the amount of Si is preferably at most 0.95% by weight, and in preferred embodiments at most 0.70% or even at most 0.60% by weight.

[0018] Aluminum is present in an amount of 0.01 0.10% by weight. Al is a deoxidizing element and improves the cleaning of Petition 870250081836, dated 11 / 09 / 2025, p. 12 / 138 7 / 54 steel. At least 0.01% by weight of Al is required to be effective. However, Al can cause surface defects and therefore the Al content is at most 0.10% by weight, preferably up to a maximum of 0.05% by weight.

[0019] Titanium is present in an amount between 0.04 and 0.25% by weight is used because it provides hardening capacity and, as a carbide-forming element, helps to form the smallest possible amount of cementite, while also providing precipitation strengthening through the formation of small Ti-based carbides. Meanwhile, Ti also combines with N, S, and C to form nitrides and carbosulfides, depending on the specific chemical composition of the steel. For this reason, at least 0.04% by weight of Ti is present to bind all the N and S in the steel and to have sufficient excess Ti to combine with the C in the steel. When more than 0.25% by weight of Ti is present, crude nitrides, carbonitrides, and Ti carbides will be formed, which are difficult to dissolve during reheating of the plate before hot rolling. Furthermore, these crude nitrides, carbonitrides, and Ti carbides lead to a deterioration in the expansion capacity of the steel holes.Preferably, 0.09 to 0.21% by weight of Ti is present to always have sufficient Ti, but without the risk of significant dulling. In certain embodiments, 0.09 - 0.20% by weight of Ti may be present, or even 0.11 - 0.20% by weight of Ti. In other embodiments, 0.12 - 0.18% by weight of Ti may be present.

[0020] Boron is not required to obtain the necessary properties of steel, but it can be present between 0.0005 and 0.005% by weight, i.e., between 5 and 50 ppm. B is very effective in increasing the hardenability of steel, which means that a low carbon content and / or lower cooling rates can be used in the exit table as long as pro-eutectic ferrite does not form or only a Petition 870250081836, dated 11 / 09 / 2025, p. 13 / 138 8 / 54 A small amount of proeutectic ferrite is formed. B is also a bonding element that is very suitable for increasing the yield strength. Preferably, at least 10 ppm of B are present to ensure that not all B is transformed into boron nitrides. When there is sufficient Ti, titanium nitrides are formed first, which prevents the formation of boron nitrides. This is preferable as it leaves boron free for an optimal contribution to the hardenability of the steel.

[0021] Nitrogen is an unavoidable element that should be present in as low a content as possible, at most 0.010% by weight of N. N forms titanium nitrides with Ti that act as dispersoids to control the size of austenite grains during reheating. However, a very high N content can lead to too many coarse TiN particles that can impair the expansion capacity of the holes. Preferably, the N content is 0.005% by weight (50 ppm) or less. A suitable minimum N content is 10 ppm.

[0022] Phosphorus is present as an impurity; at most 0.10% by weight of P should be present. When too much P is present, segregation at the grain boundaries is increased, resulting in lower toughness and weldability. Preferably, the P content is at most 0.01% by weight.

[0023] Sulfur is also present as an impurity, at most 0.01% by weight should be present. During casting, MnS particles are formed. Coarse MnS particles are undesirable because they elongate during hot rolling and impair hole expansion capacity and lead to poor shear edge quality. Ti in steel can combine with S and C to form Ti4S2C2 particles, depending on the amount of Ti present. These Ti4S2C2 particles are coarse particles that should be avoided as they also impair hole expansion capacity and quality. Petition 870250081836, dated 11 / 09 / 2025, p. 14 / 138 9 / 54 of the sheared edges. Preferably, a maximum of 0.005% by weight of S is present.

[0024] Various optional elements may be present in the steel.

[0025] Copper may be present in an amount of up to 1.5% by weight. Cu may promote low-carbon bainite microstructures and provide solid solution hardening. Preferably, a maximum of 0.6% by weight of Cu and more preferably a maximum of 0.1% by weight of Cu are present, when other elements provide the same results. In one embodiment, no Cu is added to the steel, as Cu is not an economically preferable element, therefore Cu is present only as an impurity.

[0026] Chromium may be present in an amount of up to 1.0% by weight. Cr improves the strength of steel mainly due to strengthening the transformation by increasing the hardenability. Preferably, a maximum of 0.9% by weight of Cr is present, and in certain embodiments a maximum of 0.6% by weight of Cr is present, or even a maximum of 0.5% by weight of Cr is present. In one embodiment, no Cr is added to the steel, therefore Cr is present only as an impurity.

[0027] Molybdenum may be present in an amount of up to 1.0% by weight. Mo increases hardenability and promotes a low-carbon bainitic microstructure. Furthermore, as Mo is a carbide-forming element, it can combine with Ti, Nb, or V to form carbide-based compound precipitates. These Mo-based compound carbides are known to be more thermally stable and subsequently less prone to hardening. However, Mo is not an economically preferred element, therefore it is used in smaller amounts, preferably with a maximum of 0.9% by weight. In certain embodiments, Mo is present in even smaller amounts, for example, a maximum of 0.35% in Petition 870250081836, dated 11 / 09 / 2025, page 15 / 138 10 / 54 weight% or even at most 0.2 or at most 0.1% by weight, and in one embodiment no Mo is added to the steel, therefore Mo is present as an impurity. However, for other embodiments Mo must be added, for example up to 0.8% by weight, and preferably 0.005 - 0.7% by weight of Mo, more preferably 0.1 - 0.6% by weight of Mo, even more preferably 0.2 - 0.5% by weight of Mo are added.

[0028] Nickel may be added in an amount of up to 0.5% by weight. Ni improves toughness and hardenability at high strength levels and can mitigate the negative influence of Cu with respect to lack of heat. However, from a cost perspective, a maximum of 0.3% by weight of Ni is advisable. Ni may be added up to 0.5% by weight to prevent lack of hot air when the Cu content exceeds 0.5% by weight. Preferably, a maximum of 0.3% by weight of Ni is added, more preferably a maximum of 0.2% or even a maximum of 0.1% by weight of Ni is added. In one embodiment, no Ni is added to the steel, therefore Ni is present only as an impurity.

[0029] Vanadium can be present in steel in an amount of up to 0.3% by weight. However, V is a relatively expensive element that is mainly used to replace Ti for its precipitation-strengthening effect and to reduce cementite formation through the formation of vanadium carbides. As such, preferably with a maximum of 0.2% by weight V is present in the steel. In certain embodiments, V is present in an amount of at most 0.18% by weight or even at most 0.1% by weight. It is also a possibility that no V is added to the steel, therefore V is present as an impurity.

[0030] Niobium can be present in steel at up to 0.10% by weight. Nb improves the strength of steel in part by hardening the Petition 870250081836, dated 11 / 09 / 2025, p. 16 / 138 11 / 54 precipitation, but mainly by grain refining. However, for high quantities of Nb, these effects are saturated. Therefore, preferably Nb is present with a maximum content of 0.08% by weight. In certain embodiments, a maximum of 0.06% by weight of Nb is present, and in preferable embodiments 0 - 0.04% by weight of Nb is present, preferably 0.01 - 0.04% by weight of Nb is present in the steel. In other embodiments, no Nb is added to the steel, therefore Nb is present as an impurity.

[0031] Since Ti and Nb have the same function in steel, the sum of the Ti and Nb contents must be at most 0.25% by weight.

[0032] Similarly, the sum of the Cr and Mo contents must be at most 1.0% by weight.

[0033] To obtain high strength and a high rate of hole expansion, the microstructure of hot-rolled steel must consist of (by volume %) at least 85% bainite. Preferably, the amount of bainite is as high as possible to obtain the highest possible rate of hole expansion, and with the formation of bainite a small amount of cementite is formed (less than 5%). In addition, small amounts of carbides, precipitates and unavoidable inclusions may be present in the steel. Furthermore, the steel may contain a maximum of 10% total martensite plus retained austenite and preferably contains a maximum of 5% total martensite plus retained austenite.

[0034] The objective of the present invention is to obtain a predominantly bainitic microstructure that combines, on the one hand, a sufficient degree of strength with a sufficient degree of hole expansion capacity and tensile elongation, on the other hand.

[0035] In this text, the term bainite should be understood as encompassing Ferritic Bainite (FB), Granular Bainite (GB), Upper Bainite (UB), and Cementite-Free Bainite (CFB).

[0036] Figure 1 schematically shows the definitions of Petition 870250081836, dated 11 / 09 / 2025, p. 17 / 138 12 / 54 different bainite morphologies used in this specification to describe the inventive and comparative examples, including ferritic bainite (FB), granular bainite (GB), upper bainite (UB), and cementite-free bainite (CFB) and individual building blocks, including irregularly shaped bainitic ferrite (Type 1), lath-type bainitic ferrite (Type 2), cementite (Fe3C), and retained martensite and / or austenite (M / RA):

[0037] All are considered composite microstructures, and the overall microstructure may be composed of one of these composite microstructures or consist of a mixture of two or more of these composite microstructures. In turn, the composite microstructure may be composed of one or more phase components or building blocks. These building blocks are: - irregularly shaped bainitic ferrite (BF, type 1) with relatively low internal dislocation density, - bainitic ferrite (BF, type 2) with a relatively high internal displacement density, - Cementite (Fe3C) present as relatively coarse particles at the lath boundaries, at the grain edges and / or, to some extent, also at the anterior boundaries of the austenite grains, and - retained martensite and / or austenite (M / RA).

[0038] Most of these building blocks can be identified by means of Electron Back Diffraction (EBSD), which in turn also allows the quantification of the area or volume fraction of these building blocks. This is valid for: (1) irregularly shaped bainitic ferrite (BF, type 1) with a relatively low internal dislocation density, (2) lath-shaped bainitic ferrite (BF, type 2) with a relatively high internal dislocation density, (3) martensite, and (4) retained austenite. The experimental methodology for the identification and quantification of these building blocks via EBSD is explained in detail in the description of the Examples, further on in this Petition 870250081836, dated 11 / 09 / 2025, page 18 / 138 13 / 54 document. Cementite cannot be precisely identified, much less quantified, using EBSD. Light optical microscopy on polished cross-sections of steel samples after etching for several seconds with a 4% Picral solution is commonly used to visualize cementite. However, due to the limited resolution of light optical microscopy and the small size of cementite particles, a very precise quantification of the amount of cementite is impossible. This is also true when scanning electron microscopy is used in combination with etched steel samples, as the size of cementite particles is small and other microstructural features, such as partially etched (sub)grain edges, interfere with a precise quantification of cementite. Thus, light optical microscopy in combination with Picral etching of steel samples has been used primarily to assess whether cementite is present in the microstructure.The cementite present in the overall microstructure is predominantly related to the presence of upper bainite (UB), which consists of lath-shaped bainitic ferrite (BF, type 2) and is therefore included in the volume fraction of this building block (lath-shaped bainitic ferrite (BF, type 2)).

