JP7340473B2 - Method for manufacturing hot rolled steel sheets - Google Patents

Description

The present invention relates to a method for manufacturing hot rolled steel sheets.

A hot-rolled steel plate is manufactured by winding a hot-rolled steel strip into a coil and cooling the wound coil to about room temperature. This hot-rolled steel sheet is fed out again into a strip, pickled and cold-rolled to become a cold-rolled steel sheet. A problem in manufacturing this cold-rolled steel sheet is that the steel material breaks during threading. When a break occurs in the steel material, it is necessary to stop the threading line and perform restoration work, which increases the cost for restoration and reduces production efficiency. Furthermore, breakage of steel materials can also cause equipment failure.

Japanese Patent Application Publication No. 2000-131048 Japanese Patent Application Publication No. 2002-148037

One of the causes of breakage of highly hardenable steel materials during cold rolling is cracks at the ends of the steel materials. If a crack occurs at the end of a steel material during cold rolling, stress is concentrated at the cracked portion during sheet rolling, causing the crack to grow and easily lead to breakage of the steel material.

This crack may be caused by a defect in the winding shape of the hot-rolled coil. In other words, if there is a winding defect in the coil after hot rolling, the unevenness of the end face of the coil becomes large. If there is a large convex portion on the end face of the coil, the convex portion functions as a fin, which increases the cooling rate of the convex portion during cooling of the coil. This makes it easier for hard phases such as bainite and martensite to coexist with soft phases such as ferrite when the coil is cooled. As a result, voids are generated during cold rolling of the steel material, and these voids grow, making it easy to cause cracks at the ends.

From this point of view, the present inventors believe that in order to suppress the breakage of steel materials, it is important to suppress cracks at the ends of the steel materials, and furthermore, it is important to control the unevenness of the coil end surfaces to below a certain level. found it to be important.

In addition, Patent Document 1 states that if the winding shape of the coil is disordered in a telescopic shape, it may cause problems when the coil is transported or inserted into equipment for the next process using a crane, etc., and the coil may fall or overturn. It is stated that it causes In order to solve this problem, Patent Document 1 discloses that the strip width at the scanned position at the end of rolling is measured, and the strip width measurement result is used as the unevenness measurement result of the coil end face to determine the presence or absence of a telescope. It is stated that However, Patent Document 1 does not consider the relationship between unevenness on the coil end face and cracks on the coil end.

Further, Patent Document 2 states that a coil in which the difference in measured distance between the innermost metal plates at both ends of the coil's inner diameter or the difference in the measured distance between the outermost metal plates at both ends of the coil's outer diameter exceeds a threshold value, It is described that it is determined that the tongue-shaped portion of the coil end of the metal plate is being measured. However, even in Patent Document 2, the relationship between unevenness on the end face of the coil and cracks at the end of the coil is not studied.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a method for manufacturing a hot-rolled steel sheet that can suppress breakage of a steel material during sheet passing.

The invention made to solve the above problems involves a process of winding a hot-rolled steel strip into a coil, and scanning the end face of the coil wound in the winding process with a displacement meter. A step in which the size of the unevenness is measured over the radius of the coil, and the size of the unevenness measured in the above measurement step is set based on the size of the unevenness of other coils where edge cracks have occurred in the past. The method of manufacturing a hot rolled steel sheet includes a step of comparing the method with a threshold value and predicting the presence or absence of edge cracking of the coil in a step subsequent to the winding step.

The method for manufacturing the hot rolled steel sheet includes, in the prediction step, setting the size of the unevenness on the end face of the coil measured in the measuring step based on the size of the unevenness of other coils in which edge cracks have occurred in the past. Since the presence or absence of edge cracking of the coil in a process subsequent to the winding process is predicted by comparing it with the threshold value determined, by referring to the prediction result in the prediction process, It is possible to suppress edge cracking of the coil, and in turn, it is possible to suppress breakage of the steel material during sheet threading.

In the measurement step, the size of the unevenness may be determined using the median value of the measured values as a reference. In this manner, by determining the size of the unevenness in the measuring step using the median value of the measured values as a reference, it is easier to predict whether the coil will have edge cracks in the subsequent step than in the winding step.

