Low-energy fast-paced rh vacuum degassing method

Abstract

The present application belongs to the technical field of steelmaking, and particularly discloses a low-energy-consumption fast-paced RH vacuum degassing method. The present application effectively reduces the gas hydrogen and nitrogen content in the steel by controlling the mass fraction of sulfur and oxygen in the steel before RH vacuum treatment, adopting an RH low-vacuum light treatment mode, and reasonably controlling the molten steel circulation flow in the RH vacuum process in stages, while the total RH treatment time is shortened, the vacuum steam consumption is reduced, the RH vacuum process temperature drop is reduced, the LF refining heating time and power consumption are reduced, the production rhythm is improved, and the present application has remarkable economic and social benefits.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of steelmaking, and particularly relates to a low-energy-consumption fast-paced RH vacuum degassing method. BACKGROUND

[0002] Generally, for non-nitrogen-containing steel grades, the gas content of hydrogen and nitrogen in the steel is not beneficial to the performance of the steel and is harmful. For example, the solubility of gas hydrogen in solid steel is extremely small. It dissolves into the steel liquid at high temperature, and accumulates in the organization to form high-pressure fine pores when it cannot escape in time during cooling, which sharply reduces the plasticity, toughness and fatigue strength of the steel, and can cause cracks and brittle fracture when the hydrogen content exceeds the critical value of the white point, which can cause deterioration of the performance of the steel and even scrap. If the nitrogen content is too high, the plasticity of the steel, especially the toughness, can be significantly reduced, and the weldability can be poor. Therefore, in modern steel production, hydrogen and nitrogen and other gases must be removed below the specified value. At present, most steel plants use RH and other vacuum refining equipment to remove hydrogen and nitrogen in the steel. The RH vacuum treatment technology, also known as the vacuum circulation degassing method, is jointly developed by Ruhrstahl and Heraeus two steel enterprises, and is the most widely used vacuum treatment method in the world.

[0003] At present, there is little research on the effect of different RH vacuum treatment modes on degassing, and generally the RH process is regarded as an independent degassing link, without considering the influence of the previous process on the RH degassing effect, and without minimizing the temperature loss in the RH vacuum treatment process. Therefore, the conventional RH treatment mode has the problems of long vacuum treatment cycle, unstable effect, high treatment cost, etc. Therefore, how to provide the RH process with steel liquid easy to degas, how to adopt a reasonable vacuum degree and vacuum degassing mode for the RH process, how to improve the stability of the RH degassing effect, how to shorten the total RH vacuum treatment time, and how to realize low-energy-consumption and fast-paced production of the RH vacuum treatment are the problems to be solved by the present application. SUMMARY

[0004] The present application aims to solve the above technical problems by controlling the mass fraction of sulfur and oxygen in the steel before RH vacuum treatment, adopting an RH low-vacuum light treatment mode, and reasonably controlling the circulation flow of the steel liquid in the RH vacuum process in stages, thereby effectively reducing the gas hydrogen and nitrogen content in the steel, shortening the total RH treatment time, reducing the steam consumption for vacuum pumping, reducing the temperature drop in the RH vacuum process, reducing the LF refining heating time and power consumption, improving the production rhythm, and reducing the energy consumption of the RH vacuum treatment.

[0005] In order to achieve the purpose of the present application, the technical scheme adopted is as follows: a low-energy-consumption fast-paced RH vacuum degassing method, mainly related to the LF refining and RH vacuum treatment processes in the steelmaking process, and the specific process steps include:

[0006] (1) LF refining process: 4.5-7 kg / t of granular low-sulfur active lime and 4-1 kg / t of fluorite are added in the LF refining process to adjust the slag and desulfurize, calcium carbide is used to deoxidize to form white slag, the binary basicity CaO / SiO2 of the slag is controlled between 8.0-12.0, the S content of the molten steel at the end of the LF is controlled to be ≤0.005%, and the free oxygen content is controlled to be ≤4.5 ppm;

[0007] The CaO content of the granular low-sulfur active lime is ≥88%, the S content is ≤0.06%, and the particle size is 5-30 mm. The gas evolution amount of the calcium carbide is ≥290 L / kg.

[0008] The use of granular low-sulfur active lime can improve the LF slag forming rate, the use of a small amount of fluorite can improve the fluidity of the LF slag, and the use of calcium carbide with high gas evolution amount as a deoxidizer can improve the binary basicity of the slag and improve the fluidity of the slag, thereby improving the deoxidation and desulfurization capacity of the LF slag, achieving the purpose of controlling the low-sulfur and low-oxygen content of the molten steel, and being beneficial to increasing the interfacial reaction rate and improving the degassing efficiency during RH vacuum treatment.

