Patent Application
20190010564
Aspects of the present invention relate to a rapid-cooling quenching apparatus and a rapid-cooling quenching method in which it is possible to suppress a decrease in the cooling rate of a metal sheet while reducing shape defects, which occurs in the metal sheet when rapid-cooling quenching is performed, in continuous annealing equipment in which annealing is performed while the metal sheet continuously passes through the equipment.
When a metal sheet such as a steel sheet is manufactured, material properties are made up by, for example, allowing phase transformation to occur by cooling the metal sheet after having heated the metal sheet in continuous annealing equipment. Nowadays, there is an increasing demand in the automobile industry for a high-tensile strength steel sheets (high-tensile steel sheets) having a reduced thickness in order to simultaneously achieve the weight reduction and satisfactory collision safety in automobile bodies. When a high-tensile steel sheet is manufactured, a technique for rapidly cooling a steel sheet is important. Examples of a known method for cooling a steel sheet at a highest cooling rate include a water quenching method. In the water quenching method, rapid-cooling quenching is performed on a steel sheet by dipping a heated steel sheet in water and at the same time jetting cooling water onto the heated steel sheet through quenching nozzles placed in the water. When rapid-cooling quenching is performed on a steel sheet, there is a problem in that shape defects such as warpage and wave-like deformation occur in the steel sheet. To date, various methods have been proposed in order to prevent such shape defects from occurring when rapid-cooling quenching is performed on a steel sheet.
For example, Patent Literature 1 proposes, in order to reduce wave-like deformation occurring in a metal sheet when rapid-cooling quenching is performed in a continuous annealing furnace, a tension-changing technique in which bridle rolls are placed upstream and downstream of a rapid-cooling quenching zone in order to change the tension which is applied to a steel sheet to be subjected to a rapid-cooling quenching process. In addition, Patent Literature 2 proposes a technique in which the shape of a steel sheet is corrected so as to be flat by applying tension to at least the whole region in the width direction of the front and back surfaces of the steel sheet when quenching is performed.
However, in the case of the method according to Patent Literature 1, since a large tension is applied to a high-temperature steel sheet, there is a risk of rupture occurring in the steel sheet. In addition, since a large thermal crown is formed on the bridle rolls placed upstream of the rapid-cooling quenching zone which are in contact with a high-temperature steel sheet, the bridle rolls and the steel sheet are in contact with each other unevenly in the width direction. As a result, buckling and flaws occur in the steel sheet, which results in a problem in that it is not possible to improve the shape of the steel sheet. In addition, in the case of the method according to Patent Literature 2, although there is a decrease in warpage quantity to about several mm in response to application of a tension of 15 N/mm2, there is a risk in that a contraction occurs in a steel strip due to such a high tension.
The present applicant has filed Japanese Patent Application No. 2014-240836 regarding a technique for solving such problems.
PTL 1: Japanese Unexamined Patent Application Publication No. 2011-184773
PTL 2: Japanese Unexamined Patent Application Publication No. 11-193418
Although it is certainly possible to prevent deformation of a steel sheet when rapid-cooling quenching is performed by using the rapid-cooling quenching apparatus illustrated in
Moreover, since there is only one pair of restraining rolls in the case of the rapid-cooling quenching apparatus illustrated in
From the results of the investigations conducted by the present inventors, it was found that the cooling rate of a metal sheet tends to decrease particularly in the vicinity of the restraining rolls 7 which are in contact with a high-temperature metal sheet. This will be described more specifically by using
Aspects of the present invention have been completed in view of the problems described above. An object of aspects of the present invention is to provide a rapid-cooling quenching apparatus and a rapid-cooling quenching method with which it is possible to suppress a decrease in the cooling rate of a metal sheet in the vicinity of restraining rolls while shape defects occurring in the metal sheet are reduced to the maximum extent when rapid-cooling quenching is performed.
The solution to the problem described above according to various aspects of the present invention is as follows.
[1] A rapid-cooling quenching apparatus in which a high-temperature metal sheet is dipped and cooled in a liquid, the apparatus including a water tank containing the liquid in which the metal sheet is dipped, a jetting device having a plurality of nozzles through which the liquid is jetted onto front and back surfaces of the metal sheet and at least some of which are placed in the liquid in the water tank, and a pair of restraining rolls which are placed between an entrance-side end of the jetting device and an exit-side end of the jetting device and restrain the metal sheet, in which nozzles nearest to the restraining rolls are inclined toward the restraining rolls from a horizontal plane in the jetting device.