The hot-rolled steel sheet manufacturing method may further include a step of removing a region of the coil including a position exceeding the threshold value when edge cracking is predicted in the prediction step. The method for manufacturing a thick steel plate further includes a step of removing an area including a position of the coil exceeding the threshold value when edge cracking is predicted in the prediction step, thereby preventing edge cracking in the steel strip. It is possible to prevent edge cracks in post-processing while effectively using areas where they are unlikely to occur.

In the removal step, it is preferable to cut the strip steel material in the width direction. In this way, by cutting the steel strip in the width direction in the removal step, it is possible to increase the utilization efficiency of the steel strip and prevent edge cracks in the subsequent process.

As explained above, the method for manufacturing a hot rolled steel sheet according to the present invention can suppress breakage of the steel material during sheet passing.

FIG. 1 is a flow diagram showing a method for manufacturing a hot rolled steel sheet according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing hot-rolled steel sheet manufacturing equipment used in the hot-rolled steel sheet manufacturing method of FIG. 1. FIG. 3 is a schematic diagram showing the scanning position of the end face of the coil in the method for manufacturing the hot-rolled steel sheet of FIG. 1. FIG. 4 is a flow diagram showing a method for manufacturing a hot-rolled steel sheet according to an embodiment different from the method for manufacturing a hot-rolled steel sheet in FIG. FIG. 5 is a schematic diagram showing hot-rolled steel sheet manufacturing equipment used in the hot-rolled steel sheet manufacturing method of FIG. 4. FIG. 6 is a graph showing the size of the unevenness on the end face on the outer peripheral side of the coil measured in the measurement process.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.

[First embodiment]
<Manufacturing method of hot rolled steel plate>
The manufacturing method of the hot-rolled steel sheet shown in Fig. 1 includes a step of winding a hot-rolled steel strip into a coil shape (winding step S1), and scanning the end face of the coil wound in the winding step S1 with a displacement meter. The step of measuring the size of the unevenness on the end face over the radius of the coil (measuring step S2) and the size of the unevenness measured in the measuring step S2 are performed based on the results of the step of measuring the size of the unevenness on the end face over the radius of the coil. and a step (prediction step S3) of predicting the presence or absence of edge cracking of the coil in a step subsequent to the winding step S1 by comparing the method with a threshold value set based on the size of the unevenness of other coils. Moreover, the method for manufacturing the hot-rolled steel sheet includes a step of air cooling the coil wound up in the winding step S1 (air cooling step S4). Furthermore, the method for manufacturing the hot rolled steel sheet includes a step of cold rolling the coil after air cooling in the air cooling step S4 while unwinding it into a strip (cold rolling step), and annealing the steel material after cold rolling in the above cold rolling step. It may also include a step (annealing step). Note that "coiled" refers to a spiral shape when viewed in the axial direction. The term "end face of the coil" refers to a face perpendicular to the central axis of the coil. That is, the "end surface of the coil" refers to a surface formed by the widthwise end of the steel strip. The term "coil edge cracks" includes cracks in the coil itself as well as cracks in the steel material from which the coil is developed.

In explaining the method for manufacturing the hot-rolled steel sheet, first, with reference to FIG. 2, we will explain the hot-rolled steel sheet manufacturing equipment 1 (hereinafter also simply referred to as "manufacturing equipment 1") that can carry out the method for manufacturing the hot-rolled steel sheet. explain.

[Hot-rolled steel sheet manufacturing equipment]
The manufacturing equipment 1 in FIG. 2 includes a plurality of pairs of rolling rolls 2a and a winding machine 2b that winds up a strip steel material X hot-rolled by these rolling rolls 2a into a coil shape, and constitutes a hot rolling line. Measurement is carried out by the hot rolling device 2, the measuring device 3 that constitutes a measuring line that measures the size of the unevenness on the end face of the coil X1 wound by the winding machine 2b over the radius of the coil X1, and the measuring device 3. The size of the unevenness thus obtained is compared with a threshold value set based on the size of unevenness of other coils in which edge cracking has occurred in the past, and edge cracking of coil X1 on a line subsequent to the above hot rolling line is determined. and a prediction device 4 that predicts the presence or absence of. Further, the manufacturing equipment 1 includes an air cooling device 5 that air cools the coil X1 after passing through the measurement line. The manufacturing equipment 1 may further include a cold rolling device that cold-rolls the coil X1 after being air-cooled by the air-cooling device 5, an annealing device that anneals the steel strip after cold rolling by the cold rolling device, etc. good.

