JP6089831B2 - Method for producing a differential thickness steel plate having a symmetrical thickness difference in the plate width direction - Google Patents

Description

  The present invention relates to a manufacturing method capable of efficiently rolling a differential thickness steel plate having a symmetrical plate thickness difference in the plate width direction.

  In recent years, weight reduction has been promoted in order to improve the fuel efficiency of automobiles. Specific methods for weight reduction include changing the steel grade of the member to a thinner and higher strength, changing to a lighter specific aluminum alloy or magnesium alloy, and the thickness distribution of the member. There is a method of giving to the limit where acceptable performance can be secured.

Among the methods described above, a steel plate in which a thickness distribution is given to a member is generally called a differential thickness steel plate.
The difference thickness steel plate is, for example, a material having a length of about 1000 to 2000 mm and a width of about 300 to 600 mm, a concave type with a plate thickness of 2 mm from both ends to 300 mm and a center thickness of 1.6 mm (plate Thickness difference 2 level symmetric type), conversely in the longitudinal direction from 300 mm to both ends, the plate thickness is 1.8 mm and the central part is 2.0 mm thick (plate thickness difference 2 level symmetric type), etc. There are various types depending on the application, such as those in which the plate thickness is changed to a taper shape, and those in which the plate thickness difference is multi-level symmetrical and asymmetrical.

  Among the differential thickness steel plates, a differential thickness steel plate having a plate thickness difference in the longitudinal direction is manufactured by operating a roll gap (operating a reduction position) during rolling using a rolling mill (for example, Patent Document 1).

Moreover, as a manufacturing method of the differential thickness steel plate having a plate thickness difference in the plate width direction, a method of manufacturing with a hot tandem rolling mill is disclosed in, for example, Patent Document 2, but in this way the plate in the plate width direction is disclosed. Since camber is generated when the thickness distribution is asymmetric, batch rolling cannot roll from the coil tip, the coil tip is wound on a take-up reel, and the material before and after the material to be rolled is rewound and wound up. After being constrained by the above, there is a restriction that the work roll must be manufactured by being tilted or manufactured by being continuously rolled and tilted from the coil joint.
Since the former has a distance of several tens of meters from the final stand to the take-up roll, the yield drop is large, and the latter requires a device for joining the hot coil upstream to make it continuous, resulting in an increase in equipment cost. .

JP-A-3-281010 JP-A-4-84607

The method of manufacturing a differential thickness steel plate using a rolling mill as described above is referred to herein as a differential thickness steel plate manufacturing method by a rolling method.
In the method of manufacturing a differential thickness steel sheet by the rolling method, in the method of changing the rolling thickness in the longitudinal direction of rolling, the different lengths of the thickness part of the differential thickness steel sheet are generally short, so It is difficult to measure and control the roll gap to produce a desired differential thickness steel plate due to the effect of dead time due to the distance from the roll bite outlet to the plate thickness measuring instrument. In addition, the inlet side plate thickness and the inlet side velocity and outlet side velocity are detected, and the plate thickness on the outlet side of the rolling mill is estimated using a constant mass flow rule. The roll gap is controlled based on this value, and the desired differential thickness steel plate is obtained. Manufacturing has problems such as the effect of tracking accuracy and widening, and the increase in equipment cost due to the installation of the plate thickness and plate speed detectors.

  Therefore, by conducting an experiment in advance, the relationship between the roll gap (rolling position) and the outlet side plate thickness is obtained, the number of rotations of the work roll is obtained with high accuracy, the rolling length is estimated, and based on the estimated rolling length, A method of controlling the roll gap so as to obtain a desired plate thickness (preset rolling method) is common.

  Instead of the preset rolling method described above, experiments are performed in advance to determine the deformation characteristics of the rolling mill, the rolling load at the time of rolling is measured, and the sheet thickness at the roll bite outlet is estimated from the deformation characteristics of the rolling mill and the measured rolling load. There is also a method (absolute value rolling method) for controlling the roll gap so as to obtain a desired plate thickness based on the estimated rolling length described above.

