Low-alloy alkali-corrosion-resistant cast iron, low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron and preparation process of low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron

Abstract

According to the low-alloy alkali-corrosion-resistant cast iron, the low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron and the preparation technology of the low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron, low-cost and high-yield manufacturing is achieved, a casting manufactured through the low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron has good heat resistance and alkali corrosion resistance, and the use requirement under the high-temperature alkali-corrosion working condition can be met. The invention discloses low-alloy alkali-corrosion-resistant cast iron. The cast iron comprises the following components in percentage by mass: 3.0-3.5% of C; 2.4% to 2.8% of Si; mn: 0.3 to 0.7%; 0.5 to 0.7 percent of Cr; 0.6 to 0.8 percent of Ni; less than 0.10% of P; less than 0.05% of S; and the balance of Fe. Compared with low-alloy alkali-corrosion-resistant cast iron, the low-alloy high-temperature alkali-corrosion-resistant buried pipe cast iron is internally provided with a pipeline for introducing cooling substances.

Description

Technical Field

[0001] This invention relates to the field of metallurgical ironmaking technology, and in particular to a low-alloy alkali-corrosion resistant cast iron, a low-alloy high-temperature alkali-corrosion resistant buried pipe cast iron, and their preparation process. Background Technology

[0002] In the metallurgical ironmaking industry, especially in blast furnaces, fuming furnaces, and smelting reduction furnaces, the reducing high-temperature gases and alkali metal slag inside the furnace are highly corrosive due to the influence of the raw materials and fuels fed into the furnace. The furnace temperature can reach up to 1800℃. Casting equipment needs the protection of slag skin to extend its service life. This requires these furnace casting equipment to have high temperature and alkali corrosion resistance to extend the service life of the castings under high temperature and corrosive conditions.

[0003] Corrosion-resistant cast iron is mainly classified into silicon-based, chromium-based, aluminum-based, and nickel-based corrosion-resistant cast iron. The alloying elements and their content in these types of corrosion-resistant cast iron have a significant impact on the performance of the castings. Adding sufficient silicon, chromium, aluminum, nickel, and other elements to cast iron can form a dense protective film beneath the surface of the cast iron part. This protective film has excellent thermodynamic stability and high resistivity, effectively delaying oxidation and corrosion, thus significantly improving the corrosion resistance of cast iron parts at high temperatures. These series of corrosion-resistant cast irons typically require a high degree of alloying to achieve good heat and corrosion resistance; however, high alloying also brings problems such as low production yield and high production costs. For example, excessive silicon dissolved in ferrite can cause lattice distortion and deformation, leading to excessive internal stress and easy cold cracking, thus resulting in a low yield rate for high-silicon corrosion-resistant cast iron parts. Similarly, for chromium-based, aluminum-based, and nickel-based corrosion-resistant cast irons, the high prices of chromium, aluminum, and nickel mean that adding large amounts would significantly increase production costs. Furthermore, while low-alloying can reduce production costs and increase yield rates for these series of corrosion-resistant cast irons, it cannot meet the requirements of high-temperature operating conditions.

[0004] In the metallurgical ironmaking industry, there is usually a well-established water system with convenient water resources. If steel pipes are pre-embedded inside the casting as cooling channels during the casting process, water flowing through these channels can remove a large amount of heat from the casting, thereby lowering its temperature and meeting the requirements of high-temperature conditions without incurring significant additional costs. For example, cast iron cooling walls that provide cooling for blast furnace bodies are formed by pre-embedding bent cooling water pipes in the casting mold, as shown in YB / T 4073-2007 "Cast Iron Cooling Walls for Blast Furnaces". However, the cast iron materials mentioned in this industry standard are HT150, HT200, QT400-18, and QT400-20. Castings made from these materials lack a dense oxide film on their surface and have poor corrosion resistance. Under high-temperature and corrosive conditions, casting damage often manifests as corrosive damage to the casting itself. Summary of the Invention

[0005] Existing corrosion-resistant cast irons typically require a high degree of alloying to achieve good heat and corrosion resistance, resulting in low yield and high production costs. To address these issues, this invention aims to provide a low-alloy alkali-corrosion-resistant cast iron, a low-alloy high-temperature alkali-corrosion-resistant embedded pipe cast iron, and their preparation process. This achieves low-cost, high-yield production, resulting in castings with excellent heat and alkali corrosion resistance, meeting the requirements for use under high-temperature, alkaline-corrosion conditions.

