JP2002294351A - Manufacturing method of high strength cold rolled steel sheet - Google Patents

Abstract

(57) Abstract: An object of the present invention is to provide a method capable of stably producing a high-strength cold-rolled steel sheet having less variation in strength by continuous annealing. A method of manufacturing a high-strength cold-rolled steel sheet using a continuous annealing equipment having a quenching means and a tempering means, comprising: a unit width of a steel sheet to be rolled in a temper rolling mill arranged on an outlet side of the continuous annealing equipment. The relationship between the rolling load P ₀ and the tensile strength TS _{0 of the} steel sheet to be rolled is determined in advance for each sheet thickness, and based on the relationship between the rolling load P ₀ and the tensile strength TS ₀ , the temper rolling is performed. The tensile strength TS ₁ of the rolled steel sheet is calculated from the rolling load P ₁ per unit width of the rolled steel sheet actually measured by the machine, and the steel sheet is adjusted so that the calculated tensile strength TS ₁ becomes a desired tensile strength. A method for producing a high-strength cold-rolled steel sheet, comprising controlling a quenching temperature and / or a tempering temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stably producing a high-strength cold-rolled steel sheet using a continuous annealing facility having a quenching means and a tempering means.

[0002]

BACKGROUND OF THE INVENTION The following description is a cold-rolled steel sheet manufactured using a continuous annealing equipment is a high-strength cold-rolled steel sheet tensile strength of about 50~150kgf / mm ² class.

It is effective to increase the volume ratio of martensite to obtain a high-strength cold-rolled steel sheet, but to achieve this, it is most effective to use a water quenching type continuous annealing facility. . That is, by heating to a ferrite + austenite mixed region or an austenite single-phase region and then water quenching from that temperature, a ferrite + martensite mixed structure or a martensite single-phase structure can be obtained. The higher the value, the higher the volume fraction of martensite and the higher the strength. Further, as the tempering temperature increases, the hardness of martensite decreases, so that the steel sheet strength decreases. By the way, in actual operation, since the fluctuations of the components within the component standard range and the fluctuations of the water temperature of the water quenching tank, which is affected by the outside air temperature and efficiency, affect the steel sheet strength, work is performed with the quenching and tempering temperatures fixed. In such a case, a large amount of mechanical test value deviation (out of tensile strength) may occur or a large difference in strength level may occur.

Japanese Patent Application Laid-Open No. 55-158231 discloses that when a low-alloy, low-carbon steel is rolled and continuously annealed at the A _{1 to} A ₃ transformation point, the material is measured on the exit side of the annealing apparatus, and according to the result, Control one or more of the cooling rate, strip speed, and temperature in the soaking zone, and measure the shape of the steel strip. It is shown that by controlling the strip tension and the elongation of the tension leveler, the variation in the material and the shape can be eliminated and a homogeneous steel sheet can be obtained.

[0005] Japanese Patent Application Laid-Open No. 6-330187 discloses a steel strip provided with an elongation rate by an entrance / exit bridle before and after a skin pass mill or a tension leveler at an exit side of a continuous annealing equipment. And
There is disclosed a method in which the speed of the steel strip is changed based on the change in the tension to control the annealing time at each position in the longitudinal direction of the steel strip to make the material uniform in the longitudinal direction.

[0006]

However, the method disclosed in Japanese Patent Application Laid-Open No. 55-158231 requires on-line control using a grain size meter, a magnetic hardness meter, or the like, so that equipment costs are high. In addition, there are problems that a large number of data serving as a reference of the material to be measured must be provided, and that maintenance of the data is not easy.

Further, even if the annealing time is controlled at a line speed as disclosed in JP-A-6-330187, the steel sheet strength of a high-strength cold-rolled steel sheet determined by the martensite ratio and the martensite hardness is effectively controlled. Can not. Also, Japanese Patent Application Laid-Open No. Hei 6-330187 describes that the control of the sheet temperature by controlling the temperature of the annealing furnace requires time. Since the sheet temperature is controlled mainly by the induction heating device, the responsiveness of the sheet temperature control is excellent.