[0039] Ferritic bainite (FB) is composed of irregularly shaped bainitic ferrite grains (BF, type 1) with a relatively low internal dislocation density. The excess carbon that cannot be in solution within the bainitic ferrite grains is consumed in the precipitation process with carbide-forming elements, including Ti, Nb, V, and / or Mo, resulting in ferritic bainite comprising only irregularly shaped bainitic ferrite grains and containing little or no cementite and / or M+RA. This type of bainite is favored when the transformation occurs in a temperature region that provides sufficient kinetics for precipitation with the aforementioned elements, particularly Ti. The irregularly shaped bainitic ferrite grains Petition 870250081836, dated 11 / 09 / 2025, page 19 / 138 14 / 54 irregular bainite samples of this type are ideally reinforced with Ti-based carbide precipitates. This increased temperature range for the formation of this bainite type also explains its relatively low internal dislocation density, as this bainite type is formed predominantly through a diffusion mechanism.

[0040] Granular bainite (GB) is composed of irregularly shaped bainitic ferrite (BF, type 1) grains with a relatively low internal displacement density. The excess carbon that cannot be in solution within the bainitic ferrite grains is only partially consumed in the precipitation process with carbide-forming elements, including Ti, Nb, V, and / or Mo, resulting in Granular Bainite (GB) which not only comprises irregularly shaped bainitic ferrite grains but also contains some M+RA between the irregularly shaped bainitic ferrite grains. This type of bainite is favored when the transformation occurs in a temperature region that provides sufficient kinetics for carbon partitioning across the migrating ferrite-austenite transformation interface during the phase transformation process. The irregularly shaped bainitic ferrite grains of this type of bainite are only partially reinforced with Ti-based carbide precipitates.This increased temperature range for the formation of this type of bainite also explains its relatively low internal dislocation density, as this type of bainite is formed predominantly through a diffusion mechanism. The amount of retained martensite and / or austenite has to be limited, since stress concentration around these phase components during shearing and forming operations can lead to premature fracture nucleation.

[0041] Upper bainite (UB) consists of lath-shaped bainitic ferrite (BF, type 2) with cementite at the lath edges. This type of bainite is favored by relatively high transformation temperatures. Petition 870250081836, dated 11 / 09 / 2025, p. 20 / 138 15 / 54 low and, as a consequence, this lath-shaped bainitic ferrite has a relatively high internal dislocation density, which – in general – will be higher than that of the aforementioned irregularly shaped bainitic ferrite, usually formed at higher transformation temperatures. Lath-shaped bainitic ferrite is formed predominantly through a more displaced and oriented mechanism. The lower transformation temperatures for the formation of Upper Bainite (UB) conflict with the ideal precipitation of carbon with carbide-forming elements, including Ti, Nb, V and / or Mo, as there is insufficient kinetics under these conditions. As a consequence, Upper Bainite (UB) comprises a significant amount of cementite at the lath edges.Upper Bainite (UB) has greater resistance to fracture propagation than Granular Bainite (GB), which is attributed to the considerably smaller (effective) size of the crystallographic packing (a packing corresponds to a crystallographic unit in bainite consisting of crystallographic subunits separated from each other by low-angle boundaries (<15°) and having high-angle boundaries (>15°) with other neighboring packings). The small size of the crystallographic packing of upper bainite (UB), and therefore the increased amount of high-angle boundaries, are beneficial for stopping fracture propagation. For this reason, Upper Bainite (UB), which consists of lath-shaped bainitic ferrite with some cementite between laths, is desirable for good hole expansion capability.Since EBSD cannot (accurately) detect cementite, and the amount of cementite present in the microstructure is predominantly found between the lath-type bainitic ferrite building blocks of Upper Bainite (UB), the amount of lath-type bainitic ferrite measured by EBSD also includes the amount of cementite present in the microstructure.

[0042] Cementite-free bainite (CFB) also consists of Petition 870250081836, dated 11 / 09 / 2025, p. 21 / 138 16 / 54 lath-type bainitic ferrite (BF, type 2). However, unlike upper bainite (UB), cementite-free bainite (CFB) does not contain cementite, but rather martensite and / or austenite retained at the lath boundaries. Similar to upper bainite (UB), cementite-free bainite (CFB) is favored by relatively low transformation temperatures and, as a consequence, the lath-type bainitic ferrite of this type of bainite has a relatively high internal dislocation density, which is similar to that of upper bainite (UB). Also, cementite-free bainite (CFB), like upper bainite (UB), will only be partially reinforced with Ti-based carbide precipitates.

[0043] As previously stated, the objective of the present invention is to obtain a predominantly bainitic microstructure that combines, on the one hand, a sufficient degree of strength, with a sufficient degree of hole expansion capacity and tensile elongation, on the other hand. This bainitic microstructure is predominantly composed of ferritic bainite (FB) and / or upper bainite (UB), and contains no or only a small amount of granular bainite (GB) or cementite-free bainite (CFB).

[0044] These bainitic microstructures can be obtained by means of accelerated cooling after hot rolling and performing the phase transformation at low temperature on the exit table and / or winder. The amount of martensite and / or retained austenite (M / RA) between irregularly shaped bainitic ferrite grains or lath-shaped bainitic ferrite bundles has to be controlled and the total amount of martensite plus retained austenite (M+RA) should be limited to a maximum of 10% or preferably to a maximum of 5%, or more preferably to a maximum of 3%, or even more preferably to a maximum of 2%, or even more preferably to a maximum of 1%, or most preferably to no presence of martensite plus retained austenite. Petition 870250081836, dated 11 / 09 / 2025, p. 22 / 138 17 / 54

[0045] Some amount of retained martensite plus austenite (M+RA) can be tolerated and may be beneficial for strength, uniform elongation, and suppression of discontinuous yield behavior. However, too much retained martensite plus austenite can impair the expansion capacity of the holes, since these phase components promote the nucleation of internal micro-voids and cracks during punching. A very high density of these micro-voids and cracks within the steel near the punched edge impairs the expansion capacity of the holes, as the alignment and coalescence of these micro-voids and cracks promote early macroscopic fractures and failures.

[0046] Areas enriched with carbon from segregation during casting or – primarily – through carbon splitting during phase transformation to obtain the desired bainitic microstructure, can also lead to the formation of iron carbides or cementite (FexCy). This cementite is an inherent building block of Upper Bainite (UB) and a consequence of insufficient kinetics for ideal carbide precipitation at the transformation temperatures for Upper Bainite (UB) formation. However, the amount of excess carbon available to form cementite can be limited according to the present invention, such that the amount of carbon and carbide-forming elements, including Ti, Nb, V, and Mo, are properly balanced. This is essential because a very high amount of cementite can lead to a deterioration of formability in general and hole expansion capacity in particular.However, some cementite in the overall bainitic microstructure is beneficial, as a small amount of these fairly small hard phase components can help to achieve a much better shear edge quality. The presence of a small amount of cementite in the shear-affected zone and... Petition 870250081836, dated 11 / 09 / 2025, page 23 / 138 18 / 54 located on or near the resulting sheared or drilled edge can help provide nucleation points for local failures. In this way, the presence of a small amount of cementite can help promote macroscopic fracture and subsequent separation of the steel during shearing without excessive tearing, leaving behind a smoother surface of the sheared edge in general, and the fracture zone in particular of that sheared edge. This will be beneficial for the fatigue life of the sheared edges and therefore for the performance of automotive chassis components. However, too much cementite will lead to too much internal damage within the steel, near the sheared edge, which in turn will increase the risk of coalescence of the gaps that facilitates fracture propagation and ultimately leads to premature macroscopic fracture and failure during – for example – a hole expansion capacity test.In this context, a substantial amount of Upper Bainite (UB) will be beneficial, as this type of bainite, with its small crystallographic packing size, has increased resistance against crack propagation compared to Granular Bainite (GB) with a larger crystallographic packing size.

[0047] The inventors discovered that the amount of cementite and martensite plus retained austenite can be limited and satisfactory for the present invention if the amount of elements Ti, Nb, V, and Mo represented in % by weight satisfies the following equation: f) 45 < —!-------C12^---------<22 U.45 _ (Tl_sol / ^b / *^ - 2.2 with Ti_sol defined as the amount of free Ti in solution and expressed as = Ti-(14) XN with the amount of Ti and N expressed as % by weight.

[0048] Preferably, the lower bound of this equation is 0.55, more preferably 0.75, and the upper bound is preferably 2.1, more Petition 870250081836, dated 11 / 09 / 2025, p. 24 / 138 19 / 54 preferably 1.8, to further limit the amount of cementite and / or the amount of martensite plus retained austenite.

[0049] According to a first preferred embodiment, a high-strength steel is provided with a high average strength and a very good hole expansion ratio. This steel has limited ranges for one or more of the following elements: - 0.02 - 0.06% by weight of C, preferably 0.02 - 0.05% by weight of C; - 1.30 - 2.20% by weight of Mn, preferably 1.30 - 2.00% by weight of Mn; - 0.10 - 0.60% by weight of Si; - 0.09 - 0.20% by weight of Ti, preferably 0.12 - 0.20% by weight of Ti; - 0.0010 - 0.004% by weight of B, preferably 0.0010 0.003% by weight of B; and / or contains limited tracks for one or more of the following options: - 0 - 0.5% by weight of Cu, preferably 0 - 0.1% by weight of Cu; - 0 - 0.8% by weight of Cr, preferably 0 - 0.6% by weight of Cr; - 0 - 0.35% by weight of Mo, preferably 0 - 0.2% by weight of Mo, more preferably 0 - 0.1% by weight of Mo; - 0 - 0.2% by weight of Ni, preferably 0 - 0.1% by weight of Ni; - 0 - 0.18% by weight of V, preferably 0 - 0.1% by weight of V; - 0 - 0.06% by weight of Nb, preferably 0 - 0.04% by weight of Nb, more Petition 870250081836, dated 11 / 09 / 2025, page 25 / 138 20 / 54 preferably 0.01 - 0.04% by weight of Nb, wherein 1.6% by weight < Mn + Cr + 2Mo < 2.4% by weight, the steel having a microstructure consisting of (by volume %): - at least 85% bainitic ferrite, - a maximum of 5% martensite plus retained austenite, - more than 0% and at most 5% cementite, preferably 0.01 - 4% cementite, preferably 0.02 - 3% cementite, even more preferably 0.02 - 2% cementite, preferably 0.02 - 1% cementite, - unavoidable amounts of inclusions, the sum of which can reach up to 100% of the volume.