[2] A rapid-cooling quenching apparatus in which a high-temperature metal sheet is dipped and cooled in a liquid, the apparatus including a water tank containing the liquid in which the metal sheet is dipped, a jetting device having a plurality of nozzles through which the liquid is jetted onto front and back surfaces of the metal sheet and at least some of which are placed in the liquid in the water tank, and a plurality of pairs of restraining rolls which are placed between an entrance-side end of the jetting device and an exit-side end of the jetting device and restrain the metal sheet, in which nozzles nearest to the restraining rolls are inclined toward the restraining rolls from a horizontal plane in the jetting device.
[3] The rapid-cooling quenching apparatus according to item [1] or [2], in which the nozzles nearest to the restraining rolls form an angle of 20° or more and 60° or less with the metal sheet.
[4] A rapid-cooling quenching method by which a high-temperature metal sheet is dipped and cooled in a liquid contained in a water tank, the method including restraining the metal sheet by using a pair of restraining rolls placed between an entrance-side end of a jetting device and an exit-side end of the jetting device while the liquid is jetted through nozzles in the jetting device onto front and back surfaces of the metal sheet which is dipped in the liquid, in which the liquid is jetted obliquely toward the restraining rolls through nozzles nearest to the restraining rolls.
[5] A rapid-cooling quenching method by which a high-temperature metal sheet is dipped and cooled in a liquid contained in a water tank, the method including restraining the metal sheet by using a plurality of pairs of restraining rolls placed between an entrance-side end of a jetting device and an exit-side end of the jetting device while the liquid is jetted through nozzles in the jetting device onto front and back surfaces of the metal sheet which is dipped in the liquid, in which the liquid is jetted obliquely toward the restraining rolls through nozzles nearest to the restraining rolls.
[6] The rapid-cooling quenching method according to item [4] or [5], in which the liquid is jetted from the nozzles nearest to the restraining rolls in a direction at an angle of 20° or more and 60° or less to the metal sheet.
According to aspects of the present invention, it is possible to prevent a temporary decrease in the cooling rate of a metal sheet in the vicinity of restraining rolls when rapid-cooling quenching is performed.
Hereafter, the embodiments of the present invention will be specifically described with reference to the accompanying drawings.
The jetting device 4 has a plurality of nozzles 14 and 24 for jetting water and nozzle units 34 and 44 for holding the nozzles 14 and 24 respectively. There is a gap between a pair of nozzle units 34 and 44. Water is jetted through the nozzles 14 and 24 toward the front and back surfaces of the metal sheet 5 when the metal sheet 5 passes through the gap described above. In the example in
In the example in
The entrance-side nozzle units 34a and 44a are arranged so that a portion of each unit is dipped in water and the rest is above the water. A threaded metal sheet 5 is fed through a gap between the entrance-side nozzle units 34a and 44a, which is exposed above the water, and subsequently dipped in the water, and water is jetted through the nozzles 14 and 24. A plurality of nozzles 14 and 24 are provided in the entrance-side nozzle units 34a and 44a respectively. Openings of some of the nozzles (for example, nozzles which are placed at the top of the entrance-side nozzle units 34a and 44a in
The metal sheet 5 is restrained by the restraining rolls 7 after having passed through the entrance-side nozzle units 34a and 44a. The restraining rolls 7 press both front and back surfaces of the metal sheet 5 in the water in order to prevent deformation which may occur when the metal sheet 5 is rapidly cooled. It is preferable that a pair of restraining rolls 7 be arranged with some distance between the central axes thereof in the conveying direction of the metal sheet 5. By ensuring some distance between the central axes, the force to restrain the metal sheet 5 is increased and thus it is possible to enhance the shape correcting capability. For example, it is preferable that the restraining rolls 7 be arranged with a distance of 40 mm or more and 150 mm or less, or more preferably 80 mm or more and 100 mm or less, between the central axes thereof in the conveying direction.
In addition, it is preferable that the metal sheet 5 be pushed-in by the restraining rolls 7 and threaded such that the metal sheet 5 is wound around the restraining rolls 7. By pushing-in the metal sheet 5, it is possible to increase the capability for correcting the shape of a steel sheet, and it is possible to prevent the restraining rolls 7 from idly rotating. It is preferable that the pushing-in amount by one restraining roll 7 be 0 mm or more and 2.5 mm or less, or more preferably 0.5 mm or more and 1.0 mm or less, in the case where the pushing-in amount of the metal sheet 5 being threaded in a straight line, as illustrated in
The metal sheet 5 passes through the gap between the exit-side nozzle units 34b and 44b after having passed through the restraining rolls 7. Also, at this time, water is jetted through the nozzles 14 and 24, which are fitted in the exit-side nozzle units 34b and 44b respectively, onto the front and back surface of the metal sheet 5.
