Method for creating temporary corrosion protection for a coil of an annealed steel strip, and coil unit with such a steel strip
Patent Information
- Application Number
- EP2024708189
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-02-28
- Filing Date
- 2024-02-28
- Publication Date
- 2026-01-07
AI Technical Summary
Annealed steel coils with pickled grain boundaries are susceptible to corrosion during storage due to moisture penetration through the turns, leading to damage, especially when subjected to hood annealing, as existing protective methods are inadequate in preventing moisture ingress.
Applying an anti-corrosion liquid to the end faces of the coil before cooling, allowing it to penetrate into the gap between the steel strip layers and form fluid barriers that prevent moisture from reaching the pickled grain boundaries, thereby reducing corrosion risk.
The anti-corrosion liquid effectively forms barriers that suppress moisture penetration into the central region of the gap, protecting the steel strip from corrosion and extending the usability of the coils by preventing damage from moisture exposure.
Smart Images
Figure EP2024055028_06092024_PF_FP
Abstract
Description
[0001] Method for creating a temporary corrosion protection for a coil made of an annealed steel strip and coil unit with such a steel strip
[0002] The invention is based on a method for creating temporary corrosion protection for a coil made of an annealed, cold-rolled or hot-rolled steel strip, in particular a hot-rolled, subsequently pickled and then annealed steel strip or a pickled, subsequently cold-rolled and then annealed steel strip, which is wound up into this coil having a plurality of turns with corresponding steel strip layers and a gap formed between adjacent steel strip layers, wherein the steel strip has two longitudinal edges, each forming an end face of this coil, at which the gap has an opening towards the surroundings of the coil.
[0003] The invention further relates to a corresponding device for creating temporary corrosion protection for such a coil and to a coil unit with an annealed, cold-rolled or hot-rolled steel strip, in particular a hot-rolled, subsequently pickled and then annealed steel strip or a pickled, subsequently cold-rolled and then annealed steel strip, which is wound into a coil having several turns with corresponding steel strip layers and a gap formed between the adjacent steel strip layers, wherein the steel strip has two longitudinal edges, each forming an end face of this coil, at which the gap has an opening towards the surroundings of the coil.
[0004] While the term "hot-rolled strip" or "hot-rolled steel strip" directly describes the resulting steel strip, the term "cold-rolled strip" or "cold-rolled steel strip" refers to a steel strip in which at least the last rolling step is cold rolling. This includes prior hot rolling. Therefore, the production of this cold-rolled strip naturally also includes hot rolling. The term "coil unit" describes an entire unit with the actual coil (winding) of the steel strip itself and possible additional components, such as fixing straps, etc.
[0005] Since such coils or coil units are often stored for quite long periods prior to further processing, they are sometimes treated with temporary corrosion protection. One well-known and widely used method for providing temporary corrosion protection for steel strip rolled into coils is the use of protective oils. These protective oils are applied evenly to the strip before it is wound or coiled into a coil.
[0006] A special situation arises, for example, with pickled hot-rolled strip, i.e. hot-rolled and subsequently pickled steel strip that is subjected to an annealing process, especially an annealing process as a whole in the form of a coil using so-called batch annealing, and which has partially pickled grain boundaries, making it highly susceptible to corrosion. During storage of batch-annealed coils, moisture can penetrate through the individual coil turns at the end faces. If this moisture then comes into contact with the said pickled grain boundaries, corrosion processes can intensify, damaging the steel strip to such an extent that it is unusable for many applications. Often, the immediate peripheral areas at the end faces (strip edge areas) through which the moisture penetrated are not affected at all, as there are no pickled grain boundaries there.
[0007] A similar situation also arises for other hot- or cold-rolled steel strips that are subjected to batch annealing and are susceptible to corrosion due to moisture penetrating the windings of the coiled coil, such as cold-rolled strip produced from hot-rolled strip with pickled grain boundaries, i.e. cold-rolled steel strip that has undergone the following manufacturing steps: hot rolling, pickling, cold rolling, (batch blooming).
[0008] The object of the invention is to provide a method and a device for creating a temporary corrosion protection for a coil of an annealed, cold-rolled or hot-rolled steel strip as well as a coil unit with such a coil, in which a good temporary corrosion protection is also ensured for steel strips that are annealed by batch annealing and in particular have pickled grain boundaries.
[0009] According to the invention, the object is achieved by the features of the independent claims. Preferred embodiments of the invention are specified in the subclaims, each of which may represent an aspect of the invention individually or in combination.
