阅读说明：本技术 一种提高2GPa钢焊接头拉剪力和塑性的焊接工艺 (Welding process for improving tensile shear force and plasticity of 2GPa steel welding joint ) 是由 郭伟 薛俊良 夏明生 赵光 孟根巴根 张宏强 朱颖 于 2021-08-05 设计创作，主要内容包括：本发明公开了一种提高2GPa钢焊接头拉剪力和塑性的焊接工艺,具体步骤如下：将2GPa钢的待焊区域打磨、清洗,然后置于电阻点焊机电极头之间,施加电极压力；采用电阻点焊机对2GPa钢进行临界焊接脉冲电流I-(0)探索测试；更换待焊2GPa钢,施加电极压力并采用预热脉冲电流对2GPa钢板待焊区域进行预热,然后冷却；采用焊接脉冲电流对2GPa钢板进行焊接,然后冷却；采用回火脉冲电流对已形成焊点的区域进行回火。本发明解决2GPa钢因较高碳当量导致的焊接接头力学性能较差的问题,为2GPa钢在车体广泛应用提供技术支持。(The invention discloses a welding process for improving the tensile-shear force and the plasticity of a 2GPa steel welding joint, which comprises the following specific steps: polishing and cleaning a region to be welded of 2GPa steel, then placing the region between electrode tips of a resistance spot welding machine, and applying electrode pressure; critical welding pulse current I for 2GPa steel by resistance spot welding machine 0 Exploring and testing; replacing the steel to be welded with 2GPa, applying electrode pressure, preheating the area to be welded of the steel plate with 2GPa by adopting preheating pulse current, and then cooling; welding the 2GPa steel plate by adopting a welding pulse current, and then cooling; and tempering the area where the welding point is formed by adopting tempering pulse current. The invention solves the problem of poor mechanical property of the welding joint caused by higher carbon equivalent of the 2GPa steel, and provides technical support for the wide application of the 2GPa steel in the vehicle body.)

1. A welding process for improving the tensile-shear force and the plasticity of a 2GPa steel welding joint is characterized by comprising the following specific steps:

s1, polishing and cleaning a to-be-welded area of the 2GPa steel, then placing the area between electrode tips of a resistance spot welding machine, and applying electrode pressure;

s2, adopting a resistance spot welding machine to carry out critical welding pulse current I on the 2GPa steel₀Exploring and testing;

s3, replacing the steel to be welded with 2GPa, applying electrode pressure, preheating the area to be welded of the steel plate with 2GPa by adopting preheating pulse current, and then cooling, wherein the preheating pulse current is set as I₁The preheating time is set to T₁The cooling time of the preheating is set to T_L1；

S4, welding the 2GPa steel plate by adopting a welding pulse current, and then cooling the steel plate, wherein the welding pulse current is set as I₂The welding time is set to T₂The cooling time of the weld is set to T_L2；

S5, tempering the area where the welding point is formed by tempering pulse current, wherein the tempering pulse current is set as I₃The tempering time is set to T₃。

2. A welding process for improving the tensile and shear properties of a 2GPa steel weld joint as claimed in claim 1 wherein the tip diameter in step S1 is 4-8mm and the electrode pressure is 3-5 KN.

3. A welding process for improving the tensile and shearing forces and the plasticity of a steel welding head with the thickness of 2GPa according to claim 1, wherein the critical welding pulse current I in the step S2 is the critical welding pulse current I₀The pulse current is used when the splashing occurs in the welding process of the 2GPa steel plate.

4. A welding process for improving the tensile and shear properties of a 2GPa steel welding head as claimed in claim 1, wherein the electrode pressure applied in step S3 is 3.5KN-4.5 KN.

5. A welding process for improving the tensile and shearing forces and the plasticity of a steel welding head with the thickness of 2GPa according to claim 1, wherein the pre-heating pulse current I in the step S3 is the pulse current I₁3KA-5KA, preheating time T₁0.1-0.5s, cooling time T of preheating_L1Is 0.1-0.5 s.

