Sn Plating Steel Sheet Corrosion Resistance via Crystal Orientation
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Solution Overview
Problem
Zr containing chemical treatment films on Sn plating steel sheets suffer from deteriorated corrosion resistance, leading to issues like yellowing and sulfide staining, especially when used for containers holding food or beverages containing proteins.
Innovation Solution
A method of manufacturing a chemically treated steel sheet with a mat finished Sn plating layer of β-Sn, where the crystal orientation of the Sn plating layer is preferentially arranged to the (100) plane group, and a chemical treatment layer containing Zr and phosphate compounds is applied, optimizing the crystal orientation index and composition to enhance corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Zr containing chemical treatment film is formed on a Sn plating steel sheet, then corrosion resistance is improved, but yellowing and sulfide staining occur leading to deteriorated appearance quality
Solution Approach 1:
The patent changes the crystal orientation parameters of the Sn plating layer by controlling electroplating conditions (current density, temperature, additives) to achieve preferential (200) plane orientation. This parameter change in crystal structure prevents the formation of Sn oxide and sulfide stains while maintaining corrosion resistance with Zr-containing chemical treatment.
Solution Approach 2:
The patent creates a composite structure consisting of a Sn plating layer with specific crystal orientation combined with a Zr-containing chemical treatment film. The oriented Sn layer acts as a protective barrier that prevents harmful reactions between the steel substrate and the chemical treatment film, eliminating yellowing and sulfide staining.
2Object-affected harmful factors
If crystal orientation of Sn plating is arranged to a (220) plane, then whisker formation is prevented, but corrosion resistance deteriorates
Solution Approach 1:
The patent changes the crystal orientation parameter from (220) plane to (200) plane by adjusting electroplating parameters. This parameter change simultaneously achieves whisker prevention and maintains excellent corrosion resistance when combined with Zr-containing chemical treatment.
3Reliability
If a chromate treatment is performed on a steel sheet or plating steel sheet, then corrosion resistance and coating adhesion are ensured, but environmental hazards increase due to hexavalent chromium
Solution Approach 1:
The patent replaces the hazardous chromate treatment with a Zr-containing chemical treatment that is environmentally friendly. The Zr treatment film, when applied on oriented Sn plating, provides comparable corrosion resistance and coating adhesion without the environmental hazards of hexavalent chromium.
Solution Approach 2:
The patent introduces an oriented Sn plating layer as an intermediary between the steel substrate and the Zr-containing chemical treatment. This intermediary layer enables the use of environmentally friendly Zr treatment while achieving corrosion resistance previously only attainable with chromate treatment.
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 a Sn plating steel sheet with improved corrosion resistance, preventing yellowing and sulfide staining, making it suitable for use in food and beverage containers.
Implementation Method 1
cathode electrolytic treatment is continuously performed on a steel strip in treatment liquid including Zr fluoride ion and phosphate ion, thereby coating the steel strip with a chemical treatment film
Data Source
Figure 1A~1B
Figure 2
AI summary
The chemical treatment steel sheet includes a steel sheet, a mat finished Sn plating layer that is provided as an upper layer of the steel sheet and is formed of a β-Sn, and a chemical treatment layer that is provided as an upper layer of the Sn plating layer. The Sn plating layer contains the β-Sn of 0.10 g/m2 to 20.0 g/m2 in terms of an amount of metal Sn. A crystal orientation index of a (100) plane group of the Sn plating layer is higher than crystal orientation indexes of other crystal orientation planes. The chemical treatment layer includes a Zr compound containing Zr of 0.50 mg/m2 to 50.0 mg/m2 in terms of an amount of metal Zr, and a phosphate compound.