EP1786937B1 - Killed, unalloyed or microalloyed rolled steel of the bake hardening type and method for producing the same - Google Patents

Description

The invention relates to a method for producing a calmed, unalloyed or microalloyed rolled steel, which is cold rolled after a hot rolling with subsequent coiling and then annealed recrystallizing and then shows a bake hardening effect, wherein to achieve the bake hardening effect free, dissolved nitrogen is used in a proportion of> 0.001 wt.%.

The invention further relates to a tempered, unalloyed or microalloyed cold rolled rolled steel having a bake hardening effect which has a content of free dissolved nitrogen> 0.001% by weight.

According to EN 10020, unalloyed steels are those types of steel whose composition is free of alloying elements or whose proportion of alloying elements does not exceed predetermined limit values.

For the purposes of this definition, microalloyed steels are unalloyed steels which contain low levels of alloying elements (below limit values).

The production of such steel grades as rolled steels takes place practically only in a continuous casting process, in particular continuous casting. A prerequisite for the production of a cast steel is the soothing of the steel, so its deoxidation, to prevent bubbling in the liquid steel by the formation of gaseous CO or CO ₂ due to free oxygen. This settling of the steel can be carried out with suitable alloying elements that have a high affinity for oxygen and thus set the free oxygen. As such For stabilizing the steel, aluminum has prevailed for numerous reasons. The settling of the steel requires that the sedative be added in a stoichiometric excess so that the sedative alloying element remains in excess in the steel while the corresponding bonded oxide (alumina in the case of aluminum) is removed with the slag from the molten steel ,

The excess amount of aluminum remaining in the steel has been found to be advantageous, because aluminum is a fine grain former, which favors the formability of the formed rolled steel. All standards and draft standards for common rolled steels therefore provide for a minimum content of aluminum in the steel of 0.01 for titanium addition, otherwise 0.015 or even 0.02 wt%.

Well deformable rolled steels should have the property of ensuring high strength despite their good ductility. This applies, for example, to steel sheets used in the automotive industry. It has been found that certain steel grades after cold working significantly increase their yield strength values when subjected to a heat treatment such as, for example, bake coating. At temperatures of more than 120 ° C or 170 ° C, the steel is "aged", significantly increasing the yield strength of the steel. This effect is based on the action of free, dissolved carbon, which migrates due to the effect of heat in the dislocations formed in the cold deformation in the crystal structure and blocks them at a subsequent strain. It is therefore known that a bake hardening effect at a normal C content (0.02-0.20 wt.%) Can occur only when a cold-rolled steel is recrystallized in a continuous process because of its use in the process high cooling rate, a connection of the free, dissolved carbon with iron to form cementite is prevented. When performing the recrystallizing annealing in a crucible annealing furnace in a tight bond arise so low cooling rates mean that no free carbon remains in the microstructure so that the resulting steel does not age and has no bake hardening effect.

In the former non-continuous ingot casting process, inefficient steel could be used. Therefore, it is known that aging basically occurs with free nitrogen in the microstructure. In this case, further disadvantageous properties of the steel occur. Since the aluminum used in the continuous casting process for calming is highly affine to nitrogen and sets the free nitrogen immediately, in practice this effect no longer plays any role in today's tempered rolled steels.

Accordingly, rolled steels of the type mentioned above, which have a bake-hardening effect, basically only with a normal C content (C ≥ 0.01 wt.%) Can be produced in a continuous annealing. An alternative is to reduce the C content in the vacuum process well below 0.01 wt.%. In this case, it is possible to obtain free carbon in the forming crystal structure even at low cooling rates after recrystallizing annealing because the diffusion paths of the free carbon to free iron atoms have become so large due to the low carbon concentration that a significant portion of the free carbon atoms remains unbonded in the crystal structure and can cause the bake hardening effect.

