CN118218600A - A method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation - Google Patents

Abstract

The invention relates to a method for preventing high-temperature oxidation by coating the surface of granular iron for steelmaking, which comprises the following steps of S1, preparing the granular iron: screening, crushing, bonding and sieving irregular granular iron to prepare granular iron with the grain diameter of 10-20 mm; s2, preparing a coating material: mixing CaO powder and MgO powder, wherein the composition is CaO:40% -60%, mgO:40% -60%, wherein the granularity of the powder is less than or equal to 3mm; s3, coating granular iron by using a disc granulator; s4, drying the granular iron with the coating layer by using a drying tower. The invention has the advantages that: the lime and the magnesia powder are mixed, so that the high-melting-point sintering of the part of the cladding material can be avoided, and the melting speed is effectively improved; the uniformly mixed coating materials are put into the disc, then the prepared granular iron is added in batches, and the disc granulator is started, so that the integrity of the coating of the granular iron is facilitated; the disc granulator rotates and sprays water at the same time, and finally the coated granular iron is prepared, so that the operation is beneficial to forming a firm shell outside the granular iron by the coating.

Description

A method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation

Technical Field

The invention belongs to the technical field of metallurgy, and in particular relates to a method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation.

Background technique

There are several types of granular iron, such as decarburized granular iron, ITmk3 granular iron, etc. The chemical composition of decarburized granular iron mainly depends on the iron ore used in blast furnace production. In areas with good ore resource conditions, such as Xingtai and Handan, the content of sulfur, phosphorus and non-ferrous metal elements in granular iron is very low, and it can be used as a substitute for high-quality scrap steel. The carbon content of decarburized granular iron can be adjusted between 0.2% and 2.0% according to requirements. Granular iron produced with purer iron ore has higher purity and extremely low content of harmful metal elements (Cu, Sn, Zn, As, etc.), which can completely replace imported sponge iron; the metallic iron content of decarburized granular iron is higher than that of direct reduced iron, and it does not contain gangue like direct reduced iron, which can reduce the amount of slag and power consumption in the process of electric arc furnace steelmaking; decarburized granular iron has a large specific surface area and a fast melting speed in the electric furnace. In addition, the bulk specific gravity of decarburized granular iron is large, which can reduce the number of electric furnace charging times, all of which are conducive to reducing power consumption. However, electric furnace steelmaking is limited by its own conditions, and there is a certain degree of difficulty in controlling the total oxygen and nitrogen in the corresponding steel. In the process of using granular iron, oxygen and nitrogen are inevitably introduced under high temperature conditions. The iron oxide oxidized by the high-temperature oxidation of the granular iron is brought into the molten steel. At the same time, in order to improve the yield, the granular iron is added directly into the molten steel. There is a lack of slag layer coverage, and the nitrogen increase is significant under the condition of electrode heating. Therefore, how to avoid nitrogen increase and nitrogen increase when using granular iron in electric furnaces becomes very critical.

Patent announcement number CN104651564A discloses "a method for low-temperature rapid reduction and separation of granular iron", "during induction furnace smelting, raw granular iron is continuously added according to the melting rate, and an oxygen gun is used to assist melting; during the smelting process, lime or fluorite is added to adjust the slag, and the slag is replaced; and the slag is completely removed". The above operations inevitably cause the formation of iron oxide, resulting in large iron losses. At the same time, slag-forming materials need to be added separately, which prolongs the smelting time.

Patent announcement number CN 105838839 A discloses "a method for preparing granular iron and a system for preparing granular iron". "Using molten nickel slag as raw material, the problem that traditional high-temperature nickel slag needs to be quenched or slowly cooled before further processing is solved, and high-grade granular iron is prepared. The system has high thermal utilization rate. In addition, an additive inlet is provided on the slagging device, and additives are added to the high-temperature molten nickel slag before heating treatment. The slag can be homogenized by stirring with an agitator, and the internal structure and chemical composition of the nickel slag can be directly adjusted to improve the metallurgical properties of the nickel slag. After high-temperature granulation treatment, high-calorie granulated nickel slag raw material can be provided for direct reduction in a rotary hearth furnace, eliminating processes such as pelletizing, drying and pellet preheating, shortening the reduction time of the rotary hearth furnace and reducing the energy consumption of the rotary hearth furnace." The invention mainly relates to the preparation process of granular iron, and does not involve the effective application of granular iron.

Summary of the invention

The purpose of the present invention is to provide a method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation, thereby solving the problem that granular iron is easily oxidized in a high-temperature steelmaking environment.

