A method for treating steel based on slag-steel self-reaction homogenization of rare earths

Abstract

The present application relates to the technical field of metallurgy, in particular to a method for treating steel with rare earth based on slag-steel self-reaction homogenization, which comprises the following steps: in the process of vacuum electroslag remelting, under vacuum high temperature, dissolved C in the steel can react with La2O3 in the slag to make the rare earth elements enter the molten steel, through regulating the composition of the slag, the content of C in the consumable electrode and the vacuum pressure, the content of rare earth La in the electroslag ingot can be effectively controlled. At the same time, since La2O3 in the slag and dissolved C in the steel are uniformly distributed, the dissolved La obtained by the method is also uniformly distributed, and the content of the rare earth obtained by reducing La2O3 is relatively low, so the method can realize the treatment of the steel with rare earth continuously, stably and uniformly.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metallurgy, and particularly relates to a method for treating steel based on slag-steel self-reaction homogenization of rare earth. BACKGROUND

[0002] Medium and high carbon alloy steels are widely used in the field of mechanical manufacturing. However, with the increasing demand for high-performance steel, the cleanliness of steel is required to be more stringent. Non-metallic inclusions are not conducive to the quality and performance of steel, and the electric slag remelting technology has an advantage in removing inclusions, especially large-sized inclusions, and is more adaptable and flexible compared with traditional smelting methods. Appropriate rare earth elements can purify molten steel, modify inclusions and micro-alloy in steel. Rare earth elements can deeply deoxidize and desulfurize molten steel in the steelmaking process to purify the molten steel, and rare earth elements can also react with harmful elements such as P and As to reduce the segregation of harmful elements at the grain boundary and reduce the influence of harmful elements on the performance of steel. In most cases, the expansion coefficient of inclusions is different from that of the steel matrix, which can easily lead to stress concentration and form micro-cracks during processing. Due to the strong binding capacity of rare earth elements with O and S, the rare earth elements can modify the oxygen and sulfur inclusions in the steel into rare earth inclusions, and the thermal expansion coefficient of the rare earth inclusions is similar to that of the steel, which can avoid stress concentration. Rare earth elements mainly exist in the form of rare earth inclusions in steel, and the remaining solid-solution rare earth elements segregate at the grain boundary, which can effectively reduce the segregation of harmful elements at the grain boundary. However, compared with the long process of steelmaking, the electric slag remelting process does not have the interference of refractory materials, and it is considered to be a better method to prepare rare earth steel by electric slag remelting. At present, the preparation of rare earth steel by electric slag remelting is mainly realized by adding a reducing agent to the slag, but the reducing agent is difficult to be uniformly distributed in the slag pool due to the self-consumption electrode in the center of the slag pool, thereby leading to the low content of rare earth in the middle and high content of rare earth at the edge of the electric slag ingot, and the rare earth treatment is not uniform.

[0003] Therefore, there is an urgent need for a method for preparing homogenized rare earth treated steel by electric slag remelting to meet the demand for high-performance steel. SUMMARY

[0004] The present application aims to provide a method for treating steel based on slag-steel self-reaction homogenization of rare earth, which reasonably utilizes the composition of molten slag, the carbon content of steel and the rare earth La content in the finished product steel from the perspective of thermodynamics, and proposes to use the self-reaction of slag-steel to reduce the rare earth oxides in the slag as the source of rare earth for rare earth treatment.

[0005] To achieve the above-mentioned purpose, one aspect of the present application provides a method for treating steel based on slag-steel self-reaction homogenization of rare earth, which uses a selected slag to perform vacuum electric slag remelting in a vacuum electric slag furnace with a specific steel as a consumable electrode.

[0006] Preferably, the limit vacuum of the vacuum electric slag furnace is ≤0.1 kPa.

[0007] Preferably, the mass percentage of the consumable electrode component is as follows: C 0.40-1.00%, Si 0.15-0.35%, Cr 1.40-1.65%, Mn 0.25-0.45%, P≤0.03%, Mo≤0.10%, Ni≤0.20%, S≤0.02%, O≤0.002%.

[0008] Preferably, the mass percentage of the selected slag component is as follows: CaF2 30-40%, CaO 30-40%, (Al2O3+La2O3) 20-40%.

[0009] Preferably, the vacuum pressure used in the vacuum electroslag remelting process is in the range of 1.5-5 kPa.

[0010] Preferably, the diameter of the crystallizer used by the vacuum electroslag furnace is 200-500 mm, the remelting current is 3×10 3 ~8×10 3 A, and the remelting voltage is 44-61 V.

[0011] Preferably, the La content of the steel after the vacuum electroslag remelting is 0.001-0.025%.

[0012] Compared with the prior art, the method for treating steel based on slag-steel self-reaction homogenization of rare earth provided by the embodiments of the present application has the following beneficial effects:

[0013] The method for treating steel based on slag-steel self-reaction homogenization of rare earth provided by the embodiments of the present application can realize the continuous, stable and uniform treatment of steel with rare earth. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 The technical roadmap of the method for treating steel based on slag-steel self-reaction homogenization of rare earth provided by the embodiments of the present application is provided.

