Resistance Spot Welding With Magnetic Hydrogen Release
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Solution Overview
Problem
Existing resistance spot welding methods face challenges in reducing hydrogen embrittlement and delayed fracture in high strength steel sheets, particularly due to the accumulation of hydrogen in the nugget, which is not effectively addressed by existing techniques like optimizing electrode force and current patterns, and post-weld heat treatment leads to increased costs and material property changes.
Innovation Solution
Applying a steady magnetic field to the weld mark of joined steel sheets with specific magnetic flux density and angle after welding to efficiently release hydrogen from the nugget, thereby improving delayed fracture resistance without altering the material properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If post-weld heat treatment is performed to reduce residual hydrogen, then delayed fracture resistance is improved, but production costs increase and material properties change due to microstructure changes
Solution Approach 1:
The patent extracts the heat treatment step from the welding process by applying magnetic field treatment instead. The magnetic field is applied directly to the welded portion to promote hydrogen diffusion and release, eliminating the need for separate post-weld heat treatment facilities and processes, thereby reducing production costs while maintaining delayed fracture resistance
Solution Approach 2:
The patent replaces the thermal field (heat treatment) with a magnetic field to achieve hydrogen removal. By applying a magnetic field with flux density of 0.1-15 T at an angle exceeding 0° to the weld mark, hydrogen is efficiently released from the nugget without causing microstructural changes that would alter material properties
2Productivity
If rapid cooling is applied between welding current and subsequent-current, then welding efficiency is improved, but hydrogen diffusion is suppressed and residual hydrogen in the nugget increases
Solution Approach 1:
The patent applies magnetic field treatment immediately after welding while the steel sheet is still in the cooling phase. This preliminary action promotes hydrogen diffusion and release during the cooling process itself, preventing hydrogen accumulation in the nugget without requiring additional time or slowing down the welding efficiency
Solution Approach 2:
The patent changes the physical parameter of the steel sheet by applying a magnetic field with specific flux density (0.1-15 T) and angle (exceeding 0° to the normal direction of the surface). This parameter change promotes hydrogen diffusion and release during the cooling phase, resolving the contradiction between rapid cooling efficiency and hydrogen removal
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method effectively reduces residual hydrogen in the nugget, preventing delayed fracture in welded joints, especially in high strength steel sheets, without the need for heat treatment, thus maintaining material integrity and reducing production costs.
Implementation Method 1
applying a steady magnetic field to a weld mark produced on a surface of a steel sheet after joining by the joining
Data Source
AI summary
It is provided a resistance spot welding method that is compatible with the production of a welded joint that exhibits excellent delayed fracture resistance. It is a resistance spot welding method wherein two or more overlapped steel sheets are clamped by a pair of welding electrodes, and current is applied while applying pressure to the steel sheets to form a nugget on the mutual overlapped surfaces of the steel sheets to join the steel sheets, the resistance spot welding method including, after the joining, applying a steady magnetic field to a weld mark produced on a surface of a steel sheet after joining by the joining, such that an angle θ between a normal direction of the surface of the steel sheet after joining and a direction of application of the steady magnetic field exceeds 0° and the magnetic flux density is 0.1 T to 15 T.