JPH11123415A - Lubricated rolling method and manufacture of hot rolled steel sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricated rolling method by which rolling is executed in a desired highly lubricated state in spite of change in a rolling condition and to provide the manufacturing method of a hot rolled steel sheet by which the hot rolled steel sheet having excellent deep-drawability after hot rolling to annealing is manufactured at high efficiency and high yield applying this lubricated rolling method. SOLUTION: In a rolling method in which, after mixing rolling oil and water with a mixing device 2 for oil and water which is arranged on a mill stand, it is sprayed on work rolls 1a, 1b, the temp. of water is changed. In the manufacturing method of a hot rolled steel sheet, a dead soft steel slab is heated in a heating furnace, made into a sheet bar by rough rolling with a roughing mill, a preceding material and succeeding material of this sheet bar are butted, heated and joined. The sheet bar is finish-rolled with a finishing mill by this lubricated rolling method taking the temp. on the inlet side not higher than Ar3 transformation temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lubricating rolling method and a method for producing a hot-rolled steel sheet, and more particularly to a lubricating rolling method and a method for producing a hot-rolled steel sheet suitable for producing a hot-rolled steel sheet having a high deep drawing property.

[0002]

2. Description of the Related Art Generally, a hot-rolled steel sheet has a low r value (Rankford value) representing deep drawability of about 0.8, which is difficult to apply to deep drawing materials. Later r
A hot rolling method capable of obtaining a steel sheet having a high value has been proposed. In this method, extremely low carbon steel material is subjected to high lubrication rolling in a warm temperature range (below the Ar ₃ transformation point). For example,
JP-A-62-137103 discloses that a very low carbon steel material is subjected to a finish rolling temperature: an Ar ₃ transformation point to 300 ° C., and a reduction rate (load reduction rate) of a rolling load (hereinafter also simply referred to as a load) is 30%. It is described that rolling is performed under the high lubrication conditions described above. Here, the load reduction rate is defined by the following equation (1).

[0003] Load reduction rate (%) = 100 x (non-lubricated portion load-lubricated portion load) / non-lubricated portion load ... (1) On the other hand, a wide and thin material as a hot-rolled steel sheet for deep drawing is produced with high efficiency. As a method of doing this, JP-A-6-137103 describes that a sheet bar is joined and the rolling load and rolling torque are reduced by utilizing phase transformation.

In order to lubricate hot rolling, there is generally known a method in which rolling oil is mixed with water at a predetermined concentration (premix) and sprayed onto a work roll or a backup roll. In addition, a method of spraying a solid lubricant such as grease or graphite onto a work roll by air is also known.

[0005]

However, according to the above-mentioned prior art, there are the following drawbacks, and the deep drawability of a hot-rolled steel sheet cannot be drastically improved. As described above, JP-A-62-137103 discloses that a hot-rolled steel sheet excellent in deep drawability can be manufactured by rolling at a load reduction rate of 30% or more. No lubrication method is disclosed. Therefore, when lubricating rolling is performed by the above-described known method, there is an upper limit to the load reduction rate that can be achieved depending on rolling conditions (input side thickness, roll diameter, rolling reduction, rolling speed, and the like). Even if the friction between them is sufficiently small, the load reduction rate may be able to reach only a level of less than 30%. Further, when the plate thickness is reduced, the coefficient of friction may not be sufficiently reduced in the latter stand even if the load reduction rate is about 30% in the former stand.

On the other hand, since rolling is performed in a warm temperature range, it is necessary to cool the sheet between finishing mill stands. The inter-stand plate cooling is performed by spraying cooling water onto the plate using a strip coolant usually provided between stands. However, when this is done, there is a problem that the cooling water gets on the plate and the rolling oil adhered to the rolls is washed away, so that a sufficient lubricating state cannot be obtained. Furthermore, even with a liquid lubricant, the load can be reduced at the beginning of rolling, but when the roughness of the roll increases with the progress of rolling, the friction coefficient between the roll and the material increases, and the load cannot be reduced sufficiently. .

