DE10117118C1 - Production of fine sheet metal used in the production of cans comprises casting a steel to slabs or thin slabs, cooling, re-heating, hot rolling in several passes - Google Patents

Abstract

Production of fine sheet metal having a cold strip final thickness of not more than 0.3 mm comprises casting a steel to slabs or thin slabs; cooling; re-heating to 1080-1150 deg C for a maximum of 8 hours; hot rolling in several passes in a rolling mill train at a temperature lying above the Ar3 temperature to form a hot strip; coiling at 590-660 deg C; cold rolling; and annealing in a continuous furnace. The steel contains (in wt.%) 0.0015-0.0080 C, 0.15-0.25 Mn, <= 0.02 P, 0.005-0.03 S, <= 0.02 Si, 0.0080-0.06 Al, 0.0010-0.020 N, <= 0.05 Cr, <= 0.5 Ni, <= 0.05 Cu, <= 0.02 Sn, <= 0.01 Mo, <= 0.0005 Ti, <= 0.0005 Nb, <= 0.0020 V, <= 0.007 B, <= 0.05 Co, <= 0.03 Se, Te or S, and a balance of Fe. Preferred Features: The cold strip final thickness is 0.16-0.25 mm. Annealing is carried out in a carburizing atmosphere.

Description

The invention relates to a method for producing good formable sheet metal with a cold strip final thickness of at most 0.3 mm. Such also "tinplate" called thin sheets are typically as Packaging, for the production of cans or other Thermoformed products used. Especially with the DWI ("Drawing an Wall-Ironing") - can production becomes high Requirements for the homogeneity of the material and its Properties provided. These demands are conditional on a microstructure with a formation of the grain as uniform as possible. larger Grain stretching, d. H. Grains where the ratio Length of the grain to the width of which is more than 1.4, meet the requirements of a well processable thin sheet requirements.

A method for producing sheet metal intended for the manufacture of cans is known from EP 0 896 069 A1. According to this known method, a steel is processed which has a particularly low Al content of at most 0.001%. The steel composed in this way is hot-rolled at a final temperature above Ar ₃ and then coiled at a temperature which is below 620 ° C., preferably in the range from 530 ° C. to 570 ° C. As a reason for the low Al content, EP 0 896 069 A1 states that a structure is obtained only if this upper limit is observed, in which the grains are uniformly formed to an extent sufficient for the required deformability.

For the same reasons, the steel known from BP 0 917 594 B1 contains a maximum Al content of 0.005% for the production of cans. In addition, this known steel has 0.0005 to 0.005% boron and 0.14 to 0.25% by weight Mn as necessary components in order to achieve the desired properties. The steel thus assembled is hot rolled at an end temperature above Ar ₃ - 10 ° C and coiled at a coiling temperature below 700 ° C. Hot rolling final temperatures in the range of 900 ° C ± 30 ° C combined with reel temperatures in the range of 670 ° C ± 20 ° C are recommended as particularly preferred.

When observing the in EP 0 896 069 A1 and EP 0 917 594 B1 prescribed limitation of the Al Content will get a structure that is good Behavior of the steel during deep drawing ensures. moreover the low Al contents ensure good homogeneity of the Expect very thin sheets lengthways and crossways so that the manufacture of cans with such a material can be carried out safely. The one with the generation like that Steels with low Al contents associated effort is significant, however. In particular, aluminum stands as inexpensive means of deoxidizing the steel is not to disposal. The low Al content also makes it high Reheating temperatures and also high Reel temperatures required.

Another process for the production of cans, in which, however, a steel with Al contents in the range from 0.02 to 0.05% is processed, is known from BP 0 659 890 B1. The Al content is matched to the nitrogen content of the steel in such a way that the nitrogen is essentially completely bonded to AlN. At the same time, this known steel has Mn contents of 0.5 to 3% in order to achieve sufficient strength even with the extremely low carbon contents of steels of the type in question here. Finally, EP 0 659 890 B1 recommends adding to the steel, taking into account an upper limit of 0.04% by weight, levels of niobium matched to the carbon content, in order to improve the aging behavior of the processed steel. The known steel composed in this way is hot-rolled at final temperatures above Ar ₃ , specifically cooled and then coiled at temperatures in the range from 400 ° C. to 550 ° C. After cold rolling, the cold strip obtained is annealed in a continuous annealing furnace at temperatures which are above the recrystallization temperature, preferably above 870 ° C. The high levels of Mn and the optional additional levels of Nb lead to increased strengths, but at the same time cause unfavorable properties with regard to the typical uses of thin sheets of the type in question here. High annealing temperatures must also be set during recrystallization annealing. Otherwise, according to the method known from EP 0 659 890 B1, the required softening of the thin sheet cannot be achieved.

