JP2011025255A - Method of temper-rolling metallic strip having dull surface excellent in fatigue strength, and metallic strip having dull surface - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method by temper-rolling a metallic strip having the dull-surface excellent in fatigue strength without deteriorating mechanical material in the outer layer part and significantly raising manufacturing cost, and to provide the metallic strip having the dull surface manufactured by the rolling method. <P>SOLUTION: The continuously annealed metallic strip is temper-rolled at the elongation percentage of 0.3-0.9% under the rolling lubrication condition which is ≤0.15 in the coefficient of friction by using dull work rolls whose surface roughness is 2-4 μmRa in arithmetic mean roughness. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a temper rolling method for a dull surface metal strip excellent in fatigue strength, and a dull surface metal strip produced by the rolling method.

  A metal strip having a dull surface exceeding 0.3 μm Ra is manufactured by temper rolling with a work roll called a dull roll having a rough surface roughness. In general, it is known that the degree to which the surface roughness of the dull roll is transferred to the surface roughness of the rolled material increases as the elongation rate increases and the linear load increases. For this reason, in order to increase the transfer efficiency of the surface roughness, in order to increase the elongation rate so that the surface roughness of the metal strip after temper rolling falls within the desired range, or to increase the line load, it exceeds 0.15. For example, a rolling lubricant having a high friction coefficient (for example, a water-soluble rolling lubricant or a rolling lubricant having a viscosity of 10 cSt (at 40 ° C.) or less) or a rolling mill having a large work roll diameter is employed.

  By the way, generally, the residual stress of the surface layer of the temper-rolled metal strip is tensile (see Non-Patent Document 1). If the residual stress of the surface layer of the metal strip is tensile, the fatigue strength may be inferior. Therefore, in order to compress the residual stress on the surface layer of the metal strip, there are, for example, correction by a tension leveler, shot peening (for example, see Patent Document 1), and the like. Further, Patent Document 2 discloses a technique for performing temper rolling by securing a higher friction coefficient than wet lubrication by spraying using a dull roll, but this reduces the amount of oil introduced into the roll bite. It is a temper rolling method that raises the friction coefficient and raises the rolling load to increase the transfer efficiency, and is not a temper rolling method with a lowered friction coefficient.

JP-A-8-302425 JP-A-8-215708

Plasticity and processing, 20-227 (1979-12), page 1124 Matsumoto Tomomi: Rolling Theory of Light Rolling, Materials and Processes, 18-5 (2005), 1218.

  However, in the processing with a tension leveler, the surface layer is greatly elongated compared to the center part during processing due to tensile bending, which causes new problems such as deterioration of the mechanical material of the surface layer part and the appearance of scratches on the surface layer. There arises a new problem that it is difficult to adjust or to adjust the surface roughness of the metal strip after correction by the tension leveler. In addition, although shot peening is excellent for adjusting the residual stress on the surface layer and the surface roughness of the metal strip after processing, the productivity is inferior, and a production process on a separate line is required, which increases the manufacturing cost. There was a problem that.

  Therefore, conventionally, the dull surface metal strip has been manufactured by a temper rolling mill. However, with regard to surface quality, surface roughness is adjusted from the viewpoint of rolling, and fatigue strength is adjusted from the metallurgical point of view, alloy components and structures are adjusted, and both surface roughness and fatigue strength are considered simultaneously. Was not enough.

  In view of the above problems, an object of the present invention is to provide a temper rolling method for a dull surface metal strip excellent in fatigue strength without causing deterioration of mechanical material of a surface layer portion or a significant increase in manufacturing cost, and the rolling method thereof. It is to provide a dull surface metal strip manufactured in

  The first aspect of the present invention is a temper rolling method for a dull surface metal strip, wherein a continuously annealed metal strip is a dull work roll having a work roll surface roughness of 2 μmRa or more and 4 μmRa or less in terms of arithmetic average roughness. It is characterized by performing temper rolling with an elongation of 0.3% or more and 0.9% or less under rolling lubrication conditions with a friction coefficient of 0.15 or less.