When a solid lubricant is used, the friction coefficient does not increase with time as in a liquid lubricant, but the spray tends to be non-uniform in the width direction of the plate. There is a problem that a bad shape defect occurs. Also,
According to the technique described in JP-A-6-137103, although the rolling load is reduced by reducing the deformation resistance of the rolled material due to the phase transformation, the rolling coefficient is not reduced because the rolling coefficient is not reduced. Shear strain is introduced into the material surface, and the deep drawability of the product is impaired.

As described above, in the prior art, it has been claimed that the deep drawability of a hot-rolled steel sheet can be improved by a combination of warm rolling and high lubrication rolling, but the essential high lubrication rolling is effectively performed. Therefore, a hot-rolled steel sheet having satisfactory deep drawability has not been manufactured. Accordingly, a first object of the present invention is to provide a lubricating rolling method capable of performing rolling in a desired high lubrication state regardless of changes in rolling conditions.

The present invention further provides a method for producing a hot-rolled steel sheet which can produce a hot-rolled steel sheet having excellent deep drawability after hot rolling and annealing with high efficiency and high yield by applying the lubricating rolling method. This is a second object.

[0010]

Means for Solving the Problems The present inventors have proposed the first method.
In order to achieve the object of (1), the amount of oil adhering to the roll (the amount of oil adhering to the roll), which is a major factor in the lubrication conditions, is to mix (mix) general-purpose rolling oil with water (spray water) and spray it onto the roll. ), And as a result, for example, as shown in FIG.
A valuable finding was obtained that the amount of oil adhering (= the amount of oil adhering to the roll) is a strong monotonous decreasing function of the spray water temperature. This is presumably because the viscosity of the rolling oil increases during mixing due to a decrease in the spray water temperature, and the oil easily adheres to the roll. This means that the lubricating property is effectively improved by lowering the temperature of the spray water during mixing, and the change in the spray water temperature makes it impossible to perform the rolling by the conventional method of premixing the rolling oil and water. It is suggested that dynamic lubrication control in the inside can be performed. The amount of oil adhering in FIG. 5 is a value when spraying is performed for 3 seconds under a spray pressure of 3 atm.

The lubricating rolling method according to the present invention has been completed as a result of further studies based on this finding.
The gist lies in the following (1) to (3). (1) A lubricating rolling method in which rolling oil is mixed with water and sprayed onto a work roll by an oil-water mixing device arranged on a mill stand during hot rolling, wherein the temperature of the water is changed. Method. (2) The lubricating rolling method according to (1), further comprising spraying a solid lubricant onto the work roll. (3) In a lubrication rolling method in which rolling oil is mixed with water and sprayed on a work roll by an oil-water mixing device arranged on a mill stand during hot rolling, the temperature of the water is changed, or Spray the lubricant,
In addition, a lubricating rolling method characterized in that the finishing mill outlet temperature is adjusted by changing the finishing rolling speed without using strip coolant between the finishing mill stands.

The present inventors have further studied to achieve the second object, and as a result, have found a method for manufacturing a hot-rolled steel sheet which can obtain a product exhibiting excellent deep drawability after hot-rolling-annealing. completed. The gist lies in the following (4). (4) The ultra-low carbon steel slab is heated in a heating furnace, rough-rolled in a rough mill to form a sheet bar, and the preceding and succeeding materials of the sheet bar are butt-connected and heated and joined, followed by a finishing mill. A method for producing a hot-rolled steel sheet, wherein the entrance temperature is equal to or lower than the Ar ₃ transformation point and finish rolling is performed by the lubricating rolling method according to any one of the above (1) to (3).

[0013]

According to the present invention (1), rolling oil is mixed during hot rolling in a rough mill and / or a finishing mill by utilizing the relationship shown in FIG. The amount of oil adhering to the roll can be controlled by changing the spray water temperature. Therefore, it is possible to perform hot rolling under a high-level lubrication state, which cannot be achieved by using a conventional premix of rolling oil and water, over a wide range of rolling conditions.

FIG. 1 is a schematic view showing an example of a roll lubrication device suitable for implementing the present invention (1). In FIG.
1 is a roll (work roll), 2 is an oil-water mixing device for mixing rolling oil (also simply referred to as oil, also referred to as a liquid lubricant (abbreviated as liquid)) and water, and 3 is an oil-water spraying the mixed oil-water. A spray nozzle, 4 a cooling device for changing the temperature of the mixed water, 5 a water tank,
Reference numeral 6 denotes a water pump, 7 denotes an oil tank, 8 denotes a liquid agent gear pump capable of adjusting the amount of refueling by changing the gear rotation speed, 9 denotes a rolled material (plate), and the subscripts a and b indicate upper and lower.

