Production method of nichrome nodular cast iron

Abstract

The invention provides a production method of nickel-chromium alloy nodular cast iron which is QTNi2Cr0.55 and comprises the following chemical components in percentage by weight: 3.65-3.85% of C, 2.6-2.8% of Si, less than or equal to 0.2% of Mn, less than or equal to 0.06% of P, less than or equal to 0.02% of S, 2.0 + / -0.1% of Ni, 0.55 + / -0.1% of Cr, 0.45-0.65% of Mg and the balance of Fe. A high-carbon low-silicon nodular cast iron production process is adopted, nickel supplementation is achieved while nodulizing is completed through a nickel-magnesium nodulizing agent, chromium supplementation is achieved by adding low-carbon ferrochrome into a casting ladle, the characteristics of pretreatment deoxidation of a silicon-calcium inoculant, graphitization of a silicon-strontium inoculant, long-acting inoculation of silicon-barium and the like are fully utilized, one-time bag burying inoculation is achieved, and the production efficiency is improved. And insufficient impact inoculation absorption is avoided, the appearance of carbides is effectively avoided, the pearlite content is greatly reduced, and the comprehensive performance of the casting is improved.

Description

Technical Field

[0001] This invention belongs to the field of ductile iron technology, specifically relating to a method for producing nickel-chromium alloy ductile iron. Background Technology

[0002] Ductile iron is produced by spheroidizing and inoculating to obtain spheroidal graphite, which effectively improves the mechanical properties of cast iron, especially its plasticity and toughness. It has been successfully used to cast parts subject to complex stresses and requiring high strength, toughness, and wear resistance. However, in marine engineering and other highly corrosive environments, the corrosion resistance requirements for ductile iron are even higher.

[0003] Previously, seawater corrosion-resistant valve castings were produced using materials such as stainless steel. After switching to the production process of ductile iron QTNi2Cr055, the composition requirements are: nickel content approximately 2±0.1%, chromium content 0.55±0.1%, spheroidization rate not less than grade 3, pearlitic-ferrite mixed matrix, tensile strength not less than 450MPa, yield strength not less than 350MPa, elongation after fracture not less than 3%, and Bush hardness 180-250. Initially, production was tested using a low-carbon, high-silicon (C: 3.5-3.6, Si: 3.1-3.3) ductile iron process. While the tensile strength and other requirements were met, the matrix produced a large amount of carbides, resulting in a high pearlite content, insufficient elongation after fracture, high brittleness, and a tendency for the castings to crack. The Bush hardness sometimes exceeded the requirements. Furthermore, after finishing, approximately 50% of the castings tested under hydrostatic pressure showed leakage. Dissection of the castings revealed significant shrinkage porosity. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for producing nickel-chromium alloy ductile iron, which addresses the shortcomings of the prior art. The method adopts a high-carbon, low-silicon ductile iron production process, uses nickel-magnesium spheroidizing agent to supplement nickel, and low-carbon ferrochrome to supplement chromium. It makes full use of the pretreatment deoxidation effect of silicon-calcium inoculant, the graphitization of silicon-strontium inoculant, and the long-term inoculation characteristics of silicon-barium, etc., and performs one-time embedding inoculation, thereby improving the comprehensive performance of ductile iron.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a nickel-chromium alloy ductile iron, wherein the nickel-chromium alloy ductile iron is QTNi2Cr055, and its chemical composition by weight percentage is: C 3.65-3.85%, Si 2.6-2.8%, Mn≤0.2%, P≤0.06%, S≤0.02%, Ni 2.0±0.1%, Cr 0.55±0.1%, Mg 0.45-0.65%, with the balance being Fe.

