Nitrogen-increased and strengthened large-section gray cast iron profile with phi of more than 120mm and equivalent size and preparation method of large-section gray cast iron profile

Abstract

The invention discloses a nitrogen-increased and strengthened large-section gray cast iron profile with a diameter of more than 120 mm and a considerable size. The large-section gray cast iron profile comprises the following components in percentage by weight: 3.0-3.7% of C, 1.8-3.2% of Si, 0.6-1.1% of Mn, less than or equal to 0.10% of P, less than or equal to 0.06% of S, 0.0095-0.0105% of N and the balance of Fe. The high-nitrogen manganese nitride is utilized to introduce a trace amount of nitrogen element, and the problems that the surface structure and the core structure of an existing large-section gray cast iron profile material are different, the mechanical property uniformity is poor, and the full-section sensitivity is poor are solved. The invention further discloses a preparation method of the nitrogen-increased and strengthened large-section gray cast iron profile with the diameter phi being 120 mm or above and the considerable size.

Description

Technical Field

[0001] The invention belongs to the technical field of cast iron materials and horizontal continuous casting, and specifically relates to nitrogen-enhanced large-section gray cast iron profiles with a cross-section of more than Φ120 mm or equivalent, and also relates to a preparation method of nitrogen-enhanced large-section gray cast iron profiles with a cross-section of more than Φ120 mm or equivalent. Background Art

[0002] Gray iron profiles are high-quality gray cast iron blank materials produced by horizontal continuous casting. During the production process, cast iron, scrap steel, recycled materials, ferromanganese and other furnace materials are prepared according to the required composition ratio and alloy burnout rate, and then added to the medium frequency induction furnace to melt into raw iron water. The raw iron water is poured into the holding furnace after inoculation treatment. The treated iron water is rapidly cooled and solidified in the high-purity graphite mold in the water-cooled steel sleeve. The rapid cooling of the graphite mold causes the iron water to cool rapidly and nucleate and grow. The solidification rate is much faster than sand casting. Since the crystallizer is installed at the bottom of the holding furnace, the pure iron water directly enters the crystallizer from the bottom of the holding furnace to solidify. Therefore, the horizontal continuous casting gray iron profiles do not have the conventional casting defects such as slag inclusion and sand inclusion of ordinary sand casting. At the same time, the holding furnace is equivalent to a large riser, and the gray iron profiles do not have shrinkage defects such as shrinkage cavities and shrinkage porosity of ordinary sand casting. The gray cast iron profiles have the advantages of good product quality, excellent comprehensive mechanical properties, high density, good processing performance, etc., and have been widely used in machinery, hydraulics, metallurgy, textile, printing and other industries.

[0003] Usually, the microstructure of gray cast iron profiles is fine flake graphite (usually a layer of finer D-type graphite with a periphery of 10mm, and relatively fine A-type graphite inside), and the matrix is ​​ferrite and pearlite. In general, the tensile properties of gray cast iron profiles are σ b =250-300MPa, Brinell hardness is HB150-250, and elastic modulus is E=113-157GPa. Among them, when the tensile strength is 300MPa, the bending fatigue strength of the gray cast iron profile reaches 210MPa. It can be seen that the gray cast iron profile obtained by continuous casting has excellent comprehensive mechanical properties, so it has been widely used in many industrial fields.

[0004] However, due to the effect of gravity and different solidification conditions, the cross-sectional structure of the gray cast iron profile is not symmetrical from top to bottom after solidification. The lower structure is relatively fine, while the upper structure is relatively coarse, especially for gray cast iron profiles with larger cross-sectional dimensions. The larger the cross-sectional dimension, the greater the difference in graphite morphology, stone length, number and size of eutectic groups in the surface and core structures of the gray cast iron profile, especially the difference in the aspect ratio of graphite and the distance between the arms of the secondary dendrites of primary austenite. In addition, the amount of pearlite is also different. The surface 10mm of the gray cast iron profile is basically ferrite. The amount of pearlite increases as it moves toward the core of the gray cast iron profile, and even the amount of pearlite in the core of some specially treated profiles may reach more than 95%. These directly affect its mechanical properties, especially the hardness and tensile strength of the material, and the larger the cross-sectional dimension, the greater the difference in mechanical properties from the outside to the inside of the cross-section, and the greater the difference in cross-sectional uniformity. This kind of structural non-uniformity directly affects the high-quality characteristics of gray cast iron profiles, especially for some large-sized parts that require high uniformity of internal and external structures, such as large hydraulic valve bodies and hydraulic module groups, which still cannot use gray cast iron profiles. In addition, with the application and development of high-end equipment, higher requirements are put forward for the mechanical properties of high-strength gray cast iron profiles. Some manufacturers even put forward the requirement that the tensile properties of gray cast iron profiles must reach more than 400MPa. When considering the machining performance, the hardness of gray cast iron profiles must be lower than HB240.

[0005] Manufacturers of continuously cast gray cast iron profiles are eager to solve this technical problem, but the characteristics of horizontal continuous casting determine its graphite morphology, matrix structure and mechanical properties, which undoubtedly limits the industrial application and development of this high-quality gray cast iron material from one aspect.

[0006] For gray cast iron, the conventional method to improve the uniformity of structure and performance is to add alloying elements to improve the mechanical properties of the material through alloying. However, due to cost considerations, for example, a trace amount of Sb is used to replace alloying elements such as Cu, Ni, and Mo to increase the pearlite content, thereby improving mechanical properties and reducing costs. However, the addition of Sb is often beneficial to increase the pearlite content, but at the same time, once there is a risk of deteriorating the graphite morphology, it will bring certain difficulties to stable production.

[0007] Based on this, some scholars proposed to use trace and cheap N elements to improve the strength of gray cast iron, reduce costs and improve economic benefits. For sand casting, there have been some beneficial attempts and some successful cases. For example, Japanese Chisato Okada added N elements to Fe-Mn-N alloy. For every 0.001% increase, the performance of gray cast iron can be improved by 5-7MPa and the hardness can be increased by about HB3-4. Many scholars at home and abroad have confirmed that the N element has reached a certain content, and the role of N element in strengthening gray cast iron is affirmed. However, the strengthening effect is different, and there is a large gap in the way of introducing N elements. The law of the stable absorption rate of N elements is also uncertain. It is also uncertain whether it is the result of the interaction between N elements and other alloying elements. As we all know, the solubility of N elements in molten iron is mainly affected by the temperature of molten iron and the content of alloying elements such as C, Si, and Mn. The content of C and Si determines the carbon equivalent CE. Since the reduction of CE is conducive to improving the solubility of N elements, but if CE is too low, the tendency of molten iron to white cast iron increases during solidification, affecting the subsequent processing and mechanical properties of the material. It can be seen that, especially for the stable absorption rate of N element, how to control it by selecting different additive media, processes and addition amounts, and combining cost considerations, and also considering the content of impurity elements introduced thereby. In addition, it is also necessary to control the timing of adding N element. If it is added too early, the induction heating of molten iron during the smelting process forces the molten iron to flow, and N atoms are easily merged into N2 molecules, which provides the possibility of forming bubbles. Therefore, for N-strengthened gray cast iron, the addition of N element should not be too early, and at the same time, the N content in the molten iron needs to be strictly controlled. If it is too low, the effect is not obvious, and if it is too high, N2 bubbles may be formed, which may not achieve the strengthening effect but may reduce the mechanical properties. Although there have been some useful attempts and reports on the role of N element in sand casting, however, no reports have been seen at home and abroad for horizontal continuous casting of gray cast iron profiles. At the same time, since the production processes of sand casting and horizontal continuous casting are completely different, especially the solidification conditions of the two are very different, the process parameters of sand casting have no great reference value and guiding significance for horizontal continuous casting production. In addition, for large-section gray cast iron profiles with a diameter of Φ120 mm or above and equivalent sizes, the larger the cross-sectional diameter (size), the greater the difference in structure and performance from the surface to the center of the section, that is, the more obvious the section sensitivity, and it is more important to improve the mechanical properties of the structure in the center of the profile, so as to narrow the difference in mechanical properties between the surface and the center and reduce the section sensitivity. Summary of the invention

[0008] The purpose of the present invention is to provide a large-section gray cast iron profile with a size of more than Φ120 mm or equivalent that is nitrogen-enhanced, and to introduce a trace amount of nitrogen by using high-nitrogen manganese nitride, thereby indirectly changing the solidification process of molten iron in a crystallizer, and then indirectly controlling the aspect ratio morphology of graphite in the horizontal continuous casting gray cast iron profile material, so as to prepare a large-section high-quality gray cast iron profile material with a size of more than Φ120 mm or equivalent, and solve the problems of the difference between the surface structure and the core structure of the existing large-section gray cast iron profile materials, as well as the poor uniformity of mechanical properties and the poor sensitivity of the entire section.

