Electroslag process with addition of rare earth in electroslag remelting process

Abstract

The present application relates to a kind of electric slag remelting process in electric slag process, electric slag is baked according to steel ingot baking specification before production;According to the mass percentage of slag system ratio is 65%-CaF2:25%-Al2O3:10%-CaO, lanthanum cerium rare earth silk is added in the above-mentioned slag system according to mass ratio 7:3, argon is used in remelting, and the crystallizer specification melting rate is controlled 380-450kg / h;According to the mass percentage of silica with 2~3% of slag quantity of slag material, electric slag ingot is taken out after mould and is put into furnace annealing, obtains certain yield, provides important basis for the influence of rare earth yield on material mechanical property, and the present application is added in electric slag process, different from the method of adding rare earth in existing steel.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of smelting technology, and particularly relates to an electric slag process for adding rare earth in the process of electroslag remelting applied to the field of ultra-high-strength and high-toughness materials, such as aerospace. BACKGROUND

[0002] Rare earth is a third type of sub-group element in the periodic table. The atom of rare earth element is very active in chemical property because of the outermost electron of 2. The lanthanide series element has unique chemical and physical properties due to the d electron and 4f electron, and has various important uses. If trace rare earth is added to steel, cast iron, non-ferrous metal and its alloy, and if the adding amount, adding method and adding time are appropriate, various properties of the materials can be improved; otherwise, the opposite effect will be caused due to the reasons of secondary oxidation, action with container material and uneven distribution of rare earth addition.

[0003] At present, various methods for adding rare earth in steel are applied, such as ladle internal pressing method, ingot mold internal hanging method, insertion method, continuous casting steel crystallizer internal feeding method, middle injection pipe internal feeding method, spraying method, electric slag using rare earth slag system and the like. Certain effect is obtained, but due to the reasons of secondary oxidation, action with container material and uneven addition, except for the crystallizer internal feeding method and the electric slag remelting using rare earth slag, the other methods all cause inclusion accumulation, unstable production and cannot achieve ideal effect. Therefore, it is necessary to expand based on the background, to invent a method for adding rare earth in the process of electroslag remelting, and to obtain certain yield, so as to provide important basis for studying the influence of rare earth yield on the mechanical properties of materials. SUMMARY

[0004] The present application aims at overcoming the deficiencies in the prior art and providing an electric slag process for adding rare earth in the process of electroslag remelting, which can obtain certain yield.

[0005] In order to achieve the above-mentioned purpose, the present application adopts the following technical scheme:

[0006] An electric slag process for adding rare earth in the process of electroslag remelting, which adopts low-cost high-toughness ultra-high-strength steel, and the grade is 35CrMnSiA in GB / T3077. The chemical composition includes C: 0.32-0.39%, Mn: 0.80-1.10%, Si: 1.10-1.40%, P≤0.020%, S≤0.010%, Ni:≤0.30%, Cr: 1.10-1.40%, Mo:≤0.10%, Cu:≤0.25%, and the balance is steel. The smelting mode is electric arc furnace smelting + ladle refining + vacuum degassing + electroslag remelting. The process steps for adding rare earth in the process of electroslag remelting are as follows:

[0007] Step 1), electrode blank: the surface oxide scale is cleaned during welding, the welding seam is cleaned after welding, and is placed in a baking oven for baking, and the electrode blank is baked strictly according to the steel ingot baking specification before electroslag production;

[0008] Step 2), slag amount and slag system: a self-prepared slag system is used, and the slag system is prepared according to the mass percentage of 65%-CaF2: 25%-Al2O3: 10%-CaO, wherein, in order to prevent lime from absorbing moisture, part of the lime is replaced by pre-melted slag, and the slag amount is 3-4% of the ingot weight;

[0009] Step 3), rare earth addition process: 7:3 lanthanum-cerium rare earth wire is added to the above-mentioned slag system according to the mass ratio, and the rare earth addition amount is calculated according to 0.15% of the ingot weight according to the mass percentage; considering that the rare earth is not resistant to high temperature and is easy to oxidize, the rare earth element is added in two batches: half is added together with the slag material, and the other half is added when the electrode blank alternately enters the crystallizer;