The oil / water mixing device 2 is preferably constituted by an orifice nozzle having a diameter of about 6 to 10 mm. The oil-water spray nozzle 3 is preferably of a flat type suitable for spraying uniformly over the entire roll barrel. As the rolling oil, a commercially available hot rolling oil composed of synthetic ester, mineral oil or a mixture thereof (viscosity: 50 to 300 cSt)
/ 40 ° C). As the cooling device 4, a heat exchange type cooler of a type in which a coolant such as water flows around a water pipe is preferable. The cooling capacity of the cooling device that affects the water temperature can be adjusted by changing the flow rate of the refrigerant. This change in cooling capacity is performed so that the rolling load falls within a desired range.

In a quadruple mill stand, backup rolls (not shown) are arranged above the upper roll 1a and below the lower roll 1b. In the present invention (1), an oil-water spray to the backup roll may be used in combination, but performing the oil-water spray only to the backup roll has a poor lubricating effect. Next, in the present invention (2), in addition to the present invention (1), a solid lubricant (abbreviated as a solid agent) is sprayed onto the work roll in association with the oil-water spray. This is an effective means when the roll roughness increases as the rolling progresses and the oil-water spray alone does not provide sufficient roll lubrication, causing problems such as poor shape and meandering. The solid agent spray alone tends to cause uneven lubrication in the width direction, but by using it together with the oil-water spray, the oil (liquid agent) in the oil water acts on the roll part where the solid agent does not adhere,
A uniform lubrication state can be maintained over the entire width, and the occurrence of defects such as the shape defect and meandering can be suppressed. Grease, graphite, or a mixture thereof can be suitably used as the solid agent.

FIG. 2 is a schematic diagram showing an example of a roll lubrication device suitable for carrying out the present invention (2). In addition to the apparatus of FIG. 1, an air nozzle 10 for spraying the solid agent on an air flow is arranged. Numerals 11 and 12 denote a solid material pipe and an air pipe, respectively, leading to the air nozzle 10, 13 a solid material gear pump capable of adjusting a solid material supply amount by changing a gear rotation speed, 14 an air pump, 15 a solid material tank, and a suffix a. , B indicate above and below. The same or corresponding parts as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.

Next, in the present invention (3), in addition to the present invention (1) or (2), the finishing mill outlet side temperature is changed by changing the finishing rolling speed without using the strip coolant between the finishing mill stands. Adjust. Generally, between the finishing mill stands, a strip coolant composed of a water spray device for spraying cooling water to the plate is provided, and the strip coolant is used to cool the plate and adjust the temperature of the finish mill outlet side. "Mill water cooling" is performed, but the cooling water on the plate infiltrates the roll bite, and the lubricant attached to the roll is washed away to reduce the lubrication effect. Therefore, the present invention (1) or (2) When performing, it is preferable to perform "finishing mill air cooling" without using a roll coolant. However, in the finishing mill air cooling, it is difficult to control the finishing mill outlet side temperature to a target range.

Therefore, in the present invention (3), the finish mill air cooling is performed and the finish mill outlet temperature is adjusted by changing the finish rolling speed. The change in the finish rolling speed is preferably performed in a direction in which the speed is reduced. Due to this deceleration, the air cooling time between the stands is extended, and the amount of heat removed from the rolls in the roll bite is increased, thereby lowering the plate temperature. FIG. 3 is a schematic diagram showing an example of a finishing mill speed control system suitable for implementing the present invention (3). In FIG. 3, reference numeral 20 denotes a finishing mill (finishing mill group), 20S denotes a stand (finishing mill stand) which is mounted on a work roll and is arranged in tandem to constitute a finishing mill, and 26 and 27 denote the entrance and exit of the finishing mill, respectively. Thermometer for actually measuring the material surface temperature on the side, 28 is a strip coolant between stands (not used when the present invention (3) is practiced),
Reference numeral 30 denotes a speed reducer, 31 denotes a motor, and 32 denotes a motor rotation speed control device. This finishing mill 20 is equipped with the roll lubrication device shown in FIG. 1 or FIG. The operation of the finishing mill speed control system shown in FIG. 3 which is the same as or equivalent to that in FIGS.