[0009] Another object of the present invention is to provide a method for preparing nitrogen-enhanced gray cast iron profiles with large cross-sections of Φ120 mm or larger and equivalent sizes.

[0010] The first technical solution adopted by the present invention is that the nitrogen-enhanced large-section gray cast iron profiles with a size of Φ120 mm or above and equivalent are composed of the following weight percentages: C: 3.0-3.7%, Si: 1.8-3.2%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%, N: 0.0095-0.0105%, and the rest is Fe.

[0011] The second technical solution adopted by the present invention is a method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent, comprising the following steps: Step 1, smelting molten iron and adding high-nitrogen manganese nitride; Step 2, one-time incubation and trace element adjustment; Step 3, secondary inoculation of molten iron; Step 4, pouring; Step 5, horizontal continuous casting.

[0012] The present invention is also characterized in that: Step 1 is as follows: A medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a portion of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace power is fully opened until all the furnace materials are completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the 10% burn-out amount; after all the ferroalloys are melted, the original molten iron is taken for rapid composition in front of the furnace Analyze, determine and add scrap steel, 75% ferrosilicon, carburizer or 30% ferromanganese as needed, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the gray cast iron profiles of the required size for production. Use a high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer to conduct a rapid analysis of the components before the furnace. According to the set value of the content of each alloy element, determine and add the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer; the melting temperature is 1520℃-1550℃. After all the added furnace materials are melted, reduce the smelting power to avoid excessive tumbling of the molten iron, and let the molten iron stand for 5 minutes-10 minutes to facilitate the slag in the molten iron to fully float; After removing the slag floating on the surface of the molten iron, add high-nitrogen manganese nitride blocks with a size of 30mm-40mm; immediately turn on full power to melt the high-nitrogen manganese nitride blocks after adding them, so that the high-nitrogen manganese nitride blocks melt quickly; the analysis of the N element is carried out using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0095-0.0105%, ready for tapping, inoculation and pouring; before each tapping, a quick analysis of the furnace composition and a slight adjustment of the composition are performed; Control according to the original iron liquid's C: 3.0-3.7%, Si: 1.4-2.4%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%; tapping when N: 0.0095-0.0105%; The content of each alloy element in the high nitrogen manganese nitride used is: 9-10% N, 88-90% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0013] In step 1, the melting temperature is 1520°C-1550°C, and the tapping temperature is 1420°C-1460°C.

[0014] Step 2 is as follows: (1) Baked buns In order to meet the requirements of wire feeding inoculation treatment, a suitable ladle is selected, wherein the selected ladle is a special ladle with a molten iron depth / inner diameter ≥1.5; first, the built ladle is baked for 2-4 hours using a special ladle baking device; before the molten iron is discharged, the ladle is scalded, the molten iron in the electric furnace is poured into the pre-baked ladle and left for 3-5 minutes, and then the molten iron is poured back into the electric furnace, and this is repeated three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle; (2) Iron tapping and primary inoculation The weight of each package of molten iron is controlled according to the cross-sectional size of the gray cast iron profiles produced. The first package of molten iron is 50kg-100kg more than each subsequent package of molten iron. Taking the production of gray cast iron profiles with a diameter of Φ200mm as an example, the first package of molten iron is 700kg-800kg, and the subsequent packages of molten iron are 650kg-700kg. The tapping temperature is 1420℃-1460℃; the slag is quickly removed after tapping and hoisted to the inoculation treatment platform; Commercial inoculated core wires are used to treat molten iron through wire feeding inoculation process. According to the empirical data of set composition and inoculation effect, the usage of inoculated core wires is calculated according to the following standard: (1.5m-2m) / 100kg molten iron; the diameter of commercial inoculated core wire is Φ13mm, the weight of core material is (200g-240g) / m, and the unit wire weight is (420g-440g) / mm; after inoculation treatment, the molten iron surface is deslagging for pouring; In step 2, the corresponding grade of the inoculated cored wire is YDB002, YDB005 or YDB008.

[0015] Step 3 is as follows: According to the weight of each bag of molten iron, the long-acting ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented, the total amount of the secondary inoculant is 0.2-0.3% of the amount of molten iron in the ladle, and the particle size of the secondary inoculant is 3mm-8mm; after the molten iron of the primary inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; In step 3, floating silicon inoculation is used for the second inoculation, and the added long-lasting ferrosilicon inoculant containing strontium and barium covers the spheroidizing agent.

[0016] Step 4 is as follows: First, the newly built insulation furnace is baked in a special oven for 4 to 6 hours to ensure that the water vapor in the furnace lining material is released; Secondly, before pouring molten iron, the furnace wall in the holding furnace is baked for 30 minutes to 60 minutes by using atomized diesel nozzle flame until the furnace wall is bright red; in this process, before the atomized diesel nozzle flame baking is enabled, a crystallizer is installed on the holding furnace, and a dummy head is inserted into the crystallizer. The dummy head is connected to the dummy rod and can be pulled and drawn by a traction machine; Third, pouring molten iron: pour the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production. The pouring temperature is 1350℃-1400℃.

[0017] Step 5 is as follows: After pouring molten iron into the holding furnace, it stays for 1 minute to 2 minutes, so that the molten iron entering the crystallizer can wrap around the ingot head and start ingot pulling after crystallization and solidification. Continuous casting and production is carried out at the "pull-stop-pull" process level. The gray cast iron rod pulled out of the crystallizer is the gray cast iron profile. As the length of the gray cast iron profile increases, the ingot rods are removed one by one until the traction roller of the traction machine is directly pressed on the gray cast iron profile, and then it is cut and pressed according to the required fixed length to obtain the gray cast iron profile material.

[0018] In step 5, during the horizontal continuous casting process, the traction motor speed is 900rpm, the drawing time is 0.8s-2.5s, the residence time is 25s-35s, the crystallizer length is 300mm-600mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃-70℃, and the profile crystallizer outlet temperature is controlled to be 900℃-1050℃; the drawing speed and the profile outlet temperature are controlled to prevent furnace leakage, and the molten iron pouring interval is controlled to be 8 minutes-12 minutes to prevent the molten iron from decaying and causing graphite morphology variation or carbide.