[0006] To achieve the above objectives, the technical solution adopted by the present invention to solve its technical problem is as follows: A low-alloy alkali-corrosion resistant cast iron comprises the following components in mass percentage: C: 3.0–3.5%; Si: 2.4–2.8%; Mn: 0.3–0.7%; Cr: 0.5–0.7%; Ni: 0.6–0.8%; P: <0.10%; S: <0.05%; the remainder being Fe.

[0007] A low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes, wherein the cast iron has internal pipes for circulating cooling substances, and the cast iron comprises the following components in mass percentage: C: 3.0-3.5%; Si: 2.4-2.8%; Mn: 0.3-0.7%; Cr: 0.5-0.7%; Ni: 0.6-0.8%; P: <0.10%; S: <0.05%; the remainder being Fe.

[0008] The pipeline is a seamless steel pipe, which is a steel pipe that has undergone anti-carburizing treatment, and the cooling specific surface area ratio of the steel pipe is ≥1.0.

[0009] A low-alloy high-temperature alkali-corrosion resistant embedded pipe cast iron is provided, which requires the steel pipe that has undergone anti-carburizing treatment to be embedded in the casting mold in advance. The steel pipe is made of 20 seamless steel pipe and the cooling specific surface area ratio of the steel pipe is ≥1.0.

[0010] A preparation process for low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes, characterized by comprising: (1) Preparation of embedded steel pipe: Select the size and specifications of the embedded steel pipe according to the thickness of the casting, and design the shape of the embedded steel pipe according to the shape of the casting. The size and shape design of the steel pipe must meet the specific surface area ratio ≥1.0; bend and form according to the designed size and shape; (2) Carburization prevention treatment of pre-embedded steel pipes: The steel pipes that have been bent are shot blasted, and the steel pipes after shot blasting are carburization prevention treatment and dried; the pipes are filled with chromite sand and the pipe openings are sealed. (3) Preparation of casting sand mold: Prepare a model according to the structure and size of the casting; make a casting mold using the model; place and fix the treated steel pipe in the casting mold and then close the mold; (4) Preparation of molten iron: The composition of materials such as pig iron, scrap steel, ferrosilicon, ferrochrome, ferromanganese, and ferronickel is tested; the mass percentage of each raw material in the target molten iron is calculated according to the mass percentage of each component in the target cast iron product, and the amount of each raw material to be added is determined; various raw materials are added to the electric furnace according to the amount added for smelting, and ferronickel is added to the furnace last; the molten iron tapping temperature is 1480~1520℃; (5) Spheroidizing and casting of molten iron: Prepare rare earth magnesium alloy spheroidizing agent and 75SiFe inoculant in advance, and use the inverted pouring method to carry out spheroidizing and casting of molten iron; after slag removal, cast the molten iron at a temperature of 1280-1350℃.

[0011] KC202 anti-carburizing coating was used to treat the surface of the shot-blasted steel pipes to prevent carburizing.

[0012] The following explains the main features of the present invention: (1) The mass percentage composition of low alloy alkali corrosion resistant cast iron is as follows: C: 3.0~3.5%; Si: 2.4~2.8%; Mn: 0.3~0.7%; Cr: 0.5~0.7%; Ni: 0.6~0.8%; P: <0.10%; S: <0.05%; the remainder is Fe.

[0013] Choose C: 3.0-3.5%. A higher carbon content is beneficial for graphitization and spheroidization; if it is too high, it can easily cause graphite to float.

[0014] Choose Si: 2.4-2.8%. A higher silicon content is beneficial for promoting graphitization, improving the roundness of graphite, and forming a SiO2 protective film on the surface, which is beneficial for improving the oxidation resistance and corrosion resistance of castings. However, if the content is too high, it will increase the brittleness of castings and reduce impact toughness.

