Method for reducing welding deformation and residual stress of ultra-high strength steel plate

Abstract

The present application relates to a kind of method for reducing ultra-high strength steel plate welding deformation and residual stress, including the cleaning, polishing and beveling treatment of the ultra-high strength steel plate to be welded;After treatment, steel plate is clamped using fixture, two end point welding is fixed, laser-MAG welding parameter is set;With the aid of ultrasonic treatment cover face weld two sides weld toe long position and weld surface, and the plate is naturally cooled.The present application effectively reduces welding deformation and residual stress;Method implementation is simple, and applicability is extensive;Avoid the problem that ultra-high strength steel plate postweld distortion is too large when one weld is formed, at the same time, preheating process is saved, and welding production efficiency is improved;By using ultrasonic stress relief means instead of postweld heat treatment stage, the residual stress of plate is greatly eliminated;Improve working condition adaptability;Weld toe surface indentation deformation caused by ultrasonic treatment only occurs on the surface, improves the structural reliability, and after ultrasonic treatment, the surface hardness of plate is also greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of ultra-high strength steel plate welding technology, specifically relating to a method for reducing welding deformation and residual stress in ultra-high strength steel medium and thick plates, applicable to the welding of ultra-high strength steel medium and rear plates. Background Technology

[0002] With the rapid development of steel smelting and hot rolling processes, the strength of produced steel grades has continuously improved. The production technology for steel grades with tensile strength exceeding 1700 MPa is becoming increasingly mature, showing broad application prospects in aerospace, petroleum protection, and military industries. Ultra-high-strength steel is characterized by high strength and low plasticity, making it highly sensitive to welding heat. Secondly, the heat input generated during welding causes thermal expansion and contraction of the steel, leading to shape changes. Finally, the material properties of ultra-high-strength steel and the uneven temperature distribution during welding exacerbate deformation and residual stress. To address these issues, existing technologies employ preheating and post-heat treatment to regulate the material's microstructure and temperature distribution, reduce heat input by controlling welding parameters and processes, and utilize welding equipment and fixtures to constrain deformation.

[0003] Preheating, a commonly used process in welding ultra-high-strength steel plates, is essential for controlling microstructure changes, reducing cold cracking sensitivity and brittle fracture risk during welding, alleviating residual stress, ensuring a uniform high-temperature state across the entire plate, controlling deformation, and improving the material's plasticity and ductility. Combined with post-weld treatment, preheating can significantly improve weld quality and reliability, reduce stress concentration and hot cracking risks during welding, and minimize welding defects.

[0004] In the welding of ultra-high strength steel medium-thick plates, the welding process was improved by setting up a pre-weld bead to serve a preheating function. The pre-weld bead, through the heat input of the welding arc, raises the temperature of the welding area. By rationally controlling the position and welding parameters of the pre-weld bead, local preheating of the steel plate can be achieved, reducing the temperature gradient and thermal stress during welding. Furthermore, the pre-weld bead eliminates the need for a preheating step in ultra-high strength steel welding, improving welding efficiency. In addition, using ultrasonic stress relief treatment instead of post-weld heat treatment improves adaptability to working conditions and saves processing time. Ultrasonic stress relief treatment is faster, more efficient, and more precise, and avoids the uncontrollable microstructural changes caused by heat treatment. The compressive stress generated by ultrasonic treatment increases the deformation allowance of the welded structure, further improving its reliability and stability.

[0005] Therefore, there is an urgent need to develop a method to reduce welding deformation and residual stress in ultra-high strength steel medium and thick plates, in order to solve the problems of preheating leading to grain growth in the base material and high post-weld stress levels and welding deformation in the welding of ultra-high strength steel medium and thick plates. Summary of the Invention

[0006] The purpose of this invention is to provide a method for reducing welding deformation and residual stress in ultra-high strength steel medium-thick plates, in order to solve the problems of high post-weld deformation and residual stress levels caused by changes in the microstructure of the ultra-high strength steel base material due to material properties and welding heat input, as well as excessive differences in post-weld temperature distribution.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] A method for reducing welding deformation and residual stress in ultra-high strength steel medium-thick plates includes the following steps:

[0009] S1. Clean, grind and bevel the ultra-high strength steel plates to be welded.