It is therefore not possible to produce steels without special manufacturing processes, in particular easily convertible, soft, bell-annealed grades with a bake-hardening effect. The same applies to hot strip steels, which also have no free C content and therefore can not form a bake hardening effect based thereon.

US 2003/0015263 A1 discloses a method and a rolled steel of the type mentioned. A minimum content of aluminum of 0.001% by weight is mentioned at the same time However, the aluminum is used as deoxidizer for the steel. Since another deoxidizer is not indicated, aluminum concentrations well above 0.005 weight percent are required if complete soaking of the steel is to take place. For vacuum-decarburized steels, as indicated in Tables 1 and 6 of this document, the lowest aluminum concentration is 0.009% by weight. The steel has a C content of 0.0020 wt.% And lower. For non-vacuum decarburized steels, the aluminum content is usually higher. In an example of Table 15, there is an aluminum content of 0.004 wt.%, Where the silicon content is given as 0.01 wt.%, So that no completely soaked steel can be present. Incidentally, the steels exemplified predominantly contain additional alloying elements, in particular rare earth alloying elements or molybdenum, titanium, boron, copper, nickel, chromium, vanadium, etc. The relevant embodiments for steels which according to Table 15 are suitable for a good BH Value, assume a special recrystallizing annealing, which consists of a combination of a bell annealing and a continuous annealing and therefore requires a high investment costs. The method according to the invention is carried out either with a bell annealing or with a continuous annealing.

The invention has for its object to enable the production of a calmed, unalloyed or microalloyed cold-rolled rolled steel with an improved bake-hardening effect, wherein the initial enabling a bake-hardening effect for certain steel grades should be included.

To solve this problem, the method of the type mentioned is characterized in that a steel of the composition (in wt.%) According to the invention
C 0.01-0.20
Si> 0.15
Mn <1.40
P 0.020-0.08
S <0.025
Al <0.005
optional Nb 0.01 - 0.20,
Remaining iron and unavoidable impurities
is used.

To solve the above problem, a rolled steel of the type mentioned is further characterized by the composition (in wt.%)
C 0.01-0.20
Si> 0.15
Mn <1.40
P 0.02-0.08
S <0.025
Al <0.005
optional Nb 0.01 - 0.20,
Remaining iron and unavoidable impurities
is used.

The inventive design of the free-dissolved nitrogen bake-hardening effect on a tempered rolled steel assumes fundamental changes in the previous manufacturing practice of such calmed, tempered steels. The tempering of the rolled steel must no longer take place with an excess amount of aluminum, because the excess amount of aluminum prevents the retention of a content of free nitrogen in the steel because of the high nitrogen affinity of the aluminum. Consequently, the steel must be tempered either by a means other than aluminum, or the steel must be made with a "pre-soak" with aluminum, with the addition of aluminum being somewhat substoichiometric, so that a residual sedimentation with another alloying element, preferably silicon, is made. Alternatively, pre-settling can also be achieved with a vacuum treatment. Carrying out complete reassurance with Silicon is possible, but not preferred because of the required high levels of addition.

The steel produced according to the invention is thus preferably free of aluminum, i. the aluminum content is less than 0.01% by weight, preferably less than 0.005% by weight. Should the aluminum content be higher, the proportion of free nitrogen bound thereby must be taken into account, so that the molten steel must be produced with a significantly higher proportion of free, dissolved nitrogen in order to ensure the proportion of free, dissolved nitrogen provided according to the invention.

It has been found that a certain bake hardening effect due to the free, dissolved nitrogen can be achieved by the inventive measure, which requires a completely new type of steel production for a cast steel. However, this effect is in many cases not sufficient for practical applications. It has been found that the addition of at least one further alloying element can decisively increase the based on the free nitrogen content bake-hardening effect. This can be attributed to the fact that the appropriate further alloying element promotes the diffusion of the free nitrogen (to the dislocations). A particularly suitable alloying element for this purpose is phosphorus with a proportion of ≥ 0.020% by weight, in particular ≥ 0.025% by weight, has been found. Another alloying element that significantly enhances the bake-hardening effect is niobium, which is preferably included in addition to the one alloying element (preferably phosphorus) in an amount ≥ 0.01 wt%.