[0010] In the method according to the invention for creating temporary corrosion protection for a coil made of annealed, cold-rolled or hot-rolled steel strip, in particular a hot-rolled, subsequently pickled and then annealed steel strip or a pickled, subsequently cold-rolled and then annealed steel strip, which is wound into this coil having several turns with corresponding steel strip layers and a gap formed between adjacent steel strip layers, in which the steel strip has two longitudinal edges, each forming an end face of this coil, at which the gap has an opening towards the surroundings of the coil, the following method steps are provided:
[0011] (i) providing the coil cooled after annealing of the cold-rolled or hot-rolled steel strip to a temperature Tcoii above the dew point T of the ambient atmosphere (Tcoii > T), and
[0012] (ii) Application of a corrosion protection fluid, in particular a corrosion protection oil, to the end faces of the provided coil to form a fluid barrier from the corrosion protection fluid that has penetrated into a respective edge region of the gap, which prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central region of the gap adjacent to the edge regions. The coil is then cooled to room temperature. However, it is important that the corrosion protection fluid is applied before the dew point temperature T is reached.
[0013] The fluid barriers thus formed prevent or suppress the penetration of moisture into the gap up to the areas of the strip surface where pickled grain boundaries are found, namely the central region of the gap surrounded by the edge regions on the end faces of the coil. The corrosion protection fluid penetrates into the gap in particular over the entire length of the gap or at least 90% of the total length of the gap (i.e. along the full length or almost the full length of the steel strip). In other words, each of the two fluid barriers has a macroscopically broad barrier structure over the full length or at least 90% of the total length of the gap. The corrosion protection fluid used is in particular an oil, i.e. a corrosion protection oil.
[0014] The edge areas are preferably each a few millimeters wide (approximately 2 to 9 mm) to a maximum of 500 millimeters wide (500 mm). For example, for a strip with a width of 600 mm, 80 mm wide edge areas result in a 440 mm wide central area of the gap, strip, or coil, which is protected by the fluid barriers.
[0015] According to a preferred embodiment of the method according to the invention, the penetration of the corrosion protection fluid into the gap on each end face results in an average penetration depth of between 2 and 300 mm, preferably between 3 and 200 mm, particularly preferably between 5 and 200 mm. Such penetration depths are realistic for appropriate corrosion protection fluids such as corrosion protection oils.
[0016] It is advantageous that - starting from the corresponding end face - within an edge section of 10 mm in the gap, an average corrosion protection liquid coating of at least 0.3 g / m 2 , in particular of at least 0.5 g / m 2 , while the corrosion protection fluid content in a central section of the gap in the middle between the two end faces is preferably below 0.1 g / m 2 The edge section represents the edge region, and the middle section represents the middle region. While the two edge regions contain the corrosion protection fluid, i.e., the fluid barriers, the middle region is essentially free of corrosion protection fluid. Thus, there are actually two fluid barriers in the edge regions and not a single film of corrosion protection fluid that completely wets the strip.
[0017] According to a further preferred embodiment of the method according to the invention, the following steps are provided for providing the coil cooled after annealing the cold-rolled or hot-rolled steel strip to a temperature Tcoii above the dew point T of the ambient atmosphere:
[0018] (a) hot rolling of a slab, in particular having the following composition in % by weight: C: 0.04 to 0.80, in particular 0.1 to 0.60,
[0019] Mn: 0.5 to 3.0, especially 0.8 to 2.5,
[0020] Si: 0.05 to 2.0, especially 0.1 to 0.7,
[0021] AI: 0.01 to 2.0, especially 0.01 to 0.4,
[0022] P < 0.1,
[0023] S < 0.05,
[0024] N < 0.02, and optionally one or more of the following elements:
[0025] Cr: 0.1 to 1.5, especially 0.3 to 1.2
[0026] B: 0.0001 to 0.008,
[0027] Ti: 0.01 to 0.1,
[0028] V: 0.01 to 0.3,
[0029] Nb: 0.01 to 0.1, especially 0.02 to 0.06,
[0030] Mo: 0.05 to 0.5, especially 0.1 to 0.25,
[0031] Ni: 0.15 to 0.5 and
[0032] Cu: 0.15 to 0.5,
[0033] Rest iron and unavoidable steel-associated impurities, to a hot-rolled steel strip with a final rolling temperature between 820 °C and 1050 °C,
[0034] (b) coiling the hot-rolled steel strip with a coiling temperature TH above 500 °C into a coil,
[0035] (c) pickling the hot-rolled steel strip in a pickling line and winding the pickled steel strip into the coil,
[0036] (d) annealing the coil in a bell annealing plant in the temperature range from 500°C to 1000°C in an annealing atmosphere containing more than 4% by weight of hydrogen and
[0037] (e) subsequent cooling - in particular combined with a final cooling after the hood of the hood annealing plant has been pulled out on the annealing base of the hood annealing plant or after unpacking from the annealing base on a cooling stand - down to the said temperature Tcoii of the coil.
