Duplex high-chromium cast iron alloy, and preparation method therefor and application thereof

Abstract

The present application discloses a duplex high-chromium cast iron alloy, and a preparation method therefor and an application thereof. The duplex high-chromium cast iron alloy comprises the following chemical components in percentage by mass: 1.0%-2.5% of C, 0.5%-2.0% of Si, 0.5%-2.0% of Mn, 30.0%-45.0% of Cr, 5.0%-9.0% of Ni, 1.0%-4.0% of Mo, 1.0%-4.0% of Cu, 0.1%-0.4% of V, 0.1%-0.4% of Ti, 0.2%-0.5% of rare earth, 0.1%-0.3% of N, and the remainder being Fe and inevitable impurities. The present application can improve the hardness, wear resistance, high-temperature mechanical properties and thermal fatigue resistance of alloys while maintaining corrosion resistance, and can ultimately be suitable for various industrial fields requiring high strength, wear resistance, corrosion resistance, and high-temperature resistance.

Description

Duplex high chromium cast iron alloy and preparation method and application thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy materials, in particular to a duplex high chromium cast iron alloy and a preparation method and application thereof. BACKGROUND

[0002] The conventional high chromium cast iron alloy has a high carbide content and high wear resistance, and is particularly suitable for use in high-speed fluid wear medium. However, when the medium contains a certain amount of acid, the corrosion resistance is limited. In comparison, the austenite-ferrite duplex stainless steel after solid solution treatment has high corrosion resistance, but the wear resistance is often not good enough. In order to improve the wear resistance of the duplex stainless steel, annealing at 600-950 DEG C can be performed, and the ferrite containing chromium, molybdenum and silicon can form a relatively hard intermetallic phase. However, this intermetallic phase is harmful to the duplex stainless steel, which can cause local corrosion, reduce the corrosion resistance, and also make the alloy brittle and easy to break, affecting the mechanical properties.

[0003] The operating temperature of the conventional high chromium cast iron alloy material of the slurry pump is below 100 DEG C. However, in high temperature (above 160 DEG C) working conditions, due to thermal expansion and thermal cycle effect, the stress generated in the alloy can easily cause the initiation and propagation of cracks, thereby reducing the fatigue life of the alloy. In addition, high temperature can also cause thermal fatigue of the alloy, i.e. fatigue damage caused by temperature cycle change.

[0004] Therefore, it is urgent to provide an alloy material with high wear resistance, high corrosion resistance and good high temperature mechanical properties to improve the service life of the flow part of the slurry pump.

[0005] SUMMARY

[0006] The present application aims to overcome the above technical deficiencies, and provides a duplex high chromium cast iron alloy and a preparation method and application thereof, which solve the technical problem that the alloy material in the prior art cannot simultaneously have high wear resistance and corrosion resistance and has insufficient mechanical properties at high temperature.

[0007] In a first aspect, the present application provides a duplex high chromium cast iron alloy, which has the following chemical composition in terms of mass percentage: C 1.0%-2.5%, Si 0.5%-2.0%, Mn 0.5%-2.0%, Cr 30.0%-45.0%, Ni 5.0%-9.0%, Mo 1.0%-4.0%, Cu 1.0%-4.0%, V 0.1%-0.4%, Ti 0.1%-0.4%, rare earth 0.2%-0.5%, N 0.1%-0.3%, and the balance being Fe and unavoidable impurities; the duplex high chromium cast iron alloy has an austenite + ferrite microstructure and contains carbides.

[0008] In a second aspect, the present application provides a preparation method of the dual-phase high-chromium cast iron alloy, comprising the following steps:

[0009] S1, ingredients are weighed according to the chemical composition and proportion of the dual-phase high-chromium cast iron alloy;

[0010] S2, the ingredients are prepared into molten steel;

[0011] S3, the molten steel is cast, and the alloy castings are formed after cooling and solidification;

[0012] S4, the alloy castings are heat treated to obtain the dual-phase high-chromium cast iron alloy.

[0013] In a third aspect, the present application provides application of the dual-phase high-chromium cast iron alloy in preparation of the flow part of a slurry pump.

[0014] Compared with the prior art, the present application has the following beneficial effects:

[0015] The present application can improve the hardness, wear resistance, high-temperature mechanical properties and heat fatigue resistance of the alloy while maintaining the corrosion resistance by adopting carbide-hardened austenite-ferrite dual-phase matrix structure, and finally can be applied to various industrial fields requiring high strength, wear resistance, corrosion resistance and high-temperature performance. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a microstructure diagram of the dual-phase high-chromium cast iron alloy in the embodiment 2 of the present application. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0018] In a first aspect, the present application provides a dual-phase high-chromium cast iron alloy, the chemical composition of which comprises, in terms of mass percentage: C 1.0%-2.5%, Si 0.5%-2.0%, Mn 0.5%-2.0%, Cr 30.0%-45.0%, Ni 5.0%-9.0%, Mo 1.0%-4.0%, Cu 1.0%-4.0%, V 0.1%-0.4%, Ti 0.1%-0.4%, rare earth 0.2%-0.5%, N 0.1%-0.3%, and the balance being Fe and unavoidable impurities; the microstructure of the dual-phase high-chromium cast iron alloy is austenite (γ phase) + ferrite (α phase), and contains carbides.

