JP2013245355A - METHOD FOR MANUFACTURING Al-Zn ALLOY PLATED STEEL SHEET - Google Patents

Abstract

A method of manufacturing an Al—Zn alloy plated steel sheet capable of improving the workability of a plated steel sheet while significantly reducing the processing cost by performing post-annealing more easily.
A coiled steel sheet is formed by winding an Al-Zn alloy-plated steel sheet into a coil shape, which is accommodated in a furnace body 3 of a batch-type annealing furnace 2, and the temperature outside the coil is accommodated. Is heated to 280-360 ° C. Thereafter, immediately after cooling at a cooling rate of 1 ° C./min or less, until the coiled steel plate 1 becomes low temperature, the precipitation of Zn in the Al-rich phase is promoted by the self-heating of the coiled steel plate 1, The plating layer is modified and softened.
[Selection] Figure 1

Description

  The present invention relates to a method for producing an Al—Zn alloy-plated steel sheet that is improved in workability by suppressing generation of cracks in a plating layer by bending.

  This type of plated steel sheet has higher corrosion resistance than galvanized steel sheet, and is widely used as a wall material or roofing material as it is or after being coated. The high corrosion resistance can be exhibited by the coating anticorrosive effect by Al and the sacrificial anticorrosive effect of Zn. However, this type of plated steel sheet tends to cause cracks in the plated layer due to bending or the like, and the coating film applied to the steel sheet surface is torn by this crack, and the steel sheet is exposed to deteriorate the appearance. In order to prevent the occurrence of such cracks, it has been conventionally performed to modify the plating layer by subjecting the Al—Zn alloy plated steel sheet to a post-annealing treatment.

  For example, in the method for producing an Al—Zn alloy plated steel sheet of Patent Document 1, after heating the Al—Zn alloy plated steel sheet to a temperature range of 100 to 130 ° C., the state is maintained for 400 hours, and then cooled and plated. The layer is modified and softened. Moreover, in the manufacturing method of the Al-Zn alloy plating steel plate of patent document 2, after heating to the temperature range of 150-350 degreeC and hold | maintaining the state for 0.5 hour or more, the cooling rate of 0.8 degreeC / min The plating layer is modified and softened by cooling to room temperature. Furthermore, in order to improve the mechanical properties of the steel sheet hardened by the post-annealing treatment, a separate skin pass rolling is performed.

Japanese Patent No. 3742596 Japanese Patent No. 4090051

  According to the manufacturing method of the Al-Zn alloy plated steel sheet of Patent Document 1 and Patent Document 2, the post-annealing process can be performed to soften the plating layer and improve the workability of the Al-Zn alloy plated steel sheet. However, in the Al—Zn alloy-plated steel sheet of Patent Document 1, it is necessary to keep the state heated to a temperature range of 100 to 130 ° C. for 400 hours. There is a problem in the point that the nature is low. In addition, since a large amount of fuel or electric power is consumed during the post-annealing process, it is inevitable that the production cost of the Al—Zn alloy plated steel sheet increases. Similarly, in the Al—Zn alloy-plated steel sheet of Patent Document 2, since skin pass rolling is performed in addition to the post-annealing process, it takes extra time to manufacture the Al—Zn alloy-plated steel sheet, and the power required for the rolling process is further increased. Since cost is required, it is inevitable that the manufacturing cost of the Al—Zn alloy plated steel sheet increases as a whole.

  In order to solve the above problems, the present inventors do not need to add a skin pass rolling process or the like in as short a time as possible, and impart high workability to the Al—Zn alloy plated steel sheet. investigated. Specifically, optimization of the post-annealing heating temperature, cooling rate, etc. was studied.

  The heating temperature at the time of post-annealing may basically follow ideal conditions determined from metallurgical engineering, but it may be difficult to realize these ideal conditions depending on the state of the heating equipment and the object to be heated. The ideal condition determined in the metallurgical engineering can be estimated by the Al—Zn eutectoid reaction temperature (277 ° C.). The purpose of modifying the plating layer is to promote Al-Zn eutectoid reaction to precipitate supersaturated Zn in the Al-rich phase and to coarsen fine Zn particles. These two objects are realized by heating to a temperature lower than the Al—Zn eutectoid reaction temperature and allowing Zn atoms to diffuse and move in the Al-rich phase.

  The diffusion rate of Zn atoms in the Al-rich phase can be understood from Fick's law. According to this rule, it is understood that the diffusion rate of Zn atoms increases exponentially as the heating temperature increases. From this, even in the temperature range below the Al—Zn eutectoid reaction temperature, when kept at a relatively low temperature of about 100 ° C., the diffusion rate of Zn is slow, and it takes a long time until the desired modification result is obtained. Must be kept at temperature. For example, in the case of the Al—Zn alloy-plated steel sheet of Patent Document 1, the heating time reaches 400 hours.