The object of the invention is a method specify which is the low cost manufacture of especially for packaging purposes and for the Processing into cans suitable thin sheets with good Deformation properties enabled. Likewise one for  this use particularly suitable steel composition be created.

On the basis of the prior art explained above, this object is achieved by a process for the production of highly deformable fine sheet whose final thickness is at most 0.3 mm, in particular 0.16 mm to 0.25 mm, in which a steel which ( in mass%) 0.0015-0.0080% C, 0.15-0.25% Mn, ≦ 0.02% P, 0.005-0.03% S, ≦ 0.02% Si, 0.0080 -0.06% Al, 0.0010-0.020% N, ≦ 0.05% Cr, ≦ 0.5% Ni, ≦ 0.05% Cu, ≦ 0.02% Sn, ≦ 0.01% Mo, ≦ 0.0005% Ti, ≦ 0.0005% Nb, ≦ 0.0020% V, ≦ 0.007% B, ≦ 0.05% Co, optionally Se and / or Te, the sum of the Se, Te and S is not more than 0.03%, and the balance contains iron and unavoidable impurities, is poured into slabs or thin slabs, in which the slabs or thin slabs are cooled, in which the slabs or thin slabs reach a temperature in the range of 1080 ° C up to 1150 ° C with a maximum holding time of eight hours, during which the slab or thin slab men in several passes in a hot rolling mill at a final rolling temperature above the Ar ₃ temperature to a hot strip, in which the hot strip is coiled at a coiling temperature in the range from 590 ° C to 660 ° C, at which point the hot strip is subsequently rolled is cold rolled into cold strip and in which the cold strip is subjected to annealing in a continuous furnace.

Surprisingly, it has been shown that at The procedure according to the invention is to produce thin sheets leave a homogeneous even at higher Al contents Microstructure with essentially equiaxial training  Own grains. In this way, aluminum can be used inexpensive deoxidation of the steel can be used. Because the thin sheets produced according to the invention are despite the presence of higher Al contents, that they are evenly distributed over their width and length have good properties that lead to a particular good formability, low prickliness, one good aging behavior and an uncritical one Lead recrystallization behavior. The focus of the vote according to the invention Process steps and the alloy used is available the greatest possible harmlessness of steel after the slab has been heated, the sulfur present is dissolved and titanium during hot rolling. Therefore, it will Manufacturing process according to the invention performed so that the im Hot strip excretion state almost without Transfer the change to the fine sheet obtained becomes.

In this way it is achieved that Production according to the invention only in negligible Amount of very fine precipitates, especially copper sulfides, have a diameter less than Own 50 nm. As a result, the microstructure exists Sheets produced according to the invention from a largely undrawn ferritic structure, which by a Ratio of the longitudinal extent to the width of the grain of is labeled less than 1.35. The middle one Grain diameter is typically in the range of 7 to 14 µm (determined by image analysis), preferably 8 to 10 µm, with a stronger than conventional generation pronounced texture (higher density of gamma fibers). It has been found that in the invention produced a pile density of {111} <112 <- Orientation of at least 14 is present.  

Because of its nature is according to the invention Finished sheet, especially for the coating suitable with a tin pad. This is especially true when the measurable in the recrystallized ultrafine sheet Grain sizes between 7 and 10 microns.

Significant influence on the nature of the Thin sheet produced according to the invention has the in one relatively low temperature range Reheating if necessary by continuous, in Casting of slabs produced or Thin slabs. This reheating is in one conventional, three heating zones (preheating zone, Heating zone, equalization zone) in three Stages so that a particularly homogeneous, more precisely defined in terms of sulfide formation Excretion state is reached. The one there observed reheating temperatures were in the Range from 1080 ° C to 1150 ° C.

The aim of this measure is that the sulfur in the cooled hot strip almost completely in for the Ti Setting sufficient dispersion is eliminated is present. The size of the sulfides excreted should not less than 50 nm in diameter and not less than 2 µm exceed. Coarser sulfides are said to be predominantly available. Are preferred by means of Microsensor examination of detectable sulfides with medium Diameters from 0.5 to 1.2 µm. By Transmission electron microscopic examinations finest sulfides can be determined using pull-out prints with diameters smaller than 50 nm are undesirable. This applies in particular to those larger than 50 nm Shares of fine precipitates containing copper because a significant reduction in quality  would produce thin sheets according to the invention. There an indicator in the hot strip of finely separated sulfides for further sulfur still present, the the disinfestation would interfere with his excretion, are such excretion states according to the invention avoid.