Since the (residual) calming of the rolled steel according to the invention takes place with silicon, the rolled steel according to the invention contains a proportion of ≥ 0.15% by weight of silicon, preferably ≥ 0.20% by weight of silicon.

The present invention allows for the first time without any special effort the production of ductile-glow-annealed cold tapes with a bake-hardening effect, when the steel has a normal C content (between 0.01 or 0.02 and 0.20 wt.%) ,

The present invention also makes it possible to produce those steels which are conventionally produced with a free carbon based bake hardening effect, now with a significantly improved bake hardening effect, which according to the invention has the (additional) effect of free, dissolved nitrogen is based in the crystal structure. Accordingly, it is readily possible to apply the method according to the invention also in pass-annealed rolled steels, so as to significantly enhance the already known bake hardening effect by the inventive measure.

Preferred chemical compositions of the steels according to the invention result from the limit values indicated below: C 0.01-0.20% by weight Si 0.15-0.70% by weight Mn 0.15-1.40% by weight P 0.020-0.080% by weight S 0.003-0.025% by weight al Max. 0.005% by weight Nfrei minute % 0,0010Gew. Nb Max. 0.09% by weight

The steels of the present invention have the remarkable property that the free nitrogen-based bake-hardening effect occurs only at a heat treatment after a previous deformation (BH2).

Thus, aging at room temperature or without prior deformation does not occur as much as with carbon aging. An undesirable aging process with not too long storage of the steel is therefore not to be feared.

Furthermore, in the case of the steel according to the invention, the particle size can be controlled by the proportion of the further alloying element, in particular by phosphorus. Compared to aluminum-killed steels can be an equally fine or even produce a finer grain in the steel according to the invention.

The total content of nitrogen in the steel according to the invention is ≦ 0.0090% by weight, preferably ≦ 0.075% by weight, in particular ≦ 0.0045% by weight. The nitrogen content present in the production of the melt (0.0040 ≦ N _total ≦ 0.0060% by weight) is preferably used, with the exception of addition of N.

In the following, the invention will be explained in more detail with reference to exemplary embodiments. Cold-rolled steels were produced with a recrystallizing annealing in the fixed band in the hood furnace on the one hand and in a continuous annealing annulus on the other hand. The chemical compositions used are shown in Table 1 below, wherein the composition of the number 1-5 are comparative steels. Ser. No. annealing figure C Mn S N Si P al Nb 1 H 1 0.028 0.14 0,003 0.0090 0.70 0.005 0,004 - 2 H 2 0,039 0.25 0,003 0.0065 0.33 0.005 0,004 - D 8th 3 H 3 0,039 0.25 0,003 0.0072 0.34 0.005 0,004 0.028 D 9 4 H 4 0.059 0.23 0.0065 0.60 0,004 0,004 - D 10 5 H 5 0.059 0.23 0,003 0.0075 0.58 0,004 0,003 0.024 D 11 6 H 6 0.024 0.21 0,002 0.0082 0.28 0.054 0.005 - 7 H 7 0.026 0.21 0,002 0.0084 0.56 0.054 0,004 - H = annealing in the fixed coil in the hood furnace
D = annealing in the continuous annealing

An overview of the resulting technological properties is in the FIGS. 1 to 11 (as indicated in Table 1), each for a coiling temperature after hot rolling at 500 ° C (left column) and 700 ° C (right column respectively).

FIG. 1 relates to a comparison steel with a normal C content of 0.028 wt.% And negligible proportions of sulfur, phosphorus and aluminum. The steel has been (end-) calmed with silicon and has a content of free, dissolved nitrogen of 0.0090 wt.% On. Due to its yield strength of almost 300 N / mm ^{2, it is} already a high-strength steel and has a distinct, if not high, BH 2 effect (25 to 30 N / mm ² ) at both reel temperatures after the annealing annealing.