[0010] S2. Clamp the steel plate processed in step S1 using a fixture, and spot weld it at both ends; set the laser-MAG welding parameters:

[0011] Pre-welding parameters settings: control laser power 2.5~3.5kw, laser incident angle perpendicular to the weld; control MAG welding current 75~90A, welding voltage 19~21V, welding wire tip pointing to the laser focus on the plate, wire feed speed 100~200cm / min; control welding speed 300~500mm / min.

[0012] Cover welding parameter settings: control laser power 3.0~4.5kw, laser incident angle perpendicular to the weld; control MAG welding current 100~120A, welding voltage 21~24V, welding wire tip pointing to the laser focus on the plate, wire feed speed 150~300cm / min; control welding speed 250~400mm / min.

[0013] S3. Use ultrasonic treatment to treat the narrow, elongated areas with a weld toe width of 2-3 mm on both sides of the cover weld bead and the weld surface, and wait for the plate to cool naturally.

[0014] Further, in step S1, the strength of the ultra-high strength steel plate is >1800MPa, and the plate thickness is 4.5~6mm.

[0015] Furthermore, the bevel is a double-sided V-shape, and the inner surface of the two sides of the bevel within 20mm is ground to expose the metal surface, and rust and oil stains within 50mm of the area to be welded are removed.

[0016] Furthermore, a double-sided V-shaped bevel is made with a bevel angle of 25 to 35 degrees.

[0017] Further, in step S2, the number of welding passes is at least two, and the number of preceding weld passes is at least one.

[0018] Furthermore, when the number of pre-weld passes is ≥2, the cooling interval should be controlled to be less than 20 minutes, and the plate temperature should not be less than 200℃.

[0019] Further, in step S2, the welding wire is ER120S-G high-strength steel welding wire with a diameter of 1.2 to 1.6 mm.

[0020] Further, in step S3, the diameter of the impact head in the ultrasonic treatment is 2-3 mm, and the ultrasonic vibration frequency is 150 Hz-200 Hz.

[0021] Further, in step S3, the ultrasonic stress relief treatment can be carried out before the plate is completely cooled or when it is completely cooled, the treatment temperature is below 250°C, and hydrogen removal treatment is performed after cooling to room temperature.

[0022] Compared with the prior art, the beneficial effects of the present invention are:

[0023] This invention proposes a method for welding medium-thick plates of ultra-high strength steel. By employing a preheat-free welding method and ultrasonic treatment of the weld toe positions on both sides of the weld bead, welding deformation and residual stress are effectively reduced. This method is simple to implement, widely applicable, and can be extensively used in the welding of ultra-high strength steel.

[0024] This invention reduces the heat input of each weld by setting multiple weld seams in the welding of ultra-high strength steel medium and thick plates. It controls the amount of filler wire in the pre-weld seams to keep the deformation of the plate within the controllable range of the fixture, so that the pre-weld seams play a preheating role and achieve local preheating on both sides of the steel plate. This avoids the problem of excessive deformation of ultra-high strength steel plates after welding when a single weld seam is formed. At the same time, it eliminates the preheating process and improves welding production efficiency.

[0025] This invention eliminates residual stress in sheet metal by using ultrasonic stress relief instead of post-weld heat treatment. Compared to traditional post-weld heat treatment methods, which are typically performed before the sheet metal has fully cooled and where temperature and time are difficult to control, potentially leading to overtreatment and significant changes in weld microstructure, ultrasonic stress relief can be performed while the sheet metal is fully cooled. Furthermore, the surface depressions caused by ultrasonic treatment occur only on the surface; the internal microstructure of the weld remains unaffected by heating and does not undergo grain growth. Only the internal residual stress state changes from tensile stress to compressive stress, improving structural reliability. Additionally, the surface hardness of the sheet metal is significantly enhanced after ultrasonic treatment. Attached Figure Description

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the ultrasonic treatment location in the method described in Example 1;

[0028] Figure 2 The deformation result of the steel plate after ultrasonic treatment as described in Example 1.

