Low Carbon Steelmaking via Vacuum Decarburization and Oxygen Control
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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 elevated oxygen levels, which negatively impact productivity and efficiency in steelmaking processes.
Innovation Solution
A method involving open tapping of molten steel with controlled oxygen levels, followed by decarburization and deoxidization at a vacuum tank degasser, using a process model to determine decarburization time and alloy additions, and adding flux compounds to achieve the desired carbon and sulfur levels without relying on low carbon ferro-alloys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If low carbon ferro-alloys are used to maintain low carbon levels below 0.035%, then the desired low carbon steel composition is achieved, but production costs increase significantly
Solution Approach 1:
The patent changes the oxygen content parameter in the molten steel from the conventional high level (1200-1400 ppm) to a controlled lower level (600-1120 ppm) before tapping. This parameter change eliminates the need for low carbon ferro-alloys while maintaining low carbon levels, as the reduced oxygen content prevents excessive carbide formation and refractionry wear, thereby resolving the contradiction between manufacturing precision and production cost
Solution Approach 2:
The patent extracts the decarburization process from the steelmaking furnace to the vacuum tank degasser. By removing the requirement for low carbon ferro-alloy additions and performing decarburization at the vacuum degasser instead, the process eliminates the need for expensive low carbon alloys while achieving the desired carbon levels through vacuum treatment alone
2Temperature
If elevated tapping temperatures (1700°C) are used to compensate for temperature losses during transportation, then the steel reaches the degasser at the required temperature, but refractory wear on the furnace increases
Solution Approach 1:
The patent changes the tapping temperature parameter from the conventional 1700°C to a lower range (1650-1700°C). This parameter change is made possible by the controlled oxygen level (600-1120 ppm) which reduces FeO content in the slag, thereby reducing refractory wear even at the lower temperature, thus resolving the contradiction between maintaining temperature and reducing refractory wear
Solution Approach 2:
The patent converts the harmful effect of high oxygen content into a benefit by deliberately controlling oxygen levels to be between 600-1120 ppm. This controlled oxygen level creates a slag with lower FeO content that is less corrosive to refractories, transforming the previously harmful high oxygen condition into a beneficial low-refractory-wear condition
3Stability of the object's composition
If high oxygen content (1200-1400 ppm) is maintained before tapping, then the steel composition meets conventional processing requirements, but productivity at the steelmaking furnace decreases
Solution Approach 1:
The patent changes the oxygen content parameter from the conventional high level (1200-1400 ppm) to a controlled lower level (600-1120 ppm). This parameter change reduces the time required for decarburization and eliminates the need for extended low carbon alloying operations, thereby increasing steelmaking productivity while maintaining stable composition control
4Manufacturing precision
If additional decarburization time is allocated to achieve low carbon levels below 0.035%, then the desired carbon content is achieved, but productivity at the steelmaking furnace is adversely affected
Solution Approach 1:
The patent extracts the decarburization operation from the steelmaking furnace process to the vacuum tank degasser. By performing decarburization at the vacuum degasser rather than in the furnace, the process eliminates the need for extended decarburization time in the furnace, thereby maintaining productivity while achieving the desired low carbon levels through vacuum treatment
Solution Approach 2:
The patent performs preliminary oxygen control before tapping by maintaining oxygen levels at 600-1120 ppm. This preliminary action prepares the steel for efficient decarburization at the vacuum degasser, reducing the time and complexity of subsequent carbon reduction operations and maintaining high productivity
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 production costs, and enhances steelmaking efficiency by achieving the required low carbon and sulfur levels while maintaining productivity, with cost savings of approximately $20 per ton.
Implementation Method 1
decarburizing the molten steel composition at the vacuum tank degasser by drawing a vacuum pressure less than 650 millibars
Implementation Method 2
adding one or more deoxidizers to the molten steel composition and deoxidizing the molten steel composition
Implementation Method 3
adding one or more flux compounds to desulfurize the molten steel composition
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 composition in the ladle to a VTD, decarburizing the molten steel composition at the VTD by drawing a vacuum of less than 650 millibars, after decarburizing, adding one or more deoxidizers to the molten steel composition and deoxidizing the molten steel composition, after deoxidizing, adding one or more flux compounds to desulfurize the molten steel composition, and casting the molten steel composition to form a steel with low carbon less than 0.035% by weight.