Regarding the finishing mill, the outlet temperature FDT is determined by the input side temperature FET, the rolling speed Vr, and the rolling reduction ri of each stand.
, F, (Vr, ri, H, h, k,...) Such as the input side plate thickness H, the output side plate thickness h, the material deformation resistance k, and the like. FDT = FET + f (2) The specific form of the function f can be determined by theory and experiment according to the specifications of the finishing mill.

Then, if the rolling speed changes by ΔVr,
The variation ΔFDT of the outlet side temperature is obtained by partially differentiating equation (2) with Vr.
This is given by the following equation (3). ΔFDT = (∂f / ∂Vr) ΔVr (3) The motor speed control device 32 receives the input and output from the thermometers 26 and 27.
Side temperature measured value FET _M, FDT_MOn the other hand
No output temperature target value FDT from upper computer_AGet
Difference ΔFDT between actual measured value of outlet temperature and target value_MA(= FDT
_M-FDT_A), And assign this to the left side of equation (3).
To calculate the speed variation ΔVr on the right side and calculate the rolling speed.
The number of revolutions of the motor 31 is changed so as to be changed by the amount.
Note that ∂f / ∂Vr on the right side of equation (3) is a function of temperature.
Since it includes the deformation resistance k, etc., the temperature at the time of calculating ΔVr
For example, FET_MOr FET_M, FDT_M
And the like.

[0022] Thus, it is possible to perform rolling speed control as close to FDT _M in FDT _A. Next, the present invention (4) is to manufacture a hot-rolled steel sheet having excellent deep drawability after hot rolling and annealing at a high efficiency and a high yield, so that the material is a very low carbon steel (C ≦ 0.005 wt%). The steel) slab is heated in a heating furnace, roughly rolled in a rough mill, the preceding material and the succeeding material are butt-connected and heated and joined, and the inlet side temperature is reduced to the Ar ₃ transformation point or lower by a finishing mill. ) To finish rolling by the lubricating rolling method (roll lubricating method) described in any one of (1) to (3), followed by annealing.

The main point of the method for producing a hot-rolled steel sheet having excellent deep drawability is that, during hot rolling, work strain is accumulated in ferrite and rolling with a low friction coefficient (lubricating rolling) is performed to reduce shear deformation of the material surface. The object is to suppress the growth and develop {111} texture parallel to the sheet surface by annealing after hot rolling. The reason why the material is ultra-low carbon steel (steel with C ≦ 0.005 wt%) is that a ferrite single-phase structure is formed at a relatively high temperature and a ferrite processed structure is easily obtained after hot rolling. In the case of steel with C> 0.005 wt%, a sufficient ferrite processed structure cannot be obtained after hot rolling, and {111} which is parallel to the sheet surface during the recrystallization process by annealing.
It is difficult to develop a texture.

Among the ultra-low carbon steels, C: 0.001 to 0.00
A steel containing 5 wt%, Ti: 0.01 to 0.03 wt%, and Nb: 0.01 to 0.03 wt%, the balance being iron and unavoidable impurities (called high-purity steel) is preferred. The reason is that in the steel having the above composition to which Ti and Nb are added, TiC, Nb
This is because carbides such as C precipitate and solid solution C decreases, and the development of {111} texture parallel to the plate surface is further promoted.

From the viewpoint of productivity, the slab is preferably manufactured by continuous casting. In order to obtain a work structure of ferrite after rolling, the material temperature on the entrance side of the finishing mill needs to be lower than the Ar ₃ transformation point. Recrystallization proceeds in a material that is finish-rolled from a temperature range higher than the Ar ₃ transformation point, and it becomes difficult to recrystallize by annealing after rolling. If the material temperature in the finishing mill is less than 650 ° C., the deformation resistance becomes high and rolling becomes difficult. Therefore, the material temperature on the exit side of the finishing mill is preferably 650 ° C. or more.

