Composite rare earth-magnesium-silicon alloy and application method thereof in aluminum-free deoxidized steel

Abstract

The invention discloses a composite rare earth-magnesium-silicon alloy and a use method of the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel, and belongs to the technical field of application of composite rare earth alloys in steel. When the composite rare earth-magnesium-silicon alloy is used, the composite rare earth-magnesium-silicon alloy is added after LF refining and vacuum pumping refining are finished, the adding amount of the composite rare earth-magnesium-silicon alloy is 0.3 kg / t-1. 5 kg / t after the LF refining is finished, and the adding amount of the composite rare earth-magnesium-silicon alloy is 0.3 kg / t-3. 0 kg / t after the vacuum pumping refining is finished; the main components of the composite rare earth-magnesium-silicon alloy comprise 10%-30% of rare earth Re, 5%-15% of magnesium and 5%-30% of silicon. According to the method, the composite rare earth-magnesium-silicon alloy is added into the steel to modify large-size inclusions in the steel and promote the inclusions to float upwards to be removed, deoxidized products are denatured to form fine spherical oxides and oxysulfides which are distributed in a dispersed mode, nucleation is promoted in the continuous casting process, the structure is refined, and the quality of a continuous casting billet is optimized.

Description

Technical Field

[0001] The invention belongs to the technical field of application of composite rare earth alloys in steel, and in particular relates to a composite rare earth-magnesium-silicon alloy and a method for using the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel. Background Art

[0002] In order to treat the denaturation of inclusions in steel, calcium wire feeding treatment is usually used. In recent years, magnesium treatment and rare earth treatment methods have also been developed, but rare earth treatment and magnesium treatment often use wire feeding process, which often results in violent reactions, and the alloy wire cannot be driven into the target depth, resulting in serious volatilization of rare earth and magnesium, low and unstable recovery rate, and the environmental problem of smoke caused by volatilization during wire feeding needs to be solved urgently. Secondly, the wire feeder is fixed in the LF or vacuum refining furnace process, and often cannot be operated flexibly. When executing calcium treatment, magnesium treatment, and rare earth treatment processes, the best time is often missed, and the effect of precise control cannot be achieved.

[0003] This patent proposes a composite rare earth-magnesium-silicon alloy and a method for using the rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel. The advantages are that the iron-based alloy is added to the steel as a counterweight, which effectively prevents the volatilization loss of magnesium and rare earth, and is evenly distributed in the steel, effectively improving the recovery rate of rare earth and magnesium. The alloy packaging method is flexible and simple, and can achieve the rare earth and magnesium composite processing process under the optimal conditions. Effectively avoid the technical problems faced by conventional wire feeding processes.

[0004] The effect of rare earth and magnesium composite treatment is more significant. It can effectively modify composite large-sized inclusions, deoxidation products, secondary oxidation products, and sulfides, promote the denaturation and floating of inclusions, and form a core of finely dispersed spherical oxides and oxysulfides. This core can also promote nucleation and refine the structure during the continuous casting process, thereby optimizing the quality of the continuous casting billet.

[0005] Reference 1: Composition design method and preparation method of a multi-component rare earth magnesium master alloy_202210085388.4, mainly based on the thermodynamic software FactSage, pre-designs the rare earth magnesium master alloy to adapt to the application of steel grades and solve the problem of low magnesium yield in the preparation of the master alloy. It does not explain how to solve the problems of large-sized inclusions in steel, the problem of inclusion denaturation, the method of addition and the timing of addition in the actual application of the alloy in steel. Advantages and disadvantages faced by the actual application.

[0006] Document 2: An aluminum-magnesium-calcium alloy and its application in controlling inclusions in stainless steel_201110027256.8, discloses an aluminum-magnesium-calcium alloy whose main component is aluminum. Its essence is still a deoxidized alloy with aluminum as the matrix. Magnesium and calcium are added simultaneously as modifiers. Although inclusions can be controlled, the addition of alloys with high aluminum content to steel in the later stage of smelting will inevitably lead to the risk of casting flocculence. Since the density of aluminum, calcium and magnesium is less than that of molten steel, the alloy cannot enter the molten steel well during actual application, and is more likely to enter the slag, resulting in low yield. The effect cannot be compared with the method of adding ferroalloy counterweights in this patent.

