Galvanized Hot-Rolled Steel Sheet With Controlled Oxides for Coating Adhesion
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Galvanized steel sheets containing Si face issues with bare spots and non-alloyed portions due to coating defects, leading to poor surface appearance and corrosion resistance, and existing methods either require costly processes or compromise on coating adhesion and corrosion resistance.
Innovation Solution
A high-strength galvanized hot-rolled steel sheet with controlled surface topography and oxide amounts, achieved through specific chemical composition and manufacturing processes including hot-rolling, pickling, high-pressure water descaling, continuous annealing, and hot-dip galvanizing, to ensure excellent surface appearance, coating adhesion, and post-processing corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If shot blasting and brush grinding are performed prior to pickling to prevent coating defects, then coating adhesion is improved, but manufacturing cost increases and productivity decreases
Solution Approach 1:
The invention performs preliminary action by controlling the surface state of the base metal through specific rolling conditions and oxide film formation before pickling and galvanizing. The surface roughness Ra is controlled at 0.8μm or less and oxide content is limited to 3.0 mass% or less, creating optimal surface conditions in advance that eliminate the need for subsequent shot blasting and brush grinding operations, thereby maintaining high productivity while ensuring coating adhesion.
2Reliability
If surface grinding and heating are performed to improve coating film adhesion, then coating adhesion is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The invention changes the parameters of surface roughness and oxide content to optimal ranges (Ra ≤ 0.8μm, oxide content ≤ 3.0 mass%) through controlled rolling and pickling processes. This parameter optimization creates a surface state that inherently provides good coating adhesion without requiring additional heating or grinding equipment, thereby reducing manufacturing complexity while achieving the desired coating adhesion.
3Reliability
If internal oxide layer is formed to improve coating adhesion, then coating adhesion is improved, but microcracking occurs during processing and corrosion resistance deteriorates
Solution Approach 1:
The invention applies local quality control by precisely managing the oxide distribution and concentration in the surface layer. The oxide content is controlled at 3.0 mass% or less and surface roughness Ra is controlled at 0.8μm or less, creating a uniform surface state that provides adequate coating adhesion without forming concentrated oxide clusters that would cause microcracking. This localized quality control ensures both coating adhesion and corrosion resistance.
4Reliability
If light reduction rolling is performed to improve coating adhesion, then coating adhesion is improved, but surface roughness increases and productivity decreases
Solution Approach 1:
The invention optimizes the rolling parameters by controlling the rolling reduction ratio and final surface roughness to achieve Ra ≤ 0.8μm. This parameter optimization allows the formation of adequate surface irregularities for coating adhesion while preventing excessive roughness that would require additional finishing operations, thereby maintaining manufacturing precision and productivity.
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 solution results in a steel sheet with improved surface appearance, enhanced coating adhesion, and sustained corrosion resistance, making it suitable for complex-shaped members with increased industrial applicability.
Implementation Method 1
a surface of the steel sheet having the chemical composition has a specific surface area ratio, r, of 2.5 or less, and an amount (g/m2) of Si present in the galvanized layer and an amount (g/m2) of Mn present in the galvanized layer respectively satisfy: amount of Si×r≤0.06, and amount of Mn×r≤0.10
Implementation Method 2
subsequently, performing rolling by using a roll having a surface roughness (Ra) of 0.3 to 1.0 at a rolling reduction ratio of 1 to 10%; and subsequently, performing hot-dip galvanizing
Implementation Method 3
the base steel sheet is recrystallization-annealed in an annealing furnace of a CGL and thereafter subjected to hot-dip galvanizing
Data Source
AI summary
Provided are a high-strength galvanized hot-rolled steel sheet and a method for manufacturing the steel sheet. A steel sheet has a chemical composition, and a galvanized layer is disposed on the steel sheet. The chemical composition includes, in mass %, C: 0.02% or greater and 0.30% or less, Si: 0.01% or greater and 2.5% or less, Mn: 0.3% or greater and 3.0% or less, P: 0.08% or less, S: 0.02% or less, and Al: 0.001% or greater and 0.20% or less. The galvanized layer has a coating weight per side of 20 to 120 g/m2. A surface of the steel sheet has a specific surface area ratio, r, of 2.5 or less, and an amount of Si present in the galvanized layer and an amount of Mn present in the galvanized layer respectively satisfy: amount of Si×r≤0.06, and amount of Mn×r≤0.10.