[0006] The present invention also provides a method for producing the nickel-chromium alloy ductile iron, comprising the following steps: S1, Chemicals Add 60%-70% high-purity pig iron, 20%-30% recycled material, and 10%-15% scrap steel to the bottom of the medium-frequency furnace. After the molten iron is melted evenly, raise the temperature to 1420℃-1440℃ and take a sample. Use a cast steel sample spoon with an alcohol-based coating to dig out 100mm-200mm of molten iron from below the surface of the molten iron for spectral and chemical analysis. Add carbon raisers or scrap steel, ferrosilicon, low-carbon ferrochrome, or pure nickel plates according to the chemical composition to make it meet the original chemical composition requirements of the molten iron. If the composition is not qualified, repeat the above operation. If the composition is qualified, raise the temperature to the tapping temperature of 1450℃-1500℃ and prepare to tap the furnace. The original molten iron had the following chemical composition: C 3.65-3.85%, Si 1.9-2.0%, Mn≤0.2%, P≤0.06%, S≤0.02%, Ni 1.0±0.1%, Cr 0.2±0.1%, with the balance being Fe; S2, Packaging A dam-type ladle is used. The nickel-magnesium spheroidizing agent is spread flat on the side of the spheroidizing pit inside the ladle. Low-carbon ferrochrome is spread flat on top of the spheroidizing agent. On top of the low-carbon ferrochrome, a silicon-barium inoculant or a silicon-strontium inoculant is spread flat. On top of the silicon-barium or silicon-strontium inoculant, ductile iron filings and a pressing plate are covered. The silicon-calcium inoculant is placed on the side of the non-spheroidizing pit, and the molten iron is poured directly onto it when tapping out of the furnace. S3, Unloading and Pouring After the molten iron reaches the tapping temperature, it is tapped from the furnace and then spheroidized and inoculated in the ladle before being poured. The casting temperature is controlled at 1360℃-1380℃. During pouring, a silicon-bismuth inoculant is used to inoculate the casting instantaneously with the molten iron flow. The casting can be cleaned by removing sand when it is held at 550℃ in the mold.

[0007] Preferably, the chemical composition of the nickel-magnesium spheroidizing agent is: Si 10-12%, Mg 4.6-5.8%, Ni 82-85%, with the balance being Fe, a particle size of 20-30 mm, and an addition amount of 1.2%-1.3%.

[0008] Preferably, the chemical composition of the low-carbon ferrochrome is: Cr 52-60%, C 0.2-0.3%, Si≤2.0%, P≤0.04%, S≤0.03%, with the balance being Fe, a particle size of 20-50 mm, and an addition amount of 0.64%.

[0009] Preferably, the chemical composition of the barium silicon inoculant is: Si 70-75%, Ba 2.0-3.0%, Ca 1.0-2.0%, Al≤1.5%, with the balance being Fe; the chemical composition of the strontium silicon inoculant is: Si 70-75%, Ca<0.1%, Al<0.5%, Sr0.6-1.2%, with the balance being Fe; and the amount of the barium silicon inoculant or the strontium silicon inoculant added is 0.5%.

[0010] Preferably, the amount of ductile iron filings added is 0.3%.

[0011] Preferably, the chemical composition of the silicon-calcium inoculant is: Si 50-70%, Ba 5-10%, Ca 20-35%, Al≤1.0%, with the balance being Fe, and the amount added is 0.2%.

[0012] Preferably, the chemical composition of the silicon-bismuth inoculant is: Si 68-73%, Ba 0.3-0.7%, Ca 1.0-2.0%, Al 0.5-1.5%, Bi 0.8-1.3%, with the balance being Fe, a particle size of 0.2-0.7 mm, and an addition amount of 0.1%-0.15%.

[0013] This invention has significant technical advantages compared to existing technologies: 1. This invention adopts a high-carbon, low-silicon (C: 3.65-3.85, Si: 2.6-2.8) ductile iron production process. It utilizes nickel-magnesium spheroidizing agents to complete spheroidization treatment while simultaneously replenishing nickel. Low-carbon ferrochrome is added to the ladle to replenish chromium. Apart from nickel and chromium, there is no or low alloying. It also makes full use of the pretreatment deoxidation effect of silicon-calcium inoculant, the graphitization of silicon-strontium inoculant, and the long-term inoculation characteristics of silicon-barium inoculant. One-time inoculation in the ladle avoids insufficient absorption during inoculation, effectively avoids the formation of carbides, and significantly reduces the pearlite content.

[0014] 2. Using the nickel-chromium alloy ductile iron production process of the present invention, about 40 castings were produced. The mechanical elongation rate was increased from the previous 1%-3% to 8%-11%, the hardness was reduced by about 20-30 HW, and the problems of shrinkage porosity and water leakage during water testing were reduced from 50% to 7%.