[0007] Document 3: A method for purifying molten steel of aluminum-deoxidized steel_202110409326.X, which mentions that the addition of aluminum-calcium-magnesium and magnesium-cerium alloy rods to molten steel requires the modification of the smelting process equipment, which has certain limitations. At the same time, the aluminum-calcium-magnesium and magnesium-cerium alloy rods in the patent are suitable for aluminum-deoxidized steel, but not for aluminum-free deoxidized steel. The composite rare earth-magnesium-silicon alloy proposed in this patent is suitable for aluminum-free deoxidized steel. It not only solves the problem of complex inclusions, but also can be added to molten steel in a counterweight manner. The operation is simple and effective, and the rare earth and magnesium composite treatment process can be completed simultaneously under optimal conditions. Effectively avoid the technical problems faced by conventional wire feeding processes. Summary of the invention

[0008] The purpose of the present invention is to provide a composite rare earth-magnesium-silicon alloy and a method for using the same in aluminum-free deoxidized steel, to modify composite large-sized inclusions, deoxidation products, secondary oxidation products, and sulfides, to promote the denaturation and floating of inclusions, and to form a core of finely dispersed spherical oxides and oxysulfides, which can also promote nucleation and refine the structure during continuous casting, and optimize the quality of continuous casting billets. The composite rare earth-magnesium-silicon alloy is added to the steel with an iron-based alloy counterweight, which effectively prevents the volatilization loss of magnesium and rare earths, and is evenly distributed in the steel, effectively improving the yield of rare earths and magnesium. The alloy packaging method is flexible and simple, and can realize the rare earth and magnesium composite processing process under the optimal conditions. It effectively avoids the technical problems faced by conventional wire feeding processes.

[0009] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0010] The present invention discloses a composite rare earth-magnesium-silicon alloy and a method for using the same in aluminum-free deoxidized steel. The composite rare earth-magnesium-silicon alloy is characterized in that when the composite rare earth-magnesium-silicon alloy is used, the composite rare earth-magnesium-silicon alloy is added to molten steel twice after refining in an LF refining furnace and vacuum exhaust refining; the amount of the composite rare earth-magnesium-silicon alloy added after refining in the LF refining furnace is 0.3kg / t-1.5kg / t, and the amount of the composite rare earth-magnesium-silicon alloy added after refining in the vacuum exhaust refining is 0.3kg / t-3.0kg / t; the main components of the composite rare earth-magnesium-silicon alloy in terms of mass percentage are: rare earth Re: 10%-30%, magnesium: 5%-15%, silicon 5%-30%, and the rest are iron and other impurity elements, and the total amount of the impurity elements does not exceed 1.0%.

[0011] Furthermore, the composite rare earth-magnesium-silicon alloy is in the form of irregular blocks with a particle size of 30-50 mm.

[0012] Furthermore, the composite rare earth-magnesium-silicon alloy is packed in an iron barrel or bag.

[0013] Furthermore, the composite rare earth-magnesium-silicon alloy is added after refining in the LF refining furnace, and the silicon content of the molten steel is increased by 0.001%-0.036%.

[0014] Furthermore, the composite rare earth-magnesium-silicon alloy is added after vacuum refining to increase silicon content in molten steel by 0.001%-0.072%.

[0015] Furthermore, during the production process, when LF is refined and silicon alloy is added to the steel, the effect of the composite rare earth-magnesium-silicon alloy on the silicon content of the molten steel needs to be considered.

[0016] Furthermore, before vacuum refining begins, the molten steel is stirred to cause inclusions to float for no less than 10 minutes, and the composite rare earth-magnesium-silicon alloy is added to the steel after vacuum refining is completed.

[0017] Furthermore, LF is refined to produce white slag, and the heating time of the refining process is increased from 20-30 minutes to 22-35 minutes. At the end of refining, the temperature of the molten steel is 10-30°C higher than that of conventional production, and 0.3kg / t-1.5kg / t of the composite rare earth-magnesium-silicon alloy is added to the steel.

[0018] Furthermore, the oxygen content and carbon content at the converter end point are focused on during converter steel tapping. While ensuring the converter end point steel tapping temperature ≥1560°C, ensure that the converter end point [C] ≥0.080%, [O] ≤0.0350%.

