A spheroidal graphite cast iron material, a method for manufacturing the same, and an application thereof

Abstract

The application discloses a spheroidal graphite cast iron material and a preparation method and application thereof, and belongs to the technical field of cast iron alloy materials.The spheroidal graphite cast iron material is prepared from the following components in percentage by mass: C: 3.4-3.8%, Si: 2.3-2.7%, Mn: 0.1-0.3%, Zr: 0.03-0.06%, V: 0.03-0.08%, Ce: 0.03-0.06%, Mg: 0.02-0.05%, S: less than or equal to 0.04%, P: less than or equal to 0.04%, and the rest is iron and inevitable impurities.The spheroidal graphite cast iron material is mainly prepared from a ferrite matrix to ensure the toughness and safety of the spheroidal graphite cast iron material, and trace Zr elements and alloy elements V are added to control the structure, so that the hardness and strength of the material are improved, and the spheroidal graphite cast iron is improved in wear resistance, corrosion resistance and compression resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cast iron alloy materials, and more particularly to a nodular cast iron material and a preparation method and application thereof. BACKGROUND

[0002] Nodular cast iron is an alloy material mainly composed of iron, carbon and silicon, supplemented by certain types and contents of alloying elements on the basis of the three main elements, or combined with appropriate heat treatment processes, so as to obtain a cast iron material with wide adjustable organization and performance and excellent comprehensive performance, which is widely used in various fields of production and life. In the urban water supply and drainage pipe network, nodular cast iron valves are widely used, and the service life and quality of the valves are crucial for the normal operation of the urban water supply and drainage network, and are key control components for ensuring the orderly production of the national economy, with the characteristics of large demand, high quality requirement and wide application range. However, the existing nodular cast iron valves often have insufficient strength, toughness and hardness matching during use, and cannot well meet the performance requirements of pressure resistance and erosion resistance, and in order to reduce water quality pollution of water supply pipelines, higher requirements are put forward for the corrosion resistance of the valves. Therefore, there is an urgent need for new materials and new valve preparation processes suitable for nodular cast iron valves.

[0003] The prior art discloses a kind of heat shock resistance and corrosion resistance nodular cast iron and production process, and chemical composition is as follows: C:3.5~3.7%;Si:2.0~2.6%;Mn:0.5~0.8.%;P:≤0.08%;S:≤0.03%;

[0004] Al:2.8~3.2%;Mg:0.03~0.06;RE:0.02~0.05;The rest is Fe. However, the tensile strength σb of the nodular cast iron is only 400~500Mp, the strength of the nodular cast iron material is low, and the corrosion resistance is poor, which cannot meet the application requirements of nodular cast iron in valve preparation and other fields. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the defects and deficiencies of the existing nodular cast iron material for valves, such as insufficient strength, toughness and hardness matching, and further improve the corrosion resistance, provide a nodular cast iron material, and effectively improve the strength, hardness and corrosion resistance of the nodular cast iron material by specific small amount of Ce and Zr modification treatment and appropriate V addition to regulate the content of pearlite.

[0006] Another object of the present application is to provide a preparation method of the nodular cast iron material.

[0007] Still another object of the present application is to provide a nodular cast iron material in the preparation of water supply and drainage valve castings.

[0008] A nodular cast iron material, in terms of mass percentage, each element component comprises: C:

[0009] 3.4-3.8%, Si: 2.3-2.7%, Mn: 0.1-0.3%, Zr: 0.03-0.06%, V: 0.03-0.08%, Ce: 0.03-0.06%, Mg: 0.02-0.05%, S≤0.04%, P≤0.04%, and the rest is iron and inevitable impurities.

