Non-oriented electrical steel sheet for automotive motor cores
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Solution Overview
Problem
The existing methods for producing non-oriented electrical steel sheets with high strength and low iron loss for automotive motor applications are costly due to the need for skin pass rolling after finish annealing and the high material cost of adding Ni, which increases production costs.
Innovation Solution
A non-oriented electrical steel sheet with a specific chemical composition and production process involving hot-rolling, hot-band annealing, single or multiple cold rollings with intermediate annealing, and finish annealing, which includes adjusting rolling speed, friction coefficient, and soaking temperature to achieve the desired properties of high yield stress, low iron loss, and controlled crystal grain size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If skin pass rolling is performed after finish annealing to achieve high strength, then the strength of the steel sheet is improved, but the production cost is increased
Solution Approach 1:
The patent applies preliminary action by controlling the chemical composition (specifically Si content at 2.0-3.5 mass%) and performing finish annealing before cold rolling to pre-establish the microstructure and mechanical properties. This preliminary preparation eliminates the need for subsequent skin pass rolling, thereby reducing production costs while maintaining high strength
Solution Approach 2:
The patent changes key parameters including Si content (2.0-3.5 mass%), Mn content (0.50-2.00 mass%), and Al content (0.01-3.00 mass%) to achieve the desired balance between strength and cost. By optimizing these compositional parameters and the finish annealing process, the steel sheet attains high strength without requiring additional skin pass rolling operations
2Loss of energy
If Ni is added in a substantial amount to promote crystal grain growth and reduce iron loss, then the magnetic properties are improved, but the material cost becomes higher
Solution Approach 1:
The patent replaces expensive Ni with more cost-effective alloying elements. By using Si (2.0-3.5 mass%), Mn (0.50-2.00 mass%), and Al (0.01-3.00 mass%) as primary alloying elements, the patent achieves the desired magnetic properties and crystal grain growth control without the high material cost associated with substantial Ni addition
Solution Approach 2:
The patent changes the alloying strategy by limiting Ni to 0.01-1.00 mass% and instead optimizing Si, Mn, and Al content to achieve the desired effects on crystal grain growth and iron loss reduction. This parameter change in compositional strategy maintains magnetic performance while significantly reducing material cost
3Ease of manufacture
If the same steel sheet material is used for both rotor core and stator core, then the production process is simplified, but the conflicting requirements for strength and magnetic properties cannot be simultaneously satisfied
Solution Approach 1:
The patent achieves universality by formulating a multi-functional steel sheet composition that simultaneously satisfies both rotor core strength requirements and stator core magnetic property requirements. The specific composition (Si: 2.0-3.5 mass%, Mn: 0.50-2.00 mass%, Al: 0.01-3.00 mass%, Ni: 0.01-1.00 mass%) enables the same material to be used for both applications without compromising either strength or magnetic performance
Solution Approach 2:
The patent changes the compositional parameters to a specific range that balances conflicting requirements: Si (2.0-3.5 mass%) for strength and magnetic properties, Mn (0.50-2.00 mass%) for strength, Al (0.01-3.00 mass%) for deoxidation and inclusion control, and Ni (0.01-1.00 mass%) for magnetic properties. This optimized parameter set enables universal application for both rotor and stator cores
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 allows for the production of both high-strength rotor cores and low-iron loss stator cores from the same steel sheet at a lower cost, achieving stable iron core materials for automotive motors with improved efficiency and reduced production expenses.
Implementation Method 1
subjecting the hot-rolled sheet to a hot-band annealing
Implementation Method 2
subjecting the cold-rolled sheet to a finish annealing
Data Source
AI summary
A non-oriented electrical steel sheet with an average magnetostriction λp-p at 400 Hz and 1.0 T of not more than 4.5×10−6, and area ratio of recrystallized grains at a section in rolling direction of steel sheet of 40 to 95% and an average grain size of 10 to 40 μm is obtained by subjecting a steel slab containing, in mass %, C: not more than 0.005%, Si: 2.8 to 6.5%, Mn: 0.05 to 2.0%, Al: not more than 3.0%, P: not more than 0.20%, S: not more than 0.005%, N: not more than 0.005%, Ti: not more than 0.003%, V: not more than 0.005% and Nb: not more than 0.005% and satisfying Si-2Al—Mn≥0 to hot rolling, hot-band annealing, cold rolling and finish annealing under adequate cold rolling and finish annealing conditions, and a motor core is manufactured by such a steel sheet.