A corrosion-resistant iron-based alloy powder and its preparation method

Abstract

The present invention belongs to the technical field of cemented carbides, and particularly relates to a corrosion-resistant iron-based alloy powder and a preparation method thereof. The corrosion-resistant iron-based alloy powder provided by the present invention is prepared from 5.3-7.5% of chromium, 1.0-2.0% of nickel, 4.5-7.0% of molybdenum, 2.0-4.5% of titanium, 1.4-1.8% of carbon, 0.5-1.5% of rare earth elements, 0.05-0.13% of impurities and the balance of iron. The corrosion-resistant iron-based alloy powder provided by the present invention not only has an oxide film on the surface, and the elements in the alloy are in a passivated state, but also the alloy grains are fine and the grain boundaries are arranged neatly, which can essentially solve the problem of easy corrosion of iron-based alloy materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of cemented carbides, and particularly relates to a corrosion-resistant iron-based alloy powder and a preparation method thereof. Background Art

[0002] Ferroalloy is an alloy in which one or more than two metals or non-metallic elements are fused together, and usually has excellent mechanical properties and heat resistance, so it is widely used in industrial production. Ferroalloys are widely used in the steel industry for manufacturing various types of steel. At the same time, ferroalloys are also used in industries such as electronics, aerospace, automotive, and construction for manufacturing electronic components, engine parts, building structures, etc. With the continuous progress of technology and the development of industry, ferroalloys will continue to grow and develop in the future.

[0003] For a long time, metal corrosion has been a focus of people's attention. Iron-based alloys will be corroded more or less in acidic or alkaline environments. This is because there are generally many small pores in iron-based alloys. In acidic or alkaline environments, the inner walls of the pores are in long-term contact with acidic or alkaline gases or solutions, resulting in corrosion around the pores, which seriously affects the durability of iron-based alloys. Common methods to improve the corrosion resistance of iron-based alloys are mainly to form an oxide film on the surface of the iron-based alloy or to coat a corrosion-resistant coating on the surface of the iron-based alloy. However, this can only delay the corrosion of iron-based alloy materials and cannot fundamentally solve the problem of the easy corrosion of iron-based alloy materials.

[0004] The Chinese patent application document with the publication number CN105648340A discloses a highly dense and corrosion-resistant nickel-iron alloy, and its formula is: carbon 0.11 - 0.17%, chromium 0.36 - 0.42%, silicon 0.12 - 0.21%, titanium 0.28 - 0.3%, niobium 0.10 - 0.15%, manganese 0.25 - 0.32%, copper 0.10 - 0.30%, nickel 0.68 - 0.75%, sulfur 0.03 - 0.05%, phosphorus 0.01 - 0.03%, rare earth elements 0.05 - 0.15%, unavoidable impurities less than 0.1% and the balance being iron. This formula improves the density and surface corrosion resistance of die-cast alloys by controlling the content of alloy components, but cannot fundamentally solve the problem of the easy corrosion of iron-based alloy materials. Summary of the Invention

[0005] In order to solve the technical problems of the easy corrosion of iron-based alloy materials in related technologies and the inability to fundamentally improve the easy corrosion of iron-based alloy materials, the purpose of the present invention is to provide a corrosion-resistant iron-based alloy powder and a preparation method thereof.

[0006] In order to achieve the above-mentioned invention purpose, the technical solution of the present invention is as follows:

[0007] A corrosion-resistant iron-based alloy powder, comprising the following components and their weight percentages:

[0008] Chromium 5.3 - 7.5%, nickel 1.0 - 2.0%, molybdenum 4.5 - 7.0%, titanium 2.0 - 4.5%, carbon 1.4 - 1.8%, rare earth elements 0.5 - 1.5%, impurities 0.05 - 0.13%, and the balance is iron.

[0009] Further, the corrosion-resistant iron-based alloy powder comprises the following components and their weight percentages: chromium 6.6%, nickel 1.5%, molybdenum 6.3%, titanium 3.2%, carbon 1.6%, rare earth elements 0.9%, impurities 0.09%, and the balance is iron.

[0010] The corrosion resistance of the alloy depends on the protective properties of the surface film to some extent. Chromium in the iron-based alloy powder formula provided by the present invention can form a dense chromium oxide protective film on the surface of the alloy, which can block the corrosion medium and improve the corrosion resistance of the iron-based alloy. However, the internal stress of the overly thick oxide film is relatively large, which is prone to cause cracking of the film and thus reduce the corrosion resistance of the alloy. Therefore, the addition amount of chromium element is particularly important. When the addition amount of chromium element is greater than 7.5%, the iron-based alloy material reaches the level of stainless steel. However, at this time, the internal stress of the chromium oxide film is relatively large, and the oxide film is prone to cracking, resulting in a decrease in the corrosion resistance of the iron-based alloy material.