FIG. 2 shows the results for a steel that is not fundamentally varied in composition. The comparison with FIG. 3 can be seen that the addition of niobium (0.028 wt.%) Here, to a significantly increased BH2 effect, especially for the low coil temperature of 500 ° C leads. The comparison with the FIGS. 8 and 9 , which illustrate the results with the same composition after a continuous annealing, shows that the increase of BH2 values by the addition of niobium is achieved only in the bell annealing, but not in the continuous annealing. In continuous annealing, where part of the BH2 effect is caused by free carbon, the addition of niobium is detrimental to the BH2 effect, since niobium sets some of the free carbon to carbide, resulting in an increase in Rp0 , 2 and Rm and in the reduction of the elongation values Ag and A80 precipitates.

The same statement can be the FIGS. 4 and 5 for the bell annealing on the one hand and 10 and 11 for the continuous annealing on the other hand. The FIGS. 4 and 5 further illustrate that the influence of niobium increasing the BH2 value decreases as the silicon content increases relatively. In the composition in the FIGS. 4 and 5 the silicon content is almost twice as high as in comparison figures 2 and 3.

FIG. 6 shows that a significant increase in the BH2 value can be achieved by adding phosphorus according to the invention (in this case 0.054% by weight).

FIG. 7 illustrates that after the addition of phosphorus, an increase in the silicon content has no positive effect on the BH2 value. It should be noted only an increase in the strength values with a simultaneous decrease in the parameters that are essential for ductility, namely Ag, A80 and n value.

While the results presented so far were based on laboratory experiments, an operating melt has also been prepared under industrial production conditions with the following inventive chemical composition in% by weight. C Mn S N Si P al N-free 0,061 0.26 0,008 0.0027 0.28 0,051 0,003 0.0012

From the melt, a bell annealed elo-galvanized steel has been produced. The achieved mechanical-technological properties of the steel strip are in the FIGS. 12 to 15 applied.

The FIGS. 16 to 18 show changes in the mechanical-technological properties of the steel according to the FIGS. 12 to 15 by a heat treatment at 250 ° C for three minutes, as typically occurs in a plastic tape coating.

The FIGS. 19 to 22 illustrate the measurements for hot-dip galvanized steel strip made from the same melt and the FIGS. 23 to 25 the changes in the measured values by a heat treatment at 250 ° C for three minutes, as it typically occurs for a plastic tape coating.

The steel strip produced in the above composition was hot rolled in a conventional manner and then cooled by cooling to a coiler temperature of 500 ° C and 700 ° C, respectively. After cooling in the coiler cold rolling steps are carried out in a conventional manner, by which the steel sheet has been subjected to cold deformation of well over 50%. The wound cold strip is in the coil in a hood furnace at a Temperature below 720 ° C (A1) recrystallizing annealed and cooled in the hood furnace under quasi-isothermal conditions.

In the Figures 12 ff., measured values at the beginning of the tape (A), in the middle of the tape (M) and at the tape end (E) are shown, wherein the left column represents a sample taken in the longitudinal direction of the tape and the right column each represents a transversely taken and tested sample ,

It can be seen that high strength values (lower yield strength ReL) ≥ 260 N / mm ^{2 are achieved} even with a high reel temperature. The tensile strength (Rm) is in the range of 400 N / mm ² .

The parameters A80, Ag, n-value and r-value, which are important for the forming properties, show high values which characterize the good ductility of the steel strip. The steel has a BH2 value of about 40 N / mm ² at the low reel temperature and well above 40 N / mm ² at the higher reel temperature, despite the bell annealing, as in FIG. 14 is recognizable. In contrast, the BH0 values, at least for the low reel temperature, tend to be negligible.

