Electrical Steel Sheet Coating to Suppress Nitriding in Motor Cores
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Solution Overview
Problem
Existing non-oriented electrical steel sheets for motor cores in HEV-driven motors require high strength and excellent magnetic properties, but adding Ni to enhance strength increases production costs and deteriorates magnetic properties during stress-relief annealing.
Innovation Solution
A non-oriented electrical steel sheet with specific component composition and surface coatings, including Zn and elements like Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi, to suppress nitriding during stress-relief annealing, allowing for high-strength rotor cores and low-iron-loss stator cores to be produced from the same material without using expensive Ni.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Ni is added by not less than 0.5 mass % to increase the strength of the steel sheet, then the strength is improved, but the production cost increases
Solution Approach 1:
The patent changes the compositional parameters by limiting Ni to 0.003 mass % or less and instead optimizing other alloying elements (Si: 3.0-6.5 mass %, Mn: 1.5-3.0 mass %, Cr: 0.5-2.0 mass %, Mo: 0.1-0.5 mass %) to achieve the required strength without expensive Ni additions. This parameter substitution resolves the contradiction between strength and production cost.
2Reliability
If stress-relief annealing is performed to process the steel sheet, then the magnetic properties are improved, but the iron loss increases due to nitriding in the surface layer
Solution Approach 1:
The patent applies a coating layer containing Al, Si, or P on the steel sheet surface before stress-relief annealing. This preliminary coating action prevents nitriding during the subsequent annealing process, thereby preventing deterioration of magnetic properties and avoiding increased iron loss. The coating acts as a protective barrier that enables the annealing to proceed without harmful side effects.
3Productivity
If the same steel sheet is used for both rotor core and stator core to increase material yield, then the productivity is improved, but it is difficult to satisfy both high strength requirement for rotor core and low iron loss requirement for stator core
Solution Approach 1:
The patent applies different surface treatments to different portions of the same steel sheet: the rotor core portion receives a coating layer designed for high strength (with specific alloying elements), while the stator core portion receives a coating layer optimized for low iron loss (with Al, Si, or P). This local differentiation allows both performance requirements to be satisfied simultaneously while using the same base steel sheet, thereby maintaining high material yield.
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 solution enables the production of motor cores with improved strength and efficiency by suppressing nitriding, resulting in downsized and higher output motors for HEVs and other applications.
Implementation Method 1
the deterioration of the magnetic properties caused by stress-relief annealing results from the nitriding in the steel sheet surface layer at the stress-relief annealing, and that, in order to suppress the nitriding in the steel sheet surface layer
Implementation Method 2
subjecting only the stator core to stress-relief annealing
Data Source
AI summary
In a production of a non-oriented electrical steel sheet by hot-rolling a steel slab containing Si: 2.8 to 6.5 mass % and Zn: 0.0005 to 0.0050 mass % followed by cold rolling and finish annealing, a coating agent containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi is applied to the steel sheet surface after the finish annealing to form an insulation coating with a nitriding-suppressing ability. Alternatively, an intermediate layer containing at least one element selected from Sn, Sb, P, S, Se, As, Te, B, Pb, and Bi and having a nitriding-suppressing ability is formed on the steel sheet iron matrix after the finish annealing and form an insulation coating not containing above elements is formed on the intermediate layer thus to obtain a non-oriented electrical steel sheet from which a rotor core with high strength and stator core with excellent magnetic properties after the stress-relief annealing can be obtained at the same time, and a motor core comprising a stator core and rotor core is produced from the steel sheet.