The hot rolling apparatus 2 performs rough rolling and finish rolling on a thick steel plate heated in a heating furnace (not shown), and then winds up the rolled steel strip X into a coil shape with a winding machine 2b.

The measuring device 3 scans the conveyor 3a that conveys the coil X1 wound up by the winder 2b, and the end surface of the coil X1 being conveyed on the conveyor 3a, and measures the size of the unevenness of this end surface. It has a total of 3b. As shown in FIG. 3, the displacement meter 3b measures the size of the unevenness on the end surface E of the coil X1 over the radius of the coil X1, and more preferably over the diameter. For example, a laser displacement meter is used as the displacement meter 3b. The displacement meter 3b includes a laser irradiation unit that irradiates the end surface E of the coil X1 with a laser beam, and a light receiving element that receives a portion of the light beam reflected by the end surface E. The displacement meter 3b uses the light receiving element to read the reflected light of the laser beam irradiated onto the end surface E from the laser irradiation section. The displacement meter 3b is configured to be able to measure the size of the unevenness on the end surface E of the coil X1 using a triangulation method.

The prediction device 4 is composed of, for example, a computer. The prediction device 4 stores data on the size of unevenness on the end face E of the coil X1 where edge cracks have occurred in the past, and data on the size of unevenness on the end face E of the coil X1 where edge cracks have not occurred in the past. Has a database. For example, the prediction device 4 sets a value lower than the size of the unevenness of the end face E of the coil X1 where edge cracking has occurred in the past as the threshold value. The prediction device 4 predicts that there is a risk of edge cracking of the coil X1 in a subsequent process when the size of the unevenness of the end surface E of the coil X1 measured by the measurement device 3 is larger than the above threshold value. On the other hand, the prediction device 4 predicts that there is no risk of edge cracking of the coil X1 in a subsequent process if the size of the unevenness on the end surface E of the coil X1 measured by the measurement device 3 is equal to or less than the threshold value. The prediction device 4 may have a plurality of threshold values corresponding to the composition of the strip steel material X.

The air cooling device 5 air-cools the coil X1 after the size of the unevenness of the end surface E has been measured by the measuring device 3. In the manufacturing equipment 1, the coil X1 after being wound by the winding machine 2b is heated to about 500° C. or higher. The air cooling device 5 air cools the heated coil X1 to room temperature. Since the manufacturing equipment 1 air-cools the coil X1 wound by the winder 2b, if a large protrusion exists on the end surface E of the coil X1, the cooling rate of this protrusion tends to be faster than other parts. .

[Strip steel material]
The strip steel material X is formed by heating and hot rolling a slab. The composition of the strip steel material X is not particularly limited, but for example, it has a composition of carbon, silicon, manganese, phosphorus, sulfur, chromium, nickel, molybdenum, and copper, with the balance being iron and inevitable impurities. When cold rolling the steel strip X, the winding temperature in the winding step S1 is preferably equal to or higher than Ms (martensitic transformation start temperature) of the steel strip X.

The upper limit of the carbon equivalent Ceq expressed by the following formula (1) of the steel strip X is preferably 0.75%, more preferably 0.70%. When the carbon equivalent Ceq of the strip steel material X exceeds the above upper limit, there is a high possibility that a martensite phase will be generated when the cooling rate is high in the air cooling step S4. On the other hand, the lower limit of the carbon equivalent Ceq is not particularly limited, but may be, for example, 0.55%. When the carbon equivalent Ceq is less than the lower limit, the transformation is almost completed by the winding step S1, so a martensite phase is difficult to generate, and there is a low possibility that edge cracking will occur in the coil X1 in a subsequent step. Therefore, the need for prediction by the prediction step S3 is low.
Ceq [%] = [C] + [Si] / 24 + [Mn] / 6 + [Ni] / 40 + [Cr] / 5 + [Mo] / 4 + [V] / 14... (1)
However, [C], [Si], [Mn], [Ni], [Cr], [Mo] and [V] are the contents (mass) of C, Si, Mn, Ni, Cr, Mo and V, respectively. %).

