JPH09227948A - Manufacture of hot rolled steel plate for working, excellent in formability and toughness, by using continuous hot rolling process - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve and uniformize the material of a hot rolled steel plate over the whole length by refining MnS and AlN precipitates and also refining crystalline grains, to improve reduction in yield due to inferior material at the head end, to improve the advantage in costs due to energy saving in a steel slab heating furnace, and to provide a method for continuously manufacturing a hot rolled steel plate for working, improved in productivity and excellent in formability. SOLUTION: Heating in a heating furnace is performed at <=1150 deg.C. A roughed steel plate is coiled at a temp. not lower than the Ar3 transformation point, at >=0.5% bending strain at >=0.05S<-1> bending strain rate, held for >=3sec at <=1 deg.C/S cooling rate, and uncoiled. Subsequently, the head end of this steel plate is joined to the tail end of the preceding steel plate which is roughed previous to the above steel plate and traveling ahead of it in a rolling line. Then, hot finish rolling is continuously carried out at <=(Ar3 +50) deg.C hot finishing temp. under the condition that the difference between the hot finish rolling mill inlet temp. and the hot finish rolling mill outlet temp. is regulated to <=100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot rolled steel sheet by a hot rolling continuous method, and in particular, a hot rolling for working, which has excellent toughness and excellent toughness and is used for automobiles, industrial machines and pipe materials The present invention relates to a method for continuously hot rolling a steel sheet.

[0002]

2. Description of the Related Art Conventionally, in the technical field of steel sheets for processing of automobiles and the like, cold-rolled steel sheets having good workability have been used. Hot rolled steel sheets for processing have been used.

A method for producing hot-rolled steel sheet for processing used for automobiles, industrial machines, pipe materials, etc. is to heat a continuously cast steel slab to about 1200 ° C. in a heating furnace, and then roughly roll it with a hot rolling mill. After finish rolling, it is generally cooled with cooling water and wound on a coil.

In such a conventional method for producing a hot rolled steel sheet,
Hot rolling is performed for each steel slab, and the finished steel sheet is subjected to laminar cooling with cooling water in a cooling device provided on a run-out table, and the hot rolled steel sheet at the winding temperature is wound into a coil. However, when cooling the hot-finished steel sheet, even if it is attempted to cool from the tip of the steel sheet, the tip of the steel sheet collides with the water column of the cooling water, and the steel plate deforms and stalls due to the influence of the water column, causing trouble on the passing plate. The cooling process could not be performed because of the occurrence of. This phenomenon becomes more remarkable as the plate thickness becomes thinner.

Therefore, conventionally, when cooling a hot-rolled steel sheet to the winding temperature, the tip of the hot-rolled steel sheet is pinched without cooling the front end of the hot-rolled steel sheet in order to avoid troubles in passing the steel sheet. They were bitten by rolls and then cooled. In such a conventional method for cooling a hot-rolled steel sheet, the tip portion of the steel sheet is not cooled, so that part has a defective material, and the uncooled tip portion of the steel sheet is cut off when shipping as a product. However, there is a problem that the product yield is low.

Next, the precipitation treatment will be described. In order to impart workability to a hot-rolled steel sheet, it is necessary to perform precipitation treatment as MnS or AlN in order to remove S and N which are harmful to the workability. There is known a method in which MnS or AlN is deposited on a steel sheet to precipitate it. For example, Japanese Patent Publication No. 7-74376 discloses that 1
Bending is performed in a temperature range of 100 ° C. or less and Ar of ₃ points or more,
In addition, a method of maintaining the temperature range for 10 seconds or more is disclosed.

As a result of further research on the precipitation treatment by bending strain, the present inventor not only imparts bending strain as disclosed in the prior art, but also both specific bending strain and bending strain rate. It was found that when the above condition is applied to the steel sheet, the precipitation of MnS and AlN is promoted and the elongation of the steel sheet is improved.

Regarding the material of the hot rolled steel sheet for processing,
It is necessary to have both workability and toughness. Therefore, the present inventor has researched a method for improving the material properties of a hot-rolled steel sheet for working which has improved workability as well as toughness, and the finish rolling condition is a hot finishing temperature in the range of Ar ₃ + 50 ° C. or less,
In addition, under the low isothermal rolling condition that the difference between the temperature on the hot finish rolling mill inlet side and the temperature on the hot finish rolling mill outlet side is 100 ° C or less, the hot finish rolling is continuously performed over the entire length of the steel sheet. By carrying out the present invention, it was found that it is possible to improve workability as well as toughness by making the γ grains finer, and completed the present invention.

