JPH11319916A - Hot roll lubrication method and hot rolled steel sheet manufacturing method - Google Patents

Abstract

(57) [Summary] [Problem] To provide a hot roll lubrication method capable of performing rolling in a highly lubricated state regardless of changes in rolling conditions.
Further, the present invention provides a method for producing a hot-rolled steel sheet which can obtain a hot-rolled steel sheet having excellent deep drawability by applying the lubrication method. SOLUTION: In a roll lubrication method for supplying a rolling lubricant to a work roll 1 during hot rolling, the work oil is mixed with water by an oil-water mixing device 2 while polishing the work roll with an online roll grinder. Spray. The grindstone 10 of the online roll grinder is preferably composed of two or more types of abrasive grains having different grain sizes, and the grain size of the larger abrasive grain is preferably 200 to 500 μm. Further, 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 joined by joining, and the finishing temperature is set in a finishing mill. Is adjusted to be not more than the Ar ₃ transformation point, and finish rolling is performed while performing roll lubrication by the above-described method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot roll lubrication method and a method for producing a hot rolled steel sheet, and more particularly, to a continuous type in which a leading end of a preceding bar of a sheet bar and a leading end of a following bar are joined and hot rolled. In a hot rolling method (endless rolling method), the present invention relates to a hot roll lubrication method particularly suitable for high lubrication rolling in a finishing mill and a method for producing a hot rolled steel sheet capable of obtaining a product excellent in deep drawability.

[0002]

2. Description of the Related Art Generally, a hot-rolled steel sheet has a low r value (Rankford value) indicative of 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,
Japanese Unexamined Patent Publication (Kokai) No. 62-137103 discloses that a very low carbon steel material has a finish rolling temperature: Ar ₃ points to 300 ° C. and a reduction rate (load reduction rate) of a rolling load (hereinafter, also simply referred to as a load) of 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 (load without lubrication-load with lubrication) / load without lubrication ... (1) On the other hand, a wide thin material of hot-rolled steel sheet for deep drawing For example, as described in Japanese Patent Application Laid-Open No. 6-55202, it is known that a sheet bar is joined and a rolling load and a rolling torque are reduced by utilizing phase transformation. I have.

[0004] As means for making hot rolling highly lubricated, a solid lubricant is added to the grease in an amount of 3 to 40% by weight while grinding the rolling roll with an online roll grinder to suppress wear and seizure of the rolling roll. Japanese Patent Application Laid-Open No. 7-204713 discloses a method of supplying the mixture to a rolling roll.

[0005]

However, the above-mentioned prior art has the following problems, and it has not been possible to drastically improve the deep drawability of a hot-rolled steel sheet.
JP-A-62-137103 states that a hot-rolled steel sheet with excellent deep drawability can be manufactured if the load reduction rate is 30% or more, but there is no specific lubrication method disclosed therein. You have to rely on the lubrication method. However, lubrication rolling by a normal lubrication method, that is, a lubrication method in which water is premixed with rolling oil (hereinafter also simply referred to as oil) at a predetermined concentration and sprayed onto a work roll or a backup roll,
Rolling conditions (input side thickness, roll diameter, rolling reduction,
There is an upper limit that can be reached depending on the rolling speed, etc. For example, in a finishing mill front stand, the load reduction rate is 30 even if the friction between the roll and the plate is sufficiently reduced by the usual lubrication method.
% In some cases, and with the normal lubrication method described above, when the plate thickness is reduced, the friction coefficient in the post-stage stand of the finishing mill is not sufficiently reduced, and even if the load reduction rate reaches about 30%, the r value is reduced. Hot rolled steel sheet cannot be obtained. As described above, it is difficult to obtain a hot-rolled steel sheet excellent in deep drawability by the technique described in JP-A-62-137103, which simply limits the load reduction rate without disclosing a specific lubrication method.