In the example in
In conventional examples, the nearest nozzles are arranged horizontally, but the nearest nozzles mentioned above are not arranged horizontally and are inclined so that the openings of the nozzles are oriented toward the restraining rolls 7 from a horizontal plane. More specifically, the nearest nozzles which are located at the exit-side end of the entrance-side nozzle units 34a and 44a in
Although nozzles other than the nearest nozzles are all fitted so as to be inclined in the same direction as the nearest nozzles in the example in
As illustrated in
The rapid-cooling quenching apparatus according to aspects of the present invention may have an inseparable nozzle unit which is formed in a single-piece structure in the conveying direction of the metal sheet 5. By using
In the example in
Also in the case where inseparable nozzle units are used, it is possible to prevent a decrease in the cooling rate of the metal sheet 5 in the vicinity of the restraining rolls 7 by inclining the nearest nozzles toward the restraining rolls 7.
Here, it is more preferable to use divided nozzle units (
Nozzles in the jetting device 4 are connected to piping in which a pump is fitted, although this is not illustrated. The water 2 in the water tank 1 is pumped up through the piping, pressurized and fed to nozzles 14 and 24 by using the pump in order to jet high-pressure water through the openings of the nozzles 14 and 24. In addition, the water 2 in the water tank 1 is kept at a temperature appropriate for quenching. An increase in water temperature in the water tank 1 is prevented by transferring a part of the water 2 in the water tank 1 to a cooling apparatus such as an external cooling tower in order to cool the water and by returning the cooled water 2 to the water tank 1. For example, it is preferable that the water temperature in the water tank 1 be higher than 0° C. and 50° C. or lower, or particularly preferably 10° C. or higher and 40° C. or lower.
It is preferable that the restraining rolls 7 be rotated in the circumferential direction by electricity in order to prevent a roll mark occurring in a metal sheet. Moreover, it is preferable that the restraining rolls 7 be openable and closable (capable of controlling the pushing-in amount of the metal sheet 5) as needed in order to control capability for correcting the shape of the metal sheet 5.
The restraining rolls 7 may be composed of a material having good thermal conductivity and sufficient strength to resist a load applied when the metal sheet 5 is pushed-in. Examples of a material for the restraining rolls 7 include SUS304, SUS310, and ceramic. Here, a material prescribed in JIS (Japanese Industrial Standards) corresponding to SUS304 or SUS310 may be used.
Hereafter, examples in which a plurality of pairs of restraining rolls 7 are used will be described by using
In the example in
The nearest nozzles are indicated by being blackened in
Also in the examples in which a plurality of pairs of restraining rolls are used, a preferable example of the angle a, at which the nearest nozzles are inclined, is 20° or more and 60° or less, or more preferably 30° or more and 45° or less for the same reasons as in the example in which only one pair of restraining rolls are used.
Also in the examples in which a plurality of pairs of restraining rolls are used, it is preferable that the metal sheet be pushed-in by the restraining rolls for the same reasons as in the example in which only one pair of restraining rolls are used. It is preferable that the push-in amount by each restraining roll be 0 mm or more and 2.5 mm or less. It is particularly preferable that the push-in amount be 0.5 mm or more and 1.0 mm or less.
In the examples in which a plurality of pairs of restraining rolls are used, it is preferable that the restraining rolls be arranged in a zigzag manner with some distance in the conveying direction between the restraining rolls placed on the front and back surfaces of the steel sheet. With this, it is possible to increase the shape correcting capability by increasing the force to restrain the metal sheet 5. Here, it is preferable that the distance in the conveying direction between the central axes of the nearest two restraining rolls arranged to face each other among the restraining rolls 7 be 40 mm or more and 150 mm or less, or more preferably 80 mm or more and 100 mm or less, for the same reasons as described above.
In the examples in which a plurality of pairs of restraining rolls are used, it is possible to achieve a higher capability for correcting the shape of a steel sheet when cooling is performed than in the example in which only one pair of restraining rolls is used. In particular, even in the case where a high-strength steel sheet is cooled, in which deformation tends to occur, it is possible to further reduce deformation such as warpage occurring in a steel sheet, when the steel sheet is cooled, by using a plurality of pairs of restraining rolls. On the other hand, since there is a problem regarding facility condition and there is a problem of a decrease in the cooling capability of a jetting device in the case where the number of restraining rolls is excessively large, the number of restraining rolls may be appropriately determined in consideration of such problems.