[0010] The nodular cast iron material of the present application is chemically composed, a small amount of Ce and Zr is added for modification treatment, the cleanliness of the molten steel is improved at the same time, the formed compound can be used as the graphite nucleation core, the number of graphite balls is increased, the addition of Ce can promote the spheroidization of graphite balls and improve the graphite ball morphology, the addition of Zr can promote the formation of the passivation film on the surface of the nodular cast iron and improve the corrosion resistance, V can promote the formation of pearlite structure, an appropriate amount of V is added for controlling the proportion of pearlite, and through the combined action of precipitation strengthening and fine-grain strengthening, the strength and hardness of the nodular cast iron material can be improved to a certain extent, so that the nodular cast iron material has better comprehensive mechanical properties, so as to meet the use requirements of the nodular cast iron valve.

[0011] The specific description is as follows:

[0012] Carbon and silicon: in order to adapt to the requirement that the nodular cast iron valve material should have good toughness and elongation to ensure safety during use, and in order to make the nodular cast iron material have good corrosion resistance, therefore, the matrix of the nodular cast iron material should mainly be ferrite which has good toughness and corrosion resistance. The nodular cast iron matrix structure is mainly affected by the carbon equivalent (CE=C+0.33Si), a low carbon equivalent is not conducive to the transformation of the nodular cast iron graphitization structure and the generation of ferrite structure; and a too high carbon equivalent will cause graphite floating, irregular graphite ball morphology and weakening of the mechanical properties of the material. C is the element source for the formation of graphite balls, and appropriately increasing the carbon content is helpful for the formation of the number of graphite balls, the reduction of the size of the graphite balls, the improvement of the fluidity of the molten steel and the reduction of casting defects; Si can promote the spheroidization of graphite balls, strengthen the matrix strength and promote the generation of ferrite structure, but excessive Si addition is easy to cause the segregation of Si around the graphite balls, increase the brittleness of the nodular cast iron, and the selection of a suitable Si / C ratio is very critical. The design of the nodular cast iron valve often follows the principle of high carbon and low silicon. Therefore, the nodular cast iron valve is selected in the range of Si / C ratio of 0.6-0.8 and carbon equivalent of 4.2-4.7, which is beneficial to graphitization, reduces casting defects, increases the ferrite content in the matrix, improves the plasticity and toughness, and has better comprehensive mechanical properties. Considering the above, the content of C is controlled in the range of 3.4-3.8%, and the content of Si is controlled in the range of 2.3-2.7%.

[0013] Manganese: adding a certain amount of Mn in ductile cast iron can refine graphite balls, promote graphitization, strengthen the matrix structure, increase hardness and strength, but the addition of Mn will reduce the toughness of ductile cast iron, at the same time, the addition of excessive Mn will increase the volume of graphite balls and reduce the number of graphite balls, and reduce the roundness of graphite balls. Mn is mainly brought in by scrap steel. Considering comprehensively, the content of Mn is controlled in the range of 0.1-0.3%.

[0014] Vanadium: adding a small amount of V in ductile cast iron can realize the purposes of strengthening the structure, refining the grains and increasing the hardness, so as to improve the pressure resistance and wear resistance of the ductile cast iron for valves. However, V can greatly promote the generation of pearlite, thereby reducing the toughness and corrosion resistance of the material. Considering the performance requirements of the ductile cast iron for valves, the content of V is controlled in the range of 0.03-0.08%.

[0015] Zirconium: Zr is a strong affinity element of O, S and N, which can purify the iron liquid, generate high-melting-point compounds by adding a small amount, serve as the nucleation core of graphite, increase the number of graphite, pin the grain boundaries and achieve the purpose of refining the structure. At the same time, the addition of Zr can promote the formation of passivation film on the surface of the ductile cast iron, and has a positive effect on the improvement of corrosion resistance. Considering comprehensively, the content of Zr is controlled in the range of 0.03-0.06%.

[0016] Cerium: the addition of rare earth Ce in the iron liquid can have good desulfurization and deoxidization effects, purify the iron, change the morphology and distribution of inclusions in the steel, especially the complex synergistic effect of Ce and Zr on the iron liquid, the formed compounds can serve as the nucleation core of graphite, increase the number of graphite balls, at the same time, the addition of Ce can promote the graphitization of graphite balls and improve the sphericity of graphite balls. Considering comprehensively, the content of Ce is controlled in the range of 0.03-0.06%.

