JP6428731B2 - Temper rolling mill and temper rolling method - Google Patents

Description

  The present invention relates to a temper rolling mill and a tempering roll that can reduce a rolling load applied to a work roll and impart an elongation rate capable of shape correction to the steel strip even when temper rolling a high strength steel strip. It relates to a rolling method.

  In recent years, the demand for high-strength steel strips with excellent strength has increased with the increase in added value of steel strips. Since the high-strength steel strip has a significantly larger deformation resistance than a general mild steel material, shape control in cold rolling is more difficult, and it is necessary to correct the shape after cold rolling. As demand for high-strength steel strips increases, opportunities to correct the shape of high-strength steel strips after cold rolling are increasing.

  In addition, the high strength steel strip manufactured by quenching and tempering using a continuous annealing facility after cold rolling is applied to the thermal stress and structural transformation during quenching even if the shape is controlled flat during cold rolling. In some cases, a shape defect may occur due to deformation caused by. In particular, in a high-strength steel strip containing a large amount of martensite in order to increase the strength, the shape tends to deteriorate after annealing.

  When the steel strip is out of the required range, that is, when the shape becomes defective, it is not possible to pass the plate in the next process or later, or when the steel plate cut out from the steel strip is press-formed There may be a problem that it cannot be set at the position. Therefore, when a shape defect of the steel strip occurs, it is necessary to correct the shape so that the shape is within the required range.

  Usually, the shape correction of the steel strip is performed by lightly rolling the steel strip with a temper rolling mill equipped with a pair of work rolls. At this time, tension is applied in the longitudinal direction of the steel strip, and the steel strip is flattened by applying a degree of elongation equal to or greater than a predetermined value to the steel strip.

  However, the high-strength steel strip has a problem that deformation resistance is large and temper rolling cannot be performed easily. In order to provide the high-strength steel strip with an elongation rate necessary for shape correction, it is necessary to apply a very large rolling load with a work roll. At this time, the temper rolling mill itself may not be able to withstand the rolling load. In particular, it is an existing technique to impart elongation necessary for shape correction to a thin steel sheet having a tensile strength of 1180 MPa class or more (hereinafter sometimes referred to as “TS”) having a thickness of 1.0 mm or less. In many cases, it is difficult with the equipment.

Patent documents 1 and patent documents 2 are mentioned as literature which indicated the technique to the above problems. In Patent Document 1, by performing temper rolling at a strain rate of 0.1 s ⁻¹ or more in a warm region of 60 to 120 ° C., it is possible to achieve a reduction in rolling load and temper rolling of a hard material. Techniques to do this are disclosed. Further, in Patent Document 2, temper rolling is performed using a temper rolling facility including one or more rolling stands provided with a work roll having a surface average roughness Ra of the roll in a range of 3.0 μm or more and 10.0 μm or less. A technique for temper-rolling a high-strength cold-rolled steel strip having a TS of 980 MPa or more is disclosed by increasing the average roughness Ra of the subsequent steel strip surface by 1.0 μm or more compared with that before the temper rolling. Yes.

Japanese Patent Laid-Open No. 10-5809 JP 2008-302393 A

  However, in the steel strip temper rolling method disclosed in Patent Document 1, it is necessary to manage the temperature of all steel strips subjected to temper rolling. This management is not only complicated, but also temperature management. Equipment and systems are needed. Further, in order to perform warm rolling, when the temperature distribution is generated in the width direction of the steel strip, the deformation resistance is different in the width direction, which may affect the shape after rolling. Furthermore, if the flatness is flattened in a state where the temperature distribution exists, after cooling to room temperature, variation in shape occurs due to a heat shrinkage difference caused by the temperature distribution. In addition, since the hot steel strip is rolled, there is also a problem that the shape of the work roll becomes difficult due to thermal expansion of the work roll as the rolling length increases.

  Moreover, in the manufacturing method of the steel strip currently disclosed by the said patent document 2, although roll surface average roughness Ra is provided with the work roll of the range of 3.0 micrometers or more and 10.0 micrometers or less, as rolling distance progresses, There is a problem that the surface roughness of the work roll is reduced due to wear, and the surface roughness for securing the shape correction ability and the anti-scoring property due to the intended load reducing effect cannot be maintained. In order to cope with the decrease in the surface roughness of the work roll, it is necessary to frequently replace the work roll, which causes a problem that the operation efficiency is lowered.