[0050] Due to the limited amount of carbon, the strength is not very high, but at the same time the amount of Mn + Cr + 2Mo must be at least 1.6% by weight. In this way, it is possible to obtain a microstructure with at least 85% bainitic ferrite, resulting in a very good hole expansion rate.

[0051] The limitations of all elements for this preferred embodiment are in accordance with the explanation for the choice of quantity for each element above, but chosen in such a way that the strength of the steel is not too low, as this would reduce the service performance of the steel, nor too high, as this would impair the hole expansion rate and the overall formability.

[0052] Preferably, this steel has a microstructure with a maximum of 4% retained martensite plus austenite, more preferably a microstructure with a maximum of 3% retained martensite plus austenite, more preferably a maximum of 2% retained martensite plus austenite, even more preferably a maximum of 1% retained martensite plus austenite, preferably no presence of retained martensite plus austenite. Especially martensite increases strength, Petition 870250081836, dated 11 / 09 / 2025, page 26 / 138 21 / 54 but it decreases the expansion of the steel hole, as does retained austenite, so low amounts of both phase components must be present. No martensite is best for formability.

[0053] The composition and microstructure of this preferred embodiment of the high-strength steel strip according to the invention preferably has the following mechanical properties: - a yield strength of at least 570 and at most 900 MPa, - a tensile strength of at least 760 and at most 960 MPa, - a total elongation (A50) of at least 10% and / or - a hole expansion value (λ) of at least 50%, preferably a hole expansion value (λ) of at least 60%, more preferably a hole expansion value (λ) of at least 70%, preferably a hole expansion value (λ) of at least 80%.

[0054] This type of steel is therefore very suitable for providing an essentially bainitic steel with a strength of 800 MPa and very good hole expansion for demanding automotive parts.

[0055] According to a second preferred embodiment, a high-strength steel with improved high strength and a good hole expansion ratio is provided. This steel has limited ranges for one or more of the following elements: - 0.03 - 0.12% by weight of C, preferably 0.04 - 0.09% by weight of C; - 1.50 - 2.20% by weight of Mn, preferably 1.60 - 2.00% by weight of Mn; Petition 870250081836, dated 11 / 09 / 2025, page 27 / 138 22 / 54 - 0.20 - 0.95% by weight of Si, preferably 0.40 - 0.70 by weight of Si; - 0.10 - 0.20% by weight of Ti, preferably 0.12 - 0.18% by weight of Ti; - 0.0010 - 0.004% by weight of B, preferably 0.0010 0.003% by weight of B; and / or contains limited ranges for one or more of the following optional elements: - 0 - 0.5% Cu, preferably 0 - 0.1% by weight of Cu; - 0 - 0.8% by weight of Cr, preferably 0 - 0.5% by weight of Cr; - 0 - 0.8% by weight of Mo, preferably 0.005 - 0.7% by weight of Mo, preferably 0.1 - 0.6% by weight of Mo, even more preferably 0.2 - 0.5% by weight of Mo; - 0 - 0.2% by weight of Ni, preferably 0 - 0.1% by weight of Ni; - 0 - 0.18% by weight of V, preferably 0 - 0.1% by weight of V; - 0 - 0.06% by weight of Nb, preferably 0 - 0.04% by weight of Nb, more preferably 0.01 - 0.04% by weight of Nb, wherein Mn + Cr + 2 Mo > 2.3% by weight, the steel has a microstructure consisting of (by volume %): - at least 90% bainite, - a maximum of 5% martensite plus retained austenite, - more than 0% and at most 5% cementite, preferably 0.01 - 4% cementite, preferably 0.02 - 3% cementite, even more preferably 0.02 - 2% cementite, preferably 0.02 - 1% cementite, Petition 870250081836, dated 11 / 09 / 2025, p. 28 / 138 23 / 54 - unavoidable amounts of inclusions, the total making up to 100% of the volume.

[0056] Due to the higher amounts of bonding elements, especially the higher amount of C and the amount of Mn + Cr + 2 Mo which must be at least 2.3% by weight, greater strength can be obtained. On the other hand, the microstructure contains at least 90% bainite, resulting in a slightly lower hole expansion rate.

[0057] Preferably, this steel has a microstructure with a maximum of 4% martensite plus retained austenite, preferably a microstructure with a maximum of 3% martensite plus retained austenite, preferably a further 2% martensite plus retained austenite, even more preferably 1% martensite plus retained austenite, preferably no presence of martensite plus retained austenite. Here too, the amount of martensite and retained austenite should not be high so as not to impair the hole expansion rate.

[0058] Preferably Cr + 2Mo > 0.20% by weight, more preferably Cr + 2Mo > 0.30% by weight, preferably Cr + 2Mo > 0.40% by weight. A larger amount of Cr + 2Mo is added in order to decrease the amount of Mn that must be added in an attempt to suppress centerline segregation, which can impair shear edge quality or hole expansion capability.

[0059] The composition and microstructure of this preferred embodiment of the high-strength steel strip according to the invention preferably has the following mechanical properties: - a yield strength of at least 670 and at most 990 MPa, - a tensile strength of at least 960 and at most 1380 MPa, - a total lengthening (A50) of at least 9% and / or Petition 870250081836, dated 11 / 09 / 2025, page 29 / 138 24 / 54 - a hole expansion value (λ) of at least 40%, preferably a hole expansion value (λ) of at least 45%. more preferably a hole expansion value (λ) of at least 50%.

[0060] This type of steel is therefore very suitable for providing an essentially bainitic steel with a strength of 1000 MPa and good hole expansion for demanding automotive parts.

[0061] Preferably, this type of steel has a microstructure containing at least 60% lath-shaped bainitic ferrite and a maximum of 40% irregularly shaped bainitic ferrite. As explained earlier, this is beneficial for providing a steel with high strength and a high hole expansion rate.

[0062] A car or truck component, such as an automotive chassis component, a body component, or a component of the structure or substructure of a car or truck, is preferably produced from steel strip, as described above, when a good hole expansion ratio is required.

[0063] According to a second aspect of the invention, a method for manufacturing a high-strength steel is provided, as described above. This method is presented in claims 13 and 14. Especially important are the coiling temperatures of the manufacturing methods, as can be seen from the examples below. The invention will now be explained with reference to the following non-limiting examples. EXAMPLE 1

[0064] Steels A to R with the chemical compositions shown in Table 1.1 were hot-rolled to a thickness of about 3.5 mm under the conditions shown in Tables 1.2 and 1.3, producing steel sheets 1A to 17R and 18A to 33P, respectively. These Petition 870250081836, dated 11 / 09 / 2025, p. 30 / 138 25 / 54 steel plates were produced with the aim of providing a yield strength of at least 670 and at most 990 MPa, a tensile strength of at least 960 and at most 1380 MPa, a total tensile elongation (A50) of at least 9% and a hole expansion ratio λ of at least 40%.

[0065] The forged steel blocks were reheated to a temperature (RHT) of approximately 1240°C and held at this temperature for approximately 45 minutes. After reheating, the forged blocks were hot-rolled and the thickness was reduced from 35 mm to approximately 3.5 mm in 5 rolling passes. The temperature for the last rolling pass (TIN) was in the range of 960 to 990°C. The finishing rolling temperature (FRT) was in the range of 875 to 915°C. After the last rolling pass, the hot-rolled steels were transferred to the exit table and actively cooled with a water and air mixture to a temperature (Accelerated Cooling Stop Temperature or TSAC) in the range of 450 to 495°C at a cooling rate between 40 and 100°C. Then, the steels were transferred to a furnace to replicate the slow cooling of the coil. This was done with furnace temperatures (CT - winding temperature) of 450°C (Table 1.2) and 500°C (Table 1.3).

[0066] EBSD measurements were performed on cross-sections parallel to the lamination direction (RD-ND plane) mounted on a conductive resin and mechanically polished to 1 μm. To obtain a completely deformation-free surface, the final polishing step was performed with colloidal silica (OPS).

[0067] The Scanning Electron Microscope (SEM) used for the EBSD measurements is a Zeiss Ultra 55 machine equipped with a field emission gun (FEG-SEM) and an EDAX PEGASUS XM 4 HIKARI EBSD system. EBSD scans were collected in the RDND plane of the plates. Samples were placed at a 70° angle in Petition 870250081836, dated 11 / 09 / 2025, page 31 / 138 26 / 54 SEM. The acceleration voltage was 15 kV with the high current option enabled. An aperture of 120 μm was used, and the typical working distance was 17 mm during scanning. To compensate for the high sample tilt angle, dynamic focus correction was used during scanning.

[0068] EBSD scans were captured using the software TexSEM Laboratories (TSL): Orientation Imaging Microscopy (OIM) Data Collection version 7.2. Typically, the following data collection configurations were used: Hikari 5 x 5 wire camera combined with background subtraction (standard mode). The scanning area was in all cases located at a position equal to % of the sample thickness, and care was taken to avoid including non-metallic inclusions in the scanning area as much as possible.

[0069] The EBSD scan size was, in all cases, 100 x 100 pm, with a step of 0.1 pm, and a scan rate of approximately 100 frames per second. Fe(a) and Fe(y) were used to index the Kikuchi patterns. The Hough settings used during data collection were: Pattern size of approximately 96; theta (θ) ensemble size of 1; rho (ρ) fraction of approximately 90; maximum peak count of 10; minimum peak count of 5; Hough type set to classical; Hough resolution set to low; butterfly convolution mask of 9 x 9; peak symmetry of 0.5; minimum peak magnitude of 10; maximum peak distance of 20.

[0070] EBSD scans were evaluated using TSL software. OIM Analysis version 8.0 x64 [12-14-16]. Typically, datasets were rotated 90° about the RD axis to obtain scans in the appropriate orientation relative to the measurement orientation. A standard grain dilation cleaning was performed (Grain Tolerance Angle (GTA) of 5°, minimum grain size of 5 pixels, criterion used that a grain must contain several rows for a single cleaning of Petition 870250081836, dated 11 / 09 / 2025, page 32 / 138 27 / 54 dilation iteration). After that, a pseudosymmetry cleanup was applied (GTA 5, axis angle 30°@111).

