Method for manufacturing hot press-formed parts with excellent productivity, weldability, and formability

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 manufacturing a hot press-formed member that is excellent in productivity, weldability, and formability. do. [Background technology]

[0002] Due to the demand for lighter vehicles and improved safety, high-strength steel using hot press forming methods is being developed. In the hot press forming process, the material is heated and rapidly cooled. In order to prevent scale formation at high temperatures, aluminum-plated steel is also Aluminum alloy plated steel is used. Aluminum alloy plated steel has the problem that the plated layer melts when heated rapidly. Therefore, it is generally heated at a slow rate in an atmospheric heating 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 with multiple heating zones is used. Heating is performed in a continuous heating furnace such as a tungsten furnace, with the ambient temperature gradually increasing. However, in this method, the target temperature is reached due to the slow heating rate. It must be heated in the heating furnace for a certain period of time to reach the desired temperature. This increases the time required for maintenance at this temperature, resulting in a problem of reduced productivity.

[0004] Therefore, a method of increasing the heating temperature is 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 shorten 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 usual method, shortening the time to maintain the temperature in the furnace and lowering the heating temperature are mutually exclusive. The technical problem is that they cannot be applied simultaneously because they have opposite effects on the The issue exists.

[0007] On the other hand, in addition to the above-mentioned problems, if the temperature of the heating furnace is continuously lowered to improve weldability, the forming Therefore, there is a problem that excellent productivity, weldability, and formability are further 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 yield. The object of the present invention is to provide a method for manufacturing a hot press-formed part that has improved formability.

[0010] The object 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 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; removing the heated blank from the heating furnace and transferring and placing it between an upper die and a lower die of a die attached to a press; a forming step in which forming is performed after the upper part of the mold contacts the placed blank, The heating furnace is a continuous heating furnace including sections A, B, and C arranged in order in the direction of conveyance of the blank, The heating in the section A satisfies the conditions defined by the diagram abcde having coordinates of cumulative furnace maintenance time and atmospheric temperature of about a (0.2 min, 750°C), b (1.0 min, 750°C), c (1.0 min, 800°C), d (1.5 min, 900°C), and e (0.2 min, 900°C), The heating in the section B is

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

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

[0015] [Figure 1] 1 is a graph showing a heating pattern for an aluminum-plated material with a thickness of 1.2 mm. [Figure 2] This is a graph showing a comparison of experimental values ​​and interpreted values ​​for temperature rise interpretation under various furnace atmosphere temperature conditions for an aluminum-plated material with a thickness of 1.2 mm. [Figure 3] 1 is a graph showing the preferred atmospheric temperature conditions of the present invention versus the cumulative furnace maintenance time when heating an aluminum-plated material with a thickness of 1.2 mm. [Figure 4] The photographs show the results of observing 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] This shows the heating conditions for aluminum-plated materials, taking into account changes in material thickness. [Figure 5b] This shows the heating conditions for aluminum-plated materials, taking into account changes in material thickness. [Figure 5c] This shows the heating conditions for aluminum-plated materials, taking into account changes in material thickness. [Figure 6] 1 is a graph showing a comparison between experimental values ​​and interpreted values ​​for temperature changes over time when aluminum-plated materials with thicknesses of 0.9 and 1.8 mm are cooled in air after being removed from a heating furnace. DETAILED DESCRIPTION OF THE INVENTION

[0016] The following describes a preferred embodiment of the present invention. However, the present invention may be practiced in various other embodiments. The present invention can be modified in various forms and is not limited to the embodiments described below. Furthermore, 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

[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: A step of heating the blank in a heating furnace, removing the heated blank from the heating furnace, and pressing and placing the upper mold and the lower mold of the mold attached to the upper mold. and a forming step in which forming is performed after contacting the placed blank.

[0019] In addition, in the method for manufacturing the hot press-formed member, after the forming step, the upper die of the die is An in-mold cooling stage that rapidly cools the formed material by reaching and maintaining the bottom dead center of the press. and a molding member removal step of removing the cooled molding 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. However, as an example, the composition of the plating layer is, in weight %, Si: 5 to 11%, Fe: 4.5% or more. The remainder may contain 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.