  The present invention has been conceived to solve the above-mentioned problems, and does not require large-scale equipment and complicated management for temperature control even for a high-strength steel strip, and is temper rolled. Providing a temper rolling mill and a temper rolling method capable of providing a steel strip with excellent flatness, which can impart sufficient elongation to the steel strip without increasing the load on the rolling mill sometimes. The task is to do.

Means of the present invention are as follows.
[1] A temper rolling mill characterized in that the Young's modulus of the surface layer portion of the work roll is 500 GPa or more and the Vickers hardness is 1050 HV or more.
[2] The temper rolling mill according to [1], wherein the work roll includes tungsten carbide (WC) and cobalt (Co).
[3] The temper rolling mill according to [1] or [2], wherein the work roll has a roll diameter of 300 mm to 700 mm.
[4] Temper rolling using the temper rolling mill according to any one of [1] to [3], wherein an elongation of 0.2% or more is imparted to the steel strip. Method.
[5] The temper rolling method according to [4], wherein the steel strip having a tensile strength of 980 MPa or more is temper-rolled.

  According to the present invention, even when a high-strength steel strip is rolled, the elongation necessary for shape correction can be imparted to the steel strip while preventing an increase in rolling load applied to the work roll.

FIG. 1 is an explanatory diagram of a temper rolling method. FIG. 2 is a graph showing the results of the examples. FIG. 3 is a graph showing the results of another example.

  First, temper rolling will be described with reference to FIG.

  In temper rolling, the steel strip 1 is passed between a pair of work rolls 2a and 2b and subjected to light reduction. Thereby, shape correction is made so that the steel strip 1 becomes flat. Further, before passing the steel strip 1 through the work rolls 2a and 2b, temper rolling oil may be applied to the front and back surfaces of the steel strip 1 from the nozzles 3a and 3b.

  A temper rolling mill (not shown) holds the work rolls 2a and 2b, adjusts the gap between the work rolls 2a and 2b, and adjusts the load applied to the steel strip 1. Although not shown, the temper rolling mill may be provided with a backup roll that supports the work rolls 2a and 2b.

  The steel strip 1 is rolled down by the work rolls 2a and 2b while being tensioned by payoff reels and tension reels (both not shown) located before and after the temper rolling mill. Thereby, the steel strip 1 extends in the longitudinal direction, and the shape is corrected so that the steel strip 1 becomes flat. The ratio of the elongation in the longitudinal direction of the steel strip before and after temper rolling to the longitudinal length of the steel strip before temper rolling is generally referred to as elongation. The surface property of the steel strip 1 is more easily corrected as the elongation rate is increased. On the other hand, in order to increase the elongation rate, it is necessary to apply a strong rolling load by the work rolls 2a and 2b.

  When rolling down the steel strip 1, the work rolls 2a and 2b are deformed into a flat shape. The greater the degree of deformation of the work rolls 2a, 2b, the longer the length of the contact portion (contact arc length) between the steel strip 1 and the work rolls 2a, 2b. When the contact arc length increases, the force per unit area applied to the steel strip 1 from the work rolls 2a and 2b becomes small, and it becomes necessary to apply a larger rolling load to give the steel strip 1 the necessary elongation.

  The temper rolling mill is usually set with an upper limit rolling load value (limit value) that can be tolerated. When performing temper rolling, it is necessary to perform rolling within the range of the limit value. Specifically, the limit value of the temper rolling mill itself may be used, and a lower limit value may be used in consideration of the safety factor of the roll bender of the temper rolling mill.

  In particular, when temper-rolling a high-strength steel strip, the deformation resistance of the steel strip itself is large, and it is necessary to apply a great rolling load in order to provide the elongation necessary for shape correction. In this case, since the rolling load applied to the work rolls 2a and 2b is also large, the limit value of the temper rolling mill tends to be exceeded. In other words, there is a problem that the shape correction of the high-strength steel strip cannot be sufficiently performed only by performing temper rolling within the limit value of the temper rolling mill.

  In the present invention, as the work rolls 2a and 2b, cemented carbide rolls having extremely high surface layer hardness are used. More specifically, the cemented carbide roll has a Young's modulus of 500 GPa or more and a Vickers hardness of 1050 HV or more. When the Young's modulus is 500 GPa or more, the work rolls 2a and 2b are deformed into a flat shape when the high strength steel sheet is temper-rolled, and the work rolls 2a and 2b are in contact with the steel strip 1 in the roll bite. It is possible to prevent the arc length from becoming large and prevent an excessive rolling load from being applied to the work rolls 2a and 2b.

