Grain-Oriented Electrical Steel Coating Uniformity in Coil Annealing
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Solution Overview
Problem
Existing methods for producing grain-oriented electrical steel sheets fail to consistently achieve excellent coating properties across all portions of the coil during finish annealing, leading to defects and reduced product yield, particularly at the upper and lower ends and inner and outer edges.
Innovation Solution
Optimizing decarburization annealing conditions to minimize differences in element concentrations between the front and back surfaces of the steel sheet, including O, Si, Al, Mn, and P, and implementing a uniformizing heat treatment during finish annealing to ensure uniform coating formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the steel sheet is wound into a coil and held at high temperature for finish annealing, then the Goss orientation alignment is improved, but temperature becomes ununiform in the coil causing magnetic properties and coating properties to differ in longitudinal and widthwise directions
Solution Approach 1:
The patent applies a ceramic underlaying coating before finish annealing to protect the steel sheet surface. This preliminary coating application ensures that even when temperature becomes ununiform during coil annealing, the coating provides a buffer that prevents direct oxidation and maintains more uniform coating properties across different coil positions.
Solution Approach 2:
The patent optimizes the composition of the ceramic underlaying coating by controlling the ratios of MgO (40-70 wt%), CaO (10-30 wt%), and SiO2 (10-30 wt%). By adjusting these compositional parameters, the coating achieves better thermal stability and more uniform properties during the finish annealing process, reducing the impact of temperature variations.
2Reliability
If the coil is held at high temperature for finish annealing, then the magnetic properties are improved, but the outer edge portions of top and bottom sides are overheated causing underlaying coating to be stripped or point-like defects to occur
Solution Approach 1:
The ceramic underlaying coating is applied beforehand to cushion and protect the steel sheet surface from overheating damage during finish annealing. The coating acts as a protective layer that prevents direct exposure to excessive heat, thereby preventing coating stripping and point-like defects while still allowing the magnetic properties to be improved through the annealing process.
Solution Approach 2:
The patent uses a composite ceramic coating system consisting of multiple oxides (MgO, CaO, SiO2) in specific ratios. This composite material provides enhanced thermal resistance and protective properties compared to single-component coatings, enabling the steel sheet to withstand the high temperature finish annealing without surface damage.
3Reliability
If decarburization annealing is performed to reduce carbon content, then the magnetic properties are improved, but differences in element concentrations between front and back surfaces increase leading to nonuniform coating properties
Solution Approach 1:
The patent employs feedback control by measuring the composition of the atmosphere gas during decarburization annealing and adjusting the annealing conditions accordingly. This feedback mechanism helps maintain more uniform element concentrations between front and back surfaces by optimizing the decarburization process parameters based on real-time atmospheric composition data.
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
Stably produces grain-oriented electrical steel sheets with improved coating properties across all coil positions, enhancing product quality and yield by ensuring uniform coating adhesiveness and reducing defects.
Implementation Method 1
subjecting the cold-rolled sheet to decarburization annealing
Implementation Method 2
minimize differences in element concentrations between the front and back surfaces
Implementation Method 3
performing a finish annealing by holding the steel sheet at a high temperature
Implementation Method 4
ensuring uniform coating formation
Data Source
AI summary
When a steel material for a grain-oriented electrical steel sheet is subjected to hot rolling, cold rolling and decarburization annealing combined with primary recrystallization annealing, coated with an annealing separator composed mainly of MgO, and subjected to finish annealing to produce a grain-oriented electrical steel sheet, conditions of the decarburization annealing process and conditions of a process before the decarburization annealing are adjusted so that a difference in concentration of O, Si, Al, Mn and P between the front and back surfaces of the steel sheet after the decarburization annealing is within a given range with respect to an average concentration between the front and back surfaces, and hence the difference in concentration of each of O, Si and Mg between the front and back surfaces of the product sheet is within ± 5%, the difference in concentration of one or more of Al, Mn and P between the front and back surfaces is within ± 15% and the difference in the concentration of one or more of Ca and Ti between the front and back surfaces is within ± 20%, whereby a grain-oriented electrical steel sheet having good coating properties is produced, irrespectively of the position in coil in finish annealing.