Further, according to the technique described in Japanese Patent Application Laid-Open No. 6-55202, the rolling load is reduced due to the reduction of the deformation resistance of the rolled material due to the phase transformation, but the friction coefficient between the roll and the material is not reduced. In addition, shear strain is introduced on the surface of the rolled material, and the deep drawability of the product is impaired. In addition, Japanese Patent Application Laid-Open
According to the technology described in Japanese Patent No. 204713, although a sufficient lubricating effect can be expected, it is difficult to spray a mixture of grease and a solid lubricant evenly in the width direction of the plate. There is a problem that a general shape defect is likely to occur.

Accordingly, a first object of the present invention is to provide a hot roll lubrication method capable of performing rolling in a highly lubricated state regardless of changes in rolling conditions. A second object of the present invention is to provide a method for manufacturing a hot-rolled steel sheet which can be applied to a hot-rolled steel sheet having excellent deep drawability after hot-rolling and annealing with high efficiency and high yield.

[0008]

Means for Solving the Problems The present inventors have proposed the first method.
In order to achieve the objective of (1), the roll lubrication method in which general-purpose rolling oil is mixed (mixed; premixed) with water (spray water) and sprayed onto the rolls, the amount of oil content (the The amount of oil that has been deposited on the rolls has been closely studied, and as a result, for example, as shown in FIG. Knowledge was obtained.

The grinding stone used here passes through 145 mesh and does not pass through 170 mesh (nominal size 105 μm
8888 μm, hereinafter referred to as 145 mesh abrasive grains. ), And a mixture of small and large-sized abrasive grains, and a mixture of 5 larger abrasive grains, 70, 48, 36, 32, and 28 mesh abrasive grains, each in a ratio of 30 wt%. These were manufactured using abrasive grains (B1 to B5).

[0010] More specifically, the types of the grindstones shown in Fig. 4 will be described in detail. The A grindstone is a grindstone made of 145 mesh abrasive grains (abrasive grains passing through 145 mesh and not passing through 170 mesh), and a B5 grindstone. Is the 145 mesh abrasive
A 28-mesh abrasive (abrasive that passes through 28 mesh and does not pass through 32 mesh) is a whetstone made of 30 wt% mixed abrasive. The B4 whetstone is a 32-mesh abrasive (32 mesh This is a grinding stone made of abrasive grains mixed with 30 wt%, which passes through the mesh and does not pass through 36 mesh.
The grindstone is 30wt% of the above-mentioned 145 mesh abrasive grains with 36 mesh abrasive grains (abrasive grains that pass through 36 mesh and do not pass through 42 mesh).
The B2 whetstone is made by mixing 145 mesh abrasive grains with 30 wt% of 48 mesh abrasive grains (an abrasive grain that passes through 48 mesh but does not pass through 60 mesh). The B1 whetstone is a whetstone made of abrasive grains obtained by mixing 30 wt% of 70 mesh abrasive grains (abrasive grains passing through 70 mesh but not passing through 80 mesh) with the 145 mesh abrasive grains.

By the way, the nominal size of 28 mesh is 590 μm
The nominal size of 170 mesh is 88 μm. (JI
SZ 8801) According to FIG. 4, the larger the grain size of the grindstone to be roll-polished (represented by large grain size abrasive grains in the case of mixed small and large abrasive grains), that is, the coarser the grindstone, the larger the oil adhesion amount after the grindstone polishing. It turns out that it becomes.

Next, FIG. 5 shows a load reduction ratio with respect to a rolling load obtained by performing lubrication rolling while performing roll polishing with each of the above grindstones by a laboratory rolling mill and rolling without lubrication. In this lubrication rolling, a 200 mm diameter roll is rotated at a speed of 100 m / mim,
While spraying a water-rolling oil mixture at a liquid temperature of 40 ° C. at a pressure of 3 atm into the roll, a 10 mm thick × 100 mm wide ultra-low carbon steel sheet (C: 0.003 wt%) heated to 1000 ° C. was bitten. Rolled at a rolling reduction of 30%.

