Non-Oriented Electrical Steel Sheet Phase Control for Magnetic Properties
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Solution Overview
Problem
Existing methods for manufacturing non-oriented electrical steel sheets struggle to improve magnetic properties, microstructure, and texture, while also facing challenges in reducing iron loss and maintaining mechanical properties, which are crucial for high-efficiency applications in electric vehicles.
Innovation Solution
A manufacturing method involving specific alloy compositions and controlled heat treatments, including hot-rolling, cold-rolling, and annealing processes, to optimize the microstructure and texture, with phases transformed from austenite to ferrite, enhancing magnetic properties and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If alloying elements such as Si, Mn, and Al are added to increase resistivity and reduce eddy current loss, then iron loss is reduced, but magnetic flux density decreases and rolling properties deteriorate
Solution Approach 1:
The patent applies parameter changes by precisely controlling the content ranges of alloying elements (Si: 1.5-3.5 wt%, Mn: 2.0-4.0 wt%, Al: 0.01-0.10 wt%) and impurity elements (C, S, N, Ti) to optimize the balance between resistivity and magnetic flux density. This quantitative parameter control resolves the contradiction by finding the optimal composition window where iron loss is reduced while maintaining adequate magnetic properties
Solution Approach 2:
The patent creates a composite material system by combining multiple alloying elements (Si, Mn, Al) in specific proportions, where each element contributes different properties: Si increases resistivity, Mn enhances magnetic flux density, and Al refines grain structure. This composite approach allows the material to achieve reduced iron loss while maintaining magnetic flux density through synergistic element interactions
2Loss of energy
If alloying elements are added to reduce iron loss, then energy efficiency improves, but the ability to thin the steel sheet deteriorates due to reduced rolling properties
Solution Approach 1:
The patent uses parameter changes by strictly controlling Al content (0.01-0.10 wt%) to prevent excessive grain growth while maintaining thinability. The low Al content range is specifically selected to avoid the formation of coarse AlN precipitates that would hinder rolling, thus enabling the production of thin sheets (0.1-0.5 mm) while still achieving iron loss reduction through the Si-Mn-Al composite system
Solution Approach 2:
The patent applies local quality by creating fine, uniformly distributed precipitates throughout the material matrix rather than coarse localized structures. The controlled addition of Al (0.01-0.10 wt%) ensures that precipitates form at a fine scale that does not interfere with rolling operations, allowing the material to maintain both reduced iron loss and good thinability through localized microstructural optimization
3Strength
If impurity elements form precipitates to strengthen the material, then mechanical strength improves, but magnetic properties deteriorate due to hindered magnetic domain movement
Solution Approach 1:
The patent applies parameter changes by precisely controlling impurity element contents (C: ≤0.005 wt%, S: ≤0.005 wt%, N: ≤0.005 wt%, Ti: ≤0.005 wt%) to prevent the formation of coarse precipitates that would hinder magnetic domain movement. This strict parameter control ensures that any precipitates formed are fine and uniformly distributed, maintaining magnetic properties while providing adequate mechanical strength through the alloying element system
Solution Approach 2:
The patent applies the extraction principle by removing harmful impurity elements (C, S, N, Ti) to levels ≤0.005 wt%, effectively extracting the sources of coarse precipitate formation that would deteriorate magnetic properties. By taking out these harmful elements, the patent prevents the formation of magnetic domain-hindering precipitates while maintaining mechanical strength through the controlled Si-Mn-Al alloying system
4Productivity
If conventional manufacturing processes are used, then production is maintained, but significant improvement in microstructure and texture is difficult to achieve
Solution Approach 1:
The patent applies parameter changes by optimizing heat treatment parameters (temperature ranges, holding times, cooling rates) and rolling parameters (reduction ratios, pass schedules) within specific windows that simultaneously achieve desired microstructure/texture and maintain production efficiency. The controlled heating to austenite region followed by controlled cooling to ferrite/austenite dual-phase region creates the required microstructure without requiring excessive process time
Solution Approach 2:
The patent applies preliminary action by preparing the material with controlled composition and microstructure through hot rolling and controlled cooling before cold rolling. This preliminary microstructure preparation ensures that subsequent cold rolling and heat treatment processes can achieve the desired final texture and magnetic properties more efficiently, reducing the need for multiple re-processing cycles and maintaining 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 method results in non-oriented electrical steel sheets with improved magnetic flux density, reduced iron loss, and enhanced mechanical properties, along with increased productivity and economic efficiency.
Implementation Method 1
the step of annealing the cold-rolled steel sheet includes: a step of subjecting the cold-rolled steel sheet to first heat treatment by heating to an austenite single-phase region temperature and maintaining at the temperature; and a step of subjecting the cold-rolled steel sheet, subjected to the first heat treatment, to second heat treatment by cooling to a ferrite/austenite dual-phase region temperature and maintaining at the temperature
Data Source
Figure 1~2
AI summary
Disclosed is an invention concerning a method for manufacturing non-oriented electrical steel sheets with excellent magnetic properties and the non-oriented electrical steel sheets produced thereby. In a specific embodiment, the method for manufacturing non-oriented electrical steel sheets with excellent magnetic properties includes the steps of: manufacturing a hot-rolled steel sheet using a slab containing 0.4-3.5 wt% of silicon (Si), 0 (exclusive) to 0.05 wt% (inclusive) of aluminum (Al), 0.002-3.5 wt% of austenite stabilizing elements, and the balance of iron (Fe) and other inevitable impurities; cold rolling the hot-rolled steel sheet to prepare a cold-rolled steel sheet; and cold-annealing the cold-rolled steel sheet, wherein the cold-annealing includes a primary heat treatment step of heating and maintaining the cold-rolled steel sheet up to the temperature of the austenite single-phase region; and a secondary heat treatment step of cooling and maintaining the primary heat-treated cold-rolled steel sheet down to the temperature of the ferrite and austenite dual-phase region.