A method for controlling the uniformity of manganese in Mn18Cr18N steel and Mn18Cr18N steel with uniform distribution of manganese

Abstract

The application relates to the technical field of metal smelting, in particular to a method for controlling the uniformity of manganese elements in Mn18Cr18N steel and Mn18Cr18N steel with uniformly distributed manganese elements, the method comprises the following steps: adopting an electroslag remelting method to electroslag remelt an electrode rod to obtain an electroslag ingot, and preparing the Mn18Cr18N steel; the electrode rod contains the following elements in percentage by mass: C: 0.05% to 0.1%, Mn: 18.0% to 18.5%, Si: 0.3% to 0.5%, P: less than or equal to 0.03%, S: less than or equal to 0.02%, Cr: 18.0% to 20.0%, N: more than or equal to 0.6%, and the rest is Fe; a cored wire containing metallic manganese is uniformly distributed on the electrode rod, the mass of the metallic manganese is 90 g / m to 200 g / m, one end of the cored wire is flush with one end of the electrode rod, and the other end is 100 mm to 200 mm lower than the other end of the electrode rod.

Description

Technical Field

[0001] This invention relates to the field of metal smelting technology, specifically to a method for controlling the uniformity of manganese in Mn18Cr18N steel and Mn18Cr18N steel with uniform manganese distribution. Background Technology

[0002] Generator retaining ring steel Mn18Cr18N is a high-manganese, high-nitrogen austenitic stainless steel with excellent resistance to high strength and stress corrosion, and is widely used in nuclear power and thermal power fields.

[0003] In recent years, with the continuous increase in generator unit power, the cooling medium of the units is mostly sodium chloride solution. The retaining ring must withstand stress corrosion in the sodium chloride solution environment during repeated wetting and drying processes. In order to obtain high yield strength, plasticity and toughness, reduce stress corrosion sensitivity in the humid sodium chloride medium, and reduce aging sensitivity, it is necessary to ensure that the retaining ring steel has a stable austenitic structure.

[0004] Manganese in ring-protecting steel can expand the austenite phase region and stabilize austenite. At the same time, manganese and iron atoms have similar atomic radii, and manganese forms a substitutional solid solution with iron, which can improve the strength of the ring-protecting steel. In addition, manganese has a strong affinity for sulfur and preferentially combines with sulfur than iron, which can prevent FeS from forming a thin film at the grain boundaries, thereby improving the hot working properties of the steel.

[0005] Currently, Mn18Cr18N retaining ring steel is mostly produced using a technical route of electric furnace + ladle refining + electroslag remelting. During electroslag remelting, due to favorable thermodynamic and kinetic conditions, a chemical equilibrium reaction occurs at the slag-steel interface, where manganese is converted to manganese oxide. This causes manganese loss. When the manganese oxide in the slag reaches equilibrium with the steel composition, manganese loss ceases. Even during the feeding stage, due to the decrease in molten pool temperature, the manganese oxide in the slag is reconstituted into metallic manganese in the steel, leading to an increase in the mass fraction of manganese in the steel. The final result is an uneven distribution of manganese in the axial direction of the electroslag ingot, thus affecting the stability of the austenitic structure of the retaining ring steel. However, without electroslag remelting, the cleanliness and density of the Mn18Cr18N retaining ring steel cannot be guaranteed, causing defects in flaw detection and reducing the product yield.

[0006] In view of this, the present invention is hereby proposed. Summary of the Invention

[0007] To improve the uniformity of manganese in Mn18Cr18N steel, this invention provides a method for controlling the uniformity of manganese in Mn18Cr18N steel and a Mn18Cr18N steel with uniform manganese distribution prepared by this method. The method of this invention can control the compositional deviation of manganese in Mn18Cr18N steel to within 0.5%.

[0008] This invention includes the following technical solutions:

[0009] The first aspect of the present invention provides a method for controlling the uniformity of manganese in Mn18Cr18N steel, the method comprising: electroslag remelting an electrode rod to obtain an electroslag ingot, thereby preparing Mn18Cr18N steel;

[0010] The electrode rod contains the following elements by mass percentage: C: 0.05%–0.1%, Mn: 18.0%–18.5%, Si: 0.3%–0.5%, P≤0.03%, S≤0.02%, Cr: 18.0%–20.0%, N≥0.6%, with the balance being Fe;

[0011] In some embodiments of the present invention, the electrode rod also contains other unavoidable impurities.

[0012] The electrode rod has a uniformly distributed cored wire containing metallic manganese along its axis. The metallic manganese has a mass of 90 g / m to 200 g / m. One end of the cored wire is flush with one end of the electrode rod, and the other end is 100 mm to 200 mm lower than the other end of the electrode rod. The height of the cored wire can be 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, or 200 mm lower.

