A resistance spot welding method for ultra-high-strength thermoformed steel plates

Abstract

The invention provides a resistance spot welding method for ultra-high-strength thermoformed steel plates. Based on the method, the super-high-strength thermoformed steel plates with carbon content ≥ 0.33wt% and tensile strength ≥ 1800 MPa are welded, which not only does not require a cooling section, but also improves efficiency. And it can increase the CTS strength. The resistance spot welding method comprises the following steps: 1) the first process section: applying current I1 to the ultra-high-strength thermoformed steel plate to be welded, and the time is T1; Apply current I2 to the ultra-high-strength thermoformed steel plate, and the time is T2; 3) The third process section: Then apply current I3 to the ultra-high-strength thermoformed steel plate after the second process section, and the time is T3; 4) The fourth process Segment: Next, a current I4 is applied to the ultra-high-strength hot-formed steel plate processed in the third process segment, and the time is T4.

Description

technical field [0001] The invention relates to the field of resistance spot welding, in particular to a method for resistance spot welding of ultra-high-strength thermoformed steel plates with a tensile strength above 1800 MPa. Background technique [0002] When the tensile strength of ultra-high-strength steel is greater than 1000MPa, as the strength continues to increase, its CTS spot welding strength shows a downward trend. The traditional spot welding process cannot improve the CTS welding joint strength, and post-weld tempering process is required. However, the cooling period of the post-weld tempering process is too long and the efficiency is low, which cannot meet the production cycle requirements. [0003] According to the existing spot welding technical standards, the 1.8GPa hot-formed steel plate with a thickness of 1.0-1.8mm, especially a thickness of 1.5mm-1.8mm, needs to be spot-welded with a three-stage process. Within the range of the weldable current range, ...

AI Technical Summary

Problems solved by technology

However, for ultra-high-strength hot-formed steel sheets with a carbon content ≥ 0.33wt% and a tensile strength ≥ 1800 MPa, the strength and carbon equivalent are high, the austenitization temperature is low, and the welding process is improperly controlled, which is likely to cause premature austenitization of the material. After solidification is completed, the austenite grain grows, which further deteriorates the performance; in addition, the high resistance of this ultra-high-strength thermoformed steel plate is prone to spatter during welding, which leads to poor welding defects; and the ultra-high-strength thermoformed steel plate The Ms transformation temperature is low, and it is difficult to obtain satisfactory welding results by directly applying the conventional welding process of high-strength steel plates. If the tempering process is added after welding, a long cooling cycle needs to be added, which will reduce production efficiency and increase costs.

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