[0021] According to one aspect of the present invention, the heating furnace includes sections A and B arranged in a direction in which the blank is conveyed. The heating furnace may be a continuous furnace including sections A, B, and C. In this case, the above-mentioned sections A and B The sections A and B do not necessarily have to be adjacent to each other in the direction of conveyance of the blank. The above-mentioned order should be satisfied along the direction of transfer of the rack. Each C section may consist of one heating zone, and each section may have multiple heating zones. In addition, between each section (i.e., between section A and section B, or (between Section B and Section C), and includes 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, the ambient temperature was sometimes increased in a sequential manner. .

[0023] However, this method heats up slowly, so it takes 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 productivity was poor due to the increased waiting time.

[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 will be higher than that of a normal heating element. Compared to the thermal furnace setting method, heating is performed faster, reducing the time spent in the furnace and improving productivity. At the same time, the temperature in the subsequent section C can be increased by the aforementioned 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 it is possible to solve the problem of defects.

[0025] On the other hand, the factors that determine the productivity mentioned above are minimizing the time it takes to reach 900°C, 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 heating furnace until the material is removed from the heating furnace is The time required for the layer to reach a thickness of 15 μm or less is one example of this. By doing so, we can minimize the cycle time while ensuring the desired physical properties of the final molded product. This can improve productivity.

[0026] However, if the section B set at a high temperature as described above is too wide, the food will be heated to a high temperature. If the time is maintained at this temperature for an excessively long time, the thickness of the diffusion layer will increase, resulting in poor weldability. On the other hand, if the temperature in section B is too high, the problem may occur. If the heating speed is too fast, the productivity improvement effect cannot be obtained. Maintaining a high temperature in the initial section, section A, requires a lot of energy. Therefore, there is no need to set the ambient temperature unnecessarily high at the beginning of the temperature rise. The open structure allows for the evacuation of hot air and the introduction of cold materials, ensuring a high ambient temperature from the start. There is also the problem that it cannot be set immediately.

[0027] Also, once a material has been heated to a sufficient temperature, it has already completed its transformation into austenite. Therefore, it is only necessary to maintain the temperature and time required to obtain sufficient alloying of the plating layer. If a high ambient temperature is maintained even in the final stage, the problem of reduced weldability due to an excessive increase in the thickness of the diffusion layer may occur. Therefore, a relatively low temperature may be set.

[0028] In consideration of this point, 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 used for the aluminum-plated material. In a certain section A, considering the energy saving and the impossibility of setting a high ambient temperature, Then, in section B, the highest temperature is set to heat the material quickly. , set it so that the material reaches a sufficient temperature. Then, after the material reaches a sufficient temperature, In section C, the temperature was set lower than in section B. If the heating time is set differently for each interval, the cumulative heating time for the 1.2 mm material is 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 be explained 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 in each heating zone, 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 area 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 determined by the temperature of each heating zone corresponding to each section. The temperature is considered 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 In a heating furnace that can control the ambient temperature separately, From the time when is input, from the last heating zone among the heating zones corresponding to each of the above sections It can 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 separated by a partition wall or the like, The heating zones may be separated without a partition wall or the like. If so, the above method is applied as is.

[0032] On the other hand, in the case of the heating furnace described above, if there is no partition wall, the entire heating furnace is Divide the transport direction into n equal sections (for example, 5 or more), and divide each of the equal sections into one In one implementation of the present invention, the entire furnace is divided into 20 equal zones. Each of the divided areas can be considered as one section. As mentioned above, in each section, 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 considered 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 was set to approximately 930 to 960°C in the above section B, and the ambient temperature was set to approximately 930 to 960°C in the above section C. The ambient temperature is approximately 870°C or higher and is lower than the ambient temperature selected in section B. When using this method, the final temperature can be set to a single temperature. The temperature rises faster than in the conventional method, 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 that allows sufficient alloying of the plating layer, This prevents the problem of poor weldability due to excessive generation of . Therefore, it is possible to effectively provide a hot press forming method that can achieve both high moldability and weldability.

[0034] On the other hand, Figure 2 shows the validity of the above-mentioned heating interpretation technique, and is a 1.2 mm thick material. Experimental values ​​and interpretations of heating conditions under various furnace atmosphere temperature conditions for aluminum plated materials The graph shows a comparison of the experimental values. After the attached object was kept in the heating furnace, one temperature data point was obtained 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 also important to consider that the temperature depends on the thickness of the material, the ambient temperature, and the duration of each temperature range. As mentioned above, it is important to prevent excessive time spent in a high ambient temperature area. On the other hand, if the time spent in the high ambient temperature region is too short, the heating effect will not be achieved. 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 was completed by focusing on the fact that it is necessary to select the interval between the I will explain in detail.

