Grain-Oriented Electrical Steel Heating for Edge Crack Prevention
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Solution Overview
Problem
Existing methods for producing grain-oriented electrical steel sheets face challenges in preventing edge cracks during hot rolling, particularly due to non-uniform heating and microsegregation of inhibitor-forming ingredients, which affect the magnetic properties and yield of the final product.
Innovation Solution
A method involving precise control of slab surface temperature and lateral face temperature during hot rolling, using a composition with specific ranges of C, Si, Mn, S, Se, Al, and N, along with additional elements, and incorporating steps like hot-band annealing, cold rolling, primary recrystallization annealing, and finishing annealing to prevent edge cracks and enhance magnetic properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If short-time rapid heating is used to prevent crystal texture coarsening, then productivity and equipment efficiency are improved, but heating uniformity deteriorates causing non-uniform temperature distribution in the slab
Solution Approach 1:
The heating process is divided into multiple stages: preheating, intermediate heating, and final heating to rolling temperature. Each stage uses different heating rates and temperature targets to ensure uniform heat distribution throughout the slab while maintaining high overall efficiency.
Solution Approach 2:
Preheating is performed before the main heating stage to gradually raise the slab temperature and reduce thermal gradients. This preliminary action prevents thermal shock and ensures more uniform heating during subsequent rapid heating stages.
2Loss of time
If high heating rate is applied to reduce heating time, then productivity increases, but temperature uniformity across the slab deteriorates
Solution Approach 1:
The heating process uses periodic cycling between different heating rates and holding periods. High heating rates are alternated with intermediate holding stages that allow heat to distribute uniformly, repeating this cycle until the slab reaches the target temperature range.
Solution Approach 2:
The heating rate is dynamically adjusted based on the current temperature state of the slab. The system transitions from slower preheating rates to faster heating rates as the slab approaches the target temperature, optimizing both time and uniformity at different stages.
3Reliability
If inhibitor-forming ingredients are added to prevent edge cracks, then reliability improves, but microsegregation occurs affecting magnetic properties
Solution Approach 1:
The composition parameters of inhibitor-forming ingredients are precisely controlled within specific ranges. The heating temperature profile is also optimized to ensure complete dissolution and uniform distribution of these ingredients, preventing microsegregation while maintaining their crack-prevention function.
4Stability of the object's composition
If slab heating temperature is increased to 1300°C or higher for uniform inhibitor distribution, then ingredient distribution improves, but crystal texture coarsening is promoted
Solution Approach 1:
The heating process uses periodic cycling between different heating rates and holding periods. High heating rates are alternated with intermediate holding stages that allow heat to distribute uniformly, repeating this cycle until the slab reaches the target temperature range.
Solution Approach 2:
The composition parameters of inhibitor-forming ingredients are precisely controlled within specific ranges. The heating temperature profile is also optimized to ensure complete dissolution and uniform distribution of these ingredients, preventing microsegregation while maintaining their crack-prevention function.
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 effectively reduces edge crack depth and achieves high magnetic flux density with low iron loss, improving the yield and cost-effectiveness of grain-oriented electrical steel sheet production.
Implementation Method 1
heating a steel slab having an ingredient composition containing C: 0.02 to 0.10 mass %, Si: 2.5 to 5.5 mass %, Mn: 0.01 to 0.30 mass %, S: 0.0010 to 0.040 mass %, Se: 0 to 0.040 mass %, sol. Al: 0.010 to 0.040 mass %, and N: 0.004 to 0.020 mass % with a remaining part comprising Fe and inevitable impurities; the slab is heated to 1300° C. or higher
Implementation Method 2
subjecting the sheet to finishing annealing, wherein a method using an inhibitor such as AlN and MnS, whereas Patent Literature 2 discloses a method using an inhibitor such as MnS and MnSe, both of which have industrially been put into practical use. These methods using the inhibitor are ideally conducted under a state where the inhibitors are finely and uniformly dispersed.
Implementation Method 3
the heating step includes: heating the slab until a slab surface temperature reaches a temperature of 1100 to 1300° C.; holding the slab at the temperature; once cooling the slab with a decrease amount in the slab surface temperature in a range of 50 to 200° C.; and heating the slab until the slab surface temperature reaches 1300° C. or higher
Data Source
AI summary
In the production of a grain-oriented electrical steel sheet by heating a steel slab containing, in mass %, C: 0.02 to 0.10%, Si: 2.5 to 5.5%, Mn: 0.01 to 0.30%, S: 0.0010 to 0.040%, Se: 0 to 0.040%, sol. Al: 0.010 to 0.040%; and N: 0.004 to 0.020% to 1300° C. or higher; subsequently performing hot rolling, hot-band annealing as necessary, cold rolling, and primary recrystallization annealing which also serves as decarburization annealing; applying an annealing separator on the surface of the steel sheet; and performing finishing annealing, edge cracks that may occur in the hot rolling are effectively prevented by keeping a slab lateral face temperature at a time of starting rough rolling during the hot rolling equal to or lower than a temperature Te defined by the following Expression Te=−120000 [% S]2+1400 (1) and carrying out width reduction after at least one pass in the rough rolling.