Patent Application
20240360530
This application relates to a quenching apparatus that performs annealing while continuously conveying a metal sheet, a quenching method, and a method of manufacturing a metal sheet.
In continuous annealing facilities in which annealing is performed while continuously conveying a metal sheet, the metal sheet is cooled after heated and causes a phase transformation, and the microstructure of the metal sheet is thereby made. In particular, in the automotive industry, there is an increased demand for a thinned high tension steel sheet (high tensile strength steel sheet) to achieve both a weight reduction of a vehicle body and crash safety. In manufacture of the high tensile strength steel sheet, a technique of rapidly cooling a steel sheet is important. A water quenching method is known as one of the technique in which the cooling rate of cooling of a metal sheet is highest. In the water quenching method, at the same time when a heated metal sheet is immersed in water, cooling water is jetted through a quench nozzle provided in the water to the metal sheet, and the metal sheet is thereby quenched.
At the time of quenching of the metal sheet, shape defects such as warps, wavy deformations, and the like are generated in the metal sheet. This is caused by thermal contraction or the like of the metal sheet due to being rapidly cooled. In particular, when the temperature of the metal sheet changes from a temperature Ms at which a martensitic transformation starts to a temperature Mf at which the martensitic transformation ends, sudden thermal contraction and transformation expansion occur at the same time.
Thus, various methods for preventing shape defects of metal sheets at the time of quenching have been proposed (refer to, for example, Patent Literature 1 and Patent Literature 2). Patent Literature 1 proposes a method of restraining a metal sheet by a pair of restraining rolls that are provided in a cooling fluid when the temperature of the metal sheet is in the range of (TMs+150) (C) to (TMf−150) (° C.), where TMs (° C.) is a Ms temperature at which a martensitic transformation of the metal sheet starts and TMf (° C.) is a Mf temperature at which the martensitic transformation ends.
Patent Literature 2 discloses that, while a metal sheet is restrained by restraining rolls, a distance between a position at which cooling of the metal sheet by a cooling fluid is started and the restraining rolls is controlled by a movable masking member when a quenching method in which cooling is performed by jetting water through a plurality of water jetting nozzles to surfaces of the metal sheet is performed. Further, as in Patent Literature 1, there is proposed a method in which a metal sheet with a temperature from (TMS+150) (° C.) to (TMf−150) (° C.), where TMs (° C.) is the Ms temperature at which a martensitic transformation of the metal sheet starts and TMf (° C.) is the Mf temperature at which the martensitic transformation ends, is caused to pass the restraining rolls.
In the method described in Patent Literature 1, however, the position at which the temperature of the metal sheet is in the range of (TMs+150) (° C.) to (TMf−150) (° C.) varies depending on conditions of manufacture of the metal sheet. Therefore, it may be impossible for the restraining rolls to restrain the metal sheet at a position at which the temperature of the metal sheet is in the range of (TMs+150) (° C.) to (TMf−150) (C), and variations in the shape of the metal sheet may be generated.
In the method described in Patent Literature 2, water that hits the movable masking member falls by gravity and interferes with water that is jetted through the water jetting nozzles at a lower portion of the movable masking member, thereby causing a cooling performance of cooling of the metal sheet to be unstable. In addition, since masking is performed for each nozzle, the cooling performance varies in steps (discontinuously) and, as a result, causes the position at which the temperature of the metal sheet is in the range of (TMs+150) (° C.) to (TMf−150) (° C.) to be unstable, and variations in the shape of the metal sheet may be generated.
The disclosed embodiments have been made to solve such problems, and an object of the disclosed embodiments is to provide a quenching apparatus capable of highly accurately controlling the temperature of a metal sheet at a position at which the metal sheet is restrained and suppressing generation of variations in the shape of the metal sheet at the time of quenching, a quenching method, and a method of manufacturing a metal-sheet product.