  Moreover, as above-mentioned, the work rolls 2a and 2b have the Vickers hardness of the surface layer part of 1050 HV or more. Thereby, even if it rolls repeatedly, the surface is hard to be worn out and the replacement frequency of a work roll can be decreased compared with the conventional temper rolling mill. Therefore, the operation efficiency of equipment can be further increased.

  The work roll includes a shaft portion attached to the chock and a body portion provided around the shaft portion and in contact with the steel strip. In the cemented carbide roll used by this invention, the surface layer part containing the surface of a trunk | drum should just be equipped with the above-mentioned Young's modulus and Vickers hardness. Usually, the work roll used by this invention is produced by spraying the material for thermal spray coating (for example, WC type | system | group cermet etc.) on the surface of the base material of a trunk | drum. In order to impart the aforementioned Young's modulus and Vickers hardness to the surface layer portion of the work roll, a sprayed coating of about 20 μm or more and 500 μm or less may be formed on the surface of the work roll. Similarly, the surface layer portion of the work roll having the above-described Young's modulus, Vickers hardness and the like may be in the range of about 20 μm to 500 μm from the surface of the work roll. In addition, a conventionally well-known material can be used for the base material of a trunk | drum.

  Examples of the main component of the surface layer portion (spray coating) of the cemented carbide roll include tungsten carbide (WC) and cobalt (Co). As the WC increases, the hardness increases. In order to realize the above-described hardness, it is desirable that WC is included in an amount of 85% by weight or more.

  Co has a function as a binder for WC, and the content can be adjusted as appropriate. In addition to Co, Ni, Cr, or the like can also be used as a binder for WC.

  If the diameter of the work roll is too small, there is a problem that the work roll is deformed by a load during rolling. If the diameter is too large, there is a problem that a load related to the work roll is excessive during rolling. In view of such points, the diameter of the work roll is preferably 300 mm or more and 700 mm or less. In addition, the diameter of a work roll is the length of the diameter in a cross section, Comprising: The length containing the said surface layer part is said.

  The arithmetic average roughness of the surface of the work roll (hereinafter sometimes simply referred to as “surface roughness”) is not particularly limited, but increases the surface gloss of the high-strength cold-rolled steel strip that is the main rolling target. From this point of view, the surface of the work roll is preferably a bright finish with high smoothness, and the surface roughness is more preferably 0.1 μm or more and 0.8 μm or less.

  Next, a temper rolling method using the temper rolling mill according to the present invention will be described.

  The temper rolling method of the present invention is particularly effective when applied to a high-strength cold-rolled steel strip. When rolling a high-strength cold-rolled steel strip using a conventional temper rolling mill, sufficient elongation cannot be added to the steel strip due to the flatness of the work roll, and within the limits of the temper rolling mill. Although there is a problem that the steel sheet cannot be sufficiently corrected, the present invention can sufficiently correct even a high-strength cold-rolled steel strip. Examples of the high-strength cold-rolled steel strip include a steel strip having a strength of 980 MPa or more. The upper limit of the strength is not particularly limited, and shape correction can be performed even with a steel strip having a strength of 1470 MPa or higher.

  The elongation applied to the steel strip is preferably 0.2% or more. When the elongation is 0.2% or more, even if it is a high-strength cold-rolled steel strip, shape correction can be sufficiently performed, and the front and back surfaces of the steel strip can be made sufficiently smooth. In addition, considering that the rolling load applied to the work roll (and temper rolling mill) is a size that the temper rolling mill can withstand (particularly within the limit value considering the safety factor of the roll vendor), The elongation applied to the steel strip is preferably 0.5% or less.

(Invention Example 1, Comparative Example 1)
A steel strip was passed through an experimental rolling mill, and the rolling load applied to the work roll was measured under a predetermined reduction rate. The outer diameter of the work roll of the rolling mill was 500 mm, and the surface roughness of the work roll was unified by a bright finish of 0.2 μm. As a material of the work roll, SUJ2 (Comparative Example 1) having a Young's modulus of 210 GPa and Vickers hardness of 550 HV, and a cemented carbide roll having a Young's modulus of 550 GPa and Vickers hardness of 1050 HV (invention example) Two types 1) and 2) were used. In addition, as the through plate material, there are three types: a high strength cold-rolled steel strip having a TS of about 1470 MPa, a high-strength cold-rolled steel strip having a TS of about 1180 MPa, and SPCC-SB (ordinary material) having a TS of about 300 MPa. Were used respectively.

