Non-Grain Oriented Steel Degassing Process
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Solution Overview
Problem
Conventional RH degasser processes in the steel industry have limited capability for sulfur and nitrogen removal, which is inadequate for producing high-grade non-grain oriented (NGO) steel with ultra-low residual elements like carbon, nitrogen, sulfur, and oxygen.
Innovation Solution
A method involving the EAF→LMF→RH→CC route, where liquid steel is deoxidized and desulfurized in the ladle metallurgy furnace (LMF) before being transferred to the RH degasser for carbon removal, facilitating nitrogen removal and preventing carbon pickup. This process includes oxygen blowing to introduce oxygen into the steel for decarburization and inclusion control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional RH degasser process is used, then carbon removal efficiency is high, but sulfur and nitrogen removal capability is very limited
Solution Approach 1:
The patent divides the secondary steelmaking process into distinct functional stages: primary vacuum treatment for carbon removal, followed by separate desulfurization and denitrogenation stages. This segmentation allows each stage to be optimized for its specific function, with the RH degasser dedicated to carbon removal and subsequent treatments addressing sulfur and nitrogen separately.
Solution Approach 2:
The patent introduces intermediary treatments between the RH degasser and final steel production. These intermediaries include desulfurization agents added during or after vacuum treatment, and controlled oxidation-reduction cycles that facilitate nitrogen removal. The intermediary steps bridge the gap between carbon removal and the subsequent sulfur/nitrogen removal requirements.
2Object-generated harmful factors
If EAF process is used to reduce CO2 emission, then CO2 emission is reduced by 60% to 90%, but liquid steel contains higher contents of nitrogen and sulfur
Solution Approach 1:
The patent applies preliminary desulfurization and denitrogenation treatments to the liquid steel immediately after EAF tapping and before it enters the RH degasser. By removing sulfur and nitrogen early in the process, the subsequent vacuum treatment can focus on carbon removal without interference from these residual elements, achieving both low emissions and high purity.
Solution Approach 2:
The patent utilizes parameter changes in temperature, pressure, and chemical composition throughout the processing sequence. The EAF operates at high temperature to melt scrap, then the liquid steel undergoes controlled cooling and chemical treatment to precipitate sulfur and nitrogen compounds, followed by vacuum degassing to remove carbon. Each stage optimizes specific parameters to address different residual element challenges.
3Manufacturing precision
If auxiliary equipment for powder injection is installed at RH degasser, then sulfur removal capability is improved, but device complexity increases
Solution Approach 1:
The patent extracts the desulfurization function from the RH degasser system by implementing a separate desulfurization stage using dedicated agents and equipment. This allows the RH degasser to maintain its simple, effective vacuum-based carbon removal mechanism while sulfur removal is handled by a specialized, optimized subsystem that can be independently controlled and maintained.
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 method effectively produces NGO steel with ultra-low carbon, nitrogen, and sulfur levels, achieving the required low core loss and high permeability for high-grade NGO steel, while also reducing the need for expensive scrap mixes and minimizing energy consumption.
Implementation Method 1
The vacuum processes conducted outside a primary steelmaking furnace may be utilized to further remove carbon and decrease the solubility of hydrogen and nitrogen by lowering the partial pressures of CO, H2, and N2
Implementation Method 2
removing carbon by oxygen blowing into the liquid steel at the RH degasser to produce decarburized liquid steel
Data Source
AI summary
A method of making non-grain oriented (NGO) electrical steel is disclosed. The method includes tapping liquid steel out of a primary steelmaking furnace, deoxidizing the liquid steel before or after transferring the deoxidized liquid steel to a ladle metallurgy furnace, removing sulfur at the ladle metallurgy furnace (LMF), adding fluxes and deoxidizer to the ladle slag and/or skimming off ladle slag to prevent sulfur reversion, transferring the deoxidized liquid steel from the ladle metallurgy furnace to an RH degasser for carbon removal by blowing oxygen, and adding fluxes at the RH degasser before oxygen blowing to fortify the bottom layer of the ladle slag to prevent sulfur reversion. The removal of oxygen and sulfur prior to transferring the liquid steel to the RH degasser facilitates nitrogen removal and prevents carbon pick up during the step of adding fluxes and arcing for sulfur removal. Oxygen blowing at the RH also lowers titanium pickup. The ultra low levels of carbon, nitrogen, sulfur, and titanium in the NGO steel provide excellent magnetic properties.