Method for verifying weldability of a steel sheet for a passenger car

Abstract

This invention relates to the field of steel sheet material development technology for passenger vehicles, and discloses a method for verifying the weldability of steel sheet materials for passenger vehicles, comprising the following steps: classifying the weldability of steel sheet materials according to grade to obtain a weldability series; establishing weldability recognition and exemption principles; establishing steel sheet thickness selection rules according to the distinction between cold-rolled and hot-rolled sheets; establishing steel sheet matching methods, welding methods, and welding electrode cap models; establishing a parameter library; preparing several steel sheet samples; adjusting welding parameters according to the parameter library; firstly, welding several weld points on the steel sheet samples to contaminate the electrode caps; then performing welding according to the welding parameters; and performing tensile failure testing to obtain the upper limit I of the current intensity that meets the threshold requirements. max and lower limit I min This allows for the determination of the weldability range. The weldability verification method for steel sheet materials used in passenger vehicles, as described in this invention, can accurately assess the weldability of steel sheets to avoid welding risks during the application stage. It is also easy to operate and has high verification efficiency.

Description

Technical Field

[0001] This invention relates to the field of steel sheet material development technology for passenger vehicles, and specifically to a method for verifying the weldability of steel sheet materials for passenger vehicles. Background Technology

[0002] The development of steel sheet materials for passenger vehicles involves a series of steel sheet performance approval and verification projects, among which the weldability test is a very important component of the new material approval process. Steel sheet weldability verification and welding risk assessment must be conducted in accordance with the weldability testing methods, procedures, and processes of Dongfeng Peugeot-Citroën Automobile Co., Ltd. (hereinafter referred to as DPCA).

[0003] The weldability approval test for steel plates is conducted through resistance spot welding, which is the most widely used welding method. The weldability range refers to the range of current intensities that can be obtained to meet the DPCA welding quality standards (diameter size, no spatter) under a given welding time and pressure.

[0004] However, in existing technologies, it is difficult to accurately assess solderability, and solderability verification is labor-intensive, inefficient, complex, and difficult to operate. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of the above-mentioned technologies by providing a method for verifying the weldability of steel sheet materials for passenger vehicles. This method can accurately assess the weldability of steel sheets to avoid welding risks during the application of steel sheets, and is easy to operate with high verification efficiency.

[0006] To achieve the above objectives, the weldability verification method for steel sheet materials used in passenger vehicles designed in this invention includes the following steps:

[0007] A) Rule establishment: The weldability of steel plate materials is classified according to the grade, resulting in several weldability series. Weldability recognition and exemption principles are established for steel plate materials in each weldability series. According to the distinction between cold-rolled and hot-rolled plates, the selection rules for steel plate thickness are established. The welding mode of three-layer plate combination is adopted, and the steel plate matching method, welding method and welding electrode cap model are established. A parameter library is established.

[0008] B) Preparation before welding: Make several steel plate samples according to the designed dimensions, and adjust the welding parameters according to the thickness of the steel plate samples and the parameter library established in step A).

[0009] C) Welding: First, weld 10 weld points on the steel plate sample, and then perform welding using the welding parameters determined in step B).

[0010] D) Tensile Failure Test: After welding, perform tensile failure test and metallographic examination on the steel plate sample, record the weld nugget diameter and corresponding current intensity, check whether the weld nugget diameter meets the minimum weld nugget diameter requirement, adjust the current intensity within the welding parameters, re-weld the steel plate sample, and obtain the upper limit I of the current intensity that meets the threshold requirement. max and lower limit I min ;

[0011] E) Weldability range: The weldability range of the steel plate material ΔI = I max -I min .

[0012] Preferably, in step A), the following steps are divided into a first weldability series, a second weldability series, and a third weldability series. In the first weldability series, the metallurgical path and chemical composition of the steel plate material are analyzed and evaluated to determine experimental exemption. In the second weldability series, the steel plate material is sorted and classified from difficult to easy according to the level of the metallurgical series, and exemption is granted. In the third weldability series, LME sensitivity testing is required.