[0071] EBSD Image Quality (IQ) maps were used to determine the amount of martensite. Areas with a low IQ were identified as MS areas. For the given experimental conditions, typically the lower IQ limit was ~0.4 of the maximum peak position in the IQ histogram. The lower IQ limit was, however, manually checked for each scan to avoid including granular bainite grain boundaries or upper bainitic areas in the martensite area fraction.

[0072] For the calculation of the EBSD map, the Kernel Mean Disorientation (KAM) was used, using the fifth nearest neighbor with a maximum disorientation of 5° (all points in the kernel were used for the KAM calculation). The Kernel Mean Disorientation is considered a signature for the type of bainitic ferrite, since the Kernel Mean Disorientation is a measure of the internal dislocation density. Areas with a relatively low internal dislocation density will predominantly correspond to areas that have a KAM value between 0 and 1° and are classified as irregularly shaped bainitic ferrite (BF, type 1) areas (building block of Ferritic Bainite (FB) and Granular Bainite (GB)). Areas with a relatively high internal dislocation density will predominantly correspond to areas that have a KAM value between 1-5° and are classified as bainitic ferrite (BF, type 2) plus martensite.To determine the amount of lath-type bainitic ferrite (building block of Upper Bainite (UB) and Cementite-Free Bainite (CFB)), the area fraction of martensite that was determined by the low IQ criterion described in the previous paragraph was subtracted from the area fraction with a KAM value between 1-5. Since EBSD cannot accurately detect cementite, the amount of cementite present in the microstructure is... Petition 870250081836, dated 11 / 09 / 2025, p. 33 / 138 28 / 54 predominantly present among the lath-type bainitic ferrite building blocks of Upper Bainite (UB), the amount of lath-type bainitic ferrite measured by EBSD also includes the amount of cementite present in the microstructure.

[0073] Before tensile and hole expansion capacity tests, the hot-rolled plates were sandblasted to remove the oxide layer. The reported tensile properties of plates 1A to 17R in Table 1.2 and plates 18A to 33P in Table 1.3 are based on A50 tensile geometry with tensile testing parallel to the rolling direction according to EN 10002-1 / ISO 6892-1 (2009) (Rp = 0.2% compensation or yield strength; Rm = maximum tensile strength; YR = yield ratio defined as Rp over Rm; Ag = uniform tensile elongation; A50 = tensile elongation). To determine the hole expansion ratio λ, which is a stretch flangability criterion, three square samples (90 x 90 mm2) were cut from each sheet, followed by a 10 mm diameter hole in the sample using a flat punch. The hole expansion test of the samples was performed with top burrs.A 60° conical punch was pushed upwards and the hole diameter df was measured when a crack formed through the thickness. The hole expansion rate λ was calculated using the formula below with d0 = 10 mm:. λ = df, 0° x 100% a °

[0074] The λ values ​​of plates 1A to 17R and plates 18A to 33P are presented in Tables 1.2 and 1.3, respectively.

[0075] Steels A to G are steels of the invention. For these steels, the atomic ratio A is defined as the amount of C per unit of the carbide-forming elements Nb, V, Ti, and Mo according to Petition 870250081836, dated 11 / 09 / 2025, page 34 / 138 29 / 54 _______________C / 12_______________ + + ^l^0^ is between or equal to 0.45 and 2.2 with the elements mentioned above in the equation above expressed in % by weight and the amount of titanium in solution Ti_sol defined as τί=tí—Gχ n with N given in % by weight. The inventors discovered that for A-F steels, where the atomic ratio is at least 0.6 and at most 1.6 as shown in Table 1.1, the amount of martensite plus retained austenite is at most 0.5%, as shown in Table 1.3, with the process settings as indicated in Table 1.3, and the amount of martensite plus retained austenite is at most 0.7% as indicated in Table 1.2, with the process settings as indicated in Table 1.2. The examples also show that no martensite plus retained austenite has to be present.

[0076] Steels A to G with the compositions listed in Table 1.1 and with an atomic ratio A between or equal to 0.45 and 2.2 are all considered examples of the invention, and the steel plates of the invention corresponding to 1A to 7G in Table 1.2 and 18A to 24G in Table 1.3 have a yield strength of at least 670 and at most 990 MPa, a tensile strength of at least 960 and at most 1380 MPa, a tensile elongation A50 of at least 9%, and a hole expansion ratio λ of at least 40%.

[0077] These properties are derived from microstructures consisting of a mixture of ferritic bainite (FB) and upper bainite (UB), the latter being the dominant phase constituent with a volume fraction of 60% or more and typically in the range of 65 to 80%. As a consequence, all these microstructures show evidence of the presence of cementite based on visual inspection with Petition 870250081836, dated 11 / 09 / 2025, p. 35 / 138 30 / 54 light optical microscopy. Although a precise quantification of the amount of cementite is practically impossible, the cementite fraction for all examples of the invention is estimated at a maximum of 5%. The volume fraction of Ferritic Bainite (FB) is considerably smaller for these examples of the invention, i.e., about 20 to 35%. The amount of martensite plus retained austenite (M+RA) is in all cases below 1%, and in some cases there is no martensite and / or retained austenite. Therefore, the amount of Granular Bainite (GB) and Cementite-Free Bainite (CFB) in all these inventive examples is not considered significant.

[0078] Steels H to R with the compositions listed in Table 1.1 and with an atomic ratio A above 2.2 are all considered comparative examples, and the corresponding steel plates 8H to 17R in Table 1.2 and 25H to 33P in Table 1.3 have either a very high yield strength, or a tensile strength below 960 MPa, or a very low formability in terms of tensile elongation A50 below 9% or a hole expansion rate λ below 40%.

[0079] These properties derive from microstructures which, like the examples of the invention, also consist of a mixture of ferritic bainite (FB) and upper bainite (UB), but have some essential differences from the examples of the invention, either in relation to the increase in the cementite fraction (Fe3C) or the increase in martensite + retained austenite (M+RA). These differences are highlighted below: Comparative examples of 10J to 12L are shown in Table 1.2, and comparative examples of 27J to 29L are shown in Table 1.3. Comparative examples of 13M to 17R are shown in Table 1.2, and 30M to 33P are shown in Table 1.3.

[0080] In contrast to the examples of the invention, the cementite fraction for comparative examples 10J, 11K and 12L in Table 1.2 and comparative examples 27J, 28K and 29L in Table 1.3 is estimated at Petition 870250081836, dated 11 / 09 / 2025, page 36 / 138 31 / 54 more than 5%. It is believed that this amount of cementite impairs formability, i.e., tensile elongation and / or hole expansion capacity.

[0081] For comparative examples 13M to 17R in Table 1.2 and 30M to 33P in Table 1.3, the amount of Upper Bainite (UB) is considerably lower with typical values ​​between 50% and 60%, and the amount of Ferritic Bainite (FB) is considerably higher with typical values ​​around 35% to 55%. For these comparative samples, the cementite fraction is estimated to be more than 0% and at most 5%, as in the case of the examples of the invention. However, microscopic analysis indicates that for comparative examples 3M to 17R in Table 1.2 and 30M to 33P in Table 1.3, carbon led to the formation of martensite and / or retained austenite. The amount of martensite plus retained austenite (M+RA) is in all cases above 1%, and in most cases the amount of martensite plus retained austenite is even (well) above 4%. This indicates an increase in the amount of Granular Bainite (GB) and Cementite-Free Bainite (CFB) for these comparative examples.It is believed that the smaller fraction of Upper Bainite (UB) with an increase in Ferritic Bainite (FB) and the increase in the amount of GB and / or CFB contributes to a lower hole expansion capacity for these comparative examples than that observed for the examples of the invention in this case.