In order to perform high lubrication rolling with a finishing mill, it is necessary to perform lubrication rolling according to any one of the present inventions (1) to (3). Thereby, shear deformation of the surface is effectively suppressed, and {111} texture parallel to the plate surface can be sufficiently developed by annealing. The reason why the preceding material and the following material of the rolled material (plate) are joined and finish-rolled after the rough rolling is as follows.

In this batch rolling without joining, if the leading end of the plate is lubricated, the force for pulling the plate into the roll bite will be insufficient, and poor biting will easily occur. If the tail end where tension is not applied is lubricated, the plate will meander, and it will be easy for the guide to come off and narrow down.Therefore, lubrication rolling in the finishing mill is not performed for the tail end of the plate, Part (excluding the tail end)
Only go for For this reason, in the production of a deep-drawing steel sheet by batch rolling, the tail end portion that is finish-rolled in a non-lubricated state is inevitably degraded, and the yield is poor.

On the other hand, if the preceding material and the succeeding material are joined and finish-rolled after the rough rolling, the yield is improved because the length of the leading end (unlubricated portion) with respect to the total pressure extension is reduced. FIG. 4 is a schematic diagram showing an example of a hot rolling line suitable for implementing the present invention (4). In FIG. 4, 22 is a heating furnace for heating the material (slab), 23 is a width press device for adjusting the width of the slab, 21 is a rough mill (rough mill group) for rough rolling, 21S
Is a tandem-arranged stand (coarse mill stand) that constitutes a rough mill, 24 is a coil box that winds up the rolled material 9 after rough rolling, and is discharged to the downstream side, and 25 is a facing end of the preceding material and the following material. This is a joining device for heating and joining by butt, and the subscripts a and b indicate upper and lower. The same or corresponding parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. The heating in the joining device 25 is preferably performed by induction heating. This finishing mill
20 is equipped with the roll lubrication device of FIG. 1 or preferably of FIG. 2, and preferably further equipped with a finishing mill speed control system of FIG.

[0029]

EXAMPLE Using the hot rolling line shown in FIG. 4, a hot rolled steel sheet of ultra-low carbon steel was manufactured according to the present invention (4), and at this time, the present invention (1) to (3) was carried out using a finishing mill. Lubrication rolling was performed. These processes are referred to as Examples 1 to 3. A hot-rolled steel sheet having the same composition as in Example 1 was manufactured under the same rolling conditions as in Example 1, except that the same line was used to perform lubricating rolling in a finishing mill by a conventional method without changing the spray water temperature of the oil-water spray. did. This process is a conventional example.

The specific process here will be described below. Conventional, common to Examples 1 to 3, heating continued cast ultra low carbon steel slab having a chemical composition and Ar ₃ transformation point are shown in Table 1 (200 mm thickness × 1600 mm width × 8000mm length) 950 ° C. Then, after forming a 30 mm thick sheet bar on the exit side of the coarse mill, winding it up with a coil box, and wiping it out, the leading end of the running material is brought into contact with the tail end of the preceding material by a bonding device, and induction heating and bonding are performed. Using a finishing mill, the inlet side temperature was set at 800 ° C and the outlet side temperature was set at 680 ° C, the sheet was finished into a hot-rolled steel sheet having a thickness of 1.5 mm, and wound into a coil. The bonding of the sheet bars was performed as two sets. That is, the n-th set is formed by joining the (2n-1) -th sheet bar and the (2n) -th sheet bar after the roll replacement.

In the finishing mill, lubrication was started immediately after biting the tip, and was stopped at the tail end. Lubrication was performed uniformly on all stands of the finishing mill. The rolling oil of the oil-water spray was a commercially available hot-rolling oil containing 60% of synthetic ester, 38% of mineral oil, and 2% of extreme pressure agent, and the concentration in the oil water was constant at 2%. The work roll size is 1300 mm in diameter and 2200 mm in barrel length in a coarse mill, and 700 mm in diameter and 2000 mm in barrel length in a finishing mill. The finishing mill is equipped with the roll lubrication device shown in FIG. 2 at each stand, and the finishing mill speed control system shown in FIG. As the cooling device 4 of FIG. 2, a heat exchange type cooler for flowing water around the spray water pipe at a variable flow rate is arranged.

