Manufacturing method of high-silicon solid solution nodular cast iron low-nickel-chromium corrosion-resistant nodular cast iron

Abstract

On the premise that the corrosion resistance and strength of the nodular cast iron are guaranteed, the corrosion resistance is improved by optimizing the alloy element adding amount and the process and utilizing the solid solution strengthening effect of silicon, meanwhile, generation of carbides is reduced through the low nickel-chromium using amount, toughness reduction is reduced, and the service life of the nodular cast iron is prolonged. By combining multi-stage inoculation and process control, it is guaranteed that graphite spheroidizing is sufficient and stable, poor spheroidizing is reduced, the matrix structure is refined, the graphite form is optimized, cooperation of low alloy, high corrosion resistance and high toughness is achieved, the casting strength and toughness are improved, the requirements for corrosion resistance, strength and toughness are met, and the method is suitable for the high-requirement corrosion environment.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of nodular cast iron material preparation, and particularly relates to a manufacturing method of high-silicon solid-solution nodular cast iron with low nickel-chromium corrosion-resistant. BACKGROUND

[0002] Nodular cast iron is cast iron with spheroidal graphite distributed by spheroidizing treatment (different from flaky graphite of gray cast iron), which has better strength and toughness than gray cast iron. The application scenarios of corrosion-resistant nodular cast iron (such as chemical pipelines, ocean engineering, sewage treatment equipment, etc.) determine that it must meet two core requirements, one is corrosion resistance: it needs to resist chemical or electrochemical corrosion in acid, alkali, salt mist, and humid environments to avoid wall thickness thinning and structural failure due to corrosion; the other is a certain strength: it needs to bear working load (such as pressure, tension, bending moment) to ensure the load-bearing capacity of the structure and avoid plastic deformation or fracture; these two performances are indispensable, and only corrosion-resistant but insufficient in strength will fail due to overload, and only high in strength but not corrosion-resistant will be quickly damaged due to corrosion. In order to improve the corrosion resistance of the castings, copper, nickel, chromium and other metals are often added to meet the requirements of corrosion resistance and strength, but too high chromium and copper will easily lead to the formation of carbides in the matrix structure, thereby reducing the toughness of the castings. Therefore, in order to meet the requirements of corrosion resistance, strength and toughness at the same time, the amount of alloying elements needs to be balanced and the process needs to be optimized. SUMMARY

[0003] The technical problem solved by the application is to provide a manufacturing method of high-silicon solid-solution nodular cast iron with low nickel-chromium corrosion-resistant, which optimizes the amount of alloying elements and the process under the premise of ensuring the corrosion resistance and strength of the nodular cast iron, uses the solid solution strengthening effect of silicon to improve the corrosion resistance, reduces the generation of carbides by using low nickel-chromium content to reduce the decrease in toughness, and combines multi-stage inoculation and process control to ensure full and stable spheroidization of graphite, reduce spheroidization defects, refine the matrix structure, optimize the graphite morphology, realize the synergy of low alloying, high corrosion resistance and high toughness, improve the strength and toughness of the castings, meet the requirements of corrosion resistance, strength and toughness, and be suitable for high-demand corrosion environments.