[0036] Specifically, the cumulative furnace maintenance time is on the X axis and the atmospheric temperature inside the heating furnace is on the Y axis. As a standard, the heating in the above section A 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 the figure abcde. The conditions set by the user 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 temperature rise rate. Therefore, the atmospheric temperature in the heating furnace in the above 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 a problem of poor productivity. On the other hand, if the ambient temperature in the heating furnace in section A is set to more than 900°C, Maintaining a high temperature in the initial region of the furnace leads to high energy consumption. There is a problem.

[0038] On the other hand, in heating in 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 inventors have determined a preferable atmospheric temperature in the heating furnace for heating in section A. As a result of careful consideration of the time required for maintenance, the conditions for Section A were set as shown in Figure 3. That is, it has been found that it is preferable that the ambient temperature in the above-mentioned section A is low, about 750°C. If the temperature is 100°C, the time for maintaining section A should be shortened to about 1 minute or less, and the ambient temperature in section A should be about When the temperature is as high as 900°C, the time for maintaining section A is preferably set to about 1.5 minutes or less. On the other hand, in the above-mentioned section A, taking into consideration the passage time at the entrance of the heating furnace, the maintenance time in 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, which will be described later, and in section A. Since the influence of the thickness is somewhat small in the A section, from a practical point of view, it is set regardless of the thickness of the material in the A section. (See Figure 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 ambient 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 temperature rise rate also becomes slower, whereas when the ambient temperature in 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 kept as low as possible. However, if the ambient temperature in section B is too high, the material If the temperature is too high, the weldability may be poor. It is necessary to determine

[0042] On the other hand, in this specification, from the section having an ambient temperature of about 930°C or more to the section having the highest ambient temperature The section up to the temperature (i.e., the maximum atmosphere maintenance temperature) is considered to be 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 section B is located is considered to be a section distinct from the above section B. For example, if the above 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 ambient temperature was approximately 935°C, which is lower than the maximum ambient temperature of approximately 950°C. The section with degrees can be considered as section C.

[0043] Therefore, in the present invention, the ambient temperature in the above section B is set in the range of about 930 to 960°C. If the ambient temperature in section B exceeds approximately 960°C, the heating furnace equipment will be limited. However, the temperature is set too high to alloy the coating layer, which can lead to poor weldability. In addition, when the ambient temperature in the above-mentioned section B is less than about 930°C, the temperature rise 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 section B, not only the aforementioned atmospheric temperature but also the maintenance time of section B is also determined by the temperature rise rate of the material. This affects the temperature and the maximum heating temperature of the material. In other words, if the B stage is maintained for too short a time, If the B stage is maintained for too long, the material will not be heated to a high temperature for an excessively long time. This causes excessive alloying, which increases the thickness of the diffusion layer and leads to poor weldability. There is a risk that problems may occur.

[0045] Therefore, although not particularly limited, the lower limit of the maintenance time in the above section B is To maximize the effect of increasing productivity through temperature rise, the time can be set to approximately 0.5 minutes or more. Or, to prevent excessive alloying from progressing and resulting in poor weldability, the maintenance time is The upper limit can be set to approximately 4.8 minutes. In this case, the duration of 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, which will be described later. It is necessary to pay attention to the following.

[0046] On the other hand, the cumulative time maintained 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 to raise the temperature to a sufficient level, the ambient temperature in section B must be If the temperature is low, the cumulative time in the furnace until the end of section B must be extended. If the ambient temperature is high, the cumulative time maintained 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 time when section B ends. This means the cumulative furnace heating time up to section B. This refers to the cumulative time that the heating is maintained in the furnace until the end of section B, including the time during which the heating is maintained in the furnace until the end of section B. 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 explained as follows: For example, if the time period for maintaining section A is short, the temperature may not rise sufficiently. In order to warm up, the time to maintain section B itself needs to be slightly longer, and conversely, the time to maintain section A needs to be longer. If the time is long, it is necessary to consider that the time to maintain section B may be slightly shorter. That is, in order to improve productivity by shortening the heating time, which is the objective of the present invention, It is necessary to consider 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 stage B, which is 300°C, from remaining at that temperature for a long period of time will achieve the same heating effect, Based on these results, the influence of the thickness of the material is considered to be favorable from the viewpoint of weldability. If this is not taken into consideration (i.e., the material thickness is 1.2 mm), The cumulative furnace maintenance time was maintained at a maximum of approximately 3.8 minutes when the temperature in Section B was approximately 930°C. It can be held.

