Annealing Flat Steel for Pore-Free Corrosion Coatings
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Solution Overview
Problem
Existing methods for manufacturing sheet metal components from flat steel products with corrosion protection coatings fail to meet the high requirements for weldability and organic coating adhesion, particularly in resistance welding and painting processes.
Innovation Solution
A method involving annealing a flat steel product in a continuous furnace with specific dew point and annealing temperature settings, followed by application of an aluminium-based corrosion protection coating, to create a homogeneous and pore-reduced coating that enhances weldability and organic coating adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional annealing process is used before applying the corrosion protection coating, then the steel substrate is protected against corrosive attacks, but the coating contains pores and does not meet requirements for weldability and organic coating adhesion
Solution Approach 1:
The patent applies parameter changes by precisely controlling the annealing temperature (800-950°C) and dew point temperature (-25°C to -40°C) during the annealing process. These specific parameter settings enable the formation of a pore-free, homogeneous coating while maintaining corrosion protection, directly resolving the contradiction between corrosion protection and coating quality.
Solution Approach 2:
The patent uses an inert annealing atmosphere with controlled dew point temperatures to prevent oxide formation and pore generation during the annealing process. This inert environment ensures that the corrosion protection coating forms without pores, improving both coating homogeneity and weldability while maintaining corrosion resistance.
2Ease of manufacture
If the flat steel product is heated to high temperature for hot forming, then the steel becomes sufficiently plastic for forming, but hydrogen absorption increases causing hydrogen embrittlement
Solution Approach 1:
The patent applies preliminary action by performing a controlled annealing process before hot forming to pre-equilibrate the hydrogen content in the steel substrate. This preliminary annealing at specific temperatures and dew points prepares the material for subsequent hot forming while minimizing hydrogen embrittlement risks.
Solution Approach 2:
The patent converts the potentially harmful effect of hydrogen absorption during high-temperature heating into a beneficial outcome by using controlled annealing to establish a stable hydrogen equilibrium state. This preliminary treatment actually reduces hydrogen embrittlement during subsequent forming operations.
3Reliability
If an aluminium-based corrosion protection coating is applied to protect against corrosion, then corrosion resistance is improved, but the coating adhesion for organic layers and weldability are compromised
Solution Approach 1:
The patent uses parameter changes in the annealing process (temperature and dew point) to control the chemical composition and microstructure of the aluminium-based coating. This enables the coating to achieve both corrosion resistance and improved adhesion for organic layers and weldability by optimizing the intermetallic compound formation at the steel-coating interface.
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 method results in sheet metal components with significantly reduced pore content in the corrosion protection coating, improving weldability, adhesion of organic layers, and overall performance in resistance welding and painting processes.
Implementation Method 1
annealing the flat steel product in a continuous furnace having four zones A, B, C, D, which are passed through successively by the flat steel product and in which the flat steel product is annealed under an annealing atmosphere
Implementation Method 2
heating the flat steel product or the board to a hot forming temperature which is higher than the Ac3 temperature of the steel of the flat steel product
Implementation Method 3
The Al-based protective coat can be applied to the steel substrate by hot-dip coating, also known in technical terms as 'hot-dip aluminising'
Implementation Method 4
by a gas separation process, e.g. the known PVD (Physical Vapour Deposition) or CVD (Chemical Vapour Deposition)
Implementation Method 5
due to the presence of the alkaline earth or transition metal in the coat, at most a minimal hydrogen absorption in the steel substrate occurs
Data Source
AI summary
A method for manufacturing a sheet metal component including: annealing a flat steel product comprising 0.05-0.5% C, 0.5-3% Mn, 0.06-1.7% Si, ≤0.06% P, ≤0.01% S, ≤1.0% Al, ≤0.15% Ti, ≤0.6% Nb, ≤0.01% B, ≤1.0% Cr, ≤1.0% Mo, ≤1.0% Cr+Mo, ≤0.2% Ca, ≤0.1% V, remainder iron and impurities in a continuous furnace under an atmosphere consisting of 0.1-15% hydrogen and remainder nitrogen with a specific dew point and temperature profile; applying a coating consisting of <15% Si, ≤5% Fe, in total 0.1-5% of at least one alkaline earth or transition metal and a remainder Al and unavoidable impurities; heating the flat steel product to >Ac3 and ≤1000° C. for a time sufficient to introduce a heat energy quantity >100,000-800,000 kJs; hot-forming the flat steel product to form the component; and cooling at least one section of the component at a cooling rate sufficient to generate hardening structures.