[0009] (2) RH vacuum treatment: argon is selected as the lifting gas, and the flow rate is set in stages; the vacuum treatment is divided into two stages: the first stage uses a low vacuum degree of 12-30 kPa, and the treatment time is 2-4 min; the second stage uses a low vacuum degree of 8-12 kPa, and the treatment time is 5-6 min. Among them, the lifting gas flow rate is set to 850-1100 NL / min in the first stage, and the lifting gas flow rate is set to 2000-2250 NL / min in the second stage.

[0010] The vacuum degassing effect is affected by the vacuum degree and the total treatment time, and it is generally believed that the higher the vacuum degree and the more the vacuum circulation times of the molten steel (the larger the lifting gas flow rate and the more the circulation times), the better the degassing effect, but the steam energy consumption required to maintain high vacuum is large. The present application adopts a low vacuum light treatment mode, uses a smaller lifting gas flow rate in the first stage to reduce the temperature drop of the molten steel, and uses a large lifting gas flow rate under the condition of a relatively high vacuum degree in the second stage to increase the vacuum circulation times of the molten steel, thereby achieving the purpose of low-energy-consumption rapid degassing.

[0011] The beneficial effects of the present application are:

[0012] Sulfur and oxygen are surface-active elements that are enriched on the surface of bubbles and occupy positions, which can hinder the degassing of the molten steel. Therefore, reducing the proportion of sulfur and oxygen in the steel can accelerate the interfacial reaction rate of degassing. The present application controls the mass fraction of sulfur and oxygen in the steel before RH vacuum treatment, adopts a low vacuum light treatment mode of RH, and reasonably controls the circulation flow rate of the molten steel in the RH vacuum process in stages, thereby achieving the purpose of low-energy-consumption rapid degassing of RH.

[0013] Compared with the prior art, the process of the present application effectively reduces the content of gas hydrogen and nitrogen in the steel by controlling the mass fraction of sulfur and oxygen in the steel before RH vacuum treatment, adopting RH low vacuum light treatment mode, and reasonably controlling the circulating flow of molten steel in the RH vacuum process in stages, so that the content of H in the molten steel is ≤2.0 ppm and the content of N is ≤48 ppm after the vacuum is broken. Meanwhile, the total RH treatment time is greatly shortened, the steam consumption for vacuumizing is reduced, the temperature drop in the RH vacuum process is reduced, the LF refining temperature rise time and power consumption are reduced, the RH steam consumption can be reduced by more than 30%, and the total power consumption for smelting can be reduced by more than 15%. DETAILED DESCRIPTION

[0014] The present application is not limited to the following specific embodiments, and those skilled in the art can implement the present application in other various specific embodiments according to the disclosed content of the present application, or any simple changes or modifications made by using the design structure and ideas of the present application also fall within the protection scope of the present application. It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0015] The present embodiment and comparative examples are used to illustrate the comprehensive control effect of the present application in the smelting process of ordinary medium-carbon structural steel 40CrB, and the smelting composition of the steel is C 0.40%, Si 0.25%, Mn 0.70%, P 0.015%, S 0.004%, Cr 1.00%, Al 0.025%, Ti 0.0028%, and B 0.0026%.

[0016] The granular low-sulfur active lime used in the following examples has a CaO content of ≥88%, a S content of ≤0.06%, and a particle size of 5-30 mm. The carbide used has a gas evolution capacity of ≥290 L / kg.

[0017] The present application is further described in detail below in combination with the embodiments:

[0018] Embodiment 1

[0019] (1) LF refining process: granular low-sulfur active lime 5.8 kg / t and fluorite 0.6 kg / t are added for desulfurization and slagging during the LF refining process, carbide is used for deoxidization to form white slag, the binary basicity CaO / SiO2 of the slag is controlled to be 10; the S content of the molten steel at the end of the LF is controlled to be ≤0.005%, and the free oxygen content is controlled to be ≤4.5 ppm; the H content is 4.7-4.8 ppm, and the N content is 61-62 ppm;

[0020] (2) RH vacuum treatment: RH selects argon as the lifting gas, and sets the flow rate in stages; the vacuum treatment is divided into two stages: the first stage uses a low vacuum degree of 20 kPa, the treatment time is 3 min, and the lifting gas flow rate is 1000 NL / min; the second stage uses a low vacuum degree of 10 kPa, the treatment time is 6 min, and the lifting gas flow rate is 2100 NL / min.

