KR20220129627A - Temper rolling method of cold rolled steel sheet - Google Patents

Abstract

The present invention is a method for temper rolling of a cold rolled steel sheet that does not cause problems such as jumping, which can be applied to both single-stand and multi-stand rolling mills in response to changes in the concentration or load of the temper rolling liquid in wet temper rolling provides In the temper rolling method for performing wet temper rolling on the cold-rolled steel sheet after annealing, the tension T per unit cross-sectional area of the steel sheet in temper rolling (kgf/mm 2 ) is the carbon content C (mass %) of the cold-rolled steel sheet A method of temper rolling of cold rolled steel sheet set based on

Description

Temper rolling method of cold rolled steel sheet

The present invention relates to a method for temper rolling of a cold rolled steel sheet, and more particularly, to a method for setting tension in wet temper rolling.

Cold-rolled steel sheet is manufactured by rolling the hot-rolled steel sheet to the required thickness at room temperature. In this process, since the steel plate produces work hardening, the process of annealing and softening may be required. Thereafter, temper rolling is performed for the purpose of eliminating the elongation at the yield point, correcting the shape, adjusting the surface roughness of the steel sheet, adjusting the material, and the like.

In the process of this temper rolling, there are wet temper rolling using a temper rolling liquid and dry temper rolling in which a temper rolling liquid is not used. Conventionally, especially in the field of steel sheets for cans, dry temper rolling has been the mainstream from the viewpoint of aesthetics. However, when various specifications are required for the material of the steel sheet, the elongation rate is controlled by adjusting the properties of the temper rolling liquid to perform wet temper rolling in which various materials can be manufactured.

Adjustment of the surface roughness of the steel sheet, which is one of the objectives of temper rolling, is performed by transferring the roughness of the work roll to the steel sheet. In order to stably adjust the steel sheet surface roughness, it is necessary to uniquely determine the work roll roughness and the rolling load with respect to the desired steel sheet surface roughness. On the other hand, adjustment of the material is performed by controlling the specifications, such as the elongation rate of temper rolling, to a predetermined value. As described above, the surface roughness and rolling load of the work roll are uniquely determined according to the surface roughness of the steel sheet. Here, the elongation is defined as the ratio of the difference between the thickness of the entrance plate and the thickness of the exit plate to the thickness of the exit plate. Accordingly, the adjustment of the elongation ratio is generally performed by controlling the plate thicknesses on the entry side and the exit side by controlling the tension of the steel plate before and after the rolling mill.

By the way, in wet temper rolling, a phenomenon called jumping is known. Jumping refers to so-called abnormal elongation in which elongation is unstable and fluctuates particularly when elongation is as low as 5% or less. When this jumping occurs, there is a problem that the plate thickness and material of the steel plate fluctuate greatly.

As a method of preventing this jumping, Patent Document 1 discloses a method of adjusting the concentration of the temper rolling liquid according to the material and the elongation rate. Moreover, in patent document 2, the method of using wet temper rolling and dry temper rolling together is disclosed in the rolling machine comprised with a plurality of stands.

Patent Document 1: Japanese Patent Laid-Open No. 2016-150353 Patent Document 2: Japanese Patent Laid-Open No. 2018-015801

However, in the method of preventing jumping by adjusting the concentration of the temper rolling liquid described in Patent Literature 1, the ratio of the roughness pattern transferred from the work roll to the steel sheet changes depending on the difference in concentration, and the roughness and appearance of the steel sheet change. There is a problem in that it is difficult to reliably prevent only the occurrence of jumping. Moreover, there also exists a problem that the method of using wet temper rolling and dry temper rolling described in patent document 2 together cannot be applied with the rolling mill of a single stand.

The present invention provides a method for temper rolling of a cold rolled steel sheet that does not cause jumping, which can be applied to both single-stand and multi-stand rolling mills, in response to changes in the concentration or load of the temper rolling liquid in wet temper rolling. aim to

As described above, the surface roughness of the work roll and the rolling load are uniquely determined according to the desired surface roughness of the steel sheet. In order to perform temper rolling at a predetermined elongation rate, it is also necessary to appropriately set the tension. When this tension setting is excessive, jumping, which is an abnormal extension, occurs. In addition, when the tension setting is too small, an insufficient elongation rate or a shape defect in the shape of a bellows called a cross buckle occurs.

