Non-oriented electrical steel sheet and method of producing same
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Solution Overview
Problem
Existing non-oriented electrical steel sheets face challenges in achieving low iron loss in the high frequency range without decreasing magnetic flux density or reducing sheet thickness, which affects motor efficiency and productivity.
Innovation Solution
A non-oriented electrical steel sheet with controlled Co content and surface treatment through acidizing to limit nitrogen in the surface layer, forming an oxide layer containing Al and Si, thereby reducing iron loss without affecting magnetic flux density or productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional steelmaking methods are used, then production cost is reduced, but total nitrogen content increases leading to coarse grains and poor surface quality
Solution Approach 1:
The patent applies parameter changes by controlling the nitrogen content to 50 ppm or less (a significant reduction from conventional levels) and precisely controlling the aluminum content ratio between slabs and final products. This parameter control transforms the steel quality to achieve both low nitrogen and excellent surface properties without requiring expensive conventional steelmaking methods.
Solution Approach 2:
The patent applies local quality by ensuring uniform aluminum distribution throughout the steel slab, creating consistent grain refinement throughout the material. This uniform local quality prevents surface defects and achieves coherent grains across the entire product, resolving the contradiction between cost-effective production and high surface quality.
2Manufacturing precision
If aluminum is added for grain refinement, then grain size is reduced, but non-uniform distribution causes surface defects
Solution Approach 1:
The patent applies preliminary action by adding aluminum during the steelmaking stage and maintaining it through the casting and rolling processes. This early and continuous aluminum presence ensures uniform grain refinement is established before final product formation, preventing surface defects that would otherwise require costly post-processing repairs.
3Strength
If high strength is achieved through alloying, then mechanical properties improve, but formability and paintability deteriorate
Solution Approach 1:
The patent achieves this balance by changing the chemical composition parameters to contain minimal alloying elements (0.03% or less of Ti, V, Nb, B combined) while achieving high strength through controlled grain structure (50-80% coherent grains of 5 μm or less). This parameter change enables the steel to achieve tensile strength of 1320 MPa or more while maintaining excellent formability and paintability.
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 solution achieves reduced iron loss in high frequency ranges without adding large amounts of alloying elements like Cr, maintaining magnetic flux density and productivity, and improving magnetic properties.
Implementation Method 1
aluminum which kills nitrogen bubbles in the molten state
Implementation Method 2
aluminum which refines grains by forming aluminum nitride
Data Source
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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 at at least one surface of the non-oriented electrical steel sheet, an amount of N existing as AlN in a range from the surface to a depth of 1/20 of a thickness of the non-oriented electrical steel sheet is 0.003 mass% or less, and the surface has an oxide layer containing one or both of Al and Si and having a thickness of 80 nm to 200 nm.