Non-oriented electrical steel sheet with dual-phase microstructure
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Non-oriented electrical steel sheets struggle to maintain high strength and excellent magnetic characteristics after additional heat treatment, as existing solutions do not adequately address the compatibility between strength and magnetic properties in high-speed rotation motors.
Innovation Solution
A non-oriented electrical steel sheet with a specific chemical composition and manufacturing process, including hot rolling, hot-rolled sheet annealing, cold rolling, and final annealing, to achieve a microstructure with controlled crystal structures and hardness ratios, ensuring high strength and magnetic performance even after heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the steel sheets are made to have high strength by solid solution strengthening, precipitation strengthening, or grain refining, then the strength increases, but the magnetic characteristics may degrade
Solution Approach 1:
The patent applies parameter changes by precisely controlling the chemical composition parameters (Si: 3.0-5.0%, Mn: 0.1-3.0%, P: 0.20% or less, S: 0.0018% or less, N: 0.0040% or less) and processing parameters (hot-rolled sheet annealing temperature: 900-1150°C, final annealing temperature: 700-800°C, cooling rate: 50°C/sec or higher) to achieve a balance between strength and magnetic characteristics. The controlled composition and processing parameters enable the formation of a specific microstructure that simultaneously provides high tensile strength (600 MPa or more) and excellent magnetic properties
Solution Approach 2:
The patent creates a composite microstructure consisting of two distinct crystal structures: crystal structure A (grain size 100 μm or greater, area ratio 1-30%) and crystal structure B (average grain size 25 μm or less). This composite microstructure combines the strength-providing large grains with the magnetic-property-providing fine grains, achieving both high strength and excellent magnetic characteristics simultaneously
2Strength
If the non-oriented electrical steel sheet is made to have high strength, then the blanks for rotors can be produced, but the blanks for stator cores require additional heat treatment to remove strain and enhance magnetic characteristics
Solution Approach 1:
The patent applies preliminary action by performing hot-rolled sheet annealing at 900-1150°C before cold rolling to pre-reduce strain and prepare the microstructure. This preliminary heat treatment, combined with the controlled chemical composition, ensures that the steel sheet already has improved magnetic characteristics before the final annealing step, reducing or eliminating the need for additional heat treatment of stator core blanks while maintaining high strength
3Strength
If the area ratio of crystal structure A is increased to improve strength, then high strength is achieved, but the magnetic characteristics after additional heat treatment may degrade
Solution Approach 1:
The patent applies parameter changes by optimizing the area ratio of crystal structure A to be 1-30% and controlling the Vickers hardness ratio HvA/HvB to be 1.000 or less. This specific parameter range ensures that there is enough crystal structure A to provide high strength (600 MPa or more) while maintaining sufficient crystal structure B to preserve excellent magnetic characteristics after additional heat treatment, resolving the contradiction between strength and post-heat-treatment 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 solution results in non-oriented electrical steel sheets with tensile strengths of 600 MPa or more and improved magnetic characteristics, maintaining magnetic flux density and reducing iron loss, suitable for both rotor and stator core applications.
Implementation Method 1
The strength of the steel sheets becomes high due to solid solution strengthening, precipitation strengthening, grain refining, or the like
Implementation Method 2
The strength of the steel sheets becomes high due to solid solution strengthening, precipitation strengthening, grain refining, or the like
Implementation Method 3
The strength of the steel sheets becomes high due to solid solution strengthening, precipitation strengthening, grain refining, or the like
Implementation Method 4
an eddy current is generated due to high-frequency magnetic flux, motor efficiency degrades, and heat is generated
Implementation Method 5
performing a hot-rolled sheet annealing with a maximum attainment temperature being 900 to 1150° C.; performing a final annealing with a maximum attainment temperature being 700 to 800° C.
Data Source
AI summary
This non-oriented electrical steel sheet including, as a chemical composition, by mass %: C: 0.0100% or less; Si: more than 3.0% and 5.0% or less; Mn: 0.1 to 3.0%; P: 0.20% or less: S: 0.0018% or less: N: 0.0040% or less; Al: 0 to 0.9%; one or more selected from the group consisting of Sn and Sb: 0 to 0.100%; Cr 0 to 5.0%; Ni: 0 to 5.0%; Cu: 0 to 5.0%; Ca: 0 to 0.01%; rare earth elements (REM): 0 to 0.010%; and a remainder including Fe and impurities, in which an area ratio of a crystal structure A composed of crystal grains having a grain size of 100 μm or greater in a cross section parallel to a rolled surface of the non-oriented electrical steel sheet is 1 to 30%, an average grain size of a crystal structure B that is a crystal structure other than the crystal structure A is 25 μm or less, and a Vickers hardness HvA of the crystal structure A and a Vickers hardness HvB of the crystal structure B satisfy HvA/HvB≤1.000.