JPH09227952A - Production of hot rolled steel sheet for working excellent in deep drawability using hot rolling continuing process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a hot rolled steel sheet for working of material uniform over the whole length excellent in deep drawability in which a slab contg. specified components by weight ratios in specified ranges is subjected to rough rolling, coiling, recoiling, joining, continuous finish rolling and cooling at specified temps. SOLUTION: This is a method for producing a hot rolled steel sheet for working excellent in deep drawability by a hot rolling continuing method in which a slab contg., by weight, 0.01 to 0.05% C, 0.10 to 0.30% Mn, 0.001 to 0.05% Si, <=0.02% P, 0.004 to 0.012% S, 0.01 to 0.1% Al, 0.001 to 0.007% N, and the balance Fe with inevitable impurities is heated at the MnS solid solution temp. or above and is subjected to rough rolling at >=1200 deg.C so as to regulate the total draft to >=5% to form into a sheet bar, which is thereafter coiled in the temp. range of 1200 to 1000 deg.C, is held for 3 to 180sec and is thereafter recoiled to apply the same with >=0.5% bending strain. Then, the tip of the sheet bar is joined to the tail of the preceding sheet bar, which is subjected to continuous finish rolling at the Ar3 transformation point or above, and within 0.5sec after that, cooling is executed at >=30 deg.C/sec.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a good average Rank Ford value (average r value), which is an evaluation index for deep drawing workability, and the minimum value of the r values in each direction affecting workability is The present invention relates to a method for producing a hot-rolled steel sheet for working which is excellent in deep drawability by a hot-rolling continuous method.

[0002]

2. Description of the Related Art Usually, in order to improve the average r-value of hot-rolled steel sheet for working, its constituent factors are rL value of r-value in rolling direction, rC value of r-value in width direction and rolling direction. To 4
It is necessary to improve each rD value of the r value in the 5 degree direction. Because the r value in one direction is low,
This is because the r-value in that direction has an adverse effect during processing, causing ears and lowering the processing limit.

On the other hand, in order to improve the average r value of these hot-rolled steel sheets for working, an ultra-low carbon steel containing Ti is manufactured by oil lubrication rolling, as proposed in, for example, JP-A-59-226149. Method or JP-A-62-19253
As proposed in Japanese Patent No. 9, there is a method of manufacturing by adding an alloy such as Nb or Ti. However, these methods are not economical, and the minimum value of r value in each direction is not excellent.

For these methods, the inventor of the present invention disclosed in Japanese Patent Laid-Open No.
The proposal of Japanese Patent No. 229827 was made. According to this proposal, it is possible to improve the average r value and the Δr value indicating the anisotropy of the r value in the components of the ordinary hot-rolled steel sheet for processing without any special additional element, and to improve the r value in each direction. The minimum value is also excellent. However, the average r value was only about 1.1 at most, and no r value higher than that of cold rolled steel sheets was obtained.

Therefore, the present inventor economically manufactures hot-rolled steel sheets for working having an average r-value of 1.1 or more and an excellent minimum r-value in each direction without adding a special element. The method was proposed as JP-A-7-268462. In this method, a steel slab is heated to a MnS solid solution temperature or higher, rolled at a temperature of 1200 ° C. or higher so that the total rolling reduction is 5% or higher, and then in a temperature range of 1200 to 1000 ° C. to precipitate MnS.
~ 20 minutes holding process, holding time 3 ~ 2
It was as long as 0 minutes, and this holding time hindered efficient production of steel sheets, and was not satisfactory in terms of productivity.

Next, considering the finishing temperature distribution of the hot rolled steel sheet, in order to carry out hot rolling without deteriorating the workability, the temperature of the rolled sheet bar is set to a temperature of at least the Ar ₃ transformation point or higher. There is a need. FIG. 1 is a diagram showing a finishing temperature distribution of a hot-rolled steel sheet. As shown in FIG. 1, the finish temperature of the front end of the hot-rolled sheet bar is the lowest, and the finish temperature becomes higher toward the rear end. It is considered that the reason why the finishing temperature at the rear end is increased is due to the heat generated during processing.

As described above, since the finishing temperature of the steel sheet is not uniform over the entire length of the sheet bar, there is a problem in that the material of the steel sheet is different between the tip portion and the intermediate portion.

[0008]

The present invention is excellent in deep drawability with an average r value of 1.1 or more and a minimum r value of 0.7 or more in each direction without adding a special element. Another object of the present invention is to provide a method for producing a hot-rolled hot-rolled steel sheet for working which has a short holding temperature and is capable of producing a steel sheet of a homogeneous material over its entire length with high productivity.

