Grain-oriented electrical steel sheet coating defect reduction
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Solution Overview
Problem
Conventional manufacturing methods of grain-oriented electrical steel sheets often result in defects in the glass coating film, leading to deteriorated appearance, core loss, and excitation properties due to the formation of aggregated portions in the coating film.
Innovation Solution
The method involves forming a forsterite-based glass coating film on the steel strip with a specific aggregated portion ratio of 0.15 or less, where the thickness of these portions is twice the average thickness and their size in the direction parallel to the surface is 3 µm or more, and switching the annealing atmosphere from a mixed gas to a hydrogen gas atmosphere during finish annealing to suppress the occurrence of these aggregated portions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a glass coating film is formed at the surface of the steel strip during finish annealing, then core loss is reduced and excitation properties improve, but defects occur in the coating film leading to deteriorated appearance and performance
Solution Approach 1:
The invention changes the chemical composition parameters of the steel strip by precisely controlling the content of specific elements (Al: 0.003-0.015 wt%, B: 0.0005-0.005 wt%, N: 0.001-0.005 wt%, Si: 2.0-4.8 wt%). This compositional parameter change prevents the formation of aggregated portions in the glass coating film, thereby eliminating defects while maintaining the beneficial properties of the coating.
Solution Approach 2:
The invention introduces boron (B) as an intermediary element that mediates between the aluminum content and the formation of aggregated portions. The boron interacts with aluminum and nitrogen to form a controlled nitride inhibitor structure that prevents excessive aggregation of the glass coating film, thus preventing defects while allowing the coating to form properly.
2Loss of energy
If the glass coating film is formed with conventional composition control, then the coating provides tensile tension to reduce core loss, but aggregated portions form causing defects
Solution Approach 1:
The invention modifies the compositional parameters by adding boron (0.0005-0.005 wt%) and precisely controlling aluminum (0.003-0.015 wt%) and nitrogen (0.001-0.005 wt%) contents. This parameter change alters the formation behavior of the glass coating film, preventing aggregated portions while maintaining the tensile tension property that reduces core loss.
3Reliability
If aluminum content is increased to control crystal orientation, then excitation properties improve, but aggregated portions in the glass coating film increase
Solution Approach 1:
Boron acts as an intermediary that allows higher aluminum content (0.003-0.015 wt%) to be used for controlling crystal orientation and improving excitation properties, while simultaneously preventing the formation of aggregated portions. The boron-nitrogen-aluminum interaction creates a balanced system where aluminum can fulfill its orientation control function without causing coating defects.
Solution Approach 2:
The invention changes the interrelated parameters of Al, B, and N content to achieve a new compositional balance. By adding boron and controlling nitrogen, the system allows aluminum to be present at levels sufficient for crystal orientation control without forming aggregated portions in the glass coating film.
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 approach effectively reduces defects in the glass coating film, improving yield and reducing costs while enabling stable production of grain-oriented electrical steel sheets with enhanced magnetic properties.
Implementation Method 1
a forsterite based glass coating film which is formed at a surface of the steel strip
Implementation Method 2
a control of a crystal orientation using AlN precipitates as an inhibitor is performed
Implementation Method 3
finish annealing
Data Source
Figure 1~3
Figure 4~5
Figure 6~7
AI summary
Nitriding process of a steel strip is performed. Next, annealing is performed to form a forsterite based glass coating film at a surface of the steel strip. Heating is performed up to 1000°C or more in a mixed gas atmosphere containing H2 gas and N2 gas, and a rate of N2 gas is 20 volume% or more, next, the atmosphere is switched into H2 gas atmosphere at the temperature of 1000°C or more and 1100°C or less, when the annealing is performed. An oxygen potential P (H2O)/P (H2) is set to be 0.05 to 0.3 when the temperature is 850°C or less during the heating in the mixed gas atmosphere.