Grain-Oriented Steel Sheet Nitriding for Magnetic Flux Density
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Solution Overview
Problem
Existing methods struggle to maintain a consistent and high temperature gradient throughout an industrial-scale coil during the manufacturing of grain-oriented electrical steel sheets, leading to regions with insufficient magnetic flux density improvement.
Innovation Solution
A method involving a hot rolling step, decarburization annealing, nitriding treatment, and final annealing with a controlled temperature gradient, ensuring a primary recrystallization grain size of 15 µm or less and a nitrogen content of 210 ppm or more, to enhance magnetic flux density even under small temperature gradients.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a temperature gradient of 2°C/cm or more is applied during final annealing, then magnetic flux density can be improved, but it is difficult to maintain such a high and constant temperature gradient throughout an industrial-scale coil
Solution Approach 1:
The invention changes the parameter of temperature gradient from a high value (2°C/cm or more) to a lower value (0.5°C/cm or more) while achieving the same technical effect through the combined action of nitriding treatment and controlled temperature gradient. This parameter change makes the process feasible for industrial-scale coils where maintaining high temperature gradients is difficult.
Solution Approach 2:
The nitriding treatment is performed as a preliminary action before final annealing to increase nitrogen content to 210 ppm or more. This preliminary treatment modifies the material properties so that secondary recrystallization can proceed effectively even with a smaller temperature gradient during the subsequent final annealing process.
2Manufacturing precision
If nitrogen content is increased to 210 ppm or more through nitriding treatment, then secondary recrystallization can proceed with smaller temperature gradients, but the process complexity increases
Solution Approach 1:
The invention merges the nitriding treatment with existing process steps such as decarburization annealing or intermediate annealing, rather than adding it as a completely separate operation. This integration approach increases nitrogen content while minimizing the increase in overall process complexity.
3Manufacturing precision
If primary recrystallization grain size is reduced to 15 µm or less, then magnetic flux density improves, but the annealing process requires more precise control
Solution Approach 1:
The invention changes the controlling parameter for grain size from relying solely on temperature gradient magnitude to using nitrogen content as a key parameter. By controlling nitrogen content to 210 ppm or more, the process achieves fine grain size (15 µm or less) with a smaller, more easily controlled temperature gradient.
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 stabilizes magnetic flux density across the coil by preferentially growing {110} oriented grains, achieving a high magnetic flux density of 1.940 T or more, even with a temperature gradient as low as 0.5 °C/cm, thereby improving manufacturing efficiency and product quality.
Implementation Method 1
the steel sheet is subjected to final annealing at high temperature including treatment of growing secondary recrystallization grains
Implementation Method 2
applying a temperature gradient of 2 °C/cm or more to the steel sheet in the boundary portion between the primary recrystallization region and the secondary recrystallization region
Implementation Method 3
a nitriding treatment step of increasing a nitrogen amount in the steel sheet
Implementation Method 4
a decarburization annealing step of decarburization-annealing the steel sheet after the cold rolling step
Data Source
AI summary
The method of manufacturing a grain-oriented electrical steel sheet includes: a hot rolling step; a hot-rolled sheet annealing step; a cold rolling step; a decarburization annealing step; an annealing separator applying step; a nitriding treatment step; and a final annealing step, wherein the final annealing step has a temperature raising process and a soaking process, and a temperature gradient of 0.5 °C/cm or more is generated in a boundary region between a primary recrystallization region and a secondary recrystallization region at least in one period from the start of secondary recrystallization to completion of the secondary recrystallization in the temperature raising process; and the nitriding treatment step is performed by annealing in an atmosphere containing a gas having nitriding ability at least in one stage of: during the decarburization annealing step; between the decarburization annealing step and the final annealing step; and during the temperature raising process in the final annealing step and before the start of the secondary recrystallization, so that the nitrogen amount in the steel sheet is 210 ppm or more based on mass after the nitriding treatment step.