When the finishing temperature distribution of the hot rolled steel sheet is examined, it is necessary to set the temperature of the rolled steel sheet to at least the Ar ₃ transformation point or more in order to perform hot rolling without degrading workability. There is. FIG. 1 is a diagram showing a finishing temperature distribution of a conventional hot-rolled steel sheet. As shown in FIG. 1, the finishing temperature of the front end portion of the steel sheet to be hot-rolled is the lowest, and the finishing temperature becomes higher toward the rear end portion. It is considered that the reason why the finishing temperature at the rear end is increased is due to the heat generated during processing.

Since the finishing temperature of the steel sheet is not uniform over the entire length of the steel sheet and varies, the conventional hot rolling method controls the narrow hot finishing temperature range required for the refinement of γ grains as described above. There is a problem that I can not do it.

For heating in a conventional heating furnace, the heating temperature is selected so that the minimum finishing temperature of the steel sheet to be hot-worked, that is, the finishing temperature of the tip of the steel sheet becomes a temperature not lower than the Ar ₃ transformation point. Heating to a temperature of about 1200 ° C., which is considerably higher than the _three transformation points, has been performed.

From the viewpoint of the cost balance in terms of energy saving, this heating is considered to be excessively performed except at the tip of the steel sheet, and there is a problem that the cost balance is poor.

Japanese Patent Laid-Open Publication No. 1-149922 proposes a method of heating a steel slab at a low temperature of 1150 ° C. or lower and hot rolling it into a hot rolled steel sheet excellent in workability and secondary work brittleness resistance. There is. This method prevents coarsening of crystal grains by low-temperature heating, and aims at grain refinement by recrystallization after rolling, but this method also has the problem of temperature decrease at the tip of the hot-rolled steel sheet described above. However, it is technically difficult to obtain a uniform steel sheet over the entire steel sheet, and the yield due to a defective material at the tip cannot be improved.

[0014]

SUMMARY OF THE INVENTION Therefore, the present invention
To improve the material of the hot-rolled steel sheet over the entire length and make it uniform by refining nS and AlN precipitates and making the crystal grains finer, and also to improve the yield due to material defects at the tip. It is an object of the present invention to provide a method for continuously producing a hot-rolled steel sheet for processing which has excellent toughness and excellent formability with improved productivity, which improves cost merit by energy saving in a heating furnace. Is.

[0015]

[Means for Solving the Problems]

(1) A steel slab having a carbon content of 0.5% or less is heated in a heating furnace, roughly rolled by a hot rough rolling mill to form a steel plate, then finish rolled by a hot finish rolling mill, and then cooled and coiled. winding method of manufacturing a superior processing hot rolled steel sheet in formability, characterized in that taking the rough rolling steel plate Ar ₃ bending lower than the transformation point of the temperature strain of 0.5% or more, the bending strain rate 0.05 S ^- Winding up at ¹ or more, then holding at a cooling rate of 3 seconds or more and 1 ° C./S or less, and then rewinding, and the front end of the steel plate is the rear end of the steel plate that is roughly rolled before and precedes the rolling line. The condition that the hot finishing temperature is in the range of Ar ₃ + 50 ° C. or less and the difference between the temperature on the hot finishing mill input side and the temperature on the hot finishing mill exit side is 100 ° C. or less. Of hot-rolled steel sheet for working with excellent formability and toughness, which is characterized by continuous hot finish rolling at Production method.

(2) A steel slab having a carbon content of 0.5% or less is heated in a heating furnace, roughly rolled by a hot rough rolling mill to form a steel sheet, then finish rolling by a hot finishing rolling mill, and then cooled. In the method for producing a hot-rolled steel sheet for processing excellent in formability, which is characterized in that
Heat to a low temperature of 150 ° C. or less,
Winding at a temperature equal to or higher than the r ₃ transformation point and a bending strain of 0.5% or more and a bending strain rate of 0.05 S ⁻¹ or more, and then for 3 seconds or more at 1 ° C. /
It is held at a cooling rate of S or less and then rewound, and the front end of the steel plate is joined to the rear end of the steel plate which is rough rolled before and precedes the rolling line, and the hot finishing temperature is Ar ₃ +50.
It is characterized in that hot finish rolling is continuously carried out in the range of ℃ or less and under the condition that the difference between the temperature on the hot finish rolling mill inlet side and the temperature on the hot finish rolling mill exit side is 100 ° C or less. And a method for producing a hot-rolled steel sheet for working, which has excellent formability and good toughness.