  According to a second aspect of the present invention, in the first aspect, the friction coefficient is determined in consideration of a rigid body region of the material to be rolled in the roll bite, and the work roll is deformed flatly. Using the calculated rolling calculation method, the measurement value and the calculated value of the rolling load and the advanced rate are obtained in a coupled manner. Examples of the rolling theory of such a rolling calculation method include a model disclosed in Non-Patent Document 2 and an elastoplastic finite element method. In order to obtain a highly accurate friction coefficient for use in the present invention, it is desirable to use a model that strictly handles the roll flatness in such a roll bite, thereby obtaining a dull surface metal strip having excellent fatigue strength. Can do.

  Further, a third aspect of the present invention from another viewpoint capable of achieving the friction coefficient is a rolling with a viscosity of 40 cSt (at 40 ° C.) or higher in the temper rolling method of the first aspect or the second aspect. Lubricating oil is supplied to the metal strip under rolling lubrication conditions having an emulsion concentration of 0.3% or more and 1.0% or less and an average emulsion particle size of 1.0 μm or more and 3.0 μm or less.

  In the third aspect of the present invention, in order to obtain the above friction coefficient, it is desirable to use a rolling lubricating oil having excellent lubricity, and for that purpose, a rolling lubricating oil having a viscosity of 40 cSt (at 40 ° C.) or more should be used. desirable. If the emulsion concentration is not 0.3% or more, the rolling lubricity may not be secured. If the emulsion concentration exceeds 1%, the rolling lubricity can be secured, but the concentrated oil that adheres to the rolling mill due to mill contamination is deposited on the surface of the metal strip. There is a risk of contamination by dripping. Further, if the average emulsion particle size is less than 1.0 μm, the plate-out property may deteriorate and rolling lubricity may not be ensured. If the average emulsion particle size exceeds 3.0 μm, the above-mentioned problem of mill stains may occur. This is because it may occur.

  Furthermore, the fourth aspect of the present invention is a dull surface metal strip manufactured by any one of the first to third temper rolling methods, wherein the surface roughness is an arithmetic average roughness of 0.6 μmRa or more 1 It is characterized in that the residual stress of the surface layer measured by a stress measurement method by X-ray diffraction method is compression, and a dull surface metal strip excellent in fatigue strength can be obtained.

  An example of measurement conditions for the X-ray diffraction method is shown in Table 1.

  The temper rolling method for a dull surface metal strip according to the present invention uses a continuously annealed metal strip, a dull work roll having a work roll surface roughness of 2 μmRa or more and 4 μmRa or less in arithmetic mean roughness, and a friction coefficient of 0. Perform temper rolling with an elongation of 0.3% or more and 0.9% or less under rolling lubrication conditions of 15 or less. Thereby, compressive residual stress arises on the surface of a dull surface metal strip, and a dull surface metal strip excellent in fatigue strength can be obtained. Further, the productivity can be improved and the manufacturing cost can be reduced without causing deterioration of the mechanical material of the surface layer portion and a significant increase in the manufacturing cost. Furthermore, since the dull surface metal strip of the present invention is manufactured through the temper rolling method, it has a compressive residual stress on its surface, and therefore has excellent fatigue strength.

It is a block diagram of a temper rolling mill. It is a residual stress distribution of the metal strip after rolling. However, a) a bright work roll, and b) a dull work roll. It is a figure which shows the relationship between the work roll surface roughness and elongation rate which influence on the residual stress distribution of a surface layer. It is a figure which shows the relationship between the friction coefficient which affects the residual stress distribution of a surface layer, and temper rolling conditions.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing an example of a temper rolling mill for carrying out the present invention. The temper rolling mill 11 is composed of one rolling stand, and is a quadruple rolling mill in this example. The roll of the temper rolling mill 11 includes work rolls 16 and 17 and backup rolls 21 and 22. The work rolls 16 and 17 are connected to a spindle and are driven by an electric motor (both not shown). Further, a pulse generator (not shown) is attached to the electric motor, and detects the rotation speed of the work roll. The peripheral speed of the work rolls 16 and 17 is obtained from the rotation speed of the work roll, the work roll diameter, and the gear ratio.

  A continuous annealing facility (not shown) is disposed upstream of the temper rolling mill 11. The heat-treated metal strip S is continuously supplied from the continuous annealing equipment to the temper rolling mill 11. Further, downstream of the temper rolling mill 11, an inspection table for observing the surface of the dull surface metal strip S rolled by the temper rolling mill 11 and inspecting flatness and surface roughness, A cutting machine that cuts the tempered rolled metal strip S and a take-up reel (both not shown) for winding the tempered rolled metal strip S in a coil shape are disposed downstream.

