JP7355251B2 - Metal plate quenching equipment, continuous annealing equipment, metal plate quenching method, cold rolled steel plate production method, and galvanized steel plate production method - Google Patents

Description

The present invention relates to a metal plate hardening apparatus, continuous annealing equipment, and metal plate hardening apparatus that suppresses shape defects that occur in metal plates during quenching in continuous annealing equipment that anneales metal plates while continuously passing them through. The present invention relates to a method for manufacturing a cold-rolled steel sheet and a method for manufacturing a plated steel sheet.

In the production of metal plates such as steel plates, continuous annealing equipment heats the metal plate and then cools it to cause phase transformation, thereby building up the material. In recent years, demand for thinner, high-strength steel sheets (high-strength steel) has been increasing in the automobile industry with the aim of reducing vehicle body weight and improving crash safety. Therefore, rapid cooling technology, which is advantageous in manufacturing high-strength steel sheets, is becoming increasingly important. Among various cooling methods, the cooling method using water is widely adopted because it can obtain a high cooling rate at low cost. However, because of rapid cooling, differences in temperature distribution potentially occur within the steel plate, which can cause shape defects in the steel plate due to out-of-plane deformation such as warping and wavy deformation, which poses a problem. In order to prevent such shape defects during water quenching of steel plates, various methods have been proposed in the past.

In Patent Document 1, a bridle roll is used as a tension changing means that can change the tension of a steel plate subjected to a rapid quenching process in order to suppress the wavy deformation of a metal plate that occurs during quenching in a continuous annealing furnace. A method has been proposed in which the quenching section is provided before and after the quenching section.

Patent Document 2 focuses on the fact that at the quenching start point (cooling start point), thermal stress in the compressive direction occurs in the width direction of the metal plate, causing the metal plate to buckle and cause shape defects. A method has been proposed in which out-of-plane deformation is suppressed by restraining a metal plate from both sides in a region where compressive stress is generated in the direction or in a region near the region.

Furthermore, in Patent Document 3, assuming that the temperature at the Ms point where the martensitic transformation of the metal plate starts is TMs°C, and the temperature at the Mf point where the martensitic transformation ends is TMf°C, the metal plate during rapid cooling and quenching is A method has been proposed in which a set of restraining rolls provided in the cooling liquid is used to restrain the temperature in the temperature range of TMs + 150°C to TMf - 150°C.

Furthermore, Patent Document 4 discloses a water tank containing a liquid for immersing a metal plate, a jetting device equipped with a plurality of nozzles for jetting liquid onto the front and back surfaces of the metal plate, and one or more pairs of nozzles for restraining the metal plate. Methods and devices have been proposed that include a restraining roll and injecting liquid from all nozzles of an ejection device in the direction of the restraining roll.

Japanese Patent Application Publication No. 2011-184773 Japanese Patent Application Publication No. 2003-277833 Patent No. 6094722 Patent No. 6477852

However, none of the methods disclosed in Patent Documents 1 to 4 do not take into account the thickness of the metal plate or the threading speed in the water tank when restraining the metal plate with the restraining roll, and the temperature of the metal plate does not change. There is a problem that restraint by restraint rolls cannot be performed in the range from TMs+150°C to TMf-150°C. As a result, there is a problem in that a shape defect occurs after the metal plate is hardened.

The present invention has been made in view of the above circumstances, and includes a metal sheet hardening apparatus, continuous annealing equipment, and a metal sheet hardening apparatus that suppresses shape defects that occur in metal sheets during hardening, regardless of the sheet passing speed or sheet thickness. The object of the present invention is to provide a quenching method, a method for manufacturing a cold-rolled steel sheet, and a method for manufacturing a plated steel sheet.

The gist of the present invention for solving the above problems is as follows.
[1] A water tank in which a metal plate to be threaded is immersed in a liquid to cool it, a water injection device provided in the water tank, and a plurality of pairs of restraining rolls to restrain the metal plate to be threaded inside the water tank. A quenching apparatus for a metal plate, wherein the water injection device is installed so that cooling water is injected from opposite sides of the metal plate across the front and back surfaces of the metal plate along the threading direction of the metal plate. A quenching apparatus for a metal plate, comprising a plurality of water injection nozzles, the plurality of restraining roll pairs having their positions relative to the metal plate independently adjusted based on operating conditions.
[2] The metal plate quenching apparatus according to [1], wherein the plurality of constraint roll pairs have a maximum surface height roughness Rz of both a maximum value and a minimum value of 5 μm or more and 50 μm or less.
[3] The metal plate hardening apparatus according to [1], wherein the restraining rolls of the plurality of restraining roll pairs have a roll diameter of 50 mm or more and 250 mm or less.
[4] The plurality of pairs of restraint rolls are arranged such that, when the roll diameter is Dmm, the distance between the center axes of the pair of restraint rolls facing each other with the metal plate in between is D×1/4 mm or more and Dmm or less. The metal plate quenching apparatus according to [1].
[5] Continuous annealing equipment provided with the metal plate quenching device according to any one of [1] to [4] on the outlet side of the soaking zone.
[6] After the metal plate that is continuously passed is immersed in a liquid and cooling is started, the temperature of the metal plate is lower than or equal to the martensitic transformation start temperature of the metal plate + 150°C, and the martensitic transformation end temperature - A method of quenching a metal plate, comprising restraining the metal plate using a plurality of pairs of restraining rolls whose positions relative to the metal plate are adjusted while the temperature is in a range of 150° C. or higher.
[7] A method for producing a cold-rolled steel plate, which comprises quenching the cold-rolled steel plate by the metal plate quenching method described in [6].
[8] A method for manufacturing a plated steel sheet, which comprises performing a plating treatment on the cold-rolled steel sheet following the method for manufacturing a cold-rolled steel sheet according to [7].
[9] The method for manufacturing a plated steel sheet according to [8], wherein the plating treatment is performed by any one of electrogalvanizing treatment, hot-dip galvanizing treatment, and alloying hot-dip galvanizing treatment.