[0013] Preferably, in step A), a weldability test is conducted by spot welding three layers of steel plates. The thickness range of the cold-rolled plate to be approved includes x: 0.65~0.80mm and X: 1.5~1.95mm, and the thickness range of the hot-rolled plate is X: 1.75~2.0mm. The steel plates are arranged in a three-layer configuration from top to bottom, using approved DC54D+Z140 steel plates combined with the steel plates to be approved. The thickness of the thicker DC54D+Z steel plates is E=1.45mm and E=1.95mm, and the thickness of the thinner DC54D+Z steel plates is e=0.75~0.85mm. The combination welding methods of the three layers of steel plates include cold-rolled plate x+E+e, cold-rolled plate X+E+e, cold-rolled plate X+e+e, hot-rolled plate X+E+e, and hot-rolled plate X+e+e.

[0014] Preferably, the edges of the steel plate material are cleaned to avoid shunting of the welding current.

[0015] Preferably, in the steel plate arrangement, from top to bottom, there are plates A, B, and C. In one arrangement, the angle between plate A and plates B and C is 90°. In another arrangement, the angle between plate C and plates A and B is 90°. In the welding range test of the three plates, each welding current requires 7 cross tensile specimens to verify its weldability. One specimen is used for metallographic inspection, 3 for interface testing between plates A and B, and 3 for interface testing between plates B and C.

[0016] Preferably, the welding methods include continuous welding and pulse welding, wherein the cold-rolled plate x+E+e, the cold-rolled plate X+e+e and the hot-rolled plate X+e+e are continuously welded, and the cold-rolled plate X+E+e and the hot-rolled plate X+E+e are pulse welded.

[0017] Preferably, the welding electrode cap used in the three-layer plate combination welding mode of cold-rolled plate x+E+e, cold-rolled plate X+e+e and hot-rolled plate X+e+e is model P911310112, and the welding electrode cap used in the three-layer plate combination welding mode of cold-rolled plate X+E+e and hot-rolled plate X+E+e is model Z000120926.

[0018] Preferably, in step D), the step size changes according to a step size of 200A.

[0019] Preferably, in step D), if any weld point reaches the minimum weld nugget diameter, the corresponding current intensity I is reduced by 100A and the steel plate sample is welded again. If the weld nugget diameters are all higher than the minimum weld nugget diameter, the current intensity I-100A is taken as the lower limit value I of the current intensity. min Otherwise, the current I before the 100A reduction will be used as the lower limit value I. min If more than 50% of the weld joints crack or spatter, and the current intensity I remains stable, it indicates that the upper limit of the welding range has been reached. The upper limit of the current intensity I... max =I-200A.

[0020] Preferably, in step E), I max I is the minimum value in the interface test. min This is the maximum value in interface testing, and the minimum solderability range ΔI requirement is ≥ 700 A.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. To make a rapid and accurate assessment of the weldability of steel plates in order to avoid welding risks during the application of steel plates;

[0023] 2. The weldability of materials is classified, and different verification methods and weldability verification exemption schemes are developed for each weldability level. This classification and exemption scheme greatly reduces the workload of weldability verification in the new steel plate material approval process and improves the efficiency of new material approval.

[0024] 3. A detailed full-process verification plan was defined, including experimental equipment, operating methods, experimental procedures, parameter settings, and experimental sample design. This made the entire experimental process clear, easy to operate, and ensured the effectiveness of the entire process, thus achieving excellent operability.

[0025] 4. The requirements for the diameter of the molten nugget during the experiment were clarified, and the lower limit of the current I was also clarified. minand current upper limit I max The calculation method clarifies the range of weldability currents for steel plates that meet the requirements, and allows for the preparation of detailed weldability reports. Attached Figure Description

[0026] Figure 1 This is the AB interface weldability test lap joint method in the weldability verification method for steel sheet materials for passenger vehicles of the present invention;

[0027] Figure 2 This is the BC interface weldability test lap joint method in the weldability verification method for steel sheet materials for passenger vehicles of the present invention. Detailed Implementation

[0028] The present invention will be further described in detail below with reference to specific embodiments.

