An electroslag remelting slag system for controlling nitrogen content in alloys

Abstract

An electroslag remelting slag system for controlling the nitrogen content in an alloy, wherein the weight percentages of the components of the slag system are: CaF2: 55-70%, Al2O3+AlN: 15-20%, CaO: 5-12%, MgO: 3-10%, SiO2: 1-5%. The electroslag remelting slag system for controlling the nitrogen content in an alloy provided by the present invention uses a nitrogen-containing slag system to balance the nitrogen concentration in molten steel, so that the nitrogen content is stable and controllable, thereby improving the strength and corrosion resistance of nitrogen-containing steel.

Description

Technical Field

[0001] The invention relates to the technical field of electroslag remelting, in particular to an electroslag remelting slag system for controlling the nitrogen content in an alloy. Background Art

[0002] Normally, nitrogen is considered to be one of the harmful impurities in steel. Although the solubility of nitrogen in liquid steel is very low under normal pressure, this small amount of nitrogen can cause aging embrittlement of steel. However, in high-nitrogen steel, nitrogen as an alloying element can interact with other alloying elements in steel, giving the steel many excellent properties. High-nitrogen steel has excellent mechanical properties and corrosion resistance. Nitrogen, as an important alloying element in steel, has broad development prospects. The research and application of high-nitrogen steel are increasingly valued. In order to give full play to the advantages of nitrogen alloying to increase the strength and corrosion resistance of steel, various new high-nitrogen steel smelting processes are also constantly being studied and developed.

[0003] At present, high vacuum induction furnaces are smelted under vacuum, with extremely low nitrogen partial pressure and fast denitrification rate of molten steel, making it difficult to increase nitrogen. Nitrogen is mainly increased by adding nitrogen-containing intermediate alloys after filling the furnace with argon or nitrogen, and the nitrogen recovery rate is unstable. Summary of the invention

[0004] The purpose of the present invention is to provide an electroslag remelting slag system for controlling the nitrogen content in the alloy in view of the shortcomings of the prior art, and to balance the nitrogen concentration in the molten steel by using the nitrogen-containing slag system so that the nitrogen content is stable and controllable, thereby improving the strength and corrosion resistance of the nitrogen-containing steel.

[0005] The technical solution of the present invention is:

[0006] The invention discloses an electroslag remelting slag system for controlling the nitrogen content in an alloy. The weight percentages of the components of the slag system are as follows: CaF2: 55-70%, Al2O3+AlN: 15-20%, CaO: 5-12%, MgO: 3-10%, and SiO2: 1-5%.

[0007] A further technical solution is to adjust the addition amount of the slag-based AlN and Al2O3 and the target nitrogen content of the electroslag ingot, wherein the addition amount of Al2O3 increases, the addition amount of AlN decreases; the addition amount of Al2O3 decreases, the addition amount of AlN increases; if the addition amount of AlN reaches a maximum value of Al2O3+AlN: 15-20%, Al2O3 is 0; if the addition amount of Al2O3 reaches a maximum value of Al2O3+AlN: 15-20%, AlN is 0.

[0008] A further technical solution is that the weight percentages of the components of the slag system are: CaF2: 59%, AlN: 20%, CaO: 11%, MgO: 7%, and SiO2: 3%.

[0009] A further technical solution is that the weight percentages of the components of the slag system are: CaF2: 55%, Al2O3: 18%, CaO: 12%, MgO: 10%, and SiO2: 5%.

[0010] A further technical solution is that the weight percentages of the components of the slag system are: CaF2: 70%, Al2O3: 10%, AlN: 10%, CaO: 5%, MgO: 3%, and SiO2: 2%.

[0011] The electroslag remelting slag system for controlling the nitrogen content in the alloy of the present invention is mainly composed of various fluorides and oxides:

[0012] Among them, CaF2 can reduce the melting point, viscosity and surface tension of the slag and increase the fluidity of the slag pool;

[0013] Al2O3 can significantly reduce the electrical conductivity of slag and reduce power consumption; replacing Al2O3 in the slag system with AlN or adding AlN to the slag system, AlN can balance the concentration of N element in the slag pool and the molten pool, avoid excessive burning of N element in steel, and stably control the N element content; however, too much alumina will increase the melting temperature and viscosity of the slag and reduce the desulfurization effect, so the alumina content needs to be properly controlled. Aluminum nitride, as a partial or complete substitute for alumina, should not exceed the upper limit of the alumina content.