[0019] The beneficial effects of the present invention are: (1) The gray cast iron profiles prepared by the present invention have a smooth surface, good quality, high dimensional accuracy, and are free of conventional casting defects such as sand inclusions, slag inclusions, pores, shrinkage cavities, etc. The structure is dense and uniform from the edge to the center. When the nitrogen content is 0.0095-0.0105%, the graphite is also refined, the graphite length tends to decrease, the graphite tip is passivated, the aspect ratio of the graphite is reduced, the cutting effect on the matrix is ​​weakened, the graphite curvature is increased, and the uniformity of the structure is improved. The increase in nitrogen can reduce the eutectic transformation temperature, expand the eutectic transformation temperature range, increase the supercooling of the eutectic transformation, and have a certain refinement effect and effect on the eutectic group; At the same time, nitrogen is a stabilizing element of pearlite, which can reduce the end temperature of the eutectoid transformation of gray cast iron, expand the eutectoid transformation temperature range, increase the eutectoid transformation supercooling, stabilize and increase the amount of pearlite, thereby refining the pearlite and reducing the distance between ferrite and cementite in the pearlite. Generally speaking, the higher the pearlite content, the higher the mechanical properties of gray cast iron, including tensile mechanical properties and hardness. In addition, due to the small atomic radius of nitrogen (RN = 0.75Å, R C = 0.91Å, R Fe =1.72Å, R Si =1.46Å), usually dissolved in ferrite or cementite as an interstitial solid solution, causing the ferrite or cementite lattice to distort, thereby increasing the resistance to dislocation movement. Therefore, the ferrite matrix or pearlite matrix structure can be strengthened, thereby improving the hardness and tensile strength of gray cast iron.

[0020] However, since the interstitial solid solution is a limited solid solution, the content of nitrogen atoms must be strictly controlled, otherwise there may be a risk of nitrogen bubbles or pores. Obviously, once nitrogen pores are generated, it will inevitably lead to discontinuity of the structure, which will in turn cause a significant reduction in mechanical properties and reduce the plasticity and toughness of the gray cast iron matrix.

[0021] (2) The hardness of the edge of the gray cast iron profile prepared by the present invention decreases by more than HB20, the hardness difference between the core and the surface is reduced to less than HB20, the cross-section sensitivity is significantly reduced, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, small cross-section uniformity difference, good cutting performance, and the cutting resistance is much smaller than that of steel parts. It can be high-speed fine processing, and the surface finish of the processing has relatively small fluctuations.

[0022] (3) The method of the present invention uses high-nitrogen manganese nitride as a nitrogen source. Commonly used nitrogen sources in industry include high-nitrogen manganese nitride, manganese nitride, ferromanganese nitride, ferrosilicon nitride and nitrogen. In the actual production of horizontal continuous casting, it was found that due to the relatively low nitrogen content of manganese nitride (6-7%N) and ferromanganese nitride (4-6%N), the production will affect the absorption of nitrogen and bring in more manganese; the nitrogen content of ferrosilicon nitride (26-35%N) is relatively high, and the nitrogen element is prone to aggregate into nitrogen bubbles and float during the melting process. Although the absorption rate is relatively high, it is difficult to stably control, which easily causes the nitrogen content to be unstable; directly using nitrogen, because it is difficult to introduce bubbles to the bottom of the molten iron, the bubbles float, and the absorption rate of nitrogen directly entering the molten iron is very low, and the stability is poor. It can be seen that using high-nitrogen manganese nitride as a nitrogen source is the best choice. It not only has the highest absorption rate, but also is the easiest to control the content, and the actual operation is more stable.

[0023] (4) The method of the present invention is specifically about the timing of addition and the selection of the size of the high-nitrogen manganese nitride block: the high-nitrogen manganese nitride is added in the later stage of smelting in the electric furnace during the molten iron smelting process, and the size of the high-nitrogen manganese nitride block used is 30mm-40mm, which is conducive to the rapid melting of the high-nitrogen manganese nitride block and is more conducive to improving the absorption and uniform distribution of the nitrogen element. The reason is that the timing and method of addition are very critical. The high-nitrogen manganese nitride contains 8-10% N and 85-90% Mn. When it is melted in the induction furnace, with the high-speed flow of molten iron under the action of electromagnetic induction, the nitrogen element is very easy to become a gas molecule and become a bubble floating up. In order to avoid burning and promote the absorption of nitrogen, its addition timing is very important. In addition, since the density of the high-nitrogen manganese nitride block is greater than the density of molten iron, although the induction furnace has a strong electromagnetic stirring effect, the high-nitrogen manganese nitride block is too large and may sink to the bottom of the electric furnace, which is not only not conducive to its melting, but also not conducive to the absorption and uniform distribution of nitrogen, and may cause burning of nitrogen. It can be seen that in the later stage of melting, after other metal materials and ferroalloys are melted and slag treatment is carried out, adding high nitrogen manganese nitride blocks with a size of 30mm-40mm is not only conducive to melting, but also to its homogenization. At the same time, this is conducive to reducing the difference between the internal and external structures of the gray cast iron profile, increasing the hardness of the core of the gray cast iron profile, reducing the hardness of the surface layer, and improving the mechanical processing performance of the gray cast iron profile.

[0024] (5) The method of the present invention increases the amount of the long-acting ferrosilicon inoculant containing strontium and barium during the secondary inoculation process, and adopts a secondary inoculation method to improve and prolong the inoculation effect, thereby avoiding the occurrence of carbides due to inoculation decay caused by long solidification time during the production of large-size cross-section gray cast iron profiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a photo of the gray cast iron profile material prepared by the method of the present invention; Figure 2 This is a photograph of the cross section of the gray cast iron profile material prepared by the method of the present invention. DETAILED DESCRIPTION

[0026] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] The present invention provides a large-section gray cast iron profile with a size of Φ120 mm or above and a corresponding size, which is nitrogen-enhanced and has the following composition by weight percentage: C: 3.0-3.7%, Si: 1.8-3.2%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%, N: 0.0095-0.0105%, and the rest is Fe.

[0028] High nitrogen manganese nitride is added during production, and the content of each alloy element is: 8-10% N, 85-90% Mn, other impurity elements are less than 0.1%, and the balance is Fe. The size of the selected high nitrogen manganese nitride block is 30-40mm. After adding high nitrogen manganese nitride treatment, the measured nitrogen content in the molten iron is N: 0.0095-0.0105%. High nitrogen manganese nitride is added in the later stage of smelting molten iron to increase the melting efficiency and ensure the recovery rate of nitrogen in the molten iron.

[0029] According to the cross-sectional size of the gray cast iron profile, the contents of C, Si, Mn, P and S are controlled by comprehensively considering the mechanical properties and matrix structure requirements of the gray cast iron profile.

[0030] The tensile performance index of the gray cast iron profile material of the present invention exceeds the requirements of the HT / LZ275-HT / LZ300 standard (JB / T10854-2019 horizontal continuous casting cast iron profile, Chinese machinery industry standard), and the tensile strength index at ½ radius of the gray cast iron profile with a diameter of Φ120mm-Φ400mm and a corresponding cross-section exceeds the performance index data in Table 1.

[0031] Table 1 Mechanical properties of gray iron profiles (JB / T 10854-2019 Horizontal continuous casting cast iron profiles, Chinese machinery industry standard)

[0032] like Figure 1-Figure 2 As shown, the gray cast iron profile material of the present invention has good surface quality, high dimensional accuracy, and is free of casting defects such as sand inclusions, slag inclusions, pores, shrinkage cavities, etc. The structure is dense and uniform from the center to the edge, the number of eutectic groups is significantly higher than that of sand casting, the graphite flakes are fine, and the tips of the graphite flakes are passivated regardless of type A graphite or type D and E graphite; the edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processing has relatively small fluctuations.

