A method for stepwise dephosphorization of molten iron via isomerization

Abstract

This invention relates to a metallurgical method, specifically a method for stepwise dephosphorization of molten iron. First, an oxidant is added and a mixture of lime and fluorite powder is injected for 15-35 minutes to reduce phosphorus in the steel to between 0.006-0.012%, after which the slag is removed. Then, a specially prepared composite slag and oxidant are added, followed by further injection of lime and fluorite powder for 10-30 minutes for deep dephosphorization, further reducing the final phosphorus content to below 0.0030%. This invention features a simple operation process and significant effects.

Description

Technical Field

[0001] This invention relates to the field of metallurgical technology, specifically to a method for stepwise dephosphorization of molten iron. Background Technology

[0002] Pre-dephosphorization of molten iron is a necessary step in the production of high-chromium, low-phosphorus steel. However, conventional dephosphorization methods are insufficient to remove phosphorus from molten iron to below 0.0035%. This is because although secondary dephosphorization can be performed, the dephosphorization stage involves continuous cooling, which leads to a decrease in efficiency and poor slag formation in the later stages due to high residual phosphorus content.

[0003] Pre-dephosphorization of molten iron is essential for producing high-chromium steels. The conventional method involves injecting lime powder and fluorite powder, along with oxidants such as pellets or oxygen, for coarse dephosphorization. After removing some slag, further deep dephosphorization is performed, typically achieving a final phosphorus content of ≥0.0035%. This method is time-consuming and inefficient. To achieve better dephosphorization and further reduce molten iron phosphorus, this invention provides a stepwise, heterogeneous dephosphorization method for molten iron. The innovation lies in removing the slag after the first injection, adding a specially formulated composite slag, and then performing further deep dephosphorization, which can further reduce the final phosphorus content to below 0.0030%. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a method for stepwise dephosphorization of molten iron through isomerization.

[0005] The objective of this invention is achieved as follows: a method for stepwise dephosphorization of molten iron, comprising the following steps: Step 1: First, an oxidant is added to the molten iron and a mixture of lime and fluorite powder is sprayed for 15-35 minutes to reduce the phosphorus content in the steel to between 0.006-0.012%. The slag is then removed. The amount of oxidant added is 0.75-2.0 kg / t iron. The ratio of lime to fluorite in the lime + fluorite mixture is 9:1, and the amount of lime + fluorite mixture powder added is 8-18 kg / t iron. Step 2: A special composite slag and oxidant are added, and then the lime + fluorite mixture powder is sprayed again for 10-30 minutes for deep dephosphorization to reduce the final phosphorus content to below 0.0030%. The amount of the special composite slag added is 2.0-5.5 kg / t iron.

[0006] The chemical composition and mass percentage of the specially made composite slag are as follows: SiO2: 35-45%, CaO: 15-35%, Al2O3≤10%, rare earth oxides: 1-2%, and the remainder are impurities.

[0007] The beneficial effects of this invention are as follows: The method for stepwise dephosphorization of molten iron proposed in this invention is divided into two stages. In the deep dephosphorization stage, the residue from the previous stage is removed, and a specially prepared composite slag is added for further injection, making the dephosphorization reaction more efficient. This process is simple to operate and effectively improves efficiency. Detailed Implementation

[0008] The technical solution of this invention is: a method for stepwise dephosphorization of molten iron via heterogeneity. First, an oxidant is added, and then a mixture of lime and fluorite powder is injected for 15-35 minutes to remove phosphorus from the steel to between 0.006-0.012%. The slag is then removed. The oxidant is a mixture of Fe oxides: FeO + Fe2O3, added at a rate of 0.75-2.0 kg / t iron. The ratio of lime to fluorite in the lime + fluorite mixture is 9:1, and the amount of lime + fluorite mixture added is 8-18 kg / t iron.

[0009] Adding 2-4 kg of specially made composite slag and oxidant to each ton of molten iron, followed by blowing lime and fluorite mixed powder for 10-30 minutes for deep dephosphorization, can further reduce the final phosphorus content to below 0.0030%.

[0010] The composition of the specially made composite slag is as follows: SiO2: 35-45%, CaO: 15-35%, Al2O3≤10%, rare earth oxides: 1-2%, and the remainder is impurities. Example 1

[0011] With 80t of molten iron, first add 150kg of iron oxide scale and spray a mixture of lime and fluorite powder for 25 minutes. The phosphorus content in the steel is 0.007%. Then remove the slag.

[0012] Add 200 kg of specially made composite slag and 80 kg of iron oxide scale, then blow lime and fluorite mixed powder for 20 minutes for deep dephosphorization. Sampling and analysis showed that the phosphorus content was 0.0023%.

[0013] The specially formulated composite slag consists of SiO2: 38%, CaO: 20%, Al2O3: 3.5%, rare earth oxides: 1.5%, and the remainder being impurities. Example 2

[0014] Iron oxide is produced by blowing oxygen instead of adding an oxidant.

[0015] With 80t of molten iron, oxygen was first blown and lime + fluorite mixed powder was sprayed for 20 minutes. The phosphorus mass percentage in the steel was 0.006%. The slag was then removed.

[0016] 230 kg of specially made composite slag was added, followed by oxygen blowing and then lime + fluorite mixed powder blowing for 18 minutes for deep dephosphorization. The phosphorus content was 0.0020% when sampled and analyzed.

[0017] The specially formulated composite slag consists of SiO2: 38%, CaO: 32%, Al2O3: 3%, rare earth oxides: 1.3%, and the remainder being impurities.

[0018] The above description is only a specific embodiment of the present invention, but the structural features protected by the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the scope of the present invention are covered by the patent scope of the present invention.

Claims

1. A method for isomerization stepwise dephosphorization of molten iron, characterized by: Includes the following steps: Step 1: First, add oxidant to the molten iron and spray lime + fluorite mixed powder for 15-35 minutes to remove phosphorus from the steel to between 0.006-0.012%. Remove the slag. The amount of oxidant added is 0.75-2.0 kg / t iron. The ratio of lime to fluorite in the lime + fluorite mixed powder is 9:1, and the amount of lime + fluorite mixed powder added is 8-18 kg / t iron. Step 2: Add special composite slag and oxidant, then blow lime + fluorite mixed powder for 10-30 minutes to carry out deep dephosphorization, so that the final phosphorus content is reduced to below 0.0030%. The amount of special composite slag added is 2.0-5.5 kg / t iron.

2. The method for stepwise dephosphorization of molten iron according to claim 1, characterized in that: The chemical composition and mass percentage of the specially made composite slag are as follows: SiO2: 35-45%, CaO: 15-35%, Al2O3≤10%, rare earth oxides: 1-2%, and the remainder are impurities.