In order to solve the above problems, the present inventors paid attention to the fact that the mechanical properties of the steel sheet are strongly influenced by the carbon content of the steel sheet, and earnestly studied the relationship between the carbon content and the jumping. As a result, it was discovered that the tension|tensile_strength in temper rolling is related to the carbon content of a steel plate, and came to invention the temper rolling method of the cold-rolled steel plate which solves the said subject.

The gist of the present invention is as follows.

[1] In the temper rolling method for performing wet temper rolling on the cold-rolled steel sheet after annealing, the tension T (kgf/mm 2 ) at the time of temper rolling is determined based on the carbon content C (mass %) of the cold-rolled steel sheet. A method of temper rolling of cold rolled steel sheet to set.

[2] In [1], the tension T is added to the carbon content C of the cold-rolled steel sheet, and the sheet thickness t (mm) of the cold-rolled steel sheet, the load per unit width w (tonf/mm), and the surface of the work roll A method of temper rolling of cold-rolled steel sheet set based on roughness a (μmRa).

[3] The method of temper rolling of a cold rolled steel sheet according to [2], wherein the tension T is set based on the following formula (1):

t×w×(-200×a-90)/(a×(1-logC))+17.1≤T≤t×w×(-200×a+10)/(a×(1-logC))+ 17.1… (One)

where t: plate thickness (mm) of steel sheet, w: load per unit width (tonf/mm), a: surface roughness of work roll (μmRa), C: carbon content (mass %) of steel sheet, T: per unit cross-sectional area Tension (kgf/mm2).

According to the present invention, in wet temper rolling, even when the concentration of the temper rolling liquid is changed or the load is changed, jumping, elongation defects, and bellows-shaped defects called cross buckles do not occur. Further, the present invention can be applied to both single-stand and multi-stand rolling mills.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram of the temper rolling installation which shows 1 Embodiment of the temper rolling method of this invention.

Hereinafter, the present invention will be described in more detail.

EMBODIMENT OF THE INVENTION Embodiment of this invention is described using drawing. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining one Embodiment of this invention in the temper rolling method of a cold-rolled steel sheet, and is a schematic diagram of the temper rolling facility which temper-rolls the annealed cold-rolled steel sheet. In order to perform temper rolling, the work roll 1 which presses down the steel plate 3 from top and bottom, and the backup roll 2 which hold it are provided. The temper rolling liquid is supplied from the temper rolling liquid supply nozzle 5 to perform rolling.

In order to measure the tension T (kgf/mm 2 : tension per unit cross-sectional area) applied to the steel sheet 3 , a tension meter (not shown) is provided before and after the work roll 1 . The steel sheet 3 is pressed down with a predetermined load by the upper and lower work rolls 1, and advances in the advancing direction 4 in a state in which a set tension is applied. At this time, if the tension setting is excessive, jumping occurs because the elongation rate fluctuates unstablely. If the tension setting is too small, insufficient elongation or cross buckle occurs.

In this temper rolling, the tension|tensile_strength T set based on the various factors shown below is provided by adjusting the rotation speed of the work roll 1 .

As a result of repeating and examining many experiments on the various factors which influence the occurrence of a problem among the rolling conditions in temper rolling, the present inventors found that the factor shown below had influence.

Specific factors are the sheet thickness t (mm) of the steel sheet, the load per unit width w (tonf/mm), the surface roughness a (μmRa) of the work roll, the carbon content C (mass %) of the steel sheet, and the tension T per unit cross-sectional area (kgf/kgf/ ㎟).

As a result of examining the relationship between these factors and the occurrence of jumping, it was found that jumping was more likely to occur as the values of the plate thickness t and the tension T increased. On the other hand, it turned out that the numerical value of the surface roughness a and the carbon content C of a work roll tends to generate|occur|produce the smaller one.