  However, when the heating temperature exceeds the Al—Zn eutectoid reaction temperature, the amount of Zn solid solution in the Al-rich phase increases, which is counterproductive. Moreover, it is not preferable that the heating temperature is high, because the laminated steel plates may adhere to each other by diffusion bonding. Considering the above, it can be said that the heating temperature in the post-annealing treatment determined in the metallurgical engineering is preferably 277 ° C. or somewhat lower than this.

  By the way, the ideal temperature condition obtained from metallurgical engineering is different from the industrially practicable condition. This is because the object to be heated is large and heat transfer takes time. In many cases, the plated steel sheet to be subjected to the post-annealing process is produced in a coiled form. Although the thickness of the steel sheet is about 0.2 to 0.3 mm, heating a coil body wound up 500 to 10,000 times is equivalent to heating a steel ingot having a thickness of several hundred to several thousand mm. To do. When heating such a steel ingot, the outside is easily heated, but the inside is heated with a delay of the time difference of heat transfer. Therefore, in order to equalize the temperature inside and outside the coil body, it is essential to maintain a predetermined temperature state for several hours to several hundred hours.

  In order to reconsider the post-annealing treatment, the present inventors conducted an experiment using manufacturing equipment with the aim of optimizing the retention time after the temperature rise and the cooling rate. As a result, when the coil thickness is 100 to 1000 mm, the coil body is heated until the temperature of the coil outer surface reaches 310 to 320 ° C. (about 20 hours) and cooled at a cooling rate of 1 ° C./min. It has been found that the plating layer can be modified while the time for maintaining the temperature state (holding time) is made zero. The retention time is not required because although the amount of Zn dissolved in the Al-rich phase temporarily increases at the outer part beyond the Al-Zn eutectoid reaction temperature, it precipitates as Zn particles in the subsequent cooling process. This is presumably because sufficient workability could be obtained.

  The present invention has been proposed on the basis of the above knowledge, and its purpose is to perform post-annealing more easily and in a short time, while significantly reducing the processing cost, and the workability of the Al-Zn alloy-plated steel sheet. It is providing the manufacturing method of the Al-Zn alloy plating steel plate which can improve this.

  In the method for producing an Al—Zn alloy-plated steel sheet according to the present invention, a coiled steel sheet 1 is formed by winding a molten Al—Zn-plated steel sheet into a coil shape, and this is formed into a furnace body 3 of a batch-type annealing furnace 2. And heated until the temperature outside the coil reaches 280-360 ° C. After that, it is immediately cooled at a cooling rate of 1 ° C./min or less, and the metal structure of the plating layer is modified and softened by self-heating of the coiled steel sheet 1.

  The atmosphere in the furnace is heated by the combustion burner 4 provided in the annealing furnace 2, the temperature outside the coil of the coiled steel sheet 1 is increased to 320 ° C., and the temperature inside the coil is increased to 275 ° C., and then the heating is stopped. In the state where the internal temperature of the annealing furnace 2 is adjusted so that the cooling rate becomes 1 ° C./min, the temperature outside the coil of the coiled steel plate 1 is cooled from 320 ° C. to 200 ° C., and further cooling is continued. Cool the temperature outside the coil to 100 ° C.

  The hot-dip Al—Zn plated steel sheet is formed by subjecting a steel sheet to a plating alloy composed of 55% by weight of Al, 1.6% by weight of Si, and the balance of Zn, and subjecting the steel sheet to continuous hot-dip plating.

  In the present invention, in such post-annealing treatment, the coiled steel sheet 1 is heated to a temperature somewhat higher than the Al—Zn eutectoid reaction temperature (280 to 360 ° C.), and the temperature state is not maintained. Immediately, cooling was performed at a cooling rate of 1 ° C./min or less. Thus, in the process of cooling the coiled steel sheet 1, when the Al—Zn eutectoid reaction is advanced by the self-heating of the coiled steel sheet 1, the state heated to a temperature range of 100 to 130 ° C. needs to be maintained for 400 hours. Compared with the post-annealing process of Patent Document 1 in which there is a problem, the processing time can be significantly reduced. Moreover, after heating to the temperature range of 150-350 degreeC required in the post-annealing process of patent document 2, it is not necessary to hold | maintain the state for 0.5 hour or more.