The load reduction rate is at most 18 without roll polishing.
It is about 25%, but it becomes a high value of 25% by roll polishing with A wheel of 145 mesh abrasive grains, and large abrasive grains are added to 145 mesh abrasive grains in the range of 32 mesh abrasive grains to 70 mesh abrasive grains. Roll polishing of the mixed large and small abrasive grains with a B1 to B4 grindstone resulted in an even higher value of 30 to 40%. The present invention, which has been further studied based on these findings, is the following (1) to (3). (1) In a roll lubrication method in which a rolling lubricant is supplied to a work roll during hot rolling, the work oil is mixed with water and sprayed onto the work roll while the work roll is polished with an online roll grinder. A hot roll lubrication method. (2) The grindstone of the online roll grinder is composed of two or more types of abrasive grains having different particle sizes,
(1) The method according to (1), wherein 70 to 32 mesh abrasive grains are used. (3) The ultra-low carbon steel slab is heated in a heating furnace, roughly rolled by a rough mill to form a sheet bar, and the preceding and succeeding materials of the sheet bar are joined by joining, and the finishing mill enters the side. Temperature
A method for producing a hot-rolled steel sheet, wherein the hot-rolled steel sheet is subjected to finish rolling while performing roll lubrication by the method (1) or (2) below the Ar ₃ transformation point.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention (1), a work roll is formed during hot rolling in a rough mill and / or a finishing mill by utilizing the relationships shown in FIGS. The oil adhesion amount can be controlled while polishing with an online roll grinder, and the load reduction rate can be sufficiently increased. Further, according to the present invention (2), it is possible to stably maintain the load reduction rate at a high level. Therefore, according to the present invention, it is possible to perform hot rolling under a high-level lubricating state, which cannot be achieved by conventional lubricating rolling using a simple oil-water premix spray, over a wide range of rolling conditions.

FIG. 1 is a schematic front view showing an example of a roll lubrication device and an online roll grinder suitable for carrying out the present invention (1) and (2), and FIG. 2 is a schematic side view of FIG. The roll lubrication device and the online roll grinder of the present example are used for the upper and lower work rolls 1 for rolling the strip 9.
(Additional codes a and b indicate up and down, the same applies hereinafter) and a backup roll 42 for reinforcing these from above and below.
It is located on the entry side of the heavy rolling mill.

The roll lubrication device of the present embodiment has a work roll 1
Nozzles, which are arranged in the roll barrel direction in opposition to each other, an oil / water mixer 2 for mixing and supplying oil / water to the spray nozzles 3, a water supply pump 6 for supplying water to the oil / water mixer 2, and a water supply pump 6 A water tank 5 serving as a water source, an oil supply pump 8 for supplying oil to the oil / water mixer 2, an oil tank 7 serving as an oil source for the oil supply pump 8, and an oil supply pump 8 for non-lubricating rolling.
And a three-way valve 4 for switching an oil supply path from the oil supply to the oil-water mixer 2 to a return oil path to the oil tank 7. With this configuration, it is possible to appropriately perform roll lubrication as needed.

The oil (rolling oil) is a commercially available hot rolling oil (viscosity: 50) consisting of synthetic ester, mineral oil or a mixture thereof.
(~ 300 cSt / 40 ° C). Spray nozzle 3
It is preferable to use a flat type nozzle suitable for uniformly spraying the entire area of the roll bite. The oil-water mixer 2 can be configured using an orifice nozzle, and preferably has an orifice diameter of about 6 to 10 mmφ. As the oil supply pump 8, it is preferable to use a gear pump suitable for supplying a liquid lubricant (a liquid supply amount can be controlled by operating a gear rotation speed).

The on-line roll grinder of this embodiment comprises a grindstone 10 for polishing the work roll 1, a hydraulic motor 11 for supporting the grindstone 10 and driving its rotation,
An arbor shaft 12 that supports the oscillating shaft in the roll axis direction and an oscillation motor 13 that drives the arbor shaft 12 to oscillate the hydraulic motor 11 (the oscillating wheel 10 also oscillates). Two grindstones 10 are provided on the left and right sides in the roll barrel direction. With this configuration, online roll polishing can be carried out as needed. It is preferable to dispose a wiper 41 or the like, for example, in order to prevent foreign matters such as abrasive grains falling off from the grindstone 10 and polishing powder from the roll to be polished from entering the roll bite during roll polishing.