[0033] The present invention also provides a method for preparing a large-section gray cast iron profile with a diameter of Φ120 mm or larger and a corresponding size that is nitrogen-enhanced, comprising the following steps: Step 1, smelting molten iron and adding high-nitrogen manganese nitride; A medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a portion of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated based on 10% burn-out; after all the ferroalloys are melted, the original molten iron is taken for rapid furnace front component separation Analysis, determine and add scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the gray cast iron profiles of the required size for production. Use a high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer to conduct a rapid analysis of the composition before the furnace. According to the set value of the content of each alloy element, determine and add the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer; the melting temperature is 1520℃-1550℃. After all the added furnace materials are melted, reduce the smelting power to avoid excessive tumbling of the molten iron, and let the molten iron stand for 5 minutes-10 minutes to facilitate the slag in the molten iron to fully float; After removing the slag floating on the surface of the molten iron, add high-nitrogen manganese nitride blocks with a size of 30mm-40mm; immediately turn on full power to melt the high-nitrogen manganese nitride blocks after adding them, so that the high-nitrogen manganese nitride blocks melt quickly; the analysis of the N element is carried out using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0095-0.0105%, ready for tapping, inoculation and pouring; before each tapping, a quick analysis of the furnace composition and a slight adjustment of the composition are performed; The analysis of N element is carried out by pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the nitrogen content in the raw iron water is controlled at 0.0095-0.0105%. If the nitrogen content does not meet the standard, below 0.0095%, continue to add high nitrogen nitride manganese melting until the test is qualified. If the nitrogen content is higher than 0.0105%, the tapping is postponed until the tapping, inoculation and pouring are carried out after the nitrogen content meets the standard.

[0034] Among them, the C, Si and Mn contents in the molten iron need to be adjusted according to the cross-sectional size of the gray cast iron profiles produced. Except for special requirements, S and P are impurity elements and are generally controlled as low as possible. Therefore, the original molten iron is controlled according to C: 3.0-3.7%, Si: 1.4-2.4%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%. When N: 0.0095-0.0105%, the iron is tapped, and then the wire feeding inoculation process is used for inoculation treatment. The treated molten iron is poured into the holding furnace, and the gray cast iron profiles are produced according to the "pull-stop-pull" drawing process.

[0035] The content of each alloy element in the high nitrogen manganese nitride used is: 9-10% N, 88-90% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0036] Step 2: Primary incubation and trace element adjustment (1) Baked buns In order to meet the requirements of wire feeding inoculation treatment, a ladle is selected, wherein the selected ladle is a special ladle with a molten iron depth / inner diameter ≥1.5. First, the constructed ladle is baked in a special ladle baking device for 2-4 hours. Before the molten iron is discharged, the ladle is scalded. The molten iron in the electric furnace is poured into the pre-baked ladle and kept for 3-5 minutes, and then the molten iron is poured back into the electric furnace. This is repeated three times to further increase the temperature of the refractory material in the ladle and to further remove the water vapor in the refractory material built in the ladle. In order to ensure the stability of the nitrogen content in the molten iron, this process is generally carried out before adding high-nitrogen manganese nitride blocks to the molten iron.

[0037] (2) Iron tapping and primary inoculation The weight of each package of molten iron is controlled according to the cross-sectional size of the gray cast iron profiles produced. The first package of molten iron is 50kg-100kg more than each subsequent package of molten iron. Taking the production of gray cast iron profiles with a diameter of Φ200mm as an example, the first package of molten iron is 700kg-800kg, and the subsequent packages of molten iron are 650kg-700kg. The tapping temperature is 1420℃-1460℃; after tapping, the slag is quickly removed and hoisted to the inoculation treatment platform; Commercially available inoculated core wire is used for wire feeding inoculation treatment. According to the empirical data of the set composition and inoculation effect, the usage of the inoculated core wire is calculated according to the following standard: (1.5m-2m) / 100kg molten iron. The diameter of the commercial inoculated core wire is Φ13mm, the core material weight is (200g-240g) / m, and the unit wire weight is (420g-440g) / mm; in step 2, the corresponding brand of the inoculated core wire is YDB002, YDB005 or YDB008. Among them, the corresponding brands of the inoculated core wire are shown in Table 1: Table 2. Composition of commercially available inoculated cored wire

[0038] After inoculation treatment, the molten iron surface is deslagging to prepare for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.2-0.3% of the amount of molten iron in the ladle, and the particle size of the secondary inoculant is 3mm-8mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the insulation furnace of the horizontal continuous casting production line with the flow when pouring; Step 3 adopts floating silicon inoculation during the second inoculation, and the added long-term ferrosilicon inoculant containing strontium and barium covers the spheroidizing agent.

[0039] Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 4-6 hours to ensure that the water vapor in the furnace lining material is released.

[0040] Secondly, before pouring molten iron, the furnace wall in the holding furnace is baked with an atomized diesel nozzle flame for 30-60 minutes until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is activated for baking, a crystallizer is installed on the holding furnace, and a starter head is inserted into the crystallizer. The starter head is connected to the starter rod and can be pulled and drawn by a traction machine.

[0041] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1350℃-1400℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1-2 minutes, so that the molten iron entering the crystallizer wraps the dummy head and starts dummy pulling after crystallization and solidification. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then cut and pressed according to the required fixed length to obtain the gray cast iron profile material.

[0042] In step 5, during the horizontal continuous casting process, the traction motor speed is 900rpm, the drawing time is 0.8s-2.5s, the residence time is 25s-35s, the crystallizer length is 300mm-600mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃-70℃, and the profile crystallizer outlet temperature is controlled to be 900℃-1050℃; the drawing speed and the profile outlet temperature are controlled to prevent furnace leakage, and the molten iron pouring interval is controlled to be 8-12 minutes to prevent the molten iron from decaying and causing graphite morphology variation or carbide.

[0043] The preparation method of the nitrogen-enhanced gray cast iron profile with a cross-section of Φ120 mm or larger and equivalent size according to the present invention: The main features are: (1) High nitrogen manganese nitride is used as the nitrogen source. Commonly used nitrogen sources in industry include high nitrogen manganese nitride, manganese nitride, ferromanganese nitride, ferrosilicon nitride and nitrogen. In the actual production of horizontal continuous casting, it is found that due to the relatively low nitrogen content of manganese nitride (6%-7%N) and ferromanganese nitride (4%-6%N), the absorption of nitrogen will be affected during production and more manganese will be introduced; the nitrogen content of ferrosilicon nitride (26%-35%N) is relatively high, and the nitrogen element is prone to aggregate into nitrogen bubbles and float during the melting process. Although the absorption rate is relatively high, it is difficult to control, which can easily cause the nitrogen content to be unstable; directly using nitrogen, because it is difficult to introduce bubbles to the bottom of the molten iron, the bubbles float, and the absorption rate of nitrogen directly entering the molten iron is very low, and the stability is poor. It can be seen that the use of high nitrogen manganese nitride as the nitrogen source is the best choice. It not only has the highest absorption rate, but also is the easiest to control the content, and the actual operation is more stable.

[0044] The main features are: (2) the timing of addition and the selection of the size of the high nitrogen manganese nitride block. During the molten iron smelting process, high nitrogen manganese nitride is added in the later stage of smelting in the electric furnace. The size of the high nitrogen manganese nitride block used is 30mm-40mm, which is conducive to the rapid melting of the high nitrogen manganese nitride block and is more conducive to improving the absorption and uniform distribution of nitrogen. The reason is that the timing and method of addition are very critical. High nitrogen manganese nitride contains 8-10% N and 85-90% Mn. When melting in the induction furnace, with the high-speed flow of molten iron under the action of electromagnetic induction, the nitrogen element is very easy to turn into gas molecules and become bubbles floating up. In order to avoid burning and promote the absorption of nitrogen, the timing of its addition is very important. In addition, since the density of the high nitrogen manganese nitride block is greater than the density of molten iron, although the induction furnace has a strong electromagnetic stirring effect, the high nitrogen manganese nitride block is too large and may sink to the bottom of the electric furnace, which is not only not conducive to its melting, but also not conducive to the absorption and uniform distribution of nitrogen, and may cause burning of nitrogen. It can be seen that in the later stage of melting, after other metal materials and ferroalloys are melted and slag treatment is carried out, adding high nitrogen manganese nitride blocks with a size of 30mm-40mm is not only conducive to melting, but also to its homogenization. At the same time, this is conducive to reducing the difference between the internal and external structures of the gray cast iron profile, increasing the hardness of the core of the gray cast iron profile, reducing the hardness of the surface layer, and improving the mechanical processing performance of the gray cast iron profile.