[0019] Specifically, the mass percentage content of C can be 1.0%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, etc., and can also be any other value within the range of 1.0%-2.5%.

[0020] Specifically, the mass percentage content of Si can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2.0%, etc., and can also be any other value within the range of 0.5%-2.0.

[0021] Specifically, the mass percentage content of Mn can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.7%, 2.0%, etc., and can also be any other value within the range of 0.5%-2.0.

[0022] Specifically, the mass percentage content of Cr can be 30%, 32%, 35%, 37%, 40%, 42%, 45%, etc., and can also be any other value within the range of 30.0%-45.0%.

[0023] Specifically, the mass percentage content of Ni can be 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, etc., and can also be any other value within the range of 5.0%-9.0%.

[0024] Specifically, the mass percentage content of Mo can be 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc., and can also be any other value within the range of 1.0%-4.0%.

[0025] Specifically, the mass percentage content of Cu can be 1.0%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc., and can also be any other value within the range of 1.0%-4.0%.

[0026] Specifically, the mass percentage content of V can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc., and can also be any other value within the range of 0.1%-0.4%.

[0027] Specifically, the mass percentage content of Ti can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, etc., and can also be any other value within the range of 0.1%-0.4%.

[0028] Specifically, the mass percentage content of rare earth can be 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc., and can also be any other value within the range of 0.2%-0.5%.

[0029] Specifically, the mass percentage content of N can be 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc., and can also be any other value within the range of 0.1%-0.3%.

[0030] It should be noted that in specific settings, the amount of each chemical component can be combined according to the above.

[0031] The alloying elements can change the microstructure of the metal, improve the hardness of the material, and increase the corrosion resistance. The effects of each alloying element in the dual-phase high-chromium cast iron of the present application are as follows:

[0032] Carbon: Carbon is the main element that forms carbides in high-chromium cast iron alloys. The mass fraction of carbon largely determines the volume fraction of carbides. However, excessive carbon can lead to the formation of coarse carbides, thereby reducing toughness, and in severe cases, can cause graphitization, thereby reducing the mechanical properties of the material. Taking all factors into consideration, the content of C is controlled in the range of 1.0%-2.5% in the present application.

[0033] Silicon: Silicon is a good deoxidizer. During the solidification process of high-chromium cast iron, it can promote the formation of ferrite and carbides, and help form fine and uniform carbide particles, thereby improving the overall mechanical properties. Taking all factors into consideration, the content of Si is controlled in the range of 0.5%-2.0% in the present application.

[0034] Manganese: Manganese is a strong austenite-forming element that can rapidly dissolve in the alloy matrix, thereby improving the hardenability of high-chromium cast iron. A small amount of manganese dissolved in carbides can also appropriately increase their hardness. Taking all factors into consideration, the content of Mn is controlled in the range of 0.5%-2.0% in the present application.

[0035] Chromium: Chromium can significantly improve the wear resistance of the material by forming carbides with carbon, and can also form a dense chromium oxide passivation film on the surface of the material, thereby improving its corrosion resistance. Taking all factors into consideration, the content of Cr is controlled in the range of 30.0%-45.0% in the present application.

[0036] Nickel: Nickel can expand the austenite phase region and is the main alloying element for stabilizing austenite, which is beneficial for improving the acid resistance and medium corrosion resistance of the material. Taking all factors into consideration, the content of Ni is controlled in the range of 5.0%-9.0% in the present application.

[0037] Molybdenum: Molybdenum can reduce the critical cooling speed of high-chromium cast iron, allowing uniform hardening effect on a larger cross-sectional thickness, thereby improving the hardenability of high-chromium cast iron. Taking all factors into consideration, the content of Mo is controlled in the range of 1.0%-4.0% in the present application.

[0038] Copper: Copper can improve corrosion resistance, improve mechanical properties and high temperature properties, refine grains and increase hardenability in high chromium cast iron, and significantly enhance the comprehensive performance of the alloy. Considering comprehensively, the content of Cu is controlled in the range of 1.0%-4.0% in the present application.

[0039] Vanadium: Vanadium can refine the primary austenite dendrites, thereby refining the organization and grains of the material and improving the mechanical properties. Considering comprehensively, the content of V is controlled in the range of 0.1%-0.4% in the present application.

[0040] Titanium: Titanium is a strong carbide forming element, which can refine the carbides of high chromium cast iron and improve the wear resistance. Considering comprehensively, the content of Ti is controlled in the range of 0.1%-0.4% in the present application.

[0041] Rare earth: Rare earth not only has strong deoxidizing and desulfurizing ability, which can reduce the adverse effects of harmful elements such as oxygen and sulfur on the performance of high chromium cast iron, but also can refine the grains of high chromium cast iron, change the morphology and distribution of carbides, and make them more fine, uniform and isolated, thereby improving the toughness of the matrix. Considering comprehensively, the content of rare earth is controlled in the range of 0.2%-0.5% in the present application.