6. A welding process for improving the tensile and shearing forces and the plasticity of a steel welding head with the thickness of 2GPa according to claim 1, wherein the welding pulse current I in the step S4 is the pulse current I₂Is I₀-2≤I₂≤I₀-1, welding time T₂0.3-0.8s, cooling time T of welding_L2Is 0.1-0.5 s.

7. A welding process for improving the tensile and shearing forces and the plasticity of a steel welding head with the thickness of 2GPa according to claim 1, wherein the tempering pulse current I in the step S5 is the same as the tempering pulse current I₃Is 3/4I₂≤I₃≤6/7I₂Tempering time T₃Is 1-2 s.

Technical Field

The invention relates to the technical field of welding of advanced ultrahigh-strength steel for vehicles, in particular to a welding process for improving the tensile-shearing force and plasticity of a 2GPa steel welding joint.

Background

The light weight of the automobile is a main way for reducing the energy consumption of the automobile, and the development trend of the modern automobile is to ensure the safety performance of the automobile while lightening the automobile. The advanced ultrahigh-strength steel for the vehicle has the advantages of ultrahigh strength, excellent energy absorption performance and the like, and is widely applied to manufacturing of automobile bodies. With the continuous progress of steel smelting technology, the tensile strength of the high-strength steel for vehicles is improved from 590MPa to 2000 MPa.

Resistance spot welding is widely applied to the manufacturing process of the vehicle body due to the advantages of simple operation, high production efficiency, excellent spot welding joint performance and the like, and is the most important welding process in the manufacturing process of the white vehicle body. According to statistics, about 3000-6000 resistance spot welding joints are arranged on a car body of a car.

Along with the improvement of the strength of the advanced ultrahigh-strength steel for vehicles, the proportion of carbon elements in the material is gradually increased, and the increase of the carbon equivalent in the steel brings great challenges to the welding of the advanced ultrahigh-strength steel for vehicles. The 2GPa steel is hot forming steel, is mainly used for automobile door reinforcing plates and anti-collision beams, and has tensile strength of more than or equal to 2000 MPa. The welding property is poor due to the high carbon equivalent of the 2GPa steel, so that the problems of splashing, shrinkage cavity and the like are easily caused in the resistance spot welding process, the welding process window is narrow, the pulling and shearing force of a spot welding joint is low, and the above disadvantages restrict the wide application of the 2GPa steel on the vehicle body.

Therefore, in combination with the above problems, it is an urgent need to solve the above problems by those skilled in the art to provide a welding process for improving the tensile strength and plasticity of a 2GPa steel welding joint.

Disclosure of Invention

In view of the above, the invention provides a welding process for improving the tensile force and plasticity of a 2GPa steel welding joint, which adopts small pulse current preheating, large pulse current welding and long-time tempering of the small pulse current to avoid the influence of larger secondary nucleation formed by the large pulse current in the tempering process on the tensile force and plasticity, solves the problem of poor mechanical property of the welding joint of the 2GPa steel caused by higher carbon equivalent, and provides technical support for the wide application of the 2GPa steel in a vehicle body.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a welding process for improving the tensile-shear force and plasticity of a 2GPa steel welding joint comprises the following specific steps:

s1, polishing and cleaning a to-be-welded area of the 2GPa steel, then placing the area between electrode tips of a resistance spot welding machine, and applying electrode pressure;

s2, adopting a resistance spot welding machine to carry out critical welding pulse current I on the 2GPa steel₀Exploring and testing;

s3, replacing the steel to be welded with 2GPa, applying electrode pressure, preheating the area to be welded of the steel plate with 2GPa by adopting preheating pulse current, and then cooling, wherein the preheating pulse current is set as I₁The preheating time is set to T₁The cooling time of the preheating is set to T_L1；

S4, welding the 2GPa steel plate by adopting a welding pulse current, and then cooling the steel plate, wherein the welding pulse current is set as I₂The welding time is set to T₂The cooling time of the weld is set to T_L2；

S5, tempering the area where the welding point is formed by tempering pulse current, wherein the tempering pulse current is set as I₃The tempering time is set to T₃。

Preferably, the diameter of the electrode tip in the step S1 is 4-8mm, and the electrode pressure is 3-5 KN.