[0038] According to yet another preferred embodiment of the method according to the invention, the corrosion protection fluid is applied by spraying, mechanical application, or electrostatic application. The invention further relates to a corresponding device for creating temporary corrosion protection for a coil of annealed, cold-rolled, or hot-rolled steel strip, which is wound into this multi-winding coil with corresponding steel strip layers and a gap formed between adjacent steel strip layers. The steel strip is designed either as a hot-rolled, subsequently pickled, and then annealed steel strip, or as a pickled, subsequently cold-rolled, and then annealed steel strip, and has two longitudinal edges, each forming an end face of this coil, at each of which the gap has an opening toward the coil's surroundings.It is provided that the device has at least one applicator for applying a corrosion protection fluid, in particular a corrosion protection oil, to the end faces of the provided coil to form a fluid barrier from this corrosion protection fluid that has penetrated into a respective edge region of the gap, wherein the respective fluid barrier prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central middle region of the gap adjoining the edge regions.
[0039] The corresponding applicator is in particular an applicator for applying the corrosion protection liquid by spraying or an applicator for mechanical application, i.e. brush, roller, etc. or an applicator for electrostatic application.
[0040] In the coil unit according to the invention with an annealed, cold-rolled or hot-rolled steel strip, in particular hot-rolled, subsequently pickled and then annealed steel strip or pickled, subsequently cold-rolled and then annealed steel strip, which is wound into a coil having several turns with corresponding steel strip layers and a gap formed between the adjacent steel strip layers, wherein the steel strip has two longitudinal edges, each forming an end face of this coil, at which the gap has an opening towards the environment of the coil, a fluid barrier is further provided on each of the end faces of the coil, consisting of a corrosion protection fluid that has penetrated into a respective edge region of the gap, which fluid barrier prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central region of the gap adjoining the edge regions,The fluid barriers are formed by a corrosion protection fluid, in particular a corrosion protection oil, that has penetrated into a respective edge region of the gap. The statements made in connection with the method according to the invention also apply here: The fluid barriers prevent or suppress the penetration of moisture into the gap up to the areas of the strip surface where pickled grain boundaries are found, namely the central area of the gap surrounded by the edge regions on the end faces of the coil.
[0041] According to a preferred embodiment of the invention, the corrosion protection liquid has an average penetration depth into the gap on each end face which is between 2 and 300 mm, preferably between 3 and 200 mm, particularly preferably between 5 and 200 mm.
[0042] This advantageously results in an average corrosion protection fluid coating of at least 0.3 g / m within a 10 mm edge section of the gap, starting from the corresponding end face. 2 , in particular of at least 0.5 g / m 2 , while the corrosion protection liquid content in a central section of the gap in the middle between the two end faces is preferably below 0.1 g / m 2 The edge section represents the edge region, and the middle section represents the middle region. While the two edge regions contain the corrosion protection fluid, i.e., the fluid barriers, the middle region is essentially free of corrosion protection fluid.
[0043] The steel strip has in particular the following composition in weight %:
[0044] C: 0.04 to 0.80, especially 0.1 to 0.60,
[0045] Mn: 0.5 to 3.0, especially 0.8 to 2.5,
[0046] Si: 0.05 to 2.0, especially 0.1 to 0.7,
[0047] AI: 0.01 to 2.0, especially 0.01 to 0.4,
[0048] P < 0.1,
[0049] S < 0.05,
[0050] N < 0.02, and optionally one or more of the following elements:
[0051] Cr: 0.1 to 1.5, especially 0.3 to 1.2 B: 0.0001 to 0.008, Ti: 0.01 to 0.1,
[0052] V: 0.01 to 0.3,
[0053] Nb: 0.01 to 0.1, especially 0.02 to 0.06,
[0054] Mo: 0.05 to 0.5, especially 0.1 to 0.25,
[0055] Ni: 0.15 to 0.5 and
[0056] Cu: 0.15 to 0.5,
[0057] Rest iron and unavoidable steel-associated impurities.
