A hot pressing treatment method for hot-formed steel tailor-welded parts

Abstract

A method for hot pressing treatment of hot-formed steel welded parts, comprising the following steps: placing the welded parts in a high temperature environment of 960 to 1060°C for 90 to 180 seconds, wherein the thicker the parts are, the higher the corresponding treatment temperature and the longer the treatment time. The parts are then placed in a mold for stamping and forming, and the time interval from the time the parts leave the high temperature environment to the time the parts are fully formed under the mold does not exceed 15 seconds. After the parts are fully formed, the mold continues to maintain the pressure for no less than 5 seconds. The welded parts obtained after hot pressing treatment in this way meet the performance requirements of hot-formed steel and welded joints.

Description

Technical Field

[0001] The invention belongs to the field of welding, and in particular relates to a hot pressing treatment method for hot-formed steel welded parts. Background Art

[0002] Hot-formed steel is a commonly used structural material in automobile manufacturing. It can achieve high strength of more than 1500MPa and is suitable for the processing and manufacturing of important structural parts such as A / B pillars, main longitudinal beams, door rings, etc. In the prior art, the hot pressing process of hot-formed steel usually requires the workpiece to be placed in a high temperature environment of 880-950°C for 4-8 minutes (the heating temperature and holding time vary depending on the size and thickness of the workpiece), and then quenched. In this process, in order to avoid oxidation of the steel surface at high temperatures, it is usually necessary to apply an aluminum-based coating to isolate the steel from the air, such as an aluminum-silicon coating. During the welding process, the aluminum element in the coating can easily invade the welding structure, forming a brittle phase and a ferrite structure, which affects the performance of the joint.

[0003] Since the aluminum-silicon coated hot-formed steel was proposed, the hot pressing process of hot-formed steel is aimed at the material itself, and the heat preservation temperature of the hot pressing treatment is not higher than 950℃, and the placement time is usually 5 to 8 minutes, such as disclosed in patent document 1CN101583486B; at the same time, for the laser welding of aluminum-silicon coated steel plates, the earliest patent document 2CN101426612B disclosed a method of welding after removing the coating around the welding part, and the hot pressing process of the material itself was used for the parts after welding. With the development of technology, it was found that the technology of removing the coating has problems such as incomplete removal affecting the welding quality and high welding gap requirements leading to unstable welding quality. Therefore, a new welding technology using fillers was proposed. The problem is that the laser welding parts using fillers also use the hot pressing process of the material itself. On the one hand, it is generally believed in the field that using higher temperatures will cause energy waste. Therefore, the hot pressing process of the material itself is used in actual production. However, the current temperature level requires a longer maintenance time. The lower the temperature, the longer the time. For example, Patent Document 1 maintains the temperature at 880℃~900℃ for 13 minutes, which obviously results in greater energy loss. Moreover, in laser welded parts, in order to ensure quality, the hot pressing process of thicker plates is usually used. This inevitably uses a relatively higher temperature and a longer processing time, which can easily cause excessive heat to the thinner plates in the welded parts, resulting in coarse matrix grains.

[0004] On the other hand, adding other solders to the weld joints to weaken or eliminate the adverse effects of aluminum elements in the coating is a process method with great prospects for the current use of aluminum-silicon coated hot-formed steel welding, such as laser wire welding. In the prior art, the hot pressing treatment of the welded parts manufactured using this method follows the hot pressing parameters of hot-formed steel, that is, the temperature is placed below 950°C for about 300s. The prior art does not take into account that the laser welding process is a process of rapid heating and cooling, which can easily cause element segregation in the weld area and no time for uniform diffusion. At temperatures below 950°C, a longer treatment time is also required to make the weld elements and structure more uniform.

[0005] The welded parts contain both hot-formed steel and welded seams. One of the keys to evaluating the quality of welded seams is to take tensile specimens from the welded joints after hot pressing treatment for testing. The tensile fracture position must not be in the weld, and the tensile strength and elongation at break of the joint must meet the use requirements (1500MPa-level hot-formed steel joints usually require tensile strength ≥1350MPa and elongation at break ≥5%). Summary of the invention

[0006] The object of the present invention is to provide a hot pressing treatment method for hot-formed steel welded parts. Taking into account the characteristics of filler solder welding technology, a heating temperature higher than that of the prior art is adopted to allow the weld elements to diffuse rapidly at a higher temperature, thereby achieving a welded joint that meets quality requirements within a shorter processing time than that of the prior art.