  Therefore, according to the method for producing an Al—Zn alloy-plated steel sheet of the present invention, the post-annealing process can be performed more simply and in a short time, and the fuel cost or power cost required for the process can be greatly reduced while Al—Zn. The workability of the alloy-plated steel sheet can be improved. Moreover, since it is not necessary to hold the coiled steel plate 1 for a predetermined time in a high temperature state, energy can be saved correspondingly. The heat treatment condition in the post-annealing treatment of the present invention is that the heating temperature is somewhat higher than the heating temperature of the conventional post-annealing treatment (100 to 200 ° C.), but the steel plates do not adhere to each other, and only the plating layer is appropriate. Could be modified.

  In the process in which the coiled steel sheet 1 is cooled, the precipitation of Zn in the Al-rich phase in the plating layer proceeds, resulting in an increase in the number of Zn precipitate particles and their coarsening. As a result, the Al-rich phase becomes soft, and the stress concentration on the brittle Si precipitates that are also present in the plating layer when the bending process is performed is alleviated. Therefore, it can prevent well that the crack which originated from Si precipitate generate | occur | produces in a plating layer, and, thereby, the external appearance of a process part is maintained in a favorable state.

  The temperature outside the coil of the coiled steel sheet 1 is increased to 320 ° C., and the temperature inside the coil is increased to 275 ° C. while maintaining the temperature state outside the coil and the temperature state inside the coil in a substantially uniform temperature state. This is because the Al—Zn eutectoid reaction proceeds uniformly. Until a certain time elapses after the heating of the coiled steel plate 1 is stopped, the temperature outside the coil decreases with a predetermined temperature gradient corresponding to the decrease in the atmospheric temperature in the annealing furnace 2, and conversely, The temperature tends to rise with a predetermined temperature gradient in response to the temperature of the high temperature coil outer layer. Therefore, as described above, when the heating is stopped in a state where the temperature outside the coil is raised to 320 ° C. and the temperature inside the coil is raised to 275 ° C., the temperature of the coiled steel sheet 1 can be maintained in a substantially uniform temperature state. . Further, in the process of cooling the temperature outside the coil from 320 ° C. to 200 ° C., if the internal temperature of the annealing furnace 2 is adjusted so that the cooling rate is 1 ° C./min, the precipitation of Zn in the Al-rich phase takes a long time. By proceeding, the plating layer can be more reliably modified.

  When the above-mentioned post-annealing treatment is applied to an Al—Zn alloy-plated steel plate obtained by plating a steel plate with a plating alloy composed of 55 wt% Al, 1.6 wt% Si, and the balance Zn. The workability of the Al—Zn alloy plated steel sheet can be improved by softening the layer. In particular, in the case of an Al—Zn alloy plated steel sheet plated with a plating alloy having the above composition, it hardens in 2 to 6 weeks after the plating treatment. The workability of the plated steel sheet can be improved.

It is sectional drawing of the batch type annealing furnace which shows the outline of the post-annealing process which concerns on this invention. It is a front view which shows the bending test result 1 of an Al-Zn alloy plating steel plate. It is a front view which shows the bending test result 2 of an Al-Zn alloy plating steel plate. It is a front view which shows the bending test result 3 of an Al-Zn alloy plating steel plate. It is a front view which shows the bending test result 4 of an Al-Zn alloy plating steel plate. It is a front view which shows the bending test result 5 of an Al-Zn alloy plating steel plate. It is a front view which shows the bending test result 6 of an Al-Zn alloy plating steel plate. It is a metal structure figure of the Al-Zn alloy plating layer concerning the present invention. It is a metal structure figure of the Al-Zn alloy plating layer concerning a comparative example.

(Example) Below, the Example of the manufacturing method of the plated steel plate which concerns on this invention is shown. The Al—Zn alloy-plated steel sheet to be subjected to the post-annealing process is manufactured, for example, in a continuous hot dip plating facility. There is no restriction on the thickness and width of the steel sheet to be plated, and there is no restriction on the amount of plating. However, when the amount of adhesion of plating is small, when the plated steel sheet is bent, it is difficult for the appearance deterioration of the processed part to appear. The actual coating amount was 160 g / m ² on both sides of the steel sheet. The plate thickness of the steel plate was 0.40 mm, the plate width was 985 mm, and an Al—Zn alloy plated steel plate having a total length of 3500 m was wound into a coil shape.