[0015] Choose Mn: 0.3-0.7%. Manganese is beneficial for promoting the formation of pearlite and offsetting some of the harm of S. Manganese is a positive segregation element, and too much manganese will reduce the toughness of the casting.

[0016] Choose Cr: 0.5-0.7%. Chromium is beneficial for promoting the formation of pearlite, increasing the surface hardness of castings, and forming a CrO3 protective film on the surface, which improves the oxidation and corrosion resistance of castings. However, chromium is difficult to melt, has a low absorption rate, is expensive, and is prone to forming white iron, so it should not be too high.

[0017] Choose Ni: 0.6-0.8%. Nickel is also a passivating metal, which shifts the corrosion potential in the positive direction and synergistically strengthens the protective film, thereby improving corrosion resistance in reducing corrosive media. Nickel is a precious metal, and adding too much will increase the cost.

[0018] Choose P: <0.10% or less. High phosphorus content makes it easy for phosphorus eutectic to form at grain boundaries, which significantly reduces the toughness of castings.

[0019] Choose S: ​​<0.05% or less. High sulfur content affects the spheroidizing effect, easily forms sulfide inclusions, and is prone to hot cracking.

[0020] (2) The purpose of selecting pre-embedded water pipes is to achieve water cooling, which can greatly reduce the temperature of castings under high temperature conditions, which is conducive to delaying the cracking and peeling of the protective film layer under high temperature, and to reducing the activity of electrons under high temperature, thereby improving the alkali corrosion resistance of castings under high temperature.

[0021] (3) Select 20 seamless steel pipes, which can meet the requirements of high pressure water supply and are not prone to cracking.

[0022] (4) The steel pipe design needs to make the specific surface area ratio ≥1.0 to meet the cooling requirements when water flows through the steel pipe; specific surface area ratio = outer diameter opening area of ​​the steel pipe casting part / projected area of ​​the casting working surface.

[0023] (5) Shot blasting is required on the surface of the steel pipe to improve the adhesion of the anti-carburizing coating.

[0024] (6) Applying anti-carburization treatment to the surface of the steel pipe can prevent the steel pipe from becoming brittle due to carburization during the casting process.

[0025] (7) Filling the inside of the steel pipe with chromite sand can prevent the steel pipe from being decarburized due to oxidation of the inner wall during the casting process.

[0026] (8) Nickel is a precious metal. Adding ferronickel at the end of the smelting process can reduce the loss of nickel.

[0027] (9) Spheroidizing inoculation treatment of molten iron can produce spheroidal graphite. Discontinuous graphite is not conducive to the progress of corrosion and is beneficial to improving the corrosion resistance of castings.

[0028] (10) The pouring temperature of molten iron should be 1280-1350℃. Too low a pouring temperature will reduce the fluidity of molten iron and deteriorate the casting performance, while too high a pouring temperature will cause the steel pipe to be poured through.

[0029] Compared with existing high-temperature alkali corrosion resistant cast iron, the present invention has the following beneficial effects: ① To enable low-alloy castings to have high-temperature resistance to alkali corrosion, thus meeting the requirements under high-temperature alkali corrosion conditions.

[0030] ② Unlike conventional high-alloy corrosion-resistant cast iron, low-alloy casting does not require the addition of large amounts of various precious metals, resulting in lower casting costs and better economic efficiency.

[0031] ③ Compared with high-alloy corrosion-resistant cast iron, the cast iron production process of this invention is simple and easy to operate, and the casting yield is high.

[0032] Verified in the actual blast furnace market, the blast furnace cooling wall castings produced by this invention have significant high-temperature alkali corrosion resistance in the blast furnace body, which can meet the requirements of high-temperature alkali corrosion conditions inside the blast furnace. After use, the erosion rate of the casting body is reduced by more than half compared with conventional cooling wall castings. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the present invention. Detailed Implementation

[0034] The present invention will be further described below with reference to the accompanying drawings, comparative examples, and embodiments.