To achieve the above object, the present invention is implemented through the following technical solutions:

A method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation, specifically comprising the following steps:

S1. Preparing granular iron: Screening, crushing, bonding and re-sieving the irregular granular iron to prepare granular iron with a particle size of 10 to 20 mm;

S2. Prepare coating material: mix CaO powder and MgO powder to obtain a composition of CaO: 40% to 60%, MgO: 40% to 60%, and a powder particle size of ≤3 mm;

S3, using a disc granulator to coat the pelletized iron, the steps are as follows:

a. Add the evenly mixed coating material into the disc;

b. Adding prepared granular iron;

c. Turn on the disc granulator, and spray water while the disc granulator rotates. The addition amount of granular iron, coating material and spray water is: spray water 2% to 5%, coating material 20% to 30%, granular iron: 70% to 80%, and the thickness of the final coating layer is 3 to 5 mm;

S4. Drying the granular iron with the coating layer in a drying tower at a temperature of 600 to 800° C. for 1 to 1.5 hours.

In step S3, the rotation speed of the disc granulator is 60 to 80 r/min, and the rotation time of the disc granulator is 3 to 5 min.

Compared with the prior art, the present invention has the following beneficial effects:

1. Mixing lime and magnesium oxide powder can avoid high melting point sintering in the coating material and effectively increase the melting speed;

2. Add the evenly mixed coating material into the disc, then add the prepared granular iron in batches, and start the disc granulator. This operation is conducive to the integrity of the granular iron coating;

3. The disc granulator rotates and sprays water. Use a spray pot to evenly spray an appropriate amount of water to finally prepare granular iron with a coating layer. This operation is conducive to the coating material forming a solid shell outside the granular iron;

4. Put the prepared granular iron into a drying tower for heating, temperature increase and drying, which can effectively eliminate excess moisture;

5. It can reduce the iron loss of granular iron during steelmaking and improve the recovery rate of granular iron;

6. Existing equipment can be directly used without adding new equipment. The coating method is simple and low cost.

Detailed ways

The present invention is described in detail below, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

At present, the research on granular iron is mainly focused on the production and preparation technology of granular iron, while the research on the application of granular iron in steelmaking is less. In the high temperature environment of steelmaking, granular iron is easily oxidized, which directly leads to high granular iron loss. At the same time, in order to avoid secondary oxidation and nitrogen increase, slag making operation should be carried out on the surface of molten steel. A method for coating the surface of granular iron for steelmaking to prevent high-temperature oxidation, a method for coating slag making material with the outer layer of granular iron, on the one hand, plays a role in reducing granular iron loss, on the other hand, directly slags in the process of melting granular iron, reduces additional slag making process, and is conducive to the production of high-quality steel. Specifically, the following steps are included:

S1. Preparing granular iron: Screening, crushing, bonding and re-sieving the irregular granular iron to prepare granular iron with a particle size of 10 to 20 mm;

S2. Prepare coating material: mix CaO powder and MgO powder to obtain a composition of CaO: 40% to 60%, MgO: 40% to 60%, and a powder particle size of ≤3 mm;

S3, using a disc granulator to coat the pelletized iron, the steps are as follows:

a. Add the evenly mixed coating material into the disc;

b. Adding prepared granular iron;

c. Turn on the disc granulator, spray water while the disc granulator rotates, and the addition amount of granular iron, coating material and spray water is: spray water 2% to 5%, coating material 20% to 30%, granular iron: 70% to 80%), and the thickness of the final coating layer is 3 to 5 mm;

S4. Drying the granular iron with the coating layer in a drying tower at a temperature of 600 to 800° C. for 1 to 1.5 hours.

The following examples are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to the following examples. The methods used in the following examples are conventional methods unless otherwise specified.

[Example 1]

In order to test the high temperature oxidation resistance of coated granular iron, 200 kg granular iron was divided into two parts of equal mass, one part was not treated in any way, and the other part was prepared according to the following scheme:

(1) Screening, crushing, bonding and re-screening the irregular iron particles to prepare iron particles with a diameter of 10 to 20 mm;

(2) Mix 20 kg of lime with a particle size of ≤3 mm and 30 kg of magnesium oxide powder evenly, and set aside after mixing evenly;

(3) Using a disc granulator to coat the iron pellets, first put 50 kg of uniformly mixed coating material into the disc, then add the prepared iron pellets in batches, 20 kg each time, turn on the disc granulator, rotate at 60 r/min, spray water while rotating, rotate for 3 min, and evenly spray 3 L of water with a spray pot, after 5 consecutive times, finally prepare iron pellets with a 4 mm coating layer;

(4) Put the granular iron with the coating layer into a drying tower, start heating, heat the drying tower to 650°C, dry for 1 hour, and then take it out for use;

A 500kg medium frequency induction furnace was used to carry out a high temperature oxidation resistance test. Two portions of granular iron were placed in the medium frequency furnace respectively. The temperature was raised to 1400°C and kept warm for 30 minutes. The molten iron was poured into an ingot mold and weighed. 1# represents untreated granular iron and 2# represents granular iron with a coating layer. The specific results are shown in Table 1.

