A method for improving the quality of corrosion-resistant alloy die-cast electrode rods

Abstract

The present invention provides a method for improving the quality of corrosion-resistant alloy die-cast electrode rods, which includes the production process steps of electric furnace → LF furnace → VOD refining → die-cast electrode rods → electroslag remelting → forging → annealing in sequence, adopts protective pit casting and bakes the steel ingot mold at 200-300°C, significantly reduces the cooling rate of the molten steel in the ingot mold, makes it fully shrink, and then greatly reduces or avoids the generation of shrinkage cavities and loose defects. At the same time, protective slag casting is adopted to fully utilize the effect of Al particles in the protective slag to generate heat and supplement heat, so that the inclusions in the molten steel have enough time to float to the slag and be absorbed, thereby improving the purity of the molten steel. The method of the present invention can solve the problems of shrinkage cavities, looseness and inclusion aggregation inside the corrosion-resistant alloy die-cast electrode rod, and obtain an electrode rod with a denser internal structure and higher purity, thereby avoiding the appearance of black spots in the low-magnification structure of ordinary corrosion-resistant alloy finished products, effectively improving product quality and reducing production costs.

Description

Technical Field

[0001] The present invention relates to the field of metallurgical technology, and in particular to a method for improving the quality of a corrosion-resistant alloy die-cast electrode rod. Background Art

[0002] Corrosion-resistant alloy is a super alloy resistant to corrosion by special media, mainly including iron-based alloy, nickel-based alloy and active metal, etc. Here specifically refers to nickel-based corrosion-resistant alloy, including Ni-Cr alloy, Ni-Cr-Mo alloy, Ni-Cu alloy, etc., because of its high strength and good resistance to high-temperature oxidation, hydroxide and various acid corrosion, especially in high-temperature environment, it is widely used in the manufacture of various corrosion-resistant parts in petroleum, chemical industry, electric power and other industries.

[0003] At present, the production process of high-precision corrosion-resistant alloy is EBT→LF→VOD→die-cast electrode rod→forged electrode→electroslag remelting→forging→annealing, and the production process of ordinary corrosion-resistant alloy is EBT→LF→VOD→die-cast electrode rod→electroslag remelting→forging→annealing. Compared with the production process of high-precision corrosion-resistant alloy, the production process of ordinary alloy omits the step of forging electrode, but the corrosion-resistant alloy finished product produced by the ordinary alloy production process often has black spot defects during low-magnification inspection, and it is composed of white pits and black particles under the magnification of scanning electron microscope. The existence of such defects poses a fatal risk to the later processing and service of the material.

[0004] Therefore, it is particularly important to improve the quality of die-cast electrode rods in the production process of ordinary corrosion-resistant alloys so that the finished products do not have low-magnification black spots. In the prior art, there are very few patents related to the improvement of the quality of corrosion-resistant alloy die-cast electrode rods or inventions related to the implementation of industrial equipment transformation, which makes the cost of implementation extremely high. For example: Invention patent CN 103990759 A provides a method for improving the casting quality of nickel-based high-temperature alloy ingots, which adopts the method of applying a suspension in the mold, baking, and finally pouring. This method is suitable for smelting and pouring small ingots (Ф280*1000mm) in a 500kg vacuum induction furnace; Invention patent CN 103962517A provides a casting device and a casting method for die-cast large-size electrode rods, which adopts the method of adding a die-cast chassis so that the molten steel flowing through the steel flow channel first passes through the chassis and then enters the ingot mold, which can reduce the potential energy of the molten steel when it emerges, and the situation that the emergence rate is too large due to the high distance of falling, and reduce the surface quality of the electrode rods such as splashing of the ingot caused by the emergence of too large seedlings.

[0005] Therefore, in order to improve the quality of corrosion-resistant alloy electrode rods and ultimately improve the quality of finished products, it is urgent to develop a method for improving the quality of corrosion-resistant alloy electrode rods. Summary of the invention

[0006] Based on the above technical problem that low-magnification black spots exist in the corrosion-resistant alloy finished product in the prior art, a method for improving the quality of corrosion-resistant alloy die-cast electrode rods is provided.

