Method for improving performance of butt-welded joint of high-strength rim steel

Abstract

The invention discloses a method for improving the performance of a high-strength rim steel butt-welded joint, which comprises the following steps of: 100, circling a strip-shaped plate, and then carrying out flash butt welding or resistance butt welding to form a cylindrical rim prefabricated blank with a butt-welded joint; 200, the barrel-shaped rim prefabricated blank is rapidly transferred to a slag scraping station so as to scrape metal extruded out of a welding head in the welding process; 300, the cylindrical rim prefabricated blank is directly transferred to a cooling station without rolling after slag scraping, so that a welding head is rapidly cooled; and 400, the upper surface and the lower surface of the butt welding head are polished on a polishing station. By adopting the method disclosed by the invention, surface defects caused by rolling can be eliminated, necking cracking of the joint in flaring and sizing can be eliminated or inhibited, and various losses caused by small-crack repair welding and large-crack scrapping caused by necking cracking are reduced, so that the final purposes of improving the production efficiency and reducing the production cost are achieved.

Description

Technical Field

[0001] The invention relates to a rim production method, in particular to a rim production method based on flash butt welding and resistance butt welding. Background Art

[0002] Flash butt welding and resistance butt welding have fast welding speed and high production efficiency, but they are both welding methods with large heat input. The thermal cycle during the welding process is complex, and the heat-affected zone is more than ten millimeters, which is much higher than general arc welding and laser welding.

[0003] High-strength wheel rim steel is usually a steel with C-Si-Mn as the main component or other similar component systems. The fracture strength is generally above 500MPa, and the performance requirements are achieved through fine grain strengthening, two-phase strengthening, solid solution strengthening or precipitation strengthening.

[0004] However, high-strength wheel rim steel is particularly sensitive to large heat input and complex thermal cycles, and joint softening is very likely to occur. The softening zone cannot coordinate deformation with the parent material during the subsequent expansion and sizing process. When the deformation is concentrated in the softening zone, the deformation of the softening zone is too large, and necking cracking will occur in this area. In particular, when the cooling speed of the joint after welding is slow, some tempering structures are also prone to appear, which further aggravates the softening of some areas of the joint and ultimately leads to necking cracking of the joint during expansion and sizing.

[0005] In addition, in the process of making rims, the slab blank generally needs to be flash or resistance welded to form a cylindrical shape after the rounding process, and then the welded joint is scraped and rolled, and then enters the expansion, rolling, sizing, and valve hole opening processes to prepare a finished rim. Among them, the rolling process is an important process in the production of rims. The thickness of the joint after scraping is usually greater than the thickness of the parent material, that is, excess height is generated. The thickness of the joint can be reduced by rolling, and the rolling deformation can also produce work hardening to improve the hardness and strength of the weld; the steel roller can also absorb part of the heat of the weld while rolling over the weld to reduce the temperature of the joint. However, due to the large thickness of the large wheel material, more metal is extruded after flash and resistance welding, and the residual welding slag and burrs after scraping are also more than those of small wheels. For many large commercial vehicle rim production lines that only have a rolling process between scraping and expanding, these burrs and welding slag will be rolled into the joint or the surface of the parent material after rolling to form surface quality defects.

[0006] If a grinding process is introduced to replace the rolling process, the burrs, weld excess height and welding slag can indeed be ground off together, eliminating the surface defects caused by the burrs and welding slag pressing into the joint and the base material, but it will also bring the following problems: the butt weld joint loses the possibility of improving strength through work hardening; the weld temperature is very high after scraping the slag, and grinding also has an adverse effect on the temperature reduction, which ultimately leads to a very high temperature when the joint is expanded, and the mechanical properties of the joint are reduced due to the high temperature; the high joint temperature and slow cooling rate can easily lead to softening of the joint structure, and excessive deformation in the softening zone during sizing can more easily cause necking and cracking; in order to reduce the softening of the joint and increase the cooling rate of the joint, the heat input has to be reduced as much as possible, resulting in a narrowing of the welding process range and prone to problems such as unwelded joints.