[0007] The hot pressing treatment method of the hot-formed steel tailor-welded parts of the present invention comprises the following steps:

[0008] 1) Move the welded parts into a high temperature environment of 960-1060°C, and after a period of time, move the welded parts out. The time interval from the time the welded parts are moved into the high temperature environment to the time they are moved out of the high temperature environment is t1, and the range of t1 is 90s-180s;

[0009] 2) placing the welded parts removed from the high temperature environment into a mold for hot forming, and then gradually fitting the mold to fully form the welded parts. The time from when the welded parts are removed from the high temperature environment to when the welded parts are fully formed is t2, and the range of t2 is 6 to 12 seconds;

[0010] 3) After the welded component is completely formed, the mold is kept in contact with a certain pressure for a period of time, the holding time is t3, and the range of t3 is 8 to 16 seconds; the average pressure acting on the surface of the welded component is 3 to 8 MPa.

[0011] In the solution of the present invention, the temperature of the high temperature environment and the time t1 during which the tailor-welded component is placed therein satisfy the following relationship with the thickness of the thicker plate in the tailor-welded component:

[0012] 1) When the plate thickness is not more than 1.4mm, at a temperature of 960℃ (time base 180s), t1 decreases by 12-15s for every 0.1mm decrease in plate thickness; when t1=90s (temperature base 1060℃), the temperature decreases by 12-15℃ for every 0.1mm decrease in plate thickness;

[0013] 2) When the plate thickness is not less than 1.5mm, when the temperature is 1060℃ (time base 90s), t1 increases by 4 to 6s for every 0.1mm increase in plate thickness; when t1=180s (temperature base 960℃), the temperature increases by 4 to 6℃ for every 0.1mm increase in plate thickness.

[0014] In one embodiment, after hot pressing, the weld seam of the welded component, compared with the higher strength hot-formed steel matrix in the welded component, contains the following positive increments of alloy elements in terms of mass percentage: 0.1% to 0.3% Cr, 0.8% to 1.6% Ni, 0.2% to 0.4% Mo, and 0.1% to 0.3% Cu.

[0015] In another embodiment, after hot pressing, the weld seam of the welded component, compared with the higher strength hot-formed steel matrix in the welded component, contains the following positive increments of V and the following negative increments of C in terms of mass percentage.

[0016] The surface of the hot-formed steel in the solution of the present invention has an aluminum or aluminum-based coating, the thickness of the coating without hot pressing treatment is not less than 20 microns, and the strength of the corresponding base material is not higher than 1900MPa.

[0017] In another embodiment, the surface of the hot-formed steel in the scheme of the present invention has an aluminum or aluminum-based coating, and the thickness of the coating without hot pressing treatment is not higher than 15 microns, or there is no aluminum or aluminum-based coating on the surface of the substrate, and the strength of the corresponding substrate material is not higher than 2100MPa.

[0018] In another embodiment, the filler solder of the present invention is a welding wire, and the alloy elements in the welding wire, measured in mass percentage, include: 0.12% to 0.4% C, 1.2% to 2.5% Cr, 1.5% to 2.5% Mo, 7% to 12% Ni, and 0.2 to 0.6% V.

[0019] After the hot pressing treatment, the tensile strength and elongation of the joint of the tailor-welded component reach more than 90% of the performance of the steel plate parent material after the hot pressing treatment, meeting the performance requirements of the tailor-welded component.

[0020] In addition to improving the performance of welded parts in a shorter time, the present invention also has the following technical effects: 1) the manufacturing efficiency of hot-formed steel welded parts is improved; 2) short-time processing helps to shorten the manufacturing cycle of the same production capacity and reduce overall energy consumption; 3) the welded parts have a higher temperature when removed from the high-temperature environment, which helps to reduce the pressure required for the hot forming process, thereby reducing the investment in press equipment or forming larger parts with the same tonnage of the press; 4) according to different thicknesses, a simple parameter estimation relationship is provided to facilitate the debugging of the hot pressing process in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 The temperature and time window diagram for hot-formed steel tailor-welded parts placed in a high temperature environment;

[0022] Figure 2 A schematic diagram of a treatment method for hot-formed steel welded parts placed in a high temperature environment;

[0023] Figure 3 Schematic diagram of the transfer from a high temperature environment to an unlaminated mold;

[0024] Figure 4 It is a schematic diagram of die fitting and stamping;

[0025] Figure 5 The following is a photo of the tensile fracture of a 1500MPa hot-formed steel joint punched using an embodiment of the present invention.

