Undercarriage Weld Metal Composition for Strength and Corrosion Resistance
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Solution Overview
Problem
Automobile undercarriage parts with welded joints face challenges in achieving both high strength and corrosion resistance, particularly due to issues with Si-based slag formation and strength degradation when reducing Si content, leading to potential red rust and painting defects.
Innovation Solution
The composition of the weld metal is carefully controlled to include specific ranges of C, Si, Mn, Al, Ti, and other elements to balance strength and corrosion resistance, with the coexistence of Al and Ti suppressing coarse ferrite formation and red rust, and the use of appropriate sheet thickness to prevent welding defects and enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Si content in weld metal is reduced to suppress Si-based slag formation, then corrosion resistance after painting is improved, but strength of weld metal deteriorates due to coarse ferrite formation
Solution Approach 1:
The invention changes the chemical composition parameters of the weld metal by strictly controlling Si content (≤0.05%) and Mn content (0.3-2.0%), and by adding specific amounts of Al (0.01-0.30%) and Ti (0.01-0.30%). This parameter optimization suppresses Si-based slag formation while preventing coarse ferrite formation through appropriate deoxidation, thereby resolving the contradiction between corrosion resistance and strength
Solution Approach 2:
The invention creates a composite microstructure in the weld metal by combining multiple alloying elements (Al, Ti, Mn) that work synergistically. Al and Ti provide deoxidation and suppress coarse ferrite formation, while Mn contributes to strength. This composite approach allows simultaneous achievement of high strength and corrosion resistance
2Manufacturing precision
If Si content is reduced to improve painting quality, then painting defects are suppressed, but weld metal strength decreases
Solution Approach 1:
The invention optimizes the Si content parameter to ≤0.05% to prevent Si-based slag formation that causes painting defects, while compensating for strength loss through controlled Mn content (0.3-2.0%) and addition of Al (0.01-0.30%) and Ti (0.01-0.30%). This parameter change achieves both good painting quality and adequate strength
Solution Approach 2:
The invention introduces Al and Ti as intermediary elements that mediate between the conflicting requirements. These elements provide deoxidation and suppress coarse ferrite formation, allowing low Si content (for good painting) while maintaining strength through the intermediary action of Al-Ti-Mn combination
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 weld metals with excellent strength and corrosion resistance, as evidenced by the suppression of red rust and successful tensile tests, ensuring the durability of automobile undercarriage parts.
Implementation Method 1
One of the causes for a decrease in the strength of the weld metal in the case of reducing the Si content of the weld metal is the formation of coarse ferrite due to the lack of deoxidation
Implementation Method 2
In a case where the Al content and the Ti content of the weld metal are increased more than ever, it is possible to suppress the formation of coarse ferrite in the weld metal
Data Source
Figure 1~2
AI summary
An automobile undercarriage part of the present invention is an automobile undercarriage part including a welded joint in which a first steel sheet and a second steel sheet are overlapped and a fillet weld is formed between an end surface of the first steel sheet and a surface of the second steel sheet, in which a chemical composition of a weld metal that forms the welded joint contains, with respect to a total mass of the weld metal, by mass%, C: 0.02% to 0.20%, Si: more than 0% to less than 0.10%, Mn: 0.3% to 2.0%, Al: 0.002% to 0.30%, Ti: 0.005% to 0.30%, P: more than 0% to 0.015%, and S: more than 0% to 0.030%, and the following formula (1) and formula (2) are satisfied. [Al] + [Ti] > 0.05···· Formula (1) 7 × [Mn] - 112 × [Ti] - 30 × [Al] ≤ 4.0 ···· Formula (2)