[0058] According to a further preferred embodiment of the invention, the annealed, cold-rolled, or hot-rolled steel strip is a batch-annealed, cold-rolled, or hot-rolled steel strip. During batch annealing, the steel strip is annealed as a whole in coiled form.
[0059] According to yet another preferred embodiment of the invention, the steel strip has pickled grain boundaries on its surface. Such pickled grain boundaries arise from the pickling of a steel strip that has previously been hot-rolled and coiled at a high coiling temperature and make the steel strip particularly susceptible to corrosion. The resulting product is, in particular, the said annealed, in particular batch-annealed, cold-rolled or hot-rolled steel strip.
[0060] The invention will now be explained by way of example with reference to the accompanying drawings using a preferred embodiment, wherein the features presented below may represent an aspect of the invention both individually and in combination. They show:
[0061] Fig. 1 shows a coil unit with a coil of an annealed steel strip according to a preferred embodiment of the invention in a schematic representation and
[0062] Fig. 2 shows a section through three layers of a coil of a corresponding coil unit according to a preferred embodiment of the invention.
[0063] Fig. 1 shows a schematic representation of a coil unit 10 with a steel strip 14 rolled up into a coil 12. The coil 12 has roughly the shape of a hollow cylinder with a longitudinal axis A, an outer surface on the outer circumference 16 and an inner surface on the inner circumference 18. The steel strip 14, with its longitudinal edges 20, 22, forms the end faces 24, 26 of the coil 12. The coil 12 has a plurality of turns with a corresponding number of steel strip layers 28, which are shown in section in Fig. 2. A narrow gap 30 is formed between adjacent steel strip layers 28, which extends from the inner circumference 18 to the outer circumference 16 and from one end face 24 to the other end face 26 of the coil 12.
[0064] Furthermore, the coil unit 10 has a fluid barrier 32 on each of the end faces 24, 26 of the coil 12, which prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central region of the gap 30 between the end faces 24, 26. The fluid barriers 32 are formed by a corrosion protection fluid 34 which has penetrated into a respective edge region of the gap 30 (and is shown in detail in Fig. 2), which is particularly designed as a protective oil. The corrosion protection fluid 34 has previously been applied / applied to the end faces 24, 26 by means of applicators 36 (only one of which is shown as an example in Fig. 1) of a device for creating the fluid barriers 32. The applicator 36, shown schematically here, is designed as a nozzle for spraying the corrosion protection fluid 34 and is directed onto the corresponding end face 24.
[0065] Fig. 2 shows a section through three steel strip layers 28 of a coil 12 of a corresponding coil unit 10 across the full width between the two longitudinal edges 20, 22 of the steel strip 14. On each of the end faces 24, 26 of the coil 12 formed by the longitudinal edges 20, 22, a fluid barrier 32 is constructed which is formed from the corrosion protection liquid 34 which has penetrated into a respective edge region of the gap 30. These fluid barriers 32 consist of liquid plugs that extend a short distance into the gap 30 between the individual layers 28 and form a liquid film on the respective end faces 24, 26 of the coil 12. Thus, the two fluid barriers 32 are located in edge regions 38, 40 of the gap 30 and each extend to the respective end face 24, 26, preventing moisture from the ambient atmosphere from penetrating into a central region 42 of the gap 30 adjacent to the edge regions 38, 40.Mainly in this central region 42 of the gap 30, the steel strip 14 has pickled grain boundaries 44 that are particularly susceptible to corrosion. The fluid barrier 32 is therefore understood to be a lateral barrier in the sense of a plug of corrosion protection fluid 34, rather than a full-surface film on the steel strip 14 and its individual layers 28. The gap 30 is essentially free of corrosion protection fluid 34 in its central region 42 (or the central region of the steel strip 14) between the longitudinal edges 20, 22 and the adjoining edge regions 38, 40.
[0066] The core of the invention is the application of a suitable corrosion protection liquid 34 (in particular a corrosion protection oil) after the (hood) annealing to the coil windings, whereby, due to the capillary action, the corrosion protection liquid 34 penetrates into the gap 30 between the windings / layers 28 and subsequently prevents the ingress of moisture.
[0067] It is important to apply the corrosion protection fluid 34 before the coil 12 has completely cooled down. In other words, the corrosion protection fluid 34 is applied well before the dew point temperature T is reached, so that no moisture can condense and penetrate the gap 30 between the individual coil windings / steel strip layers 28. It is characteristic that only the area 38, 40 of the edges is wetted, and not the entire surface of the steel strip 14.