According to the disclosed embodiments, by adjusting the position of restraining rolls in a conveyance direction of a metal sheet in accordance with the temperature of the metal sheet at the time of quenching of the metal sheet to control the distance from a cooling start position to the restraining rolls, it is possible to suppress variations in the shape of metal sheet generated at the time of quenching.
An embodiment will be described on the basis of the drawings.
The cooling device 10 cools the metal sheet S by using a cooling fluid CF and includes a cooling tank 11 in which the cooling fluid CF is stored and a plurality of nozzles 12 installed inside the cooling tank 11 and through which the cooling fluid CF is jetted to the surfaces of the metal sheet S. Water is stored as the cooling fluid CF in the cooling tank 11, and, for example, the metal sheet S is immersed in the water from the upper surface of the cooling tank 11 toward a conveyance direction BD. A sink roll 2 that changes the conveyance direction of the metal sheet S is installed inside the cooling tank 11.
The plurality of nozzles 12 are formed by, for example, quench nozzles or the like and are installed on two surface sides of the metal sheet S to be arranged in the conveyance direction of the metal sheet S. Consequently, the metal sheet S is cooled by the cooling fluid CF inside the cooling tank 11 and the cooling fluid CF that is jetted through the plurality of nozzles 12. Cooling the metal sheet S by thus using both the cooling tank 11 and the plurality of nozzles 12 stabilizes the boiling state of the surfaces of the metal sheet S and enables uniform shape control.
While water quenching that uses water as the cooling fluid CF is employed in the example, oil cooling that uses an oil as the cooling fluid CF may be employed. In addition, while the plurality of nozzles 12 are installed inside the cooling tank 11 in the example in
When the nozzles 12 are installed inside the cooling tank 11, the distance between the metal sheet S and the nozzles 12 is important in rapid cooling by liquid quenching. Since a vapor film generated by a boiling phenomenon is broken by liquid jet streams to perform rapid cooling, it is preferable that the nozzles 12 be installed close to the metal sheet S. The distance between the tip portion of each of the nozzles 12 and the metal sheet S is preferably more than or equal to 10 mm and less than or equal to 150 mm. When the distance is less than 10 mm, there is a possibility that the metal sheet S is deformed into a flapping state and comes into contact with the nozzles 12. In addition, when the distance is more than 150 mm, the effect of breaking the vapor film weakens and makes it difficult to ensure a sufficient cooling performance.
The restraining rolls 20 restrain the metal sheet S cooled by the cooling device 10 in the thickness direction and these rolls 20 are respectively installed on both surfaces of metal sheet S inside the cooling tank 11. A pair of the restraining rolls 20 are installed to face each other in
In consideration of the correlation between roll rigidity and a flexure due to a restraining stress, the roll diameter of each of the restraining rolls 20 is preferably more than or equal to 50 mm and less than or equal to 300 mm. The material of the restraining rolls 20 is not limited. When general steel rolls are used as the restraining rolls 20 and when the roll diameter of each of the rolls is less than 50 mm, roll rigidity is insufficient. Consequently, causing a uniform restraining force to act on the metal sheet S is made to be difficult due to a flexure, and the restraining rolls 20 may be broken. Meanwhile, when the roll diameter is more than 300 mm, a section in which a jet stream from each of the nozzles 12 does not reach the metal sheet S is lengthened, and there is a possibility that breakage of the vapor film becomes insufficient and the cooling performance decreases.
The restraining rolls 20 are installed to be movable in the conveyance direction of the metal sheet S. Here, the conveyance direction is a direction in which the metal sheet S is conveyed. Specifically, the quenching apparatus 1 for the metal sheet S includes a roll moving device 30 that moves the restraining rolls 20 and a movement control device 40 that controls the movement of the restraining rolls 20. The roll moving device 30 includes publicly known driving means, for example, a motor or the like and is configured to cause the restraining rolls 20 to move toward the conveyance direction BD of the metal sheet S or a direction opposite to the conveyance direction BD in the conveyance direction of the metal sheet S. Specifically, the roll moving device 30 can be suitably produced by combining mechanical components such as a power jack, a screw lifting device formed by a screw mechanism or a gear mechanism, and a less-resistance linear motion guide (LM guide) that uses rolling. In
When the above-described driving means is immersed in a fluid, maintenance of the driving means may be difficult. Therefore, it is preferable that the driving means be installed above a fluid surface in the cooling tank 11. In addition, it is preferable that the driving means be installed in a space that is shielded from the inside of a furnace in which the temperature is high.