In these preset rolling methods and absolute value rolling methods, the material is a cold-rolled annealing material, a hot-rolled pickling material, or a hot-rolled material, and the temperature is rolled at room temperature. In order to increase the productivity of the rolling method (to increase the production speed), a highly responsive roll gap control is necessary. Therefore, a highly responsive hydraulic reduction device is essential, but the hydraulic reduction device is expensive. The equipment cost becomes high, causing the problem of increasing the manufacturing cost.
Since these rolling methods are rolled with a slit material having a plate width of about 300 to 600 mm, they are suitable for the production of a small variety of products. ), There was a demand to manufacture the above-mentioned large quantity and small variety of differential thickness steel sheets at low cost.

  In addition, the difference thickness steel plate manufactured by the rolling method in which the rolling thickness is changed in the longitudinal direction of rolling has a different rolling reduction for each portion in the rolling direction. In order to eliminate the variation in the material, heat treatment is performed as necessary, and the surface is plated as necessary. Thereafter, press molding or hot press molding is performed to produce a member for an automobile.

  On the other hand, the present invention aims to provide a manufacturing method of a differential thickness steel plate capable of manufacturing a differential thickness steel plate having a thickness difference in the plate width direction, It is possible to manufacture at a low cost.

  In order to achieve the above-mentioned object, the present inventors have conducted intensive research and provided a roll profile corresponding to the product size distribution in the width direction of the work roll, without controlling the roll gap in the longitudinal direction, and By carrying out hot rolling, the difference thickness steel plate having a desired thickness difference in the width direction can be efficiently obtained with little variation in material in the longitudinal direction, with little manipulation of the reduction position. We have found a method that can produce steel sheets.

The present invention based on the above findings
(1) at least in the final stand of the hot tandem mill, the rolling mill of the final stand, a 4-high rolling mill comprising a pair of work rolls and a pair of backup rolls, the strip towards one of the upper and lower work rolls, barrel length a profile of the left right symmetrical directions, there are concave step in the profile, the roll profile between the step and between the step and the roll end adopted grooved work rolls is linear, the grooved work rolls The manufacturing method of the difference thickness steel plate which has the plate | board width direction symmetrical in the sheet | seat width direction characterized by employ | adopting and rolling the backup roll which gave the profile and reverse profile .
(2) In the method for manufacturing a tailor welded blank having a plate thickness difference symmetric according to the above (1), the material to be rolled after rolling, by cutting in the rolling direction and / or the plate width direction, of the asymmetrical A method for producing a differential thickness steel plate having a symmetrical thickness difference, characterized in that the product is a rolled product.
It is.

  According to the present invention, a difference thickness steel plate product having a symmetric plate thickness difference of a large quantity and a small variety, or a difference thickness steel plate product having an asymmetric plate thickness of a width capable of arranging two or more in the width direction of the material to be rolled. Can be provided at a low cost.

It is a side view of the example of the rolling apparatus used for the manufacturing method of this invention. It is a figure which shows an example of the roll set of the 4-high rolling mill which comprises the backup roll provided with the profile corresponding to a work roll profile, and a differential pressure steel plate manufactured with this rolling mill.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present specification and drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

FIG. 1 is a side view showing an example of a rolling apparatus used in the production method of the present invention.
In FIG. 1, the slab 2 is heated in the heating furnace 1, and the heated slab is moved to the roughing mill 3 and thinly rolled into a sheet shape. This sheet S is rolled to a desired thickness by a hot tandem rolling mill consisting of seven rolling mills as the finish rolling mill 4, passes through a runout table 5 that also serves as cooling, and is wound in a coil shape by a winder 6. .

  The finish rolling mills are all four-high rolling mills, and are composed of a pair of work rolls and a pair of backup rolls. Although not shown, an electric reduction device for adjusting a pass line is provided above the upper backup roll chock, and a hydraulic reduction device is provided below the lower backup roll roll chock. Although not shown, a load cell is provided on the upper chock of the upper backup roll, and the rolling load is measured.