The hydraulic motor 11 has a normal rotation speed of 1000 to 20.
It is preferable to use the one of 00m / min. The whetstone 10 is preferably formed of hard abrasive grains made of boron nitride, alumina, silicon carbide, or the like. Also, the case where large-diameter abrasive grains are mixed with 145-mesh abrasive grains has been described, but the preferred range of small-diameter abrasive grains is 280-mesh abrasive grains (passes through 280 mesh and does not pass through 350 mesh) to 100 mesh Abrasives (pass 100 mesh, do not pass 120 mesh). When a roll is polished with a grindstone formed of abrasive grains having a particle diameter in this range, the roughness of the roll after polishing is 0.5 to
0.6 μmRa.

On the other hand, according to the present invention (2), a grindstone is formed by using large and small hybrid abrasive grains obtained by mixing ordinary abrasive grains (small grain abrasive grains) with large grain abrasive grains, thereby obtaining a grinding wheel as shown in FIG. By using the characteristics of FIG. 5, the amount of oil attached can be controlled by changing the particle size of the large-grain abrasive grains, and by using the characteristics of FIG. By adjusting it, a higher stable value of the load reduction rate can be obtained.

The reason why the characteristics shown in FIGS. 4 and 5 are obtained when roll polishing using a grindstone composed of large and small mixed abrasive grains and roll lubrication using an oil-water premix spray are used is considered as follows. That is, the roll portion polished by the large-grain abrasive portion of the grindstone has a large depression. Rolling oil mechanically adheres thereto, and the amount of rolling oil introduced into the roll bite increases. For this reason, the friction coefficient is reduced, and the shear force on the plate surface side is further reduced, so that the load can be reduced.
This load reduction effect becomes even greater when the size of the large abrasive grains is 70 mesh or more (70 or less in the number of meshes).
On the other hand, if the large grains are larger than 32 mesh
In the case of less than 32), the unevenness of the roll restricts the deformation of the plate surface, the coefficient of friction between the roll and the material increases, and the load reduction amount decreases.

In the present invention (2), the preferred range of the particle size of the small-grain abrasive is 280 mesh abrasive to 100
It is a mesh abrasive. Further, a preferable particle size range of the large-grain abrasive grains is 70 mesh abrasive grains to 32 mesh abrasive grains as shown in FIG. As shown in FIG. 6, the preferred range of the mixing ratio of the large and small abrasive grains is in the range of the large grain abrasive compounding ratio: 10 to 50 wt%. If the blending ratio is less than 10 wt%, the amount of oil adhering becomes too small, while if it exceeds 50 wt%, the roll dent area expands and the deformation of the plate surface becomes excessively restrained. It seems to be.

The large and small mixed abrasive grains may be formed by mixing three or more kinds of abrasive grains having different particle diameters. However, the load reduction rate is substantially determined by the maximum abrasive grain size in the grindstone, and three or more kinds of mixed abrasive grains are mixed. In the case of (1), the load reduction rate improving effect is almost the same as that of the case of mixing two types. In the present inventions (1) and (2), it is important to spray a rolling oil (oil-water mixture) while polishing the surface of the work roll with an online roll grinder. The reason why roll polishing is performed during rolling is to maintain a suitable roll surface roughness during the rolling. In particular, because the roll is worn away at the latter stage of the hot finishing mill, the roughness imparted to the work roll before rolling disappears during rolling,
Roll polishing during rolling is even more important.

Next, the present invention (3) is intended to produce a hot rolled steel sheet having excellent deep drawability after hot rolling and annealing at a high efficiency and a high yield. 0.005 wt%
The 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-joined, and the entrance temperature is adjusted to Ar ₃ by a finishing mill. Finish rolling is performed while the hot roll lubrication of (1) or (2) is performed at the transformation point or lower. As a result, the product has excellent deep drawability after annealing.