By limiting the holding time in the oven to eight Hours of sulfur is prevented completely dissolve and as a result Precipitation can result.

So that the sulfides do not lead to a delay in recrystallization as precipitates in the course of the final annealing in the continuous furnace, hot rolling is carried out according to the invention in such a way that the hot rolling end temperature is just above the Ar ₃ temperature.

The reel temperature is also adjusted so that a the sulfur is optimally excreted. At a it would be below 590 ° C no longer excrete sulfur. Thereby, that the reel temperature simultaneously to a maximum of 660 ° C is limited, too much scaling of the Avoided hot bands, which would otherwise be a reinforced one Pickling of the tape would be required. optimized Manufacturing results can be achieved if the Reel temperature is in the range of 600 ° C to 630 ° C. The combination of the invention has been found low selected reheating temperature with a also relatively low reel temperature because the associated setting of titanium as cheap with regard to the recrystallization behavior of the steel produced according to the invention.  

With regard to the composition is special Meaning that only in steel used according to the invention minimal levels of titanium and niobium are present. Therefore, the maximum niobium content is preferred to 0.0001% and the maximum titanium content to 0.0003 Mass% limited, as far as possible Minimize the proportions of these elements in the alloy according to the invention is sought. the corresponds to the further embodiment of the invention, according to that the Nb content to less than 0.0001 mass% or even is less than 0.00005 mass%. It is have been found to have higher levels Microelement traces to a significant deterioration the softening behavior generated according to the invention Guide very thin sheets. They also have higher ones Trace levels of titanium and niobium have a negative influence on the uniformity of the grain shape. It has also shown that at higher levels Titanium and niobium undesirably high grain extensions adjust, even if the sulfur in the Hot strip is largely dissolved.

Levels of boron range from 0.0004% by mass to 0.007 Mass% have a positive effect on the formation of a globular structure. This is how boron prevents sulfur goes into solution and in the hot strip line-like segregations forms, which adversely affects the deformability of the Would affect sheet metal. If the content of boron matched to the nitrogen content in such a way that the boron content is not 0.5 times the N content exceeds, it is avoided that the thin sheets in In the course of the annealing uncontrolled nitrogen from the Record the environment.  

Levels of nickel of up to 0.05 mass% cause a Extension of the austenite area down to lower Hot strip temperatures. In this way, the emergence with regard to the deformability of thin sheets unfavorable line-shaped of the type according to the invention Elimination can be avoided particularly safely. moreover levels of Ni improve the toughness of the steel processed according to the invention.

The steels according to the invention can also be up to Contain 0.002% by mass of vanadium, because with this Limits at V no negative influences of the vanadium on the properties according to the invention produced thin sheets have been found.

Because non-metallic inclusions have a negative impact on the forming behavior, the sum of the Proportions of non-metallic inclusions in the steel according to the invention not more than 0.01% by volume be. This excludes the inclusions of alumina and Spinel one. The average inclusion diameter should be 10 µm do not exceed. To be favoured Inclusion diameter of less than 5 µm.

Another improvement in the uniformity of the structure Sheets produced according to the invention can be thereby achieve that the slabs or thin slabs before the Entry into the hot rolling mill. So lets a significant improvement in the structural state achieve if, for example, by a before the enema the hot strip mill arranged a compression device Reduction in width by up to 25% is carried out.

Also in that in the last two stitches at Hot rolling achieved at least 16% degree of deformation  is, the homogeneity of the structure can be optimized become.

The thickness of the hot strip is preferably in the range of 2 mm to 4 mm, so that in the course of cold rolling on the Final thicknesses of cold rolling in the range from 86% to 95% can be achieved.

The nature of the tape produced according to the invention allows when entering the continuous annealing furnace quick and safe softening of the hard rolling Cold strip. It has been shown that a complete The softening occurs safely when the Annealing at a comparably low temperature of a maximum of 650 ° C is carried out in a continuous furnace, the exposure time is limited to one minute can.