[0045] The main features are: (3) In the secondary inoculation process, the amount of long-lasting ferrosilicon inoculant containing strontium and barium is increased, and the secondary inoculation method is adopted to improve and prolong the inoculation effect, thereby avoiding the occurrence of carbides due to inoculation decay caused by long solidification time during the production of large-diameter gray cast iron profiles.

[0046] Example 1 Φ120mm grey cast iron profile material and its preparation.

[0047] Its composition by weight percentage is: C 3.4%, Si 3.2%, Mn 0.8%, P0.10%, S0.04%, N0.0105%, and the rest is Fe.

[0048] Step 1: molten iron smelting and addition of high nitrogen manganese nitride A 5T medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a part of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully powered until all the charges in the furnace are completely melted; the ferroalloys added to the medium frequency induction furnace are calculated based on 10% burn-out; after all the ferroalloys are melted, the original molten iron is taken out for furnace front forming The furnace is subjected to rapid analysis to determine and add scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and according to the produced Φ120mm diameter gray cast iron profile, the components of C, Si, Mn, P, and S in the original molten iron are adjusted to meet the requirements. A high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer are used to perform rapid analysis of the components in front of the furnace, and the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer is determined and added according to the set value of the content of each alloy element; the melting temperature is 1520°C, and after all the added furnace materials are melted, the smelting power is reduced to avoid excessive tumbling of the molten iron, and the molten iron is allowed to stand for 5 minutes to facilitate the full floating of the slag in the molten iron; After removing the slag floating on the surface of the molten iron, add a 30mm high-nitrogen manganese nitride block; immediately turn on the full power to melt the high-nitrogen manganese nitride block after adding it; analyze the N element using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0105%, ready for tapping, inoculation and pouring; before each tapping, perform a quick analysis of the furnace composition and make a slight adjustment of the composition; The original molten iron is controlled according to C: 3.4%, Si: 2.0%, Mn: 0.8%, P: 0.10%, S: 0.06%; iron is tapped when N: 0.0105%.

[0049] The content of each alloy element in the high nitrogen manganese nitride used is: 9% N, 88% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0050] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 3 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 4 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0051] (2) Iron tapping and primary inoculation The first batch of molten iron output is 750kg, and each subsequent batch of molten iron output is 680kg, and the tapping temperature is 1450℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 1.6m / (100kg molten iron). Commercial YDB008 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 220g / m, and a unit wire weight of 410g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron and the amount of Si to be supplemented, weigh the long-term ferrosilicon inoculant containing strontium and barium. The total amount of the secondary inoculant is 0.25% of the molten iron in the ladle, and the particle size of the secondary inoculant is 5 mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 5 hours to ensure that the water vapor in the furnace lining material is released.

[0052] Secondly, before pouring the molten iron, the furnace wall inside the holding furnace is baked for 40 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is used for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0053] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1390℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1.5 minutes, so that the molten iron entering the crystallizer wraps the dummy head and starts dummy pulling after crystallization and solidification. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then cut and pressed according to the required fixed length to obtain the gray cast iron profile material.

[0054] Among them, double-stream continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.8s, the residence time is 20s, the crystallizer length is 300mm, the water inlet temperature is room temperature, the water outlet temperature is 60℃, and the profile crystallizer outlet temperature is controlled at 960℃, so as to obtain gray cast iron profile material.

[0055] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0056] The Φ120mm gray cast iron profile material prepared in Example 1 has a tensile performance index that exceeds the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥365MPa, HB190-208. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the relative fluctuation of the surface finish of the processed surface is small. The profile obtained by this method solves the differences between the surface structure and the core structure of the existing large-section gray cast iron profile materials, as well as the problems of poor uniformity of mechanical properties and poor sensitivity of the entire section.

[0057] Example 2 Φ180mm grey cast iron profile material and its preparation.

[0058] Its composition by weight percentage is: C 3.0%, Si 1.8%, Mn 0.6%, P 0.09%, S 0.03%, N 0.0095%, and the rest is Fe.

[0059] Step 1: molten iron smelting and addition of high nitrogen manganese nitride An 8T medium frequency induction furnace is used to melt the molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a part of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace power is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the 10% burn-out amount; after all the ferroalloys are melted, the original molten iron is taken for rapid analysis of the furnace composition to confirm Determine and supplement scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the produced Φ180mm diameter gray cast iron profiles, use high-frequency infrared carbon-sulfur analyzer and photoelectric direct reading spectrometer to conduct rapid analysis of the furnace composition, and determine and supplement the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer according to the set value of each alloy element content; the melting temperature is 1550℃, and after all the added furnace materials are melted, reduce the smelting power to avoid excessive tumbling of the molten iron, and let the molten iron stand for 10 minutes to facilitate the slag in the molten iron to fully float; After removing the slag floating on the surface of the molten iron, add high-nitrogen manganese nitride blocks with a size of 30mm; after adding the high-nitrogen manganese nitride, immediately turn on the full power to melt it quickly; the analysis of the N element is carried out using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0095%, ready for tapping, inoculation and pouring; before each tapping, a quick analysis of the furnace composition and a slight adjustment of the composition are carried out; control is carried out according to the original molten iron's C: 3.0%, Si: 1.4%, Mn: 0.6%, P: 0.09%, S: 0.03%; tapping is carried out when N: 0.0095%.

[0060] The content of each alloy element in the high nitrogen manganese nitride used is: 10% N, 89% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0061] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 2 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 3 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0062] (2) Iron tapping and primary inoculation The first batch of molten iron output is 700kg, and each subsequent batch of molten iron output is 650kg, and the tapping temperature is 1420℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 1.5m / (100kg molten iron). Commercial YDB008 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 200g / m, and a unit wire weight of 420g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.2% of the molten iron in the ladle, and the particle size of the secondary inoculant is 3mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 4 hours to ensure that the water vapor in the furnace lining material is released.

[0063] Secondly, before pouring molten iron, the furnace wall inside the holding furnace is baked for 30 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before activating the atomized diesel nozzle flame for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0064] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1350℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1 minute, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0065] Among them, double-stream continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.8s, the residence time is 26s, the crystallizer length is 400mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃, and the profile crystallizer outlet temperature is controlled at 950℃, so as to obtain gray cast iron profile material.

[0066] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0067] The Φ180mm gray cast iron profile material prepared in Example 2 has tensile performance indicators that exceed the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥360MPa, HB180-195. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processed surface has relatively small fluctuations.

[0068] Example 3 Φ260mm grey cast iron profile material and its preparation.

[0069] Its composition by weight percentage is: C 3.7%, Si 3.2%, Mn 1.1%, P 0.10%, S0.04%, N0.010% and the rest is Fe.

[0070] Step 1: molten iron smelting and addition of high nitrogen manganese nitride An 8T medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the casting pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a part of low-manganese casting gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the burn-out amount of 10%; after all the ferroalloys are melted, the original molten iron is taken for furnace front forming The furnace is subjected to rapid analysis to determine and add scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and according to the produced Φ260mm diameter gray cast iron profile, the components of C, Si, Mn, P, and S in the original molten iron are adjusted to meet the requirements. A high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer are used to perform rapid analysis of the components before the furnace, and the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer is determined and added according to the set value of the content of each alloy element; the melting temperature is 1550°C, and after all the added furnace materials are melted, the smelting power is reduced to avoid excessive tumbling of the molten iron, and the molten iron is allowed to stand for 10 minutes to facilitate the full floating of the slag in the molten iron; After removing the slag floating on the surface of the molten iron, add high-nitrogen manganese nitride blocks with a size of 30mm; after adding the high-nitrogen manganese nitride, immediately turn on the full power to melt it quickly; the analysis of the N element is carried out using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0100%, ready for tapping, inoculation and pouring; before each tapping, a quick analysis of the furnace composition and a slight adjustment of the composition are carried out; control is carried out according to the original molten iron's C: 3.7%, Si: 2.4%, Mn: 1.1%, P: 0.10%, S: 0.06%; tapping is carried out when N: 0.0100%.