Table 1: Analysis of high temperature loss of different iron particles (unit: kg)

Original weight After remelting Granular iron recovery rate 1# 100 85 85% 2# 100 95 95%

From the results in Table 1, it can be seen that for the same weight of granular iron, the recovery rate of the granular iron after coating can reach 95%, while that of the granular iron without treatment is only 85%. It can be seen that the recovery rate can be significantly improved after the granular iron is coated with a high-temperature oxidation-resistant layer.

[Example 2]

In order to test the high temperature oxidation resistance of coated granular iron, 400 kg granular iron was divided into two parts of equal mass, one of which was not treated in any way, and the other was prepared according to the following scheme:

(1) Screening, crushing, bonding and re-screening the irregular iron particles to prepare iron particles with a diameter of 10 to 20 mm;

(2) Mix 40 kg of lime with a particle size of ≤ 2 mm and 60 kg of magnesium oxide powder evenly, and set aside after mixing evenly;

(3) Using a disc granulator to coat the iron pellets, first put 100 kg of the uniformly mixed coating material into the disc, then add the prepared iron pellets in batches, 40 kg each time, turn on the disc granulator, rotate at 70 r/min, spray water while rotating, rotate for 4 min, and evenly spray 6 L of water with a spray pot, after 5 consecutive times, finally prepare iron pellets with a 5 mm coating layer;

(4) putting the prepared granular iron into a drying tower, starting to heat up, heating the drying tower to 700° C., drying for 1.2 hours and taking it out for standby use;

A high-temperature antioxidant test was carried out using a 500kg medium-frequency induction furnace. Two different types of granular iron were placed in the medium-frequency furnace, heated to 1350°C, and kept warm for 45 minutes. The molten iron was poured into an ingot mold and weighed. 1# represents treated granular iron, and 2# represents granular iron with a coating layer. The specific results are shown in Table 2.

Table 2: Analysis of high temperature loss of different iron particles (unit: kg)

Original weight After remelting Granular iron recovery rate 1# 200 165 82.5 2# 200 185 92.5

From the results in Table 2, it can be seen that for the same weight of granular iron, the recovery rate of the granular iron after coating can reach 92.5%, while that of the untreated granular iron is only 82.5%. It can be seen that the recovery rate of the granular iron can be significantly improved after coating with a high-temperature oxidation-resistant layer.

The invention mixes lime and magnesium oxide powder, which can avoid high melting point sintering of the coating material locally and effectively improve the melting speed; the uniformly mixed coating material is put into the disc, and then the prepared granular iron is added in batches, and the disc granulator is turned on, so that the operation is conducive to the integrity of the granular iron coating; the disc granulator rotates while spraying water, and a proper amount of water is evenly sprayed into the disc using a watering can, so that the granular iron with a coating layer is finally prepared, and the operation is conducive to the coating material forming a solid shell outside the granular iron; the prepared granular iron is put into a drying tower for heating, temperature increase, and drying, so that excess water can be effectively eliminated; the iron loss of the granular iron in the process of steelmaking can be reduced, and the recovery rate of the granular iron can be improved; the existing equipment can be directly used without adding new equipment, and the coating method is simple and low in cost.

Claims (2)

1. The method for coating the surface of the granular iron for steelmaking with the high-temperature oxidation prevention is characterized by comprising the following steps of:

S1, preparing granular iron: screening, crushing, bonding and sieving irregular granular iron to prepare granular iron with the grain diameter of 10-20 mm;

S2, preparing a coating material: mixing CaO powder and MgO powder, wherein the composition is CaO:40% -60%, mgO:40% -60%, wherein the granularity of the powder is less than or equal to 3mm;

S3, coating granular iron by using a disc granulator, wherein the steps are as follows:

a. putting uniformly mixed cladding materials into the disc;

b. Adding prepared granular iron;

c. starting the disc granulator, and spraying water while rotating the disc granulator, wherein the adding amount of the granulated iron, the coating material and the water spraying amount is as follows: 2% -5% of water spraying amount, 20% -30% of coating material and granular iron: 70% -80%, and finally the thickness of the obtained coating layer is 3-5 mm;

S4, drying the granular iron with the coating layer by using a drying tower, wherein the temperature of the drying tower is 600-800 ℃ and the drying time is 1-1.5 h.

2. The method for coating the surface of the iron particles for steelmaking with high-temperature oxidation prevention according to claim 1, wherein in the step S3, the rotating speed of the disc granulator is 60-80 r/min, and the rotating time of the disc granulator is 3-5 min.