[0035] The low-alloy alkali-resistant cast iron (1) of the present invention has the following composition by mass percentage: C: 3.0-3.5%; Si: 2.4-2.8%; Mn: 0.3-0.7%; Cr: 0.5-0.7%; Ni: 0.6-0.8%; P: <0.10%; S: <0.05%; the remainder is Fe.

[0036] Comparative Example 1: (Pre-embedded steel pipe) The mass percentage composition of ordinary gray cast iron HT200 is as follows: C: 3.1%; Si: 1.9%; Mn: 0.7%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0037] Comparative Example 2: (Pre-embedded steel pipe) The mass percentage composition of ordinary heat-resistant cast iron HTRCr is as follows: C: 3.3%; Si: 2.1%; Mn: 0.5%; Cr: 0.6%; Ni: 0.25%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0038] Comparative Example 3: (No pre-embedded steel pipe) The mass percentage composition of low-alloy alkali-resistant cast iron is as follows: C: 3.4%; Si: 2.4%; Mn: 0.3%; Cr: 0.7%; Ni: 0.8%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0039] Example 1: (Pre-embedded steel pipe) The mass percentage composition of low-alloy alkali-resistant cast iron is as follows: C: 3.1%; Si: 2.8%; Mn: 0.7%; Cr: 0.5%; Ni: 0.6%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0040] Example 2: (Pre-embedded steel pipe) The mass percentage composition of low-alloy alkali-resistant cast iron is as follows: C: 3.3%; Si: 2.6%; Mn: 0.5%; Cr: 0.6%; Ni: 0.7%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0041] Example 3: (Pre-embedded steel pipe) The mass percentage composition of low-alloy alkali-resistant cast iron is as follows: C: 3.4%; Si: 2.4%; Mn: 0.3%; Cr: 0.7%; Ni: 0.8%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0042] like Figure 1 As shown, Comparative Example 1, Comparative Example 2, Example 1, Example 2 and Example 3 of the present invention all use the same type and batch of seamless steel pipes of the same size and shape to form pre-embedded steel pipes (3), while Comparative Example 3 is a structure without pre-embedded steel pipes (3).

[0043] Comparative Example 1, Comparative Example 2, Example 1, Example 2, and Example 3 of the present invention all used the same KC202 anti-carburization coating (2) from the same batch.

[0044] The preparation processes of Examples 1, 2, and 3 of the present invention are the same except for the mass percentage composition of the low alloy alkali corrosion resistant cast iron (1).

[0045] Compared with Example 3, Comparative Example 3 of the present invention has the same preparation process except that it does not have a pre-embedded steel pipe.

[0046] Compared with the embodiments, the comparative examples 1 and 2 of the present invention have the same preparation process methods except for the difference in the mass percentage composition of cast iron (1) and the difference in the spheroidizing inoculation process method.

[0047] The following are the specific implementation methods of Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Example 2, and Example 3: I. Preparation of pre-embedded steel pipes (Comparative Example 3 does not have this preparation process step) The projected area of ​​the working surface (4) based on the target casting is approximately 2160 cm². 2 .

[0048] Under the premise that the ratio of the cooling specific surface area of ​​the steel pipe = the outer diameter opening area of ​​the steel pipe casting part / the projected area of ​​the casting working surface is ≥1.0, the pre-embedded steel pipe (3) can be designed to be Φ60×6 20 seamless steel pipe.

[0049] (3) The steel pipes used for pre-embedded steel pipes are the same type and batch of steel pipes procured in a unified manner. The steel pipes are procured in accordance with the standard requirements of GB8163-2018 seamless steel pipes. The steel pipes must be re-inspected and verified before use.

[0050] Bend the steel pipe according to the shape of the steel pipe (3) in the attached figure. Bend a total of 5 pipes and pass a wooden ball through them to ensure that they are unobstructed and have sufficient ellipticity. The size of the wooden ball must be ≥ 0.75 times the inner diameter of the steel pipe, that is, ≥ Φ36mm.