The present invention will be described in detail below.

The hot-rolled steel sheet for processing which is excellent in formability and has good toughness produced by the present invention has a tensile strength (TS) of 400 to 500 used for automobiles, industrial machines, pipe materials and the like.
Al killed steel of MPa, Al-Si killed steel, or
The tensile strength (TS) is targeted at high tensile strength steels and pipe materials having a tensile strength of 500 MPa or more, and the components and component ranges of these steel sheets are as follows.

C: 0.5% or less, Mn: 1.6% or less,
Si: 0.8% or less, P: 0.025% or less, S: 0.
Containing 025% or less, and Ti: 0.100% or less,
Nb: 0.060% or less, V: 0.080% or less, C
a: A hot-rolled steel sheet for working, containing at least one selected from the group consisting of 0.0060% or less and Ni: 0.40% or less, the balance being substantially Fe, and having excellent formability.

C contained in the hot-rolled steel sheet for working excellent in formability is a hardening element, and if the C content increases, it becomes hard and the formability deteriorates.
It is preferable that the content is small. C can be contained up to 0.5%.

Mn is an element necessary for imparting toughness, but if it exceeds 1.6%, it deteriorates workability. S
Although i is added as a deoxidizing agent, i is hardened when the amount is increased, so i is set to 0.8% or less. P and S are inevitably contained, but if each exceeds 0.025%, the workability is adversely affected. Ti, Nb, V, Ca, and Ni improve toughness, but if they increase, workability deteriorates, so Ti: 0.1
00% or less, Nb: 0.060% or less, V: 0.080
% Or less, Ca: 0.0060% or less, Ni: 0.40%
It was as follows.

For these reasons, the components and component ranges as described above are adjusted.

Next, the precipitation process will be described.

Precipitation of MnS or AlN precipitates in the austenite region as much as possible leads to high ductility. Therefore, it is wound on a rough rolled steel plate at an Ar ₃ point or more at a bending strain of 0.5% or more and a bending strain rate of 0.05 S ^-1 or more,
Next, the precipitate is held at a cooling rate of not less than 3 seconds and not more than 1 ° C./S, and then is unwound to precipitate MnS or AlN precipitates. The bending strain is set to 0.5% or more because a larger bending strain has an effect on the formation of precipitates and the effect cannot be expected if the bending strain is less than 0.5%. The bending strain is
Since it is applied at a high temperature, even if bending strain (transition) is applied over time, the strain disappears and the effect of bending strain cannot be obtained. Therefore, it can be formed at a short bending strain rate. It's important. According to the results of the experiment, the bending strain rate was 0.0
Since the effect of improving ductility cannot be obtained unless it is 5S ^-1 or more, the bending strain rate is set to 0.05S ^-1 or more.

Further, in order to form the precipitate, it is necessary to maintain the cooling rate of 3 seconds or more and 1 ° C./S or less, and if it is more than this, there is no effect on the formation of the precipitate.

Without these requirements, MnS and AlN
Is not effectively deposited.

In the precipitation treatment of the present invention, a coil box method (Iron and Steel) for winding a steel sheet is used.
Engineer, 1981, No. 11, p. 45
2) can be used. This method has a heat retaining effect because the steel sheet is bent and wound into a coil at the same time, and can be performed without a special heating device to maintain a cooling rate of 3 seconds or more and 1 ° C./S or less. .

Then, MnS by low temperature heating described later
It has been found that when nuclei are formed by performing primary precipitation of AlN or AlN, precipitation by the precipitation treatment regulated by the above bending strain and bending strain rate is remarkably accelerated. Therefore, it is preferable to perform the precipitation treatment by combining both the precipitation treatment by low-temperature heating and the above-mentioned precipitation treatment.

Next, the crystal grain refining process will be described.

