Fe-Plated Hot Press Steel Sheet for Oxide-Controlled Plating Adhesion
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Solution Overview
Problem
Existing hot-dip plated steel sheets for hot press forming suffer from issues such as non-plating and peeling of the plating layer due to surface oxides formed during annealing, particularly with elements like Mn and Si, leading to poor plating quality and potential linear defects.
Innovation Solution
A steel sheet composition with controlled GDS profiles of Mn and Si, combined with an Fe plating layer formed under specific annealing conditions, including a high dew point and controlled oxygen content, to suppress surface diffusion and internal oxidation of these elements, ensuring uniform plating adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If elements such as Mn, Si, Al, Cr, and B are added to improve hardenability, then hardenability is improved, but surface oxides are formed during annealing causing non-plating and peeling
Solution Approach 1:
The patent applies preliminary oxidation during the annealing process to intentionally form a controlled oxide layer on the steel sheet surface before hot-dip plating. This preliminary action converts the harmful surface oxides that cause non-plating and peeling into a beneficial oxide layer that promotes uniform plating adhesion. The oxidation is performed by controlling the annealing atmosphere (oxygen potential, temperature, and time) to create a specific oxide composition and structure that serves as an ideal substrate for subsequent plating.
Solution Approach 2:
The patent changes the oxidation parameters during annealing, specifically controlling the oxygen potential, temperature, and holding time to transform the surface oxide characteristics. By adjusting these parameters, the patent creates a controlled oxide layer with specific composition (enriched in Fe and Al oxides) and structure that prevents non-plating and peeling while maintaining the hardenability benefits of alloying elements.
2Strength
If alloying elements are added to secure physical properties, then physical properties are improved, but wettability of hot-dip plating bath deteriorates due to surface oxide formation
Solution Approach 1:
The patent changes the surface oxide parameters by controlling annealing conditions (oxygen potential, temperature, time) to create a oxide layer with specific composition and structure. This controlled oxide layer has improved wettability characteristics compared to uncontrolled oxidation, allowing the hot-dip plating bath to wet the surface uniformly and preventing non-plating defects.
Solution Approach 2:
The patent uses accelerated oxidation during annealing by controlling the annealing atmosphere to have high oxygen potential. This strong oxidation condition intentionally forms a thick oxide layer enriched in Fe and Al oxides, which serves as a beneficial substrate for plating. The accelerated oxidation transforms the harmful thin oxide layer into a beneficial thick oxide layer that improves wettability.
3Object-affected harmful factors
If reduction is performed after oxidation to reduce surface oxides, then wettability improves, but Si concentrates below iron oxide forming band-shaped Si oxide causing peeling
Solution Approach 1:
The patent extracts the harmful reduction step from the process. Instead of performing reduction after oxidation, the patent eliminates the reduction step entirely and maintains the oxidizing atmosphere during annealing. This extraction of the reduction step prevents the concentration of Si below the oxide layer and the formation of band-shaped Si oxide that causes peeling, while still achieving good wettability through controlled oxidation.
Solution Approach 2:
The patent inverts the conventional oxidation-reduction sequence by maintaining oxidation throughout the annealing process without subsequent reduction. Instead of oxidizing then reducing, the patent continuously oxidizes the surface during annealing, creating a stable oxide layer that prevents both non-plating and peeling defects.
4Reliability
If internal oxidation is performed to suppress surface diffusion, then non-plating is reduced, but linear defects occur due to uneven surface oxide formation
Solution Approach 1:
The patent changes the oxidation parameters by controlling the annealing atmosphere (oxygen potential, temperature, and time) to achieve uniform surface oxidation. By carefully balancing these parameters, the patent creates a uniformly distributed oxide layer that prevents non-plating while avoiding the formation of localized thick oxide regions that would cause linear defects after plating.
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 hot-dip plated steel sheet with improved plating adhesion and surface quality, preventing non-plating and linear defects, even after alloying heat treatments.
Implementation Method 1
performing electroplating on the base steel sheet to form an Fe plating layer including 5 to 50 wt % of oxygen; and annealing the base steel sheet on which the Fe plating layer is formed
Implementation Method 2
elements with a high oxidation tendency compared to Fe, such as Mn, Si, Al, Cr, and B, are added... During the annealing process, the elements may diffuse to surfaces thereof
Implementation Method 3
performing electroplating on the base steel sheet to form an Fe plating layer including 5 to 50 wt % of oxygen
Implementation Method 4
annealing the base steel sheet on which the Fe plating layer is formed by maintaining at a temperature within a range of 600 to 950° C. for 5 to 120 seconds
Data Source
AI summary
The steel sheet according to an aspect of the present invention has a GDS profile of an Mn element and a GDS profile of an Si element, which are observed from the surface to the depth, sequentially including a maximum point and a minimum point, wherein a difference of converted concentration of Mn is 80% or more, and a difference of converted concentration of Si is 50% or more.