By carbon content of at least 0.004% by mass a too coarse hot strip structure can be avoided. There but high carbon levels on the finest sheet undesirable Aging effects, it is beneficial to the Carbon content after hot strip production Reduce. According to an advantageous embodiment of the According to the invention, the annealing of the cold strip is used for this purpose in a decarburizing atmosphere is carried out. The result in the finished sheet set carbon content is preferably between 0.002 mass% and 0.006 mass%. Through the im Decarburization carried out in a continuous furnace can do this Aging behavior of the thin sheet obtained specifically can be set.

By glowing the cold strip in an embroidering Atmosphere is carried out, alternatively or  additionally checks the strength of the thin sheet influence. The nitrogen content is preferred starting from 0.001% by mass present in the hot strip 0.004 mass% of the nitrogen content in the course of Continuous annealing to 0.008% by mass up to 0.015% by mass elevated.

The dimensional accuracy and the properties of the Finest sheet produced according to the invention can finally can be further improved in that the cold strip is subjected to re-rolling after annealing which preferably achieves a degree of re-rolling of up to 20% become.

Because of its foregoing in detail explained properties can be a steel that according to the invention (in% by mass) 0.0015-0.0080% C, 0.15- 0.25% Mn, ≦ 0.02% P, 0.005-0.03% S, ≦ 0.02% Si, 0.0080-0.06% Al, 0.0010-0.020% N, ≦ 0.05% Cr, ≦ 0.5% Ni, ≦ 0.05% Cu, ≦ 0.02% Sn, ≦ 0.01% Mo, ≦ 0.0005% Ti, ≦ 0.0005% Nb, ≦ 0.0020% V, ≦ 0.007% B, ≦ 0.05% Co, optionally Se and / or Te, the sum the contents of Se, Te and S not more than 0.03% and the rest iron and unavoidable Contains impurities in an excellent way for that Production of thin sheets of the type in question use. This is especially true when the maximum Micro alloy element trace content to a minimum is reduced. For this reason, the niobium content preferably to 0.0001 mass% or even 0.00005 Mass% and the content of titanium to a maximum of 0.0003 mass % limited. Also the sum of the shares  non-metallic inclusions on the steel preferably not more than 0.01% by volume.

The invention is described below with reference to Exemplary embodiments explained in more detail.

Table 1 shows the compositions of steels according to the invention E1 to E15 and Comparative steels V1 to V21 recorded. The Oxygen levels of the relevant steels were in the Range of steels of the type in question usual impurities on this element. They cheat typically 10-20 ppm.

Table 2 shows E1-E15 and V1-V21 for each of the steels those used in processing Process parameters, the texture coverage density of the receive sheet metal and an evaluation of the Pickling of the hot strip, the purity and the Structural homogeneity of the finished sheet is specified.

The steels E1 to E15 and Comparative steels V1 to V21 are continuous poured into thin slabs in the strand and then been cooled. After cooling, the thin slabs are been reheated. For those examples in according to the invention regulated in a Temperature range from 1080 ° C to 1150 ° C Rewarming temperature is in the column "Ah." Table 2 noted a "J".

After reheating and before entering one Multi-stand hot rolling mill are in the column "St." steels marked with "J" in Table 2  Thin slabs have been subjected to compression. In the course of this compression is the width of the slabs of 1500 mm has been reduced to 1200 mm, which reduces the Width corresponds to 20%.

The thin slabs were then run into the hot strip mill, in which they were rolled in several passes continuously to the respective hot strip thickness given in Table 2: The degree of forming achieved over the two rolling stands passed at the end of the hot rolling mill was at least 16% in each case. The hot rolling end temperatures ET, which are just above the Ar ₃ temperature, are given in Table 2.

The respective hot strip leaving the hot rolling mill then at the reel temperatures given in Table 2 HT has been coiled.

The pickling properties of the the hot strip obtained is marked with "G" = "good", "M" = "acceptable" or "S" = "bad". The Assessment results are in the "Pickling" column of the Table 2 entered.

During the subsequent cold rolling the strip is on one Cold strip thickness of less than 0.3 mm, for example 0.16 mm to 0.25 mm, cold rolled.

Then the cold strip is in a continuous annealing Temperatures of up to 650 ° C and a dwell time annealed for a maximum of one minute. To those Examples in which a Decarburization has been carried out in the column "DESCAL." Table 2 the amount in "ppm" to the carbon content has been reduced. In the  the column "Entk." examples marked with "K" decarburization has not been carried out.

