Non-oriented electrical steel sheet with phosphorus segregation
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Solution Overview
Problem
Conventional methods struggle to produce non-oriented electrical steel sheets that simultaneously offer high strength for rotor cores and low iron loss for stator cores, especially when aluminum is absent, as they either limit silicon content or result in increased viscosity during recycling, leading to shrinkage cavities.
Innovation Solution
A non-oriented electrical steel sheet with a chemical composition of C ≤ 0.005%, Si 1.5-6.0%, Mn 0.05-2.0%, P 0.03-0.15%, S ≤ 0.005%, N ≤ 0.005%, and Al ≤ 0.005%, where P is segregated to the surface layer during finish annealing, enhancing crystal grain growth and reducing iron loss, allowing for simultaneous production of high-strength rotor and low-iron-loss stator core materials.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If Al is added to increase strength for rotor core, then yield strength is improved, but viscosity of molten steel increases during recycling causing shrinkage cavities
Solution Approach 1:
The invention extracts Al from the steel composition entirely (Al ≤ 0.005 mass%) to eliminate the harmful effect of increased viscosity during recycling, while compensating for strength through optimized Si and Mn content and controlled impurity levels
Solution Approach 2:
The invention changes the chemical composition parameters by limiting Al to ≤ 0.005 mass%, Si to 1.5-6.0 mass%, and Mn to 0.05-2.0 mass%, with controlled impurity levels (C ≤ 0.005%, S ≤ 0.005%, P ≤ 0.03%, N ≤ 0.005%, Ti ≤ 0.005%, V ≤ 0.005%, Nb ≤ 0.005%, Zr ≤ 0.005%), achieving both high strength and recyclability
2Stability of the object's composition
If Si content is limited to not more than 1.2 mass% to promote crystal grain growth, then crystal grain growth is improved, but iron loss increases
Solution Approach 1:
The invention changes the Si content parameter to a higher range of 1.5-6.0 mass% (compared to the conventional ≤1.2 mass%), which simultaneously promotes crystal grain growth during stress relief annealing and reduces iron loss, while the low C and S content ensures clean grain boundaries for effective grain growth
3Strength
If a non-oriented electrical steel sheet with high strength is produced first and rotor core materials are taken out, then strength requirement is met, but the residual steel sheet requires stress relief annealing to achieve low iron loss for stator core
Solution Approach 1:
The invention creates a universal steel composition that can serve both rotor core (requiring high strength) and stator core (requiring low iron loss) applications from the same raw material, eliminating the need for separate production lines or post-annealing processes for different applications
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 enables the production of steel sheets with high yield strength and low iron loss, improving material yield and reducing costs by allowing both rotor and stator core materials to be extracted from the same raw sheet, while also facilitating recycling without the issues of increased viscosity.
Implementation Method 1
P is segregated to the surface layer during finish annealing
Implementation Method 2
subjecting the steel sheet to a stress relief annealing
Implementation Method 3
impurity elements (Ti, S, N, V, Nb, Zr, As) contained in the steel are reduced to an extremely low level for promoting crystal grain growth
Data Source
AI summary
In the production of a non-oriented electrical stress sheet by hot rolling a slab having a chemical composition comprising, by mass %, C: not more than 0.005, Si: 1.5-6.0, Mn: 0.05-2.0 and P: 0.03-0.15, subjecting to a hot band annealing, if necessary, cold rolling, finish annealing, and forming an insulation coating, the cooling from 700° C. to 500° C. in the finish annealing is conducted in an oxidizing atmosphere with an oxygen potential PH2O/PH2 of not less than 0.001 for 1-300 seconds, whereby P is segregated into the surface of the steel sheet after the finish annealing to obtain a non-oriented electrical steel sheet enhancing a crystal grain growth properties in the stress relief annealing.