[0082] To achieve a steel with a yield strength of at least 670 and at most 990 MPa, a tensile strength of at least 960 and at most 1380 MPa, a tensile elongation A50 of at least 9%, and a hole expansion ratio λ of at least 40%, the microstructure of the steel must comprise: - at least 90% bainite, or preferably at least 95% bainite, or more preferably at least 97% bainite, or even more preferably at least 98% bainite, or Petition 870250081836, dated 11 / 09 / 2025, p. 37 / 138 32 / 54 preferably at least 99% bainite, wherein the bainite consists of a mixture predominantly of upper bainite (UB) and a small contribution of ferritic bainite (FB) that are reinforced with Ti-based composite carbide precipitates and in which the overall microstructure of the steel consists of: - at least 60% bainitic lath ferrite (BF, type 2), including more than 0% and at most 5% cementite, preferably 0.01 - 4% cementite, preferably 0.02 - 3% cement, even more preferably 0.02 - 2% cementite, preferably 0.02 - 1% cementite, - a maximum of 40% irregularly shaped bainitic ferrite (BF, type 1), and - a maximum of 5% of retained martensite plus austenite (M+RA), and preferably a maximum of 3% of retained martensite plus austenite, more preferably a maximum of 2% of retained martensite plus austenite, even more preferably a maximum of 1% of retained martensite plus austenite, preferably no presence of retained martensite plus austenite. Petition 870250081836, dated 11 / 09 / 2025, page 38 / 138 Table 1.1 - Composition of steels Alloy C % by weight Si % by weight Mn % by weight Al % by weight P % by weight S ppm Ti % by weight Nb % by weight V % by weight A 0.061 0.521 1.916 0.063 0.013 10 0.162 0.001 0.006 B 0.061 0.507 1.897 0.072 0.011 10 0.158 0.001 0.005 C 0.061 0.511 1.912 0.066 0.011 8 0.163 0.001 0.005 D 0.061 0.948 1.919 0.066 0.012 13 0.165 0.002 0.005 E 0.043 0.514 1.904 0.066 0.011 11 0.156 0.002 0.006 F 0.044 0.517 1.929 0.070 0.012 10 0.181 0.002 0.005 G 0.049 0.501 1.900 0.077 0.014 8 0.159 0.002 0.007 H 0.121 0.207 1.913 0.073 0.013 4 0.122 0.001 0.006 I 0.124 0.207 1.605 0.069 0.013 11 0.122 0.001 0.006 J 0.151 0.209 1.927 0.072 0.012 7 0.122 0.001 0.006 K 0.151 0.201 1.494 0.067 0.012 11 0.118 0.001 0.005 L 0.149 0.690 1.885 0.072 0.011 9 0.120 0.001 0.006 M 0.120 0.209 1.910 0.069 0.012 15 0.116 0.029 0.005 N 0.141 0.211 1.908 0.065 0.011 15 0.113 0.002 0.006 W 0.140 0.205 1.907 0.062 0.011 14 0.115 0.001 0.004 0.011 17 0.085 0.001 0.004 Q 0.105 0.206 1.886 0.065 0.013 12 0.112 0,001 0.006 R 0.122 0.210 1.927 0.060 0.006 2 0.113 0.001 0.006 Atomic ratio C / [Ti_sol+Nb+V+Mo] with elements expressed in weight % is defined as: fTl sol—Nb / 12v——r with the amount of free Ti not bound to N expressed as Ti sol = Ti- (48) x N with Ti and N in weight % ( _ / 48+ / 93+ / 51+ / 96) V14', 33 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 39 / 138 Table 1.1 -continued- Alloy Mo % by weight Cr % by weight B ppm N ppm Cr+2Mo % by weight Mn+Cr+2Mo % by weight Ti_sol % by weight Atomic ratio* C / [Ti_sol+Nb+V+Mo] Example A 0.007 0.896 20 47 0.910 2.826 0.146 1.567 Invention B 0.150 0.303 19 49 0.603 2.500 0.141 1.103 Invention C 0.250 0.010 22 47 0.510 2.422 0.147 0.880 Invention D 0.244 0.001 24 46 0.489 2.408 0.149 0.882 Invention E 0.253 0.002 21 45 0.508 2.412 0.141 0.627 Invention F 0.245 0.002 24 44 0.492 2.421 0.166 0.598 Invention G 0.205 0.000 25 46 0.410 2.310 0.143 0.774 Invention H 0.253 0.000 3 41 0.506 2.419 0.108 2.011 Invention I 0.256 0.248 2 52 0.760 2.365 0.104 2.083 Invention J 0.206 0.000 1 55 0.412 2.339 0.103 2.847 Comparative K 0.253 0.243 2.49 0.749 2.243 0.101 2.595 Comparative L 0.004 0.299 1.54 0.307 2.192 0.101 5.460 Comparative M 0.003 0.787 1.50 0.793 2.703 0.099 3.994 Comparative N 0.004 0.782 1.54 0.790 2.698 0.094 5.493 Comparative O 0.007 0.308 2.51 0.322 2.229 0.098 5,294 Comparative P 0.104 0.787 3 55 0.995 2.899 0.066 4,645 Comparative Q 0.011 0.830 2 58 0.852 2.738 0.092 4.052 Comparative R 0.006 0.826 1 63 0.838 2.765 0.091 4.872 Comparative Atomic ratio C / [Ti_sol+Nb+V+Mo] with elements expressed in % by weight is defined as: (Tl sol—Nb / 12—M , with the amount of free Ti not bound to N expressed as Ti sol = Ti- (48) x N with Ti and N in % by weight ( _ ^8+ / 93+ / 51+^ / 96) V14 / , 34 / 54 Petition 870250081836, dated 11 / 09 / 2025, page 40 / 138 Table 1.2: Process settings, microstructures, and properties of steel coiled at 450°C. Alloy Steel PROCESS CONFIGURATIONS MICROSTRUCTURE RHT (°C) Tin (°C) FRT (°C) TsaC (°C) CT (°C) BF (%) M+RA (%) Fe3C (-) FB GB UB CFB Type 1 Type 2 Composite building blocks 1 A 1240 985 895 460 450 21.0 79.0 0.0 yes- □ - - 2 B 1240 990 900 480 450 29.0 71.0 0.0 yes- □ - - 3 C 1240 980 890 480 450 32.0 68.6 0.4 yes- □ - - 4 D 1240 980 900 480 450 24.0 75.3 0.7 yes- □ - - 5 E 1240 980 895 475 450 24.0 76.0 0.0 yes- □ - - 6 F 1240 980 900 490 450 34.0 66.0 0.0 yes- □ - - 7 G 1240 970 900 480 450 21.9 77.6 0.5 yes- □ - - 8 H 1240 970 885 465 450 20.0 79.0 1.0 yes- □ - - 9 I 1240 975 885 480 450 26.6 73.4 0.0 yes- □ - - 10 J 1240 980 890 465 450 34.0 66.0 0.0 yes+ □ - - 11 K 1240 970 890 470 450 22.1 78.0 0.0 yes+ □ - - 12 L 1240 970 875 450 450 13.2 86.9 0.0 yes+ □ - - 13 M 1240 970 880 450 450 35.0 56.0 9.0 yes- □ o □ o 14 O 1240 960 875 465 450 38.0 59.7 2.3 yes- □ oo 15 P 1240 975 880 450 450 40.0 53.9 6.1 sim- □ o □ o 16 2 1220 960 875 460 450 37.0 54.5 8.5 yes- □ o □ o 17 R 1220 965 875 460 450 36.0 59.9 4.1 yes- □ o □ o, 35 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 41 / 138 Table 1.2: -continued- Steel Alloy MECHANICAL PROPERTIES Example t(mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 1 A 3.56 962 1056 0.91 4.1 10.0 46 Invention 2 B 3.52 902 993 0.91 3.5 9.6 59 Invention 3 C 3.55 925 993 0.93 3.5 9.3 63 Invention 4 D 3.79 967 1047 0.92 4.6 10.9 40 Invention 5 E 3.53 898 968 0.93 4.7 11.7 82 Invention 6 F 3.62 929 997 0.93 3.8 11.0 52 Invention 7 G 3.54 935 998 0.94 4.4 11.1 67 Invention 8 H 3.57 939 967 0.97 3.0 9.5 77 Invention 9 I 3.48 889 967 0.92 2.9 9.0 74 Invention 10 J 3.45 951 994 0.96 2.6 8.1 38 Comparative 11 K 3.48 954 1007 0.95 2.8 7.2 39 Comparative 12 L 3.30 1066 1120 0.95 3.2 8.4 38 Comparative 13 M 3.36 853 944 0.90 4.7 9.6 36 Comparative 14 O 3.23 744 836 0.89 4.9 10.4 39 Comparative 15 P 3.45 700 953 0.73 7.4 13.1 32 Comparative 16 Q 3.32 733 912 0.80 7.4 12.7 35 Comparative 17 R 3.18 804 948 0.85 6.7 11.8 32 Comparative RHT = Reheating temperature BF, Type 1 = Bainitic ferrite with a mean kernel disorientation of 0 to 1 degree Tin = Inlet temperature in the last rolling pass BF, Type 2 = Bainitic ferrite with average kernel disorientation of 1 to 5 degrees FRT = Finishing lamination temperature M+RA = Martensite + Retained Austenite Tsac = Accelerated cooling stop temperature Fe3C = Cementite - No significant presence CT = Winding temperature FB = Ferritic Bainite Estimated volume fraction <25% 36 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 42 / 138 GB = Granular Bainite □ Estimated volume fraction 25-60% yes- = Estimated to be more than 0% and at most 5% UB = Upper Bainite Estimated volume fraction >60% yes+ = Estimated to be greater than 5% CFB = Cementite-free Bainite Table 1.3: Process settings, microstructures, and properties of steel coiled at 500°C. Alloy Steel PROCESS CONFIGURATIONS MICROSTRUCTURE RHT (°C) Tin (°C) FRT (°C) Tsac (°C) CT (°C) BF (%) M+RA (%) Fe3C (-) FB GB UB CFB Type 1 Type 2 Composite building blocks 18 A 1240 980 900 460 500 21.0 79.0 0.0 yes- □ - - 19 B 1240 985 905 470 500 29.0 70.8 0.2 yes- □ - - 20 C 1240 985 890 480 500 24.0 75.5 0.5 yes- □ - - 21 D 1240 985 900 470 500 22.0 78.0 0.0 yes- □ - - 22 E 1240 985 900 490 500 32.0 67.5 0.5 yes- □ - - 23 F 1240 980 900 495 500 30.0 70.0 0.0 yes- □ - - 24 G 1240 985 915 465 500 21.6 78.4 0.0 yes- □ - - 25 H 1240 960 885 460 500 23.4 76.1 0.5 yes- □ - - 26 I 1240 960 875 490 500 24.0 76.0 0.0 yes- □ - - 27 J 1240 970 885 460 500 23.9 76.2 0.0 yes+ □ - - 28 K 1240 990 885 485 500 25.7 74.5 0.0 yes+ □ - - 29 L 1240 975 895 455 500 14.3 85.7 0.0 yes+ □ - - 30 M 1240 985 900 460 500 42.0 50.5 7.5 yes- □ o □ o 31 N 1240 985 895 450 500 38.0 59.8 2.2 yes- □ o □ o 32 O 1240 975 900 465 500 53.0 45.6 1.4 yes- □ o □ o 33 P 1240 990 895 450 500 42.0 51.5 6.5 yes- □ o □ o. 37 / 54 Petition 870250081836, dated 11 / 09 / 2025, page 43 / 138 Table 1.3: -continued- Alloy Steel MECHANICAL PROPERTIES Example t(mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 18 A 3.57 963 1053 0.91 4.6 10.8 53 Invention 19 B 3.54 944 1015 0.93 4.1 9.8 48 Invention 20 C 3.50 925 990 0.93 4.3 10.0 64 Invention 21 D 3.65 987 1058 0.93 3.3 9.6 43 Invention 22 E 3.65 884 964 0.92 4.8 11.2 78 Invention 23 F 3.56 914 990 0.92 4.9 12.0 54 Invention 24 G 3.47 965 1002 0.96 4.3 10.9 48 Invention 25 H 3.54 899 963 0.93 4.4 9.8 45 Invention 26 I 3.47 937 991 0.95 4.3 9.5 60 Invention 27 J 3.51 891 951 0.94 4.0 8.2 50 Comparative 28 K 3.47 957 1005 0.95 3.0 7.6 69 Comparative 29 L 3.32 1073 1110 0.97 3.9 6.9 36 Comparative 30 M 3.49 801 942 0.85 6.1 11.4 36 Comparative 31 N 3.40 710 974 0.73 7.8 13.9 36 Comparative 32 O 3.46 771 851 0.91 7.3 15.6 38 Comparative 33 P 3.42 697 962 0.72 7.1 12.9 34 Comparative RHT = Reheat temperature BF, Type 1 = Bainitic ferrite with an average kernel disorientation of 0 to 1 degree Tin = Entry temperature in the last rolling pass BF,Type 2 = Bainitic ferrite with an average kernel disorientation of 1 to 5 degrees FRT = Finishing lamination temperature M+RA = Martensite + Retained Austenite Tsac = Stop temperature of accelerated cooling Fe3C = Cementite - No significant presence CT = Winding temperature FB = Ferritic bainite Estimated volume fraction <25% GB = Granular bainite Estimated volume fraction 25-60% yes- = Estimated to be more than 0% and at most 5% UB = Upper bainite Estimated volume fraction >60% yes+ = Estimated to be greater than 5% CFB = Cementite-free bainite 38 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 44 / 138 39 / 54 EXAMPLE 2

[0083] Steels A to J with the chemical compositions shown in Table 2.1 were hot-rolled to a thickness of about 3.5 mm under the conditions shown in Tables 2.2, 2.3 and 2.4, producing steel sheets 1A to 6F, 7A to 16J, and 17G to 20J, respectively. These steel sheets were produced with the aim of providing a yield strength of at least 570 and at most 900 MPa, a tensile strength of at least 760 and at most 960 MPa, a total tensile elongation (A50) of at least 10% and a hole expansion ratio λ of at least 50%.