[0015] Figure 2 The inclusion statistical results of Example 5 and Comparative Example 1 provided by the embodiments of the present application are provided.

[0016] Figure 3 The rare earth inclusions in Example 5 provided by the embodiments of the present application are provided. DETAILED DESCRIPTION

[0017] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of the present application.

[0018] The present application provides a method for treating steel based on slag-steel self-reaction homogenization, which comprises: using a specific steel as a consumable electrode, and using a selected slag to perform vacuum electroslag remelting in a vacuum electroslag furnace.

[0019] The mass percentage of the consumable electrode composition is as follows: C 0.40-1.00%, Si 0.15-0.35%, Cr 1.40-1.65%, Mn 0.25-0.45%, P≤0.03%, Mo≤0.10%, Ni≤0.20%, S≤0.02%, and O≤0.002%.

[0020] The mass percentage of the selected slag composition is as follows: CaF2 30-40%, CaO 30-40%, and (Al2O3+La2O3) 20-40%.

[0021] In the present application, the vacuum pressure used in the vacuum electroslag remelting process is in the range of 1.5-5 kPa. The smelting method is the vacuum electroslag remelting process well known in the art, the diameter of the crystallizer used in the vacuum electroslag remelting is 200-500 mm, the remelting current is 3×10 3 ~8×10 3 A, and the remelting voltage is 44-61 V.

[0022] In the present application, when the vacuum electroslag remelting is performed, the dissolved C in the steel can react with La2O3 in the slag to cause slag-steel self-reduction reaction, so that the rare earth element enters the steel liquid. The mass percentage of the slag composition is CaF2 30-40%, CaO 30-40%, and (Al2O3+La2O3) 20-40%, the mass percentage range of C content is 0.40-1.00%, and the vacuum pressure range is 1.5-5 kPa. In the present application, by adjusting the slag composition, the C content in the consumable electrode, and the vacuum pressure, the condition range is controlled within the above range, the dissolved C in the steel can react with La2O3 in the slag to cause slag-steel self-reduction reaction, so that the rare earth La enters the steel liquid, which plays a role of purifying the steel liquid, modifying the inclusions, and micro-alloying.

[0023] The application will be described in more detail below with reference to some embodiments. Since only some embodiments are used, other embodiments obtained by those skilled in the art on the basis of the embodiments of the application without creative labor are within the protection scope of the application.

[0024] Embodiment 1

[0025] A rare earth treated steel is obtained by vacuum electroslag remelting using a consumable electrode and a selected slag; wherein the mass percentage of the consumable electrode is as follows: C 1.00%, Si 0.24%, Cr 1.42%, Mn 0.31%, P 0.013%, Mo 0.01%, Ni 0.02%, S 0.003%, O 0.0017% and the balance of Fe; the mass percentage of the slag is as follows: CaF2 30%, CaO 30%, La2O3 20%, Al2O3 20%; the vacuum pressure used is 5kPa;

[0026] This embodiment is carried out under a vacuum electroslag remelting furnace, without other additives, and the consumable electrode is removed after remelting to obtain a rare earth treated steel T1.

[0027] Embodiment 2

[0028] In this embodiment, the mass percentage of the slag in embodiment 1 is replaced as follows: CaF2 35%, CaO 30%, La2O3 15%, Al2O3 20%; the remaining technical features are the same as those in embodiment 1 to obtain a rare earth treated steel T2.

[0029] Embodiment 3

[0030] In this embodiment, the mass percentage of the slag in embodiment 1 is replaced as follows: CaF2 40%, CaO 30%, La2O3 10%, Al2O3 20%; the remaining technical features are the same as those in embodiment 1 to obtain a rare earth treated steel T3.

[0031] Embodiment 4

[0032] In this embodiment, the mass percentage of the slag in embodiment 1 is replaced as follows: CaF2 35%, CaO 35%, La2O3 10%, Al2O3 20%; the remaining technical features are the same as those in embodiment 1 to obtain a rare earth treated steel T4.

[0033] Embodiment 5

[0034] In this embodiment, the mass percentage of the slag in embodiment 1 is replaced as follows: CaF2 30%, CaO 30%, La2O3 10%, Al2O3 30%; the remaining technical features are the same as those in embodiment 1 to obtain a rare earth treated steel T5.

[0035] Example 6

[0036] In this example, the C content of the consumable electrode in Example 1 is replaced by 0.80%; the rest of the technical features are the same as those in Example 1, and a rare earth treated steel T6 is obtained.

[0037] Example 7

[0038] In this example, the C content of the consumable electrode in Example 1 is replaced by 0.60%; the rest of the technical features are the same as those in Example 1, and a rare earth treated steel T7 is obtained.