Furthermore, as shown in FIG. 2, the work roll 11 of strip side of the final stand of the finishing mill, the roll profile is applied which corresponds to the product size distribution of tailor welded blank in a plate width direction. Although not shown in the drawing, a thickness gauge for measuring the thickness of the rolled metal strip is installed on the exit side of the finish rolling mill, and the measured thickness value from the thickness gauge and a preset target thickness value are provided. The roll gap is controlled by the hydraulic pressure reducing device according to the deviation.

  Although not shown, a thermometer for measuring the temperature of the metal strip is installed downstream of the runout table 5 for cooling the metal strip after rolling, and the temperature measurement value from the thermometer and the preset plate temperature The cooling condition (for example, flow rate) is controlled by the cooling device according to the deviation from the standard value.

  Although not shown, low concentration rolling lubricant (from the main tank to the rolling mill entry side so as to facilitate lubrication and wear reduction of the work roll and metal flow of the metal strip to the hole work roll is facilitated. Emulsion lubricating oil) is supplied to the roll bite entrance and the roll surface with coolant (emulsion rolling lubricating oil) for cooling the work roll on the exit side of the rolling mill. Although not shown, the emulsion lubricant is collected in a lubricant recovery layer provided at the lower part of the rolling mill and returned to the main tank.

Search experiments were conducted using the apparatus shown in FIGS.
The slab 2 is a material having a tensile strength of 600 MPa called 60 kg high tension, a plate thickness of 250 mm, a plate width of 1600 mm, and a length of 5 m. This slab is finished into a sheet S having a thickness of 50 mm by rough rolling. The work roll 11 of the rolling mill of the final stand of the finish rolling mill has a diameter of 600 mm and a cylinder length of 2000 mm, and the backup roll 12 has a diameter of 1500 mm and a cylinder length of 2000 mm.

  As shown in the lower part of FIG. 2, the target thickness of the differential thickness steel plate is 1600 mm in total length and 300 mm (tolerance 0 to ± 50) mm inside from both ends, with a plate thickness of 1.85 mm and other 1000 mm (tolerance 0 to 0). −20 mm) is a left-right symmetrical difference thickness steel plate having a plate thickness of 400 mm and a convex thickness of 2.90 mm.

  A sheet with a plate width of 1600 mm, with a metal strip temperature of 700 ° C. on the final stand entrance side, from the entry side plate thickness of 3.06 mm to 300 (tolerance 0 to +50) mm inside from both ends, the plate thickness of 1.85 mm, other The central portion 1000 (tolerance 0 to 20) mm is a convex differential pressure steel plate having a plate thickness of 2.90 mm and a width of 400 mm.

As shown in the upper part of FIG. 2, the upper work roll 11 of the final stand was processed so as to match the profile of the differential pressure steel sheet.
That is, in the roll body length direction, the roll center part 1000 mm was processed into a concave roll profile that was 1.05 mm smaller per radius than the roll end part. Using this roll, the roll gap was adjusted and rolled so that the thickness of the central portion of the differential pressure steel sheet became a target value.

  Therefore, the roll radius in the plate width direction is based on the thin portion of the differential thickness steel plate, and the portion corresponding to the thick thickness portion of the differential thickness steel plate (that is, 500 mm on one side from the roll body length center, 1000 mm in total) is the standard roll radius. About 1.05 mm smaller than that. Further, the boundary portions having different diameter differences are processed to be tapered to some extent.

In this way, initial processing is performed, a rolling experiment is performed, and the diameter difference is finely adjusted based on the data after rolling.
The work roll 11 used at this time is schematically shown in the upper part of FIG.

  When rolling the differential pressure steel sheet shown in the lower part of FIG. 2, the width of the central portion of 2.90 mm is 1000 mm, whereas the width of the 1.85 mm thick portion on both sides is the sum of the left and right sides. However, since the thickness is 600 mm, a rolling method in which the work roll 11 is supported by the backup roll 12 in a portion having a thickness of 2.90 mm at the center and a plate width of 1000 mm is preferable in terms of Hertz pressure reduction and stable operation.

