Grain-Oriented Electrical Steel Strip Annealing Process
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Solution Overview
Problem
Current processes for producing grain-oriented electrical steel strips using thin slab continuous casting face challenges in achieving high-grade magnetic characteristics due to fluctuations in magnetic properties across the strip's length and width, leading to decreased quality.
Innovation Solution
A process involving decarburization, intermediate reduction, and nitridation annealing phases with specific temperature and atmosphere conditions to form a homogeneous AlN inhibitor phase, combined with inherent inhibition during hot rolling, stabilizing the microstructure and preventing parasitic grain growth, allowing for single-stage cold rolling and improved magnetic product characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thin slab continuous casting is used to produce grain-oriented electrical steel strip, then production efficiency and productivity are improved, but magnetic property homogeneity across the strip deteriorates
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (C: 0.030-0.100 wt %, Si: 2.50-4.00 wt %, Mn: 0.160-0.300 wt %) and processing parameters (homogenization temperature above 1050° C., inductive heating temperature of 1350-1380° C., annealing temperature of 920-1150° C.) to achieve both high productivity through thin slab casting and improved magnetic property homogeneity through optimized compositional and thermal parameters
Solution Approach 2:
The patent implements preliminary action through homogenization annealing (heating to above 1050° C. and holding) performed before hot rolling to ensure uniform chemical and microstructural composition throughout the thin slab, and through inductive heating immediately before hot rolling to achieve uniform temperature distribution, thereby preventing magnetic property fluctuations in the final product while maintaining thin slab processing advantages
2Manufacturing precision
If conventional multi-stage cold rolling with intermediate annealing is used, then manufacturing precision and texture control are improved, but production time and process complexity increase
Solution Approach 1:
The patent merges multiple process functions into a single continuous annealing step that performs recrystallization, decarburization, and nitridation simultaneously at 920-1150° C. in a controlled atmosphere, eliminating the need for separate intermediate annealing stages between cold rolling passes while achieving the same texture control precision through the synergistic effect of combined processes
Solution Approach 2:
The patent changes the annealing parameters by conducting it at elevated temperatures (920-1150° C.) in a controlled atmosphere containing nitrogen and hydrogen with specific water vapor/hydrogen partial pressure ratios (0.03-0.07), which enables simultaneous recrystallization, decarburization, and nitridation to form homogeneous AlN inhibitor phase, achieving precise texture control in a single step rather than multiple stages
3Productivity
If high carbon content is used in the smelt, then productivity and hot working properties are improved, but magnetic losses increase due to carbide formation
Solution Approach 1:
The patent optimizes the carbon content parameter to a narrow range (0.030-0.100 wt %) and combines it with controlled decarburization during annealing (reducing C to below 30 ppm) to achieve sufficient hot working properties without excessive carbon that would form harmful carbides and increase magnetic losses, balancing productivity and energy efficiency through precise parameter control
Solution Approach 2:
The patent converts the potentially harmful effect of carbon by implementing controlled decarburization during annealing in a hydrogen-rich atmosphere (water vapor/hydrogen ratio 0.03-0.07), which removes excess carbon as CO gas while retaining sufficient carbon for hot working, thereby preventing carbide formation that would cause magnetic losses while maintaining productivity
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 process achieves a grain-oriented electrical steel strip with enhanced magnetic properties, including a sharp Goss texture and improved homogeneity, resulting in high-grade material suitable for transformers with reduced magnetic losses.
Implementation Method 1
feeding the thin slabs to an inductive heating device, particularly a high frequency inductive heating device, in which the thin slabs, particularly while passing are directly before the first hot rolling pass, at least for some seconds heated up to a temperature above the previous homogenization temperature of step c′), which temperature is within the temperature range of 1350° C.-1380° C.
Implementation Method 2
subjecting the cold-rolled strip to recrystallization, decarburization and nitridation annealing
Data Source
AI summary
A process for producing grain-oriented electrical steel strip by means of thin slab continuous casting and which includes continuously casting the smelt by thin slab continuous casting, subjecting the thin slabs to homogenization annealing at a maximum temperature of 1250° C. and heating to a temperature between 1350° C. and 1380° C., and continuously hot rolling the thin slabs to form a hot-rolled strip, with cooling and reeling the hot-rolled strip to form a coil and cold rolling the hot-rolled strip to a nominal thickness, with subjecting the cold-rolled strip to recrystallization, decarburization and nitridation annealing, which includes a decarburization annealing phase and a subsequent nitridation annealing phase, with an intermediate reduction annealing phase being interposed between the decarburization annealing phase and the nitridation annealing phase, whereby a cold-rolled strip is obtained, which primary recrystallized grains have a circle equivalent mean size (diameter) between 22 μm and 25 μm.