As a shape control means, there is a work roll bender 51 capable of applying an increase and decrease bender force for controlling vertical deflection of the upper and lower work rolls 16 and 17 with an upper and lower work roll chock (not shown) as a fulcrum. Is provided. A rolling load detection device 36 is disposed above the upper backup roll chock (not shown), and detects loads on the work side and the drive side. In addition, an electric reduction device 37 is disposed above the rolling load detection device 36, and a pass line is adjusted when the metal strip S is rolled. Furthermore, a hydraulic reduction device 31 for applying a rolling force is disposed below the lower backup roll chock (not shown).

  An entrance side bridle roll 61 is provided on the entrance side of the temper rolling mill 11, and an exit side bridle roll 62 is provided on the exit side. Although not shown, the spindles of these entry / exit bridle rolls 61 and 62 are connected to each other and are driven by an electric motor to control the tension on the entry and exit sides of the temper rolling mill as target values. . PLG (not shown) is attached to the entrance / exit bridle rolls 61, 62, and the elongation rate is measured by detecting the plate speed of the metal strip S before and after the temper rolling mill. The advanced rate is obtained by calculation based on the detected values of the work roll peripheral speed and the temper rolling metal strip plate speed.

  Further, a touch roll 41 is disposed between the entry side bridle roll 61 and the temper rolling mill 11 on the entry side, and a touch roll 42 is disposed between the temper rolling mill and the exit side bridle roll 62. Rolling lubricating oil supply devices 45 and 46 that are vertically paired are arranged on the entrance side of the temper rolling mill, and temper rolling lubricating oil (emulsion lubricating oil) is supplied to the upper and lower surfaces of the metal strip S. The entrance / exit side tension of the temper rolling mill 11 is detected by load detectors (not shown) attached to the touch roll 41 and the touch roll 42, respectively. An X-ray plate thickness measuring device (not shown) is provided on the exit side of the temper rolling mill, and monitors the thickness after temper rolling.

  Experiments were conducted using the wet temper rolling mill to investigate the influence of rolling factors on the residual stress of the surface layer. The coefficient of friction was changed by changing the viscosity of the rolling lubricating oil and the emulsion lubricating concentration. Note that the metal strip is a high tensile steel having a thickness of 1 mm and a strength of about 780 MPa.

  As the lubricant, an emulsion of rolling lubricating oil having a viscosity of 42 cSt (at 40 ° C.) and a viscosity of 10 cSt (at 40 ° C.) was used. The emulsion concentration was 0.5% and the average emulsion particle size was 2.5 μm. Using a bright work roll having a surface roughness of 0.3 μm Ra and a dull work roll having a surface roughness of 3.5 μm Ra, the metal strip was rolled at an elongation of 0.5%. Subsequently, the residual stress distribution of the metal strip after rolling was measured by the method shown in Table 1.

  The experimental results are shown in FIG. As a result, in the case of bright work rolls, changing the lubrication conditions has little effect on the residual stress distribution, but in the case of dull work rolls, if the lubrication conditions are improved, the residual stress distribution changes greatly, and the surface layer It was confirmed that the residual stress changed from tension to compression.

  Next, based on the above knowledge, the viscosity is 42 cSt (at 40 ° C.), and the surface roughness of the work roll is 1.1 μm Ra to 5.5 μm and the elongation (0.2% to 1.2%) under the above rolling conditions. Experiments were carried out to measure the residual stress distribution on the surface layer. The result is shown in FIG. From the figure, if the surface roughness of the work roll is too small or too large, or the elongation rate is too small or too large, the residual stress on the surface layer of the metal strip after temper rolling becomes tensile. I understood that. On the contrary, it was found that the residual stress of the surface layer is compressed when the elongation is 0.3% or more and 0.9% or less and the elongation is 2 μmRa or more and 4 μmRa or less. Furthermore, it was found that the compression stress was particularly large in the data of 2.6 μmRa to 4 μmRa. Therefore, in order to compress the residual stress of the metal strip after rolling, the surface roughness of the work roll is 2 μmRa or more and 4 μmRa or less, and the elongation is within the range of 0.3% or more and 0.9% or less. I found it necessary. More preferably, the residual stress of the surface layer can be reliably compressed by making the surface roughness of the work roll more than 2.5 μmRa to 4 μmRa or less.