[0015] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. Attached Figure Description

[0016] Figure 1 This is a metallographic diagram of the nickel-chromium ductile iron produced in Comparative Example 1; Figure 2 This is a metallographic diagram of the nickel-chromium ductile iron produced in Comparative Example 2; Figure 3 This is a metallographic diagram of nickel-chromium alloy ductile iron produced using the method of this invention. Detailed Implementation

[0017] The nickel-magnesium spheroidizing agent used in this invention is a nickel-magnesium-silicon-iron alloy spheroidizing agent with the following chemical composition: Si 10-12%, Mg 4.6-5.8%, Ni 82-85%, with the balance being Fe, and a particle size of 20-30 mm.

[0018] The chemical composition of low-carbon ferrochrome is: Cr 52-60%, C 0.2-0.3%, Si≤2.0%, P≤0.04%, S≤0.03%, with the balance being Fe, and the particle size is 20-50mm.

[0019] The chemical composition of the barium silicon inoculant is: Si 70-75%, Ba 2.0-3.0%, Ca 1.0-2.0%, Al≤1.5%, with the balance being Fe.

[0020] The chemical composition of the silicon-strontium inoculant is: Si 70-75%, Ca < 0.1%, Al < 0.5%, Sr 0.6-1.2%, with the balance being Fe.

[0021] The chemical composition of the silicon-calcium inoculant is: Si 50-70%, Ba 5-10%, Ca 20-35%, Al≤1.0%, with the balance being Fe.

[0022] The chemical composition of the silicon-bismuth inoculant is: Si 68-73%, Ba 0.3-0.7%, Ca 1.0-2.0%, Al 0.5-1.5%, Bi 0.8-1.3%, with the balance being Fe, and the particle size is 0.2-0.7 mm.

[0023] Example 1 This embodiment describes a production method for nickel-chromium alloy ductile iron, specifically for producing a certain type of butterfly plate casting. The casting liquid weighs approximately 900 kg, and is poured in three batches at a time, totaling 2700 kg. The method includes the following steps: S1, Chemicals A 3-ton medium-frequency furnace is used for molten iron processing. 1890 kg of high-purity pig iron (about 70%) is added to the bottom of the furnace, followed by 540 kg of recycled material (low-alloy ductile iron, about 20%), and finally 270 kg of briquetted carbon scrap steel (about 10%). After the molten iron is melted evenly, the temperature is raised to 1440℃ for sampling. A cast steel sample spoon with an alcohol-based coating is used to dig out 150 mm of molten iron from the surface of the molten iron for spectral and chemical analysis. The composition is analyzed, and carbon-reducing agents or scrap steel (for carbon increase or decrease), ferrosilicon, low-carbon ferrochrome, and pure nickel plates are added according to the chemical composition to meet the original molten iron chemical composition requirements in Table 1. If the composition is not qualified, the above operation is repeated. If the composition is qualified, the temperature is raised to the tapping temperature of 1450℃-1500℃ to prepare for tapping.

[0024] Table 1 Chemical composition of raw molten iron S2, Packaging A 3-ton dam-type ladle is used. 35.1 kg (1.3%) of nickel-magnesium spheroidizing agent with a particle size of 20-30 mm is placed on the spheroidizing pit side at the bottom of the ladle. After proper compaction, 17.28 kg (0.64%) of low-carbon ferrochrome with a particle size of 20-50 mm is covered on top. After proper compaction, 13.5 kg (0.5%) of silicon-strontium inoculant is spread and covered on top. Finally, 8.1 kg (0.3%) of ductile iron filings are covered on top. A pressure plate is then placed on top (the pressure plate weighs between 20 kg and 50 kg, and the pressure plate for a 3-ton ladle is about 20 kg). 5.4 kg (0.2%) of silicon-calcium inoculant is placed on the non-spheroidizing pit side (the opposite side of the spheroidizing pit). When tapping out of the furnace, molten iron is directly poured onto it.

[0025] S3, Unloading and Pouring Tapping and casting operations: When the tapping temperature reaches 1495℃, power is cut off. The ladle is hoisted to the tapping trough. After tapping out 2 / 3 of the iron (approximately 1800 kg) at once, the tapping speed is slowed down, and the iron is gradually tapped down to 2700 kg. Then, slag is removed. After slag removal, the ladle is hoisted to the casting site for pre-casting temperature measurement. Once the temperature meets the casting temperature of 1360℃-1380℃, casting is carried out. During casting, 4.05 kg (0.15%) of silicon-bismuth inoculant with a particle size of 0.2-0.7 mm is used for instantaneous inoculation with the molten iron flow. The casting is held in the resin sand mold at 550℃, then removed from the mold and cleaned at room temperature.