According to the metal plate quenching apparatus, metal plate quenching method, and steel plate manufacturing method according to the present invention, it is possible to suppress shape defects that occur in a metal plate during quenching, regardless of the plate passing speed or plate thickness.

FIG. 1 is a schematic diagram showing the configuration of a hardening apparatus of the present invention. FIG. 2 is a schematic diagram showing the configuration of a restraining roll pair of the hardening apparatus of the present invention. FIG. 2 is a schematic diagram showing the arrangement of restraining rolls of the present invention. FIG. 2 is a schematic diagram showing warping of a metal plate. FIG. 1 is a schematic diagram showing the configuration of a conventional hardening device.

Hereinafter, one embodiment of the present invention will be described using the drawings. Hereinafter, a case will be described in which water, which is inexpensive and industrially useful, is used as a cooling medium, but the cooling medium is not particularly limited as long as it is a liquid that can be used for cooling.

FIG. 1 is a diagram showing a hardening apparatus 1 for a metal plate S according to an embodiment of the present invention. The hardening apparatus 1 is applied to cooling equipment provided on the outlet side of a soaking zone of a continuous annealing furnace (continuous annealing equipment). In the quenching apparatus 1, a water injection device 3 is provided in a water tank 2 containing water for cooling so that a part of the water injection nozzle 3a is exposed upward from the water surface (W in the figure). The water injection device 3 is configured such that the water injection nozzle 3a continuously passes the metal plate S through the inside of the water tank 2 with a predetermined gap between the front and back surfaces of the metal plate S (in the drawing). A plurality of restraining roll pairs 4 are arranged along the arrow P), and a plurality of restraining roll pairs 4 are arranged along the arrow P). In addition, although four restraining roll pairs 4 are shown in FIG. 1, there is no restriction as long as there are two or more, that is, two or more pairs. These plural restraint roll pairs 4 may have a control device for adjusting their positions with respect to the metal plate S based on operating conditions.

The metal plate S may require hardening on the exit side of the continuous annealing furnace in order to obtain the desired quality. However, it is known that the rapid cooling during the quenching process causes thermal contraction and the shape becomes disordered. In particular, when the metal plate S undergoes martensitic transformation, rapid thermal contraction and transformation expansion occur simultaneously in the range from the martensitic transformation start temperature (TMs°C) to the martensitic transformation end temperature (TMf°C), and the metal plate S undergoes martensitic transformation. The stress acting within the plate S becomes maximum, and the shape of the metal plate S collapses. Note that the temperatures of TMs°C and TMf°C can be calculated from the component composition of the metal plate S.

In particular, if the temperature of the metal plate S during quenching by quenching can be physically restrained within a temperature range of TMs+150°C or lower and TMf-150°C or higher, the shape can be stabilized. A range of TMs+100°C or lower and TMf-100°C or higher is more preferable.

In contrast, a technique has been proposed in which a pair of constraining rolls 4 are provided to sandwich the surface of the metal plate S during immersion in cooling water in a temperature range that causes martensitic transformation. However, with only one simple configuration, that is, one pair of restraint rolls 4, in order to maintain the temperature of the metal plate S within an appropriate range during restraint, the threading speed of the metal plate S and the plate thickness must be adjusted. had to be restricted. Therefore, in the present invention, attention was paid to providing a plurality of restraining roll pairs 4 in the cooling water.

In the present invention, as shown in FIG. 1, by providing a plurality of restraining roll pairs 4, the distance over which the metal plate S can be restrained becomes longer, and even if the sheet passing speed increases or decreases or the sheet thickness changes, It becomes possible to reliably restrict the temperature within the temperature range of TMs+150°C or lower and TMf-150°C or higher. If restrained outside the temperature range, expansion due to transformation cannot be suppressed and the shape of the metal plate S becomes disordered. In addition, since the thickness and threading speed of the metal sheet S change depending on the product specifications and the heating and soaking capacity of the continuous annealing furnace, the number of restraining roll pairs 4 depends on the threading speed of the metal sheet S or the sheet threading speed. It is sufficient to provide a number of restraining roll pairs 4 that can restrain at least two or more restraining roll pairs 4 in the temperature range of TMs+150° C. to TMf−150° C. when the thickness changes.