[0019] Compared with the prior art, the beneficial technical effects of the present invention are:

[0020] The present invention proposes a composite rare earth-magnesium-silicon alloy and a method for using the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel. The composite rare earth-magnesium-silicon alloy mainly comprises rare earth Re: 10%-30%, magnesium: 5%-15%, silicon 5%-30%, and the rest are iron and other impurity elements, and the total amount of impurity elements does not exceed 1.0%. The composite rare earth-magnesium-silicon alloy is added to steel to modify large-sized inclusions in the steel and promote the inclusions to float and be removed, so that the deoxidation product is denatured to form fine and dispersed spherical oxides and oxysulfides, which promotes nucleation and refines the structure during the continuous casting process, and optimizes the quality of the continuous casting billet. The advantage of the composite rare earth-magnesium-silicon alloy in steel is that it is added to the steel with an iron-based alloy counterweight, which effectively prevents the volatilization loss of magnesium and rare earth, and is evenly distributed in the steel, effectively improving the recovery rate of rare earth and magnesium. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be further described below in conjunction with the accompanying drawings.

[0022] Figure 1 The morphology and composition of inclusions in aluminum-free deoxidized steel produced by conventional process;

[0023] Figure 2 The morphology and composition of inclusions in aluminum-free deoxidized steel produced by this patented method. DETAILED DESCRIPTION

[0024] A composite rare earth-magnesium-silicon alloy and a method for using the same in aluminum-free deoxidized steel, specifically comprising:

[0025] Step 1: The commonly used smelting production process of aluminum-free deoxidized steel is: converter - LF refining furnace refining - vacuum extraction refining - continuous casting.

[0026] Step 2: Pay attention to the oxygen content and carbon content at the converter end point when tapping steel from the converter. While ensuring that the tapping temperature at the converter end point is ≥1560℃, ensure that [C] at the converter end point is ≥0.080%, [O] ≤0.0350%.

[0027] The third step: LF refining to make white slag, the heating time of the refining process is increased from 20-30min to 22-35min, and the temperature of the molten steel is 10-30°C higher than that of conventional production at the end of refining. At the end of refining, 0.3kg / t-1.5kg / t of the composite rare earth-magnesium-silicon alloy is added to the steel.

[0028] Step 4: Before vacuum refining begins, the molten steel is stirred to cause inclusions to float for no less than 10 minutes. After vacuum refining is completed, 0.3kg / t to 3.0kg / t of the composite rare earth-magnesium-silicon alloy is added to the steel.

[0029] Step 5: The continuous casting production process does not require the use of special nozzles and refractory materials. The production process closely monitors the mold liquid level fluctuation curve. When using this alloy to produce aluminum-free deoxidized steel, the ladle self-opening rate must be guaranteed to be above 99%.

[0030] Example 1

[0031] Step one: prepare production raw materials.

[0032] Step 2: Aluminum-free deoxidized steel smelting production process: molten iron pretreatment - converter - LF refining furnace refining - vacuum extraction refining - continuous casting.

[0033] The third step: top and bottom combined blowing converter smelting, the converter final oxygen and carbon are fixed, the converter final steel tapping temperature is 1576℃, the converter final [C] is 0.110%, [O] is 0.0258%.

[0034] Step 4: LF refining furnace refining, refining heating time 23min, refining treatment time 41min, adding composite rare earth-magnesium-silicon alloy 0.7kg / t after heating, argon blowing and stirring time 15min. Since the addition of composite rare earth-magnesium-silicon alloy increases silicon by less than 0.01%, it can be ignored.

[0035] Step 5: Vacuum refining: After vacuum refining, add 1.2 kg / t of the composite rare earth-magnesium-silicon alloy to the steel. Since the addition of the composite rare earth-magnesium-silicon alloy increases silicon by 0.019%, the standard composition is not affected.

[0036] Step 6: During continuous casting production, the ladle opens automatically, the crystallizer liquid level fluctuation curve is stable, and the continuous casting production proceeds smoothly.

[0037] Comparative Example 1

[0038] Aluminum-free deoxidized steel smelting production process: molten iron pretreatment - converter - LF refining furnace refining - vacuum extraction refining - continuous casting.

[0039] The patented aluminum-free deoxidized steel smelting production process includes: molten iron pretreatment - converter - LF refining furnace refining - adding composite rare earth-magnesium-silicon alloy - vacuum extraction refining - adding composite rare earth-magnesium-silicon alloy - continuous casting.

[0040] Large-sized inclusions are common in aluminum-free deoxidized steel produced using the original production process. Their morphology and composition are as follows: Figure 1 shown.

[0041] Common inclusions in aluminum-free deoxidized steel produced by the method provided by this patent have the following morphology and composition: Figure 2 shown.