As a result, the relationship between the residual stress of the surface layer and the surface roughness of the work roll and the relationship between the residual stress of the surface layer and the elongation rate have been clarified, but the conditions for the lubricating oil have not yet been clarified.
Therefore, the surface roughness and elongation of the work roll are set to the following nine levels a. Work roll surface roughness: 2.0 μm Ra, elongation 0.3%
b. Work roll surface roughness: 2.0 μm Ra, elongation 0.6%
c. Work roll surface roughness: 2.0 μm Ra, elongation 0.9%
d. Work roll surface roughness: 3.0 μm Ra, elongation 0.3%
e. Work roll surface roughness: 3.0 μm Ra, elongation 0.6%
f. Work roll surface roughness: 3.0 μm Ra, elongation 0.9%
g. Work roll surface roughness: 4.0 μm Ra, elongation 0.3%
h. Work roll surface roughness: 4.0 μm Ra, elongation 0.6%
i. Work roll surface roughness: 4.0 μm Ra, elongation rate: 0.9%
Lubricating oil viscosity: 10, 20, 30, 42, 51, 62, 100 (at 40 ° C.)
Emulsion concentration: 0.1, 0.2, 0.5, 0.9, 1.0%
The experiment which changed was performed. At that time, the average particle size of the emulsion was adjusted to about 2 μm. Further, the friction coefficient at that time was determined by the method described above.

  As a result of investigating the relationship between the residual stress of the surface layer of the metal strip after the temper rolling and the friction coefficient, when the friction coefficient is 0.15 or less, the rolling conditions a to d. The residual stress of the surface layer of the metal strip after temper rolling was confirmed to be compression. FIG. 4 shows the relationship between the friction coefficient and the residual stress on the surface layer. According to this figure, ad. It was found that any of these conditions tended to be on one curve, and the friction coefficient was required to be a rolling lubrication condition of 0.15 or less.

  The friction coefficient handles the flat deformation of the work roll in consideration of the rigid body region of the material to be rolled in the roll bite, and uses a rolling calculation method with the friction coefficient and deformation resistance as unknowns. It is obtained in a coupled manner so that the calculated value matches. Although the friction coefficient may be obtained as an adjustment coefficient including other factors, the tendency that appears in FIG.

  In view of the above, the continuous annealing of the metal strip was performed using a dull work roll having a work roll surface roughness of 2 μmRa or more and 4 μmRa or less in terms of arithmetic average roughness under a rolling lubrication condition with a friction coefficient of 0.15 or less and an elongation of 0. It became clear that temper rolling of .3% to 0.9% should be performed.

  As a result of further investigation, in order to reduce the friction coefficient to 0.15 or less under the above rolling conditions, a rolling lubricant having a viscosity of 40 cSt (at 40 ° C.) or higher is used, and an emulsion concentration of 0.3% to 1.0%, And it became clear that it is good to set it as an emulsion average particle diameter of 1.0 micrometer or more and 3.0 micrometers or less. In addition, the metal strip that can be produced by such a temper rolling method has a surface roughness of 0.6 μm Ra or more and 1.8 μm Ra or less in terms of arithmetic average roughness, and a surface layer by a stress measurement method using an X-ray diffraction method. It was clarified that there is a characteristic that the residual stress is compression.

  As mentioned above, although an example of embodiment of this invention was demonstrated, this invention is not limited to the form of illustration. It is obvious for those skilled in the art that various changes or modifications can be conceived within the scope of the idea described in the claims, and these naturally belong to the technical scope of the present invention. It is understood.

  As examples and comparative examples of the present invention, the rolling method (example) according to the present invention and the conventional rolling method (comparative example) are applied, respectively, and the temper rolling mill shown in FIG. 1 is used. A high-tensile material (annealed material) having a thickness of 1 mm and a strength of 780 MPa was temper-rolled in both the comparative example and the example, and the fatigue strength was compared.