In the present invention, cooling is promoted using a water injection device 3 having a plurality of water injection nozzles 3a. As shown in FIG. 1, the water injection device 3 made up of a plurality of water injection nozzles 3a is arranged in a range extending from just above the water surface W to underwater. The water jet nozzle 3a is arranged at a position farther from the metal plate S than the restraining roll pair 4. The distance between the water injection nozzle 3a and the metal plate S is not particularly limited, but if they are close, there is a risk of contact due to warpage or vibration of the steel plate (metal plate S), and if they are far apart, ) Please note that the jet flow velocity at the time of arrival may become slow and the cooling capacity may decrease. The position where the refrigerant (3b in the figure) injected from the water injection nozzle 3a located at the top of the water injection device 3 collides with the metal plate S, that is, the jet collision position is a distance above the water surface W (A in the figure). ), and its height is preferably 10 mm.

In addition, if the jet impingement position is too close to the water surface W, the effect of fluctuations in the position of the water surface W will also affect the jet impingement position, making the vapor film removal position unstable and having a large impact on the cooling capacity. Therefore, it is inappropriate. On the other hand, if it is too far away from the water surface W, the water temperature will rise during the flow of the water flow after the water jets out, the cooling ability of the downstream part will decrease, and a transition boiling state will occur, which is unsuitable. Therefore, the distance between the water surface W and the jet collision position, indicated by distance A, is preferably about 5 to 50 mm (or 10 mm).

Conventionally, in order to suppress a decrease in the cooling rate of the metal plate S, when jetting water toward the location where the pair of restraint rolls 4 and the metal plate S come into contact (hereinafter referred to as "roll edge"), the restraint roll In the immediate vicinity of pair 4, it has been recommended that the water jet nozzle 3a be arranged at an angle (see FIG. 5).

However, if the nozzles are arranged diagonally as shown in FIG. 5, the equipment (water tank 2) will become long, so the necessary conditions were investigated through experiments and the like. As a result, it was found that the cooling rate slows down at the edge of the roll only when a vapor film remains, and when there is no vapor film, there is almost no decrease in the cooling rate. In particular, in the quenching of the metal plate S of high-strength steel sheet targeted by the present invention, the martensitic transformation start temperature (TMs°C) is about 400°C, and the martensitic transformation finishing temperature (TMf°C) is about 300°C. Therefore, it is assumed that the temperature range when restraining with the restraining roll pair 4 during quenching is approximately 150°C to 550°C. This temperature range corresponds to the nucleate boiling region to the transition boiling region, and either there is no vapor film (nucleate boiling), or even if there is a vapor film, the state is quite unstable (transition boiling). Therefore, a small amount of water jetting can destroy the steam film, and there is no need to set the nozzle obliquely toward the restraining roll pair, and there is no problem even if the nozzle is jetted perpendicularly to the metal plate S.

These conditions are satisfied when the target material is a metal plate S having a martensitic transformation start temperature (TMs°C) of 450°C or lower, preferably 400°C or lower.

As has been pointed out in the past, if the rolls are restrained at high temperatures, the cooling rate at the time of rolling will be significantly reduced unless the vapor film is removed, but it is better not to restrain them in this temperature range in the first place. , not a problem.

Therefore, in the present invention, a moving mechanism is provided in which each restraining roll pair 4 independently moves in the direction of pushing in the metal plate S or in the direction of moving away from the metal plate S, and the water injection nozzle 3a is connected to the water injection nozzle 3a so that the cooling water to be injected is A stable cooling state can be obtained even if the S is placed facing each other with the front and back surfaces sandwiched in between. In order for the cooling water injected from the water injection nozzle 3a to be injected so as to face each other with the metal plate S in between, the water injection nozzle 3a must be arranged approximately perpendicular to the passing direction of the metal plate S. be. Specifically, this "substantially vertical" means, where θ is the inclination angle of the water jet nozzle 3a with respect to the metal plate S, θ is 80° or more and 100° or less, preferably 82° or more and 98° or less, More preferably, the angle is 87° or more and 93° or less.

Specifically, the restraining roll pairs 4 at locations where the temperature of the metal plate S reaches a temperature range where there is a concern about transition boiling are evacuated, and the remaining restraining roll pairs 4 are used to restrain the metal plate. Note that the restraining roll pair 4 may have a mechanism that moves individually, or may have a mechanism that moves one roll at a time (restraint roll 4a) instead of as a pair.