[0051] The bent steel pipe is subjected to surface penetrant testing at the bending section to ensure that the surface of the bent steel pipe is free of micro-cracks, wrinkles, and scratches.

[0052] Surface shot blasting is performed on steel pipes after surface penetrant testing to remove rust and improve the adhesion of anti-carburizing coating.

[0053] Within 2 hours, spray or brush KC202 anti-carburizing coating (2) onto the steel pipe after surface shot blasting and rust removal, with a coating thickness of 0.2-0.3mm.

[0054] After the anti-carburization treatment, the steel pipes are dried in a drying room at a temperature of 40-60℃ for more than 8 hours.

[0055] The pipe is filled with chromite sand, using 40-70 mesh foundry chromite sand with a refractoriness ≥ 1700℃ (JB / T6984-2013).

[0056] II. Preparation of casting sand molds: A solid wood model was made based on the structural size of the casting, with the casting scaled down by 1.1%.

[0057] The above-mentioned solid wood model was used to make the water glass sand mold, and the sand mold strength was ≥0.9MPa.

[0058] The prepared embedded steel pipe is placed and fixed in the sand mold of the casting, the mold is closed, and the gating and riser are placed.

[0059] III. Preparation of molten iron: (Comparative Example 3 and Example 3 use the same molten iron) All comparative examples and embodiments of the present invention use the same electric furnace and the same batch of materials.

[0060] Composition analysis is performed on raw materials such as pig iron, scrap steel, ferrosilicon, ferrochrome, ferromanganese, and ferronickel.

[0061] Based on the target molten iron mass percentage and the controllable changes in composition such as carbon reduction, sulfur reduction, and silicon increase that occur during the spheroidizing inoculation process, the ingredients are proportioned, and the amount of each raw material added is determined.

[0062] Various materials are added to the electric furnace according to the specified amount for smelting. Nickel-iron is added to the furnace last. After being allowed to stand at high temperature and the slag is removed, the molten iron is taken out of the furnace at a temperature of 1480-1520℃.

[0063] At this point, the mass percentage composition of each component in the molten iron obtained in Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Example 2, and Example 3 is the same as the mass percentage composition of the original molten iron, as detailed below: The original molten iron composition of Comparative Example 1 was as follows (by mass percentage): C: 3.1%; Si: 1.3%; Mn: 0.7%; P: 0.06%; S: 0.04%; the remainder was Fe.

[0064] The composition of the original molten iron in Comparative Example 2 by mass percentage was: C: 3.3%; Si: 1.5%; Mn: 0.5%; Cr: 0.6%; Ni: 0.25%; P: 0.06%; S: 0.04%; with the remainder being Fe.

[0065] Example 1: Composition of molten iron by mass percentage: C: 3.2%; Si: 1.7%; Mn: 0.7%; Cr: 0.5%; Ni: 0.6%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0066] Example 2: Composition of molten iron by mass percentage: C: 3.4%; Si: 1.5%; Mn: 0.5%; Cr: 0.6%; Ni: 0.7%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0067] The original molten iron composition by mass percentage in Comparative Example 3 and Example 3 was as follows: C: 3.5%; Si: 1.3%; Mn: 0.3%; Cr: 0.7%; Ni: 0.8%; P: 0.06%; S: 0.04%; with the remainder being Fe.

[0068] It should be noted that the original molten iron here refers to the molten iron before spheroidizing inoculation. Compared with the target molten iron, the original molten iron of Comparative Example 3, Example 1, Example 2, and Example 3 will undergo controllable changes in carbon reduction, sulfur reduction, and silicon increase due to the spheroidizing inoculation process; while the original molten iron of Comparative Example 1 and Comparative Example 2 will only undergo controllable changes in silicon increase due to inoculation.

[0069] IV. Spheroidization and casting of molten iron: Comparative Examples 1 and 2: 0.6% of 75SiFe inoculant was added to the ladle beforehand, and the inoculation treatment was carried out by the inverted ladle pouring method. Comparative Examples 3, Examples 1, 2, and 3: 1.2% of rare earth magnesium alloy spheroidizing agent (Wuxi Jufeng spheroidizing agent D-6A) and 0.9% of 75SiFe inoculant were added to the ladle beforehand, and the spheroidizing inoculation of molten iron was carried out by the inverted ladle pouring method.