[0042] Nitrogen: Nitrogen forms austenite and improves corrosion resistance. However, as a non-metallic element, the solubility of nitrogen in metal is limited. If the amount of nitrogen added is too high, nitrogen pores will be precipitated during metal solidification, resulting in pores in the castings. Considering comprehensively, the content of N is controlled in the range of 0.1%-0.3% in the present application.

[0043] The dual-phase high chromium cast iron alloy of the present application can ensure the generation of austenite + ferrite matrix organization and a certain amount of carbides in the matrix after heat treatment by controlling the alloy composition and ratio within the above range. In the alloy composition, part of chromium and carbon form carbides, while there is still enough chromium in the matrix to form a chromium-containing oxidation film for corrosion resistance. In addition, there is enough nickel and copper to ensure a high electrode potential, so the corrosion resistance of the alloy will not be reduced due to the consumption of part of the chromium during the formation of carbides. The dual-phase high chromium cast iron alloy of the present application has excellent corrosion resistance and mechanical properties at high temperatures, and can meet the requirements of corrosion resistance and wear resistance at high temperatures (160-170°C). At high temperatures and alternating temperatures, the refined alloy organization can reduce internal stress concentration, reduce crack initiation and propagation, and improve the heat fatigue resistance of the alloy.

[0044] In the present embodiment, unavoidable impurities include S and P.

[0045] Specifically, the mass percentage of S can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc., and can also be any other value within the range of 0.01%-0.05%.

[0046] Specifically, the mass percentage of P can be 0.01%, 0.015%, 0.02%, 0.025%, 0.03%, 0.035%, 0.04%, 0.045%, 0.05%, etc., or any other value within the range of 0.01%-0.05%.

[0047] In the embodiment, the type of carbide is M 23 C6 carbide, and M 23 The volume percentage of C6 carbide is 20%-40%. If the percentage of carbide is too low, the hardness of the alloy will not be improved enough; if the percentage of carbide is too high, the matrix structure will not be formed enough, and the basic mechanical strength of the metal cannot be guaranteed.

[0048] In the embodiment, the rare earth includes at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium, and europium.

[0049] In the embodiment, the dual-phase high-chromium cast iron alloy has a Rockwell hardness >HRC40, further >HRC42.

[0050] In the embodiment, the dual-phase high-chromium cast iron alloy has a corrosion rate <0.1 mm / a, further <0.08 mm / a, after being corroded in 165℃, pH=2 sulfuric acid for 168 hours.

[0051] In a second aspect, the application provides a preparation method of a dual-phase high-chromium cast iron alloy, including the following steps:

[0052] S1, ingredients are weighed according to the chemical composition and proportion of the dual-phase high-chromium cast iron alloy;

[0053] S2, the ingredients are prepared into molten steel;

[0054] S3, the molten steel is cast, and the alloy castings are formed after cooling and solidification;

[0055] S4, the alloy castings are heat treated to obtain the dual-phase high-chromium cast iron alloy.

[0056] The application produces a matrix of austenite + ferrite and a certain amount of carbide in the matrix by combining alloy composition and heat treatment process, so that the obtained dual-phase high-chromium cast iron alloy not only has high wear resistance and high corrosion resistance, but also has good high-temperature mechanical properties. When the dual-phase high-chromium cast iron alloy is used in the overcurrent part of a slurry pump, the service life of the overcurrent part of the slurry pump can be improved.

[0057] In the embodiment, the raw materials include an iron source, a carbon source, a silicon source, a manganese source, a chromium source, a nickel source, a molybdenum source, a copper source, a vanadium source, a titanium source, a rare earth source and a nitrogen source. The types of the iron source, the carbon source, the silicon source, the manganese source, the chromium source, the nickel source, the molybdenum source, the copper source, the vanadium source, the titanium source, the rare earth source and the nitrogen source are not limited in the application, and can be selected by a person skilled in the art according to actual conditions. For example, the iron source can be pure iron or iron alloy, etc., the carbon source can be scrap steel, etc., the silicon source can be ferrosilicon, calcium silicon, etc., the manganese source can be ferromanganese, electrolytic manganese, etc., the chromium source can be ferrochrome, micro-carbon chromium, chromium nitride, etc., the nickel source can be a nickel plate, etc., the molybdenum source can be ferromolybdenum, etc., the copper source can be a copper plate, etc., the nitrogen source can be chromium nitride, etc., the vanadium source can be ferrovanadium, etc., the titanium source can be ferrotitanium, etc., and the rare earth source can be rare earth ferrosilicon alloy, etc.

[0058] In the embodiment, step S2 specifically includes:

[0059] S21, mixing and melting the iron source, the carbon source, the silicon source, the manganese source, the chromium source, the nickel source, the molybdenum source, the copper source and the nitrogen source to obtain first molten steel;

[0060] S22, performing deoxidation treatment on the first molten steel to obtain second molten steel;

[0061] S23, adding the vanadium source and the titanium source to the second molten steel to obtain third molten steel;

[0062] S24, mixing the third molten steel and the rare earth source to obtain target molten steel.

[0063] In the application, the vanadium source and the titanium source are added after the deoxidation treatment, so that the two sources jointly act in the cooling process, are enriched at the grain boundaries of carbide, hinder the preferred growth of carbide, and further refine the primary carbide.