[0071] The content of each alloy element in the high nitrogen manganese nitride used is: 9% N, 90% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0072] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 4 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 5 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0073] (2) Iron tapping and primary inoculation The first batch of molten iron output is 800kg, and each subsequent batch of molten iron output is 700kg, and the tapping temperature is 1460℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 2m / (100kg molten iron). Commercial YDB005 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 240g / m, and a unit wire weight of 440g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.3% of the molten iron in the ladle, and the particle size of the secondary inoculant is 8 mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 6 hours to ensure that the water vapor in the furnace lining material is released.

[0074] Secondly, before pouring molten iron, the furnace wall inside the holding furnace is baked for 60 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is used for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0075] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1400℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 2 minutes, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0076] Among them, single-strand continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.8s, the residence time is 28s, the crystallizer length is 450mm, the water inlet temperature is room temperature, the water outlet temperature is 70℃, and the profile crystallizer outlet temperature is controlled at 1000℃, so as to obtain gray cast iron profile material.

[0077] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0078] The Φ260mm gray cast iron profile material prepared in Example 3 has tensile performance indicators that exceed the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥382MPa, HB175-190. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processed surface has relatively small fluctuations.

[0079] Example 4 Φ400mm grey cast iron profile material and its preparation.

[0080] Its composition by weight percentage is: C 3.3%, Si 2.6%, Mn 0.9%, P0.10%, S0.04%, N0.0103%, and the rest is Fe.

[0081] Step 1: molten iron smelting and addition of high nitrogen manganese nitride An 8T medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the casting pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a part of low-manganese casting gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the burn-out amount of 10%; after all the ferroalloys are melted, the original molten iron is taken for furnace front forming The furnace is subjected to rapid analysis to determine and supplement scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and the components of C, Si, Mn, P, and S in the original molten iron are adjusted to meet the requirements according to the gray cast iron profile with a diameter of Φ400 mm produced. A high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer are used to conduct rapid analysis of the components in front of the furnace, and the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer is determined and supplemented according to the set value of the content of each alloy element; the melting temperature is 1530°C, and after all the added furnace materials are melted, the smelting power is reduced to avoid excessive tumbling of the molten iron, and the molten iron is allowed to stand for 8 minutes to facilitate the full floating of the slag in the molten iron; After removing the slag floating on the surface of the molten iron, add a 35mm high-nitrogen manganese nitride block; immediately turn on the full power to melt the high-nitrogen manganese nitride block after adding it; analyze the N element using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0103%, ready for tapping, inoculation and pouring; before each tapping, perform a quick analysis of the furnace composition and make a slight adjustment of the composition; The original molten iron is controlled according to C: 3.3%, Si: 2.2%, Mn: 0.9%, P: 0.10%, S: 0.04%; iron is tapped when N: 0.0103%.

[0082] The content of each alloy element in the high nitrogen manganese nitride used is: 9.5% N, 88% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0083] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 4 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 3 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0084] (2) Iron tapping and primary inoculation The first batch of molten iron output is 750kg, and each subsequent batch of molten iron output is 650kg, and the tapping temperature is 1430℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 1.6m / (100kg molten iron). Commercial YDB002 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 210g / m, and a unit wire weight of 430g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.2% of the molten iron in the ladle, and the particle size of the secondary inoculant is 3mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 4 hours to ensure that the water vapor in the furnace lining material is released.

[0085] Secondly, before pouring molten iron, the furnace wall inside the holding furnace is baked for 30 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before activating the atomized diesel nozzle flame for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0086] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1400℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1 minute, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0087] Among them, single-strand continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.6s, the residence time is 35s, the crystallizer length is 600mm, the water inlet temperature is room temperature, the water outlet temperature is 60℃, and the profile crystallizer outlet temperature is controlled at 960℃, so as to obtain gray cast iron profile material.

[0088] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0089] The Φ400mm gray cast iron profile material prepared in Example 4 has tensile performance indicators that exceed the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥360MPa, HB175-192. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processed surface has relatively small fluctuations.

[0090] Example 5 Φ320mm grey cast iron profile material and its preparation.

[0091] Its composition by weight percentage is: C 3.0%, Si 2.0%, Mn 0.8%, P0.10%, S0.04%, N0.0093%, and the rest is Fe.

[0092] Step 1: molten iron smelting and addition of high nitrogen manganese nitride Use 8T medium frequency induction furnace to melt molten iron. According to the above weight percentage composition, deduct the amount of silicon brought in by the long-acting ferrosilicon inoculant, calculate and weigh the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron, and the melting and adding order is to first put in a part of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, add the remaining pig iron, scrap steel, recycled materials and ferroalloys at one time, and then turn on the power of the medium frequency induction furnace until all the furnace materials are completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the 10% burn-out amount; after all the ferroalloys are melted, take the original molten iron for a quick analysis of the composition in front of the furnace to confirm Determine and add scrap steel, 75% ferrosilicon or recarburizer or 30% ferromanganese as needed, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the produced Φ320mm diameter gray cast iron profiles, use high-frequency infrared carbon-sulfur analyzer and photoelectric direct reading spectrometer to conduct rapid analysis of the composition before the furnace, and determine and add the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or recarburizer according to the set value of the content of each alloy element; the melting temperature is 1550℃, and after all the added furnace materials are melted, reduce the smelting power to avoid excessive tumbling of the molten iron, and let the molten iron stand for 5 minutes to facilitate the slag in the molten iron to float fully; After removing the slag floating on the surface of the molten iron, add a 35mm high-nitrogen manganese nitride block; immediately turn on the full power to melt the high-nitrogen manganese nitride block after adding it; analyze the N element using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0093%, ready for tapping, inoculation and pouring; before each tapping, perform a quick analysis of the furnace composition and make a slight adjustment of the composition; The original molten iron is controlled according to C: 3.0%, Si: 1.8%, Mn: 0.8%, P: 0.10%, S: 0.06%; iron is tapped when N: 0.0093%.

[0093] The content of each alloy element in the high nitrogen manganese nitride used is: 9% N, 88.5% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0094] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 3 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 4 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0095] (2) Iron tapping and primary inoculation The first batch of molten iron output is 700kg, and each subsequent batch of molten iron output is 650kg, and the tapping temperature is 1420℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 1.7m / (100kg molten iron). Commercial YDB005 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 200g / m, and a unit wire weight of 420g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.2-0.3% of the molten iron in the ladle, and the particle size of the secondary inoculant is 4mm. After the molten iron of the primary inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 5 hours to ensure that the water vapor in the furnace lining material is released.

[0096] Secondly, before pouring the molten iron, the furnace wall inside the holding furnace is baked for 40 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is used for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0097] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1400℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1 minute, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0098] Among them, single-strand continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.8s, the residence time is 32s, the crystallizer length is 520mm, the water inlet temperature is room temperature, the water outlet temperature is 55℃, and the profile crystallizer outlet temperature is controlled at 980℃, so as to obtain gray cast iron profile material.

[0099] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0100] The Φ320mm gray cast iron profile material prepared in Example 5 has tensile performance indicators that exceed the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥352MPa, HB185-200. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be high-speed fine processing, and the surface finish of the processing has relatively small fluctuations.

[0101] Example 6 310mm×310mm square section grey cast iron profile material and its preparation.

[0102] Its composition by weight percentage is: C 3.3%, Si 2.5%, Mn 0.7%, P0.08%, S0.02%, N0.0101%, and the rest is Fe.