It is therefore confirmed that by the present invention, a BH2 effect can be achieved without additional effort, which is based on the existence of free, dissolved nitrogen.

Grain size is above ASTM 9 for the high reel temperature while well above ASTM 10 for the lower reel temperature. It can be seen that a virtually perfectly round grain is produced, since in the longitudinal and transverse direction completely identical grain sizes are measured.

The FIGS. 16 to 18 illustrate the changes in the specified parameters after performing a heat treatment, as in a Coating is common, so a heat treatment for about three minutes at about 250 ° C.

It turns out that the BH2 effect is "consumed", so that the values for the upper and lower yield strength increase accordingly. It is surprising that according to Figures 17 and 18 at most slight changes in the parameters essential for the transformation take place. The changes in the elongation values are on the order of a maximum of 3%, while the changes of the n values and the r values are of the order of less than 10%, the r value even regularly improving.

The FIGS. 19 to 22 clarify the mechanical-technological parameters for a re-crystallizing annealed after the hot rolling, reeling and cold rolling in a continuous annealing steel strip, which has been hot-dip galvanized. As is known, a steel strip treated in this way has higher strength values and can be produced with a good BH 2 value which, depending on the strength, is usually of the order of 40 N / mm ² . In contrast, the inventively achieved BH2 value is according to FIG. 21 much higher and is 80 to 90 N / mm ² . Such a BH2 value has hitherto not been achievable with conventional production methods. The grain size is, depending on the reel temperature at ASTM 8.5 to 9.5, ie in the range of a fine-grained steel.

The experiment for "consuming" the BH effect as described for the bell annealed steel performs according to the FIGS. 23 to 25 to a substantial increase in strength values without appreciably affecting the forming values, with the n-value that is essential for forming tending to be even better. Also noteworthy are the very good forming parameters, which manifest themselves in the high values for the uniform elongation Ag, for the elongation A80, the n value and the surprisingly very high r values in the transverse direction (1.5 to> 1.6). Accordingly, A steel is available which provides high strength values, but with these high strength values can be formed like a much softer steel.

The low level of 0.0012 wt.% Free nitrogen indicated in the composition described is believed to be significant to the observed strain hardening prevention. Thus, a free N content which is between 0.0010 and 0.0020% by weight is preferred.

In summary, it can be stated that the invention was able to produce a bell-annealed steel strip which, given relatively high strength values, has very good forming values and, at the same time, a clear BH 2 effect. The result is a fine-grained structure with ASTM grain sizes 9.25 to 10.75. The fine grain of unalloyed steel is comparable to the fine graininess otherwise achieved with a microalloyed steel.

The result is a homogeneous structure whose grain size in the longitudinal and transverse directions is the same size.

For a hot-dip galvanized, continuously annealed steel high strength values are achieved with very good forming values. Extremely high BH2 values are achieved.

In both cases (crown annealing, continuous annealing), after a simulated coil coating (heat treatment 250 ° C for three minutes), increases in strength are achieved with only slightly altered forming values.

In summary, it can be stated that the steels according to the invention can be produced with a bake-hardening effect, which is based on the existence of free, dissolved nitrogen in the crystal structure. This effect is increased by a control of the diffusion of the free nitrogen, namely by the addition according to the invention of phosphorus and possibly also of niobium. By the addition of phosphorus can influence the grain size of the resulting steel. With the addition of niobium, an adjustment of the strength can be effected.

The steels according to the invention have consistently high elongation, r and n values, ie good deformation properties.

The steels of the invention show good BH2 values, but very low BH0 values. The bake-hardening effect therefore utilizes usable only after a previous deformation. The steels are almost free of aging at room temperature, so that there is only a slight amount of strain aging due to the free nitrogen.

The measured BH2 effect is enhanced by the addition of P according to the invention, since phosphorus activates nitrogen diffusion. The BH2 values are obtained both at a heat treatment of 120 ° C and at 170 ° C.