[0064] Preferably, in step S21, the temperature of melting is 1550-1600°C, including but not limited to 1550°C, 1560°C, 1570°C, 1580°C, 1590°C, 1600°C, etc.

[0065] Preferably, in step S21, it further includes: detecting whether the content of each component in the furnace front analysis sample meets the chemical component requirement of the target alloy; if yes, the subsequent deoxidation treatment step is continued to be executed; otherwise, the components of the furnace front analysis sample are adjusted according to the chemical components of the target alloy until the requirement of the chemical components of the target alloy is met.

[0066] Preferably, in step S22, the deoxidation treatment process includes: adding a deoxidizing agent to the first molten steel for deoxidation treatment.

[0067] In some embodiments of the present application, the deoxidizer is a silicon-calcium alloy, and the amount of the deoxidizer added is 0.1%-0.3% of the mass of the first molten steel, including but not limited to 0.1%, 0.2%, 0.3%, etc.

[0068] Preferably, in step S22, the temperature of the deoxidation treatment is 1550-1600°C, including but not limited to 1550°C, 1560°C, 1570°C, 1580°C, 1590°C, 1600°C, etc.; and the time of the deoxidation treatment is 3-10 min, including but not limited to 3 min, 5 min, 7 min, 10 min, etc.

[0069] Preferably, in step S24, the process of mixing the third molten steel and the rare earth source includes: adding the rare earth source into the ladle in advance, and then pouring the third molten steel with a temperature adjusted to 1500-1550°C into the ladle.

[0070] In the present embodiment, in step S3, the temperature of the pouring is 1400-1450°C, including but not limited to 1400°C, 1410°C, 1420°C, 1430°C, 1440°C, 1450°C, etc.

[0071] In the present embodiment, in step S4, during the heat treatment, the heating rate is ≤50°C / h, including but not limited to 10°C / h, 20°C / h, 30°C / h, 40°C / h, 50°C / h, etc.; the temperature of the heat treatment is 1000-1100°C, including but not limited to 1000°C, 1020°C, 1040°C, 1060°C, 1080°C, 1100°C, etc.; the time of the heat treatment is 2-5 hours, including but not limited to 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, etc.; and after the heat treatment, the casting is taken out and air-cooled to room temperature.

[0072] The heat treatment process of the present application is simple and time-saving. By controlling the temperature of the heat treatment within the above range, the present application can ensure that the ferrite and austenite contents in the matrix are comparable, so that the alloy has the optimal performance. If the temperature of the heat treatment is too low, the brittle phase cannot be completely dissolved into the matrix, thereby affecting the mechanical properties of the alloy, and the surrounding chromium is reduced due to the enrichment of chromium, thereby reducing the corrosion resistance; if the temperature of the heat treatment is too high, energy is wasted and the casting is severely oxidized.

[0073] In a third aspect, the present application provides the use of the above-mentioned dual-phase high-chromium cast iron alloy in the preparation of a flow part of a slurry pump.

[0074] The above-mentioned slurry pump of the present application can be applied in the fields of mining, metallurgy, etc.

[0075] Example 1

[0076] The chemical composition of the duplex high-chromium cast iron alloy provided in this embodiment is shown in Table 1.

[0077] Table 1. Alloy Chemical Composition (wt.%)

[0078] Its preparation steps include:

[0079] (1) Based on Table 1 and the alloy composition content of scrap steel, ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum, copper plate and chromium nitride, calculate the weight required for each type of furnace charge for a 400kg medium frequency furnace.

[0080] (2) After calculating and weighing the required weight according to each furnace charge, add scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride into the medium frequency furnace in the order of scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride. Heat to 1550℃. After the furnace charge is melted, the first molten steel is obtained. Add 0.2% silicon-calcium alloy of the first molten steel to the first molten steel for deoxidation treatment for 5 minutes. After deoxidation, the second molten steel is obtained.

[0081] (3) Add ferrovanadium and ferrotitanium to the second molten steel to obtain the third molten steel; when the third molten steel is adjusted to 1510℃, add rare earth ferrosilicon alloy (grade 195023) into the ladle, pour the third molten steel into the ladle to obtain the target molten steel; when the temperature of the target molten steel drops to 1400℃, pour the target molten steel into the mold cavity, and after cooling and solidification, obtain the required slurry pump casting.

[0082] (4) The slurry pump casting was heat-treated to obtain a duplex high-chromium cast iron alloy. The specific parameters of the heat treatment are as follows: the temperature was increased to 1000℃ at a rate of 50℃ per hour, held for 2 hours, and then cooled to room temperature in air.

[0083] Furnace-assigned samples (samples subjected to heat treatment in the furnace along with the castings, whose alloy composition and heat treatment process are consistent with the castings, and whose properties represent the performance of the castings) were prepared. Φ30×3mm corrosion samples were prepared and corroded in dilute sulfuric acid at 165℃ and pH=2 for 168 hours, and their uniform corrosion rate (mm / a, millimeters / year) was measured. Φ70×40mm circular samples were prepared to test Rockwell hardness (HRC). 50×30×3mm sheet samples were prepared and subjected to temperature change tests within the temperature range of 25℃-175℃ to detect whether cracks appeared on the sample surface under temperature changes. Their performance indicators are shown in Table 2.