[0029] A method for verifying the weldability of steel sheet materials for passenger vehicles, characterized by comprising the following steps:

[0030] A) Rule Establishment: Steel plate materials are classified according to their weldability based on grade, resulting in three weldability series, as shown below: First weldability series, Second weldability series, and Third weldability series:

[0031]

[0032] The thickness range for cold-rolled steel sheets to be approved is 0.65~0.80mm for thin plates and 1.5~1.95mm for thick plates. The thickness range for hot-rolled steel sheets to be approved is 1.75~2.0mm.

[0033] Weldability tests were conducted using a three-layer plate resistance spot welding method. The steel plates were arranged in a three-layer configuration from top to bottom, using DPCA-approved DC54+Z140 grade steel plates combined with steel plates to be approved for welding.

[0034] The thickness of DC54D+Z steel plate is E=1.45 and E=1.95mm for thick plates and E=0.75~0.85mm for thin plates. The combination welding methods for three layers of steel plates include cold-rolled plate X+E+e, cold-rolled plate X+E+e, cold-rolled plate X+e+e, hot-rolled plate X+E+e, and hot-rolled plate X+e+e.

[0035] Welding methods include continuous welding and pulse welding. Continuous welding is used for cold-rolled sheet x+E+e, cold-rolled sheet X+e+e, and hot-rolled sheet X+e+e, while pulse welding is used for cold-rolled sheet X+E+e and hot-rolled sheet X+E+e. The welding electrode cap model P911310112 is used for the three-layer plate combination welding mode of cold-rolled sheet x+E+e, cold-rolled sheet X+e+e, and hot-rolled sheet X+e+e, while the welding electrode cap model Z000120926 is used for the three-layer plate combination welding mode of cold-rolled sheet X+E+e and hot-rolled sheet X+E+e.

[0036] As shown below, weldability approval and exemption principles are established for steel plate materials in each weldability series:

[0037] Weldability approval and exemption principles for steel plates in the first weldability series:

[0038] In the first weldability series, analysis and evaluation are conducted based on the metallurgical pathway and chemical composition of the steel plate material:

[0039]

[0040] Weldability approval and exemption principles for steel plates in the second weldability series:

[0041] In the second weldability series, steel plate materials are sorted and classified from most difficult to easiest according to the metallurgical series:

[0042]

[0043] Weldability approval and exemption principles for steel plates in the third weldability series:

[0044] Conduct LME sensitivity testing:

[0045]

[0046] B) Pre-welding preparation: Prepare several steel plate samples. Adjust the welding parameters according to the steel plate thickness and the parameter library established in step A). ​​During sample preparation, the edges of the steel plate samples may have burrs, which may cause current shunting during the test. Therefore, it is necessary to check the samples for burrs and clean the edges of the steel plate material to avoid current shunting and possible metal spatter. Spatter may interfere with the determination of the higher current intensity range of the welding current. The following welding model is established in this step:

[0047]

[0048] In this embodiment, the sample size used for the weldability test is 38mm x 125mm, with a cross-lap joint. From top to bottom, the plates are A, B, and C. In one plate arrangement, the angle between plate A and plates B and C is 90°. In another plate arrangement, the angle between plate C and plates A and B is 90°. The welding range test for the three plates is as follows: for each welding current, seven cross-lap templates are required to verify weldability, one of which is used for metallographic inspection. Three templates are used for the interface test between plates A and B (referred to as the A combination), and three templates are used for the interface test between plates B and C (referred to as the B combination).

[0049] The specific overlap of the three boards is as follows: Figure 1 and Figure 2 As shown,

[0050] Combination A: The angle between plate A and plates B and C is 90°. This is how the interface between plates A and B and the diameter of the weld point are measured. Each welding current parameter requires 4 combined samples to be welded in this way, and one set of samples is used for metallographic inspection.

[0051] Combination B: The angle between plate C and plates A and B is 90°. This is how the BC interface and the diameter of the solder joint are measured. Each welding current parameter requires three combined samples to be welded in this way.

[0052] To ensure the accuracy of the weld point position during the test, a positioning gauge made of insulating material is required to position the welding template and welding electrode cap.