After the continuous annealing, the cold strips are finally has been rolled over. The degree of re-rolling achieved are given in the "Nwg" column of Table 2.

Then an evaluation of the received Finest sheets have been carried out. First are the Purity (Table 2: "Pure" column) and the Structural homogeneity (table 2: column "Gef.") With "G" = "Good", "M" = "acceptable" or "S" = "Bad" been classified.

A good purity is when the crowd is all non-metallic inclusions 100 ppm by volume not exceeds, the diameter of the inclusions are preferably less than 5 microns.

The structural homogeneity was across the width of the band rated as "G" = "Good" if the deviation of the average grain diameter from the layers "belt center axis" and "strip edge" of the finished sheet metal less than 1.5 µm and the grain stretch deviation between these layers was less than 0.1. Otherwise it is with "S" = "Bad" was rated (Table 2: column "Gef").

Furthermore, the structure is stretched in the thin sheet (Table 2: column "Stre") was checked. As only such examples are considered according to the invention whose aspect ratio (ratio longitudinal / Transverse (width) aspect ratio is less than 1.35 (table 2: column "Stre"). The grain extension was determined by means of a automatic image analysis system determined. It has emphasized that subjectively classified as equiaxial  Grain formation actually during a measurement Grain stretches of 1.3 (longitudinal / transverse). On more elongated structure lies in grain extensions <1.40 before. Only examples with grain extensions from at most 1.35 have been considered to be in accordance with the invention.

Because the quality of the behavior of the finest sheet metal at Processing into cans in the DWI process by the Border drawing ratio, the point freedom and the tear-free processability is also determined essential βmax value for the limit drawing ratio and the Texture occupancy density has been checked. Ripper free processable thin sheets with high coverage of at least 14 of the orientation {111} <112 <and βmax values of at least 2.1 are in the column "Verh" with "G" = "Good" rating. As "S" = "Bad" is in this A material has been assessed at least one of these criteria is not met.

Finally, an assessment of the Softening behavior generated according to the invention Finest sheets have been carried out. For this purpose is on performed a softening test on the sample sheets where measurements in a high temperature Conductivity apparatus have been made. In this apparatus becomes the one with the increasing The characteristic change associated with softening the conductivity of the sample under investigation, which it allows a certain conductivity a certain Assign softening state. As a benchmark which at a temperature of 525 ° C starting from a untreated, not softened sample up to a Softening of 50% required time was used. These attempts result for the softening needed  Times of less than 5000 seconds, that's one particularly fast softening. Because according to the invention produced very thin sheets of this criterion (Table 2: column "Ez"), they can be due to the necessary for their softening low continuous annealing temperature and short dwell time Manufacture particularly economically in a continuous furnace.

After a done if necessary The thin sheets according to the invention are coated for the DWI can manufacturing process (well drawing and subsequent high speed stretching), for Packaging or for the manufacture of Thermoformed products provided. The Finest sheet products are for a subsequent one electrolytic Sn coating, foil coating or suitable for the production of composite materials.  

Table 1

Table 2

Claims (32)

