Method for manufacturing hot press molding member excellent in productivity, weldability, and moldability

Abstract

To provide a method for manufacturing a hot press molding member.SOLUTION: This method for manufacturing the hot press molding member comprises: a step of heating an aluminum-plated steel plate blank in a heating furnace; a step of taking out the heated blank from the heating furnace and transferring and placing it between upper and lower dies of a mold attached to a press; and a molding step of contacting the blank on which the upper die of the mold is placed and then executing molding. The heating furnace is a continuous heating furnace including an A section, a B section, and a C section provided in order in a blank transferring direction. Heating in the A, B and C sections satisfies a specific condition, a highest atmospheric pressure is lower than that in the B section, and time required from placing of the blank to molding is 2 seconds or shorter.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for producing a hot press-formed part having excellent productivity, weldability, and formability. do. [Background technology]

[0002] In response to the demand for lighter vehicles and improved safety, the development of high-strength steel using hot press forming methods The application of this technology is being actively promoted. In the hot press forming process, the material is heated and rapidly cooled. In order to prevent the formation of scale at high temperatures, aluminum-plated steel is also used. Aluminum alloy plated steel is often used. Aluminum alloy plated steel has a problem in that the plated layer melts when it is heated rapidly. Therefore, it is generally heated at a slow rate in an atmospheric furnace.

[0003] As a method of heating in such an atmosphere heating furnace, heating is performed in a heating furnace set to the same atmosphere temperature. A roller hearth furnace having multiple heating zones is used. The atmosphere temperature is gradually increased in a continuous heating furnace such as a However, in this method, the heating rate is slow, so the target temperature is not reached. It must be heated in the furnace for a certain period of time to reach the desired temperature. This increases the time required to maintain the temperature at 40° C., which reduces productivity.

[0004] Therefore, a method of increasing the heating temperature was applied to shorten the maintenance time in the heating furnace. In this case, the thickness of the diffusion layer in the plating layer increases due to the increase in heating temperature. This causes a problem of poor weldability.

[0005] Therefore, to improve productivity, the heating rate must be increased to reduce the maintenance time in the furnace. In order to ensure the weldability of the produced molded products, A method is required to minimize the thickness of the diffusion layer by not maintaining the heating temperature of the ink too high. .

[0006] However, in the conventional method, the shortening of the time in the furnace and the lowering of the heating temperature are mutually exclusive. The technical problem is that they cannot be applied simultaneously because they have opposing effects on each other. The issue exists.

[0007] On the other hand, in addition to the above problems, if the temperature of the heating furnace is continuously lowered to improve weldability, Therefore, there is a problem that the excellent productivity, weldability, and formability are deteriorated. The technology that can secure both of these has not yet been developed. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Korean Patent Publication No. 2006-0054479 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention is intended to solve the above problems, and is directed to improving productivity, weldability, and formability. The object of the present invention is to provide a method for producing a hot press-formed part having improved formability.

[0010] The subject of the present invention is not limited to the above. A person having knowledge of the present invention can easily understand the addition of the present invention from the contents described throughout the specification of the present invention. There is no difficulty in understanding the objective problem. [Means for solving the problem]

[0011] One aspect of the present invention is a method for producing a hot press-formed member, heating an aluminum-based plated steel sheet blank in a heating furnace; The heated blank is removed from the heating furnace and the upper and lower dies of the die attached to the press are and transferring and placing the a forming stage in which forming is carried out after the upper part of the mold contacts the placed blank; Including, The heating furnace includes sections A, B, and C arranged in the blank conveying direction. It is a continuous heating furnace. The heating in the above A section was approximately a (0.2 min, 750°C), b (1.0 min, 750°C), c (1.0 min, 800°C), d (1.5 min, 900°C), e (0.2 min, 900°C) The conditions stipulated by the figure abcde, which has the coordinates of the furnace maintenance time and the atmospheric temperature, are met. death, Heating in section B above is

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[0012] [Equation 1] T≦8.2×t+(temp-900) / 30 (The above T is the time required for the transfer and placement stages, and the time required for molding after the blank is placed.) The unit of t is the thickness of the blank. The unit is mm. The above temp is the temperature at which the sample is taken out of the heating furnace, and the unit is °C. It is.) Effect of the Invention

[0013] According to one aspect of the present invention, there is provided a hot press formed part having improved productivity, weldability and formability. It is possible to provide a method for manufacturing the material.

[0014] The various and beneficial advantages and effects of the present invention are not limited to those described above, but may be understood by reference to the specific This can be more easily understood in the course of explaining the embodiments. [Brief description of the drawings]

[0015] [Figure 1] 1 is a graph showing a heating pattern for an aluminum-plated material having a thickness of 1.2 mm. [Diagram 2] This is a graph showing a comparison between experimental values ​​and interpretation values ​​of temperature rise interpretation under various furnace atmosphere temperature conditions for an aluminum plated material with a thickness of 1.2 mm. [Diagram 3] 1 is a graph showing preferred atmospheric temperature conditions of the present invention versus cumulative furnace maintenance time when heating an aluminum-plated material having a thickness of 1.2 mm. [Figure 4] The photographs show the observation results of the plating layer of an experimental example in which a 1.2 mm thick aluminum-plated material was heated under several heating conditions. [Figure 5a] The heating conditions for aluminum-plated materials are shown, taking into account changes in material thickness. [Figure 5b] The heating conditions for aluminum-plated materials are shown, taking into account changes in material thickness. [Figure 5c] The heating conditions for aluminum-plated materials are shown, taking into account changes in material thickness. [Figure 6] This is a graph showing a comparison between experimental values ​​and interpretation values ​​regarding the temperature change over time when aluminum-plated materials with thicknesses of 0.9 and 1.8 mm are removed from a heating furnace and cooled in air. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] The following describes the preferred embodiment of the present invention. However, the present invention may be practiced in various other embodiments. The present invention is not limited to the embodiments described below, and may be modified in various forms. In addition, the embodiments of the present invention will be more completely understood by those skilled in the art. These are provided to illustrate the principles of the present invention.

[0017] The method for producing a hot press-formed part of the present invention will be described in detail below. Unless otherwise defined herein, all terms and methods commonly used in the art are within the scope of the present invention. is also applicable.

[0018] A method for producing a hot press-formed member according to one aspect of the present invention comprises the steps of: Heating the blank in a heating furnace; removing the heated blank from the heating furnace and pressing and placing the upper mold between the upper and lower molds of the mold mounted on the upper mold. and a forming step in which forming takes place after contacting the placed blank.

[0019] In addition, in the method for producing the hot press-formed member, after the forming step, the upper die of the die is The in-mold cooling stage rapidly cools the formed material by reaching and maintaining the bottom dead center of the press. and removing the cooled molded member. Cut.

[0020] According to one aspect of the present invention, the aluminum-based plated steel sheet is an aluminum-plated steel sheet. Alternatively, it may be an aluminum alloy plated steel sheet. In this case, there is no particular limitation. However, as an example, the composition of the plating layer is, by weight, Si: 5 to 11%, Fe: 4.5% or less. The balance may include Al and other unavoidable impurities. By weight, C: 0.1-0.5%, Si: 0.1-2%, Mn: 0.5-3%, Cr: 0 .01~0.5%, Al: 0.001~1.0%, P: 0.05% or less, S: 0.02% The following is the composition: N: 0.02% or less, B: 0.002-0.005%, balance Fe and other unreacted substances. It may contain impurities to be avoided.

[0021] According to one aspect of the present invention, the heating furnace includes a section A provided in a blank conveying direction. The furnace may be a continuous furnace including sections A, B, and C. The sections A and C do not necessarily need to be adjacent to each other in the blank transport direction. In other words, the above-mentioned order should be satisfied along the direction of transfer of the roller. Each of the C sections may consist of one heating zone, or multiple heating zones may be included within each section. Also, between each section (i.e., between section A and section B, or Between Sections B and C), and additional sections set at temperatures between the preceding and following temperature ranges. That's fine.

