DE69917416T2 - Cold rolling process for steel sheet and cold rolling mill - Google Patents

Description

The The invention relates to a Nachwalzverfahren for steel and a Nachwalzwerk according to the preambles of claim 1 or claim 6 (see, for example, FR-A 00 46 46 423). The invention relates in particular to a Nachwalzverfahren for sheet steel, which is suitable for the production of food cans and a high-gloss Appearance, and a re-rolling mill to carry out the procedure.

The Rolling of sheet steel before or after coating shine should (for example steel sheet for the production of cans), usually takes place by a dry rolling process with a rolling mill with two or three more scaffolding, with each scaffold a different roller is assigned. The first device is used for example, mainly for adjusting the condition of the material (surface hardness, etc.) and requires a matte roller with high gripping force, thus a sufficient elongation is ensured. This mat roller is usually a roller, which are characterized by mattresses with weakly directed (or generally very random) surface roughness characterized by sandblasting, spark erosion or laser machining be generated. The surface roughness is normally 0.5 μm or more.

A On the other hand, an abrasive roll comprises a so-called high-gloss roll. the a reflective surface texture forms, and a so-called Riefenglanzwalze, the grinding marks (with a surface roughness (Ra) from about 0.15 μm or more) leaves behind. Some scoring rollers leave a surface roughness (Ra) of 0.5 μm or more. However, the scoring roll is not used in the first scaffold, since they are used to ensure sufficient elongation inadequately assessed.

traditionally, If you roll the steel sheet in the second frame of the rolling mill and then To improve the gloss with ridged gloss rollers, so that the impact the one in the first frame trained muzzles is mitigated. The steel sheet is then with the scoring gloss roller, a high-gloss roller or a matte roller with a surface roughness rolled, the required surface roughness of the steel sheet equivalent.

With an increasing number of Riefenglanzwalzen improved in the intermediate stands the shine; However, it takes the cost of the plant and the current Cost too, and you needed more room for the construction.

Regarding The production cost is a two scaffolding operation vorteilhaftesten. As in the unexamined Japanese patent Nos. 1-95803 is disclosed, a matte roll, for example a sandblasted matte roller, for the first scaffolding used, and a gloss roller for the last frame.

In In recent years, the required gloss level has a limited surface roughness increased. However, it is difficult to demand good gloss to meet in Nachrollwerke with low scaffold number, for example with two scaffolding, because in such factories the number of rolling operations with high-gloss rollers decreases.

you can consider using the rolling mill twice without that the number of scaffoldings increases, by putting the second frame as a roughing gloss roller used; An increase in costs due to the increased number of steps is possible but also not avoid it.

you wishes therefore, to provide a method for improving the gloss, without that additional Plants and production steps are connected.

According to one Aspect, the invention provides a Nachwalzverfahren for re-rolling a steel sheet with the help of a Nachwalzwerks ready with several rolling stands is provided, wherein at least the roller at the upper front frame a Scribe gloss roller which has a surface roughness (Ra) of 1.2 μm or less has, and at least the roller in the last frame is a gloss roller, the a surface roughness (Ra) of 0.5 μm or less. In this case, the rolling is a dry rolling and the steel sheet contains 0.012 weight percent or less carbon (C). That in the process Nachwalzwerk used preferably has two frameworks, wherein the roller in the first scaffolding a scoring mirror roll having a surface roughness (Ra) of 1.2 μm or less is, and the roller in the second frame a gloss roller with a Surface roughness (Ra) of 0.5 μm or less.

According to a further aspect, the invention provides a Nachwalzwerk for rolling steel sheet be riding having a plurality of rolling stands, wherein at least the roll at the upper front stand is a scoring roll having a surface roughness (Ra) of 1.2 μm or less, and at least the roll in the last stand is a glossy roll having a surface roughness (Ra ) between 0.15 and 0.3 μm. The Nachwalzwerk is preferably equipped with two scaffolding. In this case, the roll at the first stand is a scoring roll having a surface roughness (Ra) of 1.2 μm or less, and the roll at the second stand is a glossy roll having a surface roughness (Ra) between 0.15 and 0.3 μm.

