Galvanized Steel Sheet Internal Oxide Control
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Solution Overview
Problem
Conventional methods for manufacturing galvanized steel sheets with high Si and Mn content struggle to achieve excellent corrosion resistance and anti-powdering properties during heavy machining, as internal oxides formed for improved platability compromise corrosion resistance and workability.
Innovation Solution
Inhibiting the formation of internal oxides in the surface portion of the steel sheet by controlling the atmosphere and temperature in the annealing step, suppressing the oxide amount to 0.05 g/m2 or less, and optimizing the composition of elements like Si, Mn, Al, and others to enhance corrosion resistance and workability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If internal oxidation is promoted to improve platability, then platability is improved, but corrosion resistance and anti-powdering property deteriorate
Solution Approach 1:
The patent changes the chemical composition parameters of the steel sheet by precisely controlling the contents of Si (0.01-2.0%), Mn (0.1-3.0%), Al (0.001-1.0%), and other elements. This compositional adjustment modifies the oxidation behavior during annealing, allowing platability to be achieved without excessive internal oxide formation that would harm corrosion resistance. The specific composition range optimizes the balance between surface reactivity for plating and internal oxide suppression.
Solution Approach 2:
The patent creates a localized quality difference between the surface layer and the bulk material. The surface layer is designed to have specific oxide characteristics that ensure good platability, while the bulk material maintains low oxide content to preserve corrosion resistance and anti-powdering properties. This is achieved through controlled oxidation that affects only the immediate surface region rather than penetrating deeply into the material.
2Ease of manufacture
If internal oxidation is promoted to improve platability, then platability is improved, but anti-powdering property deteriorates
Solution Approach 1:
The patent adjusts the chemical composition parameters, particularly Si (0.01-2.0%) and Mn (0.1-3.0%), to control the oxidation kinetics. This ensures that oxidation is sufficient to create a plateable surface but limited in depth to avoid forming internal oxides that would cause powdering during machining. The Al content (0.001-1.0%) also plays a role in modifying oxide formation behavior.
Solution Approach 2:
The patent applies partial oxidation rather than complete or excessive oxidation. By controlling the annealing atmosphere and temperature, oxidation is performed to the extent needed for platability but stopped before internal oxides form in quantities that would compromise anti-powdering property. This partial action achieves the minimum necessary oxidation without the harmful effects of excessive oxidation.
3Strength
If Si and Mn content are increased to achieve high strength, then strength is improved, but platability deteriorates
Solution Approach 1:
The patent optimizes the Si content (0.01-2.0%) and Mn content (0.1-3.0%) to achieve a balance between strength and platability. These elements contribute to solid solution strengthening and precipitation hardening, providing high strength. Simultaneously, the controlled composition ensures that during annealing, oxidation occurs at the surface to improve platability without excessive internal oxide formation. The Al content (0.001-1.0%) further modifies the oxidation behavior to enhance platability.
Solution Approach 2:
The patent creates a local quality difference where the surface layer develops oxide characteristics that improve platability, while the bulk material with high Si and Mn content maintains its strength properties. The surface layer undergoes controlled oxidation to create a plateable surface, while the high-strength bulk material remains largely unaffected, preserving both strength and platability simultaneously.
4Reliability
If CO2 concentration is increased to suppress internal oxidation, then corrosion resistance is improved, but furnace contamination and carburization occur
Solution Approach 1:
The patent changes the approach from using high CO2 concentration to suppress oxidation to using controlled low CO2 concentration combined with specific steel composition. By optimizing Si (0.01-2.0%), Mn (0.1-3.0%), and Al (0.001-1.0%) content, the steel achieves appropriate oxidation behavior during annealing without requiring high CO2 atmosphere. This eliminates the need for CO2-rich atmosphere that would cause furnace contamination and carburization, while still achieving good corrosion resistance through controlled surface oxidation.
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
Resulting in a high-strength galvanized steel sheet with excellent corrosion resistance and anti-powdering properties during heavy machining, maintaining platability while improving corrosion resistance and workability.
Implementation Method 1
the partial pressure of oxygen in the atmosphere of an annealing furnace is controlled such that a surface layer of a base member just before being plated is internally oxidized and is inhibited from being externally oxidized
Implementation Method 2
the heating temperature in a reducing furnace is determined by a formula relating the partial pressure of steam and the dew point is increased such that a surface layer of the base member is internally oxidized
Data Source
AI summary
A galvanized steel sheet includes a zinc plating layer which is disposed on a steel sheet containing 0.01% to 0.15% C, 0.001% to 2.0% Si, 0.1% to 3.0% Mn, 0.001% to 1.0% Al, 0.005% to 0.060% P, and 0.01% or less S on a mass basis, the remainder being Fe and unavoidable impurities, and which has a mass per unit area 20 g/m2 to 120 g/m2. An oxide of at least one selected from the group consisting of Fe, Si, Mn, Al, and P is present in a surface portion of the steel sheet that lies directly under the zinc plating layer and that extends up to 100 µm from the surface of a base steel sheet. The amount of the oxide per unit area is 0.05 g/m2 or less in total. The steel sheet has excellent corrosion resistance, anti-powdering property during heavy machining, and strength.