Preliminary Fe Plating for High-Strength Hot-Dip Galvanized Steel Sheets
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Solution Overview
Problem
Manufacturing high tensile strength hot-dip galvanized steel sheets with Si and Mn content faces challenges such as non-coating, poor coating adhesion, and alloying delays due to oxide formation, leading to quality defects and increased costs.
Innovation Solution
A method involving electroplating with an Fe-based plating solution, controlled plating solution discharge rate, and heat treatment to form a uniform coating, using equipment with specific nozzle configurations to ensure uniform plating and minimize oxide formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Si and Mn concentrations in the steel are increased to achieve high tensile strength, then the strength is improved, but the wettability with molten zinc rapidly decreases causing non-coating and poor coating adhesion
Solution Approach 1:
The patent applies preliminary Fe plating (0.2-2.0 g/m²) to the steel sheet surface before hot-dip galvanizing. This preliminary coating of Fe creates a base layer that prevents direct contact between molten zinc and the Si-Mn enriched surface oxide layer, ensuring good coating adhesion while maintaining the high strength properties of the steel
Solution Approach 2:
The patent introduces Fe plating as an intermediary layer between the high Si-Mn steel substrate and the molten zinc coating. This intermediate Fe layer acts as a mediator that prevents the harmful interaction between zinc and the oxidizable Si-Mn elements, resolving the contradiction between maintaining steel strength and achieving good coating adhesion
2Strength
If Si and Mn are selectively oxidized and concentrated at the surface to form oxide, then the tensile strength is improved, but alloying delay arises in the alloying process leading to lower productivity
Solution Approach 1:
The patent applies preliminary Fe plating before the alloying process. This preliminary coating prevents excessive oxidation and concentration of Si-Mn at the surface during subsequent heat treatment, thereby avoiding alloying delays and maintaining high productivity while still achieving the desired strength properties
3Manufacturing precision
If Fe plating is applied to prevent non-coating phenomenon and ensure excellent coating surface quality, then the coating quality is improved, but the plating amount of 0.2 g/m2 to 2.0 g/m2 is difficult to control uniformly when using general electroplating cells
Solution Approach 1:
The patent extracts the plating solution supply function to a separate nozzle system positioned independently from the electrode structure. This allows precise control of plating solution flow rate and distribution pattern, enabling uniform application of the thin Fe plating layer (0.2-2.0 g/m²) required for the process while maintaining ease of manufacture
Solution Approach 2:
The patent introduces a separate plating solution nozzle as an intermediary device between the electroplating cell and the steel sheet surface. This intermediary nozzle system enables precise control of plating solution delivery, ensuring uniform thin Fe plating application while simplifying the manufacturing process
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
Achieves a beautiful, defect-free hot-dip coating on high tensile strength steel sheets, maintaining productivity and reducing costs by preventing non-coating and pick-up defects.
Implementation Method 1
forming Fe-based plating on the surface of the steel sheet through electroplating, by passing current using the electrode plate as an anode and the steel sheet as a cathode
Implementation Method 2
adjusting heat treatment in a direct fired furnace (DFF) and a radiant tube furnace (RTF) to the predetermined conditions to diffuse Si, Mn, or Al
Implementation Method 3
diffuse Si, Mn, or Al, which are difficult-to-coat elements contained in steel, on the surface to suppress oxide formation
Implementation Method 4
applying hot-dip galvanizing treatment to the steel sheet
Data Source
AI summary
It is proposed a method to enable manufacturing of a steel sheet having a beautiful coated layer, when applying hot-dip galvanizing to a steel sheet containing oxidizable elements. The method comprises: an electroplating step of, in a gap between a steel sheet and an electrode plate, forming Fe-based plating on the surface of the steel sheet through electroplating, by supplying an Fe-based plating solution; an annealing step of subjecting the steel sheet to heat treatment; and a hot dip coating step of applying hot-dip galvanizing to the steel sheet, and, in the electroplating step, a plating solution discharge rate, which is the ratio of the flow rate of the plating solution flowing out to the back side that is not facing the steel sheet of the electrode plate, to the flow rate of the plating solution supplied to the steel sheet, is less than 50%.