[0042] Depend on Figure 1 and Figure 2By comparison, it can be seen that the inclusions in the aluminum-free deoxidation produced by the patented method are obviously dispersed and the inclusion composition is obviously changed.

[0043] Comparative Example 2

[0044] The low-power rating results of aluminum-free deoxidized steel continuous casting billets produced using the original production process are shown in Table 1.

[0045] The low-power rating results of the aluminum-free deoxidized steel continuous casting billet produced by the method provided by this patent are shown in Table 2.

[0046] From the comparison of Table 1 and Table 2, it can be seen that the low-power rating of the aluminum-free deoxidized steel continuous casting billet produced by the patented method is significantly optimized.

[0047] Table 1 Low-power rating of aluminum-free deoxidized steel continuous casting billets produced by conventional process

[0048]

[0049] Table 2 Low-power rating of aluminum-free deoxidized continuous casting billets produced by this patented method

[0050]

[0051] The embodiments described above are only descriptions of the preferred modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A composite rare earth-magnesium-silicon alloy and a method for using the same in aluminum-free deoxidized steel, characterized in that: When the composite rare earth-magnesium-silicon alloy is used, the composite rare earth-magnesium-silicon alloy is added to the molten steel twice after the LF refining furnace refining and the vacuum pumping refining are completed; the amount of the composite rare earth-magnesium-silicon alloy added after the LF refining furnace refining is 0.3kg / t-1.5kg / t, and the amount of the composite rare earth-magnesium-silicon alloy added after the vacuum pumping refining is completed is 0.3kg / t-3.0kg / t; the main components of the composite rare earth-magnesium-silicon alloy in terms of mass percentage are: rare earth Re: 10%-30%, magnesium: 5%-15%, silicon 5%-30%, and the rest are iron and other impurity elements, and the total amount of impurity elements does not exceed 1.0%.

2. The composite rare earth-magnesium-silicon alloy and the method of using the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel according to claim 1, characterized in that: The composite rare earth-magnesium-silicon alloy is in the form of irregular blocks with a particle size of 30-50 mm.

3. The composite rare earth-magnesium-silicon alloy and the method of using the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel according to claim 1 or 2, characterized in that: The composite rare earth-magnesium-silicon alloy is packed in an iron barrel or a bag.

4. The composite rare earth-magnesium-silicon alloy and the method of using the composite rare earth-magnesium-silicon alloy in aluminum-free deoxidized steel according to claim 1, characterized in that: The composite rare earth-magnesium-silicon alloy is added after refining in the LF refining furnace, and the silicon content of the molten steel is increased by 0.001%-0.036%.

5. The composite rare earth-magnesium-silicon alloy and the method of using the same in aluminum-free deoxidized steel according to claim 1, characterized in that: The composite rare earth-magnesium-silicon alloy is added after vacuum extraction refining, and the silicon content of the molten steel is increased by 0.001%-0.072%.

6. The composite rare earth-magnesium-silicon alloy and the method of using the same in aluminum-free deoxidized steel according to claim 1, characterized in that: During the production process, when LF is refined and silicon alloy is added to the steel, the effect of the composite rare earth-magnesium-silicon alloy on the silicon content of the molten steel needs to be considered.

7. The composite rare earth-magnesium-silicon alloy and the method of using the same in aluminum-free deoxidized steel according to claim 1, characterized in that: Before vacuum refining begins, the molten steel is stirred to cause inclusions to float for no less than 10 minutes, and the composite rare earth-magnesium-silicon alloy is added to the steel after vacuum refining is completed.

8. The composite rare earth-magnesium-silicon alloy and the method of using the same in aluminum-free deoxidized steel according to claim 1, characterized in that: LF is refined to produce white slag, and the heating time of the refining process is increased from 20-30min to 22-35min. At the end of refining, the temperature of the molten steel is 10-30°C higher than that of conventional production. 0.3kg / t-1.5kg / t of the composite rare earth-magnesium-silicon alloy is added to the steel.

9. The composite rare earth-magnesium-silicon alloy and the method of using the same in aluminum-free deoxidized steel according to claim 1, characterized in that: The key point of converter steelmaking is the oxygen content and carbon content at the converter end point. While ensuring the converter end point steelmaking temperature ≥1560℃, ensure that the converter end point [C] ≥0.080%, [O] ≤0.0350%.

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