It Reference will now be made by way of example to the accompanying drawings.

It shows:

1 a curve with the relationship between the carbon content (C) and the elongation of a re-rolled steel sheet.

• (A) Der Glanz wird stark beeinträchtigt, wenn man ein Stahlblech im oberen vorderen Gerüst des Nachwalzwerks mit einer Mattwalze komprimiert, die keine gerichtete Oberflächenrauheit aufweist, beispielsweise mit einer sandgestrahlten Walze oder einer funkenerodierten Walze. Der Glanz, und insbesondere der Glanz nach dem Beschichten, verbessert sich beträchtlich, wenn das Stahlblech mit einer Riefenglanzwalze gewalzt wird, und zwar auch dann, wenn die Oberflächenrauheit mit der Rauheit vergleichbar ist, die man mit anderen Walzverfahren erhält. Da die Riefenglanzwalze Schleifspuren in einer Richtung hinterlässt, wird vermutet, dass nur einige wenige konkave Abschnitte ausgebildet werden, die sogenannten "Dullbits", die man als Hauptursache für die Verschlechterung des Glanzes ansieht.
• (B) Eine ausreichende Längung lässt sich nicht erreichen, wenn man kohlenstoffarmen Allzweckstahl walzt und dabei eine Riefenglanzwalze im oberen vorderen Gerüst verwendet. Obgleich die Ursache dafür noch unklar ist, darf man vermuten, dass die Oberflächenrauheit am Umfang so schwach ist, dass die Angriffskraft gering ist, da die Schleifspuren auf der Oberfläche beispielsweise in radialen Ebenen liegen.

The inventors of this invention have determined through extensive investigations the following facts:

• (A) The gloss is greatly degraded when compressing a steel sheet in the upper front stand of the post-rolling mill with a dull roll having no directional surface roughness, for example, a sandblasted roll or a spark eroded roll. The gloss, and especially the gloss after coating, improves considerably when the steel sheet is rolled with a scoring roll, even if the surface roughness is comparable to the roughness obtained with other rolling processes. Since the scoring roller leaves grinding marks in one direction, it is believed that only a few concave portions are formed, the so-called "dull bits", which are considered to be the main cause of the deterioration of the gloss.
• (B) Sufficient elongation can not be achieved by rolling low-carbon all-purpose steel using a scribe roll in the upper front frame. Although the reason for this is still unclear, it may be assumed that the surface roughness on the circumference is so weak that the attack force is low, since the grinding marks on the surface are, for example, in radial planes.

On the other hand can be found in a steel sheet in which the hardness is reduced before re-rolling by lowering the carbon content (C) to a certain size (so-called very low-carbon steel), a sufficient elongation Ensure the desired Hardness supplies, even if you have a Riefenglanzwalze in the upper front framework used.

Of the especially low-carbon steel is often very strong, though you roll it with a matte roller in the upper front frame; this leads to to an extraordinary Hardness. Or the elongation can, even if the hardness not overly big, the Exceed control limits. This means that a quality inspection has to be carried out before loading. used on the other hand, you can use a scoring roll instead of the matte roll, so can such an exaggerated one elongation avoid.

The reasons for the restriction the conditions in the invention will be explained below.

Composition of the desired steel sheet

The Steel sheets subjected to the re-rolling process of the invention are limited to sheets that are 0.012 weight percent or less of carbon (C), since a desired hardness is due to the elongation can not reach when using a scoring roll in the upper front scaffold and the steel sheet contains more than 0.012 weight percent C. Especially preferably contains the steel sheet 0.0080 weight percent or less of carbon. The preferred lower limit for the carbon content is 0.0010 weight percent, as lower levels can lead to excessive elongation.

