Method for improving performance of medium manganese steel resistance spot welding joint

A welding head, manganese steel technology, applied in resistance welding equipment, welding power source, welding medium, etc., can solve the problems of difference in bearing performance of spot welding joints, low bearing capacity of joints, complete interface fracture, etc., to achieve significant bearing capacity, bearing capacity The effect of ability improvement and nugget plasticity improvement

Active Publication Date: 2020-10-30
BAOSHAN IRON & STEEL CO LTD
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  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

Therefore, even for the same material, the load-bearing properties of spot welded joints prepared with different welding parameters may vary greatly
In addition, the resistance spot welding weldability of medium manganese steel is poor. The main reason is that the carbon equivalent of medium manganese steel is relatively high, between 0.35 and 0.7, which is greater than the maximum value of carbon equivalent (0.24 ), the joint tends to produce shrinkage cavities, shrinkage porosity, cracks and other defects after welding, and the joint structure is mainly hard and brittle martensite. Failure with complete interfacial fracture resulting in low joint load carrying capacity

Method used

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  • Method for improving performance of medium manganese steel resistance spot welding joint
  • Method for improving performance of medium manganese steel resistance spot welding joint
  • Method for improving performance of medium manganese steel resistance spot welding joint

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Experimental program
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Effect test

Embodiment 1

[0049] The present embodiment is used as an effect comparison example, and the technology of the present invention is not adopted. The material to be welded is 7Mn steel with a plate thickness of 1.4 mm, and its chemical composition is shown in Table 1. The adopted spot welding process parameters are common specifications, as shown in Table 2.

[0050] Table 1 Chemical composition of 7Mn steel (wt.%)

[0051] C Si Mn S P 0.13 0.22 7 0.0011 0.006

[0052] Table 2 Spot welding process parameters

[0053]

[0054] Under the welding process parameters, the electron microscope microstructure photos of the nugget are as follows: Figure 7 As shown, it is coarse martensite, the maximum cross tensile force (CTS) that the welded joint can bear is 1.71kN, and the tensile curve is as follows Figure 9 As shown in the 1# curve in the middle, the fracture mode of the welded joint is complete interfacial fracture (FIF).

Embodiment 2

[0056] This embodiment adopts the technology of the present invention. The material to be welded is 7Mn steel with a plate thickness of 1.4 mm, and its composition is shown in Table 1. The spot welding process parameters are shown in Table 3.

[0057] Table 3 Spot welding process parameters

[0058]

[0059] Using the welding process parameters in Table 3, the maximum cross tensile force (CTS) that the medium manganese steel welded joint can withstand is 3.12kN (the tensile curve is as follows: Figure 9 shown in the 2# curve), which is the comparative ratio ( Figure 9 1# curve), the fracture mode of welded joint is partial interface fracture (PIF).

Embodiment 3

[0061] This embodiment adopts the technology of the present invention. The material to be welded is 7Mn steel with a plate thickness of 1.4 mm, and its composition is shown in Table 1. The spot welding process parameters are shown in Table 4.

[0062] Table 4 Spot welding process parameters

[0063]

[0064] Using the welding process parameters in Table 4, the photo of the nugget electron microscope structure is as follows Figure 8 As shown, it is fine martensite and austenite, and the maximum cross tensile force (CTS) that the welded joint can bear is 4.62kN (the tensile curve is as shown in Figure 9 shown in the 3# curve), which is the comparative ratio ( Figure 9 270% of the 1# curve), the fracture mode of the welded joint is the button fracture (B). It can be seen that, by the method of the present invention, the joint bearing capacity and plasticity of the medium manganese steel are significantly improved.

[0065] In this embodiment, fine martensite and fine a...

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Abstract

The invention relates to a method for improving the performance of a medium manganese steel resistance spot welding joint. The method comprises the following steps that 1) the austenitizing end temperature AC3, the austenitizing initial temperature AC1 and the martensite transformation starting temperature MS of a medium manganese steel plate to be welded are tested; 2) the medium manganese steelplate is placed between two electrodes of a resistance spot welding machine, and a constant electrode pressure of 2.0-8.0 kN is applied to clamp the medium manganese steel plate; 3) a connection pulseis applied for melting the medium manganese steel in the welding area to form a required nugget size; (4) reciprocating phase change pulses are applied, the reciprocating phase change pulses are twoor more pulses, the current value and the action time of each pulse are equal or unequal, each pulse current is 3-10 kA, the action time is 3-30 cyc, and the time interval between the pulses is 5-30 cyc; and after the reciprocating phase change pulse is finished, the nugget is cooled by 5-25 cyc under the action of electrode pressure. According to the method, the bearing capacity of the medium manganese steel spot welding joint can be improved by 3 times, and the joint fracture mode is changed from complete interface fracture to button fracture.

Description

technical field [0001] The invention relates to a resistance spot welding method, in particular to a method for improving the performance of a medium manganese steel resistance spot welding joint, and solves the problem of low bearing capacity of the medium manganese steel resistance spot welding joint. Background technique [0002] In order to reduce energy consumption and reduce automobile pollutant emissions, lightweight has become an important trend in the development of automobile technology. As a member of the third-generation automotive steel family, medium manganese steel has a manganese content of 5-12%, but it is often 4-13% in the actual production process, and its alloying degree is lower than that of the second-generation automotive steel. Performance index - strong plastic product is generally 30 ~ 40GPa·%. Compared with the first-generation automotive steel, medium-manganese steel can better meet the crashworthiness requirements of modern automobiles; The pr...

Claims

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Application Information

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IPC IPC(8): B23K11/11B23K11/16B23K11/24B23K31/12B23K35/30
CPCB23K11/115B23K11/16B23K11/24B23K31/12B23K35/3073
Inventor 潘华雷鸣刘成杰吴岳孙中渠蒋浩民
Owner BAOSHAN IRON & STEEL CO LTD
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