Two-Stage Stainless Steel Refining Process for High-Phosphorus Iron
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Solution Overview
Problem
The production of high-quality austenitic or ferritic stainless steels is hindered by the inability to effectively dephosphorize molten iron with high chromium content due to thermodynamic constraints, leading to longer process times, heat losses, and increased production costs when using high-phosphorus feedstocks, which require additional intermediate steps.
Innovation Solution
A two-stage refining process in a twin-converter plant, where the first stage involves dephosphorization, desiliconization, and decarburization of the molten iron, followed by intermediate slag tapping, and the second stage includes adding a chromium-rich FeCr alloy to achieve the desired chromium content for stainless steel production, allowing for the use of high-phosphorus raw materials without electrical energy supply.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of substance
If dephosphorization is performed on molten iron with high chromium content, then phosphorus removal is required, but thermodynamic laws prevent effective dephosphorization when chromium content is high
Solution Approach 1:
The refining process is divided into two separate stages: first dephosphorization is performed on low-chromium molten iron, then chromium is added in a second stage. This segmentation allows dephosphorization to occur under favorable thermodynamic conditions (low chromium) while still producing the final high-chromium stainless steel product.
Solution Approach 2:
Dephosphorization is performed as a preliminary action before adding chromium to the molten iron. By removing phosphorus first when chromium content is low, the process avoids the thermodynamic constraints that would prevent effective dephosphorization in high-chromium melts.
2Loss of substance
If additional intermediate steps are added to process high-phosphorus feedstocks, then phosphorus removal is achieved, but process time increases
Solution Approach 1:
The patent combines dephosphorization and chromium addition into a single continuous refining process in the converter, eliminating the need for separate intermediate casting and charging operations. Molten iron with low chromium content undergoes dephosphorization, then chromium-containing alloys are added directly to the same converter without interrupting the process flow.
3Loss of substance
If intermediate casting processes are used for dephosphorization, then phosphorus removal is possible, but heat losses increase
Solution Approach 1:
The refining process maintains continuous useful action by performing dephosphorization and chromium addition in sequence within the same converter without interrupting the molten state. The molten iron remains in the converter throughout the process, eliminating cooling and reheating cycles that would cause heat losses.
4Loss of substance
If intermediate steps are introduced for high-phosphorus material processing, then phosphorus removal is achieved, but production costs increase
Solution Approach 1:
The converter serves multiple functions: it handles both dephosphorization and chromium addition, processes both low-phosphorus and high-phosphorus feedstocks, and produces various types of stainless steel. This multi-functionality eliminates the need for specialized equipment and intermediate processing facilities, reducing overall production costs.
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 enables energy-efficient production of stainless steel with reduced logistics costs and temperature losses, maintaining high productivity and product quality by separating the refining stages and avoiding chromium removal issues during dephosphorization, while utilizing high-phosphorus materials effectively.
Implementation Method 1
the first molten iron in the converter is subjected to a dephosphorization, desiliconization and decarburization treatment in a first treatment stage
Implementation Method 2
subsequent intermediate slag tapping for phosphorus removal
Implementation Method 3
a molten iron-chromium (FeCr) alloy containing sufficient chromium to produce the stainless steel is fed to the first molten iron in the converter as a second molten iron
Data Source
Figure 1
AI summary
In a process for producing an austenitic or ferritic stainless steel from a first, in particular high-carbon, iron melt (2) fed to a converter (3) designed for metallurgical refining, a solution is to be created which enables the energy-efficient production of a stainless steel melt based on an iron melt molten from a high-phosphorus raw or feed material within the framework of a refining process in production facilities customary for the production of stainless steel melts, in particular converters.This is achieved by subjecting the first iron melt (2) in the converter (3) in a first treatment stage to a dephosphorization, desilization and decarburization treatment with subsequent intermediate slag tapping for phosphorus removal, and then adding a molten iron chromium (FeCr) alloy (5) containing sufficient chromium to produce stainless steel as a second iron melt (6) to the metallurgically treated first iron melt (2) in the converter (3) in a second treatment stage, and producing a stainless steel melt (7) from the resulting mixture of iron melts by metallurgical refining.