[0011] Molybdenum can improve the corrosion resistance of the iron-based alloy material in an acidic environment and improve the resistance to pitting corrosion and crevice corrosion of the iron-based alloy material. However, the addition of molybdenum element will increase the high-temperature deformation resistance of the iron-based alloy material. Therefore, the higher the content of molybdenum element, the worse the high-temperature corrosion resistance of the iron-based alloy material. The inventor found during the research process that the addition of titanium element can convert the thermodynamically unstable metal in the iron-based alloy material from the activated state to the passivated state, thereby improving the high-temperature corrosion resistance of the iron-based alloy material.

[0012] In conventional iron-based alloy materials, carbon is the key factor affecting the corrosion resistance of the iron-based alloy material. The corrosion resistance of the iron-based alloy material decreases with the increase of carbon content. When the carbon content in the iron-based alloy material is less than 1.2%, the iron-based alloy material can reach the corrosion resistance level of stainless steel. However, carbon is evenly dispersed in the iron alloy and can act as a reducing agent during the preparation process of the iron-based alloy, reducing the oxidized metal elements in the iron-based alloy material and ensuring the mechanical properties of the iron-based alloy material. The inventor has proven through a large number of experimental studies that when the carbon content is 1.4 - 1.8%, the corrosion resistance and mechanical properties of the iron-based alloy material are excellent.

[0013] Further, the rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 3 - 7:5 - 9:11 - 13.

[0014] During the research process, the inventors found that the corrosion resistance of iron-based alloys is closely related to their microstructure, mainly including two aspects: crystal defects and grain boundaries. Crystal defects such as voids, point defects, plane defects, inclusions, etc. will all affect the corrosion behavior of materials. Grain boundaries, on the other hand, are an essential mechanism for corrosion resistance in materials. Voids, local oxidation, etc. can be caused at grain boundaries, thereby restricting the penetration and erosion of corrosive media. In the present invention, rare earth elements are introduced into the iron-based alloy powder, which can play a role in promoting grain refinement, increasing the grain boundaries in the iron-based alloy powder, and thus improving the corrosion resistance of the iron-based alloy powder. The inventors' research found that when the rare earth elements are composed of cerium, samarium, and erbium in a mass ratio of 3-7:5-9:11-13, the corrosion resistance of the iron-based alloy material is the best.

[0015] Furthermore, the rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 3:5:11.

[0016] Furthermore, the rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 5:7:12.

[0017] Further, the impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 2-5:1-3:5-9. During the research process, the inventors found that after adding three elements of antimony, arsenic, and tin to the iron-based alloy powder, the corrosion rate of the iron-based alloy powder under acidic conditions decreased significantly. It is speculated that these three elements reduced the active dissolution rate of the alloy under acidic conditions.

[0018] Furthermore, the impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 4:2:7.

[0019] The present invention also provides a preparation method of the corrosion-resistant iron-based alloy powder, specifically: putting the formulated amounts of chromium, nickel, molybdenum, titanium, carbon, rare earth elements, impurities, and iron into a vacuum induction furnace and heating until all are melted into a liquid state, then under the conditions that nitrogen is used as the atomizing medium and water is used as the cooling medium outside the furnace body, atomizing through an atomizing nozzle and drying to obtain the corrosion-resistant iron-based alloy powder.

[0020] Compared with the prior art, the corrosion-resistant iron-based alloy powder and its preparation method provided by the present invention have the following technical advantages:

[0021] (1) The corrosion rate of the corrosion-resistant iron-based alloy powder provided by the present invention when immersed in an acidic solution at room temperature for 72h is 0.32-0.41mm / a, the corrosion rate when immersed in an alkaline solution for 72h is 0.20-0.26mm / a; the corrosion rate when immersed in a salt solution for 72h is 0.12-0.20mm / a;

[0022] (2)The corrosion rate of the corrosion-resistant iron-based alloy powder provided by the present invention when immersed in an acidic solution at 50 °C for 72 h is 0.50 - 0.58 mm / a, the corrosion rate when immersed in an alkaline solution for 72 h is 0.35 - 0.43 mm / a, and the corrosion rate when immersed in a salt solution for 72 h is 0.22 - 0.31 mm / a;

[0023] (3)The corrosion-resistant iron-based alloy powder provided by the present invention not only has an oxide film on its surface, and each element in the alloy is in a passivated state, but also the alloy grains are fine and the grain boundaries are arranged neatly, which can essentially improve the problem of easy corrosion of iron-based alloy materials. Detailed implementation manners

[0024] The following will further illustrate the present invention in combination with specific embodiments, but the present invention is not limited to the following embodiments. Those skilled in the art can make various modifications according to the basic idea of the present invention, but as long as they do not depart from the basic idea of the present invention, they are within the scope of the present invention.

[0025] Example 1. A corrosion-resistant iron-based alloy powder and its preparation method

[0026] The corrosion-resistant iron-based alloy powder includes the following components and their weight percentages:

[0027] Chromium 5.3%, nickel 2.0%, molybdenum 4.5%, titanium 4.5%, carbon 1.4%, rare earth elements 1.5%, impurities 0.05%, and the balance is iron.