[0084] Table 2 shows the hardness, uniform corrosion rate, and cracking tendency of the alloy in Example 1.

[0085] (The results of Rockwell hardness and uniform corrosion rate tests are the average of three tests. No cracks in the crack tendency results mean that no cracks were found in any of the three measurements. Cracks in the crack tendency results mean that at least one crack was found in any of the three measurements.)

[0086] Example 2

[0087] The chemical composition of the duplex high-chromium cast iron alloy provided in this embodiment is shown in Table 3.

[0088] Table 3. Alloy chemical composition (wt.%)

[0089] Its preparation steps include:

[0090] (1) Based on Table 3 and the alloy composition content of scrap steel, ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum, copper plate and chromium nitride, calculate the weight required for each type of furnace charge for a 400kg medium frequency furnace.

[0091] (2) After calculating and weighing the required weight according to each furnace charge, add scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride into the medium frequency furnace in the order of scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride. Heat the furnace to 1568℃. After the furnace charge is melted, the first molten steel is obtained. Add 0.2% silicon-calcium alloy of the first molten steel to the first molten steel for deoxidation treatment for 5 minutes. After the deoxidation is completed, the second molten steel is obtained.

[0092] (3) Add ferrovanadium and ferrotitanium to the second molten steel to obtain the third molten steel; when the third molten steel is adjusted to 1517℃, add rare earth ferrosilicon alloy (grade 195023) into the ladle, pour the third molten steel into the ladle to obtain the target molten steel; when the temperature of the target molten steel drops to 1418℃, pour the target molten steel into the mold cavity, and after cooling and solidification, obtain the required slurry pump casting.

[0093] (4) The slurry pump casting was heat-treated to obtain a duplex high-chromium cast iron alloy. The specific parameters of the heat treatment were as follows: the temperature was increased to 1035°C at a rate of 40°C per hour, held for 3 hours, and then cooled to room temperature in air.

[0094] A Φ30×3mm corrosion sample was prepared from the furnace-fed samples and corroded in dilute sulfuric acid at 165℃ and pH=2 for 168 hours. The uniform corrosion rate (mm / a, millimeters / year) was measured. A Φ70×40mm circular sample was prepared to test the Rockwell hardness (HRC). A 50×30×3mm sheet sample was prepared and subjected to a temperature change test within the temperature range of 25℃-175℃ to detect whether cracks were generated on the sample surface under temperature changes. Its performance indicators are shown in Table 4.

[0095] Table 4 shows the hardness, uniform corrosion rate, and crack tendency of the alloy in Example 2.

[0096] (The results of Rockwell hardness and uniform corrosion rate tests are the average of three tests. No cracks in the crack tendency results mean that no cracks were found in any of the three measurements. Cracks in the crack tendency results mean that at least one crack was found in any of the three measurements.)

[0097] Figure 1 is a microstructure diagram of the duplex high-chromium cast iron alloy in Example 2 of this application. Referring to Figure 1, it can be seen that the microstructure has a duplex matrix of austenite (γ phase) + ferrite (α phase), and M phase is uniformly distributed around the duplex matrix. 23 C6 type carbides.

[0098] Example 3

[0099] The chemical composition of the duplex high-chromium cast iron alloy provided in this embodiment is shown in Table 5.

[0100] Table 5. Alloy Chemical Composition (wt.%)

[0101] Its preparation steps include:

[0102] (1) Based on Table 5, calculate the required weight of various furnace materials for a 400kg medium-frequency furnace by calculating the alloy composition content of scrap steel, ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum, copper plate, and chromium nitride.

[0103] (2) After calculating and weighing the required weight according to each furnace charge, add scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride into the medium frequency furnace in the order of scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride. Heat to 1585℃. After the furnace charge is melted, the first molten steel is obtained. Add 0.2% silicon-calcium alloy of the first molten steel to the first molten steel for deoxidation treatment for 5 minutes. After deoxidation, the second molten steel is obtained.

[0104] (3) Add ferrovanadium and ferrotitanium to the second molten steel to obtain the third molten steel; when the third molten steel is adjusted to 1535℃, add rare earth ferrosilicon alloy (grade 195023) into the ladle, pour the third molten steel into the ladle to obtain the target molten steel; when the temperature of the target molten steel drops to 1436℃, pour the target molten steel into the mold cavity, and after cooling and solidification, obtain the required slurry pump casting.

[0105] (4) The slurry pump casting was heat-treated to obtain a duplex high-chromium cast iron alloy. The specific parameters of the heat treatment were as follows: the temperature was increased to 1070°C at a rate of 30°C per hour, held for 4 hours, and then cooled to room temperature in air.

[0106] A Φ30×3mm corrosion sample was prepared from the furnace-fed samples and corroded in dilute sulfuric acid at 165℃ and pH=2 for 168 hours. The uniform corrosion rate (mm / a, millimeters / year) was measured. A Φ70×40mm circular sample was prepared to test the Rockwell hardness (HRC). A 50×30×3mm sheet sample was prepared and subjected to a temperature change test within the temperature range of 25℃-175℃ to detect whether cracks were generated on the sample surface under temperature changes. Its performance indicators are shown in Table 6.