[0010] Step 4), gas protection: argon gas protection is used during remelting, the flow rate is 10-30 Nm3 / h, a soft asbestos cover is used to cover the upper opening of the crystallizer, and after power failure, the argon gas continues to be blown for 5-10 min, and the flow rate is 10-20 Nm3 / h;

[0011] Step 5), melting rate: the melting rate of the crystallizer is controlled to be 380-450 kg / h;

[0012] Step 6), deoxidizer: in order to control low aluminum, no aluminum is added during slagging and remelting, 2-3% of silicon dioxide is added with the slag material according to the mass percentage, and 0.1%-0.2% of silicon-calcium powder is added according to the silicon content of the base material during remelting for deoxidation;

[0013] Step 7), electroslag ingot mold drawing condition: the surface of the electroslag ingot is observed after the mold is drawn, the surface quality is good, and the mold is drawn and then the furnace is annealed.

[0014] Compared with the prior art, the present application has the following advantages:

[0015] The electroslag process for adding rare earth in the electroslag remelting process provided by the present application has an economical, simple and convenient adding method, can obtain a certain yield, and provides an important basis for studying the influence of rare earth yield on the mechanical properties of materials. Moreover, the present application is added in the electroslag process, which is different from the existing method of adding rare earth in steel. Table 1 shows the influence of rare earth yield on the mechanical properties of 35CrMnSiA, especially the impact energy. As can be seen from the data in the table, the addition of 7:3 lanthanum-cerium rare earth wire used in the present application has little effect on the strength, the impact energy is the highest when the La+Ce yield is 25ppm, and the impact energy is obviously reduced when the yield is higher than 35ppm.

[0016] Table 1 Influence of rare earth yield on mechanical properties

[0017] Attached Figure Description

[0018] Figure 1 This is a schematic diagram showing the lanthanum, cerium, and rare earth content from the subsurface to the center of the electroslag ingot of the present invention. Detailed Implementation

[0019] The technical solution of the present invention will be described below with specific embodiments, but the scope of protection of the present invention is not limited thereto, and it is equally applicable to other specifications of products produced using this material.

[0020] This invention uses low-cost, high-toughness, ultra-high-strength steel, grade 35CrMnSiA from GB / T3077. Its main chemical composition by mass percentage is: C: 0.32-0.39%, Mn: 0.80-1.10%, Si: 1.10-1.40%, P≤0.020%, S≤0.010%, Ni: ≤0.30%, Cr: 1.10-1.40%, Mo: ≤0.10%, Cu: ≤0.25%; the balance is steel.

[0021] This low-cost, high-toughness, ultra-high-strength steel is produced using an electric arc furnace smelting process followed by ladle refining, vacuum degassing, and electroslag remelting. During the electroslag remelting process, lanthanum-cerium rare earth wire in a 7:3 ratio is added. The rare earth wire is ф10mm in diameter and is cut into several ф10*100mm sections before production. The electroslag remelting process for adding rare earth is as follows:

[0022] Step 1) Electrode blank: During welding, the surface oxide slag is cleaned. After welding, the weld seam is cleaned, and the blank is placed in a baking oven for baking. Baking is strictly performed according to the steel ingot baking specifications before electroslag production. Production details are shown in Table 2 below:

[0023] Table 2. Electroslag Ingot Production Status

[0024]

[0025] Step 2) Slag quantity and slag system: Self-prepared slag system is adopted, and the slag system ratio is 65%-CaF2:25%-Al2O3:10%-CaO by mass percentage. In order to prevent lime from absorbing moisture, the lime part is replaced by pre-melted slag, and the slag quantity is 130kg.

[0026] Step 3) Rare Earth Addition Process: During electroslag production, 4 kg of 7:3 lanthanum-cerium rare earth wire is added to the above slag system, with a slag volume of 134 kg. Considering the characteristics of rare earth elements being susceptible to high temperatures and oxidation, the rare earth elements are added in two batches: 2 kg is added with the slag material, and 2 kg is added when the electrode billets alternately enter the crystallizer.