[0084] The forged steel blocks were reheated to a temperature (RHT) of approximately 1240°C and held at this temperature for approximately 45 minutes. After reheating, the forged blocks were hot-rolled and the thickness was reduced from 35 to approximately 3.5 mm in 5 rolling passes. The temperature for the last rolling pass (TIN) was in the range of 960 to 990°C. The finishing rolling temperature (FRT) was in the range of 870 to 905°C. After the final rolling pass, the hot-rolled steels were transferred to the exit table and actively cooled with a water and air mixture to a temperature (accelerated cooling stop temperature or TSAC) at a cooling rate between 40 and 100°C. After cooling on the exit table, the steels were transferred to a furnace to replicate the slow cooling of the coil with furnace temperatures (CT - coiling temperature) of 450°C (Table 2.2), 550°C (Table 2.3) and 500°C (Table 2.4).The outlet temperatures (TE) of the outlet table for these tests were in the range of 465 to 510°C, 540 to 580°C, and 500 to 550°C, respectively.

[0085] The EBSD procedures used to determine the amount of irregularly shaped bainitic ferrite, lath-shaped bainitic ferrite, martensite, and retained austenite are identical to those described in Petition 870250081836, dated 11 / 09 / 2025, p. 45 / 138 40 / 54 EXAMPLE 1.

[0086] Before tensile and hole expansion capacity tests, the hot-rolled sheets were sandblasted to remove the oxide layer. The reported tensile properties of sheets 1A to 6F in Table 1.2, and sheets 7A to 16J in Table 2.3, and sheets 17G to 20J in Table 2.4 are based on A50 tensile geometry with tensile testing parallel to the rolling direction according to EN 10002-1 / ISO 6892-1 (2009) (Rp = 0.2% compensation or tensile strength; Rm = ultimate tensile strength; YR = yield ratio defined as Rp over Rm; Ag = uniform tensile elongation; A50 = tensile elongation). To determine the hole expansion ratio λ, which is a stretch flangability criterion, three square samples (90 x 90 mm2) were cut from each sheet, followed by a 10 mm diameter hole in the sample using a flat punch. The hole expansion test of the samples was performed with top burrs.A 60° conical punch was pushed from below and the hole diameter df was measured when a slit was formed through the thickness. The hole expansion rate λ was calculated using the formula below with d0 = 10 mm:. λ = fcío χ 100% do

[0087] The λ values ​​of plates 1A to 6F, and plates 7A to 16J, and plates 17G to 20J are shown in Tables 2.2, 2.3, and 2.4, respectively.

[0088] Steels A to I are steels of the invention. For these steels the atomic ratio A is defined as the amount of C resulting from the sum of the carbide-forming elements Nb, V, Ti, and Mo, according to C / ________________ / 12_______________ (Ti _sol / .Nb / , V / ,Mo / A( / 48+ / 93 + / 51 + / 96) is between or equal to 0.45 and 2.2 with the elements mentioned in Petition 870250081836, dated 11 / 09 / 2025, p. 46 / 138 41 / 54 equation above expressed in % by weight and the amount of titanium in solution Ti_sol defined as Ti = Ti - Gx w with N given in % by weight. The inventors discovered that for A-I steels, where the atomic ratio is at least 0.8 and at most 1.4 as shown in Table 2.1, the amount of martensite plus retained austenite is at most 0.2%, as shown in Table 2.2 with the process settings as indicated in Table 2.2, and the amount of martensite plus retained austenite is at most 3.9%, as indicated in Table 2.3, with the process settings as indicated in Table 2.3, or at most 4.2% as indicated in Table 2.4 with the process settings as indicated in Table 2.4. The examples also show that no martensite plus retained austenite has to be present, see Table 2.2.

[0089] Steels A to I with the compositions listed in Table 2.1 and with atomic ratio A between or equal to 0.45 and 2.2 are all considered examples of the invention and the corresponding steel plates of the invention 1A, 2B and 4D to 6F in Table 2.2, 7A to 15I in Table 2.3, and 17G to 19I in Table 2.4, all have a yield strength of at least 570 and at most 900 MPa, a tensile strength of at least 760 and at most 960 MPa, a tensile elongation A50 of at least 10%, and a hole expansion rate λ of at least 50%. Steel J with the composition listed in Table 2.1 and with an atomic ratio A well above 2.2 is considered a comparative example, and the corresponding steel plates 16J in Table 2.3 and 20J in Table 2.4 are considered comparative examples, since the hole expansion ratio λ is below 50%.

[0090] It is preferable to use a winding temperature between 520 and 570°C for the production of steels with a yield strength of at least 570 and at most 900 MPa, tensile strength of Petition 870250081836, dated 11 / 09 / 2025, p. 47 / 138 42 / 54 at least 760 and at most 960 MPa, a total tensile elongation (A50) of at least 10% and a hole expansion ratio λ of at least 50%. A comparison between the data corresponding to the examples of the invention presented in Tables 2.2, 2.3 and 2.4 shows that with a winding temperature of 550°C, the tensile elongation A50 is substantially greater than with a lower winding temperature of 450 or 500°C, while at the same time providing excellent hole expansion capability and good yield strength and tensile strength values. MICROSTRUCTURES OF EXAMPLES 1A to 6F COILED AT 450°C (Table 2.2):

[0091] The properties of all examples of the invention are derived from microstructures consisting of a mixture of ferritic bainite (FB) and upper bainite (UB), the latter being the dominant phase with a volume fraction of 60% or more and typically in the range of 60% to 75%. As a consequence, all these microstructures show evidence of the presence of cementite based on visual inspection with light optical microscopy. The volume fraction of Ferritic Bainite (FB) is considerably smaller for these examples of the invention, i.e., about 25 to 40%. The amount of martensite plus retained austenite (M+RA) is, in all cases, well below 1% and in some cases there is no martensite and / or retained austenite. Therefore, the amount of Granular Bainite (GB) and Cementite-Free Bainite (CFB) in all these examples of the invention is not significant.

[0092] Although the composition of C steel without added boron above 5 ppm is considered to be of the invention for the present invention, when used in combination with a coiling temperature of 450°C the corresponding 3C steel sheet (Table 2.2) has a very low tensile strength with a value falling below 760 MPa due to insufficient hardenability. This Petition 870250081836, dated 11 / 09 / 2025, page 48 / 138 43 / 54 makes 3C steel plate a comparative example for the present invention. The very low strength is explained by the increased presence of ferritic bainite (FB) at the expense of upper bainite (UB) due to the absence of a boron addition above 5 ppm and a lower degree of subsequent hardening. As the internal displacement density of ferritic bainite (FB) is considerably lower than that of upper bainite (UB) and its crystallographic packing size is larger, the strength is compromised. Microstructures of Examples 7A to 16J wound at 550°C (Table 2.3):

[0093] Winding between 520 and 570°C is the preferred option, as mentioned previously. The properties of all examples of the invention obtained with winding at 550°C are derived from microstructures consisting of a mixture of Ferritic Bainite (FB), Granular Bainite (GB), and Upper Bainite (UB), with the first (FB) being the dominant phase constituent with a volume fraction of 60% or more and typically in the range of 60% to 75%. The volume fraction of Upper Bainite (UB) is, for these examples of the invention, considerably smaller, i.e., about 25 to 40%. This smaller presence of Upper Bainite is associated with the presence of some cementite based on visual inspection with light optical microscopy after causticizing with a 4% Picral solution to selectively delineate the cementite. The amount of retained martensite plus austenite (M+RA) is below 4% in all cases, and below 3% in most cases.The smallest amount of retained martensite plus austenite (M+RA) measured for the examples of the invention is 0.5%.

[0094] Because the amount of martensite plus retained austenite is so low, the amount of Granular Bainite (GB) in all these examples of the invention is estimated to be relatively small (<25%) and because the winding temperature used is relatively high, the amount Petition 870250081836, dated 11 / 09 / 2025, p. 49 / 138 44 / 54 of Cementite-Free Bainite is considered insignificant. The relatively high winding temperature of 550°C will favor Ferritic Bainite (FB) over Upper Bainite (UB), and as this high winding temperature provides sufficient kinetics for carbide precipitation with—primarily—Ti, but also Nb, and / or Mo, the amount of carbon splitting during the phase transformation is limited, since much of the carbon is consumed in the carbide precipitation process with the aforementioned elements. This will lead to Ferritic Bainite that is enhanced with TiC or Ti-based composite carbide precipitates (including, for example, in addition to Ti, also Nb and / or Mo) with little or no martensite plus retained austenite or cementite for this purpose.

