Grain-Oriented Electrical Steel Surface Smoothing Without Forsterite
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Solution Overview
Problem
The existing methods for producing grain-oriented electrical steel sheets face challenges in achieving excellent magnetic characteristics and coating adhesion without the forsterite film, as the uneven interface between the steel sheet and the insulation coating hinders the reduction of iron loss and adhesion.
Innovation Solution
A method involving a series of processes including hot rolling, cold rolling, decarburization annealing, and the use of an annealing separator containing Al2O3 and MgO to smoothen the steel sheet surface, followed by insulation coating application, which enhances magnetic domain refinement and improves coating adhesion without forming a forsterite film.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the forsterite film is removed and the interface is smoothened to reduce iron loss, then magnetic characteristics are improved, but coating adhesion becomes insufficient
Solution Approach 1:
The patent applies preliminary chemical treatment to the steel sheet surface before coating application. The steel sheet undergoes pickling in an acidic solution to create a chemically active surface layer that enhances subsequent coating adhesion. This preliminary action ensures that even with a smooth interface, the coating will adhere properly without requiring the forsterite film's anchor effect
Solution Approach 2:
The patent changes the chemical parameters of the steel sheet surface through controlled oxidation and chemical treatment. By adjusting the surface chemistry (creating oxide layers and chemical groups), the patent achieves both smooth surface morphology for reduced iron loss and high chemical reactivity for improved coating adhesion
2Reliability
If the forsterite film is formed to ensure coating adhesion through anchor effect, then coating adhesion is improved, but magnetic characteristics deteriorate due to magnetic domain wall obstruction
Solution Approach 1:
The patent extracts and eliminates the forsterite film from the steel sheet surface structure. By removing this oxide layer that causes magnetic domain wall obstruction, the patent achieves lower iron loss while compensating for the lost anchor effect through alternative chemical adhesion mechanisms
Solution Approach 2:
The patent introduces a chemical intermediary layer through surface treatment processes. This chemically treated surface layer acts as an intermediary between the smooth steel sheet and the insulation coating, providing adhesion without the magnetic drawbacks of the forsterite film
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 results in a grain-oriented electrical steel sheet with improved magnetic characteristics and coating adhesion, effectively reducing iron loss and ensuring sufficient adhesion of the insulation coating, thereby enhancing the performance of the steel sheet.
Implementation Method 1
final annealing which is a heat treatment at 900 to 1200°C for 30 hours or more to make the steel sheet be secondary-recrystallized
Implementation Method 2
the surface of the base steel sheet is smoothened by chemical polishing or electrolytic polishing
Implementation Method 3
the insulation coating is formed by applying coating solution including, for instance, phosphoric acid or phosphate, colloidal silica, and chromic anhydride or chromate to the base steel sheet after final annealing, and by baking and drying it at 300 to 950°C for 10 seconds or more
Implementation Method 4
by baking and drying it at 300 to 950°C for 10 seconds or more
Implementation Method 5
The forsterite film which is the oxide film including Mg is formed, during final annealing which is a heat treatment at 900 to 1200°C for 30 hours or more to make the steel sheet be secondary-recrystallized, by reacting an annealing separator mainly including magnesia (MgO) with silicon dioxide (SiO2) formed on the base steel sheet during decarburization annealing
Data Source
Figure 1
AI summary
A method for producing a grain oriented electrical steel sheet includes a decarburization annealing process where an oxidation degree PH2O/PH2 is controlled, an annealing separator applying process where a mass ratio of MgO and AI2O3 in an annealing separator is controlled, a final annealing process where hydrogen in mixed gas atmosphere is controlled to 50 volume% or more, an annealing separator removing process where water-washing is conducted using solution with inhibitor and then pickling is conducted, a smoothing process where mixed gas and temperature are controlled for annealing, and an insulation coating forming process where a baking temperature and a heat treatment temperature are controlled.