[0022] In conventional atmospheric heating methods, heating is performed in a heating furnace set to the same atmospheric temperature, or multiple heating furnaces are used. A roller hearth furnace having a heating zone of In a continuous heating furnace such as .

[0023] However, this method heats up slowly, so it takes a long time to reach the target temperature. In order to ensure this, it is essential to heat the material in the heating furnace for a certain period of time. There was a problem that the increased waiting time resulted in poor productivity.

[0024] Therefore, the inventors have found that if the ambient temperature is set high during the temperature rise process in section B, the temperature rise rate is higher than that in normal heating. Heating is faster than with a thermal furnace setting method, and the time spent in the furnace is reduced, improving productivity. At the same time, the temperature in the subsequent process in section C was increased by the above-mentioned If the temperature is set lower than that of section B, the final heating temperature will be set lower and the weldability will be poor. We focused on the fact that the problem of defects can also be solved.

[0025] On the other hand, the factors that determine the productivity mentioned above are minimizing the time it takes to reach 900℃, the heating furnace Minimizing the time it takes for the material temperature in the section where it is removed from the furnace to reach the removal temperature of the furnace or the total cumulative time in the furnace until the material is removed from the furnace is Whether the time required for the layer thickness to reach 15 μm or less is one example of the above. This minimizes the cycle time that ensures the desired physical properties of the final product. This can improve productivity.

[0026] However, if the B section, which is set to a high temperature as described above, is too wide, the If the time that the diffusion layer is maintained at this temperature is too long, the thickness of the diffusion layer increases, resulting in poor weldability. In contrast, the high temperature setting in section B is too narrow. If the heating speed is too fast, the productivity improvement effect cannot be obtained. The problem is that a lot of energy is consumed to maintain the initial temperature in section A at a high temperature. Therefore, there is no need to set the ambient temperature unnecessarily high at the beginning of the heating process. The open structure allows for the evacuation of hot air and the introduction of cold materials, ensuring a high ambient temperature right from the start. There is also the problem that the setting cannot be made precisely.

[0027] In addition, once a material has been heated to a sufficient temperature, the transformation to austenite has already been completed. Therefore, it is necessary to maintain only the temperature and time required for sufficient alloying of the plating layer. If the atmospheric temperature is kept high even in the second stage, the problem of deterioration of weldability due to excessive increase in the thickness of the diffusion layer may occur. Therefore, a relatively low temperature may be set.

[0028] In consideration of this, in the present invention, as an example, an aluminum material having a thickness of 1.2 mm is used. The heating pattern shown in Figure 1 was applied to the aluminum-plated material. In a certain section A, considering energy saving and the inability to set a high ambient temperature, Then, in section B, the temperature was set to the highest in order to heat the material quickly. , set it so that the material reaches a sufficient temperature. Then, after the material reaches a sufficient temperature, In the C section, the temperature was set lower than in the B section. When the heating time is set differently for each period, the cumulative heating time for the 1.2 mm material is taken out. The temperature was maintained at 900°C for 4.5 minutes. This is derived from the heating interpretation results for radiation and convection heat transfer in the atmosphere. The heating conditions in each section will now be described in more detail.

[0029] On the other hand, in this specification, the ambient temperature in each section described later includes a number of heating zones, In a heating furnace where the atmospheric temperature can be controlled separately for each heating zone, of the ambient temperature (i.e., the area where the actual ambient temperature is maintained in one heating zone) For example, the ambient temperature in one heating zone may be the actual ambient temperature. The temperature may be measured at a representative point in the region where the temperature is maintained. However, as an example of the representative point mentioned above, the center (1 / 2) 1 / 4 in the width direction and 250 mm away from the blank position in the height direction In this case, the ambient temperature in each section is the temperature of each heating zone corresponding to each section. The ambient temperature is assumed to be maintained at the aforementioned ambient temperature in the oven.

[0030] In addition, the cumulative furnace maintenance time in each section includes the above-mentioned multiple heating zones, and each heating zone In a heating furnace where the atmospheric temperature can be controlled separately, the blank material is placed in the heating furnace. From the time when is input, from the last heating zone among the heating zones corresponding to each of the above sections It may mean the time that the blank is maintained until it is removed.

[0031] On the other hand, in the above-mentioned heating furnace, each heating zone may be divided by a partition or the like, The heating zones may be divided without partitions. Therefore, each heating zone may be divided by partitions. If so, the above method is applied as is.

[0032] In contrast, in the above-mentioned heating furnace, if there is no partition wall, the entire heating furnace is blank. Divide the transport direction into n equal sections (e.g., 5 or more), and then In one implementation of the present invention, the entire furnace is divided into 20 equal zones. Each of the equal areas can be considered as one section. As mentioned above, in each region, the center (1 / 2) is in the length direction and the width direction is 1 / 4. The temperature measured at a point 250 mm away from the blank position in the height direction was This can be regarded as the temperature at which the atmosphere is maintained.

[0033] For example, according to one aspect of the present invention, the heating in the section A is performed in an atmosphere of about 750 to 900°C. The ambient temperature is set to about 930 to 960°C in the above section B, and the ambient temperature is set to about 930 to 960°C in the above section C. The ambient temperature is about 870°C or higher and is lower than the ambient temperature selected in the above section B. When using this method, the final temperature can be set to a single temperature. The temperature rises faster than in the conventional furnace, and the time it takes to maintain the temperature in the furnace can be shortened. By controlling the temperature and time within an appropriate range where only the alloying of the plating layer is sufficiently achieved, This prevents the problem of poor weldability due to excessive generation of . It is therefore possible to effectively provide a hot press forming method capable of achieving both excellent moldability and weldability.

[0034] On the other hand, Figure 2 shows the validity of the above-mentioned heating analysis technique, and is a 1.2 mm thick material. Experimental values ​​and interpretations of heating analysis under various furnace atmosphere temperature conditions for aluminum-plated materials This is a graph showing a comparison of the experimental values. After the specimen was placed in the furnace, temperature data was obtained at one point per second. The interpretation values ​​are the results predicted by the interpretation technique described above for such conditions, and are shown in Figure 2. As can be seen, the interpreted values ​​represent the experimental values ​​well.

[0035] By analyzing the temperature rise under various conditions, the inventors have found that the temperature rise pattern of the material is as follows: It is additionally considered that the results depend on the thickness of the material, the ambient temperature, and the duration of each temperature range. As mentioned above, in order to prevent excessive time in the high ambient temperature region, On the other hand, the time spent in the high ambient temperature region is too short, making it difficult to achieve a rapid heating effect. In order to prevent this, the thickness of the material, the ambient temperature, and the time spent at each ambient temperature are important. Therefore, the inventors have found that the appropriate maintenance time is determined by the thickness of the material and the ambient temperature. The present invention has been completed by focusing on the fact that it is necessary to select the interval. I will explain in detail.

[0036] Specifically, a graph with the cumulative furnace maintenance time on the X-axis and the atmospheric temperature in the heating furnace on the Y-axis is shown below. As a reference, the heating in the above A section is approximately a (0.2 min, 750°C), b (1.0 min, 75 0°C), c (1.0 min, 800°C), d (1.5 min, 900°C), e (0.2 min, 900 The cumulative furnace maintenance time (°C) and the atmospheric temperature in the heating furnace are defined by a figure abcde having coordinates. The conditions set forth above can be satisfied.