[0007] Due to the above-mentioned problems, for rim production lines that only have a grinding process between scraping and flaring, when producing high-strength rim steel materials, the joints are very likely to suffer from necking and cracking due to temperature, strength and thickness, which greatly increases the scrap rate and repair welding costs. Summary of the invention

[0008] The object of the present invention is to provide a method for improving the performance of high-strength rim steel butt weld joints. Different from the conventional rim manufacturing method, the method does not perform a rolling process between the scraping and expanding processes, but instead uses a rapid cooling + grinding process to replace the original rolling process, so as to ultimately improve the joint strength and suppress the risk of necking cracking during expansion and sizing of the joint.

[0009] In order to achieve the above object, the present invention provides a method for improving the performance of a high-strength wheel rim steel butt weld joint, which comprises the steps of:

[0010] 100: After the strip plate is circled, flash butt welding or resistance butt welding is performed to form a cylindrical rim prefabricated blank having a butt welding joint;

[0011] 200: quickly transferring the cylindrical rim preform to the scraping station to scrape off the metal extruded from the butt welding joint during the welding process;

[0012] 300: After scraping off the slag, the cylindrical rim preform is directly transferred to the cooling station without rolling, so as to quickly cool the butt welding joint;

[0013] 400: Grind the upper and lower surfaces of the butt weld joint at the grinding station.

[0014] During the manufacturing process of the rim, when flash butt welding or resistance butt welding is performed, the heat input is very large because part of the molten metal needs to be burned and squeezed out. After welding, the temperature of the joint part is above 800℃, and the entire rim can also reach above 200℃. It takes dozens of minutes for the whole to naturally cool to room temperature. However, there is no pause between the existing post-welding processes, and the joint temperature can still reach 300℃~400℃ after scraping + grinding or scraping + rolling. At this time, when entering the expansion process, the temperature of the joint part must be 200℃~300℃ higher than the parent material. This results in a coarse structure in the joint, and the joint temperature is still higher than the parent material. Its tensile strength, yield strength, and elongation will be lower than the parent material. Therefore, it is easy to cause necking and cracking in the joint part during expansion.

[0015] In addition, in the subsequent rolling process, even if the temperature of the joint continues to drop due to the effect of the coolant, the temperature will be lower than 100°C during sizing. However, the heat treatment system and strengthening mechanism of high-strength rim steel are complex during the production process. During the long cooling process of more than ten minutes after welding, the coarse grains and subcritical heat-affected zones of the joint are very easy to soften. The strength of this area is low during sizing and it cannot coordinate deformation with the base material. All deformations are concentrated in this area, which eventually leads to necking cracking.

[0016] In addition, if only the rolling process is used between scraping and flaring, the burrs and welding slag remaining after scraping will be rolled into the joint or the base material to form surface quality defects.

[0017] Based on this, the present invention adopts a rapid cooling process to quickly cool the temperature of the joint part to room temperature, so as to prevent the temperature of the joint from being too high when entering the expansion process, and the tensile strength and yield strength from being too low, which will cause necking and cracking during the expansion process. The use of the rapid cooling process will greatly reduce the time for the joint to cool to room temperature, and can inhibit the tempering softening structure in some areas of the joint due to the tempering effect during the long cooling process, thereby preventing deformation from being concentrated in these softened areas during the expansion and sizing process, and eventually causing necking and cracking.

[0018] The grinding process after rapid cooling can completely remove the excess height, welding slag and burrs of the joint after scraping, so as to improve the surface quality of the joint.

[0019] Furthermore, in the method for improving the performance of a high-strength rim steel butt-weld joint of the present invention, the thickness of the butt-weld joint is 2 to 15 mm.

[0020] Furthermore, in the method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention, the total time required to complete step 200 is controlled to be 3 to 30 seconds.

[0021] Furthermore, in the method for improving the performance of high-strength rim steel butt-welded joints of the present invention, in step 300, the time for transferring the rim preform to the cooling station is controlled to be 3 to 20 seconds.

[0022] Furthermore, in the method for improving the performance of high-strength rim steel butt weld joints of the present invention, in step 300, a plurality of spray holes arranged in a matrix are used to spray cooling medium onto the upper and lower surfaces of the butt weld joint for rapid cooling.

[0023] Furthermore, in the method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention, in step 400, a cooling medium is used during grinding.

[0024] Furthermore, in the method for improving the performance of high-strength rim steel butt weld joints of the present invention, after step 400, the method further includes: step 500: expanding the cylindrical rim preform; and step 600: rolling, sizing and valve opening.