[0017] Residual P and S are harmful elements for ductile cast iron, which can easily cause cracking of castings, and the contents of the two in the castings should be reduced as much as possible. The content of S is controlled to be ≤0.04%, and the content of P is controlled to be ≤0.04%.

[0018] Preferably, according to the determination standard of GB / T 9441-2021, the spheroidization level of the ductile cast iron is grade 2, and the graphite size classification is grade 7. The graphite ball morphology is regular, which can strengthen the mechanical properties of the material and reduce the size of the graphite ball, thereby improving the fluidity of the steel liquid and reducing casting defects.

[0019] Preferably, according to the determination standard of GB / T 9441-2021, the pearlite content of the ductile cast iron is 12.5%-15.7%.

[0020] According to the provisions in GB / T 9441, the pearlite content can be automatically recognized by the metallographic microscope analysis software after the preparation of the metallographic sample and etching, which is closest to the volume content.

[0021] By regulating the pearlite ratio, combining with the comprehensive effect of precipitation strengthening and fine-grain strengthening, the strength and hardness of the spheroidal graphite cast iron material can be improved to some extent, so that the spheroidal graphite cast iron material has better comprehensive mechanical properties.

[0022] The application also specifically protects a preparation method of the spheroidal graphite cast iron material, which comprises the following steps:

[0023] S1. Melting, slag collecting and slagging of raw materials, controlling the content of each element to be in the range of 3.4-3.8% of C, 2.3-2.7% of Si, 0.02-0.05% of Mg, 0.1-0.3% of Mn, ≤0.04% of S, ≤0.04% of P, and the rest being iron and inevitable impurities, to obtain molten iron liquid;

[0024] S2. Laying the modifying agent, spheroidizing agent and inoculant from bottom to top in the reaction tank in turn, tamping, pressing with a 3-5mm steel plate, heating to 500-550℃, baking, pouring the molten iron liquid obtained in S1 into the ladle for spheroidizing and primary inoculation, after the molten iron liquid is completely poured, performing slag collecting and slagging, adding inoculant, and performing secondary inoculation by using the ladle covering inoculation method, wherein the modifying agent is a mixture of zirconium-iron, cerium-iron and vanadium-iron;

[0025] S3. Pouring the molten iron liquid treated in S2 into a sand mold for filling and feeding, naturally cooling to below 200℃, then opening the mold, removing the pouring and riser, shot blasting, polishing, to obtain the spheroidal graphite cast iron material.

[0026] In some specific embodiments, preferably, the raw materials in S1 are scrap steel, carburizing agent, nodular iron return material and silicon-iron, and the melting temperature is 1470-1510℃.

[0027] The synthetic spheroidal graphite cast iron using scrap steel, carburizing agent and nodular iron return material as main raw materials makes full use of the advantages of high-quality scrap steel resources in China's industrial production, meets the requirements of the national resource comprehensive utilization strategy, reduces the use of more expensive cast pig iron, reduces production cost, significantly improves the performance-price ratio of spheroidal graphite cast iron products and the economic benefits of production enterprises.

[0028] Specific operations of the molten iron liquid obtained in S1 can refer to the following:

[0029] The scrap steel, carbon additive, nodular iron re-melted material, ferrosilicon are sequentially put into smelting, the smelting temperature is 1470-1510℃, after the metal is completely melted, the slag collector is added to collect slag, then the slag is removed, the pre-chemical composition is detected, the element content is controlled to be in the range of 3.4-3.8% of C, 1.34-1.45% of Si, 0.02-0.05% of Mg, 0.1-0.3% of Mn, ≤0.04% of S, ≤0.04% of P, and the rest is iron and inevitable impurities, then the temperature is quickly raised to 1590-1600℃, and the temperature is kept for 3-5 min, the slag collector is added again to collect slag, the output power of the intermediate frequency furnace is reduced, the iron liquid is kept, when the temperature reaches 1550-1560℃, the slag is removed, and then the smelting iron liquid is obtained.