[0004] The technical solution adopted by the application is a manufacturing method of high-silicon solid-solution nodular cast iron with low nickel-chromium corrosion-resistant, including the following steps: 1) sequentially adding 60wt.% of pig iron, 15wt.% of low-manganese scrap steel and 25wt.% of recycled material into an electric frequency furnace for melting, and adding silicon carbide particles in the material melting stage to finally obtain nodular cast iron liquid; 2) The molten cast iron obtained in step 1) is sent to the sample for on-site analysis to ensure that the trace elements in the molten cast iron are in the range of 3.6wt.%≤C≤3.8wt.%, 2.8wt.%≤Si≤3.0wt.%, S≤0.015wt.%, 0.5wt.%≤Cr≤0.8wt.%, 2.0wt.%≤Ni≤3.0wt.%; 3) Put 1.5wt.%-1.7wt.% of spherulizing agent in the spheroidizing pit at the bottom of the ladle, and keep the spherulizing agent flat and compact during the process; then lay 0.3wt.%-0.8wt.% of 75SiFe inoculant on top of the spherulizing agent, followed by covering 0.2wt.%-0.5wt.% of silicon steel sheet on the 75SiFe inoculant, and then lay spheroidizing steel plate on the silicon steel sheet, compact the materials laid on the spheroidizing steel plate, and place pig iron blocks on the spheroidizing steel plate, and then put low-carbon chromium iron particles on the pig iron blocks; 4) Use the flushing inoculant to flow into the ladle with the molten iron, and when the molten iron is finished, timely remove the dross in the ladle, then add silicon carbide powder into the molten iron, and then use the crane to transport the ladle to the casting site, and measure the temperature before casting to ensure that the temperature in the ladle is between 1350℃ and 1360℃. 5) After preparation, quickly perform the casting operation and open the instantaneous inoculation device to add 0.15wt.%-0.20wt.% of bismuth silicon inoculant to the molten iron for instantaneous inoculation.

[0005] In the above step 1), the particle size of the silicon carbide particles is 20mm-30mm, and the addition amount of the silicon carbide particles is 0.8wt.%-1.2wt.%.

[0006] In the above step 3), the particle size of the low-carbon chromium iron particles is 10mm-20mm, and the addition amount of the low-carbon chromium iron particles is 0.6wt.%-1.2wt.%. In the above step 4), the particle size of the silicon carbide powder is 2mm-5mm and the addition amount of the silicon carbide powder is 0.08wt.%-0.12wt.%.

[0007] In the above step 4), the flushing inoculant is 0.6wt.%-0.8wt.% of silicon-barium inoculant.

[0008] In the above step 5), the spheroidizing rate of the castings formed after casting is more than 90%, and the tensile strength of the castings is ≥600MPA, the yield strength is ≥580MPA, the elongation is ≥9, the hardness is 230-280, and the pearlite content is 45-75%.

[0009] The advantages of the present application compared with the prior art are: 1、The technical solution ensures the corrosion resistance and strength of the nodular cast iron, optimizes the addition amount of alloying elements and the process, uses the solid solution strengthening effect of silicon to improve the corrosion resistance, and reduces the carbide generation and the decrease of toughness by using a low amount of nickel and chromium. 2、The technical solution combines multi-stage inoculation and process control to ensure the full stability of graphite nodularity, reduce nodularity defects, refine the matrix structure, optimize the graphite morphology, realize the synergy of low alloying, high corrosion resistance and high toughness, improve the strength and toughness of the castings, meet the requirements of corrosion resistance, strength and toughness, and is suitable for high requirement corrosion environment. 3、The castings produced by the technical solution do not produce carbides, other mechanical properties are qualified, ultrasonic flaw detection meets the requirements, the nodularity of the castings reaches more than 90%, the elongation is ≥9, the matrix structure is uniform, and the pearlite content is 45-75%. DETAILED DESCRIPTION

[0010] The technical solutions in the embodiments of the present application will be described clearly and completely in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0011] In this document, the terms "comprise", "contain" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. Without more limitations. The element defined by the statement "comprises a..." does not exclude the presence of another identical element in the process, method, article or device including the element.