  When rolling with the same rolling reduction using a carbide roll and SUJ2 roll, when using a carbide roll against the rolling load applied to the work roll when using the SUJ2 roll (comparative example) (Example) The ratio of the reduced rolling load was calculated. The results are shown in FIG.

When rolling a high-strength cold-rolled steel strip with a TS of 1470 MPa and 1180 MPa, a remarkable rolling load can be obtained by using a cemented carbide roll (example of the present invention) even in a light rolling region where the rolling reduction is within 5%. A reduction effect was seen. Thereby, even when rolling a high-strength steel strip on light reduction conditions, it was shown that the rolling load concerning a work roll can be reduced greatly by using a cemented carbide roll. Moreover, even when rolling SPCC-SB (normal material), the rolling load reduction effect by using a cemented carbide roll (example of the present invention) was observed.
(Invention Example 2, Comparative Example 2)
Next, the high-strength cold-rolled steel strip having a TS of 1180 MPa after cold rolling was tempered by passing it through a temper rolling mill. As a work roll of the temper rolling mill, the same carbide roll (invention example) as used in the above-mentioned invention example 1, the above-mentioned comparative example 1 having a dull finish with a surface roughness of 2.0 μm. The same SUJ2 roll (comparative example) as used, and the same SUJ2 roll (comparative example) as used in the above-mentioned comparative example 1 having a bright finish with a surface roughness of 0.2 μm were used. About the comparative example, the rolling load was applied to 1000tonf / m which is the limit value of temper rolling mill itself, the elongation rate of the steel plate was measured, and the surface shape was evaluated. Moreover, about the example of this invention, it rolled on the conditions of the rolling load 700tonf / m, and measured the elongation rate and evaluated the surface shape similarly. Incidentally, the rolling load (700 tonf / m) in the present invention is smaller than the limit load (about 800 tonf / m) in consideration of the safety factor of the roll bender of the temper rolling mill, and there is a margin for the restrictions on the equipment. I confirmed that there was. The results are shown in Table 1 below.

  As described above, in the comparative example (example using SUJ2 roll), it is not possible to apply a rolling load to a high-strength cold-rolled steel strip having a tensile strength of 1180 MPa up to an elongation rate capable of straightening the shape. Correction was not performed sufficiently and the surface properties remained poor. On the other hand, in the example of the present invention (example using a cemented carbide roll), the elongation rate capable of shape correction can be imparted to the steel strip, the shape correction can be sufficiently performed, and the surface properties are good.

  In addition, FIG. 3 is a graph in which the same experiment was performed a plurality of times under different conditions, and the trends of elongation and rolling load were summarized in a graph. In addition, about the carbide | carbonized_material roll, in addition to the example whose surface roughness is 0.2 micrometer, it experimented by changing elongation rate also about the example whose surface roughness is 0.8 micrometer. In the comparative example (example using SUJ2), when trying to give the steel strip a shape straightening elongation (about 0.2%), the limit load (about 1000 ton / m) of the temper rolling mill, The rolling load exceeding the limit load (about 800 tonf / m) considering the safety factor is applied. On the other hand, in the example of the present invention (carbide roll), even when the elongation rate (about 0.2%) capable of shape correction is given to the steel strip, the surface roughness of the work roll is approximately 0.8 μm. The rolling load can be suppressed within the mill limit load (about 1000 ton / m). Further, under the condition that the surface roughness of the work roll is 0.2 μm, the rolling load can be suppressed within a limit load (about 800 tonf / m) in consideration of the safety factor of the roll bender.

1 Steel strip 2a, 2b Work roll 3a, 3b Nozzle

Claims (4)

A temper rolling mill for temper rolling a steel strip having a tensile strength of 980 MPa or more,
The work roll is a thermal spray roll having a thermal spray coating on the surface of the body part,
The roll diameter of the work roll is 300 mm or more and 700 mm or less,
The thickness of the sprayed coating is 20 μm or more and 500 μm or less,
The Young's modulus of the surface layer portion of the work rolls is at least 500 GPa, and the Vickers hardness of Ri der than 1050HV,
The temper rolling machine arithmetic average roughness Ra of the surface of the work rolls, characterized in der Rukoto than 0.8μm or less 0.1 [mu] m. The temper rolling mill according to claim 1 , wherein the surface layer portion of the work roll includes tungsten carbide (WC) and cobalt (Co). A temper rolling method characterized by using the temper rolling machine according to claim 1 or 2 to give an elongation of 0.2% or more and 0.5% or less to a steel strip. The temper rolling method according to claim 3 , wherein the steel strip having a tensile strength of 980 MPa or more is temper-rolled.

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