The present inventor has researched a method for improving the material properties of a hot-rolled steel sheet for working which improves not only the workability but also the toughness, and the hot finishing temperature is within the range of Ar ₃ + 50 ° C. or less.
In addition, under the low isothermal rolling condition that the difference between the temperature on the inlet side of the hot finish rolling mill and the temperature on the outlet side of the hot finish rolling mill is 100 ° C. or less, and by continuously performing the hot finish rolling, the γ grains can be formed. It was found that the grain refinement occurs and the workability and toughness are improved over the entire length of the steel sheet. This will be described with reference to FIG. FIG. 2 is a diagram showing the relationship between the product of elongation (El) and tensile strength (TS), and the temperature difference (ΔT) between the inlet temperature (FT0) and the outlet temperature (FT). As shown in the figure, it can be seen that the product of El and TS (El × TS) increases as ΔT decreases. Also, if ΔT is 100 ° C or less, El
In the present invention, the temperature is set to 100 ° C. or lower because the × TS sharply increases and the effect of grain refinement is remarkable. Further, such an effect occurs in the range where the finishing temperature is Ar ₃ + 50 ° C. or lower, and at the temperature higher than this, the γ grains become coarse and the effect of refining by recrystallization cannot be obtained. According to the conventional method, even if fine graining is possible in the middle portion of the steel sheet, the tip of the steel sheet has a large temperature drop as shown in FIG. It is technically difficult to carry out fine-graining treatment over the entire length.

However, in the present invention, by making the finish rolling continuous, the tip of the steel sheet is substantially eliminated, and low isothermal rolling can be performed over the entire length of the steel sheet. By combining with the chemical treatment,
For the first time, we were able to achieve fine graining over the entire length of the steel sheet.

As a result, it was possible to obtain a hot-rolled steel sheet for working which had excellent formability and good toughness over the entire length of the steel sheet, and it was possible to improve the product yield due to the defective material at the tip portion.

Further, the temperature distribution of the hot rolled steel sheet will be described.

FIG. 3 is a diagram schematically showing the relationship between the heating furnace temperature and the finishing temperature of the hot rolled steel sheet. As shown in FIG.
In the conventional hot rolling method, usually, about 1200 ° C in a heating furnace.
Hot-rolled steel slab in a heated state, the temperature of the middle part of the hot-rolled finished steel sheet is about 900 ° C., and the tip of the hot-rolled finished steel sheet has dropped to a temperature near the Ar ₃ transformation point, respectively. Was. As described above, the temperature at the tip of the hot-rolled finished steel sheet was significantly reduced.

However, in the present invention, the tip of the roughly rolled hot-rolled steel sheet is joined to the trailing end of the preceding hot-rolled steel sheet that is roughly rolled and then the hot-rolled steel sheet is continuously hot-rolled. Since it is possible to perform rolling, and further, the hot rolling can be a constant-velocity rolling, the rolling conditions are the same over the entire length of the steel sheet, which is different from the conventional batch-type hot rolling accelerated rolling. Differently, there is no variation in the temperature drop of the hot rolled finished steel sheet. That is, according to the hot rolling continuous method of the present invention, since the tip of the steel sheet does not exist, the hot rolling conditions are only rolling corresponding to the middle portion of the conventional hot rolled finished steel sheet, so the hot rolled finished steel sheet The temperature drop is constant, the temperature drop is small as shown by the ● mark in FIG. 3, and the material can be made homogeneous over the entire length of the steel sheet.

For the above reason, in the present invention, the temperature in the heating furnace can be set lower than the conventional temperature, and according to the experiment, in order to make the temperature of the hot rolled finished steel sheet to be the Ar ₃ transformation point or higher, It has been found that low-temperature heating of 1150 ° C. or lower is sufficient. At a heating temperature of 1200 ° C. as in the conventional case, MnS and AlN are not sufficiently precipitated in the steel,
If low temperature heating below 1150 ° C is performed, MnS and A
Precipitation of 1N occurs, and as it is, grain refinement of the crystal occurs due to recrystallization, resulting in the effect of improving the workability of the steel sheet, particularly elongation and toughness, and the material is improved over the entire length of the steel sheet. It will be.

That is, a heating temperature exceeding 1150 ° C. is overheated, so that no cost advantage in energy saving can be obtained, MnS or AlN is not precipitated in the steel, and the crystal grains are coarsened to improve the material. Since it is not preferable because it is not preferable, the heating temperature in the present invention requires high temperature heating.
The heating was performed at a low temperature of 150 ° C. or lower. On the other hand, if the temperature is 950 ° C. or lower, the hot finishing temperature is lower than the Ar ₃ transformation point, which deteriorates the workability, which is not preferable.