[0007] The technical means adopted by the present invention are as follows:

[0008] A method for improving the quality of a corrosion-resistant alloy die-cast electrode rod comprises the following production process steps: electric furnace → LF furnace → VOD refining → die-cast electrode rod → electroslag remelting → forging → annealing. The specific steps are as follows:

[0009] 1) Electric furnace: the charge is melted, the temperature of molten steel is ≥1600℃, oxygen is blown for decarburization, and the final carbon content is controlled at 0.25~0.65%;

[0010] 2) LF furnace: enter the tank, add lime, refined slag and steel slag for reduction, and control the temperature between 1640℃~1690℃;

[0011] 3) VOD refining: put into the tank, vacuum carbon deoxidation, ultimate vacuum degree ≤300Pa, holding time ≥15min; break the air, add active lime, fluorite powder, Al ingot, vacuum slag; cover and evacuate, blow argon and stir to slag, slag slag time ≥20min, measure temperature, take samples, and tap steel;

[0012] 4) Die-cast electrode rod: the hanging bag temperature is 1510~1520℃, and the casting is carried out in the insulation pit;

[0013] 5) Electroslag remelting: voltage 70~40V, current 6000~13000A;

[0014] 6) Forging: two punches and two pulls, one fire to make it a success;

[0015] 7) Annealing: heating temperature 820 ~ 880 ℃, cooling with the furnace to ≤ 300 ℃ and air cooling.

[0016] Furthermore, the alloy is a nickel-based high-temperature alloy with a grade of UNS N08825.

[0017] Furthermore, the ingot mold is thoroughly cleaned before pouring, and the ingot mold is baked to a temperature of 200-300°C.

[0018] Furthermore, a special mold slag is used in the casting process, which is composed of the following components in weight percentage:

[0019] CaO: 20% to 45%, Al2O3: 5% to 20%, Na2O: 3% to 10%, CaF2: 5% to 15%, Al particles: 10% to 25% and inevitable impurities, the sum of the weight percentages of the above components is 100%.

[0020] Furthermore, the particle size of the mold slag is distributed between 100 and 300 meshes, wherein the particle size greater than 200 meshes accounts for more than 70% of the total weight.

[0021] Furthermore, the protective slag is hung twice, and the hanging positions are respectively 200-400 mm and 600-800 mm from the bottom of the ingot mold;

[0022] Furthermore, the protection pit is pre-dried two hours before pouring so that the ambient temperature in the pit is maintained above 50°C.

[0023] The quality improvement mechanism of the electrode rod of the present invention is as follows:

[0024] The main reason for the appearance of black spots in the low-magnification structure of the finished corrosion-resistant alloy is that the internal shrinkage, looseness and slag inclusions of the electrode rod fail to quickly form molten droplets when encountering strong current during the electroslag remelting process, but fall into the molten pool in the form of blocks or particles, and solidify rapidly under the rapid cooling of the crystallizer. The subsequent thermal deformation process can only be reduced but not completely removed, so black spots appear in the low-magnification structure of the finished product, referred to as black spots. The essence is the segregation of alloy elements and the aggregation of small particle inclusions.

[0025] The present invention adopts protection pit casting and bakes the steel ingot mold at 200-300°C. Compared with the common ground casting and ingot mold baking temperature of 30-100°C, the cooling rate of the molten steel in the ingot mold can be significantly reduced, so that the molten steel has sufficient time to compensate for shrinkage, thereby greatly reducing or avoiding the generation of shrinkage cavities and loose defects.

[0026] The present invention adopts special protective slag for casting, fully utilizing the heat-generating and heat-supplementing effect of Al particles in the protective slag, so that inclusions in the molten steel have enough time to float to the slag and be absorbed, thereby improving the purity of the molten steel.

[0027] The purpose of the present invention of hanging protective slag in batches is to prevent the one-time protective slag from burning too quickly and becoming thinner to lose its protective effect, and to prevent the one-time protective slag from hanging too much slag to cause local slag curling.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] The method of the present invention can solve the problems of shrinkage cavities, looseness and inclusion aggregation defects that appear inside the corrosion-resistant alloy die-cast electrode rod, obtain an electrode rod with a denser internal structure and higher purity, and prevent the electrode rod from falling off or falling off in the form of particles during the electroslag remelting process, thereby avoiding the appearance of black spots in the low-magnification structure of ordinary corrosion-resistant alloy finished products, effectively improving product quality and reducing production costs. DETAILED DESCRIPTION

[0030] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are clearly and completely described. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0032] Example 1

[0033] In this embodiment, an electric furnace + LF furnace + VOD refining is used to smelt a furnace of UNS N08825 corrosion-resistant alloy, which is cast into an electrode rod of 7.85t, φ570mm×3900mm, electroslag is remelted into an electroslag ingot of φ600mm, forged into a square billet of 100×100mm, and annealed to obtain a finished corrosion-resistant alloy. The specific composition of the electrode rod is: C 0.02%, Si 0.45%, Mn 0.65%, Ni42.0%, Cr 21.5%, Fe 30.21%, Cu 1.50%, S 0.015%, Al 0.15%, Ti 1.0%, Mo 2.5%.