[0014] CaO can increase the basicity of slag and improve desulfurization efficiency;

[0015] MgO will form a semi-solidified film on the surface of the slag pool, inhibiting the transfer of oxygen from variable-valence oxides in the slag to the molten metal pool, while providing trace amounts of Mg elements to the molten steel.

[0016] SiO2 can lower the melting point of the slag, make the surface of the ingot smooth, and also reduce the electrical conductivity of the slag.

[0017] The electroslag remelting slag system for controlling the nitrogen content in the alloy of the present invention uses a nitrogen-containing slag system to balance the nitrogen concentration in the molten steel, so that the nitrogen content is stable and controllable, thereby improving the strength and corrosion resistance of the nitrogen-containing steel. The problem of fast denitrification rate of molten steel and difficult nitrogen addition is solved. Taking the S21800 alloy as an example, its initial nitrogen content is 0.16%, and the nitrogen content is stabilized between 0.28% and 0.33% after remelting. The difference in nitrogen content from the top to the bottom of the electroslag ingot is extremely small, the nitrogen content is evenly distributed, and the yield is stable. DETAILED DESCRIPTION

[0018] Example 1

[0019] An electroslag remelting slag system for controlling the nitrogen content in an alloy, wherein the weight percentages of the components of the slag system are: CaF2: 59%, AlN: 20%, CaO: 11%, MgO: 7%, SiO2: 3%, and the slag amount is 5kg.

[0020] The specific steps of preparing electroslag ingots using the above slag system are as follows:

[0021] 1) The composition and weight percentage of the alloy in this embodiment are: Cr: 17.3, Ni: 8.4, Mn: 8.1, Si: 4.1, C: 0.05, N: 0.16, Fe balance; the metal raw materials are melted and refined in a vacuum induction melting furnace and then cast into a vacuum induction ingot, and then the surface of the vacuum induction ingot is sanded clean to prepare an electroslag remelting electrode. Electrode diameter: φ100mm; electrode length: L=1300mm.

[0022] 2) Take 5 kg of electroslag remelting slag system with controlled nitrogen content in the alloy, the weight percentage of each component of the slag system is CaF2: 59%, AlN: 20%, CaO: 11%, MgO: 7%, SiO2: 3%. Fully mix the components of the slag system, bake at 800℃ for 6-8h, melt the slag in the crystallizer to start the arc; slowly insert the electrode obtained in step 1) into the molten slag pool, and pass nitrogen for full protection, the nitrogen flow rate is 0.5L / min / m 2， After the arc is started, adjust the voltage to 35-50V and the current to 2000-4000A to melt the material;

[0023] The key smelting parameters are as follows:

[0024] a. During the startup phase, current control is adopted, and current is continuously variable: the initial current is 3000A and maintained for 5 minutes, the current is increased at a rate of 200A / min to a maximum of 4000A, and then maintained for 20 minutes; the current is reduced at a rate of 200A / min to 2000A;

[0025] b. During the smelting stage, current and voltage control is adopted, and the current is reduced in advance: the initial current is 2000A, and the current starts to be reduced after the electrode (initial electrode weight is 85kg) is melted to 70kg, and the current is reduced at a rate of 200A / min and maintained at 3500A; the voltage control setting is maintained at 45V.

[0026] c. During the filling stage, current control is adopted and the current is continuously reduced: filling begins after 10kg of electrode remains, and the current is reduced at a rate of 150A / min during the filling process, and maintained at 2000A. Smelting is stopped after 2kg of electrode remains.

[0027] 3) Before the end of remelting, heat shrinkage is performed to obtain a steel ingot; the obtained steel ingot is placed in a crystallizer and cooled for ≥15 minutes, and the diameter of the electroslag crystallizer is φ160mm; demolding is performed to obtain an electroslag ingot. After demolding, the electroslag ingot is protected by hood cooling + nitrogen until the temperature of the electroslag ingot is less than 400°C.