[0037] First, heating in section A is the temperature setting area at the front of the heating furnace, and affects the initial heating rate. Therefore, the atmospheric temperature in the heating furnace in the above-mentioned section A is in the range of about 750 to 900°C. It is preferable to set the atmospheric temperature in the heating furnace in the above-mentioned section A to less than about 750°C. If the setting is made, the initial temperature rise rate becomes too slow, resulting in poor productivity. On the other hand, if the atmospheric temperature in the heating furnace in the above-mentioned section A is set to more than about 900°C, The problem of high energy consumption due to maintaining a high temperature in the initial zone of the furnace There is a problem.

[0038] On the other hand, in the heating of section A, not only the ambient temperature but also the maintenance time affects the heating rate. In this case, in order to increase the heating rate, if the ambient temperature in section A is low, If the ambient temperature in section A is high, the maintenance time in section A is increased. Therefore, the present inventors have determined a preferable atmosphere temperature in the heating furnace for heating in the A section. As a result of careful consideration of the maintenance time, the conditions of section A are set as shown in Figure 3. In other words, it has been found that it is preferable that the atmospheric temperature in the above-mentioned section A is low, about 750°C. If the temperature is 100°C, the maintenance time in section A is shortened to about 1 minute or less, and the atmospheric temperature in section A is about When the temperature is as high as 900° C., it is preferable to keep the time in section A for about 1.5 minutes or less. On the other hand, taking into consideration the passage time at the entrance of the heating furnace, the maintenance time for the above-mentioned section A is It can be about 0.2 minutes or more.

[0039] In addition to the cumulative furnace time and ambient temperature mentioned above, the thickness of the material may also have an effect. However, the effect of thickness is reflected in the heating in sections B and C described below, and in section A Since the effect of the thickness is somewhat smaller in the A section, from a practical point of view, it is set regardless of the thickness of the material. (See FIG. 5a).

[0040] Next, the heating in section B is as follows:

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[0041] Heating in section B is the area with the highest atmospheric temperature in the heating furnace, and is a high-temperature area. If the ambient temperature in section B is low, the maximum temperature will be The high temperature becomes lower and the heating rate also becomes slower, whereas when the ambient temperature in the above section B is high, The maximum temperature will be higher and the temperature rise rate will also be higher. Therefore, the ambient temperature in section B should be as low as possible. However, if the ambient temperature in section B is too high, If the temperature is too high, the weldability may be poor. It is necessary to determine this.

[0042] On the other hand, in this specification, the section having an ambient temperature of about 930° C. or more and the section having the maximum ambient temperature The section up to the section having the maximum temperature (i.e., the maximum atmosphere maintenance temperature) is regarded as section B. A section having an ambient temperature lower than the maximum ambient temperature that follows the section having the maximum ambient temperature. The section from which the above-mentioned section B is located is considered to be a section distinct from the above-mentioned section B. For example, if the above-mentioned section B is approximately 9 The first B section has an ambient temperature of 30° C., and the second B section has an ambient temperature of about 950° C. section, followed by a section having an ambient temperature of about 935°C. The atmospheric temperature was about 935°C, which is lower than the maximum atmospheric temperature of about 950°C. The interval having the degree can be regarded as the C interval.

[0043] Therefore, in the present invention, the atmospheric temperature in the above-mentioned section B is set in the range of about 930 to 960°C. If the ambient temperature in the above B section exceeds about 960℃, the heating furnace equipment is limited. However, the temperature is set too high from the viewpoint of alloying the plating layer, which may result in reduced weldability. In addition, when the atmospheric temperature in the above-mentioned section B is less than about 930° C., the heating rate Because the temperature is too low, it takes longer to reach the target temperature, increasing cycle time and reducing productivity. There is a problem that the quality of the product deteriorates.

[0044] In the above B section, not only the above-mentioned atmospheric temperature but also the maintenance time of B section is also determined by the temperature rise rate of the material. This affects the temperature and maximum heating temperature of the material. If the temperature rise is not sufficient and the B stage is maintained for too long, the material will be heated to a high temperature for an excessively long time. This causes the thickness of the diffusion layer to increase, resulting in poor weldability. There is a risk of problems occurring.

[0045] Therefore, although not particularly limited, the lower limit of the maintenance time in the above section B is fast. In order to achieve the effect of improving productivity by increasing the temperature, the time can be set to about 0.5 minutes or more. Or, in order to prevent excessive alloying that may result in poor weldability, the maintenance time is shortened. The upper limit can be set to about 4.8 minutes. In this case, the maintenance time of the above section B is limited to section B only. This refers to the time that the material is maintained, and is a concept that is distinct from the cumulative maintenance time in the furnace described below. It is necessary to take note of the following.

[0046] On the other hand, the cumulative maintenance time in the furnace up to the above section B also depends on the temperature rise rate of the material in the high temperature region and the It affects the maximum heating temperature. In order for the temperature to rise to a sufficient level, the ambient temperature in section B must be If the temperature is low, the cumulative maintenance time in the furnace until the end of section B must be extended. When the atmospheric temperature is high, the cumulative maintenance time in the furnace until the end of section B may be shortened.

[0047] Here, the cumulative maintenance time in the furnace is not the maintenance time in section B itself, but the maintenance time at the end of section B. It means the cumulative furnace heating time up to the B section. This refers to the cumulative time that the material is heated in the furnace until the end of section B, including the time that the material is heated. For example, if there is only section A before section B, it means the time to maintain the furnace in sections A and B. However, if there is an additional section between Section A and Section B, Section A, Section B, and the additional section The importance of the cumulative maintenance time is as follows: For example, if the time for which section A is maintained is short, the temperature will not rise sufficiently. In order to warm up the body, the maintenance time of section B itself needs to be slightly longer. If the time is long, it is necessary to consider that the duration of section B may be shortened slightly. That is, in order to improve productivity by shortening the heating time, which is the objective of the present invention, It is necessary to take into account not only the duration of the interval itself but also the time before interval B.

[0048] On the other hand, the purpose of the above section B is to raise the temperature quickly, so the maintenance time of section B is unnecessarily long and the temperature is high. Preventing the temperature of the material from staying at the B stage for a long time will achieve the same heating effect while It is preferable from the viewpoint of weldability. Therefore, based on these results, the effect of material thickness is If this is not taken into account (i.e., the material thickness is 1.2 mm), The cumulative furnace maintenance time was kept at a maximum of about 3.8 minutes or less when the temperature in section B was about 930°C. It can be held.

[0049] However, the temperature rise pattern of the material also depends on the thickness of the material. By performing a temperature rise analysis for various thicknesses, they found that the cumulative furnace temperature up to section B was It was found that the internal maintenance time needs to be adjusted depending on the thickness. The cumulative furnace maintenance time is within the range regulated by the 1.2 mm material shape fghi in Figure 3. The thickness of the material increases by 0.6 mm, and the temperature increases by 0.5 minutes. Conversely, when the material thickness is reduced, the reduction in thickness increases by about 0.5 times for every 0.6 mm reduction. This may be carried out within a range where the amount of the reaction mixture is proportionally decreased.

[0050] In addition, the present inventors have been conducting further research with a view to further improving productivity and weldability. As a result, taking into account the effect of material thickness, the base material thickness t was set at 1.5 mm. It was further discovered that the heating atmosphere temperature in section B can be set to an optimized condition. Ta.

[0051] Specifically, according to one aspect of the present invention, when the t is 1.5 mm or less, the section B The ambient temperature may be greater than about 930° C. and less than about 940° C. In order to heat the material quickly, The above-mentioned B section needs to have a high ambient temperature, but due to work irregularities during actual operation, Considering that the maintenance time in the heating furnace may vary slightly, the atmosphere should not be too hot. Therefore, if the material thickness is less than 1.5 mm, In order to minimize the possibility of poor weldability, it is necessary to control the atmospheric temperature in the above-mentioned B section within the above-mentioned range. On the other hand, when the above t is 1.5 mm or less, the above section B is most advantageous in terms of miniaturization. The ambient temperature may more preferably be greater than about 930° C. and less than about 935° C., and most preferably is greater than about 930° C. The temperature may be about 931 to 934°C. This provides an effect of minimizing poor weldability. It can be further improved.

