Non-Oriented Electrical Steel Sheet Manufacturing
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Solution Overview
Problem
Existing methods for manufacturing non-oriented electrical steel sheets struggle to achieve excellent magnetic characteristics on a whole circumferential average, as they often fail to maintain sufficient magnetic properties in all directions parallel to the sheet surface.
Innovation Solution
A method involving hot rolling with a specific chemical composition and rapid cooling to refine the crystal structure, followed by controlled cold rolling and annealing processes to promote {100} grain growth and recrystallization, ensuring the chemical composition satisfies the α-γ transformation conditions and optimizing annealing temperatures to enhance magnetic flux density and reduce iron loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional hot rolling and cooling methods are used, then manufacturing process is simple, but magnetic characteristics on whole circumferential average are insufficient
Solution Approach 1:
The patent applies parameter changes by precisely controlling hot rolling temperature (Ar1 or higher), cooling rate (50-500°C/sec), and chemical composition (specific ranges of Si, Mn, Al, and other elements). These parameter optimizations enable the formation of desired crystal orientation ({100} grains) and phase transformation (austenite to ferrite), achieving excellent magnetic characteristics on whole circumferential average while maintaining process feasibility
Solution Approach 2:
The patent implements preliminary action through controlled hot rolling and rapid cooling processes that pre-establish the crystal structure and phase composition before final annealing. By performing austenite formation during hot rolling and initiating ferrite transformation through controlled cooling, the material is prepared in advance to achieve the desired magnetic properties after final annealing, rather than relying solely on the annealing process
2Manufacturing precision
If rapid cooling is applied to refine crystal structure, then magnetic flux density increases, but iron loss increases due to fine crystal structure
Solution Approach 1:
The patent resolves this contradiction through parameter changes in chemical composition, specifically optimizing Si content (1.50-4.00%) to increase electrical resistance and reduce eddy current losses, while controlling the timing and rate of cooling to achieve appropriate crystal grain size. The balanced composition and controlled thermal parameters enable simultaneous achievement of high magnetic flux density and low iron loss
Solution Approach 2:
The patent creates a composite microstructure through controlled phase transformation, producing a dual-phase structure of ferrite and retained austenite with specific crystal orientations. This composite microstructure, achieved through hot rolling at Ar1 or higher followed by controlled cooling and annealing, combines the advantages of both phases: ferrite provides magnetic softness and low loss, while oriented grains provide high magnetic flux density
3Manufacturing precision
If {100} grain growth is promoted through annealing, then magnetic characteristics improve, but manufacturing process complexity increases
Solution Approach 1:
The patent applies preliminary action by establishing the necessary crystal structure and phase composition during hot rolling and cooling processes before annealing. The hot rolling at Ar1 or higher creates austenite, and the controlled cooling initiates ferrite transformation, preparing the material in advance so that subsequent annealing only needs to promote grain growth and orientation rather than creating the basic structure from scratch, thereby simplifying the overall process
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 and reduced iron loss across all directions on the sheet surface, achieving excellent magnetic characteristics on the whole circumferential average.
Implementation Method 1
it is important to premise a chemical composition of an α-γ transformation system, to refine crystal structure by transformation into ferrite from austenite during hot rolling
Implementation Method 2
cooling of which an average cooling rate is in a range of 50 to 500° C./sec is started in 0.1 sec from completion of rolling of the final pass of the finish rolling
Implementation Method 3
performing first annealing (process annealing) under desired conditions and causing projection recrystallization (hereinafter, referred to as bulging) to occur
Data Source
AI summary
A method for manufacturing a non-oriented electrical steel sheet includes a step of obtaining a hot-rolled steel sheet by performing hot rolling on a steel material having a predetermined chemical composition, a step of performing first cold rolling on the hot-rolled steel sheet, and a step of performing first annealing after the first cold rolling. A final pass of finish rolling is performed in a temperature range equal to or higher than an Ar1 temperature, and cooling of which an average cooling rate is in a range of 50 to 500° C./sec is started in 0.1 sec from completion of rolling of the final pass of the finish rolling and is performed up to a temperature range higher than 250° C. and equal to or lower than 700° C.