First, as a comparative example, a work roll having a surface roughness of 3.0 μmRa produced by electric discharge machining was used, and a lubricating oil with a viscosity of 8 cSt (at 40 ° C.) was used with an emulsion concentration of 0.5%, an emulsion particle size of 6 μm, and an elongation of 0 .4% temper rolling was performed, and a sample after temper rolling was taken out. As a result of measuring the residual stress of the surface layer of this sample, the residual stress was a tensile stress of about 80 MPa. Further, as a result of obtaining the friction coefficient at this time, the friction coefficient was 0.19. A test piece having a width of 50 mm and a length of 100 mm was prepared from the above sample, a φ5 mm hole was made in the center of the test piece, elastic deformation of bending and bending back was performed, and the number of times until a crack occurred in the hole was determined. It was measured. This experiment was repeated 5 times and the average value was obtained.
In the case of the comparative example, cracks occurred after 5 × 10 ⁴ times.

Further, as an example of the present invention, a work roll having a surface roughness of 3.0 μmRa produced by electric discharge machining was used, and a lubricating oil having a viscosity of 40 cSt (at 40 ° C.) was used with an emulsion concentration of 0.5% and an emulsion particle size of 2 Temper rolling was performed at a thickness of 0.5 μm and an elongation of 0.4%, and a sample after the temper rolling was taken out. As a result of measuring the residual stress of the surface layer of this sample, the residual stress was a compressive stress of about 40 MPa. Further, as a result of obtaining the friction coefficient at this time, the friction coefficient was 0.10. A test piece having a width of 50 mm and a length of 100 mm was prepared from the above sample, a φ5 mm hole was made in the center of the test piece, elastic deformation of bending and bending back was performed, and the number of times until a crack occurred in the hole was determined. It was measured. This experiment was repeated 5 times and the average value was obtained.
In the case of the example of the present invention, cracks occurred at 7 × 10 ⁶ times.

  From the results of the comparative examples and examples described above, the fatigue strength of the metal strip after temper rolling is greatly improved compared to the conventional one by applying the temper rolling method of the metal strip according to the present invention. Confirmed to do. The surface roughness of the metal strip after temper rolling was 1.1 μmRa in the comparative example and 0.9 μmRa in the example of the present invention.

  Table 2 shows examples in which the surface roughness (Ra), the friction coefficient, and the elongation of the work roll were changed and evaluated within the scope of the present invention under the same temper rolling conditions as in the above Examples and Comparative Examples.

  As shown in this table, it has been clarified that the dull surface metal strip produced by the temper rolling of the present invention has a compressive (-value) residual stress in the surface layer and has high fatigue strength.

  The present invention can be applied to a dull surface metal strip excellent in fatigue strength and a method for manufacturing the same.

DESCRIPTION OF SYMBOLS 11 Wet temper rolling mill 16-17 Work roll 21-22 Backup roll 31 Hydraulic reduction device 36 Rolling load detection device 37 Electric reduction device 41-42 Touch roll 45-46 Lubricating oil supply device 51 Work roll bender 61-62 Bridle roll S metal strip

Claims (4)

Continuously annealed metal strip, a dull work roll having a work roll surface roughness of 2 μmRa or more and 4 μmRa or less in arithmetic mean roughness, and an elongation of 0.3% under rolling lubrication conditions having a friction coefficient of 0.15 or less. The method for temper rolling a dull surface metal strip, wherein the temper rolling is 0.9% or less. The friction coefficient is determined by taking into account the rigid region of the material to be rolled in the roll bite and assuming that the work roll is flatly deformed, and using a rolling calculation method with the friction coefficient and deformation resistance as unknowns, 2. The temper rolling method for a dull surface metal strip according to claim 1, wherein the measurement value and the calculated value are obtained so as to coincide with each other. The temper rolling method according to claim 1 or 2, wherein a rolling lubricating oil having a viscosity of 40 cSt (at 40 ° C) or higher has an emulsion concentration of 0.3% or more and 1.0% or less, and an average emulsion particle size of 1.0 µm or more. A temper rolling method for a dull surface metal strip, wherein the metal strip is supplied under rolling lubrication conditions of 3.0 μm or less. A dull surface metal strip manufactured by the temper rolling method according to any one of claims 1 to 3, wherein the surface roughness is an arithmetic average roughness of 0.6 μmRa or more and 1.8 μmRa or less, A dull surface metal strip, wherein the residual stress of the surface layer measured by a stress measurement method by an X-ray diffraction method is compression.

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