JP3348974B2 - Continuous heat treatment method for metal strip - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously heat-treating a metal strip, which is electrically heated to continuously heat-treat the metal strip, such as continuous annealing of a thin steel sheet.

[0002]

2. Description of the Related Art As a heating method for continuously heat-treating a metal strip such as a cold-rolled steel sheet, as described in JP-B-60-26818, a current is directly applied to the metal strip via an energizing roll. There is a method of heating by the Joule heat of the metal strip itself. Further, as described in JP-A-1-142032 and JP-A-1-187789, energizing rolls are provided before and after a metal band passage penetrating an annular transformer, and both energizing rolls are connected by a conductive member. Forming a closed circuit by the metal band, the conducting roll and the conductive member, and applying an alternating current from an external power supply to the annular transformer to generate an induced current using the closed circuit as a secondary coil. There is a method of heating a metal strip with heat.

[0003] A method of passing an electric current directly to these metal strips and heating with Joule heat includes direct-fired non-oxidative heating, radiant tube heating, and the like.
Compared to heating by heat transfer such as indirect electric heating, the heating capacity per unit time is high, the equipment can be made compact, and the heat response is very good, so heating control is easy. Are better.

[0004]

In each of the above-mentioned electric heating methods, electric current is applied to the metal strip via an electric current roll. And
The energizing roll must be in contact with the metal strip at the end on the heating start side and the end on the end side of the metal strip to energize it.However, to prevent sparking, the metal strip is sandwiched between the energizing roll and the holding roll, and Inevitably. For this reason, there is a problem that a shape defect occurs due to meandering of the metal band in the vicinity of the energizing roll and rapid cooling due to contact between the high-temperature metal band and the energizing roll at the end on the heating end side. In particular, a thin steel sheet having a thickness of 0.5 mm or less as a metal band is subjected to an annealing temperature of 600 to 90.
Shape defects are remarkable, such as in the case of continuous annealing at 0 ° C.

[0005] By the way, a metal strip to be heat-treated for annealing may have a shape defect such as an ear wave or a middle elongation in an earlier step. When a metal strip having a defective shape is sandwiched and passed between an energizing roll and a holding roll, the metal strip meanders, and the shape defect may become more severe, or the metal strip may be broken.

In order to prevent the metal band from meandering, for example, Japanese Patent Application Laid-Open No. Sho 62-67122 discloses a method in which a metal band is previously flattened at the entrance side of a vertical continuous annealing furnace and then annealed. ing. Also, Japanese Patent Application No. 4-304451 describes a method in which the above-mentioned energization heating is performed after reducing the metal band by 0.1 to 2%.

However, each of the above-mentioned methods is a method of annealing after shape correction, and requires a shape correction device separately from the annealing device.

[0008] Further, regarding a shape defect in which a rectangular vertical streak is generated in the traveling direction of a metal strip due to energization heating, Japanese Patent Application No. Hei.
In the specification of No. 101808, it is stated that a defective shape can be prevented by defining the amount of temperature drop of the metal strip due to the heat transfer in contact with the energizing roll.

[0009] However, it has become clear that in the continuous annealing of a thin steel sheet, as the width of the steel sheet increases, the shape defect cannot be prevented only by preventing the quenching of the steel sheet. The cause of shape failure is
Not only quenching of the steel sheet, but also rapid heating while holding both ends of the steel sheet in the heating device, compressive stress caused by restraining the thermal expansion of the steel sheet is applied to the steel sheet, and this is caused by the high temperature side energizing roll It is presumed that the residual stress is generated when passing through the roll, and is released after passing through the high-temperature side energizing roll portion.

[0010] As described above, the conventional methods cannot cope with all of the shape defects that occur with energizing heating of the metal strip. Therefore, the present invention provides a continuous heat treatment method that can correct a shape defect without requiring a separate shape correction device and can also prevent the occurrence of a shape defect due to electric heating.