[0030] The specific operation of spheroidizing and inoculating in S2 can refer to the following:

[0031] While the molten iron is smelted, 0.15-0.25% of crushed zirconium iron, cerium iron and vanadium iron mixed modifier (particle size ≤3mm, wrapped with thin iron sheet), 1.0-1.2% of spheroidizing agent (particle size 5-20mm), and 0.6-0.8% of inoculant (particle size 1-5mm) are weighed, the mixed modifier, spheroidizing agent and inoculant are sequentially laid from bottom to top in the bottom reaction pool of the ladle, and a 3-5mm thick steel plate is pressed on the top after being tamped, then the ladle is kept at 500-550℃ to avoid rapid temperature drop when the smelting iron liquid is poured into the ladle.

[0032] The smelting iron liquid of S1 is poured into the baked ladle for spheroidizing and primary inoculation, when the smelting iron liquid is poured into the ladle, it cannot directly impact the reaction pool, after a certain amount of smelting iron liquid is poured, the iron plate on the reaction pool is melted, and the inoculation, spheroidizing and modification are sequentially performed in the reaction pool according to the contact order of the smelting iron liquid with the inoculant, spheroidizing agent and modifier. After the smelting iron liquid is completely poured, the slag collector is scattered on the surface of the iron liquid, when the temperature drops to 1390-1410℃, the slag is removed, and 0.05-0.07% of inoculant of the mass of the molten iron is added to perform secondary inoculation by the ladle covering inoculation method.

[0033] S3. The treated iron liquid in S2 is quickly poured into a resin sand molded sand mold, after the mold is filled, 1-2 min is waited, then the molten iron is supplemented from the casting riser to perform the shrinkage compensation. After natural cooling to below 200℃, the sand mold is opened, the sand is removed, the pouring riser is removed, the shot blasting is performed, the polishing is performed, and the finished nodular cast iron material is obtained.

[0034] In some specific embodiments, preferably, the amount of the modifier in S2 is 0.15-0.25% of the mass of the smelting iron liquid, and the average particle size of the modifier is ≤3mm.

[0035] In some embodiments, preferably, the amount of spheroidizing agent in S2 is 1.0-1.2% of the mass of the molten iron liquid, and the average particle size of the spheroidizing agent is 5-20mm.

[0036] In some embodiments, preferably, the amount of primary inoculant in S2 is 0.6-0.8% of the mass of the molten iron liquid, and the average particle size of the inoculant is 1-5mm.

[0037] In some embodiments, preferably, the amount of secondary inoculant in S2 is 0.05-0.07% of the mass of the molten iron liquid, and the average particle size of the inoculant is 1-3mm.

[0038] The average particle size described above needs to be determined in combination with the size of the reaction ladle, i.e., the weight and temperature of the molten steel, and the particle size can control the reaction speed.

[0039] It should be noted that:

[0040] In the preparation method of the present application, the mass percentage of the initial molten iron composition is C: 3.4-3.8%, Si: 1.34-1.45%, Mn: 0.1-0.3%, S≤0.04%, P≤0.04%, the spheroidizing agent used in S2 is preferably QRMg8RE3 spheroidizing agent containing 38-42% Si, the primary inoculant used is preferably Si-Ba inoculant containing 68-72% Si, and the secondary inoculant used is preferably 75 ferrosilicon containing 74-76% Si, which can effectively increase the Si content during the spheroidizing and inoculating process. At the same time, the mixed modifier of zirconium iron, cerium iron and vanadium iron is reacted with the molten iron liquid at the last stage of the reaction of the molten iron liquid with the Si-Ba inoculant and the QRMg8RE3 spheroidizing agent, at which time the cleanliness of the molten iron liquid is higher, which can ensure a higher yield.