1. Process for the production of fine metal sheet with a final cold strip thickness of at most 0.3 mm,
where a steel that (in mass%)
C: 0.0015-0.0080%,
Mn: 0.15-0.25%,
P: ≦ 002%,
S: 0.005-0.03%,
Si: ≦ 0.02%,
Al: 0.0080-0.06%,
N: 0.0010-0.020%,
Cr: ≦ 0.05%,
Ni: ≦ 0.5%,
Cu: ≦ 0.05%,
Sn: ≦ 0.02%,
Mo: ≦ 0.01%,
Ti: ≦ 0.0005%,
Nb: ≦ 0.0005%,
V: ≦ 0.0020%,
B: ≦ 0.007%
Co: ≦ 0.05%,
optionally Se and / or Te, the sum of the contents of Se, Te and S being not more than 0.03%, and
the remainder contains iron and unavoidable impurities, is cast into slabs or thin slabs,
in which the slabs or thin slabs are cooled,
in which the slabs or thin slabs are reheated to a temperature in the range from 1080 ° C. to 1150 ° C. with a holding time of a maximum of eight hours,
in which the slabs or thin slabs are hot-rolled into a hot strip in several passes in a hot rolling mill at a final rolling temperature above the Ar ₃ temperature,
in which the hot strip is coiled at a reel temperature in the range from 590 ° C to 660 ° C,
in which the hot strip is then cold rolled into cold strip and
in which the cold strip is subjected to annealing in a continuous furnace. 2. The method according to claim 1, characterized characterized that the cold strip Final thickness is 0.16 mm to 0.25 mm. 3. The method according to one of the preceding claims, characterized in that the maximum niobium content is 0.0001% by mass.   4. The method according to claim 3, characterized characterized that the maximum Niobium content is 0.00005% by mass. 5. The method according to any one of the preceding claims, characterized in that the steel contains a maximum of 0.0003 mass% titanium. 6. The method according to any one of the preceding claims, characterized in that the maximum Ni content is 0.05% by mass. 7. The method according to any one of the preceding claims, characterized in that the B content is at least 0.0004% by mass. 8. The method according to claim 7, characterized characterized that the B content is at most equal to half of the N content. 9. The method according to any one of the preceding claims, characterized in that the sum of the proportions of non-metallic inclusions on the steel is not more than 0.01% by volume. 10. The method according to claim 9, characterized characterized that the middle Diameter of the non-metallic inclusions is at most 10 µm, preferably at most 5 µm.   11. The method according to any one of the preceding claims, characterized in that the slabs or thin slabs before entering the Hot rolling mill can be compressed. 12. The method according to claim 11, characterized characterized in that at the Compression a reduction in width by up to 25% is achieved. 13. The method according to any one of the preceding claims, characterized in that the one in the last two passes during hot rolling achieved degree of deformation is at least 16%. 14. The method according to any one of the preceding claims, characterized in that the final rolling temperature during hot rolling is a maximum of 50 ° C above the Ar ₃ temperature. 15. The method according to any one of the preceding claims, characterized in that the thickness of the hot strip in the range from 2 mm to 4 mm lies. 16. The method according to any one of the preceding claims, characterized in that the reel temperature in the range from 600 ° C to 630 ° C lies.   17. The method according to any one of the preceding claims, characterized in that the annealing in a decarburizing atmosphere is carried out. 18. The method according to claim 17, characterized characterized in that the Carbon content after annealing between 0.002 Mass% and 0.006 mass%. 19. The method according to any one of the preceding claims, characterized in that annealing at a temperature not exceeding 650 ° C is carried out. 20. The method according to claim 19, characterized characterized that the exposure time in the continuous furnace is at most one minute. 21. The method according to any one of the preceding claims, characterized in that the glow in an embroidering atmosphere is carried out. 22. The method according to claim 21, characterized characterized in that the Nitrogen content based on in hot strip present 0.001 mass% to 0.004 mass% in the course annealing to 0.008 mass% to 0.015 mass% is increased.   23. The method according to any one of the preceding claims, characterized in that the cold strip after the annealing of a re-rolling is subjected. 24. The method according to claim 23, characterized characterized in that during the Roughing a re-rolling degree of up to 20% is achieved becomes. 25. Use of a (in mass%)
C: 0.0015-0.0080%,
Mn: 0.15-0.25%,
P: ≦ 0.02%,
S: 0.005-0.03%,
Si: ≦ 0.02%,
Al: 0.0080-0.06%,
N: 0.0010-0.020%,
Cr: ≦ 0.05%,
Ni: ≦ 0.5%,
Cu: ≦ 0.05%,
Sn: ≦ 0.02%,
Mo: ≦ 0.01%,
Mon: ≦ 01001%,
Ti: ≦ 0.0005%,
Nb: ≦ 0.0005%,
V: ≦ 0.0020%,
B: ≦ 0.007%
Co: ≦ 0.05%,
optionally Se and / or Te, the sum of the contents of Se, Te and S being not more than 0.03%, and
the remainder being iron and steel containing unavoidable impurities for the production of easily formable thin sheet with a final cold strip thickness of at most 0.3 mm. 26. Use according to claim 25, characterized characterized that the maximum Niobium content is 0.0001% by mass. 27. Use according to claim 26, characterized characterized that the maximum Niobium content is 0.00005% by mass. 28. Use according to one of claims 25 to 27, characterized in that the steel contains a maximum of 0.0003 mass% titanium. 29. Use according to one of claims 25 to 28, characterized in that the maximum Ni content is 0.05% by mass. 30. Use according to one of claims 25 to 29, characterized in that the B content is at least 0.0004% by mass.   31. Use according to claim 30, characterized characterized that the B content is at most equal to half of the N content. 32. Use according to one of claims 25 to 31, characterized in that the sum of the proportions of non-metallic inclusions on the steel is not more than 0.01% by volume.