High-Strength Electrical Steel Sheet with Worked Structures
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Solution Overview
Problem
Current methods for producing high strength nonoriented electrical steel sheets face challenges in achieving a balance between magnetic properties and mechanical strength, particularly under high frequency conditions, and are prone to sheet breakage and high production costs due to the use of expensive elements like Ni, Mo, and Cr.
Innovation Solution
A steel sheet composition with controlled levels of C, Si, Mn, P, S, Al, N, Cu, and Nb, combined with worked structures and optimized crystal grain size before rolling, to enhance both magnetic and mechanical properties while maintaining productivity and reducing costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If high strength nonoriented electrical steel sheet is produced using solid solution strengthening ingredients (Ni, Mo, Cr), then mechanical strength is improved, but production cost increases significantly and sheet breakage occurs during rolling
Solution Approach 1:
The invention changes the chemical composition parameters by strictly limiting harmful elements (C≤0.005%, Si≤3.0%, Mn≤2.0%, P≤0.03%, S≤0.005%, Al≤0.03%, Ni≤0.03%, Cr≤0.03%, Mo≤0.03%) and using controlled amounts of beneficial elements (Ti: 0.01-0.10%, Nb: 0.01-0.10%, V: 0.01-0.10%, B: 0.0005-0.005%). This parameter optimization achieves high strength without the need for expensive solid solution strengtheners while preventing sheet breakage during rolling.
Solution Approach 2:
The invention replaces expensive long-term strengthening elements (Ni, Mo, Cr) with cheaper alternative mechanisms. Instead of relying on expensive solid solution strengthening, the patent uses controlled impurity levels and microalloying with inexpensive elements (Ti, Nb, V, B) to achieve the required strength through precipitation hardening and grain boundary strengthening, significantly reducing material cost.
2Strength
If high strength nonoriented electrical steel sheet is produced using worked structures, then mechanical strength is improved, but magnetic properties deteriorate and stable iron loss cannot be obtained
Solution Approach 1:
The invention optimizes the chemical composition parameters to enable controlled worked structures that maintain stable magnetic properties. By precisely controlling the content of alloying elements (particularly Ti, Nb, V, and B within specific ranges), the patent achieves a balance where worked structures provide mechanical strength while the controlled composition ensures stable iron loss and magnetic flux density.
Solution Approach 2:
The invention creates a composite microstructure by combining worked structures with controlled precipitation of alloying elements. The simultaneous presence of dislocation networks from working and fine precipitates from controlled alloying (Ti, Nb, V, B) creates a composite strengthening mechanism that maintains both high mechanical strength and stable magnetic properties, as the fine precipitates pin dislocations and stabilize the worked structure.
3Strength
If electrical steel sheet includes large amount of Cu to improve strength, then mechanical strength is improved, but eddy current loss increases due to Cu phase precipitation
Solution Approach 1:
The invention extracts and removes Cu from the steel composition entirely, setting the upper limit at Cu≤0.03%. This eliminates the harmful effect of Cu phase precipitation that causes increased eddy current loss. The patent achieves the required mechanical strength through alternative mechanisms (controlled impurity levels, microalloying with Ti/Nb/V/B, and worked structures) rather than relying on Cu addition.
4Strength
If electrical steel sheet uses expensive elements (Ni, Mo, Cr) for solid solution strengthening, then mechanical strength is improved, but production cost increases significantly
Solution Approach 1:
The invention replaces expensive strengthening elements (Ni, Mo, Cr) with cheaper alternative mechanisms. Instead of relying on expensive solid solution strengthening, the patent uses controlled impurity levels and microalloying with inexpensive elements (Ti, Nb, V, B) to achieve the required strength through precipitation hardening and grain boundary strengthening, significantly reducing material cost.
Solution Approach 2:
The invention changes the chemical composition parameters by strictly limiting harmful elements (C≤0.005%, Si≤3.0%, Mn≤2.0%, P≤0.03%, S≤0.005%, Al≤0.03%, Ni≤0.03%, Cr≤0.03%, Mo≤0.03%) and using controlled amounts of beneficial elements (Ti: 0.01-0.10%, Nb: 0.01-0.10%, V: 0.01-0.10%, B: 0.0005-0.005%). This parameter optimization achieves high strength without the need for expensive solid solution strengtheners while preventing sheet breakage during rolling.
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 a stable production of high strength electrical steel sheets with tensile strength of 500 MPa or more, superior magnetic flux density, and reduced iron loss, while maintaining cold rollability and annealing efficiency, thus addressing the limitations of existing technologies.
Implementation Method 1
the steel sheet structure is given worked structures and dislocation strengthening is used to increase the strength
Implementation Method 2
the crystal structure is coarsened right before forming the worked structures to finally remain in the steel sheet... reduced iron loss
Implementation Method 3
containing one or more of Mn, Ni, Mo, Cr, and other solid solution strengthening ingredients
Implementation Method 4
nonoriented electrical steel sheet in which additionally Nb etc. are incorporated in solid solution to suppress recrystallization
Implementation Method 5
annealing work efficiency... maintaining cold rollability and annealing efficiency
Data Source
Figure 1
AI summary
The present invention has as its object the production of high strength electrical steel sheet, having a high strength of a tensile strength TS of for example 500 MPa or more, having wear resistance, and having superior magnetic properties of magnetic flux density and iron loss, that is, provides a method of production of high strength electrical steel sheet containing, by mass%, C: 0.060% or less, Si: 0.2 to 6.5%, Mn: 0.05 to 3.0%, P: 0.30% or less, S or Se: 0.040% or less, Al: 2.50% or less, N: 0.020% or less, and further one or more of Cu: 0.001 to 30.0% and Nb: 0.03 to 8.0% and having worked structures remaining inside the steel sheet, said method of production of high strength electrical steel sheet coarsening an average crystal grain size D (µm) of a sheet right before a step of forming the worked structures to finally remain inside the steel sheet to D≥20 µm, imparting strain in the final working step as a preferred process, then not performing any heat treatment causing the worked structures to disappear and high strength electrical steel sheet obtained by that method.