[0041] The present application also specifically protects the application of the ductile cast iron material in the preparation of water supply and drainage valve castings.

[0042] The ductile cast iron material of the present application can meet the mechanical property requirements and corrosion resistance requirements of valve materials without heat treatment, reducing the energy consumption and time cost brought by the heat treatment process, and is a low-cost short-process preparation technology, which can be widely applied in the preparation of water supply and drainage valve castings.

[0043] Compared with the prior art, the present application has the following advantages:

[0044] The spheroidal graphite cast iron material of the present application promotes the formation of a protective passivation film of the spheroidal graphite cast iron material by adding trace Zr element, so that a spheroidal graphite cast iron material with better corrosion resistance is obtained, and on the basis of ensuring the toughness and safety of the spheroidal graphite cast iron material by taking ferrite matrix as the main body, the content of pearlite structure is appropriately increased by adding trace alloy element V, so that the hardness and strength are improved, and the wear resistance and compression resistance of the spheroidal graphite cast iron are increased.

[0045] The preparation method of the spheroidal graphite cast iron material of the present application purifies the iron liquid, strengthens the spheroidal graphite inoculation effect, increases the nucleation core of graphite, improves the number and sphericity of graphite, and refines the structure by adding zirconium iron and cerium iron in the later stage of conventional spheroidizing inoculation treatment.

[0046] The spheroidal graphite cast iron material of the present application has a tensile strength of 532-548 MPa, an elongation after fracture of 18.0-20.5%, a Brinell hardness of 198-207 HBW, a spheroidization level of 2, a graphite size classification of 7, a pearlite content of 12.5-15.7%, and a static corrosion rate in simulated seawater of 0.009-0.011 mm / a. DETAILED DESCRIPTION

[0047] The present application will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present application in any form. Unless otherwise specified, the raw materials used in the embodiments of the present application are conventional commercially available raw materials.

[0048] The test method of each performance of the spheroidal graphite cast iron obtained by the present application is as follows:

[0049] Mechanical properties: GB / T 228 metal material tensile test method at room temperature; GB / T 231.1 metal Brinell hardness test part 1: test method;

[0050] Metallographic structure: GB / T 9441 spheroidal graphite cast iron metallographic detection;

[0051] Corrosion resistance: in a simulated seawater solution, the corrosion rate is obtained by converting the electrochemical curve measured by a Gamry Interface 1000 electrochemical workstation.

[0052] Example 1

[0053] The present embodiment provides a spheroidal graphite cast iron material, and the mass percentage of the chemical composition of the spheroidal graphite cast iron is C: 3.58%, Si: 2.54%, Mn: 0.21%, Zr: 0.03%, V: 0.04%, Ce: 0.03%, Mg: 0.05%, S: 0.012%, P: 0.023%, and the rest is iron and inevitable impurities.

[0054] The preparation method of the spheroidal graphite cast iron comprises the following steps:

[0055] S1. Waste steel 800 kg, carbon additive 32 kg, ductile iron return material 750 kg, ferrosilicon 1 kg are sequentially put into a medium-frequency induction furnace for smelting, the smelting temperature is 1500 DEG C, after the metal is completely melted, a slag collector is added to collect slag, then the slag is removed, the pre-furnace chemical composition is detected, after the composition meets the requirements, the power of the furnace is increased to 1590 DEG C, and then the slag is collected again, the output power of the medium-frequency furnace is turned off, the iron liquid is left to stand, and when the furnace temperature reaches 1550 DEG C, the slag is removed, and then the furnace is discharged;

[0056] S2. The iron liquid in step S1 is poured into a ladle for spheroidizing and inoculating treatment, the ladle is obtained by sequentially laying zirconium iron, cerium iron and vanadium iron mixed modifiers 2.4 kg, QRMg8RE3 spheroidizing agent 19 kg and Si-Ba inoculant 11.5 kg from bottom to top in the reaction pool, tamping and then pressing a 5mm thick steel plate on the top, and baking the ladle to 500 DEG C for pre-treatment by using a ladle baker. After the iron liquid is completely poured, the slag collector is scattered on the surface of the iron liquid, when the temperature drops to 1390 DEG C, the slag is removed, and 1.0 kg of 75SiFe is added for secondary inoculation.