[0013] Preferably, the cored wires are axially and evenly distributed around the electrode rod.

[0014] More preferably, the cored wire is soldered onto the electrode rod.

[0015] Particularly preferably, the number of cored wires is 4 to 8; in the embodiment of the present invention, the number of cored wires is 4.

[0016] In this invention, the length of the cored wire is lower than the other end of the electrode rod, and the weight corresponding to this height is used for the subsequent shrinkage and capping process.

[0017] Furthermore, the electroslag remelting method includes the following steps: arc initiation, slag formation, smelting, electrode replacement, smelting, feeding, and cooling;

[0018] Preferably, the arc initiation is performed directly using a metal electrode;

[0019] Preferably, the electroslag remelting is a conventional atmospheric environment exchangeable support electroslag remelting;

[0020] The slag-refining step includes adding 0.003% to 0.007% of the weight of electroslag ingots of metallic manganese particles to the system 8 to 12 minutes before the end of slag-refining. The size of the metallic manganese particles is Φ1.0mm to Φ3.0mm.

[0021] Preferably, the weight of the added manganese metal particles is 0.005% of the electroslag ingot.

[0022] The electroslag remelting method is carried out in an electroslag remelting furnace crystallizer.

[0023] Furthermore, the composition of the slag in the electroslag remelting is, by mass fraction: CaF2:Al2O3:SiO2 = (60-70):(25-30):(2-5).

[0024] Furthermore, the amount of the electroslag remelting slag is 3.6% to 12% of the weight of the electrode rod, including but not limited to 3.6%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11% or 12%.

[0025] Furthermore, the electrode rod has a specification of Φ500mm~Φ600mm, and / or the diameter of the electroslag remelting furnace crystallizer is Φ650mm~Φ850mm;

[0026] Furthermore, the electrode rod weighs 2t to 4t, including but not limited to 2t, 3t or 4t.

[0027] In this invention, the electrode rod is produced by an electric furnace and ladle refining process.

[0028] In some embodiments of the present invention, the amount of electroslag remelting slag used is 180kg to 360kg, including but not limited to 180kg, 190kg, 200kg, 210kg, 220kg, 230kg, 240kg, 250kg, 260kg, 270kg, 280kg, 290kg, 300kg, 310kg, 320kg, 330kg, 340kg, 350kg or 360kg.

[0029] Furthermore, in the slag-forming step, the voltage is 40V~50V, the current is 3000A~5000A, and the slag-forming time is ≥50 minutes.

[0030] Furthermore, the melting rate of the smelting step is 500 kg / h to 720 kg / h.

[0031] In some embodiments of the present invention, the melting speed in the melting step is set according to the diameter of the crystallizer, and the corresponding current and voltage are adjusted according to the melting speed.

[0032] In the later stage of the smelting (electroslag remelting) process of this invention, the current and voltage are reduced to enter the feeding step, so that the electroslag ingot is fed and sealed.

[0033] Furthermore, the shrinkage time of the shrinkage step is ≥90 minutes.

[0034] Furthermore, the cooling step includes: keeping the electroslag ingot in the crystallizer for cooling, demolding it after the time is greater than 120 minutes, and cooling it to room temperature after demolding.

[0035] The second aspect of the present invention provides a Mn18Cr18N steel prepared by the method described in the first aspect, wherein the mass content deviation of the Mn18Cr18N steel is within 0.5%.

[0036] Preferably, the manganese content of the Mn18Cr18N steel has a deviation of 0.3% or less.

[0037] More preferably, the manganese content of the Mn18Cr18N steel has a deviation of 0.2% or less.

[0038] By adopting the above technical solution, the present invention has at least the following beneficial effects:

[0039] This invention prepares Mn18Cr18N steel by uniformly welding a cored wire of a specific length containing metallic manganese along the axial direction of an electrode rod, followed by electroslag remelting of the electrode rod to obtain an electroslag ingot. The invention further ensures the uniformity of manganese content in the Mn18Cr18N steel by adding metallic manganese particles of a specific mass and size to the system at a specific time before the slag treatment is completed.

[0040] The method of the present invention can take into account both the cleanliness and density of Mn18Cr18N steel, as well as the uniform distribution of manganese in the axial direction of Mn18Cr18N steel, thereby ensuring the stability of the austenitic structure of Mn18Cr18N steel. The method of the present invention can control the compositional deviation of manganese in Mn18Cr18N steel to within 0.5%. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 The diagram shows the welding position of the manganese cored wire on the electrode rod. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to specific examples and the accompanying drawings.

[0044] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0045] Unless otherwise defined, all scientific and technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art.

[0046] In this invention, the term "core wire" refers to a wire made by wrapping metallic manganese powder around a strip of steel, which has a coil-like appearance and is typically welded onto an electrode rod.