[0027] Step 4) Gas protection: Use down-blown argon gas for protection during remelting, with a flow rate of 10-30 Nm³. 3 / h, cover the top of the crystallizer tightly with soft asbestos; after power failure, continue to blow argon gas for 5-10 minutes at a flow rate of 10-20 Nm3 / h.

[0028] Step 5) Melting rate: For crystallizers with diameters of Φ580 / Φ620mm (Φ600 / Φ640mm), the melting rate should be controlled at 380-450 kg / h.

[0029] Step 6) Deoxidizer: In order to control low aluminum, no aluminum was added during the slag and remelting process. 2 kg of silicon dioxide was added with the slag. During the remelting process, calcium silicate powder was added according to the silicon content of the base material for deoxidation, as shown in Table 3 below.

[0030] Table 3 Deoxygenation regime

[0031]

[0032] Step 7) Electroslag ingot mold lifting status: Observe the surface of the electroslag ingot after mold lifting. The surface quality is good. After mold lifting, load it into the furnace for annealing.

[0033] The lanthanum and cerium rare earth elements in the 7A224237 and 7A7A224238 electroslag ingots produced according to the example were tested from subcutaneous to central levels at the ingot tail and riser, respectively. Details are attached. Figure 1 .

[0034] From the appendix Figure 1 As can be seen, the contents of both rare earth elements are greater than 5 ppm, with lanthanum content ranging from 7.5 to 17.5 ppm and cerium content ranging from 13 to 37.5 ppm. The average yield is 3%, proving that this method of adding rare earth elements can achieve a certain yield. This method is feasible. Subsequently, we also obtained different yields by increasing or decreasing the amount of rare earth elements added, and used this to further study the effect of yield on the mechanical properties of materials, especially on impact energy.

Claims

1. An electroslag process with addition of rare earth elements in electroslag remelting process, characterized in that: The low-cost high-toughness ultra-high-strength steel is 35CrMnSiA in GB / T3077, and the chemical composition includes C: 0.32-0.39%, Mn: 0.80-1.10%, Si: 1.10-1.40%, P≤0.020%, S≤0.010%, Ni: ≤0.30%, Cr: 1.10-1.40%, Mo: ≤0.10%, Cu: ≤0.25%, and the rest is steel; and the smelting method is electric arc furnace smelting + ladle refining + vacuum degassing + electroslag remelting, and the process steps of adding rare earth in the electroslag are as follows: Step 1), electrode billet: clean the surface oxide slag skin during welding, clean the welding seam after welding, and place it in the baking oven for baking, and strictly bake according to the steel ingot baking specification before electroslag production; Step 2), slag amount and slag system: use self-prepared slag system, and the slag system is 65%-CaF2: 25%-Al2O3: 10%-CaO according to the mass percentage, wherein in order to prevent lime from absorbing moisture, part of the lime is replaced with pre-melted slag, and the slag amount is 3-4% of the ingot weight; Step 3), rare earth addition process: add 7:3 lanthanum-cerium rare earth wire in the above slag system according to the mass ratio, and the rare earth addition amount is 0.15% of the ingot weight according to the mass percentage; considering that rare earth is not resistant to high temperature and is easy to oxidize, the rare earth elements are added in two batches: half of them are added with the slag, and the other half are added when the electrode billet alternately enters the crystallizer; Step 4), gas protection: use down-blowing argon gas protection during remelting, the flow rate is 10-30 Nm3 / h, the upper opening of the crystallizer is covered with soft asbestos, and after power failure, continue to blow argon gas for 5-10 min, the flow rate is 10-20 Nm3 / h; Step 5), melting rate: the melting rate of the crystallizer is controlled to be 380-450 kg / h; Step 6), deoxidizer: in order to control low aluminum, no aluminum is added during slagging and remelting, 2-3% of silicon dioxide is added with the slag according to the mass percentage, and 0.1%-0.2% of silicon-calcium powder is added according to the silicon content of the base material for deoxidation during remelting; Step 7), electroslag ingot mold drawing condition: observe the surface of the electroslag ingot mold drawing, the surface quality is good, and the mold is drawn after annealing in the furnace.

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