The roll moving device 30 may have a function of causing the restraining rolls 20 to move in the thickness direction of the metal sheet S and restrain the metal sheet S or release restraining. While the method of moving is not particularly limited as long moving is possible, an electric type is more preferable in consideration of responsivity.
The movement control device 40 is formed by a hardware resource such as a computer and controls the movement of the restraining rolls 20. In particular, the movement control device 40 controls the operation of the roll moving device 30 to position the restraining rolls 20 such that the metal sheet S is restrained at the position RP at which the metal sheet S has the target temperature. Here, the target temperature is preferably set in the temperature range of (TMs+150) (° C.) to (TMf−150) (° C.), where TMs (° C.) is a Ms temperature at which a martensitic transformation of the metal sheet S starts and TMf (° C.) is a Mf temperature at which the martensitic transformation ends. Consequently, the restraining rolls 20 can restrain a deformation of the metal sheet S at a position at which sudden thermal contraction and transformation expansion occur at the same time in the metal sheet S and can suppress the deformation of the metal sheet S at the time of quenching.
The movement control device 40 calculates a distance d from the cooling start position SP of cooling of the metal sheet S by the cooling fluid CF to the position RP at which the metal sheet S has the target temperature and is restrained by the restraining rolls 20, and moves the restraining rolls 20 on the basis of the calculated distance d. To calculate the distance d, the movement control device 40 uses the line speed v (mm/s) of the metal sheet S, the cooling start temperature T1 (° C.), the target temperature T2 (° C.) at which restraining is performed by the restraining rolls 20, and the cooling rate CV (° C./s) of cooling of the metal sheet S by the cooling device 10. Here, the cooling start temperature T1 is the temperature of the metal sheet S just before the cooling start position SP at which cooling of the metal sheet S by the cooling fluid CF is started. For example, the temperature just before reaching the cooling start position SP can be calculated on the basis of a cooled state of the metal sheet S until reaching the cooling start position SP or the quenching apparatus 1. Specifically, the temperature of the metal sheet S is measured at the exit side of a soaking zone of a continuous annealing furnace by a contactless thermometer. Then, on the basis of the temperature and a temperature decrease of the metal sheet S due to being naturally cooled until reaching the quenching apparatus 1, the temperature of the metal sheet S just before or at the point of time of reaching the cooling start position SP can be calculated. The above-described temperature decrease of the metal sheet S due to being naturally cooled can be obtained previously through an experiment. Note that the aforementioned parameters may be successively obtained from set values or actual operation results of a process computer and may be measured by using a speed sensor, a temperature sensor, or the like.
Specifically, the relationship between the distance d and the cooling rate CV (° C./s) is expressed by Formula (1) below.
The cooling rate CV (° C./s) can be expressed using a sheet thickness t of the metal sheet S and a coefficient α(° C.·mm/s), which indicates cooling conditions such as the shape of the nozzles or the type, the temperature, the jetting amount of the cooling fluid CF that is to be jetted, by Formula (2) below.
By substituting Formula (2) for Formula (1), the distance d can be expressed by Formula (3) below.