[0107] Table 6 shows the hardness, uniform corrosion rate, and crack tendency of the alloy in Example 3.

[0108] (The results of Rockwell hardness and uniform corrosion rate tests are the average of three tests. No cracks in the crack tendency results mean that no cracks were found in any of the three measurements. Cracks in the crack tendency results mean that at least one crack was found in any of the three measurements.)

[0109] Example 4

[0110] The chemical composition of the duplex high-chromium cast iron alloy provided in this embodiment is shown in Table 7.

[0111] Table 7. Alloy Chemical Composition (wt.%)

[0112] Its preparation steps include:

[0113] (1) Based on Table 7 and the alloy composition content of scrap steel, ferrosilicon, ferromanganese, ferrochrome, nickel plate, ferromolybdenum, copper plate and chromium nitride, calculate the weight required for each type of furnace charge for a 400kg medium frequency furnace.

[0114] (2) After calculating and weighing the required weight according to each furnace charge, add scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride into the medium frequency furnace in the order of scrap steel, nickel plate, copper plate, ferrochrome, ferromolybdenum, ferromanganese, ferrosilicon and chromium nitride. Heat to 1600℃. After the furnace charge is melted, the first molten steel is obtained. Add 0.2% silicon-calcium alloy of the first molten steel to the first molten steel for deoxidation treatment for 5 minutes. After deoxidation, the second molten steel is obtained.

[0115] (3) Add ferrovanadium and ferrotitanium to the second molten steel to obtain the third molten steel; when the third molten steel is adjusted to 1550℃, add rare earth ferrosilicon alloy (grade 195023) into the ladle, pour the third molten steel into the ladle to obtain the target molten steel; when the temperature of the target molten steel drops to 1450℃, pour the target molten steel into the mold cavity, and after cooling and solidification, obtain the required slurry pump casting.

[0116] (4) The slurry pump casting was heat-treated to obtain a duplex high-chromium cast iron alloy. The specific parameters of the heat treatment were as follows: the temperature was increased to 1100℃ at a rate of 20℃ per hour, held for 5 hours, and then cooled to room temperature in air.

[0117] A Φ30 x 3 mm corrosion specimen was prepared from the as-cast sample and was corroded in dilute sulfuric acid at 165°C and pH = 2 for 168 hours, and the uniform corrosion rate (mm / a, millimeter per year) was measured. A Φ70 x 40 mm round specimen was prepared to test the Rockwell hardness (HRC). A 50 x 30 x 3 mm sheet specimen was prepared to test the temperature change test in the temperature range of 25°C to 175°C to detect whether cracks are generated on the surface of the specimen under temperature change. The performance indexes are shown in Table 8.

[0118] Table 8 Hardness, uniform corrosion rate and crack tendency of the alloy in Example 4

[0119] (The test results of Rockwell hardness and uniform corrosion rate are the average values of three tests, and no cracks in the crack tendency results mean that no cracks are generated in three tests, and cracks in the crack tendency results mean that at least one crack is generated in three tests.)

[0120] Comparative Example 1

[0121] The cast iron alloy provided in this comparative example was adjusted according to Example 2, and the difference is that the carbon content is low, which is 0.7%, and the chemical composition is shown in Table 9.

[0122] Table 9 Chemical composition of the alloy (wt. %)

[0123] The preparation steps are consistent with Example 2.

[0124] A Φ30 x 3 mm corrosion specimen was prepared from the as-cast sample and was corroded in dilute sulfuric acid at 165°C and pH = 2 for 168 hours, and the uniform corrosion rate (mm / a, millimeter per year) was measured. A Φ70 x 40 mm round specimen was prepared to test the Rockwell hardness (HRC). A 50 x 30 x 3 mm sheet specimen was prepared to test the temperature change test in the temperature range of 25°C to 175°C to detect whether cracks are generated on the surface of the specimen under temperature change. The performance indexes are shown in Table 8.

[0125] Table 10 Hardness, uniform corrosion rate and crack tendency of the alloy in Comparative Example 1

[0126] (The test results of Rockwell hardness and uniform corrosion rate are the average values of three tests, and no cracks in the crack tendency results mean that no cracks are generated in three tests, and cracks in the crack tendency results mean that at least one crack is generated in three tests.)

[0127] The alloy prepared in this comparative example meets the requirement of uniform corrosion rate, but the hardness is low. The main reason is that the carbon content of the alloy is lower than that of Example 2, the matrix structure is ferrite, and the carbide content is lower than 15%, which cannot meet the requirement of medium wear resistance.

[0128] Comparative Example 2

[0129] The cast iron alloy provided in this comparative example is adjusted according to Example 3, and the difference is that the chromium content is lower, which is 25.2%. The chemical composition of the alloy is shown in Table 11.

[0130] Table 11 Chemical composition of the alloy (wt. %)

[0131] The preparation steps are consistent with Example 3.

