Low Carbon Steel Decarburization via Vacuum Tank Degasser
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Solution Overview
Problem
The existing methods for producing low carbon, low nitrogen, and low sulfur steels result in high refractory wear and increased costs due to the need for low carbon ferro-alloys and high oxygen levels, which negatively impact productivity and efficiency in steelmaking.
Innovation Solution
A method involving open tapping of molten steel with reduced oxygen levels, followed by decarburization and desulfurization in a vacuum tank degasser, and subsequent processing in a ladle metallurgical furnace to achieve low carbon levels below 0.035% without relying heavily on low carbon ferro-alloys, while managing refractory wear and increasing efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If carbon levels are reduced in the steelmaking furnace to below 0.025%, then low carbon steel composition is achieved, but refractory wear increases and productivity decreases
Solution Approach 1:
The patent divides the decarburization process into two stages: primary decarburization in the steelmaking furnace and secondary decarburization in the vacuum tank degasser. This segmentation allows the furnace to operate at higher carbon levels (improving productivity) while still achieving the target low carbon content (0.035% or below) through the combined process, thereby resolving the contradiction between manufacturing precision and productivity.
Solution Approach 2:
The patent performs preliminary decarburization in the steelmaking furnace to reduce carbon to a intermediate level, then uses the vacuum tank degasser for final carbon reduction. This preliminary action in the furnace avoids the need to start with very low carbon charge materials, thus improving productivity while still achieving the required final carbon level.
2Manufacturing precision
If oxygen content is increased to 1200-1400 ppm before tapping, then decarburization is enhanced, but refractory wear increases due to high FeO in slag
Solution Approach 1:
The patent extracts the harmful high-temperature decarburization step from the steelmaking furnace process and relocates it to the vacuum tank degasser. By moving the oxygen-intensive decarburization operation to the vacuum tank, the furnace operates at lower oxygen levels (600-1120 ppm), reducing FeO formation and refractory wear, while still achieving effective carbon reduction in the vacuum tank environment.
Solution Approach 2:
The vacuum tank degasser acts as an intermediary device that performs the harmful high-oxygen decarburization reaction separately from the furnace. This intermediary system allows the furnace to maintain lower oxygen levels (protecting refractories) while the vacuum tank handles the intensive decarburization that would otherwise require high oxygen and cause refractory damage.
3Manufacturing precision
If low carbon ferro-alloys are used throughout the process to maintain carbon below 0.035%, then carbon control is achieved, but production cost increases significantly
Solution Approach 1:
The patent changes the process parameters (carbon level at tapping, oxygen level, temperature) to enable effective decarburization in the vacuum tank. By operating at higher carbon levels (0.035-0.05%) before vacuum treatment and using appropriate temperature control (1650-1750°C), the process achieves the required final carbon level with reduced dependence on expensive low carbon ferro-alloys, thus resolving the cost contradiction.
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 method reduces refractory wear, decreases the need for expensive low carbon ferro-alloys, and enhances steelmaking efficiency, resulting in cost savings and improved productivity by achieving the desired low carbon, nitrogen, and sulfur levels in steel production.
Implementation Method 1
decarburizing the molten steel composition at the VTD by drawing a vacuum pressure less than 650 millibars
Implementation Method 2
adding one or more deoxidizers to the molten steel composition... deoxidizing the molten steel composition in the ladle metallurgical furnace
Implementation Method 3
adding one or more flux compounds to desulfurize the molten steel composition... desulfurizing the molten steel composition in the VTD
Data Source
AI summary
A method of making a steel with low carbon less than 0.035% by weight including steps of preparing a heat of molten steel composition in a steelmaking furnace to a tapping temperature as desired for desulfurization at a VTD, tapping open into a ladle the molten steel composition with an oxygen level between about 600 and 1120 ppm, providing slag forming compound to the ladle to form a slag cover over the molten steel composition in the ladle, transporting the molten steel to a VTD, decarburizing the molten steel composition at the VTD by drawing a vacuum of less than 650 millibars, after decarburizing, transporting the molten steel to an LMF and deoxidizing the molten steel composition, after deoxidizing, returning to the VTD to desulfurize and degas the molten steel composition, and casting the molten steel composition to form a steel with low carbon less than 0.035% by weight.