It is particularly preferable that the rapid-cooling quenching apparatus and the rapid-cooling quenching method according to aspects of the present invention be used for manufacturing a high-strength cold-rolled steel sheet (high-tensile steel sheet), or, more specifically, a steel sheet having a tensile strength of 580 MPa or more. Although there is no particular limitation on the upper limit of tensile strength, for example, the upper limit may be 1600 MPa or less. When a high-tensile steel sheet is manufactured, it is important to perform accurate microstructure control by rapidly cooling a steel sheet. In the case of conventional rapid-cooling quenching apparatuses and rapid-cooling quenching methods, since there is a decrease in the cooling rate in the vicinity of restraining rolls 7, it is not possible to make up a desired metallographic structure, which results in a problem in that the strength of a high-tensile steel sheet becomes lower than the strength desired. By manufacturing a high-tensile steel sheet by using the rapid-cooling quenching apparatus and the rapid-cooling quenching method according to aspects of the present invention, it is possible to manufacture a high-tensile steel sheet having the desired strength with more certainty by preventing a decrease in the cooling rate in the vicinity of the restraining rolls 7.
Examples of a chemical composition of a high-strength cold-rolled steel sheet include one containing, by mass %, C: 0.04% or more and 0.25% or less, Si: 0.01% or more and 2.50% or less, Mn: 0.80% or more and 3.70% or less, P: 0.001% or more and 0.090% or less, S: 0.0001% or more and 0.0050% or less, sol. Al: 0.005% or more and 0.065% or less, optionally one or more of Cr, Mo, Nb, V, Ni, Cu, and Ti: 0.5% or less each, further optionally B and Sb: 0.01% or less each, and the balance being Fe and inevitable impurities.
Here, the embodiments of the present invention may be used not only for cooling a steel sheet with water but also for cooling any kind of metal sheet other than a steel sheet, and the embodiments may also be used for rapid-cooling quenching with a coolant other than water.
Hereafter, aspects of the present invention will be described more specifically by using examples.
High-strength cold-rolled steel sheets having a thickness of 1.0 mm, a width of 1000 mm, and a tensile strength of 580 MPa grade to 1470 MPa grade were manufactured by using a rapid-cooling quenching apparatus illustrated in
In addition, the temperature of the steel sheet was measured while the steel sheet was threaded through the rapid-cooling quenching apparatus. Specifically, the temperature of the steel sheet was measured over time in the temperature-measurement region of the steel sheet by using a thermocouple-type thermometer. Here, the cooling start temperature (temperature immediately before the steel sheet entered the jetting device 4) of the steel sheet was 740° C., and the cooling stop temperature (temperature immediately after the steel sheet had come out of the water tank 1) was 50° C. The cooling rate of the steel sheet was calculated from the relationship between the elapsed time after cooling had been started and the temperature of the steel sheet. The results are shown in
In addition, the warpage quantity of the steel sheet was determined after the steel sheet had been threaded through the quenching apparatus. Description will be given specifically by using
The experiment was performed under the same conditions as Example 1 of the present invention with the exception that a rapid-cooling quenching apparatus illustrated in
In
In addition, while the tensile strength of the steel sheet which was manufactured in Example 1 of the present invention was almost 1470 MPa, the tensile strength of the steel sheet which was manufactured in Comparative example 1 was about 1400 MPa, which means there was a decrease in tensile strength. It was possible to prevent a deterioration in the property of a steel sheet due to a decrease in the cooling rate in the vicinity of the restraining rolls by applying aspects of the present invention. Here, the results regarding the warpage quantity of the steel sheet will be described below.
The same experiment as in Example 1 of the present invention was performed with the angle a being varied from 10° to 90° at intervals of 10°. Here, an example of the angle a of 90° was not included in the present invention but classified as a comparative example. The ratio of decrease in the cooling rate when the steel sheet passed in the vicinity of the restraining rolls was calculated and plotted in
As indicated in
Operation was performed under the same condition as in Example 1 of the present invention by using a rapid-cooling quenching apparatus illustrated in
Operation was performed under the same condition as in Example 1 of the present invention by using a rapid-cooling quenching apparatus illustrated in
<Evaluation of Cooling Rate>
The determination results of the cooling rate of the steel sheets in Example 3 of the present invention and Example 4 of the present invention were the same as those in Example 1 of the present invention and shown in
<Evaluation of Warpage Quantity>
The measurement results of the warpage quantity of the three kinds of steel sheets in Example 1 of the present invention, Examples 3 and 4 of the present invention, and Comparative example 1 are given in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-256541 | Dec 2015 | JP | national |
| 2016-238977 | Dec 2016 | JP | national |
This is the U.S. National Phase application of PCT/JP2016/088643, filed Dec. 26, 2016, which claims priority to Japanese Patent Application No. 2015-256541, filed Dec. 28, 2015 and Japanese Patent Application No. 2016-238977, filed Dec. 9, 2016, the disclosures of these applications being incorporated herein by reference in their entireties for all purposes.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/088643 | 12/26/2016 | WO | 00 |