[0057] S3. The iron liquid treated in step S2 is quickly poured into a sand mold of resin sand molding, after the mold is filled, about 2 minutes are waited, then the iron liquid is poured from the casting head to supplement the shrinkage. Naturally cooled to below 200 DEG C, then the box is opened, the sand is removed, the pouring head is removed, the shot blasting is performed, the polishing is performed, and the finished spheroidal graphite cast iron material is obtained.

[0058] The performance of the spheroidal graphite cast iron obtained in the embodiment is tested, and the results are as follows: the tensile strength is 532 MPa, the elongation after fracture is 20.5%, the Brinell hardness is 198 HBW, the spheroidization level is 2, the graphite size classification is 7, the pearlite content is 12.5%, and the static corrosion rate in simulated seawater is 0.011 mm / a.

[0059] Example 2

[0060] The spheroidal graphite cast iron material provided in the embodiment has the following chemical composition: C: 3.72%, Si: 2.68%, Mn: 0.18%, Zr: 0.05%, V: 0.06%, Ce: 0.04%, Mg: 0.04%, S: 0.013%, P: 0.024%, and the rest is iron and inevitable impurities.

[0061] The preparation method of the spheroidal graphite cast iron comprises the following steps:

[0062] S1. Put scrap steel 400 kg, carbon additive 16 kg, nodular iron return material 400 kg, ferrosilicon 0.5 kg into the intermediate frequency induction furnace in turn for smelting, the smelting temperature is 1480℃, after the metal is completely melted, the slag collector is added on the surface to collect slag, then the slag is removed, the chemical composition before the furnace is detected, and after the composition meets the requirements, the power of the electric furnace is increased to 1600℃, and then the slag collector is added again to collect slag, the output power of the intermediate frequency furnace is turned off, the iron liquid is left to stand, and when the temperature reaches 1560℃, the slag is removed, and then the furnace is discharged;

[0063] S2. Pour the iron liquid in step S1 into the iron ladle for spheroidizing and inoculation treatment, the iron ladle is obtained by sequentially laying zirconium iron, cerium iron and vanadium iron mixed modifier 1.7 kg, QRMg8RE3 spheroidizing agent 9.8 kg and Si-Ba inoculant 5 kg from bottom to top in the reaction pool, tamping, then pressing a 3mm thick steel plate on the top, and baking the iron ladle to 500℃ for pretreatment by using the ladle baker. After the iron liquid is completely poured, the slag collector is scattered on the surface of the iron liquid, when the temperature drops to 1405℃, the slag is removed, and 0.5kg of 75SiFe is added for secondary inoculation.

[0064] S3. Pour the treated iron liquid in step S2 into the resin sand mold quickly, wait for about 2min after the mold is filled, then supplement the iron liquid from the casting head to supplement the shrinkage. Naturally cool to below 200℃, then open the box, drop the sand, remove the pouring head, shot blasting, polishing, and quality inspection to obtain the finished nodular cast iron material.

[0065] Test the properties of the nodular cast iron obtained in this embodiment, and the results are as follows: tensile strength 543MPa, elongation after fracture 18.2%, Brinell hardness 205HBW, spheroidization level 2, graphite size classification 7, pearlite content 14.3%, and static corrosion rate in simulated seawater is 0.009mm / a.

[0066] Example 3

[0067] The embodiment provides a nodular cast iron material, the chemical composition of the nodular cast iron is as follows: C: 3.53%, Si: 2.47%, Mn: 0.22%, Zr: 0.06%, V: 0.08%, Ce: 0.06%, Mg: 0.04%, S: 0.013%, P: 0.017%, and the rest is iron and inevitable impurities.