[0026] Example 2 This embodiment describes a production method for nickel-chromium alloy ductile iron, specifically for producing a certain type of butterfly plate casting. The casting liquid weighs approximately 900 kg, and is poured in three batches at a time, totaling 2700 kg. The method includes the following steps: S1, Chemicals A 3-ton medium-frequency furnace is used for molten iron processing. 1620 kg of high-purity pig iron (about 60%) is added to the bottom of the furnace, followed by 810 kg of recycled material (low-alloy ductile iron, about 30%), and finally 270 kg of briquetted carbon scrap steel (about 10%). After the molten iron is melted evenly, the temperature is raised to 1430℃ for sampling. A cast steel sample spoon with an alcohol-based coating is used to dig out 100 mm of molten iron from the surface of the molten iron for spectral and chemical analysis. The composition is analyzed, and carbon-increasing agents or scrap steel (for increasing or decreasing carbon), ferrosilicon, low-carbon ferrochrome, and pure nickel plates are added according to the chemical composition to make it meet the original molten iron chemical composition requirements in Table 1. If the composition is not qualified, the above operation is repeated. If the composition is qualified, the temperature is raised to the tapping temperature of 1450℃-1500℃ to prepare for tapping.

[0027] S2, Packaging A 3-ton dam-type ladle is used. 32.4 kg (1.2%) of nickel-magnesium spheroidizing agent with a particle size of 20-30 mm is placed on the bottom side of the spheroidizing pit of the ladle. After proper compaction, 17.28 kg (0.64%) of low-carbon ferrochrome with a particle size of 20-50 mm is covered on top. After proper compaction, 13.5 kg (0.5%) of silicon-barium inoculant is spread and covered on top. Finally, 8.1 kg (0.3%) of ductile iron filings are covered on top, and a pressure plate is placed on top. 5.4 kg (0.2%) of silicon-calcium inoculant is placed on the non-spheroidizing pit side (opposite to the spheroidizing pit). When tapping out of the furnace, molten iron is directly poured onto it.

[0028] S3, Unloading and Pouring Tapping and casting operations: When the tapping temperature reaches 1460℃, power is cut off. The ladle is hoisted to the tapping trough. After tapping out 2 / 3 of the iron (approximately 1800kg) at once, the tapping speed is slowed down, and the iron is gradually tapped down to 2700kg. Then, slag is removed. After slag removal, the ladle is hoisted to the casting site for pre-casting temperature measurement. Once the temperature meets the casting temperature of 1360℃-1380℃, casting is carried out. During casting, 2.7kg (0.1%) of silicon-bismuth inoculant with a particle size of 0.2-0.7mm is used for instantaneous inoculation with the molten iron flow. The casting is held in the resin sand mold at 550℃, then removed from the mold and cleaned at room temperature.

[0029] Example 3 This embodiment describes a production method for nickel-chromium alloy ductile iron, specifically for producing a certain type of butterfly plate casting. The casting liquid weighs approximately 2700 kg, and is poured in three batches, totaling 900 kg. The method includes the following steps: S1, Chemicals A 3-ton medium-frequency furnace is used for molten iron processing. 1755 kg of high-purity pig iron (approximately 65%) is added to the bottom of the furnace, followed by 540 kg of recycled material (low-alloy ductile iron, approximately 20%), and finally 405 kg of briquetted carbon scrap steel (approximately 15%). After the molten iron is melted evenly, the temperature is raised to 1420℃ for sampling. A cast steel sample spoon with an alcohol-based coating is used to scoop out 200 mm of molten iron from the surface of the molten iron for spectral and chemical analysis. Based on the chemical composition, carbon-reducing agents or scrap steel (for carbon increase or decrease), ferrosilicon, low-carbon ferrochrome, and pure nickel plates are added to make the molten iron meet the original chemical composition requirements in Table 1. If the composition is not up to standard, the above operation is repeated. If the composition is up to standard, the temperature is raised to the tapping temperature of 1450℃-1500℃ to prepare for tapping.

