JPH11269556A - Manufacture of hot rolled high tensile strength steel plate excellent in deep drawability - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a hot rolled high tensile strength steel having uniform material quality in a longitudinal direction and a width direction and excellent in deep drawability. SOLUTION: The hot rolled high tensile strength steel plate is manufactured by subjecting a steel slab, having a composition consisting of, by weight, 0.10-0.20% C, 0.05-0.20% Si, 1.00-2.50% Mn, <=0.010% S, and the balance Fe with inevitable impurities to hot rolling at 1200 to 1300 deg.C heating temperature and at the finishing temperature between the Ar3 point and (Ar3 point + 100 deg.C) and to cooling down to 500 to 550 deg.C coiling temperature. In this case, the steel is finish-rolled into strip 1 with a shape of >=500 mm wavelength of waviness and <=±10% degree of steepness, and, at hot run table 3, top and bottom spray is applied at (10 to 100) deg.C/sec cooling rate. Further, in the course of cooling at the hot run table 3, at least one or more air cooling zones 8 for 1 to 3 sec are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a tensile strength of 490.
A method for producing a hot-rolled high-strength steel sheet of N / mm2 or more,
In particular, the present invention relates to a method for manufacturing a hot-rolled high-tensile steel sheet having a uniform material in the longitudinal and width directions and excellent in deep drawability by precisely controlling a cooling method in a hot run table.

[0002]

2. Description of the Related Art Steel sheets that require high deep drawability, such as propane container materials, require high safety from the application point of view, but also have high strength due to workability problems such as container transportation. There is a demand for a thinner structure. However, as the strength and thickness are reduced, the ductility is reduced, and molding by press working becomes difficult.

A propane container is manufactured by deep drawing from a single disk, and requires a material having an excellent r value (Rankford value) representing ductility and deep drawability, and further has draw wrinkles and insufficient local elongation. Uniform material properties that do not occur are required.

[0004] In order to reduce the cost of material by stably mass-producing under the same manufacturing conditions and to reduce material costs, the coil 1 as a material has uniform material characteristics in the longitudinal direction and the width direction. Is required.

[0005] It is known that by controlling the cooling rate from the end of finish rolling to the winding temperature, the metal structure can be controlled and the required strength, ductility, and the like can be obtained.

In order to make the cooling rate uniform, a laminar type spray 6 for producing laminar flow bar-like water of low pressure water capable of rapid cooling is installed above and below the hot run table 3, and from above and below the strip 1 to be passed. Water is injected and cooled.

Conventionally, cooling water 7 rides on the strip 1,
In order to prevent the material from being hardened due to the local supercooling, as shown in FIG. In the latter half, the lower laminar of strip 1 was preferentially used for cooling.

[0008]

In the prior art,
When the shape of the plate after finish rolling deteriorates in the longitudinal direction or the width direction, as shown in FIGS. 1A and 1B, the distance between the cooling nozzles on the hot run table and the strips varies, resulting in uneven cooling. Occurs. As a result, a quenched portion or a slow-cooled portion is locally formed, and the variation in the material becomes large, so that a processing defect due to drawing wrinkles or insufficient local elongation during press working has occurred. An object of the present invention is to solve these problems and to provide a method for manufacturing a hot-rolled steel sheet having a material having a uniform longitudinal and width direction and excellent in deep drawability.

[0009]

In order to achieve the above object, the invention according to claim 1 is characterized in that C: 0.10% by weight.
-0.20%, Si: 0.05-0.20%, Mn:
1.00 to 2.50%, S: ≦ 0.010%, and the balance F
e and a steel slab consisting of unavoidable impurities, the heating temperature is between 1200 and 1300 ° C., the finishing temperature of hot rolling is in the range of Ar3 point to Ar3 point + 100 ° C., and the winding temperature of the hot steel strip is In the method for producing a hot-rolled high-tensile steel sheet cooled to 500 to 550 ° C, the wavelength of the strip is 500 mm.
As described above, finish rolling is performed to a shape having a steepness of ± 10% or less, and water is injected up and down by using a cooling spray of a hot run table.
A cooling rate of 〜100 ° C./sec. According to the present invention, since the steepness of the steel plate on the hot run table is controlled to be small and the plate is passed, while the variation in the distance between the nozzle and the strip is reduced and cooling is performed by vertical and uniform water injection, the temperature distribution is uniform throughout the steel plate. Ferrite +
A pearlite texture is obtained.