However, among these factors, all factors other than the tension T are factors set within a certain range by the specifications of the product steel sheet. For this reason, the setting cannot be changed freely. That is, it was found that if factors other than the tension T were kept constant and the tension T could be set to an optimal value, the occurrence of jumping could be effectively suppressed.

So, how to set the tension T to an optimal value was examined.

As described above, when the tension T is large, jumping tends to occur, and when the tension T is small, a shape defect such as a cross buckle tends to occur. In temper rolling, there is a request to set the tension T large for the reason of stabilizing the shape, and in relation to the occurrence of jumping, it is important to find the upper limit of the tension setting. In addition, it was concluded that it was necessary to also set the lower limit of the tension setting from the viewpoint of preventing shape defects, and various experiments were performed. As a result, the method of setting the tension T as shown below was derived.

The present invention relates to a temper rolling method for performing wet temper rolling on a cold-rolled steel sheet after annealing, wherein the tension T (kgf/mm 2 ) at the time of temper rolling is determined based on the carbon content C (mass %) of the cold-rolled steel sheet. In addition to the above carbon content C (mass %), based on the sheet thickness t (mm) of the cold-rolled steel sheet, the load per unit width w (tonf/mm), and the surface roughness a (μmRa) of the work roll and, more preferably, the tension T is set based on the following formula (1).

t×w×(-200×a-90)/(a×(1-logC))+17.1≤T≤t×w×(-200×a+10)/(a×(1-logC))+ 17.1… (One)

where t: plate thickness (mm) of steel sheet, w: load per unit width (tonf/mm), a: surface roughness of work roll (μmRa), C: carbon content (mass %) of steel sheet, T: per unit cross-sectional area Tension (kgf/mm2). In addition, log in the equation is a natural logarithm.

Equation (1) above is a result obtained by performing multiple regression analysis on data summarizing calculation results by extensive experimental examples and simulations. It can be seen that an excellent steel sheet without jumping or other problems is obtained by finding the lower limit and upper limit of the tension T so as to satisfy this formula (1), and performing temper rolling by setting the tension T within the range. could

In the above formula (1), looking at the relationship between each factor and the tension T, the plate thickness t and the load w have a negative correlation with the tension T. It can be seen that as t and w increase, the value of the tension T at which jumping occurs decreases. On the other hand, the surface roughness a and the carbon content C of the work roll have a positive correlation with the tension T. For this reason, it can be seen that as a and C increase, the value of the tension T at which jumping occurs increases.

Hereinafter, the tension T of the present invention, each factor (C, t, w, a) for setting the tension, and specifications related to the operating conditions of the temper rolling will be described. Here, the cold-rolled steel sheet made into the object of the present invention is a steel sheet for automobiles, a steel sheet for cans, and other general cold-rolled steel sheets.

・About the tension T

The range of the tension T of the present invention is 5.0 kgf/mm 2 to 30.0 kgf/mm 2 . If it is out of this range, sufficient temper rolling cannot be performed, and problems, such as jumping and shape defect, arise. Preferably it is 2.0 kgf/mm<2> - 16.0 kgf/mm<2>.

The tension T set based on various factors in temper rolling is provided by adjusting the rotation speed of the work roll 1 as mentioned above.

・About carbon content C

The carbon content C (mass %) of the cold-rolled steel sheet is an element that greatly influences the tension T. The carbon content C of the cold-rolled steel sheet of the present invention is preferably 0.0005 mass% or more, and preferably 0.1 mass% or less. More preferably, it is 0.001 mass % or more, More preferably, it is 0.08 mass % or less.

The analysis of the carbon content C can be performed according to JIS G 1211-3.

・About plate thickness t

The sheet thickness t (mm) of the cold-rolled steel sheet of the present invention is preferably 0.1 mm or more, and preferably 1.0 mm or less. More preferably, it is 0.1 mm or more, More preferably, it is 0.6 mm or less.

The thickness t can be measured with a gamma-ray thickness meter, an X-ray thickness meter, or the like.