In the case of steel in which Nb, Ti, etc. are added and the precipitation strengthening is utilized, it is necessary to perform solution treatment of Nb and Ti once by heating at high temperature. Although such steel cannot be heated at a low temperature, improvement of workability and toughness can be expected by performing a grain refining treatment during finish rolling.

Further, in the present invention, the leading end of the roughly rolled hot rolled steel plate and the trailing end of the preceding hot rolled steel plate are joined by welding. Since the joined steel sheets are united, hot finish rolling can be performed continuously.If the first end of the hot rolled finished steel sheet is bitten by the pinch roll of the winding machine, then it will be continuous. The hot rolled finished steel sheet cooled to the winding temperature is then wound up by a winder. The hot-rolled finished steel sheet is cut at a predetermined length by a cutter and wound up by a winder, and the cut portion is preferably a joint.

According to the present invention, the tip of the first hot-rolled steel sheet is not cooled as in the conventional case, resulting in a defective material. However, the steel sheet continuously hot-rolled after that is the tip of the steel sheet. Since there is no, it becomes possible to cool everything,
Since there is no defective material, the product yield due to defective material at the tip can be improved.

Further, as in the invention of claim 2, 1150 ° C.
The following low-temperature heating precipitation treatment, bending strain 0.5% or more, bending
Strain rate 0.05S^-1 Cooling for 3 seconds or more and 1 ° C / S or less
Narrow range of precipitation treatment and hot finishing temperature
When combined with the crystal grain refining process to control,
The ductility and toughness of the hot rolled steel sheet can be improved.

[0042]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings.

FIG. 4 is a diagram showing an outline of a method for producing a hot-rolled steel sheet for working having excellent formability in the hot-rolling continuous method.

As shown in FIG. 4, in the heating furnace 1, for example, 11
Steels with a carbon content of 0.5% or less heated to 50 ° C or less
The rub is hot-rolled by the rough rolling mill 2 and is_Threetransformation
Bending strain 0.5% or more, bending strain rate 0.0 at temperatures above the point
5S^-1 The coil is rolled up into the rough rolled coil 3 for 3 seconds.
It is held at a cooling rate of 1 ° C./S or less and then rewound.
The tip of the unrolled rough rolling coil 3 is cut by the welding cutting machine 4.
It is then cut to form a tip groove suitable for welding. Pressure
The rough rolled steel sheet that precedes the rolling line is conveyed to the finishing mill.
Finished and rolled, but the rear end is also welded by the cutting machine 4.
It is then cut to form a trailing edge groove suitable for welding. Destination
The trailing edge of the 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 sheets, which are integrally joined by the welding device 5 and have a long length, have a hot-rolling temperature of A at the finishing rolling mill 6.
r ₃ + 50 ° C. or less, and continuously finish rolling under the condition that the difference between the temperature on the hot finish rolling mill inlet side and the temperature on the hot finish rolling mill outlet side is 100 ° C. or less, and then the runout After being water-cooled to the winding temperature by the cooling device 7 installed on the table, the coil is wound by the winding machine 9 as a coil.
When the finished steel sheet is wound up to a predetermined length, it is cut by the cutting machine 8 and wound by the winding machine 9 as another coil. In addition, it is preferable to cut the part joined by the welding device 5 in the cutting part by the cutting machine 8.

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 rolls of the winding machine. Water cooling can be performed by the device. 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.

Further, according to the present invention, as described above, the precipitation treatment in which the bending strain and the bending strain rate are regulated, and the grain refining treatment in which the finishing temperature range is regulated are included.
As described above, since the precipitation treatment and the grain refinement treatment are performed by combining the low temperature heating as described above, MnS and AlN are not used during finish rolling.
The fine precipitates and the refinement of crystal grains are promoted by using the precipitates of No. 2 as nuclei, and a hot-rolled steel sheet for working having high ductility and excellent toughness can be obtained. Further, since the hot finish rolling is performed continuously, there is no variation in temperature drop over the entire steel sheet during hot finish rolling, the material is homogeneous over the entire length of the steel sheet, and the heating temperature for heating the steel slab is also The heating temperature can be set to a low temperature of 1150 ° C. or lower, which is lower than the heating temperature of 1200 ° C. in the conventional hot rolling method.