  The coiled steel sheet 1 that has been coiled is subjected to a post-annealing treatment on the plating layer using a batch-type annealing furnace 2 shown in FIG. Specifically, the coiled steel plate 1 is accommodated in the furnace body 3 of the batch-type annealing furnace 2 and stacked in a plurality of stages, and the combustion burner is covered with the cover 5 in which the combustion burner 4 is incorporated. 4 is ignited to heat the coiled steel sheet 1. At this time, the atmosphere in the annealing furnace 2 may be any of air, an inert gas atmosphere, and a reducing atmosphere.

  While adjusting the atmospheric temperature in the annealing furnace 2, the temperature outside the coil of the coiled steel sheet 1 is increased to 320 ° C. and the temperature inside the coil to 275 ° C. 19 hours after the start of heating by the combustion burner 4. The average heating rate at this time is 15.79 ° C./hour. Thereafter, the combustion burner 4 is extinguished and cooled from 320 ° C. to 200 ° C. The cooling rate at this time is 1 ° C./min due to the heat retaining effect of the furnace body 3. Furthermore, cooling is continued and the temperature outside a coil is cooled to 100 degreeC. The time required for a series of cooling processes is 4 hours in calculation. Unless a special cooling device is used, the cooling rate decreases as the coil temperature decreases, and the actual cooling process takes about 20 hours.

  The coiled steel plate 1 in a cooled state is taken out from the furnace body 3 and transferred to the painting process. In the painting process, acrylic paint is applied on a continuous color line. The coating thickness of the paint was 10 μm. The obtained coated plated steel sheet is pressed to be processed into a roof material and a wall material to be a final product.

  As described above, in the coiled steel sheet 1 that has been subjected to the post-annealing treatment, precipitation of Zn in the Al-rich phase in the plating layer proceeds, and the number of Zn precipitate particles increases and the coarsening occurs. As a result, the Al-rich phase becomes soft, and when bending is applied, stress concentration on the brittle Si precipitates present in the plating layer is alleviated, so cracks originating from the Si precipitates are generated in the plating layer. Can be prevented well. Therefore, the appearance of the processed part can be kept in a good state. In addition, although the heating temperature of the coiled steel plate 1 when performing the post-annealing treatment is 320 ° C. as the temperature outside the coil, which is about 100 to 200 ° C. higher than the conventional heat treatment conditions, the adhesion between the steel plates occurs. I didn't.

  In order to confirm the reforming effect of the plated layer of the coiled steel plate 1 manufactured by the above heat treatment method, a plurality of test pieces are formed with the coiled steel plate 1 and each test piece is bent in the bent portion. The occurrence of cracks was confirmed by a bending test. The test piece for the bending test was formed in a strip shape with a width × length of 50 × 100 mm. The thickness is 0.40 mm. For comparison, a comparative test piece of the same size as the previous test piece was prepared for the comparative steel plate coated with acrylic paint under the same conditions without post-annealing treatment. A bending test was performed under the same conditions as the pieces.

  In the bending test, a predetermined number of indicator plates having the same thickness as the test piece are sandwiched inside the test piece, and the test piece and the test piece for comparison are bent 180 degrees at the central portion in the longitudinal direction, and cracks are generated. It was confirmed. The number of indicator plates arranged inside the test piece is 0T (0 sheets), 1T (1 sheet), 2T (2 sheets), 3T (3 sheets), 4T (4 sheets), 5T (5 sheets), The occurrence of cracks was evaluated in 6 stages. In addition, the bending radius of the test piece at 0T and the test piece for comparison is 0.4 mm, hereinafter 1T (0.6 mm), 2T (0.8 mm), 3T (1.0 mm), 4T (1.2 mm) 5T (1.4 mm).

  Test results 1 to 6 of the bending test are shown in FIGS. In FIG. 2, in the state where the index plate is not sandwiched (0T), a crack with an opening width of 40 μm or more was generated in any of the test piece and the comparative test piece, and no significant difference was observed. In addition, as shown in FIG. 3, when the test piece and the comparative test piece are bent with one index plate sandwiched between them (1T), the comparative test piece has a crack with an opening width of 40 μm or more. However, in the case of the test piece subjected to the post-annealing treatment, only fine cracks having an opening width of less than 40 μm were observed. Furthermore, as shown in FIGS. 4 to 7, no cracks were observed in the test pieces subjected to the post-annealing treatment in any case from 2T to 5T. On the other hand, in the case of the comparative specimen, the occurrence of cracks with an opening width of less than 40 μm was confirmed in any of 2T to 4T, and cracks were observed only in the case of 5T shown in FIG. I couldn't. From a comparison between the two, it was confirmed that the plating layer was modified by post-annealing.