The fact that the steel according to the invention, whose bake-hardening effect is due to the presence of free nitrogen hardly ages at room temperature, although the free nitrogen is not set, is surprising. One explanation could be a blockage of nitrogen diffusion through the silicon. This blocking can be eliminated or mitigated by the temperature treatment after deformation and by the inventive addition of phosphorus and possibly niobium.

The the Figures 12 . 13 . 15 to 20 and 22 to 25 underlying measurements are given in Tables I to IV below. Table I <b> Cold-rolled strip 01746 </ b> bell-annealed / galvanized; T Ha = 500 ° C * = Delivery condition + 250 ° C / 3min sample Location test direction ReH N / mm ² ReL N / mm ² Ru N / mm ² Agl % A80 % n-value r-value ReH * N / mm ² ReL * N / mm ² Rm * N / mm ² Agl * % A80 * % n * r * A along 287 282 399 19.9 37.1 0.193 1.20 364 323 405 19.0 34.6 0,175 1.14 crosswise 323 301 405 19.8 36.5 0.198 1.49 380 341 408 19.2 34.9 0,178 1.58 M along 279 278 404 19.7 34.9 0.193 1.24 368 328 410 18.4 33.4 0,175 1.19 crosswise 301 294 408 19.9 34.7 0.192 1.49 388 347 411 18.3 35.0 0.174 1.65 e along 295 288 406 19.9 34.1 0.196 1.12 347 325 410 18.8 31.7 0,180 1.10 crosswise 326 306 406 19.9 35.3 0.195 1.52 383 340 412 18.5 34.9 0,178 1.78 * = Delivery rate + 250 ° C / 3min sample Location test direction ReH N / mm ² ReL N / mm ² Rm N / mm ² Agl % A80 % n-value r-value ReH * N / mm ² ReL * N / mm ² Rm * N / mm ² Agl * % A80 * % n * r * A along 270 268 389 20.0 36.1 0,139 1.15 356 317 395 17.7 33.3 0,170 1.15 crosswise 299 284 392 19.2 34.5 0.183 1.63 380 336 401 18.1 33.7 0.171 1.75 M along 265 265 384 17.8 32.8 0.172 1.22 359 319 394 17.1 31.1 0.166 1.21 crosswise 277 277 390 17.5 31.0 0.166 1.69 366 336 400 16.5 30.9 0,160 1.75 e along 269 267 387 19.1 34.8 0.183 1.18 353 317 395 18.0 33.9 0.172 1.16 crosswise 282 279 389 18.2 34.5 0,170 1.63 384 338 398 16.6 33.6 0,159 1.79 sample Location test direction ReH N / mm ² ReL N / mm ² Rm N / mm ² Agl % A80 % n-value r-value ReH * N / mm ² ReL * N / mm ² Rm * N / mm ² Agl * % A80 *% n * r * A along 355 350 449 15.7 28.6 0,149 1.20 455 411 458 15.8 27.9 0,151 1.29 crosswise 366 356 454 15.3 28.8 0.143 1.69 474 415 460 15.4 26.0 0.148 1.80 e along 343 336 447 16.7 30.1 0.154 1.23 446 400 454 16.4 27.9 0.156 1.28 crosswise 357 345 450 15.6 27.1 0,149 1.62 461 409 458 15.9 28.3 0.153 1.79 E = coil center of the undivided band
* = Delivery condition + 250 ° C / 3min sample Location test direction ReH N / mm ² ReL N / mm ² Rm N / mm ² Agl % A80 % n-value r-value ReH * N / mm ² ReL * N / mm ² Rm * N / mm ² Agl * % A80 * % n * r ^* A along 304 296 419 19.0 34.0 0.184 1.14 380 345 428 18.8 33.7 0.184 1.18 crosswise 341 316 426 18.3 30.6 0,179 1.66 400 348 429 18.1 29.9 0,181 1.87 M along 311 304 430 16.2 30.5 0,151 1.25 416 371 444 16.0 28.8 0.154 1.24 crosswise 318 307 435 15.3 28.2 0,147 1.75 428 385 448 15.4 28.2 0,150 1.71 e along 315 312 434 16.5 28.8 0.154 1.16 418 378 448 15.9 28.7 0,155 1.19 crosswise 321 316 439 15.8 30.1 0,149 1.57 436 394 452 15.5 28.2 0,150 1.79 E = coil center of the undivided band
* = Delivery condition + 230 ° C / 5min