[0047] The beneficial effects of the present invention will be further illustrated below with reference to specific embodiments.

[0048] Example 1:

[0049] The electrode rod used for electroslag remelting Mn18Cr18N steel is produced by an electric furnace + ladle refining process. It has a diameter of Φ500mm, a length of 1800mm, and a weight of 2700kg. Its chemical composition is shown in Table 1. Four cored wires containing metallic manganese are welded onto the electrode rod, evenly distributed around its perimeter. Figure 1 As shown, the mass of manganese powder in the cored wire is 90 g / m, and the length of the cored wire is 1600 mm. The diameter of the crystallizer in the electroslag remelting furnace is Φ650 mm; the mass fraction ratio of the electroslag remelting slag system is CaF2:Al2O3:SiO2 = 70:27:3; the amount of electroslag remelting slag used is 200 kg; the arc is initiated directly using a metal electrode; the voltage during slag melting is 45 V, the current is 4000 A, and the slag melting time is 60 minutes; 250 g of manganese particles are added to the slag pool 10 minutes before the end of the slag melting process; after slag melting, the normal smelting process begins, and the melting during the electroslag remelting process... The melting speed is 520 kg / h; after the first electrode rod melts, the second electrode rod is switched to continue melting, with an electrode exchange time of 1 minute; after normal melting ends, the feeding stage begins, with a feeding time of 90 minutes; after feeding and capping, the electroslag ingot is kept in the crystallizer for cooling, and after cooling for 150 minutes, it is demolded and then air-cooled to room temperature. The weight of the electroslag ingot is 5200 kg. After cooling, samples of drill cuttings from the head and tail of the electroslag ingot are taken for analysis of the manganese element mass fraction, as shown in Table 1. The deviation of the manganese element from the head to the tail of the electroslag ingot is 0.3%.

[0050] Table 1 Chemical composition analysis (%) of Mn18Cr18N steel

[0051]

[0052] Example 2

[0053] The electrode rod used for electroslag remelting Mn18Cr18N steel is produced by an electric furnace + ladle refining process. It has a diameter of Φ600mm, a length of 1600mm, and a weight of 3500kg. Its chemical composition is shown in Table 2. Four cored wires containing metallic manganese are welded onto the electrode rod, evenly distributed around its perimeter. Figure 1 As shown, the mass of manganese powder in the cored wire is 120 g / m, and the length of the cored wire is 1500 mm. The diameter of the electroslag remelting furnace crystallizer is Φ850 mm; the mass fraction ratio of the electroslag remelting slag system is CaF2:Al2O3:SiO2 = 67:28:5; the amount of electroslag remelting slag used is 310 kg; arc initiation is achieved by direct arc initiation using metal electrodes; the voltage during slag formation is 45 V, the current is 5000 A, and the slag formation time is 60 minutes; 400 g of manganese particles are added to the slag pool 10 minutes before the end of the slag formation process; after slag formation, the normal smelting process begins; the melting rate during the electroslag remelting process is... The melting rate is 680 kg / h; after the first electrode rod melts, the second electrode rod is switched to continue melting, with an electrode exchange time of 55 seconds; after normal melting ends, the feeding stage begins, with a feeding time of 100 minutes; after feeding and capping, the electroslag ingot is kept in the crystallizer for cooling, and after cooling for 160 minutes, it is demolded and then air-cooled to room temperature. The weight of the electroslag ingot is 6500 kg. After cooling, samples of drill chips from the head and tail of the electroslag ingot are taken for analysis of the manganese element mass fraction, as shown in Table 2. The deviation of manganese element from the head to the tail of the electroslag ingot is 0.2%.

[0054] Table 2 Chemical composition analysis (%) of Mn18Cr18N steel

[0055]

[0056] Comparative Example 1

[0057] To compare and analyze the beneficial effects of the present invention, the electrode rod in Example 2 was smelted once using a conventional electroslag remelting process. The electrode rod for electroslag remelting Mn18Cr18N steel was produced by an electric furnace + ladle refining process, with a diameter of Φ600mm, a length of 1600mm, and a weight of 3500kg. The chemical composition is shown in Table 3. The diameter of the electroslag remelting furnace crystallizer was Φ850mm. The mass fraction ratio of the electroslag remelting slag system was CaF2:Al2O3:SiO2 = 67:28:5. The amount of electroslag remelting slag used was 310kg. Arc initiation was achieved by direct arc initiation using a metal electrode. The voltage during slag melting was 45V, and the current was... 5000A, slag formation time 60 minutes; after slag formation, enter the normal smelting process, the melting rate during the electroslag remelting process is 680 kg / h; after the first electrode rod melts, the second electrode rod is exchanged to continue melting, the electrode exchange time is 55 seconds; after the normal smelting ends, enter the feeding stage, the feeding time is 100 minutes; after the feeding and capping is completed, the electroslag ingot is kept in the crystallizer for cooling, after cooling for 160 minutes, it is demolded, and after demolding, it is air-cooled to room temperature. The weight of the electroslag ingot is 6500 kg. After cooling, samples of drill cuttings from the head and tail of the electroslag ingot are taken for analysis of the manganese element mass fraction as shown in Table 3. The manganese element deviation at the head and tail of the electroslag ingot is 0.9%.