Here, which restraining roll pair should be evacuated or used may be determined depending on the operating conditions. Operating conditions refer to heat treatment conditions and cooling conditions, and particularly the threading speed, plate thickness, quenching start temperature, and "warpage" of the metal plate are items that have a large influence. If the heat treatment conditions before quenching and the distance from the end of heat treatment to the start of cooling are at least the same among steel types of the same type, it is desirable to decide based on the sheet threading speed and sheet thickness. The method of determining the restraining roll pair to be used is not limited to the method described above (determining the roll pair to be restrained by deriving the position where the preferred temperature range described in paragraph 0018 is based on the sheet passing speed and sheet thickness). A suitable restraining roll pair may be selected and used by accumulating data on whether the shape is stable when the operating conditions and the restraining roll pair used are changed.

In other words, regarding the quenching treatment of the metal sheet S, by adjusting the position of the plurality of restraint roll pairs 4 with respect to the metal sheet S based on the sheet passing speed or sheet thickness, which are the operating conditions, it is possible to ensure that the temperature is below TMs + 150°C, TMf The metal plate S can be restrained in a suitable temperature range of −150° C. or higher. The operating conditions may be the threading speed or the thickness, or the product of the threading speed and the thickness (hereinafter referred to as "LSD"). In this case, either the threading speed or the thickness When one of them changes (increases or decreases), the LSD also changes. Adjustment of the positions of the plurality of restraint roll pairs 4 is performed based on the conditions for adjusting the restraint roll pairs 4: "restraint roll pair to be used", "distance between restraint roll pairs", "intermesh amount" and "offset amount" to be described later. ” and other adjustments.

In the case of the method of improving the shape by roll restraint, scratches may occur due to roll slip. This is because the water jet collides with the metal plate S in a turbulent state, which may cause the metal plate S to vibrate violently, and also because a water film tends to enter between the restraining roll 4a and the metal plate S, resulting in so-called hydroplaning. It is thought that this phenomenon may cause slippage. As a countermeasure for the former, it is preferable to restrain the metal plate S with a plurality of restraining roll pairs 4, and thereby the vibration level can be significantly improved. Furthermore, as a measure against the latter, if the maximum height roughness Rz of the surface of the restraining roll 4a is increased to 5 μm or more, drainage performance is improved and slips can be prevented.

However, the upper limit was set to 50 μm or less since the slip prevention effect reaches a plateau when Rz exceeds a certain level and flaws due to roughness tend to occur. The maximum height roughness Rz is specified in the Japanese Industrial Standards "JIS B 0601 Surface Roughness (2001)" and is measured and calculated in accordance with "JIS B 0633". It is a value measured with a two-dimensional roughness meter in a direction corresponding to the direction, that is, in the longitudinal direction of the restraining roll 4a. Further, as long as the measuring device can obtain a measurement result that satisfies "JIS B 0601 Surface Roughness", the method may be non-contact or contact.

There is also a suitable range for the diameter (diameter Dmm) of the restraining roll 4a for the following reasons. When the roll diameter of the restraining roll 4a is large, interference with the water flow becomes large, which makes the water flow unstable, and the situation in which the steam film is removed becomes unstable, resulting in the shape of the metal plate S becoming unstable. Further, as the diameter of the roll increases, the distance over which the refrigerant jet is obstructed by the roll increases, making it difficult to ensure a sufficient cooling length, which is undesirable. Therefore, the roll diameter is preferably 250 mm or less. On the other hand, if it is too small, roll deflection occurs when the metal plate S is restrained, and the force for restraining the metal plate S becomes weak, making it impossible to exhibit the shape improvement effect. Therefore, the roll diameter is preferably 50 mm or more.

Here, an example of the arrangement configuration of the restraining roll pair 4 is shown in FIGS. 2 and 3. It is preferable that the pair of restraining rolls 4 facing each other from the front side and the back side of the metal plate S are arranged (offset) so that the center axis of each restraining roll 4a is shifted in the sheet passing direction P of the metal plate S. At this time, it is not necessary to shift all the restraint rolls 4a in the same direction, and it is possible to change which restraint roll 4a is shifted up or down for each restraint roll pair. If the central axes are the same, the metal plate S cannot be pushed in, but if the central axes are shifted, the amount of pushing becomes variable and the restraint force increases. However, if the distance between the center axes of each of the pair of restraint rolls 4a, that is, the offset value (B in the figure) becomes too large, the corresponding part of the metal plate S cannot be restrained on the front and back sides at the same time, and the restraint effect cannot be exerted. It disappears. For these reasons, the distance between the center axes (offset value) of the pair of front and back restraining rolls 4a is preferably D×1/4 mm or more and D mm or less. Note that D is the diameter (mm) of the restraining roll 4a as described above. If it exceeds Dmm, it is possible to increase the amount of push-in of the rolls, but the roll restraint effect cannot be obtained. In other words, the straightening effect cannot be obtained by applying bending and unbending forces to the plate almost simultaneously. On the other hand, if it is less than D x 1/4 mm, although the restraining effect is strong, the straightening effect may be insufficient because the pushing amount cannot be secured, or if the plate thickness becomes thick, problems may occur where the plate cannot pass between the rolls. .