[0030] S2, Packaging A 3-ton dam-type ladle is used. 33.75 kg (1.25%) of nickel-magnesium spheroidizing agent with a particle size of 20-30 mm is placed on the spheroidizing pit side at the bottom of the ladle. After proper compaction, 17.28 kg (0.64%) of low-carbon ferrochrome with a particle size of 20-50 mm is covered on top. After proper compaction, 13.5 kg (0.5%) of silicon-strontium inoculant is spread and covered on top. Finally, 8.1 kg (0.3%) of ductile iron filings are covered on top, and a pressure plate is placed on top. 5.4 kg (0.2%) of silicon-calcium inoculant is placed on the non-spheroidizing pit side (opposite to the spheroidizing pit). When tapping out of the furnace, molten iron is directly poured onto it.

[0031] S3, Unloading and Pouring Tapping and Pouring Operations: Power is cut off when the tapping temperature reaches 1480℃. The ladle is hoisted to the tapping trough. After tapping out approximately 1800kg (2 / 3) of the iron at once, the tapping speed is slowed down, and iron is gradually tapped down to 2700kg. Slag is then removed. After slag removal, the ladle is hoisted to the pouring site for pre-pouring temperature measurement. Pouring is carried out once the temperature meets the pouring temperature range of 1360℃-1380℃. During pouring, 3.51kg (0.13%) of a silicon-bismuth inoculant with a particle size of 0.2-0.7mm is used for instantaneous inoculation with the molten iron flow. The casting is held in the resin sand mold at 550℃, then removed from the mold and cleaned at room temperature.

[0032] The nickel-chromium alloy ductile iron prepared by the method of this invention is QTNi2Cr055, and its chemical composition by weight percentage is: C 3.65-3.85%, Si 2.6-2.8%, Mn≤0.2%, P≤0.06%, S≤0.02%, Ni 2.0±0.1%, Cr0.55±0.1%, Mg 0.45-0.65%, with the balance being Fe.

[0033] Comparative Example 1 This comparative example describes a method for producing nickel-chromium ductile iron, employing a low-carbon, high-silicon (C: 3.4-3.5, Si: 3.2-3.4) large-scale inoculation process, common rare-earth magnesium spheroidizing agent, and common silicon-barium inoculating agent.

[0034] The chemical composition of molten iron is shown in Table 2: Table 2 Chemical composition of molten iron A dam-type ladle is used. 1.3% ordinary rare earth magnesium spheroidizing agent (containing about 45% silicon) is spread flat on the side of the spheroidizing pit inside the ladle. 1.0% silicon barium inoculant is spread flat on top of the spheroidizing agent, and then covered with 0.3% ductile iron filings and a pressing plate. 0.2% silicon calcium barium inoculant is placed on the side of the non-spheroidizing pit, and molten iron is poured directly onto it when tapping out of the furnace.

[0035] Comparative Example 2 This comparative example is a method for producing nickel-chromium ductile iron, which uses a high-carbon, low-silicon (C: 3.65-3.85, Si: 2.6-2.8) process, common rare-earth magnesium spheroidizing agent, and common silicon-barium inoculant.

[0036] The chemical composition of molten iron is shown in Table 3: Table 3 Chemical composition of molten iron A dam-type ladle is used. 1.3% ordinary rare earth magnesium spheroidizing agent (containing about 45% silicon) is spread flat on the side of the spheroidizing pit inside the ladle. 0.5% silicon barium inoculant is spread flat on top of the spheroidizing agent, and then covered with 0.3% spheroidizing iron filings and a pressing plate. 0.2% silicon calcium barium inoculant is placed on the side of the non-spheroidizing pit. When tapping out of the furnace, molten iron is directly poured onto it.