[0052] Alternatively, according to one aspect of the present invention, when the t exceeds 1.5 mm, the B section The ambient temperature may be greater than about 930° C. and less than about 950° C. For fast heating of the material, The above B section needs to have a high ambient temperature, but due to work abnormality measures during actual operation, Considering that the maintenance time in the heating furnace may vary slightly, the atmosphere should not be too hot. Therefore, if the material thickness exceeds 1.5 mm, By controlling the atmospheric temperature in the above-mentioned section B within the above-mentioned range, the possibility of poor weldability is minimized. This is because, when the thickness of the material is thick, the temperature in section B is higher than that in section B. This is because the material needs to be a little higher than the material used. When the thickness t exceeds 1.5 mm, the atmospheric temperature in the above-mentioned section B is more preferably about 930° C. The temperature may be more than 945°C, and most preferably about 931 to 940°C. This can further improve the weldability.

[0053] On the other hand, according to another aspect of the present invention, when the t exceeds 1.5 mm, the fast temperature rise causes From the viewpoint of improving productivity and bending property, the atmospheric temperature in the above-mentioned B section is set to be more than about 940℃ and less than 960℃. In order to ensure stable bending properties, the total cumulative maintenance time in the furnace may be controlled to be less than 100°C. It is preferable to ensure that the time is not too short, i.e., that the time is as long as possible. From the viewpoint of productivity, it is preferable to shorten the total furnace maintenance time. In order to meet this requirement, the temperature in section B must be increased to ensure rapid temperature rise, and the cumulative A more stable austenitic structure is ensured during the heating process without increasing the holding time, resulting in As a result, better bendability can be ensured.

[0054] According to one aspect of the present invention, the maximum ambient temperature (Tb) in the section B (i.e., The high ambient temperature is about 938° C. or less, more preferably about 935° C. or less, and most preferably about 938° C. or less. Preferably, the temperature may be about 934°C or lower. This allows for both excellent productivity and weldability. It is possible to plan this.

[0055] Heating in the above C section is

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[0056] Heating in the above C section affects the final temperature of the material. The reason for setting the air temperature lower than the maximum air temperature in section B is that the air temperature in section C is If the temperature is as high as in section B, the material will be heated to a high temperature for a long time, resulting in poor weldability. In other words, the heating in section B is aimed at increasing the heating rate of the material. The target is large, so the temperature is set high. The heating in section C is the final temperature of the material. Do not set the temperature too high or too low because the purpose is to control This is because it is preferable that

[0057] On the other hand, if the ambient temperature in the above section C is set to less than about 870°C, the material removal temperature The temperature is too low, and the subsequent transfer and pre-molding cooling stages are cooled to too low a temperature, resulting in the temperature during molding being too high. The problem of the viscosity becoming too low may occur, which may result in poor moldability.

[0058] According to one aspect of the present invention, the atmospheric temperature in the above-mentioned section C is set to the above-mentioned temperature in order to improve weldability. The ambient temperature in the above-mentioned section C may be lower than the ambient temperature in the above-mentioned section B. It can be set lower than the minimum ambient temperature (i.e., the minimum ambient temperature) of the section. For example, the above B section may be a first B section at about 930°C and a second B section at 960°C. When the first section B includes the first section C, the first section B is about 870° C. or more and about 9 The ambient temperature may be set to be below 30° C. (ie, less than 930° C.).

[0059] According to one aspect of the present invention, the maximum atmospheric temperature in the section C is equal to or greater than the maximum atmospheric temperature in the section B. Based on the standard of 100°C (Tb), it can be set to about Tb-20°C or less, or about Tb The maximum ambient temperature may be set to a range of -30°C or less (in this case, the maximum ambient temperature is set to the maximum The larger the temperature difference between section B and section C, the faster the temperature rise and the spread. The effect of suppressing the increase in the thickness of the diffusion layer is significant in improving weldability. In order to achieve this, the temperature in section B must be higher and the temperature in section C must be lower. In terms of setting work conditions, the range is too narrow, and the temperature in the C section is Therefore, the inventors have proposed the above-mentioned section B and If the temperature difference in section C is at the level of about 20°C, the material will It was confirmed that the temperature of section C is reached at the temperature of section B below. It is most preferable that the temperature difference between the above sections is about 20° C. or more, and the above section C is about 870° C. or more.

[0060] On the other hand, the cumulative maintenance time in the furnace until the end of section C also affects the final maintenance temperature. If the atmospheric temperature in the furnace is low, the cumulative maintenance time in the furnace until the end of the C section must be extended. If the atmospheric temperature in section C is high, the cumulative maintenance time in the furnace until the end of section C Here, the cumulative in-furnace maintenance time until the end of the above-mentioned C section may be shortened by the C section itself. This does not mean the maintenance time of the first section, but the cumulative maintenance time in the furnace up to section C. The above description is similarly applicable to the maintenance time.

[0061] The reason why the cumulative maintenance time is important is as follows. For example, C If the time to maintain the furnace until just before the section C is short, the maintenance of the section C itself is necessary for sufficient alloying. It is necessary to extend the time slightly, and conversely, if the time to maintain the furnace until just before the C section is long, It is necessary to consider that the maintenance time of the C section may be slightly shorter. The objective of the present study is to improve productivity by shortening the heating time, while at the same time achieving sufficient alloying. In addition to the duration of the C section itself, the time before the C section must also be considered. The cumulative in-furnace maintenance time until the end of the period is derived from the analysis of various examples, which will be described in detail later. It was served.

[0062] Therefore, according to one aspect of the present invention, the effect of the material thickness is not taken into consideration, and the material thickness is set to 1.2 When the standard is set at 100°C, the cumulative time in the furnace until the end of section C is about 8 When the ambient temperature is about 70°C, it takes about 3.7 to 11.7 minutes, and when the ambient temperature is about 940°C, it takes about 2 Specifically, when the atmospheric temperature in the above-mentioned section C is high, If the cumulative time in the furnace until the end of section C becomes too long, the heating time will become too long. In contrast, when the ambient temperature in section C is low, In order to compensate for this, it is necessary to extend the total cumulative in-reactor maintenance time up to stage C.

[0063] In addition, like Section B, the temperature rise pattern of the material in Section C also depends on the thickness of the material. Therefore, by performing temperature rise analysis for various thicknesses, it was found that the thickness of the It was confirmed that the cumulative time in the furnace until the end of the heating period needs to be adjusted depending on the thickness.

[0064] In other words, the cumulative furnace maintenance time until the end of section C is the same as that of the 1.2 mm material in Figure 3. Within the range specified by klm, as the material thickness increases by 0.6 mm, the minimum maintenance The duration will increase proportionally by 1 minute, and the maximum duration will increase proportionally by 2 minutes. Conversely, when the material thickness is reduced, the minimum The duration will be decreased by 1 minute in increments, and the maximum duration will be decreased by 2 minutes in increments. can be done.

[0065] Therefore, in the present invention, the shape jklm is defined, which also reflects the influence of the thickness described above. The cumulative furnace duration and ambient temperature can be set to meet the requirements.

[0066] According to one aspect of the present invention, the heating in the above-mentioned section C is performed at an ambient temperature of about 935° C. or less. or, more preferably, at an ambient temperature of about 930° C. or less. The maximum ambient temperature in the above-mentioned C section (i.e., the maximum ambient temperature) is about 935°C or less. or more preferably about 930° C. or less, which improves productivity and weldability. can be further improved.

