A production method of low-Cr pure iron

Abstract

The present invention relates to the field of smelting technology, a method for producing low-Cr pure iron, comprising the following steps: step one: converter smelting and steel tapping; step two: after entering RH, first use oxygen in steel for natural decarburization, after circulating 5-15min at a vacuum degree of ≤1.5mbar, supplement oxygen into the steel for 3-8min, without adding aluminum during the period; then fix oxygen, add aluminum for deoxidation, and control Al in the steel at ≤0.015%; at this time, the mass percentage of components in molten steel is as follows: C≤0.0028, Cr≤0.006, Al≤0.015, and the remaining elements are not limited; step three: the mass percentage of components of the continuous casting finished product is as follows: C≤0.0030, Cr≤0.008, Al≤0.010, and the remaining elements are not limited. The present invention effectively improves the oxidizability of molten steel and increases the removal rate of Cr. This process is simple to operate and has a high hit rate.

Description

Technical Field

[0001] The present invention relates to the technical field of smelting, and particularly relates to a production method of low-Cr pure iron. Background Art

[0002] A very low-Cr pure iron used in the new energy field is required to have Cr ≤ 0.008% and high added value.

[0003] This steel grade generally adopts the converter + RH + continuous casting process. Since Cr in the steel is not easily removed when its content is low, the requirement for the Cr content in the converter charge is very strict, which needs to be ≤ 0.015%, and the yield rate is not high. This seriously restricts productivity.

[0004] In order to overcome the above deficiencies of the existing process, the present invention provides a production method of very low-Cr pure iron. After tapping the boiling steel from the converter, an oxidant and an alkaline slag-making agent are added to the slag surface of the ladle to re-make a high-alkalinity slag and strongly stirred to further remove Cr. After decarburization in RH, oxygen is blown into the steel to remove Cr, and no aluminum is added during the Cr removal period. The yield rate is effectively improved. Summary of the Invention

[0005] The purpose of the present invention is to provide a production method of low-Cr pure iron for the above problems.

[0006] The purpose of the present invention is achieved as follows: A production method of low-Cr pure iron includes the following steps: Step 1: Converter smelting and tapping. After tapping the boiling steel from the converter, pellet ore and scale are added into the ladle. The total amount of pellet ore and scale is 4 - 8 kg per ton of steel, and 6 - 12 kg of alkaline slag-making material per ton of steel and 2 - 4 kg of slag melting agent per ton of steel are added. At the same time, strong stirring is carried out, and the stirring intensity is 7 Nl / min - 10 Nl / min per ton of steel to promote the reaction between steel and slag and remove Cr in the steel. At this time, a sample is taken, and the component mass percentages in the steel are as follows: C ≤ 0.05, Cr ≤ 0.008, and the other elements are not limited. Step 2: After entering RH, first decarburize naturally using the oxygen in the steel. After circulating for 5 - 15 min at a vacuum degree ≤ 1.5 mbar, oxygen is supplemented and blown into the steel for 3 - 8 min, and no aluminum is added during this period. Then, the oxygen content is determined, and aluminum is added for deoxidation, and the Al in the steel is controlled according to ≤ 0.015%. At this time, the component mass percentages in the molten steel are as follows: C ≤ 0.0028, Cr ≤ 0.006, Al ≤ 0.015, and the other elements are not limited. Step 3: The component mass percentages of the continuous casting finished product are as follows: C ≤ 0.0030, Cr ≤ 0.008, Al ≤ 0.010, and the other elements are not limited.

[0007] The component mass percentages of the hot metal charged into the converter in Step 1 are as follows: C: 1.50 - 4.5, Cr ≤ 0.020, and the other elements are not limited.

[0008] The beneficial effects of the present invention are as follows: A production method of ultra-low Cr pure iron proposed by the present invention adds oxidants such as pellet ore and scale to the ladle after tapping with boiling steel in the converter, and adds basic slag-making materials such as lime and slag melting agents such as fluorite. At the same time, strong stirring promotes the reaction of molten steel and slag, effectively removing Cr in the steel. After decarburization in RH, oxygen is blown without adding aluminum, effectively improving the oxidability of the molten steel and increasing the removal rate of Cr. This process is simple to operate and has a high hit rate. Specific embodiments

[0009] An ultra-low Cr pure iron for the new energy field is required to have Cr ≤ 0.008% and high added value. The composition of this steel grade meets the requirements of YT1 in GB / T 9971-2017 "Raw Material Pure Iron". This steel grade generally adopts the converter + RH + continuous casting process. Since Cr in the steel is not easily removed when its content is low, the requirement for the Cr content in the converter furnace charge is very strict, which needs to be ≤ 0.015%, and the smelting rate is not high, less than 30%. This seriously restricts productivity. In order to overcome the above deficiencies of the existing process, the present invention provides a production method of ultra-low Cr pure iron. Through three times of Cr removal by the converter, adding oxidants in the ladle, and blowing oxygen in RH, Cr can be removed to the required range, and the smelting rate is effectively improved. After the implementation of this process, the range of the Cr content in the converter furnace charge is relaxed to ≤ 0.020%, greatly releasing productivity, and the smelting rate reaches 87.5%.

[0010] The technical solution of the present invention is as follows.

[0011] I The process route is: converter → top slag oxidation in ladle → RH → casting.

[0012] II The composition ranges of the hot metal charged into the converter and the finished molten steel are as follows.

[0013]

[0014] Ⅳ After tapping with boiling steel in the converter, oxidants such as pellet ore and scale are added to the ladle, and basic slag-making materials such as lime and slag melting agents such as fluorite are added. At the same time, strong stirring promotes the reaction of molten steel and slag to remove Cr in the steel. Sampling is carried out at this time, and the composition ranges (%) of the steel are as follows.