[0070] After the first slag removal, all comparative and example samples were again inoculated a second time using the inverted bag flushing method with 0.2% of 3-8mm fine-particle 75SiFe inoculant.

[0071] At this point, the mass percentage composition of each component in the molten iron obtained in Comparative Example 1, Comparative Example 2, Comparative Example 3, Example 1, Example 2, and Example 3 is the target molten iron mass percentage, as detailed below: Comparative Example 1: Target molten iron mass percentage composition: C: 3.1%; Si: 1.9%; Mn: 0.7%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0072] Comparative Example 2: Target molten iron mass percentage composition: C: 3.3%; Si: 2.1%; Mn: 0.5%; Cr: 0.6%; Ni: 0.25%; P: 0.06%; S: 0.04%; the remainder is Fe.

[0073] Example 1: Target molten iron mass percentage composition: C: 3.1%; Si: 2.8%; Mn: 0.7%; Cr: 0.5%; Ni: 0.6%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0074] Example 2: Target molten iron mass percentage composition: C: 3.3%; Si: 2.6%; Mn: 0.5%; Cr: 0.6%; Ni: 0.7%; P: 0.06%; S: 0.02%; the remainder is Fe.

[0075] The target molten iron composition by mass percentage in Comparative Example 3 and Example 3 is as follows: C: 3.4%; Si: 2.4%; Mn: 0.3%; Cr: 0.7%; Ni: 0.8%; P: 0.06%; S: 0.02%; with the remainder being Fe.

[0076] After the second slag removal, the casting was carried out at a temperature of 1330℃, corresponding to the casting of a single-cast test block.

[0077] Metallographic, tensile, elongation, and hardness tests were performed on the single-cast specimens of each comparative example and embodiment.

[0078] The metallographic matrix of Comparative Example 1 is mainly pearlite, the graphite is mostly flake graphite, the tensile strength is ≥200MPa, the elongation is 0.3-0.8%, and the surface hardness is 150-230HBs.

[0079] The metallographic matrix of Comparative Example 2 is mainly pearlite, the graphite is mostly flake graphite, the tensile strength is ≥200MPa, the elongation is 0.1-0.6%, and the surface hardness is 190-270HBs.

[0080] Comparative Example 3 and Examples 1, 2, and 3 of the present invention all exhibit a metallographic matrix dominated by pearlite, with graphite primarily consisting of spheroidal graphite and a small amount of vermicular graphite, exhibiting discontinuous graphite structure. The tensile strength is ≥480 MPa, the elongation is 1-3%, and the surface hardness is 225-305 HBs.

[0081] Comparative Example 1 prepared according to the present invention refers to HT200 in GB / T9439-2010 "Gray Cast Iron Parts".

[0082] Comparative Example 2 prepared according to the present invention refers to HTRCr in GB / T9437-2009 "Heat-resistant Cast Iron Parts".

[0083] Compared with Comparative Example 1, Example 1 shows that the product surface formed a protective film with discontinuous spherical graphite, which slows down the oxidation and corrosion process. According to actual industrial application verification, under the same working conditions, the oxidation and corrosion rate of Example 1 is one-third that of Comparative Example 1.

[0084] Compared with Comparative Example 2, although a protective film could also form on the surface of the product prepared in Comparative Example 2, the protective film was unstable and easily broken, resulting in a poor corrosion retardation effect. In contrast, the product prepared in Example 2, due to the addition of a higher percentage of nickel (Ni mass percentage > 50% of Cr mass percentage), not only synergistically strengthened the protective film but also promoted a positive shift in the corrosion potential, significantly improving the product's corrosion resistance in reducing alkaline corrosion environments. Actual industrial application verification showed that, under the same operating conditions, the oxidation corrosion rate of Example 2 was half that of Comparative Example 2. Because the mass percentage of Ni in Comparative Example 2 was less than 50% of Cr mass percentage, and the inoculation method differed from Example 2 of this application, the synergistic strengthening effect was significantly weakened.