・About the load w

The load per unit width w (tonf/mm) is preferably 0.1 tonf/mm or more, and preferably 1.5 tonf/mm or less. If it is out of this range, sufficient temper rolling cannot be performed, and problems, such as jumping and shape defect, may arise. More preferably, it is 0.2 tonf/mm or more, and more preferably, it is 1.0 tonf/mm or less.

The measurement of the load w can be performed with a load cell or the like.

・About surface roughness a

The surface roughness a (μmRa) of the work roll is preferably 0.20 μmRa or more, and preferably 2.00 μmRa or less. More preferably, it is 0.25 micrometer Ra or more, More preferably, it is 1.80 micrometer Ra or less.

In addition, Ra is one parameter which shows surface roughness, and is a parameter which shows arithmetic mean roughness. The surface roughness of the work roll can be measured according to JIS B 0601.

In addition, adjustment of the surface roughness of a work roll can be performed by electric discharge machining, grindstone grinding, etc.

・Annealing conditions

First, the annealing process, which is a previous stage of the temper rolling process of the present invention, will be described.

In the general annealing process of cold-rolled steel sheet, a continuous annealing line in which an annealing furnace for performing annealing is provided before a temper rolling mill for performing temper rolling is used. This continuous annealing line has a plurality of supply reels for supplying coils (steel strips) of cold rolled steel sheets, a welding machine, a cleaning device, an annealing furnace, a temper rolling device, and a plurality of reels for winding the steel sheet.

The dispensing reel dispenses a steel sheet from a steel strip wound in a coil shape. The steel sheet is taken out from the dispensing reel and conveyed in the longitudinal direction.

Here, for example, in the case of having two dispensing reels, when dispensing from one dispensing reel is finished, dispensing from the other dispensing reel is started, and the rear end of the previous steel sheet and the front end of the rear steel sheet are welded with a welding machine, The steel plate is continuously processed.

In addition, it is not limited to having a plurality of dispensing reels, and one dispensing reel may supply the steel sheet.

The welding machine is for welding the rear end of the steel sheet supplied first and the front end of the steel sheet supplied later, and uniting them. Thereby, the steel plate longer than the length of the coil loaded in one supply reel can be processed continuously.

A cleaning device is a device for cleaning and removing oil or foreign substances adhering to the surface of a steel plate. There is no limitation in particular in the washing|cleaning method of the steel plate by a cleaning apparatus, Various washing methods used in the processing apparatus of steel plates, such as electrolytic degreasing and alkaline degreasing, can be used.

The annealing furnace is an apparatus (furnace) for annealing the cleaned steel sheet. The annealing furnace is an ordinary annealing furnace that performs heating, cracking and cooling.

As heat processing conditions, Preferably it is 600 degreeC or more, Preferably it is 850 degrees C or less, It is preferable that it is 20 second or more, and 100 second or less is preferable. Moreover, it is more preferably 650 degreeC or more, More preferably, it is 800 degrees C or less, It is more preferable that it is 25 second or more, and 90 second or less is still more preferable.

The soaking treatment conditions are preferably 600°C or higher, preferably 800°C or lower, preferably 5 seconds or longer, and preferably 60 seconds or shorter. Moreover, it is more preferably 650 degreeC or more, More preferably, it is 750 degrees C or less, It is more preferable that it is 10 second or more, and 55 second or less is still more preferable.

As the cooling treatment conditions, the cooling rate is preferably 5°C/sec or more, preferably 30°C/sec or less, cooling at 100°C or more is preferable, and cooling to 200°C or less is preferable. Further, the cooling rate is preferably 10°C/sec or more, preferably 25°C/sec or less, preferably cooling at 120°C or more, and more preferably cooling to 180°C or less.

・Operating conditions for temper rolling

As for the temper rolling mill, not only the 4-stage type rolling mill shown in FIG. 1 but also the 6-stage type etc. are applicable. Also, a single stand or a plurality of wet and dry stands can be applied.

The work roll diameter phi is preferably 450 mm or more, and is preferably 600 mm or less. In particular, it is more preferably 500 mm or more, more preferably 550 mm or less.