[0015]

[0016] V After entering RH, first use the oxygen in the steel to naturally decarburize. After circulating for 5 - 15 minutes under a vacuum degree ≤ 1.5 mbar, oxygen is blown into the steel for 3 - 8 minutes without adding aluminum. Then, the oxygen content is determined, and aluminum is added for deoxidation, and the Al content in the steel is controlled at ≤ 0.015%.

[0017] The composition ranges (%) of the molten steel at this time are as follows in the table.

[0018]

[0019] VI Continuous casting

[0020] The finished product component range (%) is as follows in the table below.

[0021]

[0022] The specific implementation manners of the present invention will be described in detail below in conjunction with the embodiments, but the specific implementation manners of the present invention are not limited to the following embodiments.

[0023] Embodiment 1

[0024] Calculated based on the converter capacity of 80t, the process route and operation steps for producing this steel grade are as follows:

[0025] I The process route is: converter → ladle top slag oxidation → RH → casting.

[0026] II The hot metal charged into the converter is as follows.

[0027]

[0028] Ⅲ The components (%) of the converter tapping as boiling steel are as follows in the table below.

[0029]

[0030] Ⅳ After the converter tapping, 400kg of iron oxide scale, 500kg of lime, and 150kg of fluorite are added to the top of the ladle. At the same time, strong stirring is carried out for 8 minutes to promote the steel slag reaction. After that, a sample is taken, and the components (%) in the steel are as follows.

[0031]

[0032] V After entering the RH, first use the oxygen in the steel for natural decarburization. After the vacuum degree is reduced to 1.5mbar, circulate for 5 minutes, and blow oxygen into the steel for 5 minutes without adding aluminum during this period. Then determine the oxygen content and add aluminum for deoxidation, and control the Al in the steel at 0.012%.

[0033] At this time, the components (%) of the molten steel are as follows in the table below.

[0034] VI Continuous casting:

[0035] The finished product components (%) are as follows in the table below.

[0036]

[0037] Embodiment 2

[0038] Calculated based on the converter tapping amount of 200t as boiling steel, the process route and operation steps for producing this steel grade are as follows:

[0039] The process route of I is: converter → ladle top slag oxidation → RH → casting.

[0040] II The hot metal charged into the converter is as follows.

[0041]

[0042] Ⅲ The composition (%) of the steel tapped from the converter as boiling steel

[0043]

[0044] Ⅳ After the converter taps the steel, 400 kg of pellet ore, 500 kg of lime, and 600 kg of fluorite are added to the top of the ladle. At the same time, strong stirring is carried out for 8 min to promote the reaction of the steel slag. After that, a sample is taken, and the composition (%) of the steel is as follows.

[0045]

[0046] V After entering RH, first use the oxygen in the steel for natural decarburization. After the vacuum degree is reduced to 1.5 mbar, circulate for 8 min, and blow oxygen into the steel for 5 min without adding aluminum during this period. After that, determine the oxygen content and add aluminum for deoxidation. The Al in the steel is controlled at 0.013%.

[0047] At this time, the composition (%) of the molten steel is as follows in the table.

[0048]

[0049] VI Continuous casting:

[0050] The composition (%) of the finished product is as follows in the table.

[0051]

[0052] Other embodiments: The oxidants at the top of the ladle also include pellet ore, ore powder, etc.; the slag melting agent can also add low-melting-point slag materials containing Al 2 O 3 .

[0053] Conventional production methods are very strict with the initial Cr content, generally requiring Cr ≤ 0.015%. After the converter taps the steel as boiling steel in the present invention, oxidants and basic slag-making agents are added to the slag surface of the ladle to re-make a high-alkalinity slag and stir for further Cr removal, and forced oxygen blowing for Cr removal after RH decarburization, so that the Cr range charged into the converter is relaxed to ≤ 0.020%, greatly releasing the productivity.

[0054] The above are only specific embodiments of the present invention, but the structural features within the protection scope of the present invention are not limited thereto. Any changes or modifications made by those skilled in the art within the field of the present invention are covered by the patent scope of the present invention.

Claims

1. A production method of low-Cr pure iron, characterized in that: It includes the following steps: Step 1: Converter smelting and tapping. After the converter taps semi-killed steel, pellet ore and scale are added into the ladle. The total amount of pellet ore and scale is 4-8 kg per ton of steel added, and 6-12 kg of basic slag-making material per ton of steel and 2-4 kg of slag melting agent per ton of steel are added. At the same time, strong stirring is carried out, and the stirring intensity is 7 NL / min - 10 NL / min per ton of steel to promote the reaction between steel and slag and remove Cr in the steel; at this time, a sample is taken, and the mass percentages of components in the steel are as follows: C ≤ 0.05, Cr ≤ 0.008, and the other elements are not limited; Step 2: After entering RH, first use the oxygen in the steel to naturally decarburize. After circulating for 5-15 min under a vacuum degree ≤ 1.5 mbar, oxygen is blown into the steel for 3-8 min without adding aluminum during this period; then the oxygen is determined, and aluminum is added for deoxidation, and the Al in the steel is controlled at ≤ 0.015%; at this time, the mass percentages of components in the molten steel are as follows: C ≤ 0.0028, Cr ≤ 0.006, Al ≤ 0.015, and the other elements are not limited; Step 3: The mass percentages of components of the continuous casting finished product are as follows: C ≤ 0.0030, Cr ≤ 0.008, Al ≤ 0.010, and the other elements are not limited.

2. The production method of low-Cr pure iron according to claim 1, characterized in that: The mass percentages of components of the hot metal charged into the converter in Step 1 are as follows: C: 1.50 - 4.5, Cr ≤ 0.020, and the other elements are not limited.

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