[0009]

[Means for Solving the Problems] C: 0.0% by weight
1 to 0.05%, Mn: 0.10 to 0.30%, Si:
0.001-0.05%, P: 0.02% or less, S
: 0.004 to 0.012%, Al: 0.01 to 0.
1%, N: 0.001 to 0.007%, and a steel slab composed of other Fe and unavoidable impurities are heated to a MnS solid solution temperature or higher, and rough rolled so that the total rolling reduction becomes 5% or more at 1200 ° C or higher. After making it into a seat bar, 1200-100
By winding in a temperature range of 0 ° C., holding for 3 to 180 seconds and then rewinding, a bending strain of 0.5% or more is imparted, and the leading end of the sheet bar is joined to the trailing end of the preceding sheet bar. , Deep drawability by a hot rolling continuous process characterized by performing finish rolling continuously at a temperature of Ar ₃ transformation point or higher, and cooling at 30 ° C./sec or higher within 0.5 seconds after completion of finish rolling. A method of manufacturing an excellent hot rolled steel sheet for processing.

The hot-rolled steel sheet for working, which is the object of the present invention, is a steel sheet generally used in this field as a hot-rolled steel sheet for working, and C: 0.01 to 0.05% by weight. , M
n: 0.10 to 0.30%, Si: 0.001 to 0.0
5%, P: 0.02% or less, S: 0.004 to 0.01
2%, AL: 0.01 to 0.1%, N: 0.001 to
It is a steel plate containing 0.007% and other Fe and unavoidable impurities.

In order to obtain a hot-rolled steel sheet for working which is excellent in deep drawability, the present inventor heats a steel slab to the MnS solid solution temperature or higher,
MnS is completely solid-solved in the steel, the solid solution S is maintained even before finish rolling, and fine MnS is precipitated during finish rolling.
0.30%, S: 0.004 to 0.012% is required), and together with it, it is important to recrystallize and destroy the texture of r formed by casting under high temperature region pressure. However, as a result of further research, when a bending strain of 0.5% or more is applied by winding and unwinding a steel sheet, nuclei are formed in a short holding time, which promotes precipitation of fine MnS during finish rolling. The present invention has been completed on the finding that it is possible. That is, according to the present invention, a holding time of 3 to 20 minutes has been conventionally required to precipitate MnS that serves as a nucleus that can promote the precipitation of fine MnS during finish rolling. The holding time could be shortened to 3 to 180 seconds.

Bending strain is applied to the seat bar of the present invention,
The coil box method (Iron and St) for winding up the sheet bar is used for the treatment for precipitating MnS serving as the core.
ee Engineer, 1981, No. 11,
P. 452) can be used. In this method, since the sheet bar is bent and wound into a coil at the same time, it has a heat retaining effect, and the above treatment can be performed without a special heating device.

In the present invention, rolling is performed at 1200 ° C. or more so that the total rolling reduction is 5% or more, because the cast texture of r formed after casting is destroyed and recrystallization is performed by rolling.

Winding so as to impart a bending strain of 0.5% or more in a temperature range of 1200 to 1000 ° C. imparts strain to the sheet bar, and the presence of the strain causes precipitation treatment of MnS, which is a core. This is because the holding time of 3 to 180 seconds is M
Precipitation of nS occurs. If it is less than 3 seconds, precipitation of MnS does not occur, and if it exceeds 180 seconds, precipitation of MnS is promoted too much and sufficient solid solution S cannot be secured before finish rolling, which is not preferable.

In finish rolling, it is important to form an austenite rolling texture and transform it into ferrite as it is in order to improve the average r value. Therefore, finish rolling should be performed at a temperature not lower than the Ar ₃ transformation point. It is something to do. In order to transform it into ferrite as it is, finish rolling A
It is necessary to complete the process just above the r ₃ transformation point and perform water cooling within 0.5 seconds at a cooling rate of 30 ° C./second or more. The winding temperature is preferably about 500 to 700 ° C. to secure the elongation.

Further, in the present invention, the leading end of the sheet bar is joined to the trailing end of the preceding sheet bar on the rolling line to perform finish rolling. In this finish rolling, since the sheet bars are continuously joined to form a long strip, the rolling can be performed at a constant velocity unlike the conventional accelerated rolling. That is,
In the conventional rolling method, the temperature of the tip of the sheet bar is remarkably lowered, and there is variation in the material between the intermediate portion and the tip portion,
The tip portion was not preferable because the material was defective, but in the present invention, since the sheet bar is joined to make it long, the rolling conditions can be made constant and the variation in material in the length direction can be eliminated. Of. Therefore, it is possible to prevent the material defect of the tip portion and improve the product yield due to the material defect.

Further, since the process of precipitating MnS by applying bending strain in a short time and the process of joining the sheet bars and continuously rolling are combined, the entire material of the sheet bar is lengthwise. That is, a hot-rolled steel sheet for processing that is uniform and has excellent deep drawability can be manufactured with high productivity without adding a special element.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an outline of a method for manufacturing a hot-rolled steel sheet for working having excellent deep drawability in the hot-rolling continuous method.