[0011]

SUMMARY OF THE INVENTION The present invention provides a low-temperature side
When a current is passed through the metal strip through a current-carrying roll composed of a metal pair and a high-temperature side current-carrying roll pair, when the metal strip is energized and heated by Joule heat, the occurrence of shape defects due to the energized heating of the metal strip occurs. so as to prevent, in a continuous heat treatment method for stretching the metal strip, pressure metal strip at high temperature current-carrying roll portion
A downward force and a tension are applied, and the stretching amount of the metal band is set to 0.1 to 1
This is a method for continuously heat-treating a metal strip, which is set to 0%. Preferably, the tension of the metal band at the high-temperature side energizing roll is set to a maximum of 7 kg / mm ² or less, and the tension UT
(Kg / mm ²⁾ the heating temperature T yield stress of the metal band at _{(℃) σ y (T)} (kg / mm 2) and the equation (1)
The film is stretched by a tension satisfying the expression (2).

[0012]

## EQU2 ## 0.5σ _y (T) ≦ UT ≦ 2.5σ _y (T) (1)

[0013]

According to the present invention, in the method of conducting continuous heat treatment by heating the metal strip by applying electric current, the metal strip is energized and heated by stretching the metal strip by 0.1 to 10% on the high-temperature side energizing roll on the heating end side of the electric heating. At the same time as correcting the shape defect of the metal strip, it is also possible to prevent the occurrence of a shape defect due to electric heating. That is, as shown in FIG.
When the metal strip 1 is heated by the Joule heat of the metal strip 1 itself and the metal strip 1 is heated through the hot roll 3, the metal strip 1 is heated while being stretched.

Shape defects such as ear waves and middle elongation that occurred before the heat treatment can be easily corrected by uniformly stretching the metal band 1. In addition, the residual stress in the metal band 1 which causes the shape defect due to the electric heating is also released by stretching the metal band 1 in one direction while being held and constrained by the metal band 1 sandwiched between the energizing roll and the holding roll. , Can be prevented.

FIG. 2 shows a metal strip 1 having a thickness of 0.15 to 0.15 mm.
A 0.05% C-containing aluminum-killed steel sheet having a width of 0.24 mm and a width of 900 mm was measured for the amount of elongation of the steel sheet after electric heating by changing the sheet temperature, tension and rolling force using the electric heating apparatus shown in FIG. It is an example of a result. As described above, the amount of stretching of the metal band 1 can be controlled by adjusting the tension of the metal band 1 and the roll rolling force.

However, when the metal band 1 is stretched under a strong pressure, local elongation such as ear waves or middle elongation is likely to occur. Rather, controlling the amount of stretching with the tension on the metal strip 1 after securing the minimum rolling force that can prevent sparking allows the metal strip 1 to be stretched uniformly over the entire sheet width, It is more effective because it is easy to pass through.

FIG. 3 shows an example of the result of measuring the amount of stretching of the steel sheet by changing the tension and temperature of the steel sheet while keeping the roll rolling force constant at 2.0 kg / mm in the same manner as in FIG.
FIG. 3 shows that the amount of elongation of the steel sheet greatly changes according to changes in the tension and temperature of the steel sheet. That is, it is understood that the shape of the steel sheet can be controlled by selecting an appropriate value for the tension according to the physical properties of the material to be heated.

Therefore, the results of heating the ultra-low carbon steel sheet containing 0.002% C having different physical properties by the same method as in FIG. 2 and observing the shape of the steel sheet are shown in FIG. It was shown to. From this figure, a tension range for obtaining a good steel plate shape can be obtained. That is, the amount by which the metal strip is stretched by the tension depends on the yield stress of the metal strip, and the yield stress of the metal strip greatly depends on the temperature and composition of the metal strip. Assuming that the yield stress of the metal strip is σ _y (T) (kg / mm ² ), if the tension of the metal band is set to 0.5 × σ _y (T) or more, in particular, a thin steel sheet having a thickness of 0.5 mm or less is 600 to 900
Even if heated to ° C., a steel sheet having a good shape can be obtained. On the other hand, when the tension of the metal band is set to 2.5 × σ _y (T) or more, excessive elongation occurs, and not only the width shrinkage becomes large, but also in extreme cases, it leads to plate breakage. From the above, the tension range for obtaining a steel sheet having a good shape shown by the relational expression (1) was obtained.
In particular, when passing a thin steel sheet, the tension is 7 kg / mm.
^If it exceeds ² , the buckling is likely to occur at a portion other than the heating device, for example, a deflector roll or a tension reel portion. Therefore, the maximum tension is set to 7 kg / mm ² or less.