Furthermore, the amount of movement I (I.M; intermesh) of the restraining roll pair 4 in the direction of pushing the metal plate S is not particularly limited, and may vary depending on the strength and arrangement of the restraining metal plate S, the number of the restraining roll pair 4, etc. The optimum range may be set for each pair of constraint rolls according to the following. However, if the amount of movement in the pushing direction is small, slipping is more likely to occur, increasing the risk of scratches. On the other hand, if it is large, it may promote shape defects, so there is a suitable value. When a steel plate is used as the metal plate S, and the plate thickness is tmm, the amount of movement of the restraining roll pair 4 in the direction of pushing the metal plate S is preferably in the range of −t to +10×tmm. Here, to explain specifically using FIG. 3, as shown in the state where the movement amount I of the restraining roll 4a with respect to the metal plate S is -tmm (see FIG. 3(a)), when the movement amount I of the restraining roll 4a with respect to the metal plate S is less than -tmm, the metal plate S The restraint effect will no longer be obtained. In addition, as shown in the state where the movement amount of the restraining roll 4a with respect to the metal plate S is +10 x tmm (see Fig. 3(b)), if it exceeds +10 x tmm, the biting of the metal plate S becomes too strong and the There is a possibility that you will not be able to board.

The position of the restraining roll pair 4 may be adjusted using warpage information of the metal plate S. The warpage information of the metal plate S may be a predicted value or a measured value, and is not particularly limited. When measuring the warpage of the metal plate S, there are three patterns for measuring the warp: in front of the water tank 2, after the water tank 2, and off-line, and any combination may be used. The warpage in the metal plate S may be measured using a laser distance meter or the like. If the measurement is performed before the metal plate S is cooled, there is an advantage that the conditions for the restraining roll pair 4 (the restraining roll pair to be used, the distance between the restraining roll pairs, the intermesh amount, the offset amount, etc.) can be determined without delay. If the measurement is made after the metal plate S has been cooled, a delay in setting due to the time difference will be unavoidable, but since the adjustment is based on the actual warpage information of the metal plate S, accurate adjustment of the restraining roll pair 4 is possible. . Off-line measurement of the warpage of the metal plate S has the advantage that it can be measured manually, although there is a large delay in setting the restraining roll pair 4.

In other words, regarding the hardening process of the metal plate S, the positions of the plurality of restraining roll pairs 4 with respect to the metal plate S are adjusted based on the operating conditions including information on the "warpage" of the metal plate S in addition to the sheet passing speed and sheet thickness. You may. In this case as well, the adjustment of the positions of the plurality of restraint roll pairs 4 is performed using the conditions for adjusting the restraint roll pairs 4: "restraint roll pair to be used", "distance between restraint roll pairs", "intermesh amount". ” and “offset amount”.

Moreover, the distance between the restraining roll pairs 4 (C in FIG. 2) is the distance between the center of the restraining roll 4a installed below the upper restraining roll pair 4 among the adjacent restraining roll pairs 4, and the distance between the lower restraining roll pair 4 and the lower restraining roll pair 4. It means the distance from the center of the restraint roll 4a installed above the restraint roll pair 4.

It is assumed that the restraining rolls 4a in the restraining roll pair 4 have a mechanism for moving toward and away from each other with respect to the passing direction P of the metal strip S. In this case, the distance between the restraining roll pairs 4 is doubled, and the number of restraining roll pairs 4 is halved. However, unless the initial distance C between the pair of restraint rolls 4 is properly set in advance, the shape correction effect cannot be obtained.

An appropriate range for the distance C is Dmm or more and 10×Dmm or less. If the distance C between the restraining roll pair 4 is less than Dmm, the water ejected from the water jet nozzle 3a will be blocked by the restraining roll pair 4 before reaching the metal plate S, and sufficient cooling capacity will not be obtained. , the distance required for shape correction becomes longer, and the apparatus becomes larger, which is undesirable. Furthermore, since the number of contact points between the metal plate S and the restraining roll pair 4 increases, the risk of surface flaws such as push-in flaws and slip flaws also increases. On the other hand, if it is larger than 10×Dmm, the distance from the metal plate S passing through one restraining roll pair 4 to being restrained by the next restraining roll pair 4 becomes long, and the effect of providing a plurality of restraining roll pairs 4 is will not be obtained.

The restraining roll 4a may be made of a material that has excellent thermal conductivity and has strength enough to withstand the load when the metal plate is pressed. Examples include heat-resistant steel (e.g. KHR12C), stainless steel (SUS304, SUS310), ceramic, etc., but CFRP material has a small roll deflection even with a small diameter, and it is easy to obtain a roll restraint effect, especially when you want to secure cooling capacity. It's advantageous.