Further, recently, high-strength steel sheets are often used by customers in press forming into complicated shapes such as car seat frames and center pillar reinforcements. There are cases where the amount of return is different and the product cannot be used as a product, and customer requirements for the strength range are becoming stricter.

It is an object of the present invention to solve the above-mentioned problems of the prior art and to provide a method capable of stably producing a high-strength cold-rolled steel sheet having less variation in strength by continuous annealing. .

[0010]

Means for Solving the Problems The present inventors have conducted continuous annealing.
Stabilizes high-strength cold-rolled steel sheets with less variation in strength
To find a way to manufacture
Was. As a result, from the operating condition data,
Constant elongation of steel sheet and tension of steel sheet before and after temper rolling mill
The unit width of the rolled steel sheet in the temper rolling mill
Rolling load P ₀And tensile strength TS of rolled steel sheet₀Toni Akira
We found that there is a certain correlation. So this
If the relationship is determined in advance for each high-strength cold-rolled steel sheet thickness,
Rolled load per unit width measured by temper rolling mill during operation
Heavy P₁Tensile strength TS of steel sheet during threading based on₁Is calculated
Measured) and the calculated tensile strength TS₁Is the desired tensile strength
Temperature and / or tempering of the steel sheet
Temperature to control the strength of cold-rolled steel sheets.
It can be seen that stable production is possible with little variation.
Was.

The method for producing a high-strength cold-rolled steel sheet according to the present invention has been made based on such knowledge and has the following features.

(1) In a method of manufacturing a high-strength cold-rolled steel sheet using a continuous annealing facility having a quenching means and a tempering means, a unit of a steel sheet to be rolled in a temper rolling mill arranged on an outlet side of the continuous annealing equipment. The relationship between the rolling load P ₀ per width and the tensile strength TS _{0 of the} steel sheet to be rolled is determined in advance for each sheet thickness of the steel sheet, and based on the relationship between the rolling load P ₀ and the tensile strength TS ₀ , the above-described adjustment is performed. actually measured to calculate the tensile strength TS ₁ of the rolled steel sheet from a rolling load P ₁ per unit width of the rolled steel plate in quality rolling mill, as the tensile strength TS ₁ that this is calculated a desired tensile strength A method for producing a high-strength cold-rolled steel sheet, comprising controlling a quenching temperature and / or a tempering temperature of the steel sheet.

(2) The method for producing a high-strength cold-rolled steel sheet according to (1), wherein the quenching means includes a water quenching means.

(3) The above (1) or (2), wherein a lot is formed with the same components in a converter or an electric furnace, and a steel sheet to be rolled is charged into a continuous annealing facility for each lot.
3. The method for producing a high-strength cold-rolled steel sheet according to item 1.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS To obtain a high-strength cold-rolled steel sheet, it is effective to increase the volume ratio of martensite, and to achieve this, it is most preferable to use continuous annealing equipment including water quenching means. Although preferred, as a quenching means, there is generally a method using a gas jet cooling method, a roll cooling method, a steam-water cooling method, or the like, or a combination thereof, in addition to a water quenching method. It is.

FIGS. 1 and 2 show one embodiment of the method for producing a high-strength cold-rolled steel sheet according to the present invention. FIG. 1 shows the inside and outlet side of a continuous annealing facility used for carrying out the present invention. In the explanatory view showing an embodiment of the method of the present invention, the tensile strength of the steel sheet during threading is calculated based on the measured rolling load per unit width of the steel sheet to be rolled by the temper rolling mill, and the calculated tensile strength is calculated. It shows a method of controlling the water quenching temperature and / or tempering temperature of a steel sheet so that the strength becomes a desired tensile strength. FIG. 2 shows an overall view of the continuous annealing equipment used for carrying out the present invention.