[0025] Furthermore, in the method for improving the performance of high-strength wheel rim steel butt weld joints described in the present invention, the tensile strength of the strip plate is 500 to 1300 MPa.

[0026] The composition weight percentage of the strips may include: C: 0.05% to 0.5%, Mn: 0.01% to 25%, Si: 0.1% to 5%.

[0027] Furthermore, in the method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention, in step 300, the rapid cooling rate is controlled to be 50-500°C / s.

[0028] Furthermore, the rapid cooling rate is controlled to be 100-500°C / s.

[0029] Furthermore, in the method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention, in step 300, the rapid cooling time is 2 to 10 seconds.

[0030] The rapid cooling step of the present invention only cools the butt-welded joint portion. In some embodiments, the cooling medium is sprayed on the upper and lower surfaces of the joint simultaneously, and the cooling of the joint portion with a thickness of 2 to 15 mm can be completed within 2 to 10 seconds without affecting the production cycle.

[0031] The method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention has the following advantages and beneficial effects:

[0032] By adopting the method of the present invention, the hardness and tensile strength of the butt welding joint are increased, and the temperature is rapidly reduced to room temperature or lower. When the rim prefabricated blank is expanded or sized, the joint does not have necking cracks or the necking crack ratio is reduced, and the rim surface has no surface defects caused by welding slag, burrs, excess height, etc.

[0033] The present invention prepares the rim by adopting a method of rapid cooling + grinding process between the scraping and flaring steps, which is better than a process using only a rolling step in improving the mechanical properties and surface quality of the rim joint, and is better than a process using only a grinding step in improving the mechanical properties of the joint.

[0034] By adopting the method described in the present invention, surface defects caused by rolling can be eliminated, necking cracking of the joint during expansion and sizing can be eliminated or suppressed, and losses caused by various small crack repair welding and large crack scrapping caused by necking cracking can be reduced, thereby achieving the ultimate goal of improving production efficiency and reducing production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A flow chart showing the steps of a method for improving the performance of a high-strength wheel rim steel butt weld joint according to an embodiment of the present invention is shown.

[0036] Figure 2 The hardness distribution curves of the joints obtained in Example 1, Comparative Example 1 and Comparative Example 2 are shown.

[0037] Figure 3 The hardness distribution curves of the joints obtained in Example 2 and Comparative Example 3 are shown. DETAILED DESCRIPTION

[0038] The method for improving the performance of high-strength wheel rim steel butt weld joints described in the present invention will be further explained and illustrated below in conjunction with specific embodiments and drawings of the specification. However, such explanation and illustration do not constitute an improper limitation on the technical solution of the present invention.

[0039] Figure 1 A flow chart showing the steps of a method for improving the performance of a high-strength wheel rim steel butt weld joint according to an embodiment of the present invention is shown.

[0040] like Figure 1 As shown, in this embodiment, the method for improving the performance of high-strength wheel rim steel butt weld joints of the present invention comprises the steps of:

[0041] 100: After the strip plate is circled, flash butt welding or resistance butt welding is performed to form a cylindrical rim prefabricated blank having a butt welding joint;

[0042] 200: quickly transferring the cylindrical rim preform to the scraping station to scrape off the metal extruded from the butt welding joint during the welding process;

[0043] 300: After scraping off the slag, the cylindrical rim preform is directly transferred to the cooling station without rolling, so as to quickly cool the butt welding joint at a cooling rate of 50 to 500°C / s. The cooling medium can be water, and the time to complete the cooling is 2 to 10 seconds;

[0044] 400: Grind the upper and lower surfaces of the butt weld joint at the grinding station. Use cooling medium during grinding. After grinding, the residual welding slag, burrs and excess height on the surface of the butt weld joint after scraping are all polished off, revealing a bright white metal surface. The surface defects that may be caused by welding slag, burrs and excess height are completely eliminated.

[0045] 500: expanding the cylindrical rim prefabricated blank;

[0046] 600: Roll forming, sizing and valve opening.

[0047] In some embodiments, a rapid cooling device may be used to rapidly cool the butt weld joint. The rapid cooling device may be disposed on a fixed base or a robot through a clamp frame, and the rapid cooling device may include an upper clamp, a lower clamp, an upper clamp cooling nozzle, a lower clamp cooling nozzle, a cooling medium recovery box, an infrared temperature probe, a clamp action servo motor and controller and a clamp frame, a cooling medium pipeline, a cooling medium flow measurement and control device, a cooling medium container, and a cooling medium pressure pump.