[0103] Step 1: molten iron smelting and addition of high nitrogen manganese nitride An 8T medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the casting pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a part of low-manganese casting gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the burn-out amount of 10%; after all the ferroalloys are melted, the original molten iron is taken for furnace front forming The furnace is subjected to rapid analysis to determine and add 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and according to the produced 310mm×310mm square cross-section gray cast iron profiles, the components of C, Si, Mn, P, and S in the original molten iron are adjusted to meet the requirements. A high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer are used to conduct rapid analysis of the components before the furnace, and according to the set values ​​of the content of each alloy element, the amount of 75% ferrosilicon, 30% ferromanganese or carburizer is determined and added; the melting temperature is 1530℃, and after all the added furnace materials are melted, the smelting power is reduced to avoid excessive tumbling of the molten iron, and the molten iron is allowed to stand for 9 minutes to facilitate the full floating of the slag in the molten iron; After removing the slag floating on the surface of the molten iron, add a 34mm high-nitrogen manganese nitride block; immediately turn on the full power to melt the high-nitrogen manganese nitride block after adding it; analyze the N element using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0101%, ready for tapping, inoculation and pouring; perform a quick analysis of the composition and fine-tune the composition before each tapping; The original molten iron is controlled according to C: 3.3%, Si: 1.9%, Mn: 0.7%, P: 0:08%, S: 0.2%; iron is tapped when N: 0.0101%.

[0104] The content of each alloy element in the high nitrogen manganese nitride used is: 9% N, 88% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0105] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.8. First, bake the built ladle in a special ladle baking machine for 3 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 3 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0106] (2) Iron tapping and primary inoculation The first batch of molten iron output is 800kg, and each subsequent batch of molten iron output is 700kg, and the tapping temperature is 1460℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as 1.5m / (100kg molten iron). Commercial YDB005 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 200g / m, and a unit wire weight of 420g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.2% of the molten iron in the ladle, and the particle size of the secondary inoculant is 3mm. After the molten iron of the first inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 4.5 hours to ensure that the water vapor in the furnace lining material is released.

[0107] Secondly, before pouring the molten iron, the furnace wall inside the holding furnace is baked for 35 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is used for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0108] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1400℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 2 minutes, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0109] Among them, single-strand continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.65s, the residence time is 35s, the crystallizer length is 600mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃, and the profile crystallizer outlet temperature is controlled at 950℃, so as to obtain gray cast iron profile material.

[0110] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0111] The 310×310mm square-section gray cast iron profile material prepared in Example 6 has a tensile performance index that exceeds the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥355MPa, HB185-200. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processed surface has relatively small fluctuations.

[0112] Example 7 310mm×400mm rectangular cross-section grey cast iron profile material and its preparation.

[0113] Its composition by weight percentage is: C 3.5%, Si 2.8%, Mn 0.8%, P0.10%, S0.02%, N0.0101%, and the rest is Fe.

[0114] Step 1: molten iron smelting and addition of high nitrogen manganese nitride Use 8T medium frequency induction furnace to melt molten iron. According to the above weight percentage composition, deduct the amount of silicon brought in by the long-acting ferrosilicon inoculant, calculate and weigh the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high nitrogen manganese nitride required for the original molten iron, and the melting and adding order is to first put in a part of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, add the remaining pig iron, scrap steel, recycled materials and ferroalloys at one time, and then turn on the power of the medium frequency induction furnace until all the furnace materials are completely melted; the ferroalloys added to the medium frequency induction furnace are calculated according to the 10% burn-out amount; after all the ferroalloys are melted, take the original molten iron for a quick analysis of the furnace composition to determine and according to It is necessary to add scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the 310mm×400mm rectangular cross-section gray cast iron profile produced. A high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer are used to quickly analyze the components before the furnace. According to the set value of each alloy element content, the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer to be added is determined and added; the melting temperature is 1550℃. After all the added furnace materials are melted, the smelting power is reduced to avoid excessive tumbling of the molten iron. The molten iron is allowed to stand for 10 minutes to facilitate the full floating of the slag in the molten iron; After removing the slag floating on the surface of the molten iron, add a 30mm high-nitrogen manganese nitride block; immediately turn on the full power to melt the high-nitrogen manganese nitride block after adding it; analyze the N element using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0101%, ready for tapping, inoculation and pouring; before each tapping, perform a quick analysis of the furnace composition and make a slight adjustment of the composition; The original molten iron is controlled according to C: 3.5%, Si: 2.3%, Mn: 0.8%, P: 0.10%, S: 0.2%; iron is tapped when N: 0.0101%.

[0115] The content of each alloy element in the high nitrogen manganese nitride used is: 10% N, 88% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

[0116] Step 2: Primary incubation and trace element adjustment (1) Baked buns Select a special ladle with a ladle (iron depth) / (inner diameter) of 1.7. First, bake the built ladle in a special ladle baking machine for 4 hours. Before adding the high-nitrogen manganese nitride block, pour the molten iron in the electric furnace into the pre-baked ladle and let it stay for 3 minutes, then pour the molten iron back into the electric furnace, and repeat three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle.

[0117] (2) Iron tapping and primary inoculation The first batch of molten iron output is 760kg, and each subsequent batch of molten iron output is 660kg, and the tapping temperature is 1420℃. After tapping, the slag is quickly removed and hoisted to the inoculation platform. Commercially available inoculation core wire is used for wire feeding inoculation. According to the empirical data of the set composition and inoculation effect, the usage of the inoculation core wire is calculated as (1.5-2)m / (100kg molten iron). Commercial YDB005 inoculation core wire is used, with a diameter of Φ13mm, a core material weight of 230g / m, and a unit wire weight of 430g / mm. After inoculation, the slag is removed from the surface of the molten iron in preparation for pouring; Step 3: Secondary inoculation of molten iron According to the weight of each bag of molten iron, the long-term ferrosilicon inoculant containing strontium and barium is weighed according to the amount of Si to be supplemented. The total amount of the secondary inoculant is 0.3% of the molten iron in the ladle, and the particle size of the secondary inoculant is 6mm. After the molten iron of the primary inoculation is deslagging, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; Step 4, pouring First, the newly built insulation furnace is baked in a special oven for 6 hours to ensure that the water vapor in the furnace lining material is released.

[0118] Secondly, before pouring the molten iron, the furnace wall inside the holding furnace is baked for 40 minutes using an atomized diesel nozzle flame until the furnace wall is bright red. During this process, before the atomized diesel nozzle flame is used for baking, a crystallizer is installed on the holding furnace, and an ingot starter is inserted into the crystallizer. The other end of the ingot starter is connected to the ingot starter rod and can be pulled and drawn by a traction machine.

[0119] Third, pouring molten iron, pouring the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production, the pouring temperature is 1360℃; Step 5, Horizontal Continuous Casting After pouring molten iron into the holding furnace, it stays for 1 minute, so that the molten iron entering the crystallizer wraps the dummy head and crystallizes and solidifies before starting the dummy pulling. The continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

[0120] Among them, single-strand continuous casting is adopted in the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.55s, the residence time is 33s, the crystallizer length is 600mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃, and the profile crystallizer outlet temperature is controlled at 950℃, so as to obtain gray cast iron profile material.

[0121] Control the drawing speed and profile outlet temperature to prevent furnace leakage, and control the molten iron pouring interval to no more than 10 minutes to prevent the molten iron from spheroidizing and inoculation decay, resulting in graphite morphology variation and carbides.

[0122] The 310×400 mm square rectangular cross-section gray cast iron profile material prepared in Example 7 has a tensile performance index that exceeds the requirements of the HT / LZ300 standard (JB / T 10854-2019 Horizontal Continuous Casting Cast Iron Profile, China Machinery Industry Standard), and has a dense and uniform structure from the center to the edge. The tensile strength of the gray cast iron profile at ½ radius is ≥367MPa, HB185-200. The edge hardness of the gray cast iron profile of the present invention decreases by more than HB20, and the hardness difference between the core and the surface is reduced to less than HB20, and the processing performance of the gray cast iron profile is improved. The gray cast iron profile material of the present invention has high strength, uniform hardness, excellent cross-sectional uniformity, good cutting performance, less cutting resistance than steel parts, can be finely processed at high speed, and the surface finish of the processed surface has relatively small fluctuations.