(winding process)
In the winding step S1, the strip steel material X hot-rolled by the plurality of pairs of rolling rolls 2a is wound into a coil shape by the winding machine 2b at a high temperature. The winding temperature in the winding step S1 is preferably equal to or higher than the Ms temperature of the steel strip X from the viewpoint of preventing the formation of a martensite phase. The lower limit of the winding temperature is preferably 400°C, more preferably 500°C, and even more preferably 560°C. On the other hand, the upper limit of the winding temperature is preferably 700°C, more preferably 670°C. If the coiling temperature is less than the lower limit, the strength of the steel strip X will become too high, and there is a risk that the load on the equipment will increase in subsequent processes such as the cold rolling process. On the other hand, if the coiling temperature exceeds the upper limit, the scale thickness on the surface of the steel strip X may increase. In addition, "winding temperature" refers to the surface temperature of the strip steel material X immediately before winding.

(Measurement process)
In the measurement step S2, the end surface E of the coil X1 conveyed on the conveyor 3a is scanned by the displacement meter 3b, and the size of the unevenness of the end surface E is measured over the radius of the coil X1, more preferably over the diameter. Measure. In the measurement step S2, it is preferable to determine the size of the unevenness on the end surface E using the median value of the measured values as a reference. Specifically, in the measurement step S2, it is preferable that the displacement meter 3b continuously measure the end surface E of the coil X1 over the radius, and determine the size of the unevenness of the end surface E based on the median value of the plurality of measured values. . In the hot-rolled steel sheet manufacturing method, a large protrusion (telescope) may be formed at the outer and/or inner end of the coil X1 due to winding misalignment. In this regard, the hot-rolled steel sheet manufacturing method calculates the size of the unevenness of the end face E based on the above median value, so that even if there is a partially large protrusion, the size of the unevenness of the entire coil X1 can be determined. can be appropriately measured, and it is easy to predict the presence or absence of edge cracking of the coil X1 in the subsequent process.

(Prediction process)
The prediction step S3 is performed by the prediction device 4. In the prediction step S3, the magnitude of the unevenness on the end surface E of the coil X1 measured by the displacement meter 3b is compared with a preset threshold value. In the prediction step S3, if the size of the unevenness on the end surface E of the coil X1 measured by the displacement meter 3b is larger than the above threshold value, it is predicted that there is a risk of edge cracking of the coil X1 in a subsequent step. On the other hand, in the prediction step S3, if the size of the unevenness on the end surface E of the coil X1 measured by the displacement meter 3b is less than or equal to the above threshold value, it is predicted that there is no risk of edge cracking of the coil X1 in the subsequent step. The threshold value is set, for example, to a value lower than the size of the unevenness on the end surface E of the coil X1 where edge cracking occurred in the past. It is preferable that the threshold value is set based on the minimum value of the unevenness of the portion where edge cracking occurred in the coil X1 where edge cracking occurred in the past. In this case, it is preferable that the threshold is set to a value smaller than the minimum value of the unevenness of the portion of the coil X1 where edge cracks have occurred in the past. This threshold value may be set corresponding to the composition of the strip steel material X.

(air cooling process)
In the air cooling step S4, the coil X1 conveyed on the conveyor 3a is air cooled to room temperature. In the air cooling process S4, if a large protruding portion exists on the end surface E of the coil X1, the cooling rate of this protruding portion tends to become faster. If a portion where the cooling rate is high is present in the coil X1, a martensite phase is likely to occur in this portion, and edge cracks are likely to occur in a subsequent process such as a cold rolling process.

In addition, in the hot-rolled steel sheet manufacturing method, the coil X1 predicted to have a risk of edge cracking in the prediction step S3 may be treated to prevent edge cracking, or may be removed from the production line. good.

<Advantages>
In the method for manufacturing the hot-rolled steel sheet, in a prediction step S3, the size of the unevenness on the end face E of the coil X1 measured in the measuring step S2 is based on the size of the unevenness of other coils in which edge cracks have occurred in the past. The presence or absence of edge cracking of the coil Edge cracking of the coil X1 can be suppressed, and in turn, breakage of the steel material during sheet passing can be suppressed.