As a result, simultaneous processing of annealing and shape correction can be performed. If the elongation is less than 0.1%, the effect of shape correction is not obtained, and if it exceeds 10%, the width of the metal band is reduced, and the dimensional accuracy is deteriorated.
And

[0020]

Example 1 Using the current-carrying heating apparatus shown in FIG. 1, a 0.20 t × 0.05% C-containing ear wave having a steepness of 1.0% was used.
850w aluminum killed steel sheet is subjected to a rolling force of 2.5 kg / mm and a tension of 2 kg / mm ² with three portions of a high-temperature side energizing roll,
It was electrically heated to 50 ° C. VT on the exit side of the hot roll 3
An R camera 6 was provided, and the amount of stretching of the steel sheet was measured while observing the steel sheet shape with the VTR camera 6. As a result, the steel sheet was stretched by 0.3%, and not only the shape of the ear wave before heating was corrected, but also a shape defect due to the electric heating did not occur, and a steel sheet having a good shape was obtained.

[0021]

Embodiment 2 Using the electric heating device shown in FIG.
% C containing 0.20t × 850w aluminum killed steel sheet
A 0.20 t × 850 w ultra-low carbon steel sheet containing 002% C was heated in the same manner as in Example 1. Roll reduction force is 2.0
kg / mm constant, plate temperature both 800 ° C, 3 kg / mm ^{2 for} aluminum-killed steel sheet, and 2.
A tension equal to the yield stress of each steel sheet at 5 kg / mm ² and 800 ° C. was set. As a result, each material was 1.
The sheet was stretched by 7%, and a steel sheet having a good shape was obtained.

[0022]

According to the present invention, the metal strip can be heated and the shape can be corrected at the same time without requiring a separate shape correcting device, and a metal strip having a good shape can be supplied to the subsequent process, and compactness can be achieved. Inexpensive continuous heat treatment becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of an electric heating device for carrying out the present invention.

FIG. 2 is a diagram showing the relationship between the elongation of a metal band and the sheet temperature, tension, and rolling force.

FIG. 3 is a diagram showing the relationship between the elongation of a metal strip and the sheet temperature and tension.

FIG. 4 is a diagram showing a relationship between tension and yield stress of a metal strip.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Metal strip 2 Low temperature side energizing roll 3 High temperature side energizing roll 4 Conductive member 5 Annular transformer 6 VTR camera

Continued on the front page (72) Inventor Masaru Fukuyama 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo Nippon Steel Corporation Inside Hirohata Works (72) Inventor Kazuhiko Sato 1 Fujimachi, Hirohata-ku, Himeji-shi, Hyogo New Nippon Steel (56) References JP-A-58-135725 (JP, A) JP-A-5-54958 (JP, A) JP-A-52-156708 (JP, A) JP-A-5-156358 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C21D 9/62 101 C21D 1/40

Claims (2)

(57) [Claims] 1. A pair of a low-temperature side energizing roll and a high-temperature side energizing roll.
When an electric current is passed through the metal strip through an energizing roll constituted by a pair and the metal strip is energized and heated by Joule heat,
To prevent occurrence of shape defect caused by the electrical heating of the metal strip in a continuous heat treatment method for stretching the metal strip, the hot
A method for continuously heat-treating a metal strip , wherein a rolling force and a tension are applied to the metal strip by a side current-carrying roll portion, and a stretching amount of the metal strip is set to 0.1 to 10%. 2. The metal strip tension at the high-temperature side energizing roll section is set to a maximum of 7 kg / mm ² or less, and the metal strip tension UT (k
g / mm ² ) with the yield stress σ _y (T) (kg / mm ² ) of the metal band at the heating temperature T (° C.).
Contraction characterized by stretching by a tension satisfying
The method for continuous heat treatment of a metal strip according to claim 1 . (1) 0.5σ _y (T) ≦ UT ≦ 2.5σ _y (T) (1)