[0026] Notes in the figure: 1 is a hot-formed steel welded component, 2 is a high-temperature environment conveyor belt, 3 is a high-temperature environment heating and insulation device, and 4 is a stamping die.

[0027] The purpose of the above drawings is to describe the present invention in detail so that those skilled in the art can understand the technical concept of the present invention, but it is not intended to limit the present invention. DETAILED DESCRIPTION

[0028] The present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings.

[0029] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The phrase appearing in various locations in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive independent or alternative embodiments. Those skilled in the art should be able to understand that the embodiments herein may be combined with other embodiments without causing structural conflicts.

[0030] like Figure 2As shown, a hot-formed steel tailor-welded component 1 with a single or multi-pass tailor-welded seam is placed on a high-temperature conveyor belt 2 and enters a high-temperature environment heating and heat preservation device 3. The temperature range of the high-temperature environment is between 960°C and 1060°C. The component 1 is removed from the high-temperature environment after a certain period of time due to the movement of the conveyor belt 2. The time from entering the high-temperature environment to removing from the high-temperature environment is t1, and the range of t1 is 90 to 180s. The component 1 removed from the high-temperature environment is transferred to Figure 3 On the stamping die 4 shown, the transfer time t2 ranges from 3 to 15 seconds. Thereafter, the stamping die is pressed down and fits with the component 1, as shown in FIG. Figure 4 As shown. The time t3 from the transfer of component 1 to the stamping die to the bonding of the stamping die is in the range of 2 to 6 seconds. After the stamping die 4 is bonded, pressure is generated on the surface of component 1, that is, the pressure acting on the unit area of ​​the surface of component 1 is in the range of 3 to 10 MPa. The time t4 for the bonded stamping die to maintain pressure is in the range of 7 to 16 seconds. After that, component 1 is taken out, and the welded component that has completed the hot pressing treatment is obtained, and both the weld and the base material meet the use requirements.

[0031] In a preferred embodiment, the temperature and time of the component 1 placed in the high temperature environment form a recommended window: 960℃+90s, 960℃+180s, 1060℃+90s, 1060℃+180s. The thicker the thicker plate in component 1, the higher the recommended temperature and the longer the corresponding placement time. In the recommended parameter selection, when the plate thickness is not more than 1.4mm (thin plate combination), when the temperature is 960℃ (time base 180s), t1 decreases by 12-15s for every 0.1mm reduction in plate thickness; when t1=90s (temperature base 1060℃), the temperature decreases by 12-15℃ for every 0.1mm reduction in plate thickness. When the plate thickness is not less than 1.5mm (thick plate combination), when the temperature is 1060℃ (time base 90s), t1 increases by 4 to 6s for every 0.1mm increase in plate thickness; when t1=180s (temperature base 960℃), the temperature increases by 4 to 6℃ for every 0.1mm increase in plate thickness.

[0032] In another embodiment, the hot-formed steel tailor-welded component 1 is composed of a plurality of steel plates with aluminum-silicon coatings on the surface connected by a tailor-welded seam, the thickness of the coating is not less than 20 microns, and the tailor-welded seam is obtained by a laser wire welding method. After the above-mentioned hot pressing process, the tailor-welded seam of the tailor-welded component is compared with the hot-formed steel matrix with higher strength in the tailor-welded component, and the alloy elements contained in the tailor-welded seam are calculated by mass percentage, and the following positive increments are produced: 0.1% to 0.3% Cr, 0.8% to 1.6% Ni, 0.2% to 0.4% Mo, 0.1% to 0.3% Cu. The corresponding strength of the stronger steel plate matrix is ​​not less than 1500MPa, and the welded component joint sampling tensile fracture is in the parent material.

[0033] In another embodiment, after the hot pressing treatment, the welded seam of the welded component 1, compared with the higher strength hot-formed steel matrix in the welded component, contains the following positive increments of V and the following negative increments of C in terms of mass percentage.

[0034] In another embodiment, the welded component 1 is composed of multiple steel plates with aluminum-silicon coating on the surface connected by welded seams, the thickness of the coating is not more than 15 microns, the matrix strength of the stronger steel plate reaches 2000MPa after hot pressing treatment, and the welded component joint sampling tensile fracture is in the base material.

[0035] Example test data: The welded parts are placed in a heating furnace. After a certain high temperature and placement time, they are removed and hot pressed. The weld joint tensile specimens are tested to obtain tensile strength and elongation data. The test results are shown in Table 1. The photo of the tensile fracture specimen is shown in Figure 5 shown.

