Fe-Based Electroplated Steel Sheet Against Zinc-Induced Weld Cracking
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Solution Overview
Problem
High-strength cold-rolled steel sheets are prone to liquid metal embrittlement cracking during resistance welding, especially when combined with galvanized steel sheets, due to residual stresses and the diffusion of zinc into crystal grain boundaries, which can lead to intergranular cracking, particularly in Si-containing steel sheets.
Innovation Solution
Forming an Fe-based electroplating layer with a coating weight of more than 20.0 g/m² on a cold-rolled steel sheet before continuous annealing, which integrates crystal orientations with the steel sheet at a high ratio, acts as a soft layer to reduce stress and suppress the penetration of molten zinc, thereby enhancing resistance to cracking in resistance welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high-strength cold-rolled steel sheets are used to achieve lightweight and high-strength automotive bodies, then strength is improved, but resistance to cracking in resistance welding deteriorates due to liquid metal embrittlement
Solution Approach 1:
An Fe-based electroplating layer is introduced as an intermediary between the Si-containing steel sheet and the welding zone. This plating layer acts as a barrier that prevents molten zinc from penetrating into the crystal grain boundaries of the base metal, thereby eliminating the liquid metal embrittlement cracking issue while preserving the high strength properties of the steel sheet
Solution Approach 2:
The invention creates a composite structure consisting of the Si-containing steel sheet substrate combined with an Fe-based electroplating layer. This composite material system combines the high strength and formability of Si-containing steel with the protective characteristics of the Fe-based plating layer, achieving both mechanical performance and welding reliability
2Strength
If Si is added to increase the strength of cold-rolled steel sheets through solid solution strengthening, then strength is improved, but resistance to cracking in resistance welding deteriorates due to increased susceptibility to liquid metal embrittlement
Solution Approach 1:
The Fe-based electroplating layer serves as a protective intermediary that specifically addresses the welding susceptibility issue caused by Si addition. The plating layer blocks the interaction between molten zinc and the Si-enriched grain boundaries, allowing the steel sheet to maintain both the high strength from Si solid solution strengthening and the welding reliability
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 Fe-based electroplated steel sheet exhibits excellent resistance to cracking in resistance welding, particularly internal cracking, by delaying zinc penetration and reducing residual stress, even when combined with galvanized steel sheets, while maintaining high strength and formability.
Implementation Method 1
when annealing is performed after the formation of the Fe-based electroplating layer, the crystal orientations of the Fe-based electroplating layer and the cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the cold-rolled steel sheet
Implementation Method 2
the Fe-based electroplating layer...acts as a soft layer to reduce stress and suppress the penetration of molten zinc, thereby enhancing resistance to cracking in resistance welding
Data Source
AI summary
Provided is a steel sheet with excellent resistance to cracking in resistance welding at a welded portion, even if the crystal orientations of an Fe-based electroplating layer and a Si-containing cold-rolled steel sheet are integrated at a high ratio at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet. Provided is an Fe-based electroplated steel sheet having a Si-containing cold-rolled steel sheet containing Si in an amount of 0.1 mass % or more and 3.0 mass % or less; and an Fe-based electroplating layer formed on at least one surface of the Si-containing cold-rolled steel sheet with a coating weight per surface of more than 20.0 g/m2, where the crystal orientations of the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet are integrated at a ratio of more than 50% at the interface between the Fe-based electroplating layer and the Si-containing cold-rolled steel sheet.