[0049]

EXAMPLES Examples of the present invention and comparative examples will be described below.

Hot-rolled steel sheets for working were manufactured under the processing conditions shown in Table 2 by using the steel materials having the components shown in Table 1.

As shown in Table 2, No. Nos. 1 to 3 are examples of the present invention. When the steel A and the steel B were compared with the comparative examples Nos. 4 to 11, TS × El and brittle transition temperature were remarkably excellent, and the material evaluation was good.

No. 1100 using A steel material of 2
The example in which the low temperature heating at 0 ° C. was performed is No. TS × El was higher than that in the example in which the A steel material of No. 1 was heated to 1200 ° C., and the material was superior when heated at a low temperature.

[0053]

[Table 1]

[0054]

[Table 2]

[0055]

EFFECTS OF THE INVENTION According to the method for producing a hot-rolled steel sheet for working excellent in formability by the hot-rolling continuous method according to the present invention, a high ductility and excellent toughness for working can be obtained by precipitation treatment and grain refining treatment. Hot-rolled steel sheet can be obtained and becomes homogeneous over the entire length of the steel sheet. Also, low-temperature heating reduces the unit consumption of the heating furnace, and further, product yield due to material defects at the tip of the hot-rolled steel sheet. Can be improved. Moreover, high productivity can be achieved.

[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 a relationship between a product of elongation (El) and tensile strength (TS), and a temperature difference (ΔT) between an inlet side temperature (FT0) and an outlet side temperature (FT).

FIG. 3 is a diagram schematically showing a relationship between a heating temperature and a finishing temperature of a hot rolled steel sheet.

FIG. 4 is a diagram showing an outline of a method for producing a hot-rolled steel sheet for processing having excellent formability by the hot-rolling continuous method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Rough rolling machine 3 Rough rolling coil 4 Cutting machine for welding 5 Welding equipment 6 Finishing rolling machine 7 Cooling device 8 Cutting machine 9 Winding machine

Claims (2)

[Claims] 1. A steel slab having a carbon content of 0.5% or less is heated in a heating furnace and roughly rolled by a hot roughing mill to form a steel plate.
Then, in a method for producing a hot-rolled steel sheet for processing excellent in formability, which is characterized in that it is cooled after rolling in a coil after finish rolling in a hot finish rolling mill, and that the rough-rolled steel sheet is heated at a temperature not lower than the Ar ₃ transformation point. Bending strain 0.5% or more, bending strain rate 0.05S
^-1 or more, then hold for 3 seconds or more at a cooling rate of 1 ° C / S or less, and then rewind, and the tip of the steel sheet is rolled after the steel sheet roughly rolled before the rolling line. Joined to the end, the hot finishing temperature is within the range of Ar ₃ + 50 ° C. or less, and the difference between the temperature on the hot finishing mill inlet side and the temperature on the hot finishing mill outlet side is 100 ° C. or less. A method for producing a hot-rolled steel sheet for working, which is excellent in formability and has good toughness, which comprises continuously performing hot finish rolling under the conditions. 2. A steel slab having a carbon content of 0.5% or less is heated in a heating furnace and roughly rolled by a hot roughing mill to form a steel plate.
Next, in the method for producing a hot-rolled steel sheet for processing excellent in formability, which is finished by a hot finish rolling mill, then cooled and wound up into a coil, the heating in the heating furnace is performed in a heating furnace.
0 ℃ the following low-temperature heating, and the rough rolling steel plate Ar ₃
Winding at a temperature above the transformation point with a bending strain of 0.5% or more and a bending strain rate of 0.05 S ^-1 or more, and then for 3 seconds or more at 1 ° C./S
It is held at the following cooling rate, then rewound, and the leading end of the steel sheet is joined to the trailing end of the steel sheet which is roughly rolled before and precedes the rolling line, and the hot finishing temperature is Ar ₃ + 50 ° C.
In the following range, the hot finish rolling is continuously performed under the condition that the difference between the temperature on the hot finish rolling mill inlet side and the temperature on the hot finish rolling mill outgoing side is 100 ° C. or less. A method for manufacturing hot-rolled steel sheet for processing, which has excellent formability and good toughness.