Non-Oriented Electrical Steel Sheet for Low High-Frequency Iron Loss
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Solution Overview
Problem
Existing non-oriented electrical steel sheets struggle to achieve both high magnetic flux density and low high-frequency iron loss without increasing productivity costs, as adding large amounts of alloying elements like Cr decreases magnetic flux density, and performing skin pass rolling decreases productivity.
Innovation Solution
A non-oriented electrical steel sheet with a specific chemical composition and a production method that includes limiting Co content, subjecting the steel sheet to acidizing to control nitrogen in the surface layer, and performing stress relief annealing, all without skin pass rolling, to reduce iron loss without compromising magnetic flux density or productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a large amount of alloying elements (Cr, Si, Al) are added to reduce iron loss, then iron loss decreases, but saturation magnetic flux density decreases
Solution Approach 1:
The patent changes the chemical composition parameters by strictly limiting Cr to 0.03% or less and Si to 3.0% or less, while optimizing Al content (0.03-3.00%). This parameter optimization reduces alloying element additions compared to conventional methods, thereby maintaining saturation magnetic flux density while still achieving low iron loss through the combined effect of controlled composition and surface oxide layer formation.
Solution Approach 2:
The patent creates a composite structure with a surface oxide layer containing Fe, Al, and Si oxides over the steel substrate. This composite material structure provides the beneficial effect of reduced iron loss at the surface while the underlying steel matrix maintains high magnetic flux density, thus resolving the contradiction between energy loss reduction and magnetic strength preservation.
2Reliability
If skin pass rolling is performed to improve magnetic properties after stress relief annealing, then magnetic properties improve, but productivity decreases and production costs increase
Solution Approach 1:
The patent performs acidizing treatment after final annealing and before stress relief annealing to pre-form a surface oxide layer. This preliminary action ensures that the oxide layer is already in place before stress relief annealing, eliminating the need for subsequent skin pass rolling to improve magnetic properties, thereby maintaining high productivity while achieving excellent magnetic performance.
Solution Approach 2:
The patent extracts or removes the skin pass rolling step from the conventional production process. By forming the oxide layer through acidizing treatment earlier in the process, the patent eliminates the need for the separate skin pass rolling operation, thus improving productivity and reducing production costs while still achieving the desired magnetic properties.
3Loss of energy
If the thickness of non-oriented electrical steel sheet is reduced to reduce eddy current loss, then eddy current loss decreases, but productivity decreases due to reduced hot-rolled sheet thickness or increased cold rolling reduction
Solution Approach 1:
The patent applies local quality by forming a surface oxide layer with specific composition (Fe, Al, Si oxides) at the surface of the steel sheet. This localized modification at the surface reduces iron loss without requiring a reduction in overall sheet thickness, thereby maintaining productivity while achieving energy efficiency. The oxide layer acts as an insulating barrier that reduces eddy current losses at the surface.
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 proposed solution effectively reduces high-frequency iron loss while maintaining high magnetic flux density and productivity, eliminating the need for large alloying element additions and skin pass rolling.
Implementation Method 1
Non-oriented electrical steel sheets are strongly required to have lower iron loss in the high frequency range
Implementation Method 2
a non-oriented electrical steel sheet with both high magnetic flux density and low iron loss in the high frequency range
Implementation Method 3
the non-oriented electrical steel sheet is processed into a core shape by blanking or the like and then subjected to stress relief annealing in order to release the strain introduced during processing
Data Source
AI summary
Provided is a non-oriented electrical steel sheet with low high-frequency iron loss without addition of a large amount of alloying elements such as Cr, which causes a decrease in magnetic flux density, and without reduction of the sheet thickness, which causes a decrease in productivity. A non-oriented electrical steel sheet comprises a certain chemical composition containing 0.0005 mass % to 0.0050 mass % of Co, wherein an amount of N existing as AlN in a range from a surface of the non-oriented electrical steel sheet to a depth of 1/20 of a sheet thickness is 0.003 mass % or less, the surface has an oxide layer containing Fe and one or both of Al and Si, and an interface between the oxide layer and a steel substrate has an oxide film consisting of one or both of Al oxide and Si oxide.