[Second embodiment]
<Manufacturing method of hot rolled steel plate>
The manufacturing method of the hot-rolled steel sheet shown in Fig. 4 includes a step of winding a hot-rolled steel strip into a coil shape (winding step S1), and scanning the end face of the coil wound in the winding step S1 with a displacement meter. Then, there is a step of measuring the size of the unevenness on the end face over the radius of the coil (measuring step S2), and the size of the unevenness measured in the measuring step S2 is compared with that of other coils in which edge cracks have occurred in the past. A step (prediction step S3) of predicting the presence or absence of edge cracking of the coil in a process subsequent to the winding step S1 by comparing it with a threshold value set based on the size of the unevenness, and a step of predicting the presence or absence of edge cracking in the coil in a step subsequent to the winding step S1. and a step of removing a region of the coil that includes a position exceeding the threshold value (removal step S5). Moreover, the method for manufacturing the hot-rolled steel sheet includes a step of air cooling the coil wound up in the winding step S1 (air cooling step S4). Furthermore, the method for manufacturing the hot rolled steel sheet includes a step of cold rolling the coil after air cooling in the air cooling step S4 while unwinding it into a strip (cold rolling step), and annealing the steel material after cold rolling in the above cold rolling step. It may also include a step (annealing step). When the method for manufacturing the hot-rolled steel sheet includes the cold rolling process, the removal process S5 can be performed after the air cooling process S4 and before the cold rolling process. In addition, each process other than the removal process S5 in the manufacturing method of the said hot rolled steel sheet can be performed by the same procedure as the manufacturing method of the hot rolled steel sheet of FIG.

[Hot-rolled steel sheet production equipment]
The hot-rolled steel sheet manufacturing method can be carried out using hot-rolled steel sheet manufacturing equipment 11 (hereinafter also simply referred to as "manufacturing equipment 11") shown in FIG. The manufacturing equipment 11 in FIG. 5 includes a plurality of pairs of rolling rolls 2a and a winding machine 2b that winds up a strip steel material X hot-rolled by these rolling rolls 2a into a coil shape, and constitutes a hot rolling line. Measurement is carried out by the hot rolling device 2, the measuring device 3 that constitutes a measuring line that measures the size of the unevenness on the end face of the coil X1 wound by the winding machine 2b over the radius of the coil X1, and the measuring device 3. The size of the unevenness thus obtained is compared with a threshold value set based on the size of unevenness of other coils in which edge cracking has occurred in the past, and edge cracking of coil X1 on a line subsequent to the above hot rolling line is determined. a prediction device 4 that predicts the presence or absence of the coil X1; an air cooling device 5 that air-cools the coil and a removal device 6 for removal. The configuration of each part of the manufacturing equipment 11 other than the removal device 6 can be the same as that of the manufacturing equipment 1 of FIG. 2.

The removal device 6 includes a feeding reel 6a that feeds out the coil X1 in the form of a strip, a shearing machine 6b that partially removes the steel strip X2 fed out from the feeding reel 6a, and a shearing machine 6b that cuts the steel strip X2 into a coil after being removed by the shearing machine 6b. It has a take-up reel 6c that takes up the winding.

(Removal process)
The removal step S5 partially removes the coil X1 after being air-cooled in the air-cooling step S4. In the hot-rolled steel sheet manufacturing method, when a large protruding portion exists on the end surface E of the coil X1, the cooling rate of this protruding portion becomes faster, and a martensite phase is likely to occur in the portion where the cooling rate is faster. Therefore, in the removal step S5, the portion where this martensite phase is likely to occur is selectively removed, thereby avoiding the possibility of edge cracking in subsequent steps such as the cold rolling step.

In the removal step S5, it is preferable to cut the strip steel material X2 across the width direction. That is, in the removal step S5, it is preferable to shear-cut the strip steel material X2 fed out from the feeding reel 6a in the width direction (direction perpendicular to the conveyance direction). In the coil X1, large irregularities exceeding the threshold set in the prediction step S3 are likely to be formed on the outer circumferential side and/or the inner circumferential side end. Therefore, in the method for manufacturing the hot-rolled steel sheet, the strip steel material X2 is cut across the width in the removal step S5, thereby selectively removing the end region in the longitudinal direction of the strip steel material X2 in which large irregularities are formed. Therefore, it is possible to easily avoid edge cracking in the subsequent process while increasing the utilization efficiency of the strip steel material X2.