[0034] The specific requirements and steps are as follows:

[0035] 1. Electric furnace: The charge is melted, the molten steel temperature is 1630℃, oxygen is blown for decarburization, and the final carbon content is controlled at 0.45%;

[0036] 2. LF furnace: enter the tank, add lime, refined slag, and steel slag for reduction, and control the temperature at 1660℃;

[0037] 3. VOD refining: put into the tank, vacuum carbon deoxidation, ultimate vacuum degree 275Pa, hold time 18min; break the air, add active lime, fluorite powder, Al ingot, vacuum slag; cover and evacuate, blow argon and stir slag, slag slag time 25min, measure temperature, take samples, tap steel;

[0038] 4. Die-cast electrode rod: hanging bag temperature 1510℃, protection pit casting;

[0039] 5. Before pouring, clean the ingot mold thoroughly and bake the ingot mold to 260℃.

[0040] 6. Special protective slag is used in the casting process: its weight percentage chemical composition is: CaO: 41%, Al2O3: 18%, Na2O: 8%, CaF2: 13%, Al particles: 20%. The particle size distribution is between 100 and 300 meshes, of which the particle size greater than 200 mesh accounts for more than 70% of the total weight.

[0041] 7. The protective slag is hung twice, and the hanging positions are 300mm and 700mm from the bottom of the ingot mold respectively;

[0042] 8. Pre-dry the protection pit two hours before pouring, and maintain the ambient temperature in the pit between 60 and 80°C.

[0043] 9. Electroslag remelting: voltage 60-50V, current 8000-11000A;

[0044] 10. Forging: two punches and two pulls, one fire makes it a success;

[0045] 11. Annealing: heating temperature 860℃, cooling to 280℃, air cooling;

[0046] After the finished corrosion-resistant alloy produced by this process was treated with hot acid etching, no black spots appeared in the macrostructure.

[0047] Example 2

[0048] This embodiment adopts electric furnace + LF furnace + VOD refining to smelt a furnace of UNS N08825 corrosion-resistant alloy, and casts it into 3.22t, Φ400mm×3200mm electrode rods. The electroslag is remelted into φ300mm electroslag ingots, forged into φ150mm round billets, and annealed to obtain the finished corrosion-resistant alloy. The specific composition of the electrode rod is: C 0.01%, Si 0.45%, Mn 0.60%, Ni40.0%, Cr 20.0%, Fe 33.77%, Cu 1.50%, S 0.015%, Al 0.15%, Ti 1.0%, Mo 2.5%.

[0049] The specific requirements and steps are as follows:

[0050] 1. Electric furnace: charge is melted, molten steel temperature is 1630℃, oxygen is blown for decarburization, and the final carbon content is controlled at 0.38%;

[0051] 2. LF furnace: enter the tank, add lime, refined slag, and steel slag for reduction, and control the temperature at 1660℃;

[0052] 3. VOD refining: put into the tank, vacuum carbon deoxidation, ultimate vacuum degree 270Pa, hold time 18min; break the air, add active lime, fluorite powder, Al ingot, vacuum slag; cover and evacuate, blow argon and stir slag, slag slag time 25min, measure temperature, take samples, tap steel;

[0053] 4. Die-cast electrode rod: hanging bag temperature 1510℃, protection pit casting;

[0054] 5. Before pouring, clean the ingot mold thoroughly and bake the ingot mold to 280℃.

[0055] 6. Special protective slag is used in the casting process: its weight percentage chemical composition is: CaO: 43%, Al2O3: 14%, Na2O: 10%, CaF2: 15%, Al particles: 18%. The particle size distribution is between 100 and 300 meshes, of which the particle size greater than 200 mesh accounts for more than 70% of the total weight.

[0056] 7. The protective slag is hung twice, and the hanging positions are 300mm and 700mm from the bottom of the ingot mold respectively;

[0057] 8. Pre-dry the protection pit two hours before pouring, and maintain the ambient temperature in the pit between 60 and 80°C.

[0058] 9. Electroslag remelting: voltage 50-40V, current 7000-9000A;

[0059] 10. Forging: two punches and two pulls, one fire makes it a success;

[0060] 11. Annealing: heating temperature 840℃, cooling to 280℃, air cooling;

[0061] After the finished corrosion-resistant alloy produced by this process was treated with hot acid etching, no black spots appeared in the macrostructure.