(Example)
Using the apparatus shown in FIG. 1, a differential thickness steel sheet having a thickness difference in the longitudinal direction was manufactured. The material and the like are the same as the conditions for manufacturing the above-described sample of the differential thickness steel sheet, and the dimensions of the differential thickness steel sheet having a thickness difference in the longitudinal direction manufactured in the present invention are also the same as the above-described conditions.

  In the examples of the present invention, rolling was performed by controlling the reduction position so that the thickness of the central portion was 2.90 mm with the thickness gauge on the delivery side of the rolling mill.

  As a conventional technique, using a single-stand four-high rolling mill on a separate line, using a work roll that is flat on both top and bottom, a metal strip having a plate width of 400 mm is obtained in advance through a rolling experiment (rolling position) and a plate. Using the thickness relationship, the rolling length is estimated from the rotation speed of the work roll, the target value of the thickness of the differential thickness steel sheet is given based on the estimated value, and the roll of the rolling mill is adjusted so that the target value of the thickness is reached. Control the gap.

  In the case of the present invention, the rolling length is estimated from the rotation speed of the work roll described above in the prior art, and a target value for the thickness of the differential thickness steel sheet is given based on the estimated value so that the target value of the thickness is obtained. Since there is no need to control the roll gap of the rolling mill, the equipment cost can be reduced. Further, since the sheet widths are different even at the same rolling speed, the productivity of the present invention is about four times that of the prior art. Furthermore, variations in quality (hardness) can be reduced.

  In the examples of the present invention, the above-described differential thickness steel plates could be manufactured at a rolling speed of 1000 m / min within a plate thickness accuracy of ± 10%, and the quality (hardness) variation was also within 5%. Also according to the prior art, it was possible to manufacture the above-described difference thickness steel plate within a plate thickness accuracy of ± 10%.

In addition, when a plurality of differential thickness steel plate products P are arranged on the left and right sides to form a bilaterally symmetric plate thickness distribution, the finished product should be divided into individual rolled products in the longitudinal direction after rolling. Can do. For example, if the differential pressure steel sheet P produced in the example shown in FIG. 2 is divided into two from the rolling center line, the thickness of 1.85 mm is 300 mm, the thickness of 2.90 mm is 500 mm, and the total width is 800 mm. Two differential thickness steel plates can be collected in the width direction.

  According to the present invention, a rolled product having a symmetrical thickness distribution can be mass-produced at a high speed and at a low cost. Furthermore, when two or more rolled products can be arranged in the plate width direction, even if the products have a plate thickness distribution that is asymmetrical, the products are arranged symmetrically with respect to the center line in the rolling direction. The material to be rolled can have a symmetrical thickness distribution, and can be rolled while suppressing the occurrence of shape defects in the longitudinal direction such as camber, greatly contributing to the efficiency and productivity of rolling operations. To do.

DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Slab 3 Rough rolling mill 4 Finish rolling mill 5 Run-out table 6 Winding machine 11 Work roll 12 Backup roll S Sheet P Difference thickness steel plate

Claims (2)

Left at least the final stand of the hot tandem mill, the rolling mill of the final stand, a 4-high rolling mill comprising a pair of work rolls and a pair of backup rolls, towards pieces of the upper and lower work rolls, the barrel length direction a profile of the right symmetry, there are concave step in the profile, the roll profile between the step and between the step and the roll end adopted grooved work rolls are straight, the profile of the grooved work rolls A method for producing a differential thickness steel sheet having a symmetrical thickness difference in the sheet width direction, wherein a backup roll provided with a reverse profile is employed and rolled. In the manufacturing method of the difference thickness steel plate which has the left-right symmetric plate | board thickness difference described in Claim 1, the rolling material after rolling is cut | disconnected in a rolling direction and / or a sheet | seat width direction, A method for producing a differential thickness steel sheet having a symmetrical thickness difference, characterized by:

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