As mentioned above, the purpose of the present invention is to reduce the complicated and uneven uneven shape that occurs when the structure expands in volume due to martensitic transformation during rapid cooling of the metal plate S. It is preferable to apply it to a method for manufacturing rolled steel sheets. Further, the cold rolled steel sheet may be subsequently subjected to plating treatment. The plating process may be performed by any one of electrogalvanizing, hot-dip galvanizing, and alloying hot-dip galvanizing.

More specifically, it is preferable to apply the present invention to the production of high-strength steel plates (high tensile strength) having a tensile strength of 580 MPa or more. The upper limit of the tensile strength is not particularly limited as long as the roll material is made of a material that can be applied to high strength, but if it is made of stainless steel (SUS304, SUS310), ceramic, etc., an effect can be expected even if the tensile strength is around 3000 MPa. can.

Examples of the above-mentioned high-strength steel sheets (high-strength steel sheets) include high-strength cold-rolled steel sheets, hot-dip galvanized steel sheets that have been subjected to surface treatment, electrogalvanized steel sheets, alloyed hot-dip galvanized steel sheets, and the like. That is, continuous annealing is carried out by implementing the quenching apparatus and quenching method for metal sheet S according to the present invention, and high-strength cold-rolled steel sheets, hot-dip galvanized steel sheets, electrogalvanized steel sheets, and alloyed hot-dip galvanized steel sheets are manufactured. It is especially suitable.

As a specific example of the composition of a high-strength steel plate, in mass%, C is 0.04% or more and 0.25% or less, Si is 0.01% or more and 2.50% or less, and Mn is 0.80% or more and 3.70%. % or less, P is 0.001% or more and 0.090% or less, S is 0.0001% or more and 0.0050% or less, sol. Al is 0.005% or more and 0.065% or less, if necessary, at least one of Cr, Mo, Nb, V, Ni, Cu, and Ti is each 0.5% or less, and if necessary , B, and Sb are each 0.01% or less, and the balance is Fe and unavoidable impurities.

Note that the embodiments of the present invention can be applied to rapid cooling of metal plates in general. Further, the present invention is not limited to the water immersion cooling mentioned as an example in the embodiment, but can be applied to any heating or cooling as a means for physically restraining and preventing deformation of a steel plate due to transformation.

Hereinafter, an example in which a metal plate was manufactured using the metal plate hardening apparatus, metal plate hardening method, and steel plate manufacturing method according to the present embodiment will be described.

Based on the quenching apparatus 1 shown in Fig. 1, a high tensile strength cold-rolled steel plate (metal plate S) with a tensile strength of 1470 MPa class with a plate thickness of 1.0 to 2.3 mm and a plate width of 1000 mm is passed through (Table 1) (see "LS" in the middle) 60 to 108 mpm, quenching start temperature 800°C, cooling water injection amount 1000T/hr, and water temperature 30°C. Further, although four restraining roll pairs 4 shown in the hardening apparatus 1 shown in FIG. 1 are arranged in the vertical direction, in this example, one to three restraining roll pairs were arranged in the vertical direction.

Here, the representative components of a high-tensile cold-rolled steel sheet with a tensile strength of 1470 MPa class are, in mass %, C 0.20%, Si 1.0%, Mn 2.3%, and P 0.005%. , S was 0.002%. Note that the temperature at the Ms point (TMs°C) of the high tensile strength cold-rolled steel sheet is 400°C, and the temperature at the Mf point (TMf°C) is 300°C. In this case, the plate temperature range in which restraint by the restraint roll pair 4 is effective is 150°C to 550°C.

The roll diameter (D) of the restraining roll 4a was 150 mm. The center axes of each of the restraining rolls 4a in the restraining roll pair 4 were shifted by 75 mm (B = 75 mm in Fig. 2) in the sheet passing direction (see "Offset value" in Table 1), but the offset value was changed under some conditions. (Invention Examples 7 to 10). The positions of the restraining roll pair 4 are 0.3 m (first restraining roll pair) and 0.75 m (second restraining roll pair) in the sheet passing direction P for Invention Examples 1 to 14, assuming that the water surface W is 0 m. installed at each location. That is, C in FIG. 2 is 0.45 m. Invention examples 15 and 16 are examples in which a pair of restraint rolls is further added at a position of 1.05 m (third pair of restraint rolls). Each pair of restraining rolls 4 can be retracted (corresponds to I.M-50mm in Table 1. - means the retracting direction (direction away from the metal plate S)), and can be used depending on the conditions. Or, it became possible to change to non-use (roll movement). In other words, I. M "-50.0 mm" indicates that the corresponding restraining roll pair 4 is completely separated from the metal plate S and has no restraining force on the metal plate S. In addition, I. of Table 1. M corresponds to I in FIG.

