Vacuum Degassing Al Addition for Precise Molten Steel Control

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Solution Overview

Problem

Existing molten steel production methods using vacuum degassing apparatuses face challenges in controlling the Al concentration of molten steel due to variations caused by reactions with slag, leading to increased processing costs and off-specification products, particularly in ultra-low carbon steel processing.

Innovation Solution

A method involving multiple additions of Al to molten steel in a vacuum degassing apparatus, predicting Al yield from slag temperature changes, and determining subsequent Al amounts using formulas (1) and (2) to control the Al concentration accurately without requiring expensive oxygen probes.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a deoxidizer is added onto a slag in a ladle, then the oxidation of Al by the slag is suppressed, but the Al concentration of molten steel varies greatly due to incomplete reduction of oxides in the slag

Engineering Contradiction:

Improvecontrol of Al concentrationVSAvoidAl concentration variation

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The deoxidation process is divided into multiple stages: first adding deoxidizer in the converter, then adding Al in the vacuum degassing apparatus. This segmentation allows controlled deoxidation at different stages, preventing excessive Al concentration variation while ensuring complete oxide reduction.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Deoxidizer is added to the molten steel in the converter before vacuum degassing. This preliminary action reduces oxides in the slag before Al is added in the vacuum apparatus, preventing excessive Al consumption and concentration variation during the subsequent vacuum deoxidation.

Inventive Principle:

Principle #10Preliminary action

2Productivity

If oxygen-blowing decarburization is performed by vacuum degassing on non-deoxidized molten steel, then FeO is formed by blowing of oxygen, but FeO reacts with Al, resulting in increased variation in Al concentration

Engineering Contradiction:

Improvedecarburization efficiencyVSAvoidAl concentration variation

Core Design Contradiction:

ProductivityVSManufacturing precision

Solution Approach 1:

Deoxidizer is added to reduce oxides before oxygen blowing in the vacuum degassing apparatus. This preliminary deoxidation prevents FeO from reacting with Al during oxygen blowing, eliminating the source of Al concentration variation while maintaining decarburization efficiency.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

Deoxidizer is added to counteract the harmful effect of FeO formation during oxygen blowing. By introducing deoxidizer before oxygen blowing, the potential harmful reaction between FeO and Al is prevented in advance.

Inventive Principle:

Principle #9Preliminary anti-action

3Measurement precision

If the concentrations of T. Fe and MnO in slag are measured using an oxygen probe, then the oxidation degree of slag is determined, but an expensive oxygen probe specifically for slag is required, significantly increasing processing cost

Engineering Contradiction:

Improveoxidation degree measurementVSAvoidprocessing cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Instead of using an expensive oxygen probe specifically for slag, the invention uses a general-purpose oxygen probe or other available measurement methods. This substitution significantly reduces processing cost while maintaining sufficient measurement precision for controlling deoxidation.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Solution Approach 2:

The invention uses alternative measurement methods or general-purpose probes to replicate the function of an expensive slag-specific oxygen probe. By using substitutes that are cheaper and more readily available, the processing cost is significantly reduced without compromising the essential measurement capability.

Inventive Principle:

Principle #26Copying

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

Achieves precise control of Al concentration in molten steel to a target of 0.01 mass % or more, reducing variations and processing costs.

Implementation Method 1

Some Al reacts with the slag, resulting in an increased variation in the Al concentration of molten steel

Methodology Applied

Scientific EffectRedox reactions: Redox Reactions

Implementation Method 2

In a vacuum degassing of non-deoxidized (undeoxidized) or partially deoxidized molten steel using a vacuum degassing apparatus such as RH or DH

Methodology Applied

Scientific EffectVacuum degassing: Vacuum

Implementation Method 3

an evaporation fraction of Al is determined from a change in the heat content of the molten steel before and after the first addition of Al

Methodology Applied

Scientific EffectExothermic reaction: Exothermic Reaction

Data Source

PatentEP4711477A1Molten steel production method

Publication Date: 2026.03.18 JFE STEEL CORP

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AI summary

There is provided a molten steel production method which can control the Al concentration of molten steel to a target content of 0.01 mass % or more, without significantly increasing processing cost, when deoxidation refining is performed using a vacuum degassing apparatus. The method for producing molten steel having an Al concentration of 0.01 mass % or more by adding Al to molten steel at least twice in a vacuum degassing apparatus, includes: predicting an Al yield from a change in the temperature of a slag before and after a first addition of Al; and using the predicted Al yield to determine an amount of Al to be added in at least one subsequent addition of Al.