[0037] Metallographic analysis was performed on the nickel-chromium ductile iron produced in this invention and Comparative Examples 1-2, and the results are as follows: Figure 1 The image shows the metallographic structure of nickel-chromium ductile iron produced in Comparative Example 1 using low-carbon, high-silicon, common rare-earth magnesium spheroidizing agent and common inoculant. The results show that there is almost no ferrite structure and about 15-20% carbides. Figure 2 The image shows the metallographic structure of nickel-chromium ductile iron produced in Comparative Example 2 using high-carbon, low-silicon, common rare-earth magnesium spheroidizing agent, and common inoculant. The results show that ferrite accounts for about 30%, and there are about 2%-3% carbides. Figure 3 The image shows the metallographic structure of nickel-chromium alloy ductile iron produced using the method of this invention. The results show that the ferrite content is increased to 50%, and the carbide content is less than 1%. These results indicate that this invention employs a high-carbon, low-silicon (C: 3.65-3.85, Si: 2.6-2.8) ductile iron production process. It utilizes a nickel-magnesium spheroidizing agent to complete the spheroidization treatment while simultaneously supplementing nickel, and adds low-carbon ferrochrome to the ladle to supplement chromium. Furthermore, it fully utilizes the pretreatment deoxidation effect of the silicon-calcium inoculant, the graphitization of the silicon-strontium inoculant, and the long-term inoculation properties of silicon-barium, achieving one-time inoculation in a single ladle. This avoids insufficient absorption during inoculation, effectively preventing the formation of carbides and significantly reducing the pearlite content.

[0038] The castings prepared in Examples 1-3 of this invention were subjected to physicochemical property testing. Tensile properties were tested according to GB / T228.1-2021 Metallic materials, tensile testing at room temperature – Part 1: Room temperature test method; hardness testing was performed according to GB / T231.1-2018 Metallic materials, Brinell hardness test method – Part 1: Test method. The results are shown in Table 4. Table 4 Properties of ductile iron The comparison results of the physical and chemical properties of the castings produced by the methods of the present invention and Comparative Examples 1-2 are shown in Table 5: Table 5. Performance comparison of nickel-chromium ductile iron produced by the present invention and comparative examples 1-2 Note: The above mechanical parameters are the average values ​​of 6 pieces produced by each method.

[0039] Using the process method of this invention, about 40 castings were produced. The mechanical elongation rate was increased from 1%-3% to 8%-11%, the hardness was reduced by about 20-30 HW, the castings passed the hydrostatic test after finishing, and the problems of shrinkage porosity and water leakage in the castings were reduced from 50% to 7%.

[0040] In addition, the present invention also conducted corrosion resistance tests on gray iron (HT200), ductile iron (QT500-7), stainless steel (304), and Comparative Example 1 (low carbon high silicon scheme), Comparative Example 2 (high carbon low silicon, ordinary rare earth magnesium spheroidizing agent and ordinary silicon barium inoculant), as well as the nickel-chromium ductile iron produced by the present invention. The methods are as follows: Corrosion resistance test: The corrosion resistance of the material was tested by immersion in a 5% NaCl solution and the corrosion weight loss rate: E = [(G1-G2) / G1] × 100%, where E is the corrosion weight loss rate, G1 is the initial weight, and G2 is the weight after removing corrosion products. The smaller the E, the better the corrosion resistance of the material. The results are shown in Table 6.

[0041] Table 6 Corrosion Resistance Test Results As can be seen from Table 6, the corrosion weight loss rate of nickel-chromium ductile iron produced by the three different production methods of the present invention and Comparative Examples 1-2 is basically close to that of stainless steel, which meets the corrosion resistance requirements and can be used for valve castings resistant to seawater corrosion.

[0042] In summary, this invention employs a high-carbon, low-silicon (C: 3.65-3.85, Si: 2.6-2.8) ductile iron production process. It utilizes a nickel-magnesium spheroidizing agent to achieve spheroidization while simultaneously replenishing nickel, and adds low-carbon ferrochrome to the ladle to replenish chromium. Apart from nickel and chromium, there is no or low alloying. Furthermore, it fully utilizes the pretreatment deoxidation effect of silicon-calcium inoculants, the graphitization of silicon-strontium inoculants, and the long-term inoculation properties of silicon-barium inoculants. One-time inoculation in the ladle avoids insufficient absorption during pouring, effectively preventing the formation of carbides and significantly reducing pearlite content. Using this nickel-chromium alloy ductile iron production process, approximately 40 castings were produced. The mechanical properties and elongation increased from the previous 1%-3% to 8%-11%, the hardness decreased by approximately 20-30 HW, and the problems of shrinkage porosity and water leakage during casting testing decreased from 50% to 7%.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A nickel-chromium alloy ductile iron, characterized in that, The nickel-chromium alloy ductile iron is QTNi2Cr055, and its chemical composition by weight percentage is: C 3.65-3.85%, Si 2.6-2.8%, Mn≤0.2%, P≤0.06%, S≤0.02%, Ni 2.0±0.1%, Cr 0.55±0.1%, Mg 0.45-0.65%, with the balance being Fe.