Inside the continuous annealing equipment shown in FIG. 1 and on the outlet side, in order from the upstream side of the line, a quenching temperature adjusting blower 4, a quenching temperature measuring plate thermometer 5, and a storage tank 1 containing water.
Water quenching section (WQ) 1 in which a steel sheet temperature is set to 0 and a steel sheet temperature is raised to a predetermined tempering temperature in a short time.
A temper section (OA) 2 in which a steel sheet is installed and a temper rolling mill 3 are arranged, and the temper rolling mill 3 includes a load detector 9 for detecting a rolling load.

The water quenching section 1 is a section for quenching a steel sheet by immersing the steel sheet in a storage tank 10 containing water. The temperature of the steel sheet immediately before water quenching is controlled by a quenching temperature adjusting blower. 4 by controlling the gas jet flow rate. By the cooling using the gas jet, the temperature of the steel sheet immediately before water quenching can be controlled in a short time.

The tempering section 2 tempers the steel sheet that has passed through the water quenching section 1 at a predetermined temperature, and changes the amount of electricity supplied to the induction heating device 8.
The tempering temperature is adjusted by performing one or more of increasing and decreasing the gas amount of the radiant tube 6 and adjusting the air volume of the cooler 7.

The temper rolling mill 3 performs a temper rolling of a quenched and tempered steel sheet, and is a four-high rolling mill (4).
There is one rolling stand constituted by Hi). The temper rolling mill 3 is provided with a load detector 9 for detecting a rolling load. Further, the elongation of the steel sheet by the temper rolling and the tension of the steel sheet before and after the temper rolling mill are kept constant.

In the rolling of the steel sheet in such a temper rolling mill 3, the rolling load P ₀ per unit width of the steel sheet to be rolled.
A correlation as shown in FIG. 3 was found between the steel sheet and the tensile strength TS ₀ of the rolled steel sheet for each sheet thickness of the high-strength cold-rolled steel sheet.
The correlation as shown in FIG. 3 can be obtained in advance for each sheet thickness of the high-strength cold-rolled steel sheet. FIG. 3 shows that in the production of a high-strength cold-rolled steel sheet having a sheet thickness of 1.59 mm, the elongation rate of the steel sheet by temper rolling was constant at 0.7%, and the tension of the steel sheet before and after the temper rolling mill was 8 kgf. / Mm ² , the rolling load P ₀ (tonf / mm) per unit width of the rolled steel sheet of the temper rolling mill 3 and the tensile strength TS ₀ (kgf / mm ² ) of the rolled steel sheet It shows an example of the relationship.

When the method of the present invention is carried out using the above equipment, the load detector 9 of the temper rolling mill 3 detects the rolling load P ₁ per unit width of the steel sheet to be rolled, calculating the tensile strength TS ₁ of the steel plate in the plate passage on the basis of P ₁ in a known relationship shown in FIG. Then, the result is fed back to the water quenching section 1 to control the water quenching temperature to obtain a desired tensile strength of the steel sheet,
Alternatively, the temperature is fed back to the tempering section 2 to control the tempering temperature so as to obtain the desired tensile strength of the steel sheet, or to control both of them.

As described above, the water quenching temperature in the water quenching section 1 is controlled by adjusting the temperature of the steel sheet immediately before water quenching by adjusting the gas jet air volume of the quenching temperature adjusting blower 4 and in the tempering section 2. The tempering temperature is controlled by changing the amount of current supplied to the induction heating device 8.
This is performed by one or more of increasing and decreasing the gas amount of the radiant tube 6 and adjusting the air volume of the cooler 7.

Furthermore, it is preferable to form a lot for each steel tapping component in a converter or an electric furnace in advance and then load the steel sheet to be rolled into a continuous annealing furnace because the accuracy of the material is improved.