The key to improving the deep drawability of a hot-rolled steel sheet is to reduce the shear strain of the material by accumulating working strain in the ferrite during hot rolling and performing rolling (lubricating rolling) with a low friction coefficient. The purpose is to develop {111} texture parallel to the sheet surface during the recrystallization process by annealing. The reason why the material is ultra-low carbon steel is that a ferrite single phase structure is formed at a relatively high temperature and a processed ferrite structure is easily obtained after hot rolling. Steel other than ultra-low carbon steel (C> 0.005 wt% steel)
In this case, the proportion of processed ferrite in the structure after hot rolling is too small, and it is difficult to develop {111} texture in the annealing process.

Among ultra-low carbon steels, C: 0.001 to 0.005
A steel (called high-purity steel) containing wt%, Ti: 0.01 to 0.03 wt%, and Nb: 0.01 to 0.03 wt%, the balance being iron and unavoidable impurities is preferable. This is because, in a steel having the above composition by adding Ti and Nb, solid solution C decreases due to precipitation of carbides such as TiC and NbC in the process of hot rolling and annealing, resulting in a decrease of {11} in the annealing process.
1｝ The development of texture is further promoted.

From the viewpoint of productivity, the slab is preferably manufactured by continuous casting. In order to obtain a sufficient amount of processed ferrite after rolling, the material temperature on the entrance side of the finishing mill needs to be lower than the Ar ₃ transformation point. This is because, in a material that has been finish-rolled from a temperature range higher than the Ar ₃ transformation point, recovery or recrystallization of ferrite proceeds during rolling, making it difficult to cause recrystallization in the annealing step.

If the material temperature on the exit side of the finishing mill is lower than 650 ° C., the deformation resistance may be excessive in the finishing mill and rolling may be difficult. Therefore, this temperature is preferably set to 650 ° C. or higher. . In order to improve the yield, it is essential to perform endless rolling in which sheet bars are successively joined after rough rolling and finish rolling is performed continuously. In discontinuous rolling (batch rolling) without sheet bar joining, especially in a finishing mill, lubricating rolling at the leading end tends to cause insufficient pulling of the plate into the roll bite, resulting in poor biting. When the part is lubricated and rolled, the back-end tension is lost and the plate is meandered and the guide is easily released and narrowing occurs at the end of the stand. Lubrication is performed only at the time of rolling. The end of the tail end which has been rolled without lubrication is inevitably deteriorated in deep drawability and is degraded.

In the endless rolling, the point of lubrication rolling at the leading end is the same as that of batch rolling. However, since the number of rolling at the tail end is reduced by the number of joining times, the lubricating pressure per total pressure extension is longer than that of batch rolling. The extension is greatly reduced, and the yield is significantly improved. FIG. 3 is a schematic side view showing an example of a hot continuous rolling line suitable for carrying out the present invention (3). In the line illustrated here, the slab heated in the heating furnace 22 is adjusted in width by the width press device 23, and is roughly rolled in the rough mill 21 including the first to third stands (R1 to R3) in tandem arrangement. It is wound up and temporarily stored in a coil box device 24, and then, while being paid out, the front end thereof is joined to the tail end of the preceding sheet bar by a joining device 25 to form one strip 9. It is configured to be fed to a finishing mill 20 comprising finishing first to seventh stands (F1 to F7) in a tandem arrangement for finish rolling. The joining device 25 is a device that abuts the leading end of the preceding material and the leading end of the succeeding material and heats and presses the same, and the heating means is formed of an induction coil that is advantageous in terms of heating efficiency. Although a run-out table, a winding device (coiler) and the like are provided downstream of the finishing mill 20, they are not shown.

The inlet and outlet sides of the finishing mill 20 have different temperatures.
Gauges (finishing mill inlet thermometer 26 and finishing mill outlet thermometer 27)
The surface temperature of the strip 9 that is placed and passes through each position
Can be measured. In carrying out the present invention (3), finish
The measured value of the inlet thermometer 26 is Ar _ThreeNot to exceed the transformation point
Adjust the upstream operating conditions. Control of exit temperature of finishing mill
Strip cooling between each stand of finishing mill 20 as a means
Strip coolant 28 is disposed.