In addition, when the restraint roll pair 4 is pushed into the metal plate S and used without retracting the restraint roll pair 4, the pushing amount into the metal plate S was basically 0 mm. That is, in Table 1, I. When M is "0.0 mm", the pair of restraining rolls 4 are pushed into the metal plate S. More specifically, I. A state in which M is "0.0 mm" means a state in which the position of the restraint roll pair 4 (restraint roll 4a) has been adjusted until the surface reaches the center position of the metal plate S. In other words, I. A state in which M is "0.0 mm" means a state in which the surface of the restraining roll pair 4 (restricting roll 4a) is pushed into the metal plate S by a distance of 1/2 of the plate thickness. On the other hand, under the conditions of Invention Example 7 and Invention Example 9, the pushing amount is changed. This is because under these conditions, the heights of the restraining rolls 4a on the front and back sides of the metal plate S are the same (offset value is 0), so it is impossible to physically push the metal plate S, and theoretically half of the plate thickness can be moved to the pass line. It would be fine to set it by shifting it in the - direction, but since there is a possibility of overloading, I set it with some margin.

Evaluations in Examples were made from two viewpoints: the amount of warpage (mm) of the metal plate S after cooling and the surface quality. The amount of warpage of the metal plate S was determined by measuring the amount of warpage (K in the figure) of the metal plate S in the width direction of the metal plate S, as shown in FIG. In addition, the surface quality of the metal plate S was determined by taking a total of three samples of plate width x 1 m length from the conveying tip, center, and rear end of the metal plate S, and observing the appearance of each sample. When observing the front and back sides of the three boards, if there are no more than 2 defects such as surface flaws in total, it is good ("〇" in Table 1), and if defects are found in 3 or more places in total, it is good. It was classified as having a defect ("×" in Table 1).

Next, Examples related to Comparative Examples 1 to 5 and Invention Examples 1 to 16 shown in Table 1 will be described.

In Comparative Example 1, the metal plate S was cooled by not providing the restraining roll pair 4 and setting the water injection direction of the water injection nozzle 3a in a direction perpendicular to the passing direction P of the metal plate S. The amount of warpage of the metal plate S was 34.5 mm, and a defective shape occurred.

In Comparative Examples 2 to 5, there was one restraining roll pair 4, and in Comparative Example 5, the water jet direction was set at 60° with respect to the steel plate. In Comparative Examples 3 and 4, the amount of warpage was improved because the restraint roll pair 4 was located in the suitable restraint temperature range derived from the transformation temperature of the metal plate, but in Comparative Examples 2 and 5, the warpage could not be improved. From these results, it is clear that a single pair of constraint rolls 4 cannot cope with changes in the product (LSD) of the passing speed and thickness of the metal sheet S, and that if the water jet direction is oblique, the shape may change. It got worse. The reason for this is that the substantial cooling capacity has decreased and the temperature of the metal plate S passing through the restraining roll pair 4 has increased.

On the other hand, Invention Examples 1 to 6 show the results under the condition that two restraining roll pairs 4 are arranged. Inventive Examples 1 to 3 are those in which the restraining roll pair 4 to be used is selected according to the LSD (the state of movement of the restraining roll pair 4 is selected), and it has been confirmed that it can be applied to a wide range of LSDs. Note that the metal plates targeted by the present invention are mainly thin steel plates, and the cooling status of the plates can be adjusted using an LSD. Therefore, as the LSD becomes larger, it becomes difficult to cool, and the martensitic transformation start and end positions are further away from the cooling start position, so it is preferable to select the restraining roll pair 4 located at the lower side of FIG. 1. On the other hand, since the smaller the LSD, the easier the cooling becomes, the martensitic transformation start and end positions approach the cooling start position, and it is preferable to select the restraining roll pair 4 located above in FIG. 1.

On the other hand, in Inventive Examples 4 to 6, two restraining roll pairs 4 were used together, and there were conditions that worsened the warpage of the metal plate S. Therefore, in order to cope with changes in the sheet passing speed and sheet thickness, a retracting function of the restraining rolls 4a (a function of moving the restraining roll pair 4) is required.

Invention examples 7 to 14 are based on the conditions of invention example 2, and the offset value of the restraining roll pair 4 (the distance between the restraining rolls 4a in the threading direction P of the metal strip S) and the maximum height roughness of the restraining roll 4a are This is a modification of Rz. When the offset value was set to 0 (Inventive Examples 7 and 9), the amount of warpage was worse than the result of Inventive Example 2 due to the setting restrictions on the pushing amount of the restraining roll 4a as described above. On the other hand, in Invention Example 8 and Invention Example 10 in which the offset value was 200 mm, the amount of warpage of the metal plate S deteriorated under the condition that the plate thickness was 1 mm. From this, it was confirmed that the offset value needs to be set appropriately.

Further, from Invention Examples 11 to 14, it was confirmed that the appearance of the metal plate S may deteriorate depending on the maximum height roughness Rz of the restraining roll 4a. In order to maintain the appearance of the surface of the metal plate S, it was confirmed that it is best to set the maximum height roughness Rz such that both the maximum value and the minimum value are within the range of 5 μm to 50 μm.

