Grain Oriented Steel Cooling Control for Magnetic Uniformity
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Solution Overview
Problem
Grain oriented electrical steel sheets exhibit lower magnetic properties, particularly higher iron loss, at the tip portion of a coil compared to the middle portion, due to deviations in sheet thickness and excessive cooling during the hot rolling process, leading to unstable secondary recrystallization and inhibited magnetic flux density.
Innovation Solution
Control both the upper and lower limit temperatures during the cooling process after hot rolling to maintain the steel sheet temperature within specific ranges, ensuring uniform inhibitor precipitation and preventing excessive cooling of the tip portion, thereby stabilizing magnetic properties across the entire coil length.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the steel sheet is cooled rapidly during hot rolling to reduce production time, then productivity is improved, but the tip portion of the coil becomes excessively cooled leading to deteriorated magnetic properties
Solution Approach 1:
The patent applies different cooling control strategies to different portions of the coil. The tip portion (first 10% of coil length) is controlled to maintain temperature above 650°C at 3 seconds after finish rolling, while the middle portion follows the conventional cooling curve T(t) ≤ FDT - 50√t. This local differentiation ensures uniform magnetic properties throughout the coil while maintaining overall production efficiency.
2Quantity of substance
If the cooling rate is increased to prevent inhibitor precipitation, then magnetic flux density is improved, but iron loss increases due to excessive cooling of the tip portion
Solution Approach 1:
The patent implements preliminary temperature control for the tip portion before the main cooling process begins. By ensuring the tip portion temperature remains above 650°C at 3 seconds after finish rolling, the inhibitor precipitation is controlled in advance, preventing both excessive cooling damage and ensuring proper magnetic properties are achieved during subsequent cooling.
3Use of energy by moving object
If the coil tip portion is allowed to cool excessively to maintain overall cooling efficiency, then energy efficiency is improved, but secondary recrystallization becomes unstable leading to lower magnetic flux density
Solution Approach 1:
The patent implements location-specific temperature control where the tip portion (first 10% of coil length) is protected from excessive cooling by maintaining temperature above 650°C at 3 seconds after finish rolling. This localized approach ensures stable secondary recrystallization and uniform magnetic properties in the tip portion while allowing efficient cooling of the middle portion to maintain overall energy efficiency.
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 ensures grain oriented electrical steel sheets with consistent magnetic properties throughout the coil length, preventing deteriorations in iron loss and maintaining high magnetic flux density by optimizing cooling conditions and chemical composition.
Implementation Method 1
A slab with a thickness of 100 to 300 mm that has been controlled so as to have a predetermined chemical composition is heated to a temperature of 1250°C or above and subjected to hot rolling
Implementation Method 2
the steel sheet temperature at a lapse of 2 to 6 seconds from the completion of the finish rolling satisfies Equation (1)... controlling the steel sheet temperature so as to satisfy Equation (1) below throughout the entire coil length during cooling after the completion of finish rolling
Implementation Method 3
the hot-rolled sheet or the hot-rolled and annealed sheet is cold rolled... the cold-rolled sheet is subjected to decarburization annealing... the steel sheet is subjected to finish annealing for secondary recrystallization and purification
Implementation Method 4
it is important to control the precipitation state of a dispersed phase called an inhibitor such that the inhibitor will be dispersed uniformly with an appropriate size throughout the steel... controlling the behavior of inhibitors from the precipitation of inhibitors during hot rolling
Data Source
Figure 1~2
AI summary
In a method for manufacturing grain oriented electrical steel sheets containing, in terms of mass%, C at 0.01 to 0.10%, Si at 2.5 to 4.5%, Mn at 0.02 to 0.12%, Al at 0.005 to 0.10% and N at 0.004 to 0.015%, as well as one or two selected from Se at 0.005 to 0.06% and S at 0.005 to 0.06%, the steel sheet temperature is controlled so as to satisfy T (t) < FDT - (FDT - 700) x t/6 (wherein T (t): steel sheet temperature (°C), FDT: finishing temperature (°C) and t: time (sec) after the completion of finish rolling) throughout the entire length of a coil during cooling after the completion of finish rolling in hot rolling, and further the steel sheet temperature of a tip portion of the coil representing 10% of the length of the coil is controlled to be not less than 650°C at a lapse of 3 seconds from the completion of hot rolling, thus manufacturing a grain oriented electrical steel sheet exhibiting excellent magnetic properties throughout the entire coil length.