Steel Sheet Coating for Can Making Weldability
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Solution Overview
Problem
Steel sheets for can making, as described in previous patents, face challenges in achieving both excellent weldability and post-working corrosion resistance, particularly in severely worked portions of can bodies.
Innovation Solution
A steel sheet with an iron-nickel diffusion layer, a metallic chromium layer featuring flat-like and granular sublayers, and a chromium oxide layer is developed, where the iron-nickel diffusion layer enhances corrosion resistance and the metallic chromium layer improves weldability by reducing contact resistance through granular protrusions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If TFS is welded without polishing the surface chromium oxide layer, then productivity is improved and maintenance load is reduced, but contact resistance increases and weldability deteriorates
Solution Approach 1:
The invention creates local conductive pathways through granular protrusions of metallic chromium that penetrate the chromium oxide layer. These protrusions are distributed non-uniformly across the surface, providing localized low-resistance contact points while maintaining the overall integrity of the oxide layer for corrosion protection.
Solution Approach 2:
The granular protrusions of metallic chromium are formed in advance during the electrolytic chromating process, before welding occurs. This preliminary formation of conductive structures eliminates the need for post-plating mechanical polishing to achieve good weldability.
2Reliability
If a thick metallic chromium layer is used to ensure weldability, then contact resistance is reduced, but corrosion resistance deteriorates due to insufficient sacrificial protection
Solution Approach 1:
The invention changes the morphological parameters of the metallic chromium layer, creating granular protrusions with specific size distributions (average diameter 0.5-5 μm). This morphological transformation allows a thin chromium layer to provide both weldability through conductive protrusions and corrosion resistance through sufficient material coverage.
Solution Approach 2:
The plating structure forms a composite system with multiple layers: metallic chromium layer with granular protrusions, chromium oxide layer, and hydrated chromium oxide layer. Each layer contributes different properties - the metallic chromium provides conductivity for welding, while the oxide and hydroxide layers provide corrosion protection through sacrificial mechanisms.
3Reliability
If mechanical polishing is performed to remove the chromium oxide layer for welding, then contact resistance is reduced, but the plated film is damaged and base metal is exposed
Solution Approach 1:
The conductive granular protrusions are formed in advance during electrolytic chromating, eliminating the need for subsequent mechanical polishing. This preliminary creation of conductive pathways allows welding to proceed without damaging the protective oxide and hydroxide layers.
Solution Approach 2:
The invention extracts only the essential function of removing oxide interference for welding by creating localized conductive protrusions, while leaving the bulk oxide layer intact to maintain corrosion protection. This selective approach removes only what is necessary for welding without sacrificing overall film integrity.
4Object-affected harmful factors
If tinplate is used to provide sacrificial protection and excellent corrosion resistance, then corrosion resistance is improved, but weldability deteriorates due to the insulating chromium oxide layer
Solution Approach 1:
The invention creates local conductive pathways through granular protrusions of metallic chromium that penetrate the chromium oxide layer. These protrusions are distributed non-uniformly across the surface, providing localized low-resistance contact points while maintaining the overall integrity of the oxide layer for corrosion protection.
Solution Approach 2:
The plating structure forms a composite system with multiple layers: metallic chromium layer with granular protrusions, chromium oxide layer, and hydrated chromium oxide layer. Each layer contributes different properties - the metallic chromium provides conductivity for welding, while the oxide and hydroxide layers provide corrosion protection through sacrificial mechanisms.
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 ensures excellent weldability and post-working corrosion resistance, suppressing cracks and maintaining an electrochemically stable state, thereby enhancing the overall performance of the steel sheet for can making.
Implementation Method 1
an iron-nickel diffusion layer, a metallic chromium layer
Implementation Method 2
a chromium oxide layer on at least one surface of the steel sheet
Implementation Method 3
anterior and posterior cathodic electrolytic treatments and metallic chromium is formed into granular protrusions
Data Source
AI summary
A steel sheet for can making and methods for manufacturing the same. The steel sheet includes, in order from a steel sheet side, an iron-nickel diffusion layer, a metallic chromium layer, and a chromium oxide layer. The iron-nickel diffusion layer has a nickel coating weight of 50 mg/m2 to 500 mg/m2 per surface of the steel sheet and a thickness of 0.060 μm to 0.500 μm per surface of the steel sheet. The metallic chromium layer includes a flat-like metallic chromium sublayer and a granular metallic chromium sublayer placed on a surface of the flat-like metallic chromium sublayer. The total chromium coating weight of both sublayers per surface of the steel sheet is 60 mg/m2 to 200 mg/m2. The chromium oxide layer has a chromium coating weight 3 mg/m2 to 10 mg/m2 per surface of the steel sheet in terms of metallic chromium.