[0025]

EXAMPLE Using the continuous annealing equipment shown in FIGS. 1 and 2, C: 0.15%, Si: 0.4%, Mn: 1.2.
%, P: 0.016%, S: 0.004%, and a steel plate having a thickness of 1.59 mm made of other trace elements is continuously annealed,
Temper rolling was performed at an elongation of 0.7%. The continuous annealing equipment out tone is arranged on the side of rolling machine load detector detects a rolling load P ₁ per unit width of the rolled steel sheet, the rolled steel plate showing this rolling load P ₁ in FIG. 3 rolling load P ₀ (tonf / mm) and the tensile strength of the rolled steel plate T per unit width
Based on the relationship with S ₀ (kgf / mm ² ), the tensile strength TS ₁ of the steel sheet being passed is calculated. Then, the result was fed back to the water quenching section 1 to control the water quenching temperature of the steel sheet by adjusting the temperature of the steel sheet immediately before water quenching to the gas jet air volume of the quenching temperature adjusting blower 4. Similarly, the results are fed back to the tempering section 2 to change the amount of electricity supplied to the induction heating device 8, increase or decrease the amount of gas in the radiant tube 6, and adjust the amount of air in the cooler 7. The tempering temperature was controlled.

Specifically, the desired tensile strength is set to 1 kgf /
To change mm ² , the quenching temperature had to be changed by 2 ° C. Similarly, the desired tensile strength is set to 1 kgf / mm.
^To change the tempering temperature, it was necessary to change the tempering temperature by 10 ° C. That is, the tensile strength is actually 100 kgf / m
The quenching temperature was increased by 10 ° C. from 680 ° C. to 690 ° C. to correct from m ² to 105 kgf / mm ² . Similarly, the tensile strength is increased from 110 kgf / mm ² to 105 kgf / mm ^2.
tempering temperature from 200 ° C to 250 to correct to mm ²
C. to 50.degree. As a result, FIG. 4 (a) shows the variation before the method of the present invention is carried out, while FIG. 4 (b) shows that the tensile strength of the rolled steel sheet is 100 kg Strength 102-108kgf /
mm ² , all of which were within the acceptable range, and there was no deviation from the mechanical test values. In addition, the variation in the tensile strength distribution could be narrowed as compared with FIG.

[0027]

As described above, according to the present invention, there is provided a method for producing a high-strength cold-rolled steel sheet using a continuous annealing facility provided with a quenching means and a tempering means. It can be manufactured stably with little variation.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing an embodiment of the method of the present invention, the inside and the discharge side of a continuous annealing facility used for carrying out the present invention.

FIG. 2 is an overall view of a continuous annealing facility provided for carrying out the present invention.

FIG. 3 shows the rolling load P ₀ per unit width of the rolled steel sheet and the tensile strength TS _{0 of the} rolled steel sheet in the temper rolling mill of the present invention.
Explanatory diagram showing an example of the relationship with

FIGS. 4A and 4B are explanatory diagrams showing variations in tensile strength of a rolled steel sheet showing examples of the method of the present invention, wherein FIG. 4A shows variations before the method of the present invention is performed, and FIG. The variation after the implementation is shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Water quenching section 2 Tempering section 3 Temper rolling mill 4 Hardening temperature adjustment blower 5 Hardening temperature measuring plate thermometer 6 Radiant tube 7 Cooler 8 Induction heating device 9 Load detector 10 Storage tank

Claims (3)

[Claims] 1. A method for producing a high-strength cold-rolled steel sheet using a continuous annealing equipment having a quenching means and a tempering means, comprising: The relationship between the permissible rolling load P ₀ and the tensile strength TS _{0 of the} steel sheet to be rolled is determined in advance for each sheet thickness of the steel sheet, and based on the relationship between the rolling load P ₀ and the tensile strength TS ₀ , calculate the tensile strength TS ₁ of the rolled steel sheet from a rolling load P ₁ per unit width of the rolled steel sheet is measured in a rolling mill, tensile strength TS ₁ that the calculated
A method of controlling a quenching temperature and / or a tempering temperature of a steel sheet so that the steel sheet has a desired tensile strength. 2. The method for producing a high-strength cold-rolled steel sheet according to claim 1, wherein the quenching means includes a water quenching means. 3. The high-strength cold-rolling according to claim 1, wherein a lot is formed with the same components in a converter or an electric furnace, and a rolled steel sheet is charged into a continuous annealing facility for each lot. Steel plate manufacturing method.