1 Figure 9 is a graph showing the relationship between the carbon content and the elongation of the post-rolled steel sheet and derived from studies made by the inventors of the invention. In the first stand, scoring mirror rolls having a surface roughness (Ra) of 0.6 μm, scoring mirror rolls having a surface roughness (Ra) of 0.15 μm and sandblasted matte rolls having a surface roughness (Ra) of 0.6 μm were used. One received the in 1 with SB 0.6, SB 0.15 and SD 0.6, respectively. Each post mill included two scaffolds. In the second frame, a scoring mirror roll having a surface roughness of 0.2 μm was used. Under the rolling conditions used, a steel sheet having a content of 0.002 wt% of carbon gave an elongation of 1.6 percent ± 0.2 Percent.

Out 1 It can be seen that the elongation of the extra low carbon steel became unstable when the sandblasted matte roll was used in the first stand (in addition to a low gloss). On the other hand, a desired elongation can not be secured when the scoring glaze roller having a surface roughness (Ra) of 0.15 μm was used in the first stand. When the scoring mirror roll having a surface roughness (Ra) of 0.6 μm was used in the first stand, the desired elongation could be maintained for steel sheets having a content of 0.0012 wt% or less of carbon. However, with steel sheets having a carbon content of more than 0.0080% by weight, the elongation becomes slightly unstable; this leads to a decrease in elongation.

The Contains sheet steel preferably either 0.02 weight percent titanium (Ti) or 0.1 weight percent niobium (Nb) or both fabrics, hence the softness and machinability is ensured. For Ti and Nb become lower limits of 0.005 wt% and 0.002, respectively Weight percent required.

For the oxygen deprivation and the stabilization of nitrogen (N) may be aluminum (Al) in 0.15 weight percent or less.

you preferred that further components in the conventional composition range are present, for example, 0.2 weight percent or less Silicon (Si), 0.5 weight percent or less manganese (Mn) (a Content of 0.1% by weight or more is particularly preferable); 0.05 weight percent or less phosphorus (P) and 0.03 weight percent or less sulfur (S). The contents are particularly preferred Si, P and S are 0.05 wt% or less, 0.02 wt% or less and 0.02 weight percent or less.

On Desire may be added to calcium (Ca). The rest is made up Fe and random Elements and impurities.

The roller at the front upper scaffolding

in the front scaffolding at least the top roller is a ridged gloss roller having a surface roughness (Ra) of 1.2 μm Or less. The gloss before or after coating is poor if you have a matte roll or a scoring roll with a surface roughness (Ra) of more than 1.2 μm used. The preferable lower limit of the surface roughness (Ra) is 0.20 μm or more. Is the surface roughness (Ra) below 0.20 μm, so does the elongation (Hardness) to be insufficiently trained. The most preferred surface roughness (Ra) is in the range of 0.5 to 1.0 μm.

The Machining of the rolled surface is not particularly limited. With regard to wear resistance a coating with chromium (Cr) can take place.

The roller at the last frame

According to the procedure the invention should at least the roller on the last frame a Glossy roller with a surface roughness (Ra) of 0.5 μm or less, so that a given level of gloss or a higher one Level is ensured. Dependent from the target surface roughness you can use a glossy roller or a scoring roller. Nevertheless, a desired Gloss (even after coating) can not be ensured if the surface roughness (Ra) exceeds 0.5 μm. The surface roughness however, is preferably less than the surface roughness of the roll in the first Framework. The effect of the invention is particularly evident when a roll with a surface roughness (Ra) in the range of approximately 0.15 to 0.3 μm used according to the device the invention is used, wherein the gloss requirements with a usual Roller not met become.

Although the gloss decreases when the surface roughness of the roller in the upper front scaffolding gets bigger, is a gloss improvement even then detectable if one Grooved roller used in place of the matte roller in the upper front frame, and the rolls each have the same surface roughness.

Even though the lower level of surface roughness and also the surface treatment After rolling are not particularly limited, the surface can with Cr be coated to improve the wear resistance.

