Steel Sheet Fe Pre-plating Suppresses Surface Oxides
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Solution Overview
Problem
Existing steel sheets face challenges in maintaining excellent plating characteristics due to surface oxides formed during annealing, which can lead to non-plating or peeling of the plating layer during hot-dip plating.
Innovation Solution
A steel sheet with a specific composition of Mn and Si, where the GDS profile shows two or more valleys with Mn and Si amounts 60% or less of the parent material within 1 μm from the surface, and a method involving Fe pre-plating followed by annealing in an atmosphere with a dew point temperature of 10° C. or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If alloy elements such as Mn, Si, Al, Cr, B are added to increase hardenability, then martensite can be easily formed during cooling, but surface oxides are formed during annealing which deteriorate plating wettability and cause non-plating or plating peeling
Solution Approach 1:
The patent applies preliminary action by forming an Fe plating layer on the steel sheet surface before annealing. This Fe plating layer acts as a protective barrier during subsequent annealing, preventing oxidation of alloy elements (Mn, Si, Al, Cr, B) that would otherwise form surface oxides and deteriorate plating quality. The Fe plating layer is formed through electroplating or hot-dip plating, and its presence ensures that even when alloy elements are present in the steel, they do not oxidize during annealing, thus maintaining excellent plating characteristics.
Solution Approach 2:
The patent uses an Fe plating layer as an intermediary substance between the steel substrate and the annealing atmosphere. This intermediate layer selectively prevents oxygen from reaching and oxidizing the alloy elements in the steel, while allowing the annealing process to proceed normally for the base steel. The Fe plating layer thus mediates the interaction between the steel and the oxidizing atmosphere, protecting the harmful alloy elements from oxidation.
2Reliability
If reduction-annealing is performed in a reducing atmosphere to remove iron oxide, then plating wettability improves, but Si may be concentrated directly under the iron oxide to form Si oxide bands causing peeling at the interface between reduced iron and base iron
Solution Approach 1:
The patent applies preliminary action by forming the Fe plating layer before annealing, which prevents the formation of surface oxides in the first place. This eliminates the need for subsequent reduction-annealing steps that could cause Si oxidation and peeling issues. By addressing the oxidation problem preemptively with the Fe plating layer, the patent avoids the harmful side effects of reduction processes.
Solution Approach 2:
The patent converts the potential harm of alloy elements (which tend to oxidize and form surface oxides) into a benefit by using the Fe plating layer to control and direct the oxidation behavior. The Fe plating layer itself can undergo controlled oxidation and reduction, but this protects the underlying alloy elements from forming harmful surface oxides. The Fe acts as a sacrificial protective layer that benefits the overall plating quality.
3Reliability
If high dew point is maintained in annealing furnace to internally oxidize alloy components, then external oxidation is reduced, but the effect is minimal when large amount of Mn is added
Solution Approach 1:
The patent applies preliminary action by forming the Fe plating layer before annealing, which provides immediate and effective protection against oxidation. This preliminary protective measure is more reliable and effective than relying on high dew point control during annealing, especially when large amounts of Mn are present. The Fe plating layer provides a physical barrier that is more effective than attempting to control oxidation through atmosphere composition alone.
Solution Approach 2:
The Fe plating layer serves as an intermediary that provides consistent and reliable oxidation protection regardless of the alloy composition. Unlike high dew point control which may be ineffective with large amounts of Mn, the Fe plating layer provides a physical barrier that consistently prevents oxidation of alloy elements, making the plating process effective across a wide range of steel compositions.
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
This approach effectively suppresses the formation of surface oxides, thereby improving plating adhesion and reducing the occurrence of non-plating or peeling during hot-dip plating, resulting in a steel sheet with enhanced plating characteristics.
Implementation Method 1
components having high affinity for oxygen such as Si, Mn, Al, or the like, may be internally oxidized to a certain depth from a surface layer of the steel sheet
Implementation Method 2
during the annealing process, the alloy elements may diffuse to the surface of the steel material, and may react with a small amount of oxygen or water vapor present in an annealing furnace to form single or composite oxides of the elements
Data Source
AI summary
The present invention relates to a steel sheet that can be used in automobiles, etc., and relates to a steel sheet that can ensure improved plating characteristics, and a manufacturing method therefor.