In the movement control device 40, the cooling rate CV(C/s) or α(° C. ·mm/s) that is previously obtained through an experiment, a numerical analysis, and the like is stored. Then, the movement control device 40 obtains the distance d by using Formula (1) or Formula (3) and moves the restraining rolls 20 such that the metal sheet S is restrained at a position corresponding to the obtained distance d. Note that the cooling rate CV is a value that is determined in accordance with the sheet thickness and the like. When the sheet thickness is 1 to 2 mm, the cooling rate CV=1000 to 2000 (° C./s), and α=500 to 2000 (° C.·mm/s). Thus, in the movement control device 40, the cooling rate CV may be set to 1500 (° C./s), which is an intermediate value in the aforementioned range. In this case, a may be treated as 1250 (° C.·mm/s), which is an intermediate value. As described above, cooling conditions α obtained by the above-described cooling rate CV, the sheet thickness t, and Formula (2) may be set.
With reference to
The line speed of the metal sheet S fluctuates even with respect to a single metal sheet S (in one coil). Therefore, it is more preferable, since a yield by shape defects of portions such as a leading end and a tail end of the metal sheet S where the speed decreases can be improved, that the metal sheet S be movable in the conveyance direction or a direction opposite to the conveyance direction while being restrained by the restraining rolls 20. Alternatively, the movement control device 40 may calculate the distance d and move the restraining rolls 20 for every set period.
The movement distance of the restraining rolls 20 for adjusting the restraining rolls 20 to be at the position RP, at which the metal sheet S is restrained, based on the distance d can be estimated as substantially 10 mm to 150 mm actually. As illustrated in
Here, a case in which the restraining rolls 20 are moved by a larger amount than in the above-described example will be described. When the composition, the sheet thickness, the line speed, and the like of the metal sheet S are greatly varied, it is required to move the restraining rolls 20 by 150 mm or more to position the restraining rolls 20 at the position RP at which the metal sheet S is restrained. A configuration that moves the restraining rolls 20 by 150 mm or more will be described.
As illustrated in
Next, an operation of the quenching apparatus 50 illustrated in
In the state illustrated in
Note that the interval between the nozzles 12 may be widened to about 10 mm to 150 mm, substantially similarly to the example illustrated in
According to the aforementioned embodiment, it is possible by installing the restraining rolls 20 to be movable in the conveyance direction to control the distance from the cooling start position to the restraining rolls 20 and to restrain the metal sheet S having the target temperature T2 by the restraining rolls 20 regardless of conditions of manufacture of the metal sheet S. As a result, it becomes possible to suppress shape defects of the metal sheet S generated due to conditions of manufacture of the metal sheet S during quenching in continuous annealing facilities.
In other words, the temperature of the metal sheet S conveyed to the quenching apparatus 1 varies depending on conditions of manufacture of the metal sheet, for example, the line speed v, the cooling start temperature T1 of the metal sheet S, the sheet thickness t of the metal sheet S, and the like. Therefore, when the distance d is set to be constant regardless of conditions of manufacture, the temperature of the metal sheet S when the metal sheet S reaches the restraining rolls 20 also varies.
It has been found that varying the positions of the restraining rolls 20 is effective to precisely perform shape control at an optimal temperature position, which is different depending on conditions of manufacture to solve this problem. Since the restraining rolls 20 themselves move, it is possible, without causing instability of the cooling form, to restrain the metal sheet S in the target temperature range even when conditions of manufacture vary.
In particular, it is possible to reduce a shape having intricate uneven irregularities, which are generated when a martensitic transformation occurs during rapid cooling of the metal sheet S and causes volume expansion of the microstructure. Therefore, the deformation suppressing effect is increased in particular when the metal sheet S is a high strength steel sheet (high tensile strength steel sheet). Specifically, application to manufacture of a steel sheet whose tensile strength is more than or equal to 580 MPa is preferable. While the upper limit of the tensile strength is not particularly limited, the tensile strength may be less than or equal to 2000 MPa in one example. As examples of the aforementioned high strength steel sheet (high tensile strength steel sheet), there are presented a high strength cold rolled steel sheet, and a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, a hot-dip galvannealed steel sheet, and the like that are obtained by performing a surface treatment on high strength cold rolled steel sheets.