In the line of this example, the rolls shown in FIGS. 1 and 2 are provided on the entrance side of all the finishing stands (F1 to F7) so that the present invention (1) and (2) can be carried out without excess or deficiency. While a lubricating device (not shown in FIG. 3) is provided, an on-line roll grinder (typically shown by a grindstone 10 in FIG. 3) has a reduced plate thickness, increases the frictional force between the plate and the roll, and causes a shear strain on the plate. Is easily introduced excessively and therefore low friction rolling becomes particularly important.
To F7).

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In producing an ultra-low carbon hot rolled steel sheet by endless rolling using the hot continuous rolling line shown in FIG. 3, a finishing post-stage stand (F4 to F7) uses the present invention (1) and (2). The present invention (3) was carried out in a form in which roll lubrication was performed, and the rolling load reduction rate and the product r value after annealing were determined in Examples 1 and 2, respectively, without using an online roll grinder in the same line. This was compared with a conventional example in which lubrication was performed. (Common Conditions) conventional example, common to Examples 1 and 2, a continuous casting made of ultra low carbon steel slab having a chemical composition and Ar ₃ transformation point shown in Table 1 (200 mm thickness × 1600 mm width × 8000mm length) The material is heated to 950 ° C. in a heating furnace, roughly rolled into a 35 mm-thick sheet bar by a coarse mill, wound up by a coil box device, and joined to the preceding sheet bar by a joining device while being discharged. Joining is made up to two sheet bars and this is counted as one set. This joining sheet bar is set one set at a time on the entrance side by a finishing mill at 800
℃, exit temperature 680 ℃, rolling speed 900m / min, exit plate thickness
It was finish-rolled into a 1.5 mm strip and wound up to form a hot rolled coil. The strip is cut at the joint before winding, and is separately wound. The comparison between the load reduction rate and the r value was performed for the third set (third set: fifth and sixth coils) from the start of rolling after the replacement of the finishing mill work roll. The annealing condition after finish rolling is 850 ° C x 2h
And

The roll lubrication in the finishing mill was the same for all stands, and started immediately after biting the tip and stopped at the tail end. The rolling oil used was synthetic ester 60%, mineral oil 38
% And an extreme pressure agent of 2%. The oil concentration of the oil-water mixture was 2%, and the oil-water spray water temperature was 40 ° C. The work roll diameter x barrel length is 1300 for each rough stand.
mmφ × 2200mm, 700mmφ × 2000mm for each finishing stand. (Individual conditions) In the conventional example, an online roll grinder is not used.

In Embodiments 1 and 2, roll polishing is started from the previous set (second set) using an online roll grinder, and this roll polishing is compared with the comparison set (third set).
Set) until the completion of rolling. Each grinding wheel makes one reciprocation between its own end and the center of the roll barrel during rolling. Rolling was performed for each type of whetstone. In Example 1, a grindstone made of 145 mesh abrasive grains (nominal size: 105 to 88 μm) was used.

In Example 2, two types of whetstones were used. One is that the abrasive grains of Example 1 are 70 mesh abrasive grains (nominal size 210 to 17).
7 μm) at a mixing ratio of 40 wt%, and is a grindstone made of large and small mixed abrasive grains (rolling at this time is referred to as Example 2A).
The other is a 36 mesh abrasive (nominal size)
420-350 μm) at a blending ratio of 20 wt%. A grindstone made of large and small hybrid abrasive grains (rolling at this time is referred to as Example 2B).
It is. (Results) The relationship between the F7 rolling load and the F7 rolling distance of the third set, which is a comparative set, is shown in FIG. 7 for the conventional example and Example 1, and FIG. 8 for the conventional examples and Examples 2A and 2B. From FIG. 7, in Example 1 in which oil-water spray and roll polishing were combined during rolling, even if the grindstone was a normal grindstone, the rolling load in the steady portion was higher than in the conventional example in which only the oil-water spray was performed without roll polishing. Decreased further. Also,
As shown in FIG. 8, in Example 2 using a grindstone made of large and small mixed abrasive grains, the rolling load in the steady portion was further reduced from the level in FIG. The F7 coefficient of friction in Example 2 was a sufficiently low value of 0.09 to 0.15. Table 2 shows the load reduction rate at each F7 together with the product r value after annealing. In addition, the test piece for r value measurement was taken from the stationary part end of the 6th coil.

