CN116117294A

CN116117294A - Resistance spot welding process of 2000 MPa-grade hot forming steel with aluminum-silicon coating

Info

Publication number: CN116117294A
Application number: CN202310269654.3A
Authority: CN
Inventors: 孟根巴根; 王秋雨; 许晓; 孟凡月; 牟永胜; 刘立学; 林果; 赵光; 王玉慧
Original assignee: Tangshan Iron and Steel Group Co Ltd; HBIS Co Ltd Tangshan Branch; Hegang Leting Steel Co Ltd
Current assignee: Tangshan Iron and Steel Group Co Ltd; HBIS Co Ltd Tangshan Branch; Hegang Leting Steel Co Ltd
Priority date: 2023-03-20
Filing date: 2023-03-20
Publication date: 2023-05-16

Abstract

The invention discloses a resistance spot welding process of 2000 MPa-grade hot forming steel with an aluminum silicon coating, which comprises the following steps: 1) Carrying out first welding on the steel plate to be welded; welding current I for first welding ₁ =I ₂ - (0.8-1.2) KA, welding time 500 ms-1000 ms, cooling time 20 ms-40 ms; 2) Carrying out secondary welding on the steel plate to be welded; welding current I for the second welding ₂ =i-0.2 KA, welding time 200 ms-320 ms, cooling time 20 ms-40 ms, wherein I is the spatter current; 3) Tempering welding is carried out on the steel plate to be welded; welding current I of tempering welding ₃ =0.5I ₁ ～0.7I ₁ The tempering pulse time is 120 ms-500 ms. The process greatly improves the cross stretching performance, prevents the occurrence of macroscopic defects of the spot welding joint, and solves the problem of lower cross stretching performance of the aluminum-silicon coating welding joint, thereby improving the comprehensive performance of the welding spot.

Description

Resistance spot welding process of 2000 MPa-grade hot forming steel with aluminum-silicon coating

Technical Field

The invention relates to a welding process, in particular to a resistance spot welding process of 2000 MPa-grade hot forming steel with an aluminum-silicon coating.

Background

The hot formed ultra-high strength steel has been widely used for manufacturing automobile safety structures for impact resistance, collision and the like by virtue of its advantages of high strength, high energy absorption rate, strong forming ability, low rebound quantity, good anti-dent performance and the like. To prevent the surface oxidation and decarburization of the steel sheet during hot stamping, it is common to preset an aluminum-silicon coating on the surface of the steel sheet, which has been accepted and used in a large number by most automobile main frame factories. Low cost, easy to handle and high efficiency resistance spot welding is an important welding method in the automotive industry, with approximately 4000-6000 resistance spot welds per car body. Resistance spot welding is a method of applying pressure to a combined weldment through an electrode and welding by using resistance heat generated by passing current through a contact surface and an adjacent area of a joint, and has been widely used in the fields of aerospace, electronics, automobiles, household appliances and the like. Because of the special physical and chemical properties of the ultra-high strength hot stamping forming steel, the defects of shrinkage cavity and the like in the center of a welding core are easily caused by the large thermal expansion coefficient and higher high-temperature plasticity, the comprehensive mechanical properties of welding spots are extremely important for ensuring the quality of welding spots of automobile plates, and particularly, the cross-shaped tensile performance index is a main performance index; the cross tensile property of the aluminum-silicon coating 2000 MPa-grade hot-forming steel after resistance spot welding connection in the current automobile manufacturing process is lower, so that the use of 2000 MPa-grade hot-forming steel is seriously affected, and the improvement of the cross tensile property of the aluminum-silicon coating 2000 MPa-grade hot-forming steel is very necessary.

The Chinese patent application of application number 202110897788.0 provides a welding process for improving the tensile shear force and plasticity of a 2GPa steel welding head; the process solves the problem that the mechanical property of the welded joint is poor due to the higher carbon equivalent of 2GPa steel, but only the tensile and shearing properties are carried out, and the important plasticity index cross tensile property of the welding spot is not tested.