Invention example 15 is an example in which quenching was performed with reference to invention examples 4 to 6. By using a plurality of restraining roll pairs 4, the effect of straightening the metal plate S to some extent was obtained. Invention example 16 changes the rolls to be used for a plurality of restraint roll pairs 4 based on the product (LSD) of the sheet passing speed and sheet thickness of the metal sheet S and the warpage of the metal sheet S, and By making adjustments to change the restraint position of S and the distance between the pair of restraint rolls, it was possible to suppress the amount of warpage of the metal plate S to 3.1 mm. In this example (invention example 16), the restraint roll pair to be used was selected and the distance between the restraint roll pairs was adjusted accordingly, but the item to be adjusted may be the intermesh amount or the offset amount. To measure the warpage of the metal plate S, a laser displacement meter is installed at any position in the sheet passing direction P of the metal plate S, and based on the warp measurement result from the laser displacement meter, a plurality of restraining roll pairs 4 are measured. You may adjust various conditions.

The history of the invention of the metal plate quenching apparatus, metal plate quenching method, and steel plate manufacturing method according to the present invention is the result of intensive studies to solve the above-mentioned problems. , we obtained the following findings.

In order to make the shape of the metal plate S good, the metal plate S is restrained by restraining rolls 4a so as not to be deformed out of plane in the temperature range from (T _Ms +150) (°C) to (T _Mf -150) (°C). However, in order to achieve the above conditions with only one restraining roll pair 4, it was necessary to significantly restrict the threading speed and thickness of the metal sheet S. On the other hand, we have come to the conclusion that if a plurality of restraining roll pairs 4 are employed, the range of conditions for passing through the restraining roll pairs 4 within a favorable temperature range can be significantly relaxed.

In this way, it is sufficient to install a plurality of restraining roll pairs 4 to deal with changes in the LS, plate thickness, etc. of the metal plate S, but if the restraining roll pairs 4 are not installed under appropriate conditions, the shape of the metal plate S will change. may not be stabilized, or abrasions caused by the restraining roll pair 4 may occur.

The instability of the shape of the metal plate S was caused by the instability of the cooling capacity, and this was presumed to be due to the instability of the steam film removal performance by the water flow. In general, in water quenching cooling, the contact state (boiling form) between the metal plate S and water during cooling changes from the high temperature side to film boiling, transition boiling, and nucleate boiling depending on the temperature range of the metal plate S. It was known that the cooling rate and cooling uniformity change accordingly. In order to achieve rapid cooling with high temperature uniformity, it is important to perform cooling only in the nucleate boiling region, and for this purpose, we believe that uniform removal of the vapor film is important. In order to achieve this, a method has been put into practical use in which slit nozzles are installed on the front and back sides of the metal plate S and water jets are sprayed onto the metal plate S.

Further, as a result of studies conducted by the present inventors, it was found that a multi-stage parallel jet flow in which a plurality of water injection nozzles 3a for injecting a cooling medium are arranged in parallel fluctuates greatly due to the influence of the surrounding flow. When the jet fluctuates, the collision position with the metal plate S also fluctuates, making removal of the vapor film unstable. Therefore, it has been found that simply adding the constraining roll 4a may make the steam film removal state unstable and may even worsen the shape of the metal plate S. On the other hand, scratches that occur on the surface of the metal plate S are defects caused by slipping of the restraining roll 4a, and hydroplaning occurs when a water film is formed between the restraining roll 4a and the metal plate S. I thought this was caused by a phenomenon.

1 Quenching device 2 Water tank 3 Water injection device 3a Water injection nozzle 3b Refrigerant injected from the water injection nozzle 4 Restraint roll pair 4a Restraint roll D Roll diameter P Sheet passing direction Rz Maximum height roughness S Metal plate K Warpage amount W Water surface A Distance from the water surface to the cooling start point B Distance between the center axes of a pair of facing restraint rolls (offset value)
C Distance between a pair of restraint rolls I Amount of movement of restraint rolls in the direction of pushing the metal plate (I.M)

Claims (4)

After the continuously passed metal plate is immersed in liquid and cooling begins,
Using a plurality of constraining roll pairs whose positions relative to the metal plate are adjusted while the temperature of the metal plate is within the range of the martensitic transformation start temperature of the metal plate + 150 ° C. or lower and the martensitic transformation end temperature - 150 ° C. or higher. A method for quenching a metal plate, the method comprising: restraining the metal plate. A method for producing a cold-rolled steel sheet, comprising quenching the cold-rolled steel sheet by the method for quenching a metal sheet according to claim 1 . A method for manufacturing a plated steel sheet, which comprises performing a plating treatment on the cold rolled steel sheet following the method for manufacturing a cold rolled steel sheet according to claim 2 . The method for manufacturing a plated steel sheet according to claim 3 , wherein the plating treatment is performed by any one of electrogalvanizing treatment, hot-dip galvanizing treatment, and alloying hot-dip galvanizing treatment.

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