Galvanized Steel Sheet Surface Oxidation Control
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Solution Overview
Problem
High strength galvanized steel sheets with tensile strength of 1,000 MPa or higher face issues with surface quality, plating adhesion, and formability due to oxidation of components like Si, Mn, and Al, leading to bare spots and plating delamination during the manufacturing process.
Innovation Solution
A high strength galvanized steel sheet is manufactured with a specific composition and processing method, including a galvanized layer formed on a cold-rolled steel sheet with controlled compositions of C, Si, Mn, Al, and other elements, and subjected to reheating, hot rolling, pickling, recrystallization annealing, and galvanizing, ensuring excellent surface qualities and adhesion by inhibiting surface diffusion of oxidizable components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high levels of Si, Mn, or Al are added to obtain high strength steel sheets with tensile strength of 1,000 MPa or higher, then strength is improved, but surface oxidation occurs leading to bare spots and deteriorated surface qualities
Solution Approach 1:
The patent applies preliminary anti-action by adding Ti and Nb to the steel composition before the oxidation problem occurs. These elements form oxides preferentially during the annealing process, creating a protective oxide layer that prevents Si, Mn, and Al from oxidizing on the surface. This preliminary protective measure eliminates bare spots and surface oxidation while maintaining the high strength properties achieved through Si, Mn, and Al addition.
Solution Approach 2:
The patent uses Ti and Nb as intermediary elements that mediate between the high strength components (Si, Mn, Al) and the oxidation environment. These intermediary elements form stable oxides that act as a barrier, preventing direct interaction between oxygen and the oxidizable components. The Ti and Nb oxides serve as a protective interface that allows the steel to maintain both high strength and good surface quality.
2Strength
If high strength steel sheets with tensile strength of 1,000 MPa or higher are produced, then strength is improved, but plating adhesion deteriorates due to oxide presence on the steel sheet surface
Solution Approach 1:
The patent applies preliminary anti-action by adding Ti and Nb to prevent oxide formation before galvanizing. These elements form stable oxides during annealing that create a clean surface suitable for galvanizing. The preliminary formation of Ti and Nb oxides prevents the formation of harmful Si, Mn, and Al oxides that would interfere with plating adhesion, thereby ensuring both high strength and reliable plating attachment.
Solution Approach 2:
The patent changes the chemical composition parameters by adding specific amounts of Ti (0.01-0.1 wt%) and Nb (0.01-0.1 wt%). This parameter change alters the oxidation behavior during annealing, causing Ti and Nb to form protective oxides instead of Si, Mn, and Al oxides. The controlled addition of these elements transforms the surface chemistry to enable both high strength and good plating adhesion.
3Strength
If the amount of oxidizable components (Si, Mn, Al) is increased to achieve high strength, then strength is improved, but bare spots and plating delamination occur more intensely
Solution Approach 1:
The patent converts the harmful effect of increased oxidizable components into a benefit by adding Ti and Nb that form even more stable oxides. The high oxidizability of Ti and Nb is used to their advantage - they oxidize preferentially and form a protective layer that prevents the oxidation of Si, Mn, and Al. This converts the potential harm of having oxidizable components into a beneficial protective mechanism that eliminates bare spots and plating delamination.
Solution Approach 2:
The patent employs a form of accelerated oxidation by utilizing the strong oxidizing tendency of Ti and Nb. These elements have a higher affinity for oxygen than Si, Mn, and Al, causing them to oxidize more rapidly and completely during the annealing process. This accelerated oxidation of Ti and Nb creates a protective oxide layer that prevents further oxidation and eliminates the formation of bare spots and plating delamination.
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 a galvanized steel sheet with enhanced surface qualities, improved plating adhesion, and formability, maintaining a tensile strength of 1,000 MPa or higher while preventing bare spots and delamination, thus suitable for automotive body structures.
Implementation Method 1
high strength steel sheets containing Si, Mn, or Al may react with a trace of oxygen or water vapor existing in an annealing furnace to form single or complex oxides of Si, Mn, or Al
Implementation Method 2
the Fe oxide is reduced by reduction annealing in a reducing atmosphere
Data Source
AI summary
A high strength galvanized steel sheet having excellent surface qualities, plating adhesion, and formability is provided, wherein a galvanized layer is formed on a cold-rolled steel sheet comprising 0.1-0.3 wt % of C, 1-2.5 wt % of Si, 2.5-8 wt % of Mn, 0.001-0.5 wt % of sol. Al, at most 0.04 wt % of P, at most 0.015 wt % of S, at most 0.02 wt % of N (excluding 0 wt %), 0.1-0.7 wt % of Cr, at most 0.1 wt % of Mo, (48/14)*[N] to 0.1 wt % of Ti, 0.005-0.5 wt % of Ni, 0.01-0.07 wt % of Sb, at most 0.1 wt % of Nb, and at most 0.005 wt % of B, with the remainder being Fe and other inevitable impurities.