The temper rolling liquid supply nozzles 5 are provided on the front side and the back side of the steel sheet 3, respectively, and between the steel sheet 3 and the work roll 1 on the upstream side (inlet side) in the advancing direction of the steel sheet 3 . supply the temper rolling liquid to That is, the temper rolling liquid supply nozzle 5 supplies the temper rolling liquid to the front side and back side of the steel sheet 3 . By supplying the temper rolling liquid between the steel sheet 3 and the work roll 1, foreign matter is prevented from entering between the work roll 1 and the steel sheet 3, and defects occur in the steel sheet 3 is preventing

In FIG. 1 , the temper rolling liquid supply nozzle 5 is provided on the inlet side and the temper rolling liquid is supplied between the steel plate 3 and the work roll 1 , but the present invention is not limited thereto. A temper rolling liquid supply nozzle 5 may be provided on the surface of the work roll 1 or between the work roll 1 and the backup roll 2 to supply the temper rolling liquid. Further, in the case of a six-stage rolling mill, a temper rolling liquid supply nozzle 5 is provided between the work roll 1 and an intermediate roll provided between the work roll 1 and the backup roll 2 to supply the temper rolling liquid. good night. Moreover, you may provide the temper rolling liquid supply nozzle similarly not only on the inlet side but also on the exit side.

Although the kind of temper rolling liquid of this invention is not specifically limited, Specifically, surfactant, a fatty acid, etc. are mentioned.

The supply temperature of the temper rolling liquid is preferably 10°C or higher, and is preferably adjusted to 60°C or lower. More preferably, it is 20 degreeC or more, More preferably, it is 50 degrees C or less.

Example

Hereinafter, the present invention will be specifically described by way of Examples, but the present invention is not limited to these Examples.

First, the roughness of the surface of the work roll was adjusted by grinding with a grindstone using a four-stage temper rolling mill having a work roll diameter of ? 520 mm shown in FIG. 1 . Moreover, the temper rolling liquid which consists of surfactant, a fatty acid, etc. was adjusted to 20-40 degreeC, and was supplied from the inlet side of a rolling mill.

As the target steel sheet, low coal having a carbon content C of 0.04% by mass and extremely low coal having a carbon content of 0.0014% by mass or 0.0024% by mass were used.

The plate thickness t of the steel plate was prepared as 0.2 mm, 0.25 mm and 0.3 mm. The load w per unit width to the steel sheet was 0.3 tonf/mm, 0.5 tonf/mm, and 0.6 tonf/mm. The surface roughness a of the work roll was adjusted to 0.28 µmRa, 0.47 µmRa, and 0.88 µmRa.

The operation in which each factor was combined as described above was performed, and the calculated value obtained from the above-described tension setting equation (1) based on the above factors was compared with the actually set tension value. Table 1 shows the results of examining the actual occurrence of jumping and the occurrence of shape defects.

With respect to the occurrence of jumping, the presence or absence of the occurrence of jumping was judged by the elongation rate calculated from the difference in peripheral speed of the front and rear rolls of the temper rolling mill. Specifically, it was judged that jumping was occurring when the elongation rate was 5% or more. In addition, with respect to the occurrence of shape defect, the presence or absence of occurrence of shape defect was judged by the height of the wave on the surface of the steel sheet. The height of the wave on the surface of the steel sheet was measured with a stylus type measuring instrument, and it was judged that the shape generation was defective if the height difference was 0.1 mm or more.

As Example 1, a steel sheet having a carbon content C of 0.04 mass %, 0.0024 mass %, 0.0014 mass % was used, and the plate thickness t, which is another factor, was 0.2 mm, the load w was 0.3 tonf/mm, and the work roll surface roughness was a was carried out by fixing at 0.28 μmRa. These values were substituted into Formula (1), and the lower limit and upper limit of the tension T were obtained. When the tension of the actual operation was set within the range of the upper and lower limits (Examples 1-1, 1-5, and 1-8), neither jumping nor shape defects occurred, but when it was set to a value outside the upper limit (Example 1-1, 1-5, 1-8) In Examples 1-2, 1-6, and 1-9), jumping occurred, and when the value was set outside the lower limit (Examples 1-3, 1-4, 1-7), shape defects occurred.