[0029] In the figure, 1. Deformation after ultrasonic treatment; 2. Original state before treatment; 3. Ultra-high strength steel plate; 4. Ultra-high strength weld; 5. Location of ultrasonic stress relief treatment. Detailed Implementation

[0030] The present invention will be further described below with reference to embodiments:

[0031] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0032] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0033] This invention proposes for the first time a method to reduce welding deformation and residual stress in ultra-high strength steel medium-thick plates, including laser-MAG automated welding, a monitoring system, and ultrasonic stress relief treatment, specifically comprising the following steps:

[0034] 1. Clean the 4.5-6mm thick ultra-high strength steel (>1800MPa) plate to be welded with acetone, grind the inner surface of the 20mm on both sides of the bevel to expose the metal surface, remove rust and oil stains within 50mm of the area to be welded, and open a double-sided V-shaped bevel with a bevel angle of 25-35°.

[0035] 2. Clamp the steel plate processed in step 1 using a fixture, and spot weld it at both ends; set the laser-MAG welding parameters:

[0036] Pre-welding parameters settings: control laser power 2.5~3.5kw, laser incident angle perpendicular to the weld; control MAG welding current 75~90A, welding voltage 19~21V, welding wire tip pointing to the laser focus on the plate, wire feed speed 100~200cm / min; control welding speed 300~500mm / min.

[0037] Cover welding parameter settings: control laser power 3.0~4.5kw, laser incident angle perpendicular to the weld; control MAG welding current 100~120A, welding voltage 21~24V, welding wire tip pointing to the laser focus on the plate, wire feed speed 150~300cm / min; control welding speed 250~400mm / min.

[0038] Specifically, the number of welding passes is at least two, and the number of preceding welding passes is at least one.

[0039] The preheating effect is achieved by controlling the difference in heat conduction and thermal expansion between weld passes to reduce welding deformation of ultra-high strength steel plates.

[0040] When the number of pre-weld passes is ≥2, the cooling interval should be controlled to be less than 20 minutes and the plate temperature should not be less than 200℃.

[0041] The welding wire is ER120S-G high-strength steel welding wire with a diameter of 1.2 to 1.6 mm.

[0042] The preheating effect is achieved by controlling the difference in heat conduction and thermal expansion between weld passes to reduce welding deformation of ultra-high strength steel plates.

[0043] 3. Use ultrasonic waves to treat the narrow, elongated areas (2-3 mm wide) on both sides of the cover weld bead and the weld surface, and allow the plate to cool naturally. The diameter of the impact head used in the ultrasonic treatment is 2-3 mm, and the ultrasonic vibration frequency is 150 Hz-200 Hz.

[0044] The ultrasonic stress relief treatment can be carried out before or after the plate has fully cooled down, at a temperature below 250°C, and after cooling to room temperature, hydrogen removal treatment is performed.

[0045] This invention reduces the heat input of each weld by setting multiple weld seams in the welding of ultra-high strength steel medium-thick plates. By controlling the amount of filler wire in the pre-weld seams, the deformation of the plate is kept within the controllable range of the fixture, thus enabling the pre-weld seams to play a preheating role and achieving local preheating on both sides of the steel plate. This avoids the problem of excessive deformation of the ultra-high strength steel plate after welding when a single weld seam is formed. At the same time, it eliminates the preheating process and improves welding production efficiency.

[0046] This invention significantly eliminates residual stress in sheet metal by using ultrasonic stress relief instead of post-weld heat treatment. Compared to traditional post-weld heat treatment methods, which typically involve heat treatment before the sheet metal has fully cooled, and where temperature and time are difficult to control, potentially leading to overtreatment and significant alterations to the weld microstructure, ultrasonic stress relief can be performed while the sheet metal is fully cooled. Furthermore, the surface depression deformation caused by ultrasonic treatment occurs only on the surface; the internal microstructure of the weld metal is not affected by heating and does not undergo grain growth. Only the internal residual stress state changes from tensile stress to compressive stress, improving structural reliability. Additionally, the surface hardness of the sheet metal is also greatly enhanced after ultrasonic treatment.

[0047] Figure 1 This diagram illustrates a multi-pass weld in a medium-thick ultra-high strength steel plate. In the diagram, 3 represents the ultra-high strength steel plate, 4 represents the multi-pass weld, and 5 represents the location of the ultrasonic stress relief treatment, including the uppermost surface of the weld and the weld toes on both sides. This improved welding process allows for localized preheating of the steel plate, reducing the temperature gradient and thermal stress during welding.