[0132] Φ30×3mm corrosion samples were prepared from the furnace samples, and were corroded in dilute sulfuric acid at 165℃ and pH=2 for 168 hours. The uniform corrosion rate (mm / a, millimeter per year) was measured. Φ70×40mm round samples were prepared to test the Rockwell hardness (HRC). 50×30×3mm sheet samples were prepared to conduct temperature change test in the temperature range of 25℃-175℃ to detect whether cracks are generated on the surface of the sample under temperature change. The performance indicators are shown in Table 12.

[0133] Table 12 Hardness, uniform corrosion rate and crack tendency of the alloy in Comparative Example 2

[0134] (The test results of Rockwell hardness and uniform corrosion rate are the average values of three tests. In the crack tendency results, no cracks mean that there is no crack in three measurements, and cracks mean that at least one crack is generated in three measurements.)

[0135] The hardness of the alloy prepared in this comparative example meets the requirement, but the uniform corrosion rate at high temperature is high, with an average value of 0.272mm / a. The main reason is that the Cr content of the alloy is too low. After Cr and C in the alloy generate carbide, the Cr in the matrix is low, which leads to the selective corrosion of the electrode potential lower than the carbide.

[0136] Comparative Example 3

[0137] The cast iron alloy provided in this comparative example is adjusted according to Example 4, and the difference is that the nickel content is lower, which is 4.5%. The chemical composition of the alloy is shown in Table 13.

[0138] Table 13 Chemical composition of the alloy (wt. %)

[0139] The preparation steps are consistent with Example 4.

[0140] The uniform corrosion rate (mm / a, millimeter per year) of the Φ30x3mm corrosion sample taken from the furnace was measured by corroding in 165℃, pH=2 dilute sulfuric acid for 168 hours. The round Φ70x40mm sample was used to test the Rockwell hardness (HRC). The 50x30x3mm sheet sample was used to test the temperature change test in the temperature range of 25-175℃ to detect whether the sample surface had cracks under temperature change. The performance indexes are shown in Table 14.

[0141] Table 14 Hardness, uniform corrosion rate and crack tendency of the alloy in Comparative Example 3

[0142] (The test results of Rockwell hardness and uniform corrosion rate are the average values of three tests. No cracks in the crack tendency results mean that there are no cracks in three measurements. Cracks in the crack tendency results mean that at least one crack is generated in three measurements.)

[0143] The hardness and uniform corrosion rate of the alloy produced in the comparative example meet the requirements, but after careful observation of the sample surface after the temperature change test, it is found that the sample has micro-cracks in the local part. The main reason is that the low Ni content leads to the microstructure of the alloy to be ferrite + carbide. Compared with the austenitic structure, the high temperature mechanical properties of the ferrite structure are worse.

[0144] Comparative Example 4

[0145] The cast iron alloy provided in the comparative example is adjusted according to Example 3, and the difference lies in the different heat treatment parameters. The specific parameters are as follows: heating to 950℃ at a rate of 30℃ per hour, holding for 4 hours, and then cooling to room temperature in air.

[0146] The uniform corrosion rate (mm / a, millimeter per year) of the Φ30x3mm corrosion sample taken from the furnace was measured by corroding in 165℃, pH=2 dilute sulfuric acid for 168 hours. The round Φ70x40mm sample was used to test the Rockwell hardness (HRC). The 50x30x3mm sheet sample was used to test the temperature change test in the temperature range of 25-175℃ to detect whether the sample surface had cracks under temperature change. The performance indexes are shown in Table 14.

[0147] Table 15 Hardness, uniform corrosion rate and crack tendency of the alloy in Comparative Example 4

[0148] (The test results of Rockwell hardness and uniform corrosion rate are the average values of three tests. No cracks in the crack tendency results mean that there are no cracks in three measurements. Cracks in the crack tendency results mean that at least one crack is generated in three measurements.)

[0149] The alloy made in the present comparative example has higher hardness than Example 3, but the average uniform corrosion rate is 0.401 mm / a, which does not meet the corrosion resistance requirement, and cracks are generated on the surface of the sample after temperature change test. The main reason is that the as-cast structure of the material is composed of austenite, σ brittle phase and M 23 C6 carbide, and the σ brittle phase is not completely dissolved in the matrix structure due to the low heat treatment temperature. The σ phase is a phase with high hardness, but it reduces the toughness of the material and increases the crack tendency. At the same time, the σ phase reduces the corrosion resistance due to the chromium enrichment in the surrounding area.

[0150] Comparative Example 5

[0151] The same test methods as in the examples were used to test the hardness, uniform corrosion rate and crack tendency of BTSCr36Mo2Ni2Cu, and the performance indicators of BTSCr36Mo2Ni2Cu are shown in Table 16.

[0152] Table 16 Hardness, uniform corrosion rate and crack tendency of BTSCr36Mo2Ni2Cu

[0153] (The test results of Rockwell hardness and uniform corrosion rate are the average of three tests, and the crack tendency results without cracks mean that there is no crack in three measurements, and the crack tendency results with cracks mean that at least one crack is generated in three measurements.)