<Advantages>
The hot-rolled steel sheet manufacturing method further includes a step of removing an area including a position exceeding the above-mentioned threshold value of the coil X1 when edge cracking is predicted in the prediction step S3. Edge cracks in subsequent processes can be avoided in advance while making effective use of areas that are less likely to cause cracks.

[Other embodiments]
The above embodiments do not limit the configuration of the present invention. Therefore, in the above embodiment, it is possible to omit, replace, or add components of each part of the above embodiment based on the description of this specification and common general technical knowledge, and all of these are interpreted as falling within the scope of the present invention. Should.

For example, the method for manufacturing the hot rolled steel sheet does not need to include the above-mentioned air cooling step. Moreover, even when the method for manufacturing the hot-rolled steel sheet includes the above-mentioned air-cooling step, it is also possible to perform the above-mentioned removal step before this air-cooling step.

In the removal step, it is also possible to remove both widthwise end portions of the strip steel material in the longitudinal direction. However, in the removal step, it is preferable to cut the strip steel material in the width direction so that the resulting hot rolled steel sheet satisfies specified standard values.

The method for producing a hot rolled steel sheet may include, instead of the removal step, a step of annealing the strip steel material when it is predicted that edge cracking will occur in the prediction step. In the method for manufacturing a hot-rolled steel sheet, edge cracking of the coil can also be avoided by annealing the coil predicted to have edge cracking before cold rolling.

In the measurement step, it is also possible to determine the size of the unevenness on the end face of the coil based on the average value, mode, etc. of the unevenness on the end face of the coil. However, as mentioned above, in the measurement process, even if there is a large protruding part such as a telescope, the median value of the measured value is It is preferable to determine the size of the unevenness on the end face of the coil using as a reference.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[Manufacturing example]
[No. 1]
A steel plate was manufactured using manufacturing equipment 11 shown in FIG. In this example, a steel plate was manufactured using a manufacturing facility equipped with a cold rolling device downstream of the removing device 6 in FIG. 5. In this production example, the plate thickness after the air cooling process described below is 2.08 mm, the plate width after this air cooling process is 1011 mm, the plate thickness after cold rolling is 1.1 mm, and the coiling temperature of the steel strip is 650 ° C. Met. Further, the carbon equivalent Ceq of this steel strip obtained from the above equation (1) was 0.6642 [%], and the Ms temperature obtained from the following equation (2) was 374°C.
Ms[℃]=539-423×[C]-30.4×[Mn]-17.7×[Ni]-12.1×[Cr]-7.5×[Mo]...(2)
However, [C], [Mn], [Ni], [Cr], and [Mo] indicate the content (mass%) of C, Mn, Ni, Cr, and Mo, respectively.

No. In No. 1, the size of the unevenness on the end face of the coil wound up in the above-described winding process was measured by the above-mentioned measurement process, and after this measurement process, the coil was air-cooled to room temperature by the above-described air cooling process. Further, after this air cooling step, the strip steel material was cut in a region extending 51 m in the longitudinal direction from the outer circumferential end of the coil across the width direction by the above-mentioned removal step. Subsequently, the cut steel strip was cold rolled in a cold rolling mill. In the measurement step, the size of the unevenness was determined based on the median value of the measured values. No. The quality of the steel strip in step 1, the winding temperature [°C] in the above-mentioned winding process, the removed length [m] in the longitudinal direction based on the outer peripheral end of the coil in the above-mentioned removal process, and the edge after cold rolling. Table 1 shows the presence or absence of cracks. Further, FIG. 6 shows the size of the unevenness on the end face on the outer peripheral side of the coil measured in the above measurement process. In FIG. 6, the case where the end face of the coil opposite to the conveyor projects in a direction away from the conveyor is shown as a plus, and the case where it is recessed toward the conveyor is shown as a minus.

[No. 2]
No. No. 1 was prepared using steel having the same composition as No. 1. A steel plate was manufactured in the same manner as in Step 1. No. The quality of the steel strip in 2, the winding temperature [°C] in the above-mentioned winding process, the removed length [m] in the longitudinal direction based on the outer peripheral end of the coil in the above-mentioned removal process, and the edge after cold rolling. Table 1 shows the presence or absence of cracks. Further, FIG. 6 shows the size of the unevenness on the end face on the outer peripheral side of the coil measured in the above measurement process.