Disclosure of Invention

The invention aims to provide a resistance spot welding process of 2000 MPa-grade hot forming steel with an aluminum-silicon coating so as to effectively improve the comprehensive performance of welding spots.

In order to solve the technical problems, the invention adopts the following technical scheme: (1) carrying out first welding on a steel plate to be welded; welding current I for first welding ₁ =I ₂ - (0.8-1.2) KA, welding time 500 ms-1000 ms, cooling time 20 ms-40 ms;

(2) Carrying out secondary welding on the steel plate to be welded; welding current I for the second welding ₂ =i-0.2 KA, welding time 200 ms-320 ms, cooling time 20 ms-40 ms, wherein I is the spatter current;

(3) Tempering welding is carried out on the steel plate to be welded; welding current I of tempering welding ₃ =0.5I ₁ ～0.7I ₁ The tempering pulse time is 120 ms-500 ms.

Further, the electrode pressure in the welding process is 3.5 KN-4.5 KN. Further, the electrode pressure is maintained for 200ms to 300ms after the welding current is stopped.

Further, the hot forming steel is in a quenched state and has a thickness of 1.2 mm-1.8 mm, and the number of weldments is two layers of steel plates in lap joint.

The beneficial effects of adopting above-mentioned technical scheme to produce lie in: the invention adopts a first welding-second welding-tempering welding process, and the first welding is performed by applying a long-time and high welding current one-time non-splashing welding to the 2000 MPa-level hot forming steel of the aluminum-silicon coating, so that the width of a softening area is widened; the melted welding spots are further melted in the second welding to obtain a larger nugget diameter and higher tensile shear strength; tempering welding is carried out to slowly cool the molten core metal, so that the plasticity of the welding spot is improved; thereby greatly improving the cross stretching performance, preventing the occurrence of macroscopic defects of the spot welding joint, such as shrinkage porosity, shrinkage cavity and crack, solving the problem of lower cross stretching performance of the 2000 MPa-grade hot forming steel welding joint of the aluminum-silicon coating, thereby improving the comprehensive performance of the welding spot.

Drawings

The invention will be described in further detail with reference to the drawings and the detailed description.

FIG. 1 is a diagram of a resistance spot welding process according to the present invention;

FIG. 2 is a plot of the width of the softening zone for process conditions according to examples 1, 2 and 3 of the present invention;

FIG. 3 is a photograph of a cross-shaped tensile specimen of example 3 of the present invention broken;

FIG. 4 is a photograph of a cross-shaped tensile specimen of example 6 of the present invention broken;

FIG. 5 is a photograph of a cross-shaped tensile specimen of example 7 of the present invention broken.

Detailed Description

The brand of the 2000MPa grade aluminum silicon coating hot stamping forming steel plate is CR1300/2000HS+AS, the thickness is 1.2 mm-1.8 mm, and the quenching state is achieved; the chemical components of the brand steel plate are as follows by mass percent: 0.30 to 0.40 percent of C, 0.20 to 0.30 percent of Si, 1.10 to 1.50 percent of Mn, less than or equal to 0.02 percent of P, less than or equal to 0.02 percent of S, 0.030 to 0.050 percent of Als, 0.0015 to 0.0025 percent of B, 0.020 to 0.050 percent of Ti, 0.10 to 0.50 percent of Cr, 0.10 to 0.50 percent of V, and the balance of Fe and unavoidable impurity elements; the thickness of one side of the Al-Si coating is 25+/-5 um, and the Al-Si coating comprises the following components in percentage by mass: al is more than or equal to 85%, si is 5-11%, fe is 2-4%, and the balance is other unavoidable impurity elements.