[0012] The high-silicon solid solution nodular iron low-nickel chromium corrosion-resistant nodular cast iron manufacturing method comprises the following steps: 1) sequentially adding 60wt.% of pig iron, 15wt.% of low manganese scrap and 25wt.% of recycled material into an electric frequency furnace for smelting, and adding 1.0wt.% of silicon carbide particles with a particle size of 20mm-30mm in the melting smelting stage, finally obtaining a ductile iron original iron liquid; introducing silicon carbide particles for smelting, which not only ensures the stability of the base composition of the iron liquid, but also increases the silicon content through silicon carbide, laying the foundation for high silicon solid solution characteristics, and the use of recycled materials improves the utilization rate of raw materials; the particle size range of silicon carbide particles is clear, which can ensure uniform dissolution during smelting, avoid incomplete melting caused by too large particles or excessive burning caused by too small particles, improve the solid solution efficiency of silicon element, and enhance the corrosion resistance of the casting; 2) The ductile iron original iron liquid obtained in step 1) is sent for sample analysis before the furnace to ensure that the trace elements in the ductile iron original iron liquid are in the range of: 3.6wt.%≤C≤3.8wt.%, 2.8wt.%≤Si≤3.0wt.%, S≤0.015wt.%, 0.5wt.%Cr≤0.8wt.%, 2.0wt.%Ni≤3.0wt.%; Si can continuously increase the eutectic transformation temperature and effectively reduce the generation of cementite, and its ability to promote graphitization is only second to C; secondly, Si can also promote the formation of ferrite and inhibit the generation of pearlite; through furnace detection, the range of trace elements is strictly controlled, which balances the corrosion resistance and mechanical properties while ensuring corrosion resistance, and low nickel chromium can avoid the decrease of toughness caused by high alloy elements; 3) Put 1.5wt.%-1.7wt.% of spherulitizing agent in the spherulitizing pit at the bottom of the ladle, and keep the spherulitizing agent flat and compact during the process; then lay 0.5wt.% of 75SiFe inoculant on the spherulitizing agent, which plays a role in preliminary inoculation, and then cover 0.3wt.% of silicon steel sheet on the 75SiFe inoculant, which can isolate air to some extent and reduce oxidation of the material in the subsequent process; then lay spherulitizing steel plate on the silicon steel sheet, which compacts all the laid materials, and place pig iron blocks on the spherulitizing steel plate; then, put 0.9wt.% of low-carbon chromium iron particles with a particle size range of 10mm-20mm on the pig iron blocks, wherein 4-6 pig iron blocks are laid, and the size of the low-carbon chromium iron particles is limited to ensure their uniform distribution in the subsequent reaction and fully play the role of chromium element in corrosion resistance; the laying order, proportion and compaction treatment of the spherulitizing agent and each inoculant are specified to ensure sufficient and stable spherulitizing reaction and reduce spherulitizing problems; 4) The silicon-barium inoculant is poured into the ladle with the molten iron, accounting for 0.6wt.%-0.8wt.% of the weight of the molten iron. The silicon-barium inoculant and the 75SiFe inoculant work together to further improve the inoculation effect, and the instant inoculation can refine the grains in the last stage of pouring, effectively improve the microstructure of the castings, and improve the mechanical properties of the castings. After the molten iron is poured out, the dross in the ladle is promptly removed to avoid affecting the quality of the castings. Then, silicon carbide powder is added to the molten iron, and then the ladle is transported to the pouring site by the overhead crane. The temperature is measured before pouring to ensure that the temperature in the ladle is between 1350°C and 1360°C. This temperature range can ensure that the molten iron has appropriate fluidity and reactivity. The particle size of the silicon carbide powder is 2mm-5mm, and the addition amount of the silicon carbide powder is 0.08wt.%-0.12wt.%. Small particle size silicon carbide powder can be more uniformly dispersed in the molten iron, and with precise addition amount, it can further supplement silicon elements in subsequent processing, while assisting in purifying the molten iron, reducing inclusions, and improving the purity of the castings. The main function of the silicon carbide powder is inoculation to prevent the formation of carbides, thereby reducing the elongation rate and reducing the brittleness of the matrix. 5) After preparation, the pouring operation is quickly performed, and the instant inoculation device is opened to add 0.15wt.%-0.20wt.% of bismuth silicon inoculant to the molten iron for instant inoculation, which can optimize the graphite morphology and improve the spheroidization rate at the moment of pouring to ensure the consistency of the performance of the castings. The spheroidization rate of the castings formed after pouring is more than 90%, and the tensile strength of the castings is ≥600MPA, the yield strength is ≥580MPA, the elongation is ≥9, the hardness is 230-280, and the pearlite content is 45-75%. By specifying specific performance parameters, it is directly proved that the manufacturing method can stably produce nodular cast iron with high corrosion resistance, high strength and toughness, verifying the practicality and advancement of the technical scheme.

