Grain-Oriented Steel Sheet Decarburization Annealing
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Solution Overview
Problem
Conventional methods for manufacturing grain-oriented electrical steel sheets fail to achieve sufficient improvements in iron loss properties required for advanced energy conservation, despite efforts to decrease sheet thickness, increase Si content, improve crystal orientation, and refine grain size.
Innovation Solution
Optimizing the heating rate during decarburization annealing and controlling the annealing atmosphere to refine secondary grain size and enhance tension imparted by the forsterite film, resulting in a synergistic effect that significantly reduces iron loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional heating rates are used during decarburization annealing, then production efficiency is maintained, but grain size of secondary recrystallized grains cannot be sufficiently refined
Solution Approach 1:
The patent applies preliminary action by performing rapid heating to 700-750°C before the main decarburization annealing process. This preliminary rapid heating stage prepares the steel sheet by increasing presence density of Goss-oriented grains in primary recrystallization texture, which sets the foundation for subsequent grain-size refinement during the slower main annealing process. This two-stage approach allows grain refinement without excessively extending total processing time.
2Strength
If subscales are formed on strained steel sheets, then oxidation protection is provided, but tension imparted by forsterite film is reduced
Solution Approach 1:
The patent applies preliminary action by performing a preliminary heating stage at 700-750°C in a non-oxidizing atmosphere before subscale formation. This preliminary heating releases strains introduced to the steel sheet during cold rolling and intermediate annealing. By eliminating strains before subscale formation, the subsequent forsterite film can impart maximum tension to the steel sheet, achieving the desired mechanical properties.
3Loss of energy
If multiple process steps are added to refine grain size and enhance forsterite film tension, then iron loss properties improve, but manufacturing complexity increases
Solution Approach 1:
The patent merges multiple functions into the decarburization annealing process itself. The rapid heating stage serves dual purposes: it refines the primary recrystallization texture by increasing Goss-oriented grain density and releases strains in the steel sheet. The subsequent slower heating stage performs both decarburization and promotes secondary recrystallization. By combining these functions in a single integrated process rather than separate steps, the patent achieves improved iron loss properties without proportionally increasing manufacturing complexity.
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 combination of grain-size refinement and enhanced forsterite film tension leads to substantially better iron loss properties in grain-oriented electrical steel sheets, with a significant decrease in iron loss values compared to conventional methods.
Implementation Method 1
A steel sheet is to be heated at heating rate of 50°C/second or higher at least in a temperature range of 500°C to 700°C in decarburization annealing so that presence density of Goss-oriented grains in primary recrystallization texture increases
Implementation Method 2
heating a steel sheet in a non-oxidizing atmosphere to a temperature range of 700°C to 750°C to release strains introduced to the steel sheet
Implementation Method 3
allowing subscales to be formed on the steel sheet in an oxidizing atmosphere in decarburization annealing process
Data Source
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AI summary
According to the present invention, a grain oriented electrical steel sheet in which iron loss has been further reduced can be obtained by carrying out decarburization annealing as continuous annealing including: (1) heating the steel sheet to a temperature in the range of 700°C to 750°C at heating rate of 50°C/second or higher at least in a temperature range of 500°C to 700°C in an atmosphere having oxidation potential P(H2O)/P(H2) equal to or lower than 0.05; (2) then cooling the steel sheet to a temperature range below 700°C in an atmosphere having oxidation potential P(H2O)/P(H2) equal to or lower than 0.05; and (3) reheating the steel sheet to a temperature in the range of 800°C to 900°C and retaining the steel sheet at the temperature for soaking in an atmosphere having oxidation potential P(H2O)/P(H2) equal to or higher than 0.3.