[0032]

[Table 1]

In the conventional example, the rolling speed in the finishing mill is 900
m / min, and the spray water temperature of the oil-water spray was fixed at 40 ° C. The value of 40 ° C. corresponds to the median value of a common temperature range of 35 to 45 ° C. of water commonly used for plate cooling water and roll cooling water in addition to oil-water spray water. On the other hand, in Example 1, the rolling speed in the finishing mill was set to 900 m / min, which is the same as the conventional example, and the spray water temperature of the oil-water spray was changed during rolling.

FIG. 6 shows the relationship between the spray water temperature (a), the rolling load (b), and the rolling distance in the F7 (= finishing mill seventh) stand according to the second set of the conventional example and the first embodiment. It is a graph. The rolling reduction of F7 is 25%. As shown in the figure, in the conventional example, the load reduction (meaning the load reduction of the lubricated portion relative to the non-lubricated portion, the same applies hereinafter) is small.
In the first embodiment, the load reduction rate (defined by the formula (1)) is 30%.
That was all. In addition, it can be seen from the figure that when the spray water temperature is raised / lowered within one set, the load is sensitively decreased / increased accordingly. As described above, according to the present invention (1), since the rolling load can be dynamically and accurately controlled over a wide range, a much larger load reduction rate than in the past can be easily achieved.

Next, in Example 2, in addition to Example 1, a solid lubricant (grease) was sprayed from the air nozzle 10 shown in FIG. The grease spray amount is 200g / min /
Roll. FIG. 7 is a graph showing the relationship between the spray water temperature (a), the rolling load (b), and the rolling distance in the F7 stand according to the fifteenth set of the conventional example and Example 2. As shown in the figure, in the conventional example, the roll roughness increased due to the progress of rolling, and the load reduction decreased (compared with FIG. 6 of the second set). On the other hand, in Example 2, the spray water temperature was lowered to 15 ° C in the latter half of the 15th set,
Spraying at a rate of 0 g / min / roll resulted in an even greater load reduction than in the first half. As described above, according to the present invention (2), even when the roughness of the rolling roll becomes rough, it is possible to easily achieve a much larger load reduction rate than in the past.

Next, the third embodiment is a third embodiment in which the present invention (3) is applied to the first and second embodiments (air cooling between stands to adjust the rolling speed so that the finish mill exit side temperature falls within a target range).
A, 3B. FIG. 8 shows a conventional example and Example 3A,
It is a graph which shows the relationship between the spray water temperature (a) and the rolling load (b), and the rolling distance in the F7 stand which concerns on the 15th set of 3B. As can be seen from the figure, in both Examples 3A and 3B, a sufficient load reduction was obtained as compared with the conventional example, and the amount of load reduction was larger in Example 3B with grease spray than in Example 3A with oil-water spray alone.

FIG. 9 shows the rolling speed (a) and FD of the F7 stand according to the fifteenth set of the conventional example and Example 3A.
It is a graph which shows the relationship between T (= finish mill exit side temperature) (b) and rolling distance. As shown, in Example 3A, the rolling speed was changed in the range of 400 to 700 mpm (the same applies to Example 3B). In Example 3A, in which the rolling speed was changed by air cooling between stands in order to control the FDT to 680 ° C., temperature control accuracy equal to or higher than that of the conventional example in which the rolling speed was fixed and water cooling between stands was performed appropriately was obtained. Note that the temperature control accuracy of Example 3B was almost the same as that of Example 3A.

As described above, according to the present invention (3), the FD
A larger load reduction than before can be obtained while maintaining the T management accuracy at or above the conventional level. F of conventional example and Examples 1 to 3
Table 2 summarizes the load reduction rates at the seven stands.
From the table, it can be seen that according to the present invention, a load reduction rate of 30% or more, which cannot be obtained conventionally, can be obtained.

[0039]

[Table 2]

This is evidence that the lubricating rolling method of the present invention can effectively reduce the frictional force between the roll and the plate. In addition, the coefficient of friction between the roll and the plate in the lubricated parts of Examples 1 to 3 was about 0.10 to 0.14, which was a sufficiently low value for hot rolling. Table 2 shows that, for the steel sheet coils of the conventional example and Examples 1 to 3, test pieces were taken from the locations where the load reduction rates of Table 1 were obtained, and were subjected to annealing at 850 ° C. for 2 hours to obtain r values. The results of the survey are also shown. The r value of the conventional example is
In contrast to 0.91 to 0.95, in Examples 1 to 3, 1.20 to 0.95.
A remarkably high r value of 1.35 was obtained. Thus, according to the present invention, hot-rolled-a hot-rolled steel sheet exhibiting a high r value after annealing,
That is, it is clear that a hot-rolled steel sheet having excellent deep drawability can be manufactured.