[0036]

[Table 1]

[0037]

[Table 2]

As shown in Table 2, in Example 1, a much higher load reduction rate and r value were obtained than in the conventional example, and in Example 2, even higher load reduction rates and r values were obtained than in Example 1. Thus, it is apparent that the present invention can produce a hot-rolled steel sheet having deep drawability superior to that of the related art. The above embodiment relates to the present invention (3) in which the present inventions (1) and (2) are applied to endless rolling, but the present inventions (1) and (2) are limited to the hot rolling mode. Since the invention relates to a roll lubrication method that is not performed, it can be preferably applied to not only endless rolling but also batch rolling.

[0039]

As described above, according to the present invention, a hot-rolled steel sheet which can be hot-rolled in a lubricated state at a higher level than the conventional one and which can exhibit excellent deep drawability after hot-rolling-annealing can be obtained at a 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 front view showing an example of a roll lubrication device and an online roll grinder suitable for carrying out the present invention (1) and (2).

FIG. 2 is a schematic side view of FIG.

FIG. 3 is a schematic side view showing an example of a continuous hot rolling line suitable for carrying out the present invention (3).

FIG. 4 is a graph showing the relationship between the oil adhesion amount and the abrasive particle diameter of a grindstone.

FIG. 5 is a graph showing the relationship between the load reduction rate and the abrasive grain size of a grindstone.

FIG. 6 is a graph showing a relationship between a load reduction rate and a compounding ratio of a large-diameter abrasive grain of a grindstone.

FIG. 7 is a graph showing the relationship between the F7 rolling load and the F7 rolling distance of a third set according to the conventional example and Example 1.

FIG. 8 is a graph showing the relationship between F7 rolling load and F7 rolling distance of a third set according to the conventional example and Examples 2A and 2B.

[Explanation of symbols]

 Reference Signs List 1 work roll 2 oil-water mixer 3 spray nozzle 4 three-way valve 5 water tank 6 water supply pump 7 oil tank 8 oil supply pump 9 strip 10 grinding wheel 11 hydraulic motor 12 arbor shaft 13 oscillation motor 20 finishing mill 21 coarse mill 22 heating furnace 23 width Pressing device 24 Coil box device 25 Joining device 26 Finishing mill inlet thermometer 27 Finishing mill outlet thermometer 28 Strip coolant 41 Wiper 42 Backup roll

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁶ Identification code FI B24B 5/37 B24B 5/37 B24D 3/00 330 B24D 3/00 330G (72) Inventor Masanori Kitahama Kawasaki, Chuo-ku, Chiba-shi, Chiba No. 1 Kawasaki Steel Engineering Co., Ltd. (72) Inventor Yoshio Yarita 1 Kawasaki-cho Chuo-ku Chiba City Chiba Pref.

Claims (3)

[Claims] 1. A roll lubrication method for supplying a rolling lubricant to a work roll during hot rolling, wherein the work roll is polished with an on-line roll grinder and a rolling oil mixed with water is sprayed onto the work roll by an oil-water mixing device. A hot roll lubrication method. 2. The grinding wheel of the online roll grinder is composed of two or more kinds of abrasive grains having different particle diameters, and the abrasive grains on the larger side are 70 mesh abrasive grains to 32 mesh abrasive grains. Item 7. The method according to Item 1. 3. An ultra-low carbon steel slab is heated in a heating furnace, rough-rolled in a rough mill to form a sheet bar, and a preceding material and a succeeding material of the sheet bar are butt-joined and joined, and the finished mill is used. _3. A method for producing a hot-rolled steel sheet, wherein the entrance-side temperature is equal to or lower than the Ar ₃ transformation point and finish rolling is performed while performing roll lubrication by the method according to claim 1 or 2.