Non-Oriented Electrical Steel Composition for Strength and Punching Roundness
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Solution Overview
Problem
Existing non-oriented electrical steel sheets with high strength and excellent magnetic properties after additional heat treatment still face challenges with fatigue properties and roundness after punching, as well as deformation of stator cores during additional heat treatment.
Innovation Solution
A non-oriented electrical steel sheet with a specific chemical composition and microstructure, including a mixed structure of crystal grains with a coarse grain size and smaller crystal grains, is developed. This composition and structure are optimized to achieve high strength, excellent magnetic properties, improved fatigue properties, and enhanced roundness after punching and additional heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid-solution strengthening is used to enhance steel sheet strength, then tensile strength is improved, but cold rolling becomes difficult and productivity decreases due to required warm rolling process
Solution Approach 1:
The invention changes the strengthening mechanism from solid-solution strengthening to precipitation hardening by controlling the addition of Ti and V elements and applying specific heat treatment parameters (temperature range 500-850°C, holding time 1-24 hours). This allows the steel to achieve high tensile strength (≥65 kgf/mm²) while maintaining cold rollability and eliminating the need for warm rolling, thereby improving productivity.
2Strength
If high strength is achieved through increased Si and alloying elements, then tensile strength is improved, but magnetic properties deteriorate
Solution Approach 1:
The invention optimizes the Si content to 2.0-3.5% (avoiding excessive Si that harms magnetic properties) and uses controlled precipitation hardening through Ti (0.01-1.0%) and V (0.01-1.0%) additions. The specific heat treatment parameters (500-850°C, 1-24 hours) are designed to precipitate strengthening phases without significantly affecting magnetic properties, achieving tensile strength ≥65 kgf/mm² while maintaining acceptable magnetic characteristics.
3Reliability
If additional heat treatment is applied to stator cores after punching and stacking, then magnetic properties are improved, but deformation occurs reducing roundness
Solution Approach 1:
The invention applies preliminary heat treatment during the steel sheet manufacturing process (final annealing at 500-850°C for 1-24 hours) to establish a controlled microstructure with specific grain size (10-50 μm) and phase distribution before punching and stacking. This preliminary structural preparation reduces internal stresses and prevents deformation during subsequent additional heat treatment of assembled cores, maintaining roundness while achieving excellent magnetic properties (iron loss ≤1.55 W/kg at 400 Hz, 1.5 T).
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 proposed solution achieves high strength and excellent magnetic properties before and after additional heat treatment, while also improving fatigue properties and roundness, thereby addressing the limitations of existing technologies.
Implementation Method 1
the strength of the steel sheet is enhanced by increasing the amount of Si and solid-solution strengthening with Ti, W, Mo, Mn, Ni, Co, and Al
Implementation Method 2
the steel sheet has: Ti: 0.01% to 1.0%, V: 0.01% to 1.0%, a tensile strength of ≥65 kgf/mm², and cold rollability
Implementation Method 3
additional heat treatment may be performed after a stator core and a rotor core are punched and stacked
Data Source
AI summary
There is provided a non-oriented electrical steel sheet having a predetermined chemical composition, in which an area fraction of a crystal structure A composed of crystal grains having a grain size of 100 µm or more is 1% to 30% in a cross section parallel to a rolled plane of the non-oriented electrical steel sheet, an average grain size of a crystal structure B which is a crystal structure other than the crystal structure A is 40 µm or less, and a Vickers hardness HvA of the crystal structure A and a Vickers hardness HvB of the crystal structure B satisfy Equation 1 ((HvA2+HvB2)/2-(HvA+HvB)2/4≤7.0).