Low-Nitrogen Steel Refining via Aluminum Nitride Formation
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Solution Overview
Problem
Current methods for producing low-nitrogen steel using electric furnaces face challenges such as high refinement costs, environmental pollution from CO2 emission, and inefficiencies in nitrogen removal, particularly when using existing facilities and iron scrap as primary materials.
Innovation Solution
A method involving the addition of metallic-Al containing materials and CaO to molten steel, followed by oxygen blowing, which forms a slag with CaO and Al2O3, controlling Al content between 0.02 and 0.08 mass%, and performing nitrogen removal treatments in a VOD or RH degassing system without adding carbon-containing materials, to achieve effective nitrogen reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional decarburization reaction with carbon source and oxygen blowing is used for nitrogen removal, then nitrogen content can be reduced to about 30 ppm, but CO2 emission increases and facility costs increase
Solution Approach 1:
The invention changes the chemical reaction parameters by using aluminum instead of carbon as the reducing agent. This substitution fundamentally alters the reaction pathway from carbon-based decarburization to aluminum-based reduction, eliminating CO2 generation while achieving nitrogen removal through aluminum nitride formation and subsequent vacuum degassing
Solution Approach 2:
The invention uses strong oxidizing conditions by blowing oxygen during the aluminum addition process. This accelerates the oxidation of aluminum to form Al2O3 slag while simultaneously promoting nitrogen removal through controlled AlN formation and decomposition, enhancing the efficiency of nitrogen extraction without carbon-based reactions
2Manufacturing precision
If conventional decarburization reaction with carbon source and oxygen blowing is used for nitrogen removal, then nitrogen content can be reduced to about 30 ppm, but refinement costs increase
Solution Approach 1:
The invention employs aluminum, which is generally more economical than the combination of carbon sources, oxygen blowing infrastructure, and extended processing time required by conventional methods. The aluminum-based process achieves nitrogen removal in a more direct and efficient manner, reducing overall refinement costs
Solution Approach 2:
By changing the chemical mechanism from carbon-based decarburization to aluminum-based reduction with vacuum degassing, the process achieves nitrogen removal with different operational parameters that are more cost-effective, eliminating the need for extensive carbon source additions and prolonged oxygen blowing operations
3Ease of manufacture
If electric furnace is used instead of blast furnace for melting, then facility costs are reduced and CO2 emission is reduced, but nitrogen removal efficiency is insufficient with nitrogen content reaching only 50-100 ppm
Solution Approach 1:
The invention introduces aluminum as an intermediary substance that facilitates nitrogen removal in the electric furnace. Aluminum reacts with nitrogen to form AlN, which then decomposes under vacuum to release nitrogen gas, serving as a chemical mediator that enables efficient nitrogen extraction without requiring blast furnace infrastructure
Solution Approach 2:
The invention changes the nitrogen removal mechanism by introducing aluminum-based chemistry and vacuum degassing parameters to the electric furnace process. This combination of chemical reaction parameters (aluminum addition, oxygen blowing for oxidation control) and physical parameters (vacuum pressure) achieves nitrogen content reduction to 20 ppm or less, overcoming the limitations of conventional electric furnace processing
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 low-nitrogen steel with nitrogen content reduced to 20 ppm or less, while reducing refinement costs and CO2 emissions, and utilizing existing facilities efficiently.
Implementation Method 1
nitrogen removal treatment... adding a metallic-Al containing material into a molten steel... an Al content of the molten steel is controlled to a range of 0.02 mass % or more and 0.08 mass % or less
Implementation Method 2
a carbon (symbol; C) source, such as a carbon-containing material, is added in a converter into a molten iron, and then an oxygen containing gas is blown into to promote decarburization reaction
Implementation Method 3
nitrogen removal proceeds as nitrogen in the molten steel is gasified at the interface of the gas and the molten steel
Implementation Method 4
when the molten steel is processed in an RH degassing system, further nitrogen removal is performed even by reducing pressure
Data Source
Figure 1A~1D
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AI summary
Molten steel is refined in an electric furnace by using iron scrap as a main iron source, and is tapped into a separate refining vessel. Thereafter, metallic-Al containing material and CaO are added onto a bath surface of the molten steel, and an oxygen containing gas is supplied to the molten steel. Thereby, a nitrogen-removal reaction utilizing an AlN formation reaction is caused to proceed. Consequently, even in the case of molten steel having a low carbon content, a low-nitrogen steel can be refined and produced at low costs.