[0068] If a corrosion protection oil is used, a mixture with heptane can be used to optimize the oil used, for example, to (temporarily) reduce the viscosity for better penetration of the corrosion protection oil into the gap 30 between the individual coil windings / steel strip layers 28.
[0069] Reference symbol
[0070] 10 coil units
[0071] 12 coils
[0072] 14 steel band
[0073] 16 outer circumference
[0074] 18 inner circumference
[0075] 20 Longitudinal edge (steel band)
[0076] 22 Longitudinal edge (steel band)
[0077] 24 Front side (coil)
[0078] 26 Front side (coil)
[0079] 28 steel band layers
[0080] 30 gap
[0081] 32 Fluid barrier
[0082] 34 Corrosion protection fluid
[0083] 36 Applicator
[0084] 38 Marginal area
[0085] 40 Marginal area
[0086] 42 Middle area, central
[0087] 44 pickled grain boundaries
[0088] A Longitudinal axis (Coil)
Claims
Patent claims 1. A method for providing temporary corrosion protection for a coil (12) made from an annealed, cold-rolled, or hot-rolled steel strip (14), in particular a hot-rolled, subsequently pickled, and then annealed steel strip (14) or a pickled, subsequently cold-rolled, and then annealed steel strip (14), which is wound into a coil (12) having multiple turns with corresponding steel strip layers (28) and a gap (30) formed between adjacent steel strip layers (28), wherein the steel strip (14) has two longitudinal edges (20, 22), each forming an end face (24, 26) of this coil (12), at which the gap (30) has an opening toward the surroundings of the coil (12), characterized by the steps: - providing the coil (12) cooled to a temperature Tcoii above the dew point T of the ambient atmosphere after annealing the cold-rolled or hot-rolled steel strip (14), and - Application of a corrosion protection liquid (34), in particular a corrosion protection oil, to the end faces (24, 26) of the provided coil (12) to form a fluid barrier (32) from the corrosion protection liquid (34) that has penetrated into a respective edge region (38, 40) of the gap (30), which fluid barrier prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central middle region (42) of the gap (30) adjoining the edge regions (38, 40).
2. Method according to claim 1, characterized in that when the corrosion protection liquid (34) penetrates on each end face (24, 26), an average penetration depth of the corrosion protection liquid (34) into the gap (30) of between 2 and 300 mm, preferably between 3 and 200 mm, particularly preferably between 5 and 200 mm, results.
3. Method according to claim 1 or 2, characterized in that - starting from the corresponding end face (24, 26) - within an edge section of 10 mm in the gap (30) an average corrosion protection liquid coating of at least 0.3 g / m 2 , in particular of at least 0.5 g / m 2 , while the corrosion protection liquid content in a central section of the gap (30) in the middle between the two end faces (24, 26) is preferably below 0.1 g / m 2 lies.
4. Method according to one of claims 1 to 3, characterized by the following steps for providing the coil (12) cooled after annealing the hot-rolled steel strip (14) to a temperature Tcoii above the dew point T of the ambient atmosphere: - Hot rolling of a slab, in particular with the following composition in % by weight: C: 0.04 to 0.80, especially 0.1 to 0.60, Mn: 0.5 to 3.0, especially 0.8 to 2.5, Si: 0.05 to 2.0, especially 0.1 to 0.7, AI: 0.01 to 2.0, especially 0.01 to 0.4, P < 0.1, S < 0.05, N < 0.02, and optionally one or more of the following elements: Cr: 0.1 to 1.5, especially 0.3 to 1.2 B: 0.0001 to 0.008, Ti: 0.01 to 0.1, V: 0.01 to 0.3, Nb: 0.01 to 0.1, especially 0.02 to 0.06, Mo: 0.05 to 0.5, especially 0.1 to 0.25, Ni: 0.15 to 0.5 and Cu: 0.15 to 0.5, Rest iron and unavoidable steel-accompanying impurities, to a hot-rolled steel strip (14) with a final rolling temperature between 820 °C and 1050 °C, - coiling the hot-rolled steel strip (14) with a coiling temperature TH above 500 °C into a coil (12), - pickling the hot-rolled steel strip (14) in a pickling plant and winding the pickled steel strip (14) into the coil (12), - annealing the coil (12) in a bell annealing plant in the temperature range from 500°C to 1000°C in an annealing atmosphere containing more than 4% by weight of hydrogen and - subsequent cooling - particularly combined with a final cooling after the hood of the hood annealing plant has been pulled out on the annealing base of the hood annealing plant Plant or after packing from the annealing base on a cooling stand - up to the said temperature Tcoii of the coil (12).
