A smelting method for reducing hydrogen content of molten steel before vacuum reduction

Abstract

The present application relates to the technical field of metallurgy, in particular to a smelting method for reducing hydrogen content of molten steel before vacuumizing. The process is electric furnace-LF furnace-VD furnace-continuous casting, wherein slag is added in the electric furnace tapping process without adding lime; the argon gas is adjusted to the minimum stirring state after the electric furnace is tapped, and the molten steel is not exposed to absorb gas; the argon gas flow is rapidly reduced to 10 L / min when the molten steel is refined in the LF furnace, and after the molten steel surface is calm, the lime is added through the old top material, the argon gas flow is adjusted to 30 L / min, and the power is supplied for 3 minutes, and then the normal refining operation is continued. The present application can effectively reduce the H content of the molten steel before vacuumizing, reduce the vacuum holding time, reduce the slag consumption, reduce the refractory consumption, and has great significance for the steel metallurgy industry, truly achieves the effect of reducing cost and increasing benefit, and has great economic benefit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, in particular to a smelting method for reducing hydrogen content of molten steel before vacuum. BACKGROUND

[0002] H is the most harmful element in general steel, and the dissolution of hydrogen in steel can cause hydrogen embrittlement, white spots and other defects. Hydrogen, like oxygen and nitrogen, has very low solubility in solid steel, dissolves into molten steel at high temperature, and accumulates in the structure to form high-pressure fine pores when it cannot escape during cooling, which can cause a sharp decrease in plasticity, toughness and fatigue strength of steel, and even cause cracks and brittle fracture. "Hydrogen embrittlement" mainly occurs in martensitic steel, and is not very prominent in ferrite steel. On the other hand, H can increase the magnetic permeability of steel, but also increase the coercive force and iron loss (the coercive force can increase by 0.5-2 times after adding H).

[0003] With the development of China's steel industry, the quality requirements for steel are getting higher and higher. Now, except for threaded, small-sized ordinary-purpose wire rods and round steels, the smelting process path needs to go through a vacuum treatment path to reduce the H content in molten steel to different degrees, so as to avoid the occurrence of white spots and other defects caused by high H content on the material.

[0004] The H content in molten steel mainly comes from the absorption of moisture in the air, moisture in the slag, crystallization water in the alloy, rust on the scrap steel, and water brought in after the reaction of natural gas used in the smelting cluster gun. High H residue in steel can cause white spot defects, which generally need to be quickly and effectively reduced by long holding time under high vacuum to avoid white spot defects on the material. The temperature loss of different steel grades under high vacuum holding is up to 1.8-2.2℃ per minute, which has a great impact on energy consumption, refractory loss, and efficient operation of the production process path. Therefore, how to reduce the H content of molten steel before vacuum is of great significance. SUMMARY

[0005] The present application overcomes the shortcomings of the prior art and provides a smelting method for reducing the hydrogen content of molten steel before vacuum, which is an electric furnace-LF furnace-VD furnace-continuous casting process, wherein:

[0006] (1) The slag is added during the tapping process of the electric furnace, and no lime is added;

[0007] (2) After the argon gas is adjusted to the minimum stirring state, the molten steel is not exposed to air;

[0008] (3) When the molten steel reaches the LF furnace for refining, the argon gas flow is quickly reduced to 10 L / min. After the molten steel surface is calm, lime is added through the old material, the argon gas flow is adjusted to 30 L / min, and power is supplied for 3 minutes. Then, the argon gas flow is continuously adjusted to the normal process requirement, and the normal refining operation is restored according to the modularization of other process requirements.

[0009] The slag brought into the molten steel in the tapping process of the primary refining furnace can be reduced by the step (1), the water in the air absorbed in the molten steel transfer process of the primary refining furnace can be greatly reduced by the step (2), and the slag brought into the molten steel in the refining process can be reduced by the step (3), so that the H content of the molten steel before vacuum is effectively reduced, and the high vacuum holding time is reduced.

[0010] The further defined technical solution of the present application is:

[0011] Further, when the lime needs to be added during the LF furnace refining, the argon flow is rapidly reduced to 10 L / min, and then the lime is added through the old top charging after the molten steel surface is calm.

[0012] Further, after the lime is added through the old top charging, the high-temperature molten steel is used to roast the lime on the molten steel surface for 5-8 minutes.

[0013] Further, the slag is a pre-melted modified refining slag.

[0014] Further, when the VD furnace vacuum treatment is performed, the argon flow is adjusted to 80-100 L / min.

[0015] Further, when the VD furnace vacuum treatment is performed, the vacuum is maintained for 3-5 minutes, and the holding time under high vacuum degree is reduced by 4 minutes compared with the original process.

[0016] The beneficial effects of the present application are:

[0017] (1) The smelting method for reducing the hydrogen content of molten steel before vacuum provided by the present application can reduce the H content of the molten steel before vacuum by 2-3.5 ppm through the H detection of the molten steel before and after vacuum, and the H content of the molten steel after vacuum meets the requirements of the original process after the holding time under high vacuum degree is reduced by 4 minutes;

[0018] (2) The present application can effectively reduce the H content of the molten steel before vacuum, reduce the vacuum holding time, reduce the slag consumption, and reduce the refractory consumption, which is of great significance to the steel and iron metallurgy industry, truly achieves the effect of reducing cost and increasing efficiency, and has great economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The process flow chart of the smelting method for reducing the hydrogen content of molten steel before vacuum of the present application is shown in the figure;

[0020] Figure 2 The hydrogen content data of the Hydrogenometer for molten steel in Example 1 of the present application is shown in the figure;

[0021] Figure 3 The hydrogen content data of the Hydrogenometer for molten steel in Example 2 of the present application is shown in the figure. DETAILED DESCRIPTION Example 1

[0022] 23701817 furnace, steel grade 30Mn2Cr, process route: EAF-LF-VD-CC.

