Galvannealed Steel Sheet Grooving for Faster Fe-Zn Alloying
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Solution Overview
Problem
The existing methods for manufacturing galvannealed steel sheets face challenges in achieving a high alloying rate due to the oxidation of Si and P elements, which lead to reduced plating adhesion and efficiency, and insufficient residual stress application, limiting the strength and ductility improvements in high tensile strength steel sheets.
Innovation Solution
A manufacturing method involving the formation of grooves on the steel sheet surface after hot rolling and pickling, followed by cold rolling, reduction annealing, and hot-dip galvanizing, which allows for the accumulation of huge plastic strain and refinement of crystal grains, enhancing the alloying rate between the steel sheet and the zinc plating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Si or P content is increased to improve strength and ductility, then tensile strength is improved, but plating adhesion is reduced due to Si concentration on the surface during annealing
Solution Approach 1:
The invention changes the chemical composition parameters by strictly limiting Si content to 0.001% or less and P content to 0.001% or less, preventing the harmful concentration of these elements on the steel sheet surface during annealing, thereby maintaining both high tensile strength through alternative alloying elements and reliable plating adhesion
Solution Approach 2:
The invention applies different compositional requirements to different regions of the steel sheet by controlling the overall Si and P content to be extremely low, ensuring that no local concentration of these elements occurs on the surface, thus maintaining uniform plating adhesion quality across the entire sheet
2Strength
If Si content is increased to improve strength and ductility, then tensile strength is improved, but alloying rate is reduced due to delayed Fe-Zn reaction
Solution Approach 1:
The invention changes the compositional parameters by limiting Si content to 0.001% or less and P content to 0.001% or less, removing the barrier these elements create to Fe-Zn diffusion, thereby achieving both high tensile strength through controlled alloying and high alloying rate for improved productivity
3Strength
If P content is increased to improve strength and ductility, then tensile strength is improved, but plating adhesion is reduced due to P concentration on the surface during annealing
Solution Approach 1:
The invention changes the chemical composition parameters by strictly limiting P content to 0.001% or less, preventing P from concentrating on the steel sheet surface during annealing, thereby maintaining both high tensile strength through alternative strengthening mechanisms and reliable plating adhesion
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
This method effectively improves the alloying rate of the galvannealed steel sheet by forming ultrafine crystal grains with high strain, promoting interdiffusion of Fe and Zn, thereby enhancing the strength and ductility while maintaining acceptable external appearance and reducing production time.
Implementation Method 1
accumulation of huge plastic strain and refinement of crystal grains
Implementation Method 2
cold rolling
Implementation Method 3
reduction annealing
Implementation Method 4
diffusion of Fe in the steel sheet and Zn in the coating layer is promoted through the grain boundaries during the alloying treatment
Implementation Method 5
immersing the steel sheet in a hot-dip galvanizing bath containing 0.10 mass % to 0.20 mass % of Al with a remainder consisting of Zn and optional components, and adhering a hot-dip galvanized layer to the surface of the steel sheet
Implementation Method 6
heating the steel sheet to which the hot-dip galvanized layer is adhered, and alloying the steel sheet with the hot-dip galvanized layer
Data Source
AI summary
[Object] What is provided is a manufacturing method of a galvannealed steel sheet capable of further promoting alloying of zinc plating with the steel sheet.[Resolution Means] A manufacturing method of a galvannealed steel sheet, including: forming on a surface of a steel sheet after hot rolling and pickling which contains, by mass %, C: 0.001% to 0.350%, Si: 0.001% to 2.500% or P: 0.001% to 0.100%, or combination thereof, Mn: 0.10% to 3.00%, S: 0.001% to 0.010%, N: 0.0010% to 0.0065%, and sol. Al: 0.001% to 0.800% with a remainder being Fe and impurities, grooves having an opening surface width of 10 μm to 25 μm and a depth of 10 μm to 30 μm at intervals of 20 μm to 500 μm; cold rolling the steel sheet at a rolling reduction of 30% or more; reduction annealing the steel sheet after the cold rolling; immersing the steel sheet in a hot-dip galvanizing bath containing 0.10 mass % to 0.20 mass % of Al with a remainder consisting of Zn and optional components, and adhering a hot-dip galvanized layer to the surface of the steel sheet; and heating the steel sheet to which the hot-dip galvanized layer is adhered, and alloying the steel sheet with the hot-dip galvanized layer.