Hot-dip galvanized steel sheet with refined interface layer
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Solution Overview
Problem
Conventional hot-dip galvanized steel sheets face issues with plating adhesion, fatigue resistance, and corrosion resistance, particularly during severe bending and hole expansion processes, where the plated layer can peel off, leading to loss of corrosion resistance and premature rusting.
Innovation Solution
A hot-dip galvanized steel sheet with a controlled microstructure and chemical composition, including a volume fraction of hard phases at the interface between the plating layer and the base steel sheet, and the formation of a ζ phase (FeZn13) in the plated layer, which suppresses peeling and enhances adhesion without requiring alloying treatments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional hot-dip galvanized steel sheet is subjected to severe bending or hole expansion working, then formability is achieved, but the plated layer peels off from the base steel sheet causing loss of corrosion resistance
Solution Approach 1:
The invention changes the chemical composition parameters of the base steel sheet, specifically controlling carbon content (0.15-0.40%), silicon content (0.01-2.50%), and manganese content (1.50-3.50%), to optimize the microstructure and prevent plating peeling during severe forming operations while maintaining formability
Solution Approach 2:
The invention creates a composite structure at the interface between the plated layer and base steel sheet by forming a refined layer with specific microstructure (ferrite phase with controlled grain size of 0.1-5.0 μm) and controlled oxide distribution, which acts as a transition zone improving bonding between the galvanized layer and steel substrate
2Reliability
If carbon is removed from the surface part of base steel sheet to enhance plating adhesion, then adhesion is improved, but strength of the region is significantly decreased
Solution Approach 1:
Instead of removing carbon, the invention optimizes carbon content to 0.15-0.40% and controls the microstructure by forming a refined layer with specific grain size (0.1-5.0 μm) and phase composition (ferrite with controlled volume fraction), maintaining both adhesion and strength through microstructural control rather than compositional depletion
Solution Approach 2:
The invention creates local quality differences by forming a refined layer at the surface with specific properties (fine grain ferrite structure, controlled oxide distribution) that differs from the bulk material, providing enhanced adhesion at the interface while maintaining overall material strength
3Reliability
If oxide is formed on the surface of steel sheet to enhance plating adhesion, then adhesion is improved, but carbon is bound to oxygen and released from steel sheet causing strength decrease
Solution Approach 1:
The invention controls the types and amounts of oxides formed by optimizing the chemical composition (Si: 0.01-2.50%, Mn: 1.50-3.50%, C: 0.15-0.40%) and processing conditions, forming a refined layer with controlled oxide distribution that enhances adhesion without excessive carbon depletion
Solution Approach 2:
The invention uses silicon and manganese oxides as intermediary substances in the refined layer that facilitate bonding between the plated layer and steel sheet without requiring excessive carbon oxidation, thereby maintaining steel sheet strength while improving adhesion
4Reliability
If alloying treatment is performed to form ζ phase in plated layer to suppress peeling, then plating adhesion is enhanced, but manufacturing complexity increases
Solution Approach 1:
The invention performs preliminary action by optimizing the chemical composition of the base steel sheet (C: 0.15-0.40%, Si: 0.01-2.50%, Mn: 1.50-3.50%) before galvanizing to ensure proper microstructure formation and adhesion, eliminating the need for subsequent alloying treatments
Solution Approach 2:
The invention enables self-service by designing a base steel sheet composition that automatically forms the desired refined layer microstructure (ferrite phase with 0.1-5.0 μm grain size) and promotes proper intermetallic layer formation during standard hot-dip galvanizing, without requiring additional alloying steps
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 solution provides improved formability, fatigue resistance, weldability, corrosion resistance, and plating adhesion, maintaining the steel sheet's strength and preventing premature rusting.
Implementation Method 1
the formation of a ζ phase (FeZn13) in the plated layer, which suppresses peeling and enhances adhesion
Data Source
Figure 1~2
AI summary
A hot-dip galvanized steel sheet wherein the hot-dip galvanized steel sheet comprises a base steel sheet and a hot-dip galvanized layer, a ferrite phase is, by volume fraction, 50% or less in a range of 1/8 thickness to 3/8 thickness centered at a position of 1/4 thickness from the surface of the base steel sheet, a hard structure is 50% or more, wherein the hot-dip galvanized steel sheet has the hot-dip galvanized layer in which Fe is 5.0% or less and Al is 1.0% or less, and columnar grains formed of a ζ phase is 20% or more in an entire interface between the plated layer and the base steel sheet, on the surface of the base steel sheet in which a volume fraction of a residual austenite is 3% or less and a ratio of a volume fraction of the hard structure is 0.10 times or more to 0.90 times or less of that of the hard structure in the range of 1/8 thickness to 3/8 thickness in a range of 20 µm depth in a steel sheet direction originating an interface between the hot-dip galvanized layer and the base steel sheet, and wherein the hot-dip galvanized steel sheet has a refined layer at the side of the interface in the base steel sheet, and wherein an average thickness of the refined layer, an average grain size of ferrite in the refined layer and a maximum size of the oxide included in the refined layer are defined respectively.