[0095] Steel plate 16J is a comparative example, as the expansion rate of the holes λ is below 50%. The microstructure of this steel plate has a slightly lower amount of ferritic bainite (FB) than the examples of the invention in Table 2.3 and, consequently, a slightly higher fraction of upper bainite (UB). However, the fractions of both bainitic morphologies approach those of the examples of the invention in this Table. The amount of retained martensite plus austenite in comparative example 16J is in the same range as that of the examples of the invention and well below 2%, like many of the examples of the invention in Table 2.3. The amount of carbon that can remain in solid solution in the steel matrix is ​​quite low and is assumed to be less than 0.02% by weight. Excess carbon will lead to the formation of (1) cementite, (2) martensite and / or retained austenite, and / or (3) carbide precipitates with elements such as Ti, Nb, V, and / or Mo.The process conditions and alloy composition will control the extent to which these microstructural elements are formed. Since the amount of carbon in the comparative example 16J is much greater than that of all examples of the invention (Table 2.1) and the sum of... Petition 870250081836, dated 11 / 09 / 2025, page 50 / 138 45 / 54 The quantity of carbide-forming elements Ti, Nb, V, and / or Mo is much lower, the atomic ratio A of the comparative example is well above 2.2 with a value of 3.45. Due to this much higher atomic ratio A and the observation that the amount of martensite plus retained austenite in comparative example 16J is similar to that of the examples of the invention, it leads to the conclusion that the microstructure of comparative example 16J must contain substantially more cementite than all the other examples of the invention. This is confirmed by visual inspection of the microstructures of all examples shown in Table 2.3 after causticizing with a 4% Picral solution to selectively delineate the cementite. Although a precise quantification of the amount of cementite is practically impossible, the cementite fraction for comparative example 16J is estimated to be above 5%, while that of the examples of the invention is estimated to be well below 5%. MICROSTRUCTURES OF EXAMPLES 17G to 20J WOUND AT 500°C (Table 2.4):

[0096] The properties of all examples of the invention, except for example 19I, are derived from microstructures consisting of a mixture of Ferritic Bainite (FB), Granular Bainite (GB), and Upper Bainite (UB). Inventive example 19I has a microstructure that also consists of a mixture of ferritic bainite (FB) and upper bainite (UB), but which does not have a significant amount of granular bainite (GB), as the amount of martensite plus retained austenite is well below 1%. The amount of ferritic bainite (FB) is typically in the range of 40 to 60%, while the amount of upper bainite is typically in the range of 35 to 60%. This lower presence of upper bainite is associated with the presence of some cementite based on visual inspection with light optical microscopy after causticizing with a 4% Picral solution to selectively delineate the cementite. The amount of martensite plus retained austenite (M+RA) is Petition 870250081836, dated 11 / 09 / 2025, p. 51 / 138 46 / 54 in all cases below 5%, and in most cases below 3%. The lowest amount of retained martensite plus austenite (M+RA) measured for the examples of the invention is 0.4%.

[0097] Because the amount of retained martensite plus austenite is so low, the amount of Granular Bainite (GB) in most examples of the invention in Table 2.4 is estimated to be relatively small (<25%) and because the winding temperature used is still relatively high, the amount of Cementite-Free Bainite is estimated to be insignificant. The relatively high winding temperature of 500°C likely favors Ferritic Bainite (FB) over Upper Bainite (UB) and because this high winding temperature provides sufficient kinetics for at least partial carbide precipitation with – mainly – Ti, but also Nb, and / or Mo, the amount of carbon partitioning during the phase transformation is limited, since much of the carbon is consumed in the carbide precipitation process with the aforementioned elements.This will lead to ferritic bainite which is partially reinforced with precipitates of TiC or Ti-based compound carbide (including, for example, in addition to Ti also Nb and / or Mo) with subsequently only little or almost no martensite plus austenite or cementite for this purpose.

[0098] Steel plate 20J is a comparative example, as the hole expansion rate λ is below 50%. The microstructure of this steel plate has a similar amount of ferritic bainite (FB) and upper bainite (UB) as the examples of the invention in Table 2.4. The amount of retained martensite plus austenite in comparative example 20J is in the same range as that of the examples of the invention and well below 3%, like many of the examples of the invention in Table 2.4. The amount of carbon that can remain in solid solution in the steel matrix is ​​quite low and is assumed to be less than 0.02% by weight. Petition 870250081836, dated 11 / 09 / 2025, p. 52 / 138 47 / 54 Excess carbon will lead to the formation of (1) cementite, (2) martensite and / or retained austenite, and / or (3) carbide precipitates with elements such as Ti, Nb, V, and / or Mo. The process conditions and alloy composition will control the extent to which these microstructural elements are formed. As the amount of carbon in comparative example 20J is much greater than that of all examples of the invention (Table 2.1) and the sum of the amount of carbide-forming elements Ti, Nb, V, and / or Mo is much smaller, the atomic ratio A of the comparative example is well above 2.2 with a value of 3.45. Due to this much higher atomic ratio A and the observation that the amount of martensite plus retained austenite in comparative example 20J is similar to that of the examples of the invention, it leads to the conclusion that the microstructure of comparative example 20J must contain substantially more cementite than all other examples of the invention.This is confirmed by visual inspection of the microstructures of all examples shown in Table 2.4 after causticizing with a 4% Picral solution to selectively delineate the cementite. Although a precise quantification of the amount of cementite is practically impossible, the cementite fraction for the comparative example 20J is estimated to be above 5%, while that of the examples of the invention is estimated to be well below 5%.