[0053] C) Welding: To complete the required welding test, a welding machine with the following performance characteristics is required:

[0054]

[0055] Ten weld points were first welded onto the steel plate sample. The electrode cap was then contaminated with a coating to reduce dispersion at the lower limit of the welding range. This is essential for maintaining stable weld quality from the beginning of the experiment. The welding parameters selected for electrode cap contamination are as follows:

[0056]

[0057] Then, welding is performed using the welding parameters determined in step B). The specific parameters are as follows:

[0058]

[0059] D) Tensile Failure Test: After welding, a tensile failure test is performed on the steel plate sample. The weld nugget diameter and corresponding current intensity are recorded in 200A increments. The weld nugget diameter is checked to ensure it meets the minimum weld nugget diameter requirement. The current intensity within the welding parameters is adjusted, and the steel plate sample is re-welded to obtain the upper limit I of the current intensity that meets the threshold requirement. max and lower limit I min ;

[0060] E) Weldability range: The weldability range of the steel plate material ΔI = I max -I min , ΔI≥700 A.

[0061] In step D) above, if any weld joint reaches the minimum weld nugget diameter, the corresponding current intensity I is reduced by 100A and the steel plate sample is welded again. If the weld nugget diameter is higher than the minimum weld nugget diameter, the current intensity I-100A is taken as the lower limit value I of the current intensity. min Otherwise, retain the current intensity I as the lower limit value I. min If more than 50% of the weld joints crack or spatter, and the current intensity I remains stable, it indicates that the upper limit of the welding range has been reached. The upper limit of the current intensity I... max =I-200A.

[0062] The requirements for the diameter of the molten core are as follows:

[0063]

[0064] In the above experiments, the parameters were all based on the 50Hz frequency of the Chinese power grid. The welding current was single-phase AC and its effective value could be adjusted. The effectiveness of the welding current should be measured by a periodically calibrated kiloampere-type device.

[0065] In addition, in the above experiments, metallographic cross-sectional analysis must be performed on the samples with the upper and lower limits of the welding range to check the morphology of the weld nugget.

[0066] Metallographic experiments on solder joints include:

[0067] 1. Examine the cross-sectional micrographs of the weld joints at the lower and upper limits of the weld range to see the shape and location of the weld nugget relative to the component, as well as any potential cracking under all test conditions;

[0068] 2. Test the microhardness curve of the solder joint.

[0069] After the weldability test is completed, weldability curves can be compiled based on different welding currents and the weld diameter under these currents.

[0070] This invention provides a method for verifying the weldability of steel sheet materials for passenger vehicles. It accurately assesses the weldability of steel sheets to avoid welding risks during application. The method categorizes the materials by weldability, developing different verification methods and exemption schemes for each weldability level. This categorization and exemption scheme significantly reduces the workload of weldability verification during the approval process for new steel sheet materials, improving the efficiency of new material approval. The method clearly defines a detailed, end-to-end verification scheme, including experimental equipment, operating methods, experimental procedures, parameter settings, and experimental sample design. This ensures a clear, easy-to-operate, and effective experimental process, resulting in excellent operability. The method also clarifies the requirements for the weld nugget diameter and the lower current limit I during the experiment. min and current upper limit I max The calculation method clarifies the range of weldability currents for steel plates that meet the requirements, and allows for the preparation of detailed weldability reports.

Claims

1. A method of verifying the weldability of a passenger car steel sheet material, characterized in that: Includes the following steps: A) Rule Establishment: Steel plate materials are classified according to their weldability based on grade, resulting in several weldability series. Weldability approval and exemption principles are established for each weldability series, which are divided into three weldability series: first weldability series, second weldability series, and third weldability series. In the first weldability series, the metallurgical path and chemical composition of the steel plate materials are analyzed and evaluated to determine experimental exemptions. In the second weldability series, the steel plate materials are sorted and classified according to the metallurgical series from most difficult to easiest, and exemptions are granted accordingly. In the third weldability series, LME sensitivity testing is required. Based on the distinction between cold-rolled and hot-rolled plates, rules for selecting steel plate thickness are established. A three-layer plate combination welding mode is adopted, and the steel plate matching method, welding method, and welding electrode cap model are established, and a parameter library is created. B) Preparation before welding: Make several steel plate samples according to the designed dimensions, and adjust the welding parameters according to the thickness of the steel plate samples and the parameter library established in step A). C) Welding: First, weld 10 weld points on the steel plate sample, and then perform welding using the welding parameters determined in step B). D) Tensile Failure Test: After welding, perform tensile failure test and metallographic examination on the steel plate sample, record the weld nugget diameter and corresponding current intensity, check whether the weld nugget diameter meets the minimum weld nugget diameter requirement, adjust the current intensity within the welding parameters, re-weld the steel plate sample, and obtain the upper limit I of the current intensity that meets the threshold requirement. max and lower limit I min ; E) weldability range: weldability range ΔI = I of the steel sheet material max -I min .