2. A method for producing nickel-chromium alloy ductile iron as described in claim 1, characterized in that, Includes the following steps: S1, Chemicals Add 60%-70% high-purity pig iron, 20%-30% recycled material, and 10%-15% scrap steel to the bottom of the medium-frequency furnace. After the molten iron is melted evenly, raise the temperature to 1420℃-1440℃ and take a sample. Use a cast steel sample spoon with an alcohol-based coating to dig out 100mm-200mm of molten iron from below the surface of the molten iron for spectral and chemical analysis. Add carbon raisers or scrap steel, ferrosilicon, low-carbon ferrochrome, or pure nickel plates according to the chemical composition to make it meet the original chemical composition requirements of the molten iron. If the composition is not qualified, repeat the above operation. If the composition is qualified, raise the temperature to the tapping temperature of 1450℃-1500℃ and prepare to tap the furnace. The original molten iron had the following chemical composition: C 3.65-3.85%, Si 1.9-2.0%, Mn≤0.2%, P≤0.06%, S≤0.02%, Ni 1.0±0.1%, Cr 0.2±0.1%, with the balance being Fe; S2, Packaging A dam-type ladle is used. The nickel-magnesium spheroidizing agent is spread flat on the side of the spheroidizing pit inside the ladle. Low-carbon ferrochrome is spread flat on top of the spheroidizing agent. On top of the low-carbon ferrochrome, a silicon-barium inoculant or a silicon-strontium inoculant is spread flat. On top of the silicon-barium or silicon-strontium inoculant, ductile iron filings and a pressing plate are covered. The silicon-calcium inoculant is placed on the side of the non-spheroidizing pit, and the molten iron is poured directly onto it when tapping out of the furnace. S3, unloading and pouring After the molten iron reaches the tapping temperature, it is tapped from the furnace and then spheroidized and inoculated in the ladle before being poured. The casting temperature is controlled at 1360℃-1380℃. During pouring, a silicon-bismuth inoculant is used to inoculate the casting instantaneously with the molten iron flow. The casting can be cleaned by removing sand when it is held at 550℃ in the mold.

3. The method according to claim 2, characterized in that, The chemical composition of the nickel-magnesium spheroidizing agent is: Si 10-12%, Mg 4.6-5.8%, Ni 82-85%, with the balance being Fe, a particle size of 20-30 mm, and an addition amount of 1.2%-1.3%.

4. The method according to claim 2, characterized in that, The chemical composition of the low-carbon ferrochrome is: Cr 52-60%, C 0.2-0.3%, Si≤2.0%, P≤0.04%, S≤0.03%, with the balance being Fe, and the particle size is 20-50mm, with an addition amount of 0.64%.

5. The method according to claim 2, characterized in that, The chemical composition of the barium silicon inoculant is: Si 70-75%, Ba 2.0-3.0%, Ca 1.0-2.0%, Al≤1.5%, with the balance being Fe; The chemical composition of the silicon-strontium inoculant is: Si 70-75%, Ca < 0.1%, Al < 0.5%, Sr 0.6-1.2%, with the balance being Fe; The amount of the barium silicon inoculant or strontium silicon inoculant added is 0.5%.

6. The method according to claim 2, characterized in that, The amount of ductile iron filings added is 0.3%.

7. The method according to claim 2, characterized in that, The chemical composition of the silicon-calcium inoculant is: Si 50-70%, Ba 5-10%, Ca 20-35%, Al≤1.0%, with the balance being Fe, and the amount added is 0.2%.

8. The method according to claim 2, characterized in that, The chemical composition of the silicon-bismuth inoculant is: Si 68-73%, Ba 0.3-0.7%, Ca 1.0-2.0%, Al 0.5-1.5%, Bi 0.8-1.3%, with the balance being Fe. The particle size is 0.2-0.7 mm, and the addition amount is 0.1%-0.15%.

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