Non-oriented electrical steel sheet heating method
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Solution Overview
Problem
Existing methods for increasing the magnetic flux density of non-oriented electrical steel sheets, such as induction heating and radiant heating, are not stable and often require costly equipment or result in surface defects, and previous techniques cannot be directly applied to non-oriented steel sheets.
Innovation Solution
A method involving hot rolling, cold rolling with intermediate annealing, and final annealing using a combination of induction and radiant heating with specific heating rates and chemical compositions to achieve a recrystallization ratio of less than 80% and {100} intensity of 8 or less, optimizing the γ phase ratio and reheating treatments to enhance magnetic flux density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If induction heating method is used to increase heating rate during final annealing, then magnetic flux density may be increased, but the effect is unstable and equipment cost increases
Solution Approach 1:
The patent combines induction heating and radiant heating methods to achieve both high heating rate and stable magnetic flux density effect. Induction heating provides rapid heating capability while radiant heating ensures uniform temperature distribution and stable texture development, resolving the instability issue of pure induction heating.
Solution Approach 2:
The patent optimizes specific parameter ranges including heating rate (5-50°C/s), final annealing temperature (800-950°C), and soaking time (5-60 seconds) to achieve stable magnetic flux density improvement. These parameter optimizations ensure reliable texture control during recrystallization.
2Speed
If electrical resistance heating is used for rapid heating, then heating rate can be increased, but sparks are generated and surface defects occur
Solution Approach 1:
The patent replaces electrical resistance heating (which causes sparks and surface defects) with induction heating combined with radiant heating. This substitution eliminates contact between heating elements and the steel sheet, preventing surface defects while maintaining high heating rates through electromagnetic induction.
3Temperature
If heating rate of final annealing is increased to change texture, then magnetic flux density can be increased, but equipment cost increases due to cooling and reheating requirements
Solution Approach 1:
The patent achieves continuous heating from room temperature to final annealing temperature using induction heating followed by radiant heating, eliminating the need for intermediate cooling and reheating cycles. This continuous heating process maintains high heating rates throughout while reducing equipment complexity and cost.
4Reliability
If recrystallization ratio before final cold rolling is low, then texture control is difficult, but induction heating alone cannot achieve stable magnetic flux density improvement
Solution Approach 1:
The patent combines induction heating (for rapid heating) with radiant heating (for uniform temperature distribution and texture control) to achieve stable magnetic flux density improvement even when recrystallization ratio before final cold rolling is low. The radiant heating component ensures proper texture development during the annealing 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
Stably increases the magnetic flux density of non-oriented electrical steel sheets by adjusting the heating rates and chemical compositions during the annealing process, even with a low recrystallization ratio before final cold rolling, while reducing equipment costs and preventing surface defects.
Implementation Method 1
it was clear that this technique could not provide a stable effect of increasing the magnetic flux density. The Examples of PTL 2 did not use an induction heating method
Implementation Method 2
PTL 5 is an invention in which heating is performed by a combination of induction heating and radiant heating
Implementation Method 3
when the heating rate of decarburization annealing (primary recrystallization annealing) is increased, grains with the {110} orientation of a decarburization annealed sheet are increased, the secondary recrystallization microstructure is refined
Data Source
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AI summary
To stably improve the magnetic flux density by utilizing induction heating and radiant heating during final annealing of a non-oriented electrical steel sheet. A method of manufacturing a non-oriented electrical steel sheet, including subjecting a slab having a predetermined chemical composition to hot rolling with or without performing hot-rolled sheet annealing, and then to cold rolling either once, or twice or more with intermediate annealing performed therebetween, and then to final annealing, wherein the slab has a ratio of y phase of 30 % or more at a slab heating temperature, a reheating treatment is performed to raise a material temperature by 20 °C or more between a start and an end of the hot rolling, a material before final cold rolling has a recrystallization ratio of less than 80 % and a {100}<011> intensity of 8 or less in a 1/4 layer, and in the final annealing, an average heating rate from 600 °C to 720 °C is 50 °C/s or higher, and an average heating rate from 720 °C to 760 °C is 5 °C/s or higher.