[0021] Example 2

[0022] The first stage uses a low vacuum degree of 25 kPa, the treatment time is 2 min, and the rest of the operations are the same as in Example 1.

[0023] Example 3

[0024] The second stage uses a low vacuum degree of 12 kPa, the treatment time is 5 min, and the rest of the operations are the same as in Example 1.

[0025] Example 4

[0026] The second stage lifting gas flow rate is 2000 NL / min, and the rest of the operations are the same as in Example 1.

[0027] Comparative Example 1

[0028] In Example 1, "the slag binary basicity CaO / SiO2 is controlled to be 10" is modified to "the slag binary basicity CaO / SiO2 is controlled to be 7.5", and the other conditions are the same as in Example 1.

[0029] Comparative Example 2

[0030] In Example 1, "the first stage lifting gas flow rate is 1000 NL / min" is modified to "the first stage lifting gas flow rate is 700 NL / min", and the other conditions are the same as in Example 1.

[0031] Comparative Example 3

[0032] In Example 1, "the second stage lifting gas flow rate is 2100 NL / min" is modified to "the second stage lifting gas flow rate is 1500 NL / min", and the other conditions are the same as in Example 1.

[0033] Comparative Example 4

[0034] In Example 1, "the second stage lifting gas flow rate is 2100 NL / min" is modified to "the second stage lifting gas flow rate is 2400 NL / min", and the other conditions are the same as in Example 1.

[0035] Comparative Example 5

[0036] In Example 1, "the second stage treatment time is 6 min" is modified to "the second stage treatment time is 10 min", and the other conditions are the same as in Example 1.

[0037] Comparative Example 6

[0038] The "first stage, low vacuum degree of 20 kPa; second stage, low vacuum degree of 10 kPa" in Example 1 was modified to "first stage, high vacuum degree of 0.1 kPa; second stage, high vacuum degree of 0.1 kPa", and other conditions were the same as in Example 1.

[0039] The gas content of the molten steel and energy consumption in the smelting process of the molten steel prepared in Examples 1-4 and Comparative Examples 1-6 are shown in Table 1.

[0040] Table 1 Gas content of the molten steel and energy consumption in the smelting process of the molten steel prepared in Examples 1-4 and Comparative Examples 1-6

[0041]

[0042] The above description is merely preferred specific embodiments of the present application, but the protection scope of the present application is not limited thereto, and any person skilled in the art, according to the technical range disclosed in the present application and the technical concept thereof, can make equivalent replacements or changes within the technical range disclosed in the present application, and all of them should be covered within the protection scope of the present application.

Claims

1. A low energy fast cycle RH degassing process, characterized in that, The method mainly involves LF refining and RH vacuum treatment process in the steelmaking process, and the specific process steps include: (1) LF refining process: 4.5-7 kg / t of granular low-sulfur active lime and 0.4-1 kg / t of fluorite are added for slagging and desulfurization in the LF refining process, calcium carbide is used for deoxidation to form white slag, the binary basicity CaO / SiO2 of the slag is controlled between 8.0-12.0, the S content of the molten steel at the end of the LF process is controlled to be ≤0.005%, and the free oxygen content is controlled to be ≤4.5 ppm; (2) RH vacuum treatment: argon is selected as the lifting gas in the RH, and the flow rate is set in stages; the vacuum treatment is divided into two stages: the first stage uses a low vacuum degree of 12-30 kPa, the treatment time is 2-4 min, and the lifting gas flow rate is 850-1100 NL / min; the second stage uses a low vacuum degree of 8-12 kPa, the treatment time is 5-6 min, and the lifting gas flow rate is 2000-2250 NL / min.

2. The low energy fast cycle RH degassing process of claim 1, wherein: After breaking the vacuum, the H content of the molten steel is ≤2.0 ppm, and the N content is ≤48 ppm.

3. The low energy fast cycle RH degassing process of claim 1 wherein: The granular low-sulfur active lime in step (1) has a CaO content of ≥88%, an S content of ≤0.06%, and a particle size of 5-30 mm.

4. The low energy fast cycle RH degassing process of claim 1 wherein: The calcium carbide in step (1) has a gas evolution amount of ≥290 L / kg.

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