Next, as Example 2, a steel plate having a plate thickness t of 0.2 mm, 0.25 mm, and 0.3 mm was used, the carbon content C, which is another factor, was 0.04 mass %, the load w was 0.3 tonf/mm, and the work roll surface The roughness a was fixed to 0.28 μmRa and carried out. These values were substituted into Formula (1), and the lower limit and upper limit of the tension T were obtained. In addition, when the tension of the actual operation was set within the range of the lower limit (Examples 2-1, 2-3, 2-6), neither jumping nor shape defects occurred, but when it was set to a value outside the upper limit (Example 2-1, 2-3, 2-6) In Examples 2-4 and 2-7), jumping occurred, and when the value was set outside the lower limit (Examples 2-2 and 2-5), shape defects occurred.

Then, as Example 3, the load w is set to 0.3 tonf/mm, 0.5 tonf/mm, and 0.6 tonf/mm, the carbon content C, which is another factor, is 0.04 mass %, the plate thickness t is 0.2 mm, the workpiece The roll surface roughness a was fixed to 0.28 µmRa and performed. These values were substituted into Formula (1), and the lower limit and upper limit of the tension T were obtained. When the tension of the actual operation was set within the range of the upper and lower limits (Examples 3-1, 3-3, 3-6), neither jumping nor shape defects occurred, but when it was set to a value outside the upper limit (Example 3-1, 3-3, 3-6) In Examples 3-4 and 3-7), jumping occurred, and when the value was set outside the lower limit (Examples 3-2 and 3-5), shape defects occurred.

Finally, as Example 4, a work roll having a surface roughness a of 0.28 µmRa, 0.47 µmRa, and 0.88 µmRa is used, the carbon content C, which is another factor, is 0.04 mass %, the plate thickness t is 0.2 mm, the load w is It was carried out by fixing at 0.3 tonf/mm. These values were substituted into Formula (1), and the lower limit and upper limit of the tension T were obtained. In addition, when the tension of the actual operation was set within the range of the lower limit (Examples 4-1, 4-3, 4-6), neither jumping nor shape defects occurred, but when it was set to a value outside the upper limit (Example 4-1, 4-3, 4-6) In Examples 4-4 and 4-7), jumping occurred, and when the value was set outside the lower limit (Examples 4-2 and 4-5), shape defects occurred.

From the above results, it was found that if the tension of the actual operation is set within the upper and lower limits of the tension obtained by the formula (1) of the present invention, good temper rolling can be performed without the problems such as jumping as described above.

[Table 1]

One; work roll 2; backup roll
3; grater 4; arrow indicating the direction of progress
5; temper rolling fluid supply nozzle

Claims (3)

In the temper rolling method for performing wet temper rolling on the cold rolled steel sheet after annealing, cold rolling in which the tension T (kgf/mm 2 ) at the time of temper rolling is set based on the carbon content C (mass %) of the cold rolled steel sheet The method of temper rolling of steel sheet. The method of claim 1,
The tension T is added to the carbon content C of the cold-rolled steel sheet, and based on the sheet thickness t (mm) of the cold-rolled steel sheet, the load per unit width w (tonf/mm), and the surface roughness a (μmRa) of the work roll A method of temper rolling of cold rolled steel sheet to set. 3. The method of claim 2,
A method of temper rolling of a cold rolled steel sheet in which the tension T is set based on the following formula (1):
t×w×(-200×a-90)/(a×(1-logC))+17.1≤T≤t×w×(-200×a+10)/(a×(1-logC))+ 17.1… (One)
where t: plate thickness (mm) of steel sheet, w: load per unit width (tonf/mm), a: surface roughness of work roll (μmRa), C: carbon content (mass %) of steel sheet, T: per unit cross-sectional area Tension (kgf/mm2).

Images