5. Method according to one of claims 1 to 4, characterized in that the application of the corrosion protection liquid (34) is carried out by spraying or by mechanical application or by electrostatic application.
6. Device for creating temporary corrosion protection for a coil (12) from an annealed, cold-rolled or hot-rolled steel strip (14), which is wound into this coil (12) having several turns with corresponding steel strip layers (28) and a gap (30) formed between adjacent steel strip layers (28), wherein the steel strip (14) is designed either as a hot-rolled, subsequently pickled and then annealed steel strip (14) or as a pickled, subsequently cold-rolled and then annealed steel strip (16) and has two longitudinal edges (20, 22), each forming an end face (24, 26) of this coil (12), at which the gap (30) each has an opening towards the surroundings of the coil (12), characterized in that the device comprises at least one applicator (36) for applying a corrosion protection liquid (34), in particular a corrosion protection oil, on the front sides (24,26) of the provided coil (12) for forming a respective fluid barrier (32) from which corrosion protection fluid (34) has penetrated into a respective edge region (38, 40) of the gap (30), wherein the fluid barriers (32) prevent or at least reduce the penetration of moisture from the ambient atmosphere into a central region (42) of the gap (30) adjoining the edge regions (38, 40).
7. Coil unit (10) with an annealed, cold-rolled or hot-rolled steel strip (14), in particular hot-rolled, subsequently pickled and then annealed steel strip (14) or pickled, subsequently cold-rolled and then annealed steel strip (14), which is wound into a coil (12) having several turns with corresponding steel strip layers (28) and a gap (30) formed between the adjacent steel strip layers (28), wherein the steel strip (14) has two longitudinal edges (20, 22), each forming an end face (24, 26) of this coil (12), at which the gap (30) has an opening towards the surroundings of the coil (12), and with a fluid barrier (32) on each of the end faces (24, 26) of the coil (12) made of a material inserted into a respective edge region (38, 40) of the gap (30) Corrosion protection liquid (34) which prevents or at least reduces the penetration of moisture from the ambient atmosphere into a central region (42) of the gap (30) adjoining the edge regions (38, 40), wherein the fluid barriers (32) are formed by a corrosion protection liquid (34), in particular a corrosion protection oil, which has penetrated into a respective edge region of the gap (30).
8. Coil unit (10) according to claim 7, characterized in that the corrosion protection liquid (34) on each end face (24, 26) has an average penetration depth into the gap (30) which is between 2 and 300 mm, preferably between 3 and 200 mm, particularly preferably between 5 and 200 mm.
9. Coil unit (10) according to claim 7 or 8, characterized in that - starting from the corresponding end face (24, 26) - within an edge section of 10 mm in the gap (30) an average corrosion protection liquid coating of at least 0.3 g / m 2 , in particular of at least 0.5 g / m 2 , while the corrosion protection liquid content in a central section of the gap (30) in the middle between the two end faces (24, 26) is preferably below 0.1 g / m 2 lies.
10. Coil unit (10) according to one of claims 7 to 9, characterized in that the steel strip (14) has the following composition in weight %: C: 0.04 to 0.80, in particular 0.1 to 0.60, Mn: 0.5 to 3.0, in particular 0.8 to 2.5, Si: 0.05 to 2.0, in particular 0.1 to 0.7, Al: 0.01 to 2.0, in particular 0.01 to 0.4, P < 0.1, S < 0.05, N < 0.02, and optionally one or more of the following elements: Cr: 0.1 to 1.5, especially 0.3 to 1.2 B: 0.0001 to 0.008, Ti: 0.01 to 0.1, V: 0.01 to 0.3, Nb: 0.01 to 0.1, especially 0.02 to 0.06, Mo: 0.05 to 0.5, especially 0.1 to 0.25, Ni: 0.15 to 0.5 and Cu: 0.15 to 0.5, Rest iron and unavoidable steel-associated impurities.
11. Coil unit (10) according to one of claims 7 to 10, characterized in that the annealed, cold-rolled, or hot-rolled steel strip (14) is a batch-annealed, cold-rolled, or hot-rolled steel strip (14).
12. Coil unit (10) according to one of claims 7 to 11, characterized in that the steel strip (14) has pickled grain boundaries (44) on its surface.