As a specific example of the composition of the high strength steel sheet, there is presented an example in which, in mass %, C is contained by more than or equal to 0.04% and less than or equal to 0.35%, Si is contained by more than or equal to 0.01% and less than or equal to 2.50%, Mn is contained by more than or equal to 0.80% and less than or equal to 3.70%, P is contained by more than or equal to 0.001% and less than or equal to 0.090%, S is contained by more than or equal to 0.0001% and less than or equal to 0.0050%, sol.Al is contained by more than or equal to 0.005% and less than or equal to 0.065%, at least one or more of Cr, Mo, Nb, V, Ni, Cu, and Ti are each contained, as necessary, by less than or equal to 0.5%, B and Sb are each further contained, as necessary, by less than or equal to 0.01%, and the remainder is constituted by Fe and incidental impurities. Note that the metal sheet S is not limited to a steel sheet and may be a metal sheet other than a steel sheet.
An example of the disclosed embodiments will be described. As an example, quenching of a high tensile strength cold rolled steel sheet that is in a tensile strength class of 1470 MPa and that has the sheet thickness t of 1.0 mm and a sheet width of 1000 mm was performed by using the quenching apparatus 1 according to the aforementioned embodiment. As the composition of the high tensile strength cold rolled steel sheet in the tensile strength class of 1470 MPa, C is contained by 0.20%, Si is contained by 1.0%, Mn is contained by 2.3%, P is contained by 0.005%, and S is contained by 0.002% in mass %. A temperature TMs, which is the Ms temperature of the high tensile strength cold rolled steel sheet, is 300° C., and a temperature TMf, which is the Mf temperature thereof, is 250° C. Therefore, the target temperature T2 at a time of passing the restraining rolls 20 may be simply set in the range of 450° C. to 100° C., and the target temperature T2 was set to 400° C. In addition, the cooling start temperature T1was set to 800° C. with the target temperature T2 set to 400° C. The temperature of the cooling fluid CF was 30° C., and the cooling rate CV was set to 1500 (° C./s).
The line speed v was varied in the range of 1000 to 3000 mm/s as a variation in conditions of manufacture, and in accordance with the variation in the line speed v, the distance d (mm) was controlled in the range in which d=267to 800 mm on the basis of Formula (1). Ten steel sheets after being cooled were collected at every 100 m in the longitudinal direction (that is, the same direction as the conveyance direction of the steel sheets), and the warp amount of each of the steel sheets was checked.
In Comparative example 1, as illustrated in
As illustrated in
Note that the disclosure is not intended to be limited to the aforementioned embodiment, and various changes can be added thereto. For example, while the target temperature T2is (TMs+150) (° C.) to (TMf−150) (° C.) in the example presented in the aforementioned embodiment, the target temperature T2 is not limited thereto. The target temperature T2 may be not limited to (TMs+150) (° C.) to (TMf−150) (° C.) when absence of variations in the shape of the metal sheet S in terms of, for example, the warp amount and the like is simply required from the point of view of ensuring flexibility in processing and operation in subsequent steps.
In this case, the target temperature T2 is previously determined in consideration of a predicted shape (for example, the warp amount) while ensuring of flexibility in processing and operation in subsequent steps and the like are taken into consideration, and the distance d from the cooling start position to the restraining rolls 20 is controlled by positional adjustment of the restraining rolls 20. Then, the temperature of the metal sheet S at the time of passing the restraining rolls 20 is caused to be the previously determined temperature T2 so that the shape (for example, the warp amount) of the metal sheet S is substantially the same, for example, a variation in the warp amount defined in
Further, the restraining rolls 20 are not limited to being provided as a pair. A plurality of pairs of the restraining rolls 20 or a plurality of the restraining rolls 20 may be provided. In such a case, positions of the restraining roll pairs as a whole may be collectively controlled, or a mechanism that controls the position and opening/closing of each of a plurality of the restraining rolls may be employed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-136141 | Aug 2021 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2022/029364 | 7/29/2022 | WO |