[0067] According to one aspect of the present invention, the maintenance time in the section C may be about 0.5 minutes or more, If the maintenance time in section C is less than about 0.5 minutes, the final maintenance temperature cannot be reached. There is a possibility, but it is not limited to this.

[0068] Meanwhile, according to one aspect of the present invention, when the t is 1.5 mm or less, the atmosphere in the section C is The ambient temperature may be greater than or equal to about 870° C. and less than 880° C. This is because the high temperature maintained during heating If the thickness of the material is 1.5 mm or less, the alloying of the plating layer will proceed extremely quickly. In this case, the temperature in section C, which is the final maintenance temperature, is maintained at a low temperature of about 870°C or higher and less than 880°C. This is because it is most advantageous in terms of weldability.

[0069] Alternatively, according to one aspect of the present invention, when the t exceeds 1.5 mm, the C section The ambient temperature may be greater than or equal to about 870° C. and less than 900° C. This is because the ambient temperature is maintained at a high temperature during heating. This causes the alloying of the plating layer to proceed extremely quickly, and when the material thickness exceeds 1.5 mm, In this case, the temperature in section C, which is the final maintenance temperature, is maintained at a low temperature of about 870°C or higher and less than 900°C. This is because it is most advantageous in terms of weldability. The temperature in section C must be slightly higher than that of thinner materials. It is.

[0070] That is, according to one aspect of the present invention, in order to achieve the intended effect of the present invention, each B The duration of each of the sections B and C is preferably about 0.5 minutes or more. The maintenance time in section C does not mean the cumulative time, but the maintenance time of each section B itself. and C section itself. At least one of the above sections B and C When the maintenance time between the two sections is less than about 0.5 minutes, the temperature rises quickly in section B and the minimum temperature in section C is low. There is a risk that it may be difficult to expect the effect of reaching the final maintenance temperature, but this is not limited to this. do not have.

[0071] Meanwhile, according to one aspect of the present invention, the heating step is carried out such that the value of the following relational expression 2 is 2 or more: In this case, since the value of the above Relation 2 is an empirical value, , the units are not specified.

[0072]

number

[0073] On the other hand, in the heating furnace, the nth section is a section maintained at a specific atmospheric temperature. , means the nth section in the blank transport direction, and exists in the blank transport direction Each section can be divided according to the atmospheric temperature. In this case, the heating in the n-th section The furnace maintenance time does not mean the cumulative maintenance time in the heating furnace, but the maintenance time of each section itself.

[0074] In this case, the explanation of the heating furnace and each section will be the same as above, except for the maintenance time in each section described later. The explanation of the above is equally applicable.

[0075] In addition, the maintenance time in each section includes the above-mentioned multiple heating zones, and each heating zone is mutually In a heating furnace capable of controlling the atmospheric temperature separately, the temperature in each heating zone corresponding to each section is maintained. For example, in the case where one heating zone corresponds to one section, The time that the material is maintained in one heating zone is the time when the blank is inserted. It can mean from the time when the blank is removed from one of the heating zones.

[0076] In addition, as described above, the above-mentioned section B is a section having an ambient temperature of about 930° C. or higher and a section having an ambient temperature of about 930° C. or higher. The final section of the above section B is the section with the highest atmospheric temperature. In this case, the section B is the section having the maximum atmospheric temperature (i.e., the maximum atmospheric temperature). After B, the blank is transported in the blank direction, except for B section, and is divided by the furnace atmosphere temperature after B section. It means an interval that exists in a divided manner.

[0077] As an example, in section A (ambient temperature: T1, maintenance time: t1), section B (ambient temperature: T 2, maintenance time: t2), the first C section (ambient temperature: T3, maintenance time: t3), the second C A case where there is a section (ambient temperature: T4, maintenance time: t4) will be explained. In this case, Equation 2 is [{(T1-870)×t1 / t total ×0.1334×1}+{(T 2-870)×t2 / t total ×0.1334×3}+{(T3-870)×t3 / t total ×0.1334×(-1)}+{(T4-870)×t4 / t total × 0.1334×(−1)}] / t.

[0078] The inventors have carefully studied the temperature and time patterns of the heating furnace in the heating step. As a result, productivity, weldability, formability, and product shape precision have been improved. We further investigated how this could be achieved.

[0079] That is, in the heating stage, the heating atmosphere temperature in each section is based on 870°C. The difference is the percentage of time each section takes up in the entire process multiplied by 0.1334 (V cal )of As a benchmark, the effect on the molded parts was studied. Specifically, the maximum ambient temperature was maintained. Before the section, it is preferable to have a large value from the viewpoint of productivity, so the above V cal The value is a (+) sign (i.e., k corresponds to (+1)), and among these, the area maintained at the highest ambient temperature Since the effect of the above V cal The value is affected by (+3) times (i.e., k In addition, in the section after section B, the above V cal A smaller value indicates diffusion. The value has a (-) sign because it is preferable from the standpoint of weldability to reduce the layer thickness. V in each section cal The sum of the values, divided by t, taking into account the effect of thickness, must be 2 or more. In addition to the aforementioned productivity, weldability, and formability, the combination of heating furnace sections under the appropriate conditions The twisting phenomenon that occurs when the product is cooled in air after being removed is reduced, and the product shape accuracy is improved. It has been found that the degree can be further improved.

[0080] In addition, the inventors conducted a detailed process analysis of the cooling process in the hot press forming process. The heated blank was removed from the heating furnace. After that, it is transferred to a die installed in the press. During this transfer process, it is cooled by air. Next, after placing the blank on the lower die, the blank supply jig is moved out of the press operating range. When the press slide is moved away from the blank, it starts to descend, and after a certain time the upper die comes into contact with the blank. Forming essentially begins when the upper die comes into contact with the blank. Thus, a certain amount of time is required from when the blank is placed until forming takes place. However, during this time, not only is the blank cooled as a whole, but the lower die Or it comes into contact with a structure such as a lifter that supports the blank of the lower die, causing a sudden Therefore, in order to ensure overall safe molding, air cooling is required. The time required for the transfer process, which is the main process of forming, as well as the time required for the blank to be placed and formed, It was also found that it was necessary to minimize the time required before the product was released. After molding is complete, rapid cooling while the mold is in perfect contact is important in order to ensure the proper physical properties. It goes without saying that the present invention will not be described further. The cooling time inside the mold and the time required from when the blank is placed until it is formed are controlled. It was found that this was important in terms of ensuring physical properties and moldability, and the following analysis was carried out.

[0081] On the other hand, Figure 6 shows the results of the test on aluminum-plated steel sheets with thicknesses of 0.9 and 1.8 mm heated to 900℃. Temperature change over time when the material is heated, removed from the furnace, and cooled in air 6 is a comparison graph of the experimental values ​​and the interpretation values ​​for the air cooling process. As shown in FIG. 6, the interpretation values It can be seen that it predicts the experimental values ​​well.

[0082] In the present invention, by utilizing such interpretation technology, various material thicknesses, heating furnace removal temperatures, The time required for the steps of transferring and placing the blank, and the time required for forming after the blank is placed As a result of careful consideration of the correlation between the sum of the time required up to the previous time and the time required for the next time, it was found that the following relational expression 1 must be satisfied. I discovered there was a need.

[0083] [Equation 1] T≦8.2×t+(temp-900) / 30 (The above T is the time required for the transfer and placement stages, and the time required for molding after the blank is placed.) The unit of t is the thickness of the material. The unit is mm. The above temp indicates the temperature at which the sample is removed from the heating furnace, and the unit is °C. (

[0084] In this case, since the above relational expression 1 is an empirically obtained value, it is not necessary to determine the unit. The unit of T is s (seconds), t is mm, and the unit of temp is ℃. do.