Further, the invention according to claim 2 is the invention according to claim 1, wherein in the cooling process in the hot run table, air cooling is performed at least once or more for 1 to 3 seconds during vertical cooling by cooling spray. In addition to providing an area, cooling is performed. According to the present invention, in cooling the strip on the hot run table, generation of a bainite structure due to generation of a local quenched portion is suppressed, and a uniform ferrite + pearlite structure is obtained over the entire steel sheet.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied in detail the steel composition, the metal structure, the hot rolling conditions thereof, and the tensile properties and deep drawability of a steel sheet. As a result, it was found that a high-strength hot-rolled steel sheet having a uniform material in the longitudinal and width directions of the coil and excellent in press formability and deep drawing properties was obtained. Hereinafter, matters for specifying the present invention will be described.

C: 0.10 to 0.20% C is a solid solution strengthening element, and 0.10% to secure strength.
However, if it exceeds 0.20%, ductility and r
Value (deepness) is deteriorated, and the weldability is also significantly deteriorated.

Si: 0.05-0.20% The addition of Si effectively acts to improve the strength of the steel sheet, but the excessive addition causes deterioration of the skin due to accelerated formation of scale and
In order to cause deterioration of weldability, which is important as a propane container, the range is limited to 0.05 to 0.20%.

Mn: 1.00 to 2.50% Mn is an element for stabilizing austenite and is a solid solution strengthening element. If the content is less than 1.00%, it is not sufficient to obtain such an effect, and if it exceeds 2.50%, the stability of the ferrite structure is impaired, and the ductility is reduced.

S: ≦ 0.010% If a large amount of S is contained, it causes an increase in MnS and causes deterioration of workability. Therefore, the content is limited to a range of 0.010% or less.

Next, the manufacturing method according to the present invention will be described. Immediately after continuous casting of the steel slab having the above composition, or after reheating, the heating temperature is from 1200 to 1300.
Extracted from the heating furnace at ℃ and subjected to hot rolling.

In this case, the finishing temperature on the exit side of the finishing mill is from Ar 3 to Ar 3 + 100 ° C. When the finishing temperature is lower than the Ar3 point, the formed ferrite appears as processed ferrite, and the structure after rolling becomes non-uniform. On the other hand, Ar 3 points + 10
If the temperature is higher than 0 ° C., the structure becomes coarse, the ductility of the material is similarly deteriorated, and it becomes difficult to control the cooling rate for cooling to the target winding temperature, so that the required material cannot be obtained.

Next, the strip 1 is cooled on the hot run table 3, and as shown in FIG. 2 (b), laminar type cooling devices provided on the upper and lower sides are uniformly used.
This is to uniformly inject water from above and below the strip 1 to prevent the occurrence of cooling unevenness due to the deterioration of the sheet thickness shape, suppress the formation of bainite structure due to rapid cooling, and obtain a uniform ferrite + pearlite structure over the entire area of the steel sheet. It is. Also, the upper and lower cooling water amounts are between the finishing temperature Ar3 point and Ar
After finishing hot rolling under the condition of 3 points + 100 ° C.,
By giving an amount of water at a cooling rate of 100 ° C./s and cooling to a winding temperature of 500 to 550 ° C., 490 N
/ Mm 2 or more can be produced.

The cooling on the hot run table 3 is performed as follows.
Steepness λ of steel plate for uniform cooling over the entire steel plate
Is ± 10% when the wavelength L of the strip 1 is 500 mm or more.
It is necessary to finish the finish rolling as follows. Here, the steepness λ can be obtained by the definition of the following equation as shown in FIG. Steepness λ = h / L × 100 (%) 1 equation h: wave height, L: wavelength

Substantially hot-rolled product thickness 1.5 to 1.5
The wavelength L of the large undulation in the longitudinal direction and the width direction of the steel sheet at 6.0 mm is usually 500 mm or more. Cooling nozzle 6
The relationship between the variation in the distance h between the steel plates 1 and the steepness is, as is apparent from the equation 1, the greater the wavelength L, the greater the variation in the distance. Here, the steepness λ of the steel sheet 1 is set to be ± 10% or less when the wavelength L of the strip 1 is 500 mm or more, in order to obtain a substantially uniform cooling rate over the entire area of the steel sheet. Is required to be 50 mm or less.