[0049] However, the temperature rise pattern of the material also depends on the thickness of the material. By analyzing the temperature rise 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 specified by the 1.2 mm material shapes f, g, and hi in Figure 3. The time should be increased by approximately 0.5 minutes for every 0.6 mm increase in material thickness. Conversely, when the material thickness is reduced, the time required for the workpiece to be cut increases by approximately 0.5 minutes for every 0.6 mm reduction. This may be done within a range where the amount of the oxidant is proportionally reduced.

[0050] Furthermore, the inventors have been conducting further research with a view to further improving productivity and weldability. As a result, taking into consideration the influence of material thickness, the thickness of the material was set to 1.5 mm as the standard. 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 t is 1.5 mm or less, Section B The ambient temperature may be greater than about 930°C and less than about 940°C. The above-mentioned B section needs to have a high ambient temperature, but due to abnormal work measures in 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 is less than 1.5 mm thick, Therefore, controlling the atmospheric temperature in section B within the above range will minimize the possibility of poor weldability. 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 The temperature may be about 931 to 934°C. This provides the effect of minimizing poor weldability. 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. The above B section needs to have a high ambient temperature, but due to work abnormality measures in actual operation, Considering that the maintenance time in the heating furnace may vary slightly, the atmosphere should not be too hot. Therefore, if the thickness of the material is more than 1.5 mm, Controlling the atmospheric temperature in the above section B within the above range minimizes the possibility of poor weldability. This is because when the thickness of the material increases, the temperature in section B is higher than that in the case of a thin material. This is because it is necessary to make the material a little higher than the material itself. If the thickness t exceeds 1.5 mm, the ambient temperature in the section B is preferably about 930°C. The temperature may be more than 945°C and most preferably about 931 to 940°C. This can further improve weldability.

[0053] On the other hand, according to another aspect of the present invention, when the t exceeds 1.5 mm, the temperature rise is rapid. In order to improve productivity and bendability, the ambient temperature in the above section B should be between approximately 940°C and 960°C. To ensure stable bending properties, the total cumulative maintenance time in the furnace should be controlled to be It is preferable to ensure that the length is not too short, that is, to secure it as long as possible. From the viewpoint of productivity, it is preferable to shorten the total furnace maintenance time. In order to satisfy this requirement, the temperature in section B must be increased to ensure a rapid temperature rise, and the cumulative temperature in the entire furnace must be reduced. This ensures a more stable austenite structure 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 maximum 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 less. This allows for both excellent productivity and weldability. This can be achieved.

[0055] Heating in the above section C is

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[0056] Heating in the above section C affects the final temperature of the material. The reason for setting the air temperature lower than the maximum ambient temperature in section B above is that the ambient temperature in section C If the temperature is as high as in section B, the material will be heated at a high temperature for a long time, resulting in poor weldability. In other words, heating in section B is intended to increase 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, as 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 approximately 870°C, the material removal temperature If the temperature is too low, the material will be cooled to too low a temperature in the subsequent transfer and pre-molding cooling stages, resulting in the temperature during molding being too low. The problem of excessively low viscosity may occur, which may result in poor moldability.

[0058] According to one aspect of the present invention, the atmospheric temperature in the section C is set to the above temperature in order to improve weldability. The ambient temperature in the section C may be lower than the ambient temperature in the section B. Alternatively, the ambient temperature in the section C may be lower than the ambient temperature in the section B. It can be set lower than the minimum ambient temperature (i.e., minimum ambient temperature) of the section. For example, the above-mentioned 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 is included, the temperature in the section C is about 870°C or higher and about 90°C or lower than the temperature in the first section B. The ambient temperature may be set to be below 30°C (ie, below 930°C).

[0059] According to one aspect of the present invention, the maximum ambient temperature in the section C is equal to or greater than the maximum ambient temperature in the section B. Based on the temperature (Tb), it can be set to about Tb-20°C or less, or about Tb The temperature may be set to a range of -30°C or less (in this case, the maximum ambient temperature is the same as above). The larger the temperature difference between section B and section C, the faster the temperature rise and the expansion. 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 high and the temperature in section C must be low. In terms of setting working conditions, the range is too narrow, and the temperature in section C is too low. Therefore, the inventors have decided to separate the above-mentioned section B and If the temperature difference in section C is about 20°C, the material will It was confirmed that the temperature of section C was reached at the time of section B. It is most preferable that the temperature difference between the first and second sections is about 20°C or more, and the temperature difference between the first and second sections is about 870°C or more.