[0048] The upper clamp and the lower clamp can be arranged on the clamp frame and can move along the clamp frame to clamp cylindrical rim prefabricated blanks of different thicknesses and widths. The pressure and movement of the upper and lower clamps can be controlled by the clamp movement servo motor and controller.

[0049] The upper and lower clamps are respectively provided with upper and lower clamp cooling nozzles. During the rapid cooling process, these cooling nozzles simultaneously spray cooling medium, such as water, on the upper and lower surfaces of the butt weld joint to achieve rapid cooling. The upper and lower clamp cooling nozzles are each provided with multiple spray holes, which are arranged in a matrix and evenly distributed on the upper and lower clamps.

[0050] In a more specific example, a nozzle with a width of 50 mm can be set on the upper and lower clamps to cool the 50 mm width range of the butt welding joint. The nozzle spacing can be 6 to 10 mm, the nozzle angle can be 5° to 45°, and the nozzle diameter can be 0.5 to 10 mm.

[0051] The cooling medium recovery box may be located below the lower clamp, and the upper and lower clamps are connected to the cooling medium recovery box.

[0052] In order to measure the surface temperature of the butt welding joint, an infrared temperature probe can also be set on the upper clamp or the lower clamp. The cooling medium flow measurement and control device is connected to the cooling medium pressure pump, and the flow rate and flow velocity of the cooling medium can be adjusted by controlling the cooling medium pressure pump, and the cooling speed can be controlled based on the temperature data fed back by the infrared temperature probe.

[0053] The present invention uses Examples 1-6 and Comparative Examples 1-3 to verify the implementation effect of the present invention.

[0054] The strip plates of Examples 1-3 and Comparative Examples 1-2 are made of B650CL hot-rolled plates, the parent material structure is mainly ferrite and a small amount of pearlite, the tensile strength is 650MPa, and the mass percentage of each component is: C: 0.056%, Si: 0.099%, Mn: 1.67%, P: 0.01%, S: 0.001%, and the balance is Fe and other unavoidable impurities.

[0055] In Example 1-3 and Comparative Example 1-2, in step 100, the strip plate is firstly rounded by a rounding machine, and then the two ends of the rounded strip are flash butt welded to form a cylindrical rim preform. The flash butt welding adopts a pulsating flash butt welding machine, with a preheating current of 200A (primary current), a preheating distance of 3.5mm, a burning amount of 4.0mm, an upsetting charging time of 0.2s, and an upsetting distance of 3.5mm.

[0056] The strip plates of Examples 4-6 and Comparative Example 3 all adopt B780CL hot-rolled plates. The parent material structure is mainly ferrite, bainite and martensite, and the tensile strength is 750 MPa. The mass percentage of each component is: C: 0.12%, Si: 0.3%, Mn: 0.2%, P: 0.02%, S: 0.005%, Als: 0.015%, and the balance is Fe and other inevitable impurities.

[0057] In Example 4-6 and Comparative Example 3, in step 100, the strip plate is first rounded with a rounding machine, and then the two ends of the rounded strip are resistance-welded to form a cylindrical blank. In Example 4, the preheating current is 200kA, the welding current is 300kA, the preheating time is 2s, the welding time is 2s, and the upsetting charging time is 0.5s; in Example 5, the preheating current is 100kA, the welding current is 200kA, the preheating time is 0.5s, the welding time is 0.7s, and the upsetting charging time is 0.2s; in Example 6, the preheating current is 400kA, the welding current is 800kA, the preheating time is 2.5s, the welding time is 4s, and the upsetting charging time is 1s.

[0058] Comparative Example 1 does not adopt the rapid cooling step 300 and the grinding step 400, and only has a rolling step between step 200 and step 500, and the remaining steps are the same as those of Example 1.

[0059] Comparative Example 2 does not adopt the rapid cooling step 300, and there is only a grinding step between step 200 and step 500, and the remaining steps are the same as those of Example 1.

[0060] Comparative Example 3 does not adopt the rapid cooling step 300, and there is only a grinding step between step 200 and step 500, and the remaining steps are the same as those of Example 2.