[0041]

As described above, according to the present invention, a hot-rolled steel sheet capable of performing hot rolling in a lubricated state at a higher level than the conventional one and exhibiting excellent deep drawability after hot rolling-annealing can be obtained with high efficiency. It has a remarkable effect that it can be manufactured at a high yield.

[Brief description of the drawings]

FIG. 1 is a schematic view showing an example of a roll lubrication device suitable for implementing the present invention (1).

FIG. 2 is a schematic diagram showing an example of a roll lubrication device suitable for implementing the present invention (2).

FIG. 3 is a schematic diagram showing an example of a finishing mill speed control system suitable for implementing the present invention (3).

FIG. 4 is a schematic diagram showing an example of a hot rolling line suitable for implementing the present invention (4).

FIG. 5 is a graph showing the relationship between spray water temperature and the amount of adhered oil.

FIG. 6 shows an F7 according to a second set of the conventional example and the first embodiment.
It is a graph which shows the relationship between the spray water temperature (a) in a stand, a rolling load (b), and a rolling distance.

FIG. 7 shows an F7 according to a fifteenth set of the conventional example and the second embodiment.
It is a graph which shows the relationship between the spray water temperature (a) in a stand, a rolling load (b), and a rolling distance.

FIG. 8 is a graph showing the relationship between the spray water temperature (a) and the rolling load (b) and the rolling distance in the F7 stand according to the fifteenth set of the conventional example and Examples 3A and 3B.

FIG. 9 is a diagram illustrating an F according to a fifteenth set of the conventional example and the example 3A.
It is a graph which shows the relationship between rolling speed (a) and FDT (b) in 7 stands, and rolling distance.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Roll (work roll) 2 Oil-water mixing device 3 Oil-water spray nozzle 4 Cooling device 5 Water tank 6 Water pump 7 Oil tank 8 Liquid agent gear pump 9 Rolled material (plate) 10 Air nozzle 11 Solid agent piping 12 Air piping 13 Solid agent gear pump 14 Air pump 15 Solid agent tank 20 Finishing mill (finishing mill group) 20S stand (finishing mill stand) 21 Coarse mill (coarse mill group) 21S stand (coarse mill stand) 22 Heating furnace 23 Width press device 24 Coil box 25 Joining device 26, 27 Thermometer 28 Strip coolant 30 Reducer 31 Motor 32 Motor speed controller

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI C21D 9/48 C21D 9/48 S (72) Inventor Masanori Kitahama 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Pref. Inside the research laboratory (72) Inventor Yasuo Yarida 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Prefecture Kawasaki Steel Engineering Co., Ltd. In the laboratory

Claims (4)

[Claims] 1. A lubricating rolling method in which rolling oil is mixed with water and sprayed onto a work roll by an oil-water mixing device disposed on a mill stand during hot rolling, wherein the temperature of the water is changed. Lubrication rolling method. 2. The method according to claim 1, further comprising spraying a solid lubricant onto the work roll. 3. A lubricating rolling method in which rolling oil is mixed with water and sprayed onto a work roll by an oil-water mixing device arranged on a mill stand during hot rolling, wherein the temperature of the water is changed, or A solid lubricant is sprayed on the finishing mill, and the finishing mill outlet temperature is adjusted by changing the finishing rolling speed without using a strip coolant between the finishing mill stands. 4. A very low carbon steel slab is heated in a heating furnace, roughly rolled in a rough mill to form a sheet bar, and a preceding material and a succeeding material of the sheet bar are abutted and heated and joined to form a finishing mill. A method for producing a hot-rolled steel sheet, wherein the hot rolling steel sheet is subjected to finish rolling by the lubricating rolling method according to any one of claims 1 to _{3, wherein the} inlet temperature is not more than the Ar3 transformation point.