[0028] 4) Sampling and analysis

[0029] Three sampling positions are roughly evenly distributed at the top, middle and bottom of the electroslag ingot, with a longitudinal spacing of about 150 mm. Samples are taken from the surface of the electroslag ingot and analyzed using an oxygen, nitrogen and hydrogen analyzer. The N element detection results at different positions are shown in Table 1:

[0030] Table 1

[0031]

[0032] Example 2

[0033] An electroslag remelting slag system for controlling the nitrogen content in an alloy, wherein the weight percentages of the components of the slag system are: CaF2: 55%, Al2O3: 18%, CaO: 12%, MgO: 10%, SiO2: 5%, and the slag amount is 5kg.

[0034] The specific steps of preparing electroslag ingots using the above slag system are as follows:

[0035] 1) The composition and weight percentage of the alloy in this embodiment are: Cr: 17.3, Ni: 8.4, Mn: 8.1, Si: 4.1, C: 0.05, N: 0.16, Fe balance; the metal raw materials are melted and refined in a vacuum induction melting furnace and then cast into a vacuum induction ingot, and then the surface of the vacuum induction ingot is sanded clean to prepare an electroslag remelting electrode. Electrode diameter: φ100mm; electrode length: L=1300mm.

[0036] 2) Take 5 kg of electroslag remelting slag system with controlled nitrogen content in the alloy, the weight percentage of each component of the slag system is CaF2: 55%, Al2O3: 18%, CaO: 12%, MgO: 10%, SiO2: 5%. Fully mix the components of the slag system, bake at 800℃ for 6-8h, melt the slag in the crystallizer to start the arc; slowly insert the electrode obtained in step 1) into the molten slag pool, and pass nitrogen for full protection, the nitrogen flow rate is 0.5L / min / m 2 , after power on and arcing, adjust the voltage to 35-50V and the current to 2000-4100A to chemically react the material;

[0037] The key smelting parameters are as follows:

[0038] a. During the startup phase, current control is adopted, and the current is continuously variable: the initial current is 2500A and maintained for 5 minutes, the current is increased at a rate of 200A / min to a maximum of 4100A, and then maintained for 20 minutes; the current is reduced at a rate of 200A / min to 2100A;

[0039] b. During the smelting stage, current and voltage control are adopted, and the current is reduced in advance: the initial current is 2000A, and the current starts to be reduced after the electrode (initial electrode weight is 95kg) is melted to 80kg, and the current is reduced at a rate of 200A / min and maintained at 3500A; the voltage control setting is maintained at 45V.

[0040] c. During the filling stage, current control is adopted and the current is continuously reduced: filling begins after 10kg of electrode remains, and the current is reduced at a rate of 150A / min during the filling process, and maintained at 2000A. Smelting is stopped after about 3kg of electrode remains.

[0041] 3) Before the end of remelting, heat shrinkage is performed to obtain a steel ingot; the obtained steel ingot is placed in a crystallizer and cooled for ≥15 minutes, and the diameter of the electroslag crystallizer is φ160mm; demolding is performed to obtain an electroslag ingot. After demolding, the electroslag ingot is protected by hood cooling + nitrogen until the temperature of the electroslag ingot is less than 400°C.

[0042] 4) Sampling and analysis

[0043] Three sampling positions are roughly evenly distributed at the top, middle and bottom of the electroslag ingot, with a longitudinal spacing of about 150 mm. Samples are taken from the surface of the electroslag ingot and analyzed using an oxygen, nitrogen and hydrogen analyzer. The N element detection results at different positions are shown in Table 2:

[0044] Table 2

[0045]

[0046] Example 3

[0047] An electroslag remelting slag system for controlling the nitrogen content in an alloy, wherein the weight percentages of the components of the slag system are: CaF2: 70%, Al2O3: 10%, AlN: 10%, CaO: 5%, MgO: 3%, SiO2: 2%, and the slag amount is 5kg.