[0060] On the other hand, the cumulative time in the furnace until the end of Section C also affects the final temperature. If the ambient temperature is low, the cumulative time in the furnace until the end of section C must be extended. If the ambient temperature in section C is high, the cumulative time in the furnace until section C is finished Here, the cumulative time in the furnace until the end of the above-mentioned section C may be shortened. This does not mean the maintenance time of the furnace, but the cumulative maintenance time up to the 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 furnace maintenance time up to the section C is short, the maintenance time of the section C itself is necessary for sufficient alloying. The time needs to be slightly longer, and conversely, if the time to maintain the furnace until just before section C is long, It is necessary to consider that the maintenance time of section C may be slightly shortened. The objective is to improve productivity by shortening the heating time, and to achieve sufficient alloying. It is necessary to consider not only the maintenance time of the C section itself but also the time before the C section. The cumulative time in the furnace 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 influence of the thickness of the material is not taken into consideration, and the material thickness is 1.2 When the temperature is set at 800 K, the cumulative time in the furnace until the end of section C is approximately When the ambient temperature is 70°C, it takes about 3.7 to 11.7 minutes, and when the ambient temperature is 940°C, it takes about 2 minutes. Specifically, when the ambient temperature in the above section C is high, If the cumulative time in the furnace until the end of section C is too long, the heating time will be too long. On the other hand, when the ambient temperature in section C is low, To compensate for this, it is necessary to lengthen the total cumulative in-furnace maintenance time up to stage C.

[0063] Furthermore, similar to section B, the temperature rise pattern of the material in section C also depends on the thickness of the material. Therefore, by performing temperature-elevation analysis for various thicknesses, it is possible to determine whether the thickness of the C-section is 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] That is, the cumulative furnace maintenance time until the end of section C is the same as that of the 1.2 mm material shown 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 thickness of the material is reduced, the minimum The duration will be reduced by 1 minute, and the maximum duration will be reduced by 2 minutes. can be done.

[0065] Therefore, in the present invention, the thickness is defined by the figure jklm, which also reflects the influence of the thickness. The cumulative furnace maintenance time and atmospheric temperature can be set to meet the requirements.

[0066] According to one aspect of the present invention, the heating in the 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 section C (i.e., the maximum ambient temperature) is approximately 935°C or less. or more preferably about 930°C or less, thereby improving 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 approximately 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 The ambient temperature may be about 870°C or more but less than 880°C. This is because the ambient temperature is maintained at a high temperature during heating. If the thickness of the material is 1.5 mm or less, alloying of the coating 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 approximately 870°C or higher and less than 880°C. This 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 thickness of the material 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 approximately 870°C or higher and less than 900°C. This is because it is most advantageous in terms of weldability. , taking into consideration that the temperature in section C needs to be slightly higher than that of thin materials. 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 maintenance time in each of 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 If the maintenance time between the two sections is less than about 0.5 minutes, the temperature rises rapidly in section B and the minimum temperature rises slowly in section C. Although it may be difficult to expect the effect of reaching the final maintenance temperature, it 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 relational expression 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 by the ambient temperature. 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 given in (2) is equally applicable.

[0075] In addition, the maintenance time in each section includes the above-mentioned multiple heating zones, and each heating zone is In a heating furnace that can separately control the atmospheric temperature, the temperature maintained in each heating zone corresponding to each section is For example, when 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. This may mean from the time when the blank is removed from one of the heating zones.

[0076] Furthermore, as mentioned above, the section B is a section having an ambient temperature of about 930°C or higher. The final section of Section B is the section with the highest ambient temperature. In this case, Section B refers to the section having the highest ambient temperature (i.e., the highest ambient temperature). After B, the blank is transported in the direction other than B, and is divided by the furnace atmosphere temperature after B. It means a section that exists in a divided form.

[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 The 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 accuracy have been further improved. We further investigated how this could be done.