[0085] According to one aspect of the invention, T is greater than about 10 seconds, and more preferably greater than about 11 seconds. That is, in the present invention, even if the T exceeds about 10 seconds, excellent moldability is obtained. This allows the system to be applied to equipment with a relatively slow transfer speed. This eliminates the need for unnecessary capital investment and ensures economic efficiency.

[0086] On the other hand, according to one aspect of the present invention, the above-mentioned material is used, although it is not particularly limited. The thickness (t) of the material may be in the range of about 0.6 to 2.6 mm. If it is less than 1 mm, the material will be too thin and there will be problems with sagging during transportation in the continuous heating furnace. If it exceeds about 2.6 mm, the material becomes too thick and the aluminum It may not be easy to produce miniature plated materials.

[0087] As mentioned above, cooling is done by air cooling during the transfer process and forming after the blank is placed. The cooling is done by the lower die before the blank is placed on the mold. Before this happens, lifters that support the lower die or the blank of the lower die are used. The areas in contact with the structure cool faster than the areas that are not in contact and are air-cooled. Therefore, in terms of the overall air cooling of the blank, the above relational expression 1-1 [T≦8.2×t] However, after the blank is placed on the lower die, the upper die comes into contact with it and the forming begins. We also found that it is important to ensure that the time required before the procedure is carried out is not too long.

[0088] Therefore, the time required from when the blank is placed until forming begins is less than 2 seconds. The inventors heated a 1.2 mm thick material and removed it at 900°C. After that, the mold was moved for 8 seconds and contacted with the lower die lifter for 1 second. The mold was moved for 7 seconds and contacted with the lower die lifter for 1 second. The condition was that the material was in contact with the lower die lifter for 2 seconds, and the condition was that the material was transported for 6 seconds and in contact with the lower die lifter for 3 seconds. The temperature of each part that came into contact with the lifter was observed. If contact occurs, the affected area will cool by 50°C or more compared to areas that are not in contact. Therefore, before the molding step, the lower part of the mold is in contact with the upper part of the mold. The time for cooling in the mold alone (i.e., from when the blank is placed in place until forming takes place) If the heating time exceeds 2 seconds, the blank area that is not in contact with the lower die is heated to 700°C. However, the part of the die that comes into contact with the lower die is cooled to a level of 650°C. The temperature is cooled to a level that is deemed unworkable in the hot press forming process. This can lead to problems with parts not being molded and becoming scrap. There is room for improvement.

[0089] Therefore, most preferably, forming begins when the heated blank contacts the upper die. The process is performed so as to satisfy the above-mentioned relational expression 1 until the blank is placed. The time required from when the mixture is mixed to when molding is performed can be controlled to less than 2 seconds.

[0090] According to one aspect of the present invention, the thickness of the plating layer of the blank is 20 μm or more. If the thickness of the plating layer of the blank is less than 20 μm, the plating layer of the blank may be Heating is performed when the plating layer is thin, and the alloying proceeds quickly, causing the diffusion layer to grow even faster. That is, when the plating amount is reduced, the rate at which the thickness of the diffusion layer increases increases, The thickness of the blank plating layer is set to 20μ because it may be difficult to achieve the desired physical properties. It is preferable to control the thickness of the plating layer of the blank to be 1.0 mm or more. Preferably, the thickness is 25 μm or more. This suppresses the rate at which the thickness of the diffusion layer increases, On the other hand, the upper limit of the thickness of the plating layer of the blank is particularly Although not limited thereto, if the thickness of the plating layer is unnecessarily increased, the alloying rate of the plating layer becomes slow. Therefore, the 33μm or less laser that is widely used in industry is Bell is enough.

[0091] According to one aspect of the present invention, the thickness of the diffusion layer of the molded member may be 15 μm or less. The diffusion layer has poor conductivity and high resistance. Therefore, the thickness of the diffusion layer is too thick. When this occurs, localized heat is generated during welding, causing spatter. Therefore, the thickness of the diffusion layer is set to 15 μm. It is preferable to control the temperature to the following value. On the other hand, the diffusion layer of the molded member is an intermetallic layer of Fe and Al. The intermetallic compound of Fe and Al includes FeAl, Fe3Al, etc. In addition, a part of the components derived from the plating layer may be further included.

[0092] According to one aspect of the present invention, the thickness of the alloy layer of the molded member may be 27 to 50 μm. When the thickness of the alloy layer of the formed part is less than 27 μm, the problem of insufficient corrosion resistance occurs. If the thickness of the alloy layer exceeds 50 μm, the plating layer will be burned onto the mold during molding. From the viewpoint of further improving the above-mentioned effect, the above-mentioned molding part The thickness of the alloy layer of the material may more preferably be 35 to 50 μm. The thickness of the alloy layer of a material means the total thickness of the coating including the diffusion layer.

[0093] According to one aspect of the present invention, the thickness of the diffusion layer of the molded member relative to the thickness of the alloy layer of the molded member The thickness ratio (thickness of the diffusion layer / thickness of the alloy layer) is 0.5 or less, and more preferably 0.3 By satisfying the above conditions, the thickness of the alloy layer of the formed member can be increased. When the thickness of the diffusion layer becomes too thick, spatter occurs, resulting in poor weldability. This can prevent the above problem. EXAMPLES

[0094] (Example) The present invention will be described in more detail below with reference to examples. However, the following examples are merely illustrative of the present invention. The above-mentioned examples are merely for illustrative purposes and are not intended to limit the scope of the present invention. It should be noted that the scope of the present invention is defined in the claims. The determination shall be based on the matters set forth above and matters that can be reasonably inferred therefrom.

[0095] (Experimental Example 1) By weight, C: 0.22%, Si: 0.3%, Mn: 1.2%, Cr: 0.2%, Al: :0.03%, P:0.01%, S:0.001%, N:0.003%, B:0.003 %, the balance being Fe and other unavoidable impurities, was placed in a plating bath of Al- The plated steel sheet was obtained by immersing it in a 9% Si-3% Fe solution. For aluminum-plated steel sheets, blanks were prepared to satisfy the conditions in Tables 1 and 2 below. It is heated in a heating furnace, transferred between the upper and lower dies of a mold, cooled by placing it on the lower die, and then molded. The hot press-formed parts were manufactured through the steps of forming, pressing, and ejecting. In a heating furnace in which the atmospheric temperature is controlled separately in each heating zone, The temperature of the atmosphere in the zone is measured by a thermocouple and shown in the table below. The temperature maintained in each section of the test is shown as the temperature maintained in each section of the test. Based on each heating zone corresponding to the blank, from the time of inserting the blank to the time of removing it The cumulative maintenance time in each section was measured and is shown in Table 1 below. From the time when the blank is fed, the blank is heated in each heating zone corresponding to each heating furnace. The time until the ink was removed was measured and is shown in Table 1 below.

[0096] Meanwhile, the characteristics of each of the invention examples and comparative examples shown in Tables 1 and 2 below were evaluated according to the following criteria. Ta.

[0097] <Time to reach 900℃> Using the results of the calculation of the temperature of the material put into the heating furnace using the interpretation method described above, The time it takes to reach 00℃ first is classified as follows, and productivity is determined based on this. did.

[0098] ○: When it takes 180 seconds or less to reach 900℃ ×: When it takes more than 180 seconds to reach 900℃

[0099] <Weldability> Weldability is determined by the range of welding current during resistance welding (the minimum current at which the minimum nugget diameter can be obtained). The range between the maximum current value at which spatter occurs and the maximum current value at which spatter occurs is as follows: In this case, the welding current range was determined by utilizing a correlation equation between the thickness of the diffusion layer and the welding current range.