[0036] Table 1

[0037]

[0038] In industry applications, 1500MPa-level hot-formed steel butt welded joints are usually required to have a tensile strength of ≥1350MPa and an elongation at break of ≥5%. As shown in Table 1, the technical solution of the present invention can be used to obtain a butt welded joint that meets the requirements. At the same time, Samples 2 and 6 in Table 1 provide treatment solutions that exceed the time range, and their performance can meet the requirements, but the elongation is relatively low. It can be seen that the range given by the present invention is a preferred range.

[0039] The purpose of the above embodiments is to further explain the present invention in detail in conjunction with the accompanying drawings so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the claims of the present invention, the optimization or equivalent replacement of the components or methods involved, and the combination of implementation methods in different embodiments without conflict of principle, all fall within the protection scope of the present invention.

Claims

1. A method for hot pressing a hot-formed steel tailor-welded component, comprising the following steps: Laser welding is performed on the hot-formed steel before hot pressing treatment, and a filler solder is added to obtain a welded component having at least one weld seam; the filler solder is a welding wire, and the alloy elements in the welding wire, measured by mass percentage, include: 0.12% to 0.4% C, 1.2% to 2.5% Cr, 1.5% to 2.5% Mo, 7% to 12% Ni, and 0.2% to 0.6% V; The tailor-welded parts are subjected to hot pressing treatment, including: 1) Move the welded parts into a high temperature environment, and after a period of time, move the welded parts out. The time interval between moving the welded parts into the high temperature environment and moving them out of the high temperature environment is t1. The temperature of the high temperature environment is 960-1060°C, and the range of t1 is 90s-180s. 2) The welded parts removed from the high temperature environment are placed in a mold for hot forming, and then the mold is gradually fitted to fully form the welded parts; 3) After the welded parts are fully formed, the mold is kept in contact with each other at a certain pressure for a period of time, and then the mold is opened to take out the welded parts; After hot pressing, the weld seam of the welded component, compared with the higher-strength hot-formed steel matrix in the welded component, contains the following positive increases in alloy elements, measured in mass percentage: 0.1%-0.3% Cr, 0.8%-1.6% Ni, 0.2%-0.4% Mo, and 0.1%-0.3% Cu.

2. The hot pressing treatment method of hot-formed steel tailor-welded parts according to claim 1, characterized in that: The time range from removing the welded parts from the high temperature environment to fully forming the welded parts is 6 to 12 seconds. The time range for the mold to maintain pressure after the welded parts are fully formed is 8 to 16 seconds. The average pressure acting on the surface of the welded parts is 3 to 8 MPa.

3. The hot pressing treatment method of hot-formed steel tailor-welded parts according to claim 1, characterized in that: The temperature of the high temperature environment, the time t1 for placing the tailor-welded component therein, and the thickness of the thicker plate in the tailor-welded component satisfy the following relationship: 1) When the plate thickness is not more than 1.4mm, at a temperature of 960℃ and a time base of 180s, t1 decreases by 12~15s for every 0.1mm decrease in plate thickness; when t1=90s and a temperature base of 1060℃, the temperature decreases by 12~15℃ for every 0.1mm decrease in plate thickness; 2) When the plate thickness is not less than 1.5mm, when the temperature is 1060℃ and the time base is 90s, t1 increases by 4~6s for every 0.1mm increase in plate thickness; when t1=180s and the temperature base is 960℃, the temperature increases by 4~6℃ for every 0.1mm increase in plate thickness.

4. The hot pressing treatment method of hot-formed steel tailor-welded parts according to claim 3, characterized in that: After hot pressing, the weld seam of the welded component, compared with the higher-strength hot-formed steel matrix in the welded component, contains the following positive increments of V by mass% and the following negative increments of C by mass% by mass%.

5. The hot pressing treatment method of hot-formed steel tailor-welded parts according to claim 1, characterized in that: The surface of the hot-formed steel has an aluminum or aluminum-based coating, the thickness of the coating without hot pressing treatment is not less than 20 microns, and the strength of the corresponding base material is not higher than 1900 MPa.

6. The hot pressing treatment method of hot-formed steel tailor-welded parts according to claim 1, characterized in that: The surface of the hot-formed steel has aluminum or aluminum-based coating, and the thickness of the coating without hot pressing treatment is not higher than 15 microns, or the substrate surface has no aluminum or aluminum-based coating, and the strength of the corresponding substrate material is not higher than 2100MPa.

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