[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, we studied the effect on the molded parts. Specifically, the maximum ambient temperature was maintained. Before the section, a large value is preferable from the viewpoint of productivity, so the above V cal The value is a (+) sign (i.e., k is (+1)), and among these, the area maintained at the highest ambient temperature The influence of the above V cal The value is affected by (+3) times (i.e., k corresponds to the integer 3). In addition, in the section after section B, cal A small value indicates diffusion. The value has a (-) sign because it is preferable to reduce the layer thickness and improve weldability. 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 productivity, weldability, and formability mentioned above, by combining heating furnace sections under the appropriate conditions, This reduces the twisting phenomenon that occurs when the product is cooled in air after removal, and improves product shape accuracy. It was found that the degree of

[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 mold 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 once the upper die comes into contact with the blank. Thus, a certain amount of time is required from when the blank is placed until it is formed. However, during this time, not only is the blank cooled as a whole, but the lower die Or it may come 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 safe molding, air cooling is required. The time required for the transfer process, which is the main process, is also the time required for the blank to be placed and then formed. It was also found that it is necessary to minimize the time required before the product is 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 this invention will not be further explained. 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 aluminum-plated steel sheets with thicknesses of 0.9 and 1.8 mm heated to 900°C. Temperature change over time when heated and then removed from the furnace and cooled in air This is a comparison graph of the experimental values ​​and the interpreted values ​​for the air cooling process. As shown in Figure 6, the interpreted values It can be seen that the experimental values ​​are well predicted.

[0082] In the present invention, by utilizing such interpretation technology, various material thicknesses, heating furnace removal temperatures, The time required for the step 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 required time and the time required up to that point, 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 stage of transporting and placing the blank, and the time required for forming 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. (It is.)

[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, excellent moldability can be obtained even if the T exceeds about 10 seconds. This allows the system to be applied to equipment with a slightly slower speed of the transfer device. 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, although not particularly limited, the above-mentioned material 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 sagging will occur during transport 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 aluminum-plated materials.

[0087] As mentioned above, cooling is carried out by air cooling during the transfer process and by forming the blank after it is placed. The cooling process is carried out by the lower die before the blank is placed on the mold. Before the process begins, the lower die or the lifter that supports the blank of the lower die is used. The area in contact with the structure cools faster than the area that is not in contact and is 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 learned 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 placing the blank to forming is less than 2 seconds. The inventors heated a 1.2 mm thick material and removed it at 900°C. After that, the material was transported for 8 seconds and contacted with the lower die lifter for 1 second. The material was transported 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 down by more than 50°C compared to areas that are not in contact. Therefore, before the molding stage, the bottom of the mold is in contact with the upper mold. The time it takes for the blank to cool in the mold only (i.e., from the time the blank is placed in place until forming occurs) If the required time exceeds 2 seconds, the blank area that is not in contact with the lower die of the die is heated to 700°C. However, the part of the mold that comes into contact with the lower mold 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 the part not being formed and becoming scrap. There is room for improvement.

[0089] Therefore, most preferably, the heated blank contacts the upper die and forming begins. The process is carried out so as to satisfy the above-mentioned relational expression 1 until the blank is placed. The time required from the time the mixture is mixed until molding 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 Heating is performed when the thickness of the plating layer is thin, and 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, and The thickness of the blank plating layer is 20μm 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 / 2 m or more. Preferably, the thickness may be 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 will be slowed down. 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, if the diffusion layer is too thick, When welding, large amounts of heat are generated locally, causing spatter. Therefore, the thickness of the diffusion layer is set to 15 μm. On the other hand, the diffusion layer of the molded member is an intermetallic layer of Fe and Al. The intermetallic compounds of Fe and Al include FeAl, Fe3Al, etc. In addition, it may further contain some of the components derived from the plating layer.

[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. If the thickness of the alloy layer of the formed part is less than 27 μm, the problem of insufficient corrosion resistance will arise. 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 the 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 formed member relative to the thickness of the alloy layer of the formed 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. If the thickness of the diffusion layer becomes too thick, spatter will be generated, resulting in poor weldability. This can prevent the above problem. [Example]

[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 present invention is not limited to the above embodiments, and is not intended to limit the scope of the present invention. It should be noted that the scope of the present invention is not limited to the scope of the claims. The matter is determined by the matters set out above and matters that can be reasonably inferred from them.

[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 Fe and other unavoidable impurities. 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 meet the conditions in Tables 1 and 2 below. It is heated in a heating furnace, transferred between the upper and lower dies of the mold, and then cooled and molded by placing it on the lower die. The hot press-formed parts were manufactured through the molding and removal steps. 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 using a thermocouple and is shown in the table below. The temperature maintained in each section is shown as the temperature maintained in each section. 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 moment the blank is fed in, the blank material is transferred from 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] On the other hand, 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℃> By utilizing the results of the calculation of the temperature of the material put into the heating furnace using the above interpretation method, The product is classified as follows according to the time it takes to reach 00°C first, and productivity is determined based on this. did.