[0100] AA: When the welding current range is 2.3KA or more A: When the welding current range is 2.0KA or more and less than 2.3KA A-: Welding current range is 1.5KA or more and less than 2.0KA B: Welding current range is 1.0KA or more and less than 1.5KA C: Welding current range is less than 1.0KA

[0101] <Moldability> Formability is a control standard for reducing the occurrence of product defects. Blank temperature before forming6 Based on the standard temperature of 50°C, the following classification was made:

[0102] ○: When the blank temperature immediately before forming is 650℃ or higher ×: When the blank temperature immediately before forming is less than 650°C

[0103] [Table 1]

[0104] [Table 2]

[0105] As shown in Tables 1 and 2 above, the entire furnace was set to a single atmospheric temperature of 900°C. Compared with Comparative Example 1, Examples 1 and 2 of the present invention have a shorter time to reach the final maintenance temperature. This has confirmed that the overall cycle time can be reduced. From this, it was confirmed that productivity was further improved.

[0106] In addition, the heating conditions in the heating furnace, the lower die placement and cooling conditions, and the relational expression 1 are all satisfied according to the present invention. In addition, it was confirmed that Examples 3 to 6 were excellent in productivity, weldability, and formability.

[0107] In addition, Example 6 of the invention, in which the ambient temperature in Section B is greater than 930°C and less than 940°C, is different from other inventions. It was confirmed that the weldability was improved compared to the previous example.

[0108] In contrast, in Comparative Example 2, in which the entire heating furnace was set to a single temperature of 940°C, the temperature rose faster. Although this is effective, the final maintenance temperature is kept high at 940°C, which results in poor weldability. there was.

[0109] In addition, a comparison was made of the other method, in which the highest temperature, 940°C, was placed at the very end. In Example 3, the time required to reach the final maintenance temperature is long, which is poor in productivity, and the final temperature The temperature reached 940°C, which resulted in poor weldability.

[0110] In addition, in Comparative Example 4, in which only the atmospheric temperature in Section A was changed to 700°C, the temperature reached 900°C. The time is 200 seconds, and the temperature rise is not completed by the end of the B stage, which results in poor productivity. There was a problem.

[0111] On the other hand, if one or more of the heating conditions in the heating furnace, the lower die placement and cooling conditions, and the relational expression 1 are Comparative Examples 5 to 8, which do not satisfy the above requirements, are inferior in one or more of the productivity, weldability, and formability. I confirmed that there is.

[0112] (Experimental Example 2) The hot pressing was carried out in the same manner as in Experimental Example 1, except that the conditions in Tables 3 and 4 were changed. In addition, except for the evaluation of productivity by the following method, The characteristics were evaluated according to the same criteria as in the above-mentioned Experimental Example 1.

[0113] <Whether or not an additional heating process is necessary> Using the results of the calculation of the temperature of the material put into the heating furnace using the above interpretation method, The productivity was judged by classifying them as follows.

[0114] ○: When the material temperature reaches the set ambient temperature in section C when the material is removed ×: When removing the material, the temperature of the material did not reach the set ambient temperature of the C section. When an additional heating process is required to obtain the desired properties

[0115] [Table 3]

[0116] [Table 4]

[0117] As shown in Tables 3 and 4 above, the heating conditions in the heating furnace of the present invention, the lower die placement cooling conditions Inventive Examples 7 to 13, which satisfy all of the conditions and Relational Formula 1, are excellent in productivity, weldability, and formability. We confirmed that this is the case.

[0118] In particular, the maximum ambient temperature in section C is Tb based on the maximum ambient temperature in section B (Tb). Invention Examples 8 to 13, which satisfy the condition of -20°C or less, have better weldability than Invention Example 7, which does not satisfy this condition. It was confirmed that the improvement was

[0119] In addition, Example 10 of the present invention, in which the atmospheric temperature in Section C is 870°C or higher and lower than 880°C, is different from other inventions. It was confirmed that the weldability was improved compared to the clear example.

[0120] In contrast, the heating conditions in the heating furnace, the lower die placement cooling conditions, and one of the relational expressions 1 Comparative Examples 9 to 17, which do not satisfy the above conditions, have one or more of productivity, weldability, and formability. It was confirmed that the conditions were inferior to those of the

[0121] In particular, Comparative Examples 18 to 20 do not satisfy the conditions of the above-mentioned Relational Formula 1, and therefore are not comparable to the invention examples. It was confirmed that the moldability was inferior to that of the conventional one.

[0122] (Experimental Example 3) A hot press forming member was manufactured in the same manner as in the aforementioned Experimental Example 1, except that the conditions in Tables 5 and 6 below were changed. Also, except for evaluating by the following method in relation to productivity, the characteristics were evaluated based on the same criteria as in the aforementioned Experimental Example 1.

[0123] <Whether there is a section where the temperature of the material is maintained in section B> After the blank material was heated to the set maximum atmosphere temperature in section B, it was classified as follows depending on whether the time for maintaining that temperature existed in section B, and productivity was evaluated based on this. This is because in section B, it is only necessary to achieve the effect of increasing the heating rate, so it is preferable not to maintain it in an unnecessarily high temperature range for a long time.

[0124] ○: When there is no additional maintenance time ×: When there is additional maintenance time

[0125]

Table 5

[0126]

Table 6

[0127] As shown in Tables 5 and 6 above, for Invention Examples 14 and 15 that satisfy all of the heating conditions in the heating furnace of the present invention, the lower die placement cooling conditions, and Relational Expression 1, it was confirmed that both productivity, weldability, and formability are excellent.

[0128] On the other hand, for Comparative Examples 21 and 22 that do not satisfy the heating conditions in the aforementioned heating furnace, it was confirmed that they are inferior in productivity.

[0129] (Experimental Example 4) The hot pressing was carried out in the same manner as in Experimental Example 1, except that the conditions in Tables 7 and 8 were changed. In addition, except for the evaluation of productivity by the following method, The characteristics were evaluated according to the same criteria as in the above-mentioned Experimental Example 1.

[0130] <Whether or not the time has passed since the thickness of the diffusion layer reaches 15 μm> The time at which the thickness of the diffusion layer, which is usually regulated by automobile manufacturers to ensure physical properties, reaches 15 μm. Based on this, productivity was evaluated according to the following classification:

[0131] ○: The total cumulative maintenance time from the time the material is removed from the heating furnace is 1 When it takes less than 5μm ×: The total cumulative maintenance time until the material is removed from the heating furnace is 1 If the time to reach 5μm is exceeded

[0132] [Table 7]

[0133] [Table 8]

[0134] As shown in Tables 7 and 8 above, the heating conditions in the heating furnace of the present invention, the lower die placement cooling conditions Inventive Examples 16 and 17, which satisfy all of the conditions and Relational Formula 1, the productivity, weldability, and formability are all excellent. I confirmed that it was excellent.

[0135] In contrast, in Comparative Example 23, which does not satisfy the heating conditions in the heating furnace, productivity and weldability were poor. It was confirmed that it was inferior to

[0136] In addition, Comparative Example 24, which does not satisfy the above-mentioned heating conditions in the heating furnace and the lower die placement and cooling conditions, The productivity, weldability, and formability were all poor.

[0137] On the other hand, a scanning electron microscope (SEM) photograph of the plating layer of the above-mentioned experimental example is shown in Fig. 4. As shown in.

[0138] (Experimental Example 5) The hot rolling was carried out in the same manner as in Experimental Example 4, except that the conditions in Tables 9 and 10 were changed. Press-molded members were produced, and their properties were evaluated based on the same criteria as in Experimental Example 4.