[0058] Table 3 Chemical composition analysis (%) of Mn18Cr18N steel

[0059]

[0060] It should be noted that the components or steps in the above embodiments can be interchanged, substituted, added, or deleted. Therefore, the combinations formed by these reasonable permutations and transformations should also fall within the protection scope of this invention, and the protection scope of this invention should not be limited to the above embodiments.

[0061] The above are exemplary embodiments disclosed in this invention. The order of the disclosed embodiments is merely for descriptive purposes and does not represent the superiority or inferiority of the embodiments. However, it should be noted that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the disclosed embodiments of this invention (including the claims) is limited to these examples. Various changes and modifications can be made without departing from the scope defined by the claims. The functions, steps, and / or actions of the methods according to the disclosed embodiments described herein do not need to be performed in any particular order. Furthermore, although the elements disclosed in the embodiments of this invention may be described or claimed individually, they may be understood as multiple unless explicitly limited to a singular.

[0062] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention (including the claims) is limited to these examples. Within the framework of the invention, technical features of the above embodiments or different embodiments can be combined, and many other variations of the different aspects of the invention as described above exist, which are not provided in the details for the sake of brevity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the invention should be included within the protection scope of the invention.

Claims

1. A method for controlling the uniformity of manganese element in Mn18Cr18N steel, characterized in that, The method includes: electroslag remelting an electrode rod to obtain an electroslag ingot, thereby preparing Mn18Cr18N steel; the electrode rod contains the following elements by mass percentage: C: 0.05%~0.1%, Mn: 18.0%~18.5%, Si: 0.3%~0.5%, P≤0.03%, S≤0.02%, Cr: 18.0%~20.0%, N≥0.6%, with the balance being Fe; The electroslag remelting method includes slag-forming and feeding steps. The slag-forming step includes adding 0.003% to 0.007% of the weight of electroslag ingot metallic manganese particles to the system 8 to 12 minutes before the end of slag-forming. The size of the metallic manganese particles is Φ1.0mm to Φ3.0mm. The electrode rod has a uniformly distributed cored wire containing metallic manganese along its axis. The metallic manganese has a mass of 90g / m to 200g / m. One end of the cored wire is flush with one end of the electrode rod, and the other end is 100mm to 200mm lower than the other end of the electrode rod. The weight corresponding to the 100mm to 200mm height is used for the shrinkage and capping process.

2. The method as described in claim 1, characterized in that, The electroslag remelting method further includes the following steps: arc initiation, melting, electrode replacement, melting and cooling; The electroslag remelting method is carried out in an electroslag remelting furnace crystallizer; The electrode replacement process involves electroslag ingots weighing 3t to 6t after electroslag remelting, and a single electrode rod weighing 2t to 4t before remelting. Once one electrode rod is melted, another electrode rod needs to be exchanged to continue melting. This process is completed within 2 minutes.

3. The method as described in claim 1, characterized in that, The composition of the slag in the electroslag remelting process is as follows, by mass fraction: CaF2:Al2O3:SiO2 = (60~70):(25~30):(2~5).

4. The method as described in claim 3, characterized in that, The amount of electroslag remelting slag used is 3.6% to 12% of the weight of the electrode rod.

5. The method as described in claim 2, characterized in that, The electrode rod has a diameter of Φ500mm~Φ600mm, and / or the diameter of the electroslag remelting furnace crystallizer has a diameter of Φ650mm~Φ850mm.

6. The method as described in claim 1, characterized in that, The slag-refining step involves a voltage of 40V~50V, a current of 3000A~5000A, and a slag-refining time of ≥50 minutes.

7. The method as described in claim 2, characterized in that, The melting rate of the smelting step is 500 kg / h to 720 kg / h.

8. The method as described in claim 1, characterized in that, The shrinkage time for the shrinkage step is ≥90 minutes.

9. The method as described in claim 2, characterized in that, The cooling step includes: keeping the electroslag ingot in the crystallizer for cooling, demolding it after the time is greater than 120 minutes, and cooling it to room temperature after demolding.

10. The Mn18Cr18N steel prepared by the method according to any one of claims 1 to 9, characterized in that, The manganese content of the Mn18Cr18N steel has a deviation of less than 0.5%.

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