Arc Welded Joint Hardness Control for Corrosion Resistance
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Solution Overview
Problem
Existing arc welded joints in automobiles, particularly those made from high-strength steel sheets with tensile strength below 640 MPa, face challenges in maintaining strength in corrosive environments due to corrosion, and existing techniques do not effectively address rusting and joint strength degradation.
Innovation Solution
The development of an arc welded joint with a slag-covered area ratio of 20% or less and specific Vickers hardness distribution in the weld metal, combined with an arc welding method using a shielding gas with controlled oxidizing gas levels and intermittent short-circuiting, to suppress rusting and enhance joint strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional arc welding is used on high-strength steel sheets with tensile strength below 640 MPa, then welding can be performed, but the joint strength decreases in corrosive environments due to rusting and corrosion
Solution Approach 1:
The invention changes the chemical composition parameters of the shielding gas (specific ratios of O2, CO2, and Ar) to control the oxidation level during welding. This parameter change reduces slag formation and creates a weld metal composition that resists corrosion, thereby maintaining joint strength in corrosive environments without requiring higher base material strength
Solution Approach 2:
The invention creates local quality differences by controlling the chemical composition of the weld metal specifically (through shielding gas selection) to have high resistance to corrosion, while the base material can vary in strength. The weld metal is locally optimized with specific alloying elements from the wire and shielding gas interaction to provide corrosion resistance at the critical joint region
2Strength
If steel sheets with higher tensile strength (640 MPa or more) are used to improve joint strength, then fracture mode improves, but the weight of members cannot be reduced and applicability to chassis is limited
Solution Approach 1:
The invention changes the welding process parameters (shielding gas composition, wire composition) to produce a weld metal with optimized chemical composition that achieves high strength and corrosion resistance. This allows using lower strength base materials (below 640 MPa) while still achieving excellent joint strength, thereby reducing member weight for the same strength requirement
3Strength
If the weld metal has high strength to prevent fracture, then joint strength is improved, but the weld becomes more susceptible to corrosion and rusting over time
Solution Approach 1:
The invention optimizes the chemical composition parameters of the weld metal by controlling the shielding gas composition (O2, CO2, Ar ratios) and wire composition. This creates a weld metal with specific alloying elements that provide both high strength and inherent corrosion resistance, breaking the trade-off between strength and corrosion susceptibility
Solution Approach 2:
The invention creates a composite chemical composition in the weld metal by combining elements from the base material, welding wire, and shielding gas atmosphere. The resulting composite material has synergistic properties of high strength and corrosion resistance that neither component alone would provide
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 approach results in an arc welded joint with improved resistance to rusting and maintained strength even in corrosive environments, ensuring stable joint strength and reduced corrosion impact.
Implementation Method 1
a weld formed by arc welding of an overlap of at least two steel sheets
Implementation Method 2
using a shielding gas including Ar gas and an oxidizing gas, the oxidizing gas satisfying the relationship of the formula (2)
Implementation Method 3
the Vickers hardness of a weld metal and the Vickers hardness of softened portions of a weld heat affected zone
Data Source
AI summary
An arc welded joint and an arc welding method. The arc welded joint has a weld formed by arc welding of an overlap of at least two steel sheets. A slag-covered area ratio is 20% or less. A Vickers hardness of a weld metal and a Vickers hardness of softened portions of a weld heat affected zone in the weld satisfy a specified relationship.