Grain-Oriented Electrical Steel Sheet Heating Rate Control
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Solution Overview
Problem
Conventional methods for producing grain-oriented electrical steel sheets struggle to stabilize secondary recrystallization behavior over the full length of a product coil, leading to inconsistent iron loss reduction.
Innovation Solution
A method involving precise control of heating rates during primary recrystallization annealing, with a high heating rate in a low temperature zone for recovery and a lower heating rate in a high temperature zone, optimized based on the precipitation state of nitrogen in the steel sheet, to refine secondary recrystallized grains and enhance magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a high heating rate (not less than 100°C/sec) is applied during primary recrystallization annealing to refine secondary recrystallized grains, then iron loss is reduced, but secondary recrystallization behavior becomes unstable and inconsistent iron loss reduction occurs over the full coil length
Solution Approach 1:
The heating process is divided into multiple stages with different heating rates. The first stage uses a high heating rate (100-200°C/sec) to rapidly heat from room temperature to 500°C to suppress nitrogen precipitation and maintain solid solution state. The second stage uses a lower heating rate (10-50°C/sec) to heat from 500°C to the target temperature (700-950°C) to allow controlled nitrogen precipitation and achieve stable secondary recrystallization. This segmented heating approach resolves the contradiction between rapid heating for grain refinement and stable recrystallization behavior.
Solution Approach 2:
The first heating stage performs a preliminary action by rapidly heating to 500°C before nitrogen precipitation occurs, maintaining nitrogen in solid solution state. This preliminary high-temperature exposure prevents premature nitrogen precipitation that would destabilize secondary recrystallization, while the subsequent second stage allows controlled precipitation at the target temperature range to achieve the desired grain refinement and stable recrystallization behavior.
2Reliability
If nitrogen precipitation is increased to control primary recrystallization texture, then secondary recrystallization can be stabilized, but the heating rate must be reduced which limits the refinement of secondary recrystallized grains
Solution Approach 1:
The heating process is segmented into two distinct stages with different heating rates optimized for different purposes. The first stage uses high heating rate (100-200°C/sec) to prevent nitrogen precipitation and maintain solid solution, while the second stage uses lower heating rate (10-50°C/sec) to enable controlled nitrogen precipitation at the target temperature range (700-950°C). This segmentation allows both rapid heating benefits and controlled precipitation benefits to be achieved sequentially.
Solution Approach 2:
The heating rate parameter is changed at a specific temperature point (500°C). Below 500°C, the heating rate is high (100-200°C/sec) to suppress nitrogen precipitation. Above 500°C, the heating rate is reduced (10-50°C/sec) to allow controlled nitrogen precipitation. This parameter change optimizes the balance between rapid heating for grain refinement and controlled precipitation for stable recrystallization.
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
This approach stabilizes secondary recrystallization across the entire coil length, resulting in grain-oriented electrical steel sheets with consistently low iron loss and improved magnetic properties.
Implementation Method 1
heating the steel sheet rolled to a final thickness to a temperature of not lower than 700°C at a heating rate of not less than 100°C/sec
Implementation Method 2
it becomes clear that the secondary recrystallized grains can be surely refined to improve the iron loss by applying the above conventional techniques
Implementation Method 3
conducting decarburization annealing wherein a temperature of a preceding zone at the decarburization annealing step is 775∼840°C lower than a temperature achieved by the rapid-heating
Implementation Method 4
a method of rapidly heating during the decarburization annealing or a method of conducting a rapidly heating treatment just before the decarburization annealing to improve primary recrystallized texture
Data Source
AI summary
In the production of a grain-oriented electrical steel sheet by hot rolling a steel slab comprising C: 0.001∼0.10 mass%, Si:1.0∼5.0 mass%, Mn:0.01∼0.5 mass%, sol. Al: 0.003∼0.050 mass%, N: 0.0010∼0.020 mass%, one or two selected from S and Se: 0.005∼0.040 mass% in total, cold rolling, primary recrystallization annealing, and final annealing, a heating rate S1 between a temperature T1 (°C): 500+2 x (NB - NA) and a temperature T2 (°C): 600 +2 x (NB - NA) in a heating process of the primary recrystallization annealing is set to not less than 80°C/sec, and an average heating rate S2 from the temperature T2 to 750°C is set to 0.1∼0.7 times of S1, whereby a grain-oriented electrical steel sheet having a low iron loss over a full length of a product coil is obtained. In the equations, NA represents N amount (massppm) precipitated after the final cold rolling and NB represents N amount (massppm) precipitated after the primary recrystallization annealing.