[0048] The specific steps of preparing electroslag ingots using the above slag system are as follows:

[0049] 1) The composition and weight percentage of the alloy in this embodiment are: Cr: 17.3, Ni: 8.4, Mn: 8.1, Si: 4.1, C: 0.05, N: 0.16, Fe balance; the metal raw materials are melted and refined in a vacuum induction melting furnace and then cast into a vacuum induction ingot, and then the surface of the vacuum induction ingot is sanded clean to prepare an electroslag remelting electrode. Electrode diameter: φ100mm; electrode length: L=1300mm.

[0050] 2) Take 5 kg of electroslag remelting slag system with controlled nitrogen content in the alloy, the weight percentage of each component of the slag system is CaF2: 70%, Al2O3: 10%, AlN: 10%, CaO: 5%, MgO: 3%, SiO2: 2%. Fully mix the components of the slag system, bake at 800℃ for 6-8h, melt the slag in the crystallizer to start the arc; slowly insert the electrode obtained in step 1) into the molten slag pool, and pass nitrogen for full protection, the nitrogen flow rate is 0.5L / min / m 2 , after power on and arcing, adjust the voltage to 35-50V and the current to 2000-4100A to chemically react the material;

[0051] The key smelting parameters are as follows:

[0052] a. During the startup phase, current control is adopted, and current is continuously variable: the initial current is 2800A and maintained for 5 minutes, the current is increased at a rate of 200A / min to a maximum of 4000A, and then maintained for 20 minutes; the current is reduced at a rate of 200A / min to 2000A;

[0053] b. During the smelting stage, current and voltage control is adopted, and the current is reduced in advance: the initial current is 2000A, and the current starts to be reduced after the electrode (initial electrode weight is 85kg) is melted to 70kg, and the current is reduced at a rate of 200A / min and maintained at 3500A; the voltage control setting is maintained at 45V.

[0054] c. During the filling stage, current control is adopted and the current is continuously reduced: filling begins after 10kg of electrode remains, and the current is reduced at a rate of 150A / min during the filling process, and maintained at 2000A. Smelting is stopped after about 2kg of electrode remains.

[0055] 3) Before the end of remelting, heat shrinkage is performed to obtain a steel ingot; the obtained steel ingot is placed in a crystallizer and cooled for ≥15 minutes, and the diameter of the electroslag crystallizer is φ160mm; demolding is performed to obtain an electroslag ingot. After demolding, the electroslag ingot is protected by hood cooling + nitrogen until the temperature of the electroslag ingot is less than 400°C.

[0056] 4) Sampling and analysis

[0057] Three sampling positions are roughly evenly distributed at the top, middle and bottom of the electroslag ingot, with a longitudinal spacing of about 150 mm. Samples are taken from the surface of the electroslag ingot and analyzed using an oxygen, nitrogen and hydrogen analyzer. The N element detection results at different positions are shown in Table 3:

[0058] Table 3

[0059]

[0060] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification made to the present invention by those skilled in the art without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. An electroslag remelting slag system for controlling nitrogen content in an alloy, characterized in that: The weight percentages of the components of the slag system are: CaF2: 55-70%, Al2O3+AlN: 20%, CaO: 5-12%, MgO: 3-10%, SiO2: 1-5%; the addition amounts of AlN and Al2O3 in the slag system are adjusted according to the target nitrogen content of the electroslag ingot, wherein the addition amount of Al2O3 increases, the addition amount of AlN decreases; the addition amount of Al2O3 decreases, the addition amount of AlN increases; if the addition amount of AlN reaches the maximum value of Al2O3+AlN: 20%, Al2O3 is 0; if the addition amount of Al2O3 reaches the maximum value of Al2O3+AlN: 20%, AlN is 0.

2. The slag system according to claim 1, characterized in that: The weight percentages of the components of the slag system are: CaF2: 59%, AlN: 20%, CaO: 11%, MgO: 7%, and SiO2: 3%.

3. The slag system according to claim 1, characterized in that: The weight percentages of the components of the slag system are: CaF2: 70%, Al2O3: 10%, AlN: 10%, CaO: 5%, MgO: 3%, and SiO2: 2%.

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