[0068] The preparation method of the nodular cast iron comprises the following steps:

[0069] S1. Put scrap steel 600 kg, carbon additive 24 kg, nodular iron return material 200 kg, ferrosilicon 0.75 kg into the intermediate frequency induction furnace in turn for melting, the melting temperature is 1490℃, after the metal is completely melted, the slag collector is added on the surface to collect slag, then the slag is removed, the chemical composition before the furnace is detected, and after the composition meets the requirements, the power of the electric furnace is increased to 1600℃, and then the slag collector is added again to collect slag, the output power of the intermediate frequency furnace is turned off, and the iron liquid is left to stand until the tapping temperature 1560℃ is reached, then the slag is removed, and then the furnace is tapped;

[0070] S2. Pour the molten iron in step S1 into the ladle for spheroidizing and inoculation treatment, the ladle is obtained by sequentially laying zirconium iron, cerium iron and vanadium iron mixed modifier 2.5 kg, QRMg8RE3 spheroidizing agent 9.1 kg and Si-Ba inoculant 5.7 kg in the reaction pool from bottom to top, tamping, and then pressing a 3mm thick steel plate on the top and baking the ladle to 500℃ for heat preservation pretreatment. After the molten iron is completely poured, the slag collector is added on the surface of the molten iron, and when the temperature drops to 1400℃, the slag is removed, and 0.45 kg of 75SiFe is added for secondary inoculation.

[0071] S3. Pour the treated molten iron in step S2 into the resin sand mold quickly, wait for about 2 min after the mold is filled, then supplement the molten iron from the casting head to supplement the shrinkage. Naturally cool to below 200℃, then open the box, drop the sand, remove the pouring head, shot blasting, polishing, and quality inspection to obtain the finished nodular cast iron material.

[0072] Test the properties of the nodular cast iron obtained in this embodiment, and the results are as follows: tensile strength 548 MPa, elongation after fracture 18.0%, Brinell hardness 207 HBW, spheroidization level 2, graphite size classification 7, pearlite content 15.7%, and static corrosion rate in simulated seawater 0.010 mm / a.

[0073] Comparative Example 1

[0074] The mass percentage of the chemical composition of the nodular cast iron in this comparative example is C: 3.71%, Si: 2.69%, Mn: 0.18%, Mg: 0.04%, S: 0.015%, P: 0.027%, and the rest is iron and unavoidable impurities.

[0075] The preparation method of Comparative Example 1 and Example 2 is different in that no zirconium iron, cerium iron and vanadium iron mixed modifier is added during spheroidizing and inoculation treatment in the ladle, and the nodular cast iron does not contain Zr, V and Ce elements.

[0076] The properties of the spheroidal graphite cast iron obtained are as follows: tensile strength 488 MPa, elongation after fracture 24.5%, Brinell hardness 183 HBW, spheroidization grade 3, graphite size grade 6, pearlite content 4.7%, and static corrosion rate in simulated seawater 0.017 mm / a. Compared with Example 2, the strength, hardness and corrosion resistance of the spheroidal graphite cast iron of this comparative example have certain gaps, the elongation is improved to a certain extent, and the corrosion resistance of the material is also severely decreased.

[0077] Comparative Example 2

[0078] The spheroidal graphite cast iron material provided in this example has the following chemical composition by mass percentage: C: 3.61%, Si: 2.49%, Mn: 0.21%, Zr: 0.08%, V: 0.12%, Ce: 0.03%, Mg: 0.04%, S: 0.014%, P: 0.017%, and the balance being iron and inevitable impurities.

[0079] The spheroidal graphite cast iron is prepared according to the method of Example 2, except that the Zr content is 0.08% and the V content is 0.12%.