[No. 3]
No. No. 1 was prepared using steel having the same composition as No. 1. A steel plate was manufactured in the same manner as in Step 1. No. The quality of the steel strip in step 3, the winding temperature [°C] in the above-mentioned winding process, the removed length [m] in the longitudinal direction based on the outer peripheral end of the coil in the above-mentioned removal process, and the edge after cold rolling. Table 1 shows the presence or absence of cracks. Further, FIG. 6 shows the size of the unevenness on the end face on the outer peripheral side of the coil measured in the above measurement process. In addition, No. In No. 3, edge cracks have occurred in the steel strip after cold rolling. Table 1 shows the distance from the outer peripheral end of the coil to the part where edge cracking occurred at the position farthest from this end, converted into the length of the coil after hot rolling. Moreover, FIG. 6 shows a portion where the unevenness of the end face of the coil was the smallest among the portions where edge cracking occurred in the coil. As shown in FIG. In No. 3, edge cracks occur at positions where the size of the unevenness is 15 mm (-15 mm in FIG. 6), while edge cracks do not occur at positions where the size of the unevenness is less than 15 mm.

[No. 4]
No. No. 1 was prepared using steel having the same composition as No. 1. A steel plate was manufactured in the same manner as in Step 1. No. The quality of the steel strip in step 4, the winding temperature [°C] in the above-mentioned winding process, the removed length [m] in the longitudinal direction based on the outer peripheral end of the coil in the above-mentioned removal process, and the edge after cold rolling. Table 1 shows the presence or absence of cracks. Further, FIG. 6 shows the size of the unevenness on the end face on the outer peripheral side of the coil measured in the above measurement process. In addition, No. In No. 4, edge cracks have occurred in the steel strip after cold rolling. Table 1 shows the distance from the outer peripheral end of the coil to the part where edge cracking occurred at the position farthest from this end, converted into the length of the coil after hot rolling. Moreover, FIG. 6 shows a portion where the unevenness of the end face of the coil was the smallest among the portions where edge cracking occurred in the coil. As shown in FIG. In No. 4, edge cracking occurs at a position where the size of the unevenness is 43 mm (−43 mm in FIG. 6), while no edge cracking occurs at a position where the size of the unevenness is less than 43 mm.

As shown in Table 1 and FIG. 6, even if the quality of the steel strips is the same, there is a difference in the presence or absence of edge cracking in the subsequent process depending on the size of the unevenness on the end face of the coil. On the other hand, as shown in FIG. 1~No. According to the manufacturing example No. 4, it can be seen that, for example, if the area including the position where the size of the unevenness on the end face of the coil was 10 mm or more was removed, edge cracking in the subsequent process could be prevented. That is, No. 1~No. From the manufacturing example No. 4, it can be seen that edge cracking of the coil can be avoided by setting the threshold value to 10 mm in the above-mentioned prediction process and removing a region including a position exceeding this threshold value in the above-mentioned removal process.

As explained above, the method for manufacturing a hot rolled steel sheet of the present invention can suppress breakage of the steel material during sheet passing by suppressing edge cracking of the coil in the post-process.

1, 11 Hot rolled steel sheet manufacturing equipment 2 Hot rolling device 2a Roll roll 2b Winding machine 3 Measuring device 3a Conveyor 3b Displacement meter 4 Prediction device 5 Air cooling device 6 Removal device 6a Payout reel 6b Shearing machine 6c Take-up reel X, X2 Steel strip X1 Coil E End face

Claims (4)

A process of winding hot rolled steel strip into a coil,
scanning the end face of the coil wound up in the winding process with a displacement meter and measuring the size of the unevenness of the end face over the radius of the coil;
The size of the unevenness measured in the above measurement process is compared with a threshold value set based on the size of the unevenness of other coils in which edge cracks have occurred in the past, and A method for producing a hot-rolled steel sheet, comprising: a step of predicting the presence or absence of edge cracking. The method for manufacturing a hot-rolled steel sheet according to claim 1, wherein in the measuring step, the size of the unevenness is determined based on a median value of the measured values. The method for manufacturing a hot-rolled steel sheet according to claim 1 or 2, further comprising a step of removing a region of the coil including a position exceeding the threshold value when edge cracking is predicted to be present in the prediction step. The method for manufacturing a hot rolled steel sheet according to claim 3, wherein in the removing step, the strip steel material is cut across the width direction.

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