In general, the shape of the steel sheet in the longitudinal direction is caused by the thickness of the sheet, the rolling speed and the roll speed ratio of the hot run table 3 and the like, and the width direction is caused by the rolling shape such as edge elongation, quarter elongation, and flat rolling. However, the steepness in this case can be controlled by a known work roll offset control or a hot run table speed control in a known finishing mill in the longitudinal direction, and can be controlled by a well-known sheet crown control or the like in the width direction. .

Further, in addition to the uniform water injection pattern on the hot run table 3, the air cooling area 8 of 1 to 3 seconds is provided once or more during the time, so that the cooling is more uniform than in the case of continuous cooling. Material can be obtained. This is a water injection pattern in which an air-cooling area 8 is provided between the upper and lower water-cooling areas and the water-cooling area shown in FIG. 2 (c). It is presumed that partial differences such as the spraying strength of the cooling water 7 hitting the air are temporarily avoided, and the surrounding material is uniform and stable.

[0023]

EXAMPLE A hot-rolled steel sheet having a thickness of 2.53 mm was prepared by subjecting a steel type having the steel composition shown in claim 1 to hot rolling under the three hot rolling conditions shown in FIG. Test (a)
In the test (b), the water injection pattern was set equal to the upper and lower sides in the test (b). FIG. 3 shows the results of deep drawing of the steel sheet obtained by this manufacturing method. It can be seen that the number of defective sheets per coil of the steel sheet obtained according to the present invention was significantly improved as compared with the conventional manufacturing method, and that a good deep drawing result was obtained.

[0024]

As described above, according to the manufacturing method of the present invention, a high-strength hot-rolled steel sheet having a uniform material in the longitudinal and width directions and excellent in deep drawability can be obtained. Therefore, the steel sheet manufactured according to the present invention can be manufactured as a material such as a propane container or the like which requires deep drawability, with less defective material portions and a uniform material over the entire area of the coil, and the manufacturing yield can be significantly improved. To play.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a relationship between a lower water injection effect and a steepness in a longitudinal direction and a width direction of a steel sheet.

FIGS. 2A and 2B are schematic diagrams showing a cooling pattern from the end of hot rolling to winding up, wherein FIG. 2A shows a conventional lower-priority water injection pattern, FIG.
(C) shows an upper / lower uniform + air cooling water injection pattern of the present invention.

FIG. 3 is a diagram showing the number of defective machining per coil for each water injection pattern.

[Explanation of symbols]

 Reference Signs List 1 strip (steel sheet, coil) 2 finishing mill 3 hot run table 4 winder 5 roll 6 cooling spray (nozzle) 7 cooling water 8 air cooling area

Claims (2)

[Claims] C: 0.10 to 0.20 by weight%
%, Si: 0.05 to 0.20%, Mn: 1.00
2.50%, S: ≦ 0.010%, a steel slab consisting of the balance Fe and unavoidable impurities was heated at a heating temperature of 120%.
A method for producing a hot-rolled high-tensile steel sheet in which the hot-rolling temperature of a hot steel strip is cooled to 500 to 550 ° C. in a range of 0 to 1300 ° C. and the finishing temperature of hot rolling is in the range of Ar 3 to Ar 3 points + 100 ° C. The wavelength (L) of the strip (1) is 500 m
m, and finish-rolled to a shape with a steepness (λ) of ± 10% or less, and a cooling spray (6) of a hot run table (3)
A method for producing a hot-rolled high-strength steel sheet excellent in deep drawability, characterized in that a cooling rate of 10 to 100 ° C./second is applied by vertical water injection using the above method. 2. A cooling process in the hot run table (6), wherein at least one or more air cooling zones (8) for 1 to 3 seconds are provided between upper and lower water cooling by the cooling spray (6). 2. The method for producing a hot-rolled high-tensile steel sheet according to claim 1, which is excellent in deep drawability.