[0085] Compared with Comparative Example 3, the product made in Comparative Example 3 did not have a pre-embedded steel pipe, so it could not effectively cool the product online. The casting was used under high temperature conditions for a long time, and the protective film formed on the surface of the product was easily broken and damaged at high temperature. Moreover, high temperature accelerated the migration speed of electron ions. According to actual industrial application verification, the oxidation corrosion rate of Example 3 under the same working conditions was one-tenth that of Comparative Example 3.

[0086] The low-alloy alkali-resistant castings produced by this invention have been verified and used in equipment such as blast furnaces, fuming furnaces, and tunnel kilns. They exhibit significant high-temperature alkali corrosion resistance and can meet the requirements of high-temperature alkali corrosion conditions inside the furnace. After use, the corrosion rate of the casting body is reduced by more than half compared to conventional castings.

[0087] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that for those skilled in the art and any person skilled in the art, any equivalent substitutions or changes made to the technical solution and inventive concept of the present invention without departing from the overall concept of the present invention, as well as any changes and improvements made, should also be considered within the scope of protection of the present invention.

Claims

1. A low-alloy alkali-corrosion-resistant cast iron, characterized in that: The cast iron comprises the following components by mass percentage: C: 3.0–3.5%; Si: 2.4–2.8%; Mn: 0.3–0.7%; Cr: 0.5–0.7%; Ni: 0.6–0.8%; P: <0.10%; S: <0.05%; the remainder is Fe.

2. A low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes, characterized in that: The cast iron has internal pipes for circulating cooling substances. The cast iron comprises the following components by mass percentage: C: 3.0–3.5%; Si: 2.4–2.8%; Mn: 0.3–0.7%; Cr: 0.5–0.7%; Ni: 0.6–0.8%; P: <0.10%; S: <0.05%; the remainder is Fe.

3. The low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes according to claim 2, characterized in that: The pipeline is a seamless steel pipe, which is a steel pipe that has undergone anti-carburizing treatment, and the cooling specific surface area ratio of the steel pipe is ≥1.

0.

4. The low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes according to claim 3, characterized in that: The steel pipe is made of 20 seamless steel pipe.

5. The preparation process of low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes according to claim 2, characterized in that: Includes the following steps: (1) Preparation of embedded steel pipe: Select the size and specifications of the embedded steel pipe according to the thickness of the casting, and design the shape of the embedded steel pipe according to the shape of the casting. The size and shape design of the steel pipe must meet the specific surface area ratio ≥1.0; bend and form according to the designed size and shape; (2) Carburization prevention treatment of pre-embedded steel pipes: The steel pipes that have been bent are shot blasted, and the steel pipes after shot blasting are carburization prevention treatment and dried; the pipes are filled with chromite sand and the pipe openings are sealed. (3) Preparation of casting sand mold: Prepare a model according to the structure and size of the casting; make a casting mold using the model; place and fix the treated steel pipe in the casting mold and then close the mold; (4) Preparation of molten iron: The composition of materials such as pig iron, scrap steel, ferrosilicon, ferrochrome, ferromanganese, and ferronickel is tested; the mass percentage of each raw material in the target molten iron is calculated according to the mass percentage of each component in the target cast iron product, and the amount of each raw material to be added is determined; various raw materials are added to the electric furnace according to the amount added for smelting, and ferronickel is added to the furnace last; the molten iron tapping temperature is 1480~1520℃; (5) Spheroidizing and casting of molten iron: Prepare rare earth magnesium alloy spheroidizing agent and 75SiFe inoculant in advance, and use the inverted pouring method to carry out spheroidizing and casting of molten iron; after slag removal, cast the molten iron at a temperature of 1280-1350℃.

6. The preparation process of low-alloy high-temperature alkali-corrosion-resistant cast iron for embedded pipes according to claim 5, characterized in that: The steel pipe after shot blasting is treated with KC202 anti-carburizing coating to prevent surface carburizing. The pipe is then filled with chromite sand and the pipe opening is sealed.

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