As shown in FIG. 3, the slab heated in the heating furnace 1 to the MnS solid solution temperature or higher is hot-rolled by the rough rolling mill 2, and the bending strain at 1100 to 1200 ° C. is 0.5% or more. Is wound into a rough rolled coil 3 and then held for 3 to 180 seconds or more and then rewound. Uncoiling rough rolled coil 3
The tip of is cut by the welding cutting machine 4 to form a tip groove suitable for welding. The preceding rough-rolled steel sheet is conveyed to the finish rolling machine and finish-rolled, and the rear end thereof is also cut by the welding cutting machine 4 to form a rear end groove suitable for welding. The rear end of the preceding rough rolled steel sheet and the front end of the subsequent rough rolled steel sheet are welded and joined by the welding device 5.

The welding device 5 is composed of a moving carriage and is controlled so as to be able to move in synchronization with the moving speed of the rear end of the rough rolled steel sheet. The trailing end and the trailing end of the rough rolled steel sheet are welded together. As a welding method, a laser beam welding method is suitable, but other known welding methods can also be applied.

The rough-rolled steel sheet, which is integrally joined by the welding device 5 and becomes long, is finish-rolled continuously by a finishing rolling mill 6, and then cooled to a winding temperature by a cooling device 7 installed on a hot run table. After being cooled, it is wound by the winding machine 10 as a coil. When the finished steel sheet is wound up by a predetermined length, it is cut by the cutting machine 9 and wound up by the winding machine 10 as another coil. The cutting site by the cutting machine 9 is
It is preferable to cut the portion joined by the welding device 6.

In the present invention, the leading end of the rough rolled steel plate is joined to the trailing end of the preceding rough rolled steel plate on the rolling line to form a long steel plate, so that hot finish rolling can be continuously performed.
Therefore, the hot-rolled steel sheet does not have a tip other than the first tip, and the steel sheet is always supported by the pinch roll 8, so that the hot-finished steel sheet is continuously cooled by a cooling device. It becomes possible to cool. Therefore, the tip portion of the steel sheet, which is not cooled and becomes defective in the material as in the conventional batch-type hot rolling method, is eliminated except at the beginning.

[0023]

EXAMPLES The chemical components of the test steel are shown in Table 1. Tables 2 and 3 show the manufacturing conditions and the r-value measurement results of examples carried out using these test steels.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3] As shown in Tables 2 and 3, the steel Nos. 1 to 5 of the present invention have good average r values of 1.1 or more and minimum r values of 0.7 or more in each direction.

Compared with the present invention, Steel No. 6 was out of the lower limit of Mn content, Steel No. 7 was out of the upper limit, Steel No. 8 was out of the lower limit of S content, Steel No. 9 was out of the upper limit, Steel No. 10 whose heating temperature is below the MnS solid solution temperature, Steel No. 11 that did not satisfy the total rolling reduction in the high temperature range, Steel No. 12 that did not satisfy the high temperature rolling end temperature, and the holding time at 1100 to 1000 ° C. Steel No. 13 that did not exist, Steel No. 14 that did not satisfy bending strain, Steel No. 1 whose finish rolling finish temperature was Ar ₃ or less
5, steel No. 16 having a time of less than 0.5 seconds after finishing rolling until the start of cooling, and steel No. 17 having a slow cooling rate after finishing rolling all have an average r value of not reaching 1.1. The minimum r value was also less than 0.7.

[0028]

According to the present invention, the average r value is 1.1 or more without adding any special element, the minimum r value in each direction is 0.7 or more, and the homogeneity is uniform over the entire length of the steel sheet. A hot-rolled steel sheet for working which is excellent in deep drawability of the material can be produced with high productivity by enabling MnS precipitation treatment at a short holding temperature.

[Brief description of drawings]

FIG. 1 is a diagram showing a finishing temperature distribution of a hot rolled steel sheet.

FIG. 2 is a diagram showing an outline of an embodiment of the hot rolling continuous method of the present invention.

[Explanation of symbols]

 1 Heating Furnace 2 Rough Rolling Machine 3 Rough Rolling Coil 4 Cutting Machine for Welding 5 Welding Device 6 Finishing Rolling Machine 7 Cooling Device 8 Pin Troll 9 Cutting Machine 10 Winding Machine

Claims (1)

[Claims] 1. C: 0.01-0.05 by weight
%, Mn: 0.10 to 0.30%, Si: 0.001 to
0.05%, P: 0.02% or less, S: 0.004
-0.012%, Al: 0.01-0.1%, N:
A steel slab composed of 0.001 to 0.007%, other Fe and unavoidable impurities is heated to a MnS solid solution temperature or higher,
After the sheet bar is roughly rolled so that the total rolling reduction is 5% or more at 0 ° C or higher, the sheet bar is wound up in a temperature range of 1200 to 1000 ° C, held for 3 to 180 seconds, and then rewound to bend. A strain of 0.5% or more is applied, and the front end of the sheet bar is joined to the rear end of the preceding sheet bar, and Ar
Excellent deep drawability by the hot rolling continuous method characterized by performing finish rolling continuously at a temperature of ₃ transformation points or more and cooling at 30 ° C / sec or more within 0.5 seconds after completion of finish rolling. Manufacturing method of hot rolled steel sheet for processing.