Fe-Based Electroplated Steel Sheet for Weld Crack Resistance
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Solution Overview
Problem
Hot-dip galvanized steel sheets experience liquid metal embrittlement (LME) and grain boundary cracks during resistance welding, particularly due to residual stress and zinc diffusion, which worsens with increased steel sheet strength, making it challenging to achieve both high strength and resistance to resistance-weld cracking.
Innovation Solution
An Fe-based electroplated steel sheet is produced by subjecting a base steel sheet with Si content between 0.50% and 3.00% to an Fe-based electroplating treatment using a solution containing Fe ions and transition metal ions, followed by annealing, to form a fine-grained Fe-based electroplated layer that reduces residual stress and inhibits zinc penetration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the strength of the steel sheet is increased, then the safety and fuel efficiency are improved, but the residual stress increases and liquid metal embrittlement cracks occur during resistance welding
Solution Approach 1:
An Fe-based electroplated layer is introduced as an intermediary between the hot-dip galvanized layer and the base steel sheet. This intermediate layer acts as a barrier to zinc diffusion during resistance welding, preventing liquid metal embrittlement while allowing the base steel sheet to maintain high strength through Si-based solid solution strengthening
Solution Approach 2:
The steel sheet employs a composite structure consisting of a base steel sheet with Si content of 0.50-3.00 mass%, an Fe-based electroplated layer containing transition metals, and a hot-dip galvanized layer. This composite structure combines the high strength of Si-strengthened steel with the crack-resistant properties of the Fe-based electroplated layer
2Strength
If Si is added to achieve strength enhancement, then the strength increases, but the formability may be impaired
Solution Approach 1:
The Si content is precisely controlled within the range of 0.50-3.00 mass%, which is sufficient to achieve the desired strength enhancement through solid solution strengthening but limited enough to avoid excessive impairment of formability. This parameter optimization balances strength and formability
3Reliability
If the Fe ions content in electroplating solution is increased, then the coating amount increases and crack resistance improves, but the production cost increases
Solution Approach 1:
The Fe ions content in the electroplating solution is optimized to 1.0 mass% or more, which provides sufficient coating amount to achieve the desired crack resistance. This parameter setting balances the need for adequate protection with cost considerations by avoiding excessive Fe ions content
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 results in a steel sheet with high strength and excellent resistance to resistance-weld cracking, as the Fe-based electroplated layer acts as a soft layer to alleviate stress and suppress internal cracks, enhancing the toughness of the welded portion.
Implementation Method 1
subjecting a base steel sheet containing Si in an amount of 0.50 to 3.00 mass % to an Fe-based electroplating treatment using an Fe-based electroplating solution containing Fe ions and transition metal ions other than the Fe ions to form an Fe-based electroplated layer
Implementation Method 2
then subjecting the base steel sheet to an annealing treatment
Implementation Method 3
zinc of a plating layer melts and diffuses into crystal grain boundaries, and therefore liquid metal embrittlement (LME) may occur... the Fe-based electroplated layer acts as a soft layer to alleviate stress and suppress internal cracks
Data Source
AI summary
A base steel sheet containing Si in an amount of 0.50 to 3.00 mass % is subjected to an Fe-based electroplating treatment using an Fe-based electroplating solution containing Fe ions and transition metal ions other than the Fe ions to form an Fe-based electroplated layer, and then to an annealing treatment. In the Fe-based electroplating solution, a content of the Fe ions is 1.0 mass % or more and a content of the transition metal ions is 10 to 1000 mass ppm. A coating amount of the Fe-based electroplated layer per one surface of the base steel sheet is 1.0 g/m2 or more. Thus, a steel sheet having high strength and excellent resistance to resistance-weld cracking of a welded portion is obtained.