Non-Oriented Electrical Steel Sheet for Punching Roundness
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Solution Overview
Problem
Existing non-oriented electrical steel sheets have high strength before additional heat treatment and excellent magnetic properties afterward, but they lack improved fatigue properties and roundness after punching, and there are concerns about 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 varying sizes, is developed. This sheet has a chemical composition optimized for high strength and magnetic properties, with a crystal structure A of coarse grains and a structure B of smaller grains, and is processed using hot rolling, hot-band annealing, cold rolling, and final annealing to achieve the desired properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional heat treatment is applied after punching and stacking to improve magnetic properties, then magnetic properties are improved, but deformation of stator cores occurs and roundness deteriorates
Solution Approach 1:
The patent applies parameter changes by optimizing the chemical composition (specific elements and their ratios) and controlling heat treatment parameters (temperature, time, atmosphere) to achieve a balance where magnetic properties are improved while minimizing deformation. The controlled atmosphere and temperature profile prevent excessive oxidation and distortion during heat treatment.
Solution Approach 2:
The patent uses composite material principles by creating a multi-layer coating structure on the electrical steel sheets. This coating system provides protective functions that maintain dimensional stability during heat treatment while allowing magnetic property enhancement, thus preserving roundness while improving magnetic characteristics.
2Strength
If high strength is achieved before additional heat treatment, then mechanical properties are improved, but fatigue properties and roundness after punching are insufficient
Solution Approach 1:
The patent optimizes chemical composition parameters (element ratios and concentrations) and microstructural parameters (grain size distribution, phase composition) to achieve a material state that simultaneously provides high strength and good fatigue resistance. The controlled composition enables solid solution strengthening while maintaining ductility and fatigue performance.
3Strength
If chemical composition is optimized for high strength, then strength is improved, but magnetic properties after heat treatment are insufficient
Solution Approach 1:
The patent employs parameter changes by precisely controlling chemical composition within optimized ranges and adjusting heat treatment parameters (temperature, time, cooling rate) to transform the material properties. This enables the steel to achieve both high strength and excellent magnetic properties after heat treatment by controlling phase transformation and microstructure development.
Solution Approach 2:
The patent creates a composite microstructure with specific phase distributions (martensite, ferrite, austenite phases in controlled proportions) that provides both mechanical strength and magnetic performance. The multi-phase composite structure allows simultaneous optimization of strength and magnetic properties.
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 resulting non-oriented electrical steel sheet exhibits high strength before additional heat treatment, excellent magnetic properties afterward, improved fatigue properties, and enhanced roundness after punching, while minimizing deformation of stator cores during additional heat treatment.
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
heating a slab having the chemical composition according to claim 1 at 1000° C. to 1200° C. and carrying out hot rolling to manufacture a hot-rolled steel sheet; subjecting the hot-rolled steel sheet to hot-band annealing
Implementation Method 3
subjecting the hot-rolled steel sheet after the hot-band annealing to cold rolling or warm rolling
Implementation Method 4
subjecting the intermediate steel sheet to final annealing that satisfies Equation 2 below with respect to a temperature increase rate S1 (° C./second) in a temperature increase process from 500° C. to 600° C. with a maximum reaching temperature of 700° C. to 850° C.
Implementation Method 5
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).