[0061] Table 1 lists the specific process parameters in each step of Examples 1-6 of the present invention and Comparative Examples 1-3.

[0062] Table 1.

[0063]

[0064] Table 2 lists the surface temperatures of the butt weld joints when entering the expansion step and the proportion of necking cracking occurring in the expansion and sizing steps of Examples 1-6 of the present invention and Comparative Examples 1-3.

[0065]

[0066]

[0067] Note: The data in Table 2 are the average surface temperature and the statistical results of the sizing necking cracking rate of 1000 samples produced in each embodiment and comparative example.

[0068] It can be seen from Table 2 that in the process of producing rims, the use of a rapid cooling step can significantly reduce the temperature of the butt weld joint before entering the expansion process, and the cracking ratio in the subsequent expansion and necking step can be greatly reduced.

[0069] In addition, the cross-sectional metallographic hardness test of the butt welded joints of the rim preforms after grinding in Example 1, Comparative Example 1 and Comparative Example 2 was performed. Figure 2 The hardness distribution curve is shown. Figure 2 It can be seen that the joint hardness of Example 1 is the highest overall, followed by Comparative Example 1, and the lowest is Comparative Example 2. This phenomenon shows that the rapid cooling + grinding process can effectively reduce the softening of the joint area caused by the long cooling time of the joint, and can effectively inhibit the necking cracking of the joint during the expansion and sizing process.

[0070] The cross-sectional metallographic hardness test of the butt welded joints of the rim preforms after grinding in Example 2 and Comparative Example 3 was performed. Figure 3 The hardness distribution curve is shown. Figure 3 It can be seen that the overall hardness of the butt weld joint of Example 2 is significantly higher than that of Comparative Example 3. This phenomenon shows that the rapid cooling + grinding process can effectively reduce the softening of the joint area caused by the long cooling time of the joint, thereby effectively reducing the necking cracking of the joint during the expansion and sizing process.

[0071] It should be noted that the combination of the various technical features in this case is not limited to the combination described in the claims of this case or the combination described in the specific embodiments. All technical features recorded in this case can be freely combined or combined in any way unless there is a contradiction between them.

[0072] It should also be noted that the above-listed embodiments are only specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made therewith can be directly derived or easily associated with the contents disclosed by those skilled in the art from the present invention, and all should belong to the protection scope of the present invention.

Claims

1. A method for improving the performance of high-strength rim steel butt weld joints, characterized in that: Includes steps: 100: After the strip plate is circled, flash butt welding or resistance butt welding is performed to form a cylindrical rim prefabricated blank having a butt welding joint; 200: quickly transferring the cylindrical rim preform to the scraping station to scrape off the metal extruded from the butt welding joint during the welding process; 300: After scraping off the slag, the cylindrical rim preform is directly transferred to the cooling station without rolling, so as to quickly cool the butt welding joint; 400: Grind the upper and lower surfaces of the butt weld joint at the grinding station.

2. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: The thickness of the butt welding joint is 2 to 15 mm.

3. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: The total time to complete step 200 is controlled to be 3 to 30 seconds.

4. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: In step 300, the time for transferring the rim preform to the cooling station is controlled to be 3 to 20 seconds.

5. The method for improving the performance of high-strength wheel rim steel butt weld joints according to claim 1, characterized in that: In step 300, a plurality of spray holes arranged in a matrix are used to spray cooling medium onto the upper and lower surfaces of the butt welding joint for rapid cooling.

6. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: In step 400, a cooling medium is used during grinding.

7. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: After step 400, the following steps are included: step 500: expanding the cylindrical rim preform; and step 600: rolling, sizing and valve opening.

8. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: The tensile strength of the strip plate is 500-1300 MPa.

9. The method for improving the performance of high-strength wheel rim steel butt weld joints according to any one of claims 1 to 8, characterized in that: In step 300, the rapid cooling rate is controlled to be 50-500°C / s.

10. The method for improving the performance of high-strength rim steel butt weld joints according to claim 9, characterized in that: In step 300, the rapid cooling rate is controlled to be 100-500°C / s.

11. The method for improving the performance of high-strength rim steel butt weld joints according to claim 1, characterized in that: In step 300, the rapid cooling time is 2 to 10 seconds.

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