As shown in fig. 1, the process steps of the resistance spot welding process of the aluminum-silicon coating 2000 MPa-grade hot-formed steel are as follows:

(1) After cleaning the surface of the steel plate to be welded, overlapping two layers of steel plates; using an intermediate frequency inverter resistance welder, wherein a larger electrode pressure is adopted in the welding process, and the electrode pressure is 3.5 KN-4.5 KN;

(2) Welding for the first time: carrying out first welding on the steel plate to be welded; welding current I for first welding ₁ =I ₂ - (0.8-1.2) KA, welding time t _w1 500 ms-1000 ms, cooling time t _c1 20ms to 40ms;

(3) And (3) welding for the second time: carrying out secondary welding on the steel plate to be welded; welding current I for the second welding ₂ =i-0.2 KA, welding time t _w2 200 ms-320 ms, cooling time t _c2 20ms to 40ms; i is a splash current, namely a minimum current for generating welding splash when single pulse spot welding is adopted;

(5) Tempering welding: tempering welding is carried out on the steel plate to be welded; welding current I of tempering welding ₃ =0.5I ₁ ～0.7I ₁ Tempering pulse time t _w3 120 ms-500 ms, cooling time t _c3 20ms to 40ms; holding time t after the welding current is stopped _H 200ms to 300ms.

Examples 1 to 7: the resistance spot welding process of the 2000 MPa-grade hot forming steel with the aluminum-silicon coating adopts the following specific process.

(1) The brand of the steel plate is CR1300/2000HS+AS, the thickness is 1.2 mm-1.8 mm, the above first welding-second welding-tempering welding process is adopted, and the specific process parameters of each embodiment are shown in Table 1;

table 1: process parameters of the various embodiments

In Table 1, the splash current I was 7.8KA for each of the examples and comparative examples; the comparative example is a comparative case using a conventional process.

(2) The performance of the welded joint obtained in each example is detected, the tensile and shear test sample of the comparative example is interface fracture, the cross tensile force is button fracture mode, the tensile and shear force of the welding spot and the cross tensile force of the example are button fracture mode, and the detection results are shown in Table 2;

table 2: welded joint performance results for various embodiments

FIG. 2 is a plot of softening zone widths for different process conditions described in examples 1, 2 and 3; as can be seen from table 2 and fig. 2, the technology adopts the method of welding with small current for a long time and then welding with large current for a short time, and then tempering, thereby ensuring that the welding without splashing is realized in the welding process of the 2000 MPa-level hot forming steel of the aluminum-silicon coating; firstly, welding with small current for a long time and then welding with large current for a short time to obtain a larger nugget diameter and a heat-affected softening area, and increasing the nugget diameter can improve the strength of welding spots; the tempering current is slow cooling, so that the plasticity of the welding spots is improved; thereby greatly improving the cross stretching performance and the tensile strength and shearing strength. Fig. 3, fig. 4 and fig. 5 are photographs showing the breaking of the cross tensile test specimen according to examples 3, 6 and 7, respectively, and it can be seen from fig. 3, fig. 4 and fig. 5 that the larger the cross tensile test specimen button is along with the increase of tempering time, the better the comprehensive performance of the welding spots is.

Claims

1. A resistance spot welding process of 2000 MPa-grade hot forming steel with an aluminum silicon coating is characterized by comprising the following steps: (1) carrying out first welding on a steel plate to be welded; welding current I for first welding ₁ =I ₂ - (0.8-1.2) KA, welding time 500 ms-1000 ms, cooling time 20 ms-40 ms;

2. The resistance spot welding process for 2000 MPa-grade aluminum-silicon plated hot-formed steel according to claim 1, wherein: the electrode pressure in the welding process is 3.5 KN-4.5 KN.

3. The resistance spot welding process for 2000 MPa-grade aluminum-silicon plated hot-formed steel according to claim 2, wherein: the electrode pressure is maintained for 200ms to 300ms after the welding current is stopped.

4. A resistance spot welding process of 2000 MPa-grade hot-formed steel with an aluminum-silicon coating according to claim 1, 2 or 3, characterized in that: the hot forming steel is in a quenched state and has a thickness of 1.2-1.8 mm, and the number of weldments is two layers of steel plates which are overlapped.