[0099] To obtain a steel with a yield strength of at least 570 and at most 900 MPa, a tensile strength of at least 760 and at most 960 MPa, a tensile elongation A50 of at least 10%, and a hole expansion ratio λ of at least 50%, the microstructure of the steel must comprise: - at least 90% bainite, or preferably at least 95% bainite, or more preferably at least 97% bainite, or even more preferably at least 98% bainite, or most preferably at least 99% bainite, Petition 870250081836, dated 11 / 09 / 2025, p. 53 / 138 48 / 54 in which Bainite consists of: - a mixture of Upper Bainite (UB), Ferritic Bainite (FB) and, optionally, Granular Bainite (GB), which are reinforced with Ti-based compound carbide precipitates, or - preferably a mixture predominantly of ferritic bainite (FB) and a smaller fraction of upper bainite (UB) and granular bainite (GB), which are reinforced with Ti-based composite carbide precipitates, and in which the overall microstructure of the steel preferably consists of: - a maximum of 40% bainitic ferrite (BF, type 2), including more than 0% and a maximum of 5% cementite, preferably 0.01 - 4% cementite, preferably 0.02 - 3% cementite, even more preferably 0.02 - 2% cementite, preferably 0.02 - 1% cementite, - at least 60% irregularly shaped bainitic ferrite (BF, type 1), and - a maximum of 5% of martensite plus retained austenite (M + AR), and preferably a maximum of 3% of martensite plus retained austenite, more preferably a maximum of 2% of martensite plus retained austenite, even more preferably a maximum of 1% of martensite plus retained austenite, preferably no presence of martensite plus retained austenite. Petition 870250081836, dated 11 / 09 / 2025, p. 54 / 138 Table 2.1: Steel compositions. Alloy C % by weight Si % by weight Mn % by weight Al % by weight P % by weight S ppm Ti % by weight Nb % by weight V % by weight Mo % by weight A 0.031 0.509 1.863 0.053 0.012 4 0.157 0.001 0.005 0.005 B 0.032 0.477 1.826 0.048 0.013 7 0.159 0.001 0.006 0.004 C 0.032 0.503 1.850 0.059 0.013 6 0.158 0.001 0.005 0.005 D 0.031 0.497 1.377 0.048 0.012 7 0.159 0.001 0.005 0.005 E 0.032 0.217 1.836 0.046 0.012 3 0.152 0.001 0.005 0.003 F 0.032 0.211 1.363 0.041 0.012 10 0.109 0.001 0.005 0.097 G 0.041 0.488 1.356 0.050 0.011 14 0.152 0.001 0.008 0.004 H 0.039 0.213 1.354 0.047 0.011 19 0.125 0.000 0.005 0.003 I 0.038 0.209 1.369 0.046 0.011 19 0.106 0.039 0.004 0.004 J 0.093 0.178 1.232 0.031 0.011 15 0.118 0.001 0.005 0.003 49 / 54 Table 2.1: -continued Cr alloy % by weight B ppm N ppm Cr+2Mo % by weight Mn+Cr+2Mo % by weight Ti_sol % by weight Atomic ratio* C / [Ti_sol+Nb+V+Mo] Example A 0.002 20 53 0.012 1.875 0.139 0.845 Invention B 0.514 19 61 0.522 2.348 0.138 0.876 Invention C 0.002 1 52 0.012 1.862 0.140 0.866 Invention D 0.523 18 51 0.533 1.910 0.142 0.828 Invention E 0.533 17 57 0.539 2.375 0.132 0.923 Invention Petition 870250081836, dated 11 / 09 / 2025, p. 55 / 138 Cr alloy % by weight B ppm N ppm Cr+2Mo % by weight Mn+Cr+2Mo % by weight Ti_sol % by weight Atomic ratio* Cl [Ti_sol+Nb+V+Mo] Example F 0.522 18 59 0.716 2.079 0.089 0.897 Invention G 0.507 19 46 0.515 1.871 0.136 1.123 Invention H 0.499 18 49 0.505 1.859 0.108 1.366 Invention I 0.500 20 55 0.508 1.877 0.087 1.346 Invention J 0.909 1 49 0.915 2.147 0.101 3.453 Comparative Atomic ratio C / [Ti_sol+Nb+V+Mc] with elements expressed in weight % is defined as: ,Tl sol—Nbí2 vi—Mo, 3 with the amount of free Ti not bound to N expressed as Ti sol = Ti- ) x N with Ti and N in weight % V / 48+ / 93+ / 51+ / 96} V14 / Table 2.2: Process settings, microstructures, and properties of steel coiled at 450°C. 50 / 54 Alloy Steel PROCESS CONFIGURATIONS MICROSTRUCTURE RHT (°C) Tin (°C) FRT (°C) TsAC (°C) CT (°C) BF (%) M+RA (%) Fe3C (-) FB GB UB CFB Tlpol Type 2 Composite Building Blocks 1 A 1240 965 870 465 450 27.0 73.0 0.0 yes- □ - - 2 B 1240 960 870 485 450 30.0 70.0 0.0 yes- □ - - 3 C 1240 965 860 480 450 63.0 36.8 0.2 yes- - □ - 4 D 1240 990 890 510 450 39.0 60.8 0.2 yes- □ - - 5 E 1240 975 875 490 450 32.0 67.8 0.2 yes- □ - - 6 F 1240 985 880 500 450 39.0 61.0 0.0 yes- □ - - Petition 870250081836, dated 11 / 09 / 2025, p. 56 / 138 Table 2.2: -continued- Alloy Steel MECHANICAL PROPERTIES Example t (mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 1 A 3.35 794 858 0.93 4.4 10.1 109 Invention 2 B 3.54 838 909 0.92 4.2 10.1 99 Invention 3 C 3.38 664 731 0.91 5.8 12.4 98 Comparative 4 D 3.73 737 829 0.89 5.4 12.3 112 Invention 5 E 3.47 805 887 0.91 3.4 10.7 106 Invention 6 F 3.36 712 786 0.91 4.4 10.5 96 Invention RHT = Reheating temperature BF, Type 1 = Bainitic Ferrite with a descaling Tin = Entry temperature in the last BF pass, Type 2 = Bainitic Ferrite with a descaling FRT = Finishing lamination temperature M+RA = Martensite + Retained Austenite Tsac = Stop temperature of accelerated cooling Fe3C = Cementite CT = Winding temperature FB = Ferritic Bainite GB = Granular Bainite sim- = Estimated to be greater than 0% and at most UB = Upper Bainite sim+ = Estimated to be greater than 5% CFB = Cementite-Free Bainite average Kernel orientation of 0 to 1 degrees average Kernel orientation of 1 to 5 degrees - No significant presence of O Vol. fractionEstimated <25% □ Estimated volume fraction 25-60% Estimated volume fraction >60%. 51 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 57 / 138 Table 2.3: Process settings, microstructures, and properties of steel coiled at 550°C Alloy Steel PROCESS CONFIGURATIONS MICROSTRUCTURE RHT (°C) Tin (°C) FRT (°C) Tsac (°C) CT (°C) BF (%) M+RA (%) Fe3C (-) FB GB UB CFB Type 1 Type 2 Composite building blocks 7 A 1240 990 890 545 550 64.0 34.1 1.9 yes- O □ - 8 B 1240 980 880 555 550 68.0 28.2 3.8 yes- O □ - 9 C 1240 985 880 580 550 60.0 39.5 0.5 yes- O □ - 10 D 1240 975 875 550 550 60.0 38.7 1.3 yes - □ - 11 E 1240 970 870 540 550 61.0 36.5 2.5 yes - □ - 12 F 1240 980 880 550 550 61.0 36.3 2.7 yes - □ - 13 G 1240 985 900 550 550 71.0 27.2 1.8 yes - □ - 14 H 1240 975 895 555 550 67.0 29.1 3.9 yes - □ - 15 I 1240 985 905 550 550 66.0 30.3 3.7 yes- o □ - 16 J 1240 980 890 555 550 52.0 46.9 1.1 yes+ □ o □ - 52 / 54 Table 2.3: Process settings, microstructures, and properties of steel coiled at 550°C Alloy Steel MECHANICAL PROPERTIES Example t (mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 7 A 3.62 702 829 0.85 7.4 15.8 82 Invention 8 B 3.48 697 836 0.83 6.8 14.4 98 Invention 9 C 3.71 713 800 0.89 8.2 17.4 101 Invention 10 D 3.70 743 840 0.88 6.7 14.7 89 Invention 11 E 3.26 700 868 0.81 6.7 13.8 81 Invention Petition 870250081836, dated 11 / 09 / 2025, page 58 / 138 Alloy Steel MECHANICAL PROPERTIES Example t (mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 12 F 3.54 600 754 0.80 7.0 14.6 87 Invention 13 G 3.51 718 839 0.86 7.9 17.1 85 Invention 14 H 3.43 625 772 0.81 8.3 17.5 83 Invention 15 I 3.49 626 780 0.80 7.7 15.8 81 Invention 16 J 3.38 736 856 0.86 8.1 14.2 46 Comparative RHT = Reheating temperature BF, Tipol = Bainitic Ferrite with an average Kernel disorientation of 0 to 1 degrees Tin = Entry temperature in the last BF, Type 2 = Bainitic Ferrite with an average Kernel disorientation of 1 to 5 degrees rolling pass FRT = Finishing rolling temperature M+RA = Martensite + Retained Austenite Tsac = Stop temperature of accelerated cooling Fe3C = Cementite - No significant presence CT = Winding temperature FB = Ferritic Bainite Estimated volume fraction <25% GB = Granular Bainite Estimated volume fraction 25-60% = Estimated to be more than 0% and in the UB = Upper Bainite Volume fractionEstimated >60% Maximum 5% yes+ = Estimated to be more than 5% CFB = Cementite-Free Bainite. 53 / 54 Petition 870250081836, dated 11 / 09 / 2025, p. 59 / 138 Table 2.4: Process settings, microstructures, and properties of steel coiled at 500°C Alloy Steel PROCESS CONFIGURATIONS MICROSTRUCTURE RHT (°C) Tin (°C) FRT (°C) Tsac (°C) CT (°C) BF (%) M+RA (%) Fe3C (-) FB GB UB CFB Type 1 Type 2 Composite building blocks 17 G 1240 985 890 515 500 59.0 36.8 4.2 yes- □ O □ - 18 H 1240 980 890 520 500 44.0 53.6 2.4 yes- □ O □ - 19 I 1240 975 900 500 500 40.0 59.6 0.4 yes- □ - □ - 20 J 1240 965 890 550 500 54.0 44.6 1.4 yes+ □ o □ - Table 2.4: -continued- Alloy Steel MECHANICAL PROPERTIES Example t (mm) Rp (MPa) Rm (MPa) YR (au) Ag (%) A50 (%) λ (%) 17 G 3.53 650 829 0.78 5.6 11.2 74 Invention 18 H 3.59 681 781 0.87 5.2 11.4 91 Invention 19 I 3.47 735 799 0.92 6.2 12.2 88 Invention 20 J 3.66 643 779 0.83 6.0 12.9 48 Comparative RHT = Entry temperature in the last BF, Type 1 = Bainitic Ferrite with an average Kernel disorientation of 0 to 1 degrees Tin = Temperature of BF lamination, Type 2 = Bainitic Ferrite with an average Kernel disorientation of 1 to 5 degrees FRT = Stop temperature of accelerated cooling M+RA = Martensite + Austenite Tsac = Winding temperature Fe3C = Cementite - No significant presence CT = Entry temperature on the last rolling pass FB = Ferritic Bainite Estimated volume fraction <25% GB = Granular Bainite Estimated volume fraction 25-60% = Estimated to be more than 0% and UB = Upper Bainite Volume fractionEstimated >60% maximum 5% yes+ = Estimated to be more than 5% CFB = Cementite-Free Bainite.

Claims

CLAIMS 1. High-strength hot-rolled steel strip, characterized in that it consists of: • 0.02 - 0.13% by weight of C; • 1.20 - 2.20% by weight of Mn; • 0.10 - 1.00% by weight of Si; • 0.01 - 0.10% by weight of Al_tot; • 0.09 - 0.18% by weight of Ti; • 0.001 - 0.010% by weight of N; • 0.005 - 0.2% by weight of Mo; • 0 - 0.10% by weight of P; • 0 - 0.01% by weight of S; optionally 0 - 0.005% by weight of B; optionally one or more of: • 0 - 1.5% by weight of Cu; • 0 - 1.0% by weight of Cr; • 0 - 0.50% by weight of Ni; • 0 - 0.30% by weight of V; • 0 - 0.04% by weight of Nb; wherein Ti + Nb < 0.25% by weight, wherein Cr + Mo < 1.0% by weight, wherein Mn + Cr + 2Mo > 2.3% by weight, the remainder being iron and unavoidable impurities, wherein the steel has limited ranges for one or more of the following elements: • 0.03 - 0.12% by weight of C; • 1.50 - 2.20% by weight of Mn; • 0.20 - 0.95% by weight of Si; • 0.10 - 0.18% by weight of Ti; • 0.0010 - 0.004% by weight of B;Petition 870250081836, dated 11 / 09 / 2025, page 61 / 138 2 / 4 • 0.005 - 0.2% by weight of Mo; and / or contains limited ranges for one or more of the following optional elements: • 0 - 0.5% by weight of Cu; • 0 - 0.9% by weight of Cr; • 0 - 0.2% by weight of Ni; • 0 - 0.18% by weight of V; • 0 - 0.04% by weight of Nb, wherein the steel has a microstructure consisting of (by volume %): - at least 90% bainite, - a maximum of 5% martensite plus retained austenite, - more than 0% and a maximum of 5% cementite, - unavoidable amounts of inclusions, the total amounting to up to 100% by volume;wherein the steel strip contains at least 60% lath-type bainitic ferrite and at most 40% irregularly shaped bainitic ferrite, wherein the steel strip has the following mechanical properties: - tensile strength of at least 760 and at most 960 MPa, - total elongation (A50) of at least 10%, - hole expansion ratio (λ) value of at least 50%, or wherein the steel strip has the following mechanical properties: - tensile strength of at least 960 and at most 1380 MPa, - total elongation (A50) of at least 9%, Petition 870250081836, dated 11 / 09 / 2025, p. 62 / 138 3 / 4 hole expansion rate value (λ) of at least 40%, where the equation _______________C / 12_______________ (^%+ + + ^ / 90) has a lower limit of 0.45 and an upper limit of 2.2, where Ti_sol is defined as Ti soi = Ti - (48) x N.; 2. High-strength steel strip according to claim 1, characterized in that the equation has a lower limit of 0.55 and an upper limit of 2.

1.

3. High-strength steel strip, according to claim 1 or 2, characterized in that the steel has a microstructure with a maximum of 4% martensite plus retained austenite.

4. High-strength steel strip according to any one of claims 1 to 3, characterized in that: Cr + 2Mo > 0.20% by weight.

5. High-strength steel strip, according to any one of claims 1 to 4, characterized in that the steel strip has the following mechanical properties: - a yield strength of at least 670 and at most 990 MPa, - a tensile strength of at least 960 and at most 1380 MPa, - a total elongation (A50) of at least 9%, - a hole expansion ratio (λ) of at least 40%.

6. A car or truck component, such as an automotive chassis component, a body component, or a structural or substructure component of a car or truck, said component characterized in that it is produced from steel strip, as defined in any one of claims 1 to 5. Petition 870250081836, dated 11 / 09 / 2025, p. 63 / 138 4 / 4 7. A method for producing a high-strength steel strip, as defined in any one of claims 1 to 5, characterized in that it comprises the steps of: - casting a slab, followed by the step of reheating the solidified slab to a temperature between 1050 and 1260°C and hot rolling said slab, or casting a slab or strip followed directly by the step of hot rolling said slab or strip and - hot rolling the steel slab or strip with an entry temperature into the final rolling stand between 960 and 1100°C and - finishing said hot rolling with a finishing rolling temperature between 850 and 1080°C and - cooling the hot-rolled steel strip with a cooling rate between 10 and 250°C / s to a temperature on the exit table between 550 and 420°C, followed by - coiling between 370 and 580°C.

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