[0154] The hardness of the alloy in the present comparative example is comparable to that of the examples of the present application, but the corrosion wear rate is significantly higher than that of the examples of the present application, and cracks are generated on the surface of the sample during temperature change test in the temperature range of 25-175°C, which shows that the dual-phase high chromium cast iron alloy of the present application has obvious advantages compared to the existing high chromium corrosion-resistant high wear cast iron.

[0155] Application Example

[0156] The slag pump castings made in Examples 1-4 do not have cracks, shrinkage holes, pores and other defects after processing, and after trial use in simulated working conditions and actual field, the corrosion rate is 40%-50% lower than that of the existing high chromium corrosion-resistant high wear cast iron BTSCr36Mo2Ni2Cu material, and the service life is about 1.5 times that of the BTSCr36Mo2Ni2Cu material in a factory test.

[0157] In summary, the dual-phase high-chromium cast iron alloy of the present application forms austenite + ferrite + 20%-40% carbide organization through effective design of the alloying composition of each element. After heat treatment, the hardness of the material is above HRC40, the corrosion test is carried out in sulfuric acid at 165°C, pH=2, the corrosion rate is less than 0.08mm / a, which reaches the corrosion resistance standard (<0.1mm / a), and the temperature change test is carried out in the temperature range of 25°C-175°C, and no cracks are generated on the surface of the sample.

[0158] The specific embodiments of the present application described above do not constitute a limitation on the protection scope of the present application. Any various other corresponding changes and modifications made according to the technical concept of the present application shall be included in the protection scope of the claims of the present application.

Claims

1. A dual phase high chromium cast iron alloy, characterized in that, The chemical composition includes, by mass percentage, C 1.0%-2.5%, Si 0.5%-2.0%, Mn 0.5%-2.0%, Cr 30.0%-45.0%, Ni 5.0%-9.0%, Mo 1.0%-4.0%, Cu 1.0%-4.0%, V 0.1%-0.4%, Ti 0.1%-0.4%, rare earth 0.2%-0.5%, N 0.1%-0.3%, and the rest is Fe and inevitable impurities; the microstructure of the duplex high-chromium cast iron alloy is austenite + ferrite, and contains carbides.

2. The dual-phase high-chromium cast-iron alloy according to claim 1, characterized in that, The type of carbide is M 23 C6 carbide, and the M 23 The volume fraction of C6 carbide is 20%-40%.

3. The dual-phase high-chromium cast-iron alloy according to claim 1, characterized in that, The rare earth includes at least one of lanthanum, cerium, praseodymium, neodymium, promethium, samarium and europium.

4. The dual-phase high-chromium cast-iron alloy according to claim 1, characterized in that, The Rockwell hardness of the duplex high-chromium cast iron alloy is greater than HRC40; the corrosion rate of the duplex high-chromium cast iron alloy is less than 0.1 mm / a after corrosion in sulfuric acid with pH=2 at 165℃ for 168 hours.

5. A method of producing the dual-phase high-chromium cast iron alloy according to any one of claims 1 to 4, characterized by, The method comprises the following steps: raw materials are weighed according to the chemical composition and proportion of the duplex high-chromium cast iron alloy; the raw materials are prepared into molten steel; the molten steel is cast and cooled to form an alloy casting; the alloy casting is heat treated to obtain the duplex high-chromium cast iron alloy.

6. The method of claim 5, wherein the duplex high chromium cast iron alloy is prepared by the steps of: The step of preparing the raw materials into molten steel comprises: iron source, carbon source, silicon source, manganese source, chromium source, nickel source, molybdenum source, copper source and nitrogen source are mixed and smelted to dissolve and clear to obtain first molten steel; the first molten steel is deoxidized to obtain second molten steel; vanadium source and titanium source are added to the second molten steel to obtain third molten steel; the third molten steel is mixed with rare earth source to obtain target molten steel.

7. The method for preparing the duplex high-chromium cast iron alloy according to claim 6, characterized in that, The smelting temperature is 1550-1600℃; the deoxidation process comprises adding deoxidizer to the first molten steel for deoxidation; the deoxidizer is silicon-calcium alloy, and the amount of the deoxidizer is 0.1%-0.3% of the mass of the first molten steel; the deoxidation temperature is 1550-1600℃, and the deoxidation time is 3-10 min; the process of mixing the third molten steel with rare earth source comprises: the rare earth source is added to a ladle in advance, and then the third molten steel with a temperature of 1500-1550℃ is poured into the ladle.

8. The method of claim 5, wherein the alloy is prepared by the steps of: melting the alloying elements in a vacuum induction furnace; adding the alloying elements to the molten alloy; and pouring the molten alloy into a mold. The casting temperature is 1400-1450℃.

9. The method of claim 5, wherein the alloy is prepared by the steps of: melting the alloying elements in a vacuum induction furnace; pouring the molten alloy into a graphite crucible; and pouring the molten alloy into a mold. In the heat treatment process, the heating rate is less than or equal to 50℃ / h, the heat treatment temperature is 1000-1100℃, and the heat treatment time is 2-5 hours; after the heat treatment, the alloy is taken out of the furnace and air-cooled to room temperature.

10. Use of the duplex high-chromium cast iron alloy according to any one of claims 1-4 in the preparation of flow parts of a slurry pump.

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