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

[0099] <Weldability> Weldability is determined by the welding current range during resistance welding (the minimum current that can secure the minimum nugget diameter). 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 using 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 rate of defective products. The temperature was classified as follows, based on 50°C.

[0102] ○: When the blank temperature just before forming is 650°C 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, Invention Examples 1 and 2 have a shorter time to reach the final holding temperature. This has confirmed that the overall cycle time can be reduced. This confirmed that productivity would be further improved.

[0106] In addition, the heating conditions in the heating furnace according to the present invention, the lower die placement cooling conditions, and the relational expression 1 are all satisfied. In addition, it was confirmed that invention 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 above 930°C and below 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 more quickly. Although this effect is obtained, the final maintenance temperature is kept at a high temperature of 940°C, which results in poor weldability. there was.

[0109] In addition, as another method, we compared the method of placing the highest temperature, 940℃, at the very rear stage. In Example 3, it takes a long time to reach the final holding temperature, 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 ambient 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 time the B stage is finished, 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 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 below were changed. In addition, except for the evaluation of productivity using the following method, The characteristics were evaluated using the same criteria as in Experimental Example 1 above.

[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 ambient temperature of the set C section when removing the material ×: When removing the material, the temperature of the material did not reach the ambient temperature of the set C section. When an additional heating process is required to achieve 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). In Invention Examples 8 to 13 that satisfy below - 20°C, it was confirmed that the weldability is better than that of Invention Example 7 which does not satisfy this condition.

[0119] Also, in Invention Example 10 where the ambient temperature in the C section satisfies 870°C or more and less than 880°C, it was confirmed that the weldability is more improved compared to other invention examples.

[0120] In contrast, Comparative Examples 9 to 17 that do not satisfy one or more of the heating conditions in the above - mentioned heating furnace, the lower die placement cooling conditions, and Relational Expression 1 were confirmed to be inferior in one or more of productivity, weldability, and formability.

[0121] In particular, Comparative Examples 18 to 20 were confirmed to be inferior in formability compared to the invention examples because they do not satisfy the conditions of Relational Expression 1 mentioned above.

[0122] (Experimental Example 3) Hot - press - formed members were manufactured in the same manner as in Experimental Example 1 above, except that the conditions in Tables 5 and 6 below were changed. Also, the characteristics were evaluated based on the same criteria as in Experimental Example 1 above, except that the evaluation was carried out by the following method in relation to productivity.

[0123] <Whether there is a section where the temperature of the material is maintained in the B section> After the blank material is heated to the set maximum ambient temperature in the B section, it is classified as follows according to whether there is a time during which the temperature is maintained in the B section, and productivity is evaluated based on this. This is because in the B section, it is only necessary to achieve the effect of increasing the heating rate, and it is preferable not to maintain it for a long time in an unnecessarily high - temperature region.

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

[0125] [Table 5]

[0126] [Table 6]

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

[0128] In contrast, Comparative Examples 21 and 22, which do not satisfy the heating conditions in the heating furnace, have poor productivity. confirmed to be inferior.

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

[0130] <Whether or not the time has come for the diffusion layer to become 15 μm thick> 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 by classifying it as follows:

[0131] ○: The total cumulative maintenance time until the material is removed from the heating furnace is 1 If 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 5 μm 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, Comparative Example 23, which does not satisfy the heating conditions in the heating furnace, had poor productivity and weldability. It was confirmed that it was inferior to

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

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

[0138] (Experimental Example 5) The same method as in Experimental Example 4 was used except that the conditions in Tables 9 and 10 below were changed. Press-molded members were produced and their properties were evaluated using 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 plating layer of the blank is 20 μm or more, and the formed part The thickness of the diffusion layer of the molded part is 15 μm or less, the thickness of the alloy layer of the molded part is 27 to 50 μm, and the thickness of the plating of the part is 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 invention, which satisfies all of the following 33 points, 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 procedures as above were followed except that the hot press formed parts were manufactured to meet the conditions in Tables 11 to 13 below. A blank of 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 Experimental Example 1, and additionally evaluating the shape accuracy of the formed part. was measured.

[0143] <Whether 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, whether the temperature of the material has reached the removal temperature of the heating furnace or not 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 invention. Compared with Comparative Examples 25 and 26, which are not used, at least one of productivity and weldability is superior. was.

