Galvanized Steel Sheet Oxidation Control for Coating Adhesion
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Solution Overview
Problem
High strength galvanized steel sheets containing Si, Mn, and Cr face challenges in achieving sufficient coating adhesiveness, corrosion resistance, and fatigue resistance due to oxidation issues, particularly when subjected to alloying treatments, which affect the balance of strength and ductility required for automotive applications.
Innovation Solution
Controlling the end-point temperature of oxidation treatment based on Si and Cr content to form sufficient iron oxides, performing oxidation treatment before reduction annealing and galvanizing, and optimizing the oxidation furnace atmosphere to prevent oxide concentration on the surface and promote iron oxide coverage, thereby enhancing coating adhesiveness and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Si and Mn are added to increase steel sheet strength, then strength is improved, but coating adhesiveness deteriorates due to oxide formation on the surface
Solution Approach 1:
The patent applies preliminary action by performing oxidation treatment before reduction annealing and galvanizing. This pre-oxidation creates a controlled oxide layer that prevents excessive oxide formation during subsequent heating processes, thereby maintaining coating adhesiveness while preserving the strength-enhancing Si and Mn elements in the steel sheet.
Solution Approach 2:
The patent utilizes parameter changes by controlling the end-point temperature of oxidation treatment based on Si and Cr content. By precisely adjusting the oxidation temperature and atmosphere parameters, the patent optimizes the oxide layer formation to prevent bare spots and improve coating adhesiveness without compromising the strength benefits of Si and Mn addition.
2Reliability
If oxidation treatment is performed to form oxide layer for coating adhesiveness, then coating adhesiveness is improved, but excessive oxide concentration on surface causes bare spots
Solution Approach 1:
The patent applies parameter changes by specifying the end-point temperature of oxidation treatment as a function of Si and Cr content in the steel sheet. This controlled parameter adjustment ensures uniform oxide distribution and prevents excessive oxide concentration that would cause bare spots, while still forming sufficient oxide for good coating adhesiveness.
Solution Approach 2:
The patent implements feedback control by determining the oxidation treatment conditions based on the specific composition (Si and Cr content) of the steel sheet. This compositional feedback allows optimization of the oxidation process for each steel grade, preventing both insufficient oxidation (poor adhesiveness) and excessive oxidation (bare spots).
3Strength
If Cr is added to improve strength and ductility balance, then strength-ductility balance is improved, but oxidation resistance increases making oxide formation difficult
Solution Approach 1:
The patent utilizes parameter changes by establishing a specific relationship between Cr content and the end-point temperature of oxidation treatment. As Cr content increases and oxidation resistance improves, the oxidation temperature is adjusted accordingly to compensate for the reduced oxidation tendency, ensuring sufficient oxide layer formation for good coating adhesiveness while maintaining the strength and ductility benefits of Cr addition.
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 high strength galvanized steel sheets with improved coating adhesiveness, corrosion resistance, and fatigue resistance, ensuring a stable quality and balance of properties suitable for automotive applications.
Implementation Method 1
oxidation treatment in an oxidation zone to form a specific amount of iron oxides
Implementation Method 2
reduction annealing in a reducing atmosphere of N2 + H2 in which oxidation of Fe does not occur (oxidized Fe is reduced)
Data Source
Figure 1~2
AI summary
A high strength galvanized steel sheet excellent in terms of coating adhesiveness which is made from a base material that is a high strength steel sheet containing Si, Mn, and Cr and a method for manufacturing the galvanized steel sheet are provided. The method includes performing an oxidation treatment on steel containing Si, Mn, and Cr in an oxidation furnace under the condition that an exit temperature is T, reduction annealing and a galvanizing treatment, or optionally, further an alloying treatment under conditions that heating is performed at a temperature of 460°C or higher and 600°C or lower for an alloying treatment time of 10 seconds or more and 60 seconds or less, where the exit temperature T satisfies the hollowing expressions: where [Si]: Si content of the steel by mass%, and [Cr]: Cr content of the steel by mass%.