Claims (18)

1. Method for producing a killed, unalloyed or microalloyed rolled steel, which, after hot rolling with subsequent coiling, is cold-rolled and subsequently subjected to recrystallization annealing, and then exhibits a bake hardening effect, wherein the bake hardening effect is achieved by using free, dissolved nitrogen in a proportion of > 0.001% by weight, characterized in that use is made of a steel of the composition (in % by weight)
   C 0.01 - 0.20,
   Si ≥ 0.15,
   Mn ≤ 1.40,
   P 0.020 - 0.08,
   S ≤ 0.025,
   Al ≤ 0.005,
   optionally Nb 0.01 - 0.20,
   remainder iron and unavoidable impurities.
2. Method according to Claim 1, characterized in that the recrystallization annealing is performed as continuous annealing or as batch annealing while firmly coiled.
3. Method according to Claim 1 or 2, characterized in that the proportion of C is between 0.02 and 0.20% by weight.
4. Method according to one of Claims 1 to 3, characterized in that the proportion of silicon is between 0.20 and 0.70% by weight.
5. Method according to one of Claims 1 to 4, characterized in that the proportion of phosphorus is between 0.020 and 0.080% by weight.
6. Method according to one of Claims 1 to 5, characterized in that an additional bake hardening effect is established with free carbon.
7. Method according to one of Claims 1 to 6, characterized in that the potential bake hardening effect is spent in the course of a heat treatment, taking place before the deformation, at between 150 and 300°C for several minutes to increase the strength properties.
8. Killed, unalloyed or microalloyed cold-rolled steel with a bake hardening effect and having a content of free, dissolved nitrogen > 0.001% by weight, characterized by the composition (in % by weight)
   C 0.01 - 0.20,
   Si > 0.15,
   Mn < 1.40,
   P 0.02 - 0.08,
   S < 0.025,
   Al < 0.005,
   optionally Nb 0.01 - 0.20,
   remainder iron and unavoidable impurities.
9. Rolled steel according to Claim 8, having a C content of 0.02 - 0.20% by weight.
10. Rolled steel according to Claim 8 or 9, characterized by a proportion of silicon of 0.20 - 0.70% by weight.
11. Rolled steel according to one of Claims 8 to 10, characterized by a proportion of phosphorus of between 0.020 and 0.080% by weight.
12. Rolled steel according to one of Claims 8 to 11, characterized by BH₂ values ≥ 75 N/mm² with Re values ≥ 290 N/mm² after hot-dip galvanizing.
13. Rolled steel according to one of Claims 8 to 12, characterized by Re values ≥ 330 N/mm² with n values ≥ 0.15 and a reduced BH₂ effect.
14. Rolled steel according to Claim 12 or 13, characterized by a grain size ASTM ≥ 8.5.
15. Rolled steel according to one of Claims 8 to 12, characterized by a lower yield strength ReL ≥ 260 N/mm² and a BH₂ value ≥ 40 N/mm² after recrystallization batch annealing.
16. Rolled steel according to Claim 15, characterized by n values ≥ 0.17 and grain sizes ASTM ≥ 9.
17. Rolled steel according to Claim 16, characterized by grain sizes ASTM ≥ 10.
18. Rolled steel according to one of Claims 8 to 17, characterized by a sheet thickness of ≥ 0.05 mm.

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