[0149] Furthermore, for the molded parts obtained from each of the invention examples and comparative examples, 10 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 normal required shape accuracy range of + / -0.5mm. The number of measurement points that met the criteria of + / -0.4 mm was counted. When evaluating the relative improvement effect of shape accuracy, Examples 20 to 22 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 bendability was evaluated by the following method. The characteristics were evaluated using the same criteria as in Experimental Example 3 described above.

[0151] <Bendability> The bendability is measured by a three-point bending test, measuring the bending angle when the maximum load is generated, 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 satisfied the above requirements, were excellent in productivity, weldability, and formability. If the thickness of the rank exceeds 1.5 mm and the temperature in the above section B exceeds 940°C, Inventive Example 24, 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 manufacturing a hot press-formed member, heating an aluminum-based plated steel sheet blank in a heating furnace; removing the heated blank from the heating furnace and transferring and placing it between an upper die and a lower die of a die attached to a press; a forming step in which forming is performed after the upper part of the mold contacts the placed blank, The heating furnace is a continuous heating furnace including sections A, B, and C arranged in order in a blank transport direction, The heating in the section A satisfies the conditions defined by the graph abcde having coordinates of cumulative furnace maintenance time and atmospheric temperature of about a (0.2 min, 750°C), b (1.0 min, 750°C), c (1.0 min, 800°C), d (1.5 min, 900°C), and e (0.2 min, 900°C), The heating in section B is [Equation 1] The conditions defined by the diagram fghi having coordinates of the cumulative furnace maintenance time and the atmospheric temperature are satisfied, The heating in the section C is [Equation 2] The conditions defined by the graph jklm having the coordinates of the cumulative furnace maintenance time and the atmospheric temperature are satisfied, and the maximum atmospheric temperature is lower than the maximum atmospheric temperature of the section B, The t represents the thickness of the blank (mm), When the t is 1.5 mm or less, the ambient temperature in the B section is greater than 930°C and less than 940°C; When the t exceeds 1.5 mm, the ambient temperature in the section B is greater than 940°C and less than 960°C; The thickness of the plating layer of the blank is 20 μm or more; A method for manufacturing a hot press formed part.

2. A method for manufacturing a hot press-formed part as described in claim 1, which satisfies the following relationship 1. [Relationship 1] T≦8.2×t+(temp-900) / 30 (The above T represents the sum of the time required for the steps of transferring and placing the blank and the time required from the time the blank is placed until the time before forming, and is expressed in seconds. The "temp" represents the temperature at which the sample is removed from the heating furnace, and is expressed in °C.

3. A method for manufacturing a hot press-formed part as described in claim 1, wherein the time required from when the blank is placed to when forming is performed is 2 seconds or less.

4. A method for manufacturing a hot press-formed part as described in claim 1, wherein heating in section C is carried out at an ambient temperature of 930°C or less.

5. A method for manufacturing a hot press-formed part as described in claim 1, wherein the maximum ambient temperature in section C is Tb-20°C or less, based on the maximum ambient temperature (Tb) in section B.

6. 2. The method for producing a hot-press-formed member according to claim 1, wherein t is 1.5 mm or less, and the atmospheric temperature in section C is 870°C or higher and lower than 880°C.

7. The method for producing a hot-press-formed member according to claim 1, wherein the t exceeds 1.5 mm and the atmospheric temperature in section C is 870°C or higher and lower than 900°C.

8. 2. The method for manufacturing a hot press-formed part according to claim 1, wherein the sum of the time required for the transporting and placing step and the time required from placing the blank to before forming exceeds 10 seconds.

9. The method for manufacturing a hot press-formed member according to claim 1, wherein the thickness of the plating layer of the blank is 25 μm or more.

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

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

12. The method for manufacturing a hot press-formed part according to claim 1 , wherein the heating step is performed so that the value of the following relational expression 2 satisfies 2 or more: [Equation 3] (In the above-mentioned relational formula 2, the T ｎ represents the furnace atmosphere temperature in the nth section in the blank transport direction, and is expressed in °C. ｎ represents the heating furnace maintenance time in the nth section in the blank transport direction, and is expressed in minutes. ｔｏｔａｌ represents the total maintenance time in the heating furnace, in minutes; x represents the number of sections maintained at a specific ambient temperature in the heating furnace; k is an integer of 3 if it is the final section among section B, an integer of -1 if it is a section after section B, and an integer of 1 otherwise; t represents the thickness of the blank, in mm.

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