[0013] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application.

[0014] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron, characterized in that... Includes the following steps: 1) Add 60wt.% pig iron, 15wt.% low-manganese scrap steel and 25wt.% recycled material to the electric frequency furnace in sequence for smelting, and add silicon carbide particles during the chemical smelting stage to finally obtain ductile iron raw molten iron. 2) The ductile iron molten iron obtained in step 1) is sampled before the furnace to ensure that the trace element range in the ductile iron molten iron is: 3.6wt.%≤C≤3.8wt.%, 2.8wt.%≤Si≤3.0wt.%, S≤0.015wt.%, 0.5wt.%Cr≤0.8wt.%, 2.0wt.%Ni≤3.0wt.%. 3) Place 1.5wt.% to 1.7wt.% of spheroidizing agent by weight of molten iron into the spheroidizing pit at the bottom of the ladle, keeping the spheroidizing agent flat and compact during the process; then lay 0.3wt.% to 0.8wt.% of 75SiFe inoculant by weight of molten iron on top of the spheroidizing agent, followed by covering the 75SiFe inoculant with 0.2wt.% to 0.5wt.% of silicon steel sheet by weight of molten iron, then lay the spheroidizing steel plate on the silicon steel sheet, compacting all the laid materials with the spheroidizing steel plate, and then place a pig iron block on the spheroidizing steel plate. Finally, place low-carbon ferrochrome granules on the pig iron block. 4) The inoculant is poured into the ladle along with the molten iron. After the molten iron is poured out, the slag in the ladle is removed in time. Then silicon carbide powder is added to the molten iron. The ladle is then transported to the pouring site by overhead crane. The temperature is measured before pouring to ensure that the temperature in the ladle is between 1350℃ and 1360℃. 5) Once preparations are complete, quickly proceed with the pouring operation and turn on the instant inoculation device. Add 0.15wt.% to 0.20wt.% of silicon bismuth inoculant to the molten iron for instant inoculation.

2. The method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron according to claim 1, characterized in that: In step 1) above, the particle size of the silicon carbide particles is 20 mm to 30 mm, and the amount of silicon carbide particles added is 0.8 wt.% to 1.2 wt.%.

3. The method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron according to claim 1, characterized in that: In step 3) above, the particle size range of the low carbon ferrochrome particles is 10mm to 20mm, the amount of low carbon ferrochrome particles added is 0.6wt.% to 1.2wt.%, the amount of spheroidized steel plate laid is 0.3wt.%, and 4 to 6 pig iron blocks are laid.

4. The method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron according to claim 1, characterized in that: In step 4) above, the particle size of the silicon carbide powder is 2 mm to 5 mm and the amount of silicon carbide powder added is 0.08 wt.% to 0.12 wt.%.

5. The method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron according to claim 1, characterized in that: In step 4) above, the inoculant is a barium silicon inoculant accounting for 0.6 wt.% to 0.8 wt.% of the weight of the molten iron.

6. The method for manufacturing high-silicon solid solution ductile iron and low-nickel-chromium corrosion-resistant ductile iron according to claim 1, characterized in that: In step 5) above, the spheroidization rate of the casting formed after casting is above 90%, and the tensile strength of the casting is ≥600MPa, the yield strength is ≥580MPa, the elongation is ≥9, the hardness is 230-280, and the pearlite content is 45-75%.