2. The method for verifying the weldability of steel sheet materials for passenger vehicles as described in claim 1, characterized in that: In step A), a weldability test is conducted using spot welding of three layers of steel plates. The thickness range of the cold-rolled plates to be approved includes x: 0.65~0.80mm and X: 1.5~1.95mm, and the thickness range of the hot-rolled plates is X: 1.75~2.0mm. The steel plates are arranged in a three-layer configuration from top to bottom, using approved DC54D+Z140 steel plates combined with the steel plates to be approved. The thickness of the thicker DC54D+Z140 steel plates is E=1.45mm and E=1.95mm, and the thickness of the thinner DC54D+Z140 steel plates is e=0.75~0.85mm. The combination welding methods of the three layers of steel plates include cold-rolled plate x+E+e, cold-rolled plate X+E+e, cold-rolled plate X+e+e, hot-rolled plate X+E+e, and hot-rolled plate X+e+e.

3. The method of claim 2, wherein the steel sheet material for a passenger car is a steel sheet material for a passenger car as defined in any one of claims 1 to 3. Clean the edges of the steel plate material.

4. The method of claim 3, wherein the steel sheet material for a passenger car is a steel sheet material for a passenger car as defined in any one of claims 1 to 3. In the steel plate arrangement, from top to bottom, there are plates A, B, and C. In one arrangement, the angle between plate A and plates B and C is 90°. In another arrangement, the angle between plate C and plates A and B is 90°. In the welding range test of the three plates, each welding current requires 7 cross tensile specimens to verify its weldability. One specimen is used for metallographic inspection, 3 for interface testing between plates A and B, and 3 for interface testing between plates B and C.

5. The method of claim 2, wherein the steel sheet material for an automobile is a steel sheet material for a body of an automobile. The welding methods include continuous welding and pulse welding. Cold-rolled sheet x+E+e, cold-rolled sheet X+e+e, and hot-rolled sheet X+e+e are continuous welding, while cold-rolled sheet X+E+e and hot-rolled sheet X+E+e are pulse welding.

6. The method for verifying the weldability of steel sheet materials for passenger vehicles as described in claim 5, characterized in that: The welding electrode cap model used for the three-layer plate combination welding mode of cold-rolled plate X+E+e, cold-rolled plate X+e+e and hot-rolled plate X+e+e is P911310112, and the welding electrode cap model used for the three-layer plate combination welding mode of cold-rolled plate X+E+e and hot-rolled plate X+E+e is Z000120926.

7. The method for verifying the weldability of steel sheet materials for passenger vehicles as described in claim 1, characterized in that: In step D), the step size changes according to 200A.

8. The method for verifying the weldability of steel sheet materials for passenger vehicles as described in claim 1, characterized in that: In step D), if any weld joint reaches the minimum weld nugget diameter, the corresponding current intensity I is reduced by 100A and the steel plate sample is welded again. If the weld nugget diameter is higher than the minimum weld nugget diameter, the current intensity I-100A is taken as the lower limit value of the current intensity I. min Otherwise, the current I before the 100A reduction will be used as the lower limit value I. min If more than 50% of the weld joints crack or spatter, and the current intensity I remains stable, it indicates that the upper limit of the welding range has been reached. The upper limit of the current intensity I... max =I-200A.

9. The method for verifying the weldability of steel sheet materials for passenger vehicles as described in claim 1, characterized in that: In step E), I max is the minimum value in the interface test, I min is the maximum value in the interface test, and the minimum weldability range ΔI requires: ≥ 700 A.

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