Claims

1. Nitrogen-enhanced large-section grey cast iron profiles with a diameter of Φ120 mm or larger and equivalent, characterized in that: Its composition by weight percentage is: C: 3.0-3.7%, Si: 1.8-3.2%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%, N: 0.0095-0.0105%, and the rest is Fe.

2. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 1, characterized in that: The following steps are involved: Step 1, smelting molten iron and adding high-nitrogen manganese nitride; Step 2, one-time incubation; Step 3, secondary inoculation of molten iron; Step 4, pouring; Step 5, horizontal continuous casting.

3. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 2, characterized in that: Step 1 is as follows: A medium frequency induction furnace is used to melt molten iron. According to the above weight percentage composition, the amount of silicon brought in by the long-acting ferrosilicon inoculant is deducted, and the foundry pig iron, scrap steel, recycled materials, 30% ferromanganese, 75% ferrosilicon and high-nitrogen manganese nitride required for the original molten iron are calculated and weighed. The order of melting and adding materials is to first put in a portion of low-manganese foundry gray cast iron pig iron to cover the bottom of the furnace. After this batch of pig iron is melted, the remaining pig iron, scrap steel, recycled materials and ferroalloys are added at one time, and then the medium frequency induction furnace is fully turned on to wait for all the furnace materials in the furnace to be completely melted; the ferroalloys added to the medium frequency induction furnace are calculated based on 10% burn-out; after all the ferroalloys are melted, the original molten iron is taken for rapid furnace front component separation Analysis, determine and add scrap steel, 75% ferrosilicon or carburizer or 30% ferromanganese as needed, and adjust the C, Si, Mn, P, S components in the original molten iron to meet the requirements according to the gray cast iron profiles of the required size for production. Use a high-frequency infrared carbon-sulfur analyzer and a photoelectric direct-reading spectrometer to conduct a rapid analysis of the composition before the furnace. According to the set value of the content of each alloy element, determine and add the amount of scrap steel, 75% ferrosilicon, 30% ferromanganese or carburizer; the melting temperature is 1520℃-1550℃. After all the added furnace materials are melted, reduce the smelting power to avoid excessive tumbling of the molten iron, and let the molten iron stand for 5 minutes-10 minutes to facilitate the slag in the molten iron to fully float; After removing the slag floating on the surface of the molten iron, add high-nitrogen manganese nitride blocks with a size of 30mm-40mm; immediately turn on full power to melt the high-nitrogen manganese nitride blocks after adding them, so that the high-nitrogen manganese nitride blocks melt quickly; the analysis of the N element is carried out using a pulse infrared thermal conductivity oxygen and nitrogen analyzer, and the actual nitrogen content in the original molten iron is 0.0095-0.0105%, ready for tapping, inoculation and pouring; before each tapping, a quick analysis of the furnace composition and a slight adjustment of the composition are performed; Control according to the original iron liquid's C: 3.0-3.7%, Si: 1.4-2.4%, Mn: 0.6-1.1%, P≤0.10%, S≤0.06%; tapping when N: 0.0095-0.0105%; The content of each alloy element in the high nitrogen manganese nitride used is: 9-10% N, 88-90% Mn, other impurity elements are less than 0.1%, and the balance is Fe.

4. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 3, characterized in that: In step 1, the melting temperature is 1520°C-1550°C, and the tapping temperature is 1420°C-1460°C.

5. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 4, characterized in that: Step 2 is as follows: (1) Baked buns In order to meet the requirements of wire feeding inoculation treatment, a ladle is selected, wherein the selected ladle is a special ladle with a molten iron depth / inner diameter ≥1.5; first, the built ladle is baked for 2 hours to 4 hours using a special ladle baking device; before the molten iron is discharged, the ladle is scalded, the molten iron in the electric furnace is poured into the pre-baked ladle and kept for 3 minutes to 5 minutes, and then the molten iron is poured back into the electric furnace, and this is repeated three times to further increase the temperature of the refractory material in the ladle and further remove the water vapor in the refractory material built in the ladle; (2) Iron tapping and primary inoculation The weight of each bag of molten iron is controlled according to the cross-sectional size of the gray cast iron profiles produced. The first bag of molten iron is 50kg-100kg more than each subsequent bag of molten iron, and the tapping temperature is 1420℃-1460℃; after tapping, the slag is quickly removed and hoisted to the inoculation treatment platform; Commercially available inoculated core wire is used for wire feeding inoculation treatment. According to the empirical data of set composition and inoculation effect, the usage of inoculated core wire is calculated according to the following standard: (1.5m-2m) / 100kg molten iron; the diameter of commercial inoculated core wire is Φ13mm, the core material weight is (200g-240g) / m, and the unit wire weight is (420g-440g) / mm; after inoculation treatment, the slag is removed from the surface of the molten iron in preparation for pouring.

6. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 5, characterized in that: In step 2, the corresponding grade of the inoculated cored wire is YDB002, YDB005 or YDB008.

7. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 5, characterized in that: Step 3 is as follows: According to the weight of each bag of molten iron and the amount of Si to be supplemented, weigh the long-acting ferrosilicon inoculant containing strontium and barium, the total amount of the secondary inoculant is 0.2-0.3% of the amount of molten iron in the ladle, and the particle size of the secondary inoculant is 3mm-8mm; after the molten iron of the primary inoculation is slag-scraped, the inoculant treated with the secondary inoculation is sprinkled on the upper surface of the molten iron in the ladle, and poured into the holding furnace of the horizontal continuous casting production line along with the flow when pouring; In step 3, floating silicon inoculation is used for the second inoculation, and the added long-lasting ferrosilicon inoculant containing strontium and barium covers the spheroidizing agent.

8. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 7, characterized in that: Step 4 is as follows: First, the newly built insulation furnace is baked in a special oven for 4 to 6 hours to ensure that the water vapor in the furnace lining material is released; Secondly, before pouring molten iron, the furnace wall in the holding furnace is baked for 30 minutes to 60 minutes by using atomized diesel nozzle flame until the furnace wall is bright red; in this process, before the atomized diesel nozzle flame baking is enabled, a crystallizer is installed on the holding furnace, and a dummy head is inserted into the crystallizer. The dummy head is connected to the dummy rod and can be pulled and drawn by a traction machine; Third, pouring molten iron: pour the molten iron after inoculation treatment into the holding furnace through the pouring port of the holding furnace to prepare for horizontal continuous casting production. The pouring temperature is 1350℃-1400℃.

9. The method for preparing nitrogen-enhanced gray cast iron profiles with a cross-section of Φ120 mm or larger and equivalent according to claim 8, characterized in that: Step 5 is as follows: After pouring molten iron into the holding furnace, it stays there for 1-2 minutes, so that the molten iron entering the crystallizer wraps around the dummy head and starts dummy pulling after crystallization and solidification. Continuous casting production is carried out at the "pull-stop-pull" process level. The gray cast iron bars pulled out of the crystallizer are gray cast iron profiles. As the length of the gray cast iron profile increases, the dummy rods are removed one by one until the traction roller of the traction machine directly presses on the gray cast iron profile, and then the gray cast iron profile material is obtained by cutting and pressing according to the required fixed length.

10. The method for preparing nitrogen-enhanced gray cast iron profiles with a large cross-section of Φ120 mm or larger and equivalent size according to claim 9, characterized in that: In step 5, during the horizontal continuous casting process, the traction motor speed is 900rpm, the pulling time is 0.8s-2.5s, the residence time is 25s-35s, the crystallizer length is 300mm-600mm, the water inlet temperature is room temperature, the water outlet temperature is 50℃-70℃, and the profile crystallizer outlet temperature is controlled to be 900℃-1050℃; the molten iron pouring interval is controlled to be 8 minutes-12 minutes.

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