Rollers for scaffolding, the away from the described scaffolding distinguish (three frameworks or more)

bright rolls is preferably used for the rollers of the scaffolding between the upper front scaffold and the last frame. A roller with a surface roughness in the area of the surface roughness of the front and rear scaffolding is particularly suitable for the rollers used in the scaffolding between the front scaffolding and the last frame be used to ensure a required gloss. Especially Preferably, the surface roughness of each roll is designed in the order from the front roller to the following rollers gradually fine.

additional conditions

To the Rerolling is a dry rolling that uses no lubrication of steel sheet required. An elongation of 3 percent or less is suitable. An elongation of 1.5 percent ± 1 Percent is particularly preferred. An elongation of 1.5 percent ± 0.5 percent is especially preferred. The target hardness can be 50 to 60 for HR30T be.

The Post-rolling coating processes are not referred to separately. The target steel of the invention may be various coating methods which are generally used for coating steel sheets for tin cans be used, for example, the coating with tin or with Chrome or with nickel (Ni) or a chromate treatment of the surfaces after these coating operations.

In The invention has the gloss with an angle of the incident Light of 20 degrees and with the help of a gloss meter according to JIS Z8741 measured.

The Nachwalzwerk the invention can be used in a production line in which only re-rolling, or you can do it at the outlet a continuous annealing furnace Install.

example

After the cold rolled steel sheet having the components shown in Table 1 was subjected to recrystallization annealing (continuous annealing), the steel sheet was regrooved with a re-rolling mill having two to three stands and under the conditions shown in Table 2. The conditions not shown in Table 2 are similar to the conditions under which 1.5 percent elongation is obtained by means of Scaffold No. 1 SD 0.6 and Scaffold No. 2 MB 0.5 shown at No 1 in Table 2. After measuring the hardness (HR30T) of each steel sheet, the tin was coated with tin (coating weight of 2.8 g / m ² ). This was followed by a gloss measurement after a reflow treatment. The gloss was evaluated in the following four steps:
⌾: 1300 to 1500
o: 1100 to less than 1300
Δ: 900 to less than 1100
x: less than 900.

The Results are shown in Table 2. Table 2 proves that those according to the invention obtained steel sheets a higher Gloss as the steel sheet of Comparative Example.

The Invention allows producing a steel sheet suitable for manufacturing, for example of cans, and only by the application Rolling in one direction with a Nachwalzwerk, the two or at the most three scaffolding having.

Claims (10)

Nachwalzverfahren for re-rolling a steel sheet by means of a Nachwalzwerks which is provided with a plurality of rolling stands, wherein at least the roller on the upper front frame a Riefenglanzwal ze, which has a surface roughness (Ra) of 1.2 μm or less, and at least the roller in the last stand is a gloss roller having a surface roughness (Ra) of 0.5 μm or less, characterized in that the finish rolling is a dry rolling and that the steel sheet contains 0.012 weight percent or less of C. Nachwalzverfahren according to claim 1, wherein the Nachwalzwerk a work with two scaffolding is. Nachwalzverfahren according to claim 1 or 2, wherein the Sheet steel between 0.001 and 0.008 weight percent carbon contains. Nachwalzverfahren according to claim 1, 2 or 3, wherein the steel sheet additionally between 0.005 and 0.2 weight percent Ti and / or between 0.002 and 0.1 weight percent Nb. Post-rolling process according to any preceding one Claim, wherein the steel sheet additionally not more than 0.15 Weight percent Al, not more than 0.2 weight percent Si, between 0.1 and 0.5 weight percent Mn, not more than 0.05 weight percent P and not more than 0.03 weight percent S contains. Nachwalzwerk for Sheet steel, the several rolling stands wherein at least the roller at the upper front frame a Scribe gloss roller which has a surface roughness (Ra) of 1.2 μm or less has, characterized in that at least the roller in the last framework a glossy roller having a surface roughness (Ra) between 0.15 and 0.3 μm Has. Nachwalzwerk according to claim 6, which is a work with two scaffolding is. A rolling mill according to claim 6 or 7, wherein the scoring mirror roller of the front scaffolding a surface roughness of at least 0.20 μm Has. A rolling mill according to claim 8, wherein the scoring mirror roll of the front scaffolding a surface roughness from 0.5 to 1.0 μm Has. A rolling mill according to any one of claims 6 to 9, wherein the glossy roller of the last stand a glossy roller or a ridged gloss roller is.