[0139] [Table 9]

[0140] [Table 10]

[0141] As shown in Tables 9 and 10 above, the thickness of the blank plating layer is 20 μm or more, and the molded part The thickness of the diffusion layer of the molded part is 15μm or less, the thickness of the alloy layer of the molded part is 27~50μm, and the plating The ratio of the thickness of the diffusion layer of the above molded part to the thickness of the alloy layer (thickness of the diffusion layer / thickness of the alloy layer) Example 18 of the present application, which satisfies all of the following 33 conditions, is an invention that does not satisfy one or more of the above conditions. It was confirmed that the weldability was further improved compared to Example 19.

[0142] (Experimental Example 6) The same procedure as above was followed except that the hot press-formed parts were manufactured to satisfy the conditions in Tables 11 to 13 below. A blank of a plated steel sheet was formed in the same manner as in the above-mentioned Experimental Example 1. The effect of formability was evaluated by applying the same evaluation method as in the above-mentioned Experimental Example 1, and additionally evaluating the shape accuracy of the molded part. was measured.

[0143] <Whether or not the temperature of the material reaches the removal temperature of the heating furnace when it is removed from the heating furnace> Also, when removing the material from the heating furnace, did the material temperature reach the removal temperature of the heating furnace? The productivity was evaluated according to the following criteria.

[0144] ○: When the material temperature reaches the removal temperature of the heating furnace when it is removed from the heating furnace ×: When the material temperature does not reach the removal temperature of the heating furnace when it is removed from the heating furnace. If

[0145] [Table 11]

[0146] [Table 12]

[0147] [Table 13]

[0148] As shown in Tables 11 to 13 above, Examples 20 to 23 of the present invention satisfy Relational Formula 2 of the present application. Compared with Comparative Examples 25 and 26, which are not used, at least one of the productivity and weldability is superior. was.

[0149] Furthermore, for each molded member obtained from each of the invention examples and comparative examples, ten identical measurement sites were At this point, a checking fixture is used to check the shape. The shape accuracy was measured and the conditions were more severe than the usual shape accuracy requirement of + / - 0.5 mm. The number of measurement points that satisfied the ±0.4 mm range was counted. When the relative improvement effect of shape accuracy was evaluated, Examples 20 to 22 of the present invention were superior to Comparative Example 25. It was confirmed that the shape accuracy was improved by 25% compared to Comparative Example 25. It was confirmed that the standards were at the same level.

[0150] (Experimental Example 7) The hot pressing was carried out in the same manner as in Experimental Example 3, except that the conditions were changed to those in Table 14 below. In addition, the same procedures as those described above were carried out except that the bending property was evaluated by the following method. The characteristics were evaluated according to the same criteria as in Experimental Example 3 described above.

[0151] <Bending property> The bendability is measured by a three-point bending test, measuring the bending angle at which the maximum load occurs, and They were classified according to the following criteria.

[0152] AA: When the bending angle at maximum load exceeds 50 degrees A: When the bending angle at maximum load is 45 to 50 degrees

[0153] [Table 14]

[0154] [Table 15]

[0155] As shown in Tables 14 and 15 above, the manufacturing conditions of the hot press-formed member according to the present invention are Inventive Examples 24 and 25, which satisfy the above requirements, were excellent in productivity, weldability, and formability. If the thickness of the rank exceeds 1.5 mm, the temperature in the above B section exceeds 940°C. Example 24 of the invention, which satisfies the condition of 0°C or less, has the above-mentioned productivity and It was confirmed that the alloy has superior bendability as well as weldability and formability.

Claims

1. A method for producing a hot press-formed part, comprising: heating an aluminum-based plated steel sheet blank in a heating furnace; The heated blank is removed from the heating furnace and the upper and lower dies of the die attached to the press are and transferring and placing the a forming step in which forming is performed after the upper part of the mold contacts the placed blank; Including, The heating furnace includes sections A, B, and C arranged in the blank conveying direction. It is a continuous heating furnace. The heating in the A section was performed in a time period of about a (0.2 min, 750° C.), b (1.0 min, 750° C.), c (1.0 min, 750° C.), (1.0 min, 800°C), (1.5 min, 900°C), and (0.2 min, 900°C) The conditions stipulated by the figure a, b, c, e having the coordinates of the furnace maintenance time and the atmospheric temperature are satisfied. death, The heating in the B section is [0010] The conditions are defined by the graph fghi having the coordinates of the cumulative furnace maintenance time and the atmospheric temperature. Fulfilling, The heating in the C section is [0025] The conditions are defined by a graph jklm having coordinates of the cumulative furnace maintenance time and the atmospheric temperature. The maximum atmospheric temperature is lower than the maximum atmospheric temperature in the B section. The following relational expression 1 is satisfied, The time required from when the blank is placed to when forming is performed is 2 seconds or less. A method for manufacturing a hot press formed part. [Relationship 1] T≦8.2×t+(temp-900) / 30 (The above T is the time required for the steps of transferring and placing the blank and the time required for forming the blank after it is placed.) The unit of t is the thickness of the blank. The unit of the temperature is mm. The temperature is the temperature at which the sample is taken out of the heating furnace. It is.)

2. 2. The hot rolling method according to claim 1, wherein the heating in the C section is performed at an ambient temperature of 930° C. or less. A method for manufacturing a press-molded part.

3. The maximum ambient temperature in the C section is T based on the maximum ambient temperature (Tb) in the B section. The method for producing a hot press-formed member according to claim 1, wherein the temperature is −20 ° C. or lower.

4. The t is 1.5 mm or less, and the atmospheric temperature in the B section is more than 930° C. and less than 940° C. The method for producing a hot press-formed part according to claim 1 ,

5. The t is 1.5 mm or less, and the atmospheric temperature in the C section is 870° C. or more and less than 880° C. The method for producing a hot press-formed part according to claim 1 ,

6. The t exceeds 1.5 mm, and the atmospheric temperature in the C section is 870° C. or more and less than 900° C. The method for producing a hot press-formed part according to claim 1 ,

7. The t is more than 1.5 mm, and the atmospheric temperature in the B section is more than 940° C. and not more than 960° C. The method for producing a hot press-formed part according to claim 1 ,

8. The time required for the step of transferring and placing the blank and the time required for forming the blank after the blank is placed.

2. The method for producing the hot press-formed part according to claim 1, wherein the sum of the time required for the step (a) to the step (c) exceeds 10 seconds. method.

9. The hot press forming method according to claim 1, wherein the thickness of the plating layer of the blank is 25 μm or more. Manufacturing method of shaped components.

10. After the forming step, the upper die of the die reaches and maintains the bottom dead center of the press. an in-mold cooling stage in which the molded material is rapidly cooled; and removing the cooled molded member. The thickness of the diffusion layer of the molding member is 15 μm or less, The hot press forming method according to claim 1, wherein the thickness of the alloy layer of the formed member is 35 to 50 μm. Manufacturing method of shaped components.

11. After the forming step, the upper die of the die reaches and maintains the bottom dead center of the press. an in-mold cooling stage in which the molded material is rapidly cooled; and removing the cooled molded member. The ratio of the thickness of the diffusion layer of the molded member to the thickness of the alloy layer of the molded member (thickness of the diffusion layer 2. The method for producing a hot press-formed part according to claim 1, wherein the thickness of the alloy layer is 0.33 or less. Law.

12. The heating step is performed so that the value of the following relational expression 2 is 2 or more. The method for producing the hot press-formed member described above. [0030] (In the above-mentioned Relational Formula 2, the T ｎ is the furnace atmosphere in the nth section in the blank transport direction The temperature is expressed in °C. ｎ is the heating temperature in the nth section in the blank transport direction. The t represents the furnace maintenance time, and is expressed in minutes. ｔｏｔａｌ represents the total time in the furnace The unit is minutes. x represents the number of sections in the heating furnace that are maintained at a specific atmospheric temperature. k is an integer of 3 if it is the final section of section B, and is an integer of 3 if it is the section after section B. -1, otherwise 1. The t represents the thickness of the blank; The unit is mm.)

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