[0039] Example 8

[0040] In this example, the C content of the consumable electrode in Example 1 is replaced by 0.40%; the rest of the technical features are the same as those in Example 1, and a rare earth treated steel T8 is obtained.

[0041] Example 9

[0042] In this example, the vacuum pressure in Example 5 is replaced by 2 kPa; the rest of the technical features are the same as those in Example 5, and a rare earth treated steel T9 is obtained.

[0043] Example 10

[0044] In this example, the vacuum pressure in Example 5 is replaced by 1.5 kPa; the rest of the technical features are the same as those in Example 5, and a rare earth treated steel T10 is obtained.

[0045] Comparative Example 1

[0046] The electroslag remelting of Comparative Example 5 is carried out in a protective atmosphere of argon; the rest of the technical features are the same as those in Example 5, and a rare earth treated steel C1 is obtained.

[0047] The technical route of the present application is shown in Figure 1 The rare earth treated steels obtained in Examples 1-10 and Comparative Example 1 are sampled at the same position for detection of the La, O and S content, and the samples of Example 1 and Comparative Example 1 are observed and analyzed by SEM and the inclusions are counted; the component detection results are shown in Table 1, the inclusion counting results of Example 5 and Comparative Example 1 are shown in Figure 2 , and the rare earth inclusions in Example 5 are shown in Figure 3 .

[0048] Table 1: La, O and S component detection results of the rare earth treated steel samples obtained in Examples 1-10 and Comparative Example 1 (mass percentage, %)

[0049] La O S T1 0.0072 0.0012 0.0014 T2 0.0052 0.0010 0.0013 T3 0.0031 0.0010 0.0015 T4 0.0039 0.0009 0.0016 T5 0.0021 0.0011 0.0015 T6 0.0046 0.0010 0.0014 T7 0.0033 0.0011 0.0015 T8 0.0011 0.0014 0.0018 T9 0.0128 0.0010 0.0012 T10 0.0221 0.0008 0.0011 C1 - 0.0024 0.0018

[0050] From the detection results of Table 1, it can be seen that the rare earth La content of Examples 1-10 is relatively ideal by the vacuum slag steel self-reaction, and the O and S contents of Examples 1-10 are also slightly reduced, which shows that the slag steel self-reaction homogenization rare earth treatment of the application can obtain a relatively ideal rare earth La content, and can effectively purify the molten steel and improve the performance of the steel.

[0051] From Figure 2 It can be seen that after the vacuum slag steel self-reaction homogenization rare earth treatment, the maximum size and average size of the inclusions and the proportion of large inclusions are all reduced.

[0052] Figure 3 It shows that a certain amount of dissolved La in the slag steel self-reaction process of Example 5 reacts with the dissolved oxygen in the molten steel to produce rare earth oxides.

[0053] Although the embodiments of the application have been shown and described, it is to be understood that for the purpose of the present application, the changes, modifications, equivalents, and variations of these embodiments are possible without departing from the principles and spirit of the application, and the scope of the application is defined by the appended claims and their equivalents.

Claims

1. A method for homogenizing rare earth treated steel based on slag-steel self-reaction, characterized in that: Using specific steel as consumable electrode and selected slag for vacuum electroslag remelting in a vacuum electroslag furnace; The ultimate vacuum of the vacuum electroslag furnace is ≤0.1 kPa; The mass percentages of the consumable electrode components are as follows: C 0.40-1.00%, Si 0.15-0.35%, Cr 1.40-1.65%, Mn 0.25-0.45%, P≤0.03%, Mo≤0.10%, Ni≤0.20%, S≤0.02%, O≤0.002%; The mass percentages of the selected slag components are as follows: CaF2 30-40%, CaO 30-40%, (Al2O3+La2O3) 20-40%; During vacuum electroslag remelting, dissolved carbon in the steel can react with La2O3 in the slag to generate a slag-steel self-reduction reaction, allowing rare earth elements to enter the molten steel. The mass percentages of the slag components are CaF2 30-40%, CaO 30-40%, and (Al2O3+La2O3) 20-40%, the mass percentage range of the carbon content is 0.40-1.00%, and the vacuum pressure range is 1.5-5 kPa. The present invention can control the condition range within the above range by regulating the slag composition, the carbon content in the consumable electrode, and the vacuum pressure, so that the rare earth La enters the molten steel through the slag-steel self-reduction reaction between the dissolved carbon in the steel and La2O3 in the slag, thereby playing the role of purifying the molten steel, modifying inclusions, and microalloying.

2. The method according to claim 1, wherein The vacuum pressure range used in the vacuum electroslag remelting process is: 1.5~5 kPa.

3. The method according to claim 1, wherein The diameter of the crystallizer used in the vacuum electroslag furnace is 200~500mm, and the remelting current is 3×10 3 ~8×10 3 A, the remelting voltage is 44~61V.

4. The method according to claim 1, wherein The La content of steel after vacuum electroslag remelting is: 0.001~0.025%.

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