[0062] Comparative Example

[0063] A furnace of UNS N08825 corrosion-resistant alloy was smelted by electric furnace + LF furnace + VOD refining, and cast into 7.85t, Ф570mm×3900mm electrode rods, electroslag remelted into φ600mm electroslag ingots, forged into φ180mm round billets, and annealed to obtain the finished corrosion-resistant alloy. The specific composition of the electrode rod is: C 0.01%, Si 0.39%, Mn 0.54%, Ni 43.5%, Cr21.5%, Fe 28.49%, Cu 1.50%, S 0.015%, Al 0.15%, Ti 1.10%, Mo 2.8%.

[0064] The specific requirements and steps are as follows:

[0065] 1. Electric furnace: charge is melted, molten steel temperature is 1610℃, oxygen is blown for decarburization, and the final carbon content is controlled at 0.50%;

[0066] 2. LF furnace: enter the tank, add lime, refined slag, and steel slag for reduction, and control the temperature at 1650℃;

[0067] 3. VOD refining: put into the tank, vacuum carbon deoxidation, ultimate vacuum degree 270Pa, hold time 18min; break the air, add active lime, fluorite powder, Al ingot, vacuum slag; cover and evacuate, blow argon and stir slag, slag slag time 25min, measure temperature, take samples, tap steel;

[0068] 4. Die-cast electrode rod: hanging bag temperature 1520℃, ground pouring;

[0069] 5. Before pouring, clean the ingot mold thoroughly and bake the ingot mold to 70℃.

[0070] 6. Ordinary protective slag is used in the casting process: its weight percentage chemical composition is: CaO: 30%, Al2O3: 36%, MgO: 17%, CaF2: 17%. The particle size distribution is between 100 and 300 meshes, of which the particle size greater than 200 mesh accounts for more than 70% of the total weight.

[0071] 7. The protection slag hanging method is one-time hanging slag, and the hanging position is 550mm from the bottom of the ingot mold;

[0072] 8. Electroslag remelting: voltage 60-50V, current 9000-10000A;

[0073] 9. Forging: two punches and two pulls, one fire makes it a success;

[0074] 10. Annealing: heating temperature 860℃, cooling to 280℃, air cooling;

[0075] After the finished corrosion-resistant alloy produced by this process was treated with hot acid etching, black spot defects were found in the macrostructure.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for improving the quality of corrosion-resistant alloy die-cast electrode rods, comprising the production process steps of electric furnace → LF furnace → VOD refining → die-cast electrode rods → electroslag remelting → forging → annealing; characterized in that The specific steps are as follows: 1) Electric furnace: the charge is melted, the temperature of molten steel is ≥1600℃, oxygen is blown for decarburization, and the final carbon content is controlled at 0.25~0.65%; 2) LF furnace: enter the tank, add lime, refined slag and steel slag for reduction, and control the temperature between 1640℃~1690℃; 3) VOD refining: put into the tank, vacuum carbon deoxidation, ultimate vacuum degree ≤300Pa, holding time ≥15min; break the air, add active lime, fluorite powder, Al ingot, vacuum slag; cover and evacuate, blow argon and stir to slag, slag slag time ≥20min, measure temperature, take samples, and tap steel; 4) Die-cast electrode rod: the hanging bag temperature is 1510~1520℃, and the casting is carried out in the insulation pit; 5) Electroslag remelting: voltage 70~40V, current 6000~13000A; 6) Forging: two punches and two pulls, one fire to make it a success; 7) Annealing: heating temperature 820~880℃, cooling with the furnace to ≤300℃ and air cooling out of the furnace; Before pouring, the ingot mold is thoroughly cleaned and baked to a temperature of 200-300°C. Special protective slag is used during the pouring process, which is composed of the following components in weight percentage: CaO: 20% to 45%, Al2O3: 5% to 20%, Na2O: 3% to 10%, CaF2: 5% to 15%, Al particles: 10% to 25% and inevitable impurities, the sum of the weight percentages of the above components is 100%.

2. The method for improving the quality of corrosion-resistant alloy die-cast electrode rods according to claim 1, characterized in that: The alloy is a nickel-based high-temperature alloy with a grade of UNS N08825.

3. The method for improving the quality of corrosion-resistant alloy die-cast electrode rods according to claim 1, characterized in that: The particle size of the protective slag is distributed between 100 and 300 meshes, wherein the particle size greater than 200 meshes accounts for more than 70% of the total weight.

4. The method for improving the quality of corrosion-resistant alloy die-cast electrode rods according to claim 3, characterized in that: The protective slag is hung twice, and the hanging positions are 200-400mm and 600-800mm from the bottom of the ingot mold respectively.

5. The method for improving the quality of corrosion-resistant alloy die-cast electrode rods according to claim 1, characterized in that: The protection pit should be pre-dried two hours before pouring to maintain the ambient temperature in the pit above 50°C.