Preferably, the critical welding pulse current I in step S2₀The pulse current is used when the splashing occurs in the welding process of the 2GPa steel plate.

Preferably, the electrode pressure applied in step S3 is 3.5KN to 4.5 KN.

Preferably, the preheating pulse current I in the step S3₁3KA-5KA, preheating time T₁0.1-0.5s, cooling time T of preheating_L1Is 0.1-0.5 s.

Preferably, the welding pulse current I in the step S4₂Is I₀-2≤I₂≤I₀-1, welding time T₂0.3-0.8s, cooling time T of welding_L2Is 0.1-0.5 s.

Preferably, the tempering pulse current I in the step S5₃Is 3/4I₂≤I₃≤6/7I₂Tempering time T₃Is 1-2 s.

By adopting the technical scheme, the invention has the following beneficial effects:

(1) the invention applies a preheating current I₁Preheating the 2GPa steel before welding, reducing the temperature gradient between a welding area and a base metal in the welding process, and reducing the temperature nonuniformity between the welding area and the base metal, thereby effectively reducing the welding stress and avoiding the occurrence of welding cracks;

(2) the invention passes through the tempering pulse current I₃Pulse current I for welding 2GPa steel₂The welded primary nucleation is tempered, so that the carbon distribution in the welding fusion line area of the primary nucleation is more uniform, the hardness difference between the welding fusion line and the surrounding area is reduced, and the problem of low tensile and shearing force and plasticity caused by the crack initiation and expansion of the 2GPa steel resistance spot welding joint along the fusion line in the stretching process is solved;

(3) according to the invention, the resistance spot welding is carried out on the 2GPa steel by the three-pulse current combined by the preheating pulse current, the welding pulse current and the tempering pulse current, so that the fracture path of the original single-welding pulse joint is changed, and the tensile shear force and the plasticity of the 2GPa steel spot-welded joint are improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.

FIG. 1 is a schematic view of a welding process of the present invention;

FIG. 2 is a schematic view of the welding process parameters of the present invention;

FIG. 3 is a drawing of a 2GPa steel resistance spot weld joint configuration of the present invention, wherein FIG. 3(a) is a three-pulse current formed weld joint and FIG. 3(b) is a single-pulse current formed weld joint;

FIG. 4 is a drawing showing a 2GPa break path of a steel resistance spot weld joint of the present invention, wherein FIG. 4(a) is a weld joint formed by three pulses of current and FIG. 4(b) is a weld joint formed by a single pulse of welding current.

Detailed Description

The technical solutions in the embodiments of the present invention are clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

In the embodiment of the invention, preheating, welding and tempering are carried out to weld 2GPa steel as an example, the thickness of the 2GPa steel is 1.4mm, the tensile strength is 2000MPa, the flow chart of the method is shown in figure 1, and the specific steps are as follows:

s1, removing surface impurities such as an oxide layer, iron rust and the like of a to-be-welded area of 2GPa steel by using an angle grinder, wiping the polished area by using non-woven fabric adhered with acetone, removing oil stains on the surface of the to-be-welded area, then lapping two 2GPa steel plates subjected to surface treatment, placing the two steel plates between two electrode tips of a resistance spot welding machine, wherein the diameter of each electrode tip is 6mm, starting the resistance spot welding machine and applying an electrode pressure of 4 KN;

s2, adopting a resistance spot welding machine to carry out critical welding pulse current I on the 2GPa steel₀Exploration test to obtain I₀Is 8 KA;

s3, replacing the steel to be welded with 2GPa, applying 4KN electrode pressure, preheating the area to be welded of the steel plate with 2GPa for 0.2S by adopting 4KA preheating pulse current, reducing the temperature nonuniformity between the area to be welded and the base metal, and then cooling for 0.4S;

s4, welding the 2GPa steel plate by adopting 7KA welding pulse current for 0.32S, and then cooling for 0.4S;

and S5, tempering the area where the welding spots are formed by adopting 6KA tempering pulse current for 2S.