[0023] The slag material is added with lime 5.5-7 Kg / ton in the EAF tapping process, and with 2.5 Kg / ton of pre-melted modified refining slag. The modification is that lime is not added, and 1 Kg / ton of pre-melted modified refining slag is added. In this embodiment, 100 Kg of pre-melted modified refining slag is added in the tapping process. The argon gas is adjusted to the minimum stirring state after the EAF tapping is completed, and the molten steel is not exposed to the atmosphere for gas absorption. After the bypass top is opened to release the argon gas, the flow rate is quickly reduced to 10 L / min. After the molten steel surface is calm, 500 Kg of lime is added by the old ladle in the LF, and the high-temperature molten steel is used to roast the lime on the molten steel surface for 5 minutes. The argon flow rate is adjusted to 30 L / min, and power is supplied for 3 minutes. Then the argon flow rate is continuously adjusted to the normal process requirement, and the normal refining operation is restored according to the modularization of other process requirements. The VD vacuum treatment is performed for 14 minutes, and the high vacuum degree is maintained for 4 minutes. The high vacuum degree maintenance time is reduced by 4 minutes compared to the original process. The hydrogen content is 1.7 ppm (see Table 1), which meets the process requirement (≤2.0 ppm). Figure 2 H2), which meets the process requirement (≤2.0 ppm). Example 2

[0024] 23702010 furnace, steel grade 40Mn2-MH, process route: EAF-LF-VD-CC.

[0025] In this embodiment, 100 Kg of pre-melted modified refining slag is added in the tapping process. The argon gas is adjusted to the minimum stirring state after the EAF tapping is completed, and the molten steel is not exposed to the atmosphere for gas absorption. After the bypass top is opened to release the argon gas, the flow rate is quickly reduced to 10 L / min. After the molten steel surface is calm, 500 Kg of lime is added by the old ladle in the LF, and the high-temperature molten steel is used to roast the lime on the molten steel surface for 7 minutes. The argon flow rate is adjusted to 30 L / min, and power is supplied for 3 minutes. Then the argon flow rate is continuously adjusted to the normal process requirement, and the normal refining operation is restored according to the modularization of other process requirements. The VD vacuum treatment is performed for 16 minutes, and the high vacuum degree is maintained for 4 minutes. The high vacuum degree maintenance time is reduced by 4 minutes compared to the original process. The hydrogen content is 1.9 ppm (see Table 1), which meets the process requirement (≤2.0 ppm). Figure 3 H2), which meets the process requirement (≤2.0 ppm).

[0026] Based on the investigation of the whole process of increasing H in the smelting process, the water in the slag is one of the main reasons. According to examples 1 and 2, it can be known that the smelting method for reducing the hydrogen content of molten steel before vacuum provided by the application can effectively reduce the hydrogen content of molten steel before vacuum, reduce the vacuum holding time, reduce the slag consumption, reduce the refractory consumption, and is effective for all vacuum process steel grades. Through the test, the high vacuum holding time is reduced by 4 minutes, the refining power consumption is reduced by 400 kwh, the slag alloy is reduced by 250 Kg, the ladle life is increased by 2 furnaces, and the comprehensive cost reduction is 12.1 yuan / ton of steel. Taking a 100-ton ultra-high power electric arc furnace as an example, the annual output of special steel is 120 tons, the vacuum ratio is 90%, the hydrogen content of molten steel before vacuum is effectively reduced, the high vacuum holding time is reduced, and the slag consumption is reduced, which has great significance, and all kinds of consumption reduction in the iron and steel smelting industry is extraordinary, and the effect of cost reduction and benefit increase is truly achieved, which has great economic benefits.

[0027] In addition to the above examples, the present application can have other implementation manners. Any technical solution formed by equivalent replacement or equivalent transformation falls within the protection scope required by the present application.

Claims

1. A smelting method for reducing the hydrogen content of molten steel before vacuum reduction, the process being electric furnace-LF furnace-VD furnace-continuous casting, characterized in that: (1) during tapping of the electric furnace, slag is added without lime; (2) after tapping of the electric furnace, the argon flow is adjusted to the minimum stirring state, and the molten steel is not exposed to air for absorption; (3) after the molten steel is transferred to the LF furnace for refining, the argon flow is rapidly reduced to 10 L / min, after the molten steel surface is calm, lime is added through the old charging material, the argon flow is adjusted to 30 L / min, and power is supplied for 3 minutes, then normal refining operation is continued; during the LF furnace refining, when lime needs to be added, the argon flow is rapidly reduced to 10 L / min, after the molten steel surface is calm, lime is added through the old charging material; after the lime is added through the old charging material, the high-temperature molten steel is used to roast the lime on the molten steel surface for 5-8 minutes; the slag is 1 kg / ton of pre-melted modified refining slag; during VD furnace vacuum treatment, the argon flow is adjusted to 80-100 L / min; during VD furnace vacuum treatment, the vacuum is maintained for 3-5 minutes. ​ ​ ​ ​

Images