  The metal structures of the test piece subjected to the bending test and the plating layer of the comparative test piece were confirmed with a scanning electron microscope. Specifically, a steel plate that has been subjected to post-annealing treatment and a comparative steel plate that has not been subjected to post-annealing treatment are prepared, each steel plate is cut and subjected to mechanical polishing on the cut surface, and then precisely polished with an ion beam The metal structure of the plating layer was confirmed by. The observation results with a scanning electron microscope are shown in FIGS. As can be understood from FIG. 8, it can be seen that countless Zn particles (white spots) are precipitated in the Al-rich phase in the plated layer that has been subjected to the post-annealing treatment. On the other hand, in the case of the comparative steel plate, almost no Zn particles are precipitated in the Al-rich phase as shown in FIG.

  As described above, according to the post-annealing method according to the above-described embodiment, the plating layer can be softened in a shorter time (40 hours at the shortest) than the conventional post-annealing method. High workability can be imparted to the steel sheet. In addition, since the post-annealing process can be performed in a shorter time than the conventional post-annealing process, the amount of fuel or power consumed during the post-annealing process can be significantly reduced, and the Al—Zn alloy plated steel sheet Manufacturing cost can be reduced.

  The temperature outside the coil of the coiled steel sheet according to the present invention is preferably 280 to 360 ° C. in order to impart the intended performance to the plating layer. When the temperature outside the coil is less than 280 ° C., precipitation of supersaturated Zn in the Al-rich phase does not proceed, and post-annealing is performed in a shorter time, which is a feature of the present invention, to soften the plating layer. I can't. On the other hand, if the temperature outside the coil exceeds 360 ° C., the amount of Zn solid solution in the Al-rich phase increases, so that it is difficult to obtain the high degree of workability targeted by the present invention. Furthermore, when the temperature outside the coil exceeds 360 ° C., there is a possibility that the laminated steel plates may adhere to each other, which is not preferable. More preferably, the temperature outside the coil is selected within a range of 300 to 340 ° C. In addition, the time required to heat the coiled steel sheet 1 should be determined by the total volume of the coiled steel sheet 1. For example, if the coil winding thickness is reduced, the temperature raising time is short, and conversely It is necessary to lengthen the temperature raising time to avoid a large deviation in the temperature distribution of the entire coil.

  Post-annealing after plating is preferably performed in a batch annealing furnace. In order to perform the post-annealing process, it takes about 20 hours to heat the coiled steel sheet 1, and further, it takes 4 hours or more to cool from 300 ° C. to room temperature at a cooling rate of 1 ° C./min. Therefore, when a series of post-annealing processes are continuously performed as in a painting line, the energy consumption of the production facility and the size of the facility become inefficient.

  In the above embodiment, the coiled steel plate 1 is heated by the combustion burner 4, but this is not necessary, and the coiled steel plate 1 may be heated by electric heating. Although the cooling rate of the coiled steel sheet 1 is set to 1 ° C./min or less, if the cooling rate exceeds 1 ° C./min, it becomes difficult to sufficiently progress the precipitation of Zn in the Al-rich phase during the cooling process, and the Zn precipitate It is difficult to increase the number of particles and to achieve coarsening.

1 Coiled Steel Plate 2 Annealing Furnace 3 Furnace Body 4 Combustion Burner 5 Cover

Claims (3)

  A coiled steel sheet (1) obtained by winding an Al—Zn alloy-plated steel sheet in a coil shape is accommodated in the furnace body (3) of a batch-type annealing furnace (2), and the temperature outside the coil is 280 to 800. After heating to 360 ° C., it is immediately cooled at a cooling rate of 1 ° C./min or less, and the metal structure of the plating layer is modified and softened by self-heating of the coiled steel plate (1). A method for producing an Al—Zn alloy-plated steel sheet.   The atmosphere inside the furnace is heated by the combustion burner (4) provided in the annealing furnace (2), and the temperature outside the coil of the coiled steel plate (1) is raised to 320 ° C and the temperature inside the coil to 275 ° C. Then, the heating is stopped, and the temperature outside the coil of the coiled steel sheet (1) is adjusted from 320 ° C. to 200 ° C. with the internal temperature of the annealing furnace (2) adjusted so that the cooling rate becomes 1 ° C./min. The manufacturing method of the Al-Zn alloy plating steel plate of Claim 1 which cools and also continues cooling and cools the temperature of a coil outer side to 100 degreeC.   The Al—Zn alloy-plated steel sheet is formed by subjecting a steel sheet to a plating alloy composed of 55% by weight of Al, 1.6% by weight of Si, and the balance of Zn, by subjecting the steel sheet to continuous hot dip plating. The manufacturing method of the Al-Zn alloy plated steel plate of 1 or 2.