[0048] Figure 2 This is a schematic diagram showing the deformation results of a steel plate after ultrasonic treatment. 1 represents the deformation after ultrasonic treatment, and 2 represents the original state before treatment. From... Figure 2 As can be seen, this method greatly eliminates the residual stress in the plate.

[0049] Example 1

[0050] A method for reducing welding deformation and residual stress in ultra-high strength steel medium-thick plates, specifically comprising the following steps:

[0051] 1. Clean the 4.5mm thick ultra-high strength steel (>1800MPa) plate to be welded with acetone, grind the inner surface of the 20mm on both sides of the bevel to expose the metal surface, remove rust and oil stains within 50mm of the area to be welded, and open a double-sided V-shaped bevel with a bevel angle of 30°.

[0052] 2. Clamp the steel plate processed in step 1 using a fixture, spot weld it at both ends, and fill the gap with 1.2mm ER120S-G welding wire; set the laser-MAG welding parameters:

[0053] Pre-weld parameters: control laser power 3.0kw, laser incident angle perpendicular to the weld; control MAG welding current 83A, welding voltage 19V, welding wire tip pointing to the laser focus on the plate, wire feed speed 160cm / min; control welding speed 340mm / min; number of pre-weld passes is 2, the filler wire amount of the two welds reaches 50% and 90% of the weld respectively, and the interval between the two welds is 15min.

[0054] Cover welding parameter settings: control laser power 4.0kw, laser incident angle perpendicular to the weld; control MAG welding current 107A, welding voltage 21V, welding wire tip pointing to the laser focus on the plate, wire feed speed 230cm / min; control welding speed 300mm / min.

[0055] 3. Use ultrasonic waves to treat the narrow, elongated area (3mm wide) on both sides of the cover weld bead and the weld surface. Select an impact head with a diameter of 3mm and control the ultrasonic vibration frequency at 150Hz. Perform this process when the plate is completely cooled.

[0056] This embodiment achieves the connection of ultra-high strength steel plates with tensile strength ≥1800MPa. The stress level after welding was significantly reduced and no obvious welding deformation was observed by comparative measurement using the blind hole method.

[0057] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A method for reducing welding deformation and residual stress in ultra-high strength steel medium-thick plates, characterized in that, Includes the following steps: S1. Clean, grind and bevel the ultra-high strength steel plates to be welded; S2. Clamp the steel plate processed in step S1 using a fixture, and spot weld it at both ends; set the laser-MAG welding parameters: Pre-welding parameters: control laser power 2.5~3.5kw, laser incident angle perpendicular to the weld; control MAG welding current 75~90A, welding voltage 19~21V, welding wire tip pointing to the laser focus on the plate, wire feed speed 100~200cm / min; control welding speed 300~500mm / min. Cover welding parameter settings: control laser power 3.0~4.5kw, laser incident angle perpendicular to the weld; control MAG welding current 100~120A, welding voltage 21~24V, welding wire tip pointing to the laser focus on the plate, wire feed speed 150~300cm / min; control welding speed 250~400mm / min; S3. Use ultrasonic waves to treat the narrow, elongated areas with a weld toe width of 2-3mm on both sides of the cover weld and the weld surface, and allow the plate to cool naturally. Step S1: The strength of the ultra-high strength steel plate is >1800MPa, and the plate thickness is 4.5~6mm; the bevel is a double-sided V-shape, and the inner surface of the two sides of the bevel within 20mm is ground to expose the metal surface, and rust and oil stains within 50mm of the area to be welded are removed; the double-sided V-shaped bevel is opened with a bevel angle of 25~35°. Step S2: The number of welding passes shall be at least two, and the number of preceding weld passes shall be at least one; when the number of preceding weld passes is ≥2, the cooling interval shall be controlled to be less than 20 minutes, and the plate temperature shall not be less than 200℃; the welding wire shall be ER120S-G high-strength steel welding wire with a diameter of 1.2~1.6mm. In step S3, the diameter of the impact head in the ultrasonic treatment is 2~3mm, and the ultrasonic vibration frequency is 150Hz~200Hz. The ultrasonic stress relief treatment is carried out when the plate is not completely cooled or is completely cooled, the treatment temperature is below 250℃, and hydrogen removal treatment is performed after cooling to room temperature.

Images