Comparative example 1:

comparative example 1 takes preheating pulse current and welding pulse current double pulse current welding 2GPa steel as an example, the thickness of the 2GPa steel is 1.4mm, the tensile strength is 2000MPa, and the specific steps are as follows:

s1, removing surface impurities such as an oxide layer, rust and the like of a to-be-welded area of 2GPa steel by using an angle grinder, wiping the polished area by using non-woven fabric adhered with acetone, removing oil stains on the surface of the to-be-welded area, and then lapping two 2GPa steel plates with processed surfaces and placing the two steel plates between two electrode heads (with the diameter of 6mm) of a resistance spot welding machine; starting a resistance spot welding machine and applying 4KN electrode pressure;

s2, preheating the 2GPa steel for 0.2S by adopting 4KA preheating pulse current, reducing the temperature nonuniformity between the area to be welded and the base metal, and then cooling for 0.4S;

and S3, welding the 2GPa steel by adopting 7KA welding pulse current, wherein the welding time is 0.32S.

Comparative example 2:

comparative example 2 takes the welding of 2GPa steel by double pulse current of welding pulse current and tempering pulse current as an example, the thickness of the 2GPa steel is 1.4mm, the tensile strength is 2000MPa, and the specific steps are as follows:

s1, removing surface impurities such as an oxide layer, rust and the like of a to-be-welded area of 2GPa steel by using an angle grinder, wiping the polished area by using non-woven fabric adhered with acetone, removing oil stains on the surface of the to-be-welded area, and then lapping two 2GPa steel plates with processed surfaces and placing the two steel plates between two electrode heads (with the diameter of 6mm) of a resistance spot welding machine; starting a resistance spot welding machine and applying 4KN electrode pressure;

s2, welding the 2GPa steel by adopting 7KA welding pulse current for 0.32S, and then cooling for 0.4S;

s3, tempering the area where the 2GPa steel forms the nuclei by adopting 6KA tempering pulse current, wherein the tempering time is 2S.

Comparative example 3:

comparative example 3 a single pulse welding current was used to weld 2GPa steel, the 2GPa steel having a thickness of 1.4mm and a tensile strength of 2000MPa, the specific steps are as follows:

s1, removing surface impurities such as an oxide layer, rust and the like of a to-be-welded area of 2GPa steel by using an angle grinder, wiping the polished area by using non-woven fabric adhered with acetone, removing oil stains on the surface of the to-be-welded area, and then lapping two 2GPa steel plates with processed surfaces and placing the two steel plates between two electrode heads (with the diameter of 6mm) of a resistance spot welding machine; starting a resistance spot welding machine and applying 4KN electrode pressure;

and S2, welding the 2GPa steel by adopting 7KA welding pulse current, wherein the welding time is 0.32S.

Statistics of the results of the 2GPa steel spot welded joint primary weld line with surrounding area micro vickers hardness value, tensile force and plasticity (maximum tensile-shear force versus displacement) in example 1, comparative example 2 and comparative example 3 are shown in table 1:

TABLE 1

Through the analysis of experimental examples and comparative examples, the three-pulse current combined by the preheating pulse current, the welding pulse current and the tempering pulse current can effectively improve the tensile force and the plasticity of the 2GPa steel spot-welded joint. The invention preheats the base metal and the area to be welded before welding through the preheating pulse current, effectively reduces the temperature gradient between the welding area and the base metal and restrains the generation of welding cracks. The invention applies tempering pulse current to temper the nucleated welding area, obviously reduces the hardness difference between the primary fusion line area and the surrounding area, changes the fracture path of the 2GPa steel spot-welded joint and effectively improves the comprehensive mechanical property of the 2GPa steel spot-welded joint. The resistance spot welding process adopted by the invention has the advantages of simple program design, high production efficiency and no other additional operation and equipment, and is very suitable for manufacturing the actual vehicle body.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.