Hot-Dip Galvanized Steel Substrate Bare Spot Reduction
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Solution Overview
Problem
The existing methods for producing high-strength hot-dip galvanized or hot-dip galvannealed steel sheets require complex and costly equipment setups to control atmospheric conditions, leading to increased costs and inefficiencies in suppressing bare spots caused by the oxidation of Si and Mn elements.
Innovation Solution
A steel substrate with specific chemical compositions (C: 0.06-0.3%, Si: 1.00-1.6%, Mn: 1-3%, Al: 0.1% or less, and a Si/Mn ratio of 1.0 or less, subjected to reduction annealing in a nitrogen atmosphere with 5-10% H2, is used to control the formation of oxides and enhance zinc wettability, thereby reducing bare spots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Si and Mn are added to improve strength and ductility, then mechanical properties are enhanced, but oxidation occurs leading to bare spot formation
Solution Approach 1:
The patent applies inert atmosphere by conducting reduction annealing in a nitrogen atmosphere containing 5-10% H2. This reducing environment prevents oxidation of Si and Mn elements during the annealing process, thereby eliminating the formation of oxides that cause bare spots while allowing the steel sheet to achieve the desired strength properties from Si and Mn addition.
Solution Approach 2:
The patent changes the chemical composition parameters by controlling Si content at 1.00-1.6%, Mn content at 1-3%, and maintaining Si/Mn ratio at 1.0 or less. Additionally, the atmosphere composition is changed to nitrogen with 5-10% H2, and temperature parameters are controlled at 600-620°C for 20 seconds or more. These parameter changes optimize both strength and prevent oxidation.
2Object-generated harmful factors
If complex atmospheric control is implemented to suppress oxidation, then bare spot occurrence is reduced, but equipment investment and production cost increase significantly
Solution Approach 1:
The patent uses a simple nitrogen atmosphere containing 5-10% H2 for reduction annealing, which can be implemented in existing annealing furnaces without requiring complex multi-section furnace configurations. This approach suppresses oxidation and prevents bare spots while maintaining equipment simplicity and reducing investment costs.
Solution Approach 2:
The patent simplifies the process by using a uniform atmosphere composition (nitrogen with 5-10% H2) throughout the annealing process, eliminating the need for complex atmospheric control systems with multiple sections having different atmosphere compositions. The temperature range of 600-620°C is also optimized to achieve the desired effect without requiring extreme temperature conditions.
3Device complexity
If uniform atmosphere control is applied throughout the furnace, then equipment complexity is reduced, but oxidation suppression effectiveness decreases
Solution Approach 1:
The patent achieves effective oxidation suppression using a uniform nitrogen atmosphere containing 5-10% H2 throughout the furnace. The key is the specific composition ratio and the reduction annealing temperature range of 600-620°C, which creates a reducing environment that prevents oxidation without requiring complex atmospheric zonation.
Solution Approach 2:
The patent optimizes the atmosphere composition to nitrogen with 5-10% H2 and controls the temperature at 600-620°C for 20 seconds or more. These parameter changes create a reducing atmosphere that effectively suppresses oxidation of Si and Mn throughout the uniform furnace environment, eliminating the need for complex atmospheric control while maintaining oxidation protection.
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 efficiently produces high-strength hot-dip galvanized or hot-dip galvannealed steel sheets with reduced bare spots at a lower cost, ensuring a high Fe exposure rate and improved reactivity with molten zinc.
Implementation Method 1
subjecting a steel sheet containing in percent by mass, C: 0.06% to 0.3%, Si: 1.00% to 1.6%, Mn: 1% to 3%, and Al: more than 0% and 0.1% or less, and satisfying a ratio of Si/Mn of 1.0 or less to reduction annealing
Implementation Method 2
Si and Mn are easily oxidizable elements that are more likely to be oxidized than Fe is. For this reason, even in a reducing atmosphere for Fe, Si and Mn are often easily oxidized and concentrated on the steel sheet surface to form oxides.
Data Source
AI summary
Provided is a technique in which a reduction annealing method is used to efficiently produce a high-strength hot-dip galvanizing substrate or high-strength hot-dip galvannealing substrate, which is useful as a raw material for producing a high-strength plated steel sheet suppressed in the occurrence of bare spot. The substrate for hot-dip galvanizing or hot-dip galvannealing of the present invention satisfies the following condition: when the mapping intensity of Fe, which is obtained by using an electron probe microanalyser in a measurement field of view of 33.6 μm×41.4 μm on the surface after reduction annealing, of 0 to 240 is divided into 16 parts at an interval of 15, the area occupied by a mapping intensity of 195 or more has 70% or more.