High-Strength Galvanized Steel Sheet Manufacturing via Pickling
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Solution Overview
Problem
The challenge is to manufacture high-strength galvanized steel sheets with excellent strength-elongation balance, coating adhesiveness, and surface appearance, particularly for automobile components, where easily oxidizable elements like Si and Mn form oxides that deteriorate wettability and adhesiveness during the galvanizing process.
Innovation Solution
A method involving two annealing processes, with pickling in an oxidizing aqueous solution followed by rinsing and then pickling in a non-oxidizing solution, to remove Si oxides and form minute asperities on the steel surface, enhancing coating adhesiveness through an anchor effect, while maintaining a clean surface for galvanizing treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If large amounts of Si and Mn are added to increase steel strength, then strength is improved, but coating wettability deteriorates due to oxide formation on the surface
Solution Approach 1:
The patent applies preliminary action by performing pickling treatment before the galvanizing process to remove oxides formed during annealing. This preliminary oxide removal enables the subsequent galvanizing treatment to proceed effectively even when Si and Mn contents are high, thus resolving the contradiction between achieving high strength and maintaining good coating wettability.
Solution Approach 2:
The patent changes the chemical state of the steel sheet surface by controlling the pickling process parameters (acid concentration, temperature, time) to selectively remove oxides while preserving the beneficial alloy elements Si and Mn in the bulk material. This parameter control allows high-strength composition to coexist with good coating wettability.
2Stability of the object's composition
If annealing is performed to improve steel properties, then strength and ductility are improved, but oxides form on the surface that deteriorate coating adhesiveness
Solution Approach 1:
The patent performs pickling treatment as a preliminary action before the galvanizing process to remove the oxides that formed during annealing. This allows the annealing process to be used for improving material properties while preventing the oxide-related adhesiveness problems through subsequent oxide removal.
Solution Approach 2:
The patent converts the harmful oxide formation during annealing into a beneficial process by using the pickling treatment to remove these oxides. The annealing process still provides the desired microstructural benefits, while the pickling step eliminates the harmful surface oxides, effectively turning a harmful effect into a beneficial outcome.
3Object-affected harmful factors
If pickling is performed to remove oxides, then coating wettability is improved, but Si oxides are difficult to remove due to poor reactivity
Solution Approach 1:
The patent changes the pickling solution parameters by using a mixture of acids with different characteristics (e.g., hydrochloric acid and sulfuric acid) and controlling temperature and concentration to enhance the reactivity toward Si oxides. This parameter optimization makes the pickling process more effective at removing difficult-to-remove Si oxides.
Solution Approach 2:
The patent employs a composite pickling solution system combining multiple acids and additives to create a chemically active mixture that enhances oxide removal efficiency. The synergistic effect of different chemical components enables effective removal of Si oxides that would be difficult to remove with a single acid alone.
4Object-affected harmful factors
If rolling process is added to form asperity for anchor effect, then coating adhesiveness is improved, but manufacturing complexity increases
Solution Approach 1:
The patent replaces the mechanical rolling process with a chemical pickling process to create surface asperities. Instead of mechanically deforming the surface through rolling, the pickling solution chemically etches the surface to create similar anchoring features, thereby achieving the same adhesiveness improvement without the added mechanical processing step.
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 method achieves a high-strength galvanized steel sheet with improved strength-elongation balance, surface appearance, and coating adhesiveness, enabling weight reduction in automobile bodies and enhanced fuel efficiency.
Implementation Method 1
pickling is performed to dissolve and remove oxides formed on the surface of the steel sheet
Implementation Method 2
Easily oxidizable elements in steel are selectively oxidized even in a non-oxidizing atmosphere or a reducing atmosphere, which is generally used, and concentrated on the surface of a steel sheet to form oxides on the surface
Implementation Method 3
minute asperity is formed on the surface of a steel sheet to achieve an anchor effect at a coating interface
Data Source
AI summary
An object is to provide a method for manufacturing a high-strength galvanized steel sheet excellent in terms of strength-elongation balance, coating adhesiveness, and surface appearance. A first heating process of heating a steel sheet having a predetermined chemical composition to a temperature range of 800°C or higher and 950°C or lower in an atmosphere having a H2 concentration of 0.05 vol% or more and 30.0 vol% or less and a dew point of 0°C or lower, a first pickling process of pickling the steel sheet which has been subjected to the first heating process in an oxidizing acidic aqueous solution and of rinsing the pickled steel sheet in water, a second pickling process of pickling the steel sheet which has been subjected to the first pickling process in a non-oxidizing acidic aqueous solution and of rinsing the pickled steel sheet in water, a second heating process of holding the steel sheet which has been subjected to the second pickling process in a temperature range of 700°C or higher and 900°C or lower in an atmosphere having a H2 concentration of 0.05 vol% or more and 30.0 vol% or less and a dew point of 0°C or lower for 20 seconds or more and 300 seconds or less, and a process of performing a galvanizing treatment on the steel sheet which has been subjected to the second heating process are performed.