[0080] The properties of the spheroidal graphite cast iron obtained are as follows: tensile strength 488 MPa, elongation after fracture 24.5%, Brinell hardness 183 HBW, spheroidization grade 3, graphite size grade 6, pearlite content 4.7%, and static corrosion rate in simulated seawater 0.017 mm / a. Compared with Example 2, the strength, hardness and corrosion resistance of the spheroidal graphite cast iron of this comparative example have certain gaps, the elongation is improved to a certain extent, and the corrosion resistance of the material is also severely decreased.

[0081] Obviously, the above embodiments of the present application are merely exemplary and are not intended to limit the implementation modes of the present application. Based on the above description, other different forms of changes or modifications can be made by those skilled in the art. Here, it is not necessary or possible to exhaust all the implementation modes. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A method of producing a spheroidal graphite cast iron material, characterized by, It comprises the following steps: S1. Melting, slag collecting and slagging of raw materials, controlling the content of each element in the range of 3.4-3.8% of C, 2.3-2.7% of Si, 0.02-0.05% of Mg, 0.1-0.3% of Mn, ≤0.04% of S, ≤0.04% of P, and the rest being iron and inevitable impurities, to obtain molten iron liquid; S2. Laying the modifier, spheroidizing agent and primary inoculant agent in the reaction tank from bottom to top, tamping and then pressing with 3-5 mm steel plate, heating to 500-550℃ for heat preservation to perform baking, pouring the molten iron liquid obtained in S1 into the ladle for spheroidizing and primary inoculation, after the molten iron liquid is completely poured in, performing slag collecting and slagging, and adding secondary inoculant agent, and performing secondary inoculation by ladle covering inoculation method, wherein the modifier is a mixture of zirconium iron, cerium iron and vanadium iron; S3. Pouring the treated iron liquid in S2 into a sand mold for filling and feeding, and naturally cooling to below 200℃, then opening the mold, removing the pouring and running risers, shot blasting, polishing, to obtain the ductile cast iron material; The ductile cast iron material comprises the following elements in mass percentage: 3.4-3.8% of C, 2.3-2.7% of Si, 0.1-0.3% of Mn, 0.03-0.06% of Zr, 0.03-0.08% of V, 0.03-0.06% of Ce, 0.02-0.05% of Mg, ≤0.04% of S, ≤0.04% of P, and the rest being iron and inevitable impurities.

2. The method of producing a spheroidal graphite cast iron material according to claim 1, characterized by, According to the determination standard of GB / T 9441-2021, the spheroidization level of the ductile cast iron is level 2, and the graphite size is level 7.

3. The method of producing a spheroidal graphite cast iron material according to claim 1, wherein According to the determination standard of GB / T 9441-2021, the pearlite content of the ductile cast iron is 12.5%-15.7%.

4. The method of producing a spheroidal graphite cast iron material according to claim 1, characterized by, The raw materials in S1 are scrap steel, carburizing agent, ductile iron return-to-furnace material and silicon iron, and the melting temperature is 1470-1510℃.

5. The method of producing a spheroidal graphite cast iron material according to claim 1, wherein The amount of the modifier in S2 is 0.15-0.25% of the mass of the molten iron liquid, and the average particle size of the modifier is ≤3 mm.

6. The method of producing a spheroidal graphite cast iron material according to claim 1, wherein The amount of the spheroidizing agent in S2 is 1.0-1.2% of the mass of the molten iron liquid, and the average particle size of the spheroidizing agent is 5-20 mm.

7. The method of producing a spheroidal graphite cast iron material according to claim 1, wherein The amount of the primary inoculant agent in S2 is 0.6-0.8% of the mass of the molten iron liquid, and the average particle size of the inoculant agent is 1-5 mm.

8. The method of producing a spheroidal graphite cast iron material according to claim 1, wherein The amount of the secondary inoculant agent in S2 is 0.05-0.07% of the mass of the molten iron liquid, and the average particle size of the inoculant agent is 1-3 mm.

9. The ductile cast iron material prepared by the preparation method of claim 1 is applied to the preparation of water supply and drainage valve castings.