[0028] The rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 3:5:11. The impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 5:3:9.

[0029] The preparation method of the corrosion-resistant iron-based alloy powder is specifically as follows: Put the formulated amounts of chromium, nickel, molybdenum, titanium, carbon, rare earth elements, impurities, and iron into a vacuum induction furnace and heat until all are melted into a liquid state. Then, under the conditions that nitrogen is used as the atomizing medium and water is used as the cooling medium outside the furnace body, atomize through an atomizing nozzle and dry to obtain the corrosion-resistant iron-based alloy powder.

[0030] Example 2. A corrosion-resistant iron-based alloy powder and its preparation method

[0031] The corrosion-resistant iron-based alloy powder includes the following components and their weight percentages:

[0032] Chromium 7.5%, nickel 1.0%, molybdenum 7.0%, titanium 2.0%, carbon 1.8%, rare earth elements 0.5%, impurities 0.13%, and the balance is iron.

[0033] The rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 7:9:13. The impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 2:1:5.

[0034] The preparation method of the corrosion-resistant iron-based alloy powder is as follows: Put the formulated amounts of chromium, nickel, molybdenum, titanium, carbon, rare earth elements, impurities, and iron into a vacuum induction furnace and heat until all are melted into a liquid state. Then, under the conditions of nitrogen as the atomizing medium and water as the cooling medium outside the furnace body, atomize through an atomizing nozzle and dry to obtain the corrosion-resistant iron-based alloy powder.

[0035] Example 3. A corrosion-resistant iron-based alloy powder and its preparation method

[0036] The corrosion-resistant iron-based alloy powder includes the following components and their weight percentages:

[0037] The corrosion-resistant iron-based alloy powder includes the following components and their weight percentages: chromium 6.6%, nickel 1.5%, molybdenum 6.3%, titanium 3.2%, carbon 1.6%, rare earth elements 0.9%, impurities 0.09%, and the balance is iron.

[0038] The rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 5:7:12. The impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 4:2:7.

[0039] The preparation method of the corrosion-resistant iron-based alloy powder is as follows: Put the formulated amounts of chromium, nickel, molybdenum, titanium, carbon, rare earth elements, impurities, and iron into a vacuum induction furnace and heat until all are melted into a liquid state. Then, under the conditions of nitrogen as the atomizing medium and water as the cooling medium outside the furnace body, atomize through an atomizing nozzle and dry to obtain the corrosion-resistant iron-based alloy powder.

[0040] Example 4. A corrosion-resistant iron-based alloy powder and its preparation method

[0041] The corrosion-resistant iron-based alloy powder includes the following components and their weight percentages:

[0042] Chromium 6.1%, nickel 1.6%, molybdenum 5.2%, titanium 3.1%, carbon 1.5%, rare earth elements 0.9%, impurities 0.09%, and the balance is iron.

[0043] The rare earth elements in the corrosion-resistant iron-based alloy powder are composed of cerium, samarium, and erbium in a mass ratio of 4:6:11. The impurities in the corrosion-resistant iron-based alloy powder are composed of antimony, arsenic, and tin in a mass ratio of 3:2:8.

[0044] The preparation method of the corrosion-resistant iron-based alloy powder is the same as that in Example 3.

[0045] Comparative Example 1

[0046] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that the addition amount of chromium in the iron-based alloy powder formulation of this comparative example is 12%.

[0047] Comparative Example 2

[0048] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in the iron-based alloy powder formulation of this comparative example, an equal amount of scandium is used to replace titanium.

[0049] Comparative Example 3

[0050] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in the iron-based alloy powder formulation of this comparative example, an equal amount of iron is used to replace titanium.

[0051] Comparative Example 4

[0052] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 4. The difference between this comparative example and Example 4 is that the amount of carbon used in the iron-based alloy powder formulation of this comparative example is 0.5%.

[0053] Comparative Example 5

[0054] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 4. The difference between this comparative example and Example 4 is that the amount of carbon used in the iron-based alloy powder formulation of this comparative example is 2.5%.

[0055] Comparative Example 6

[0056] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in this comparative example, an equal amount of neodymium is used to replace cerium in the rare earth elements.

[0057] Comparative Example 7

[0058] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in this comparative example, an equal amount of praseodymium is used to replace samarium in the rare earth elements.

[0059] Comparative Example 8

[0060] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in this comparative example, the rare earth elements are composed of cerium, samarium, and erbium in a mass ratio of 14:9:2.

[0061] Comparative Example 9

[0062] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that the impurities in the iron-based alloy powder formulation in this comparative example are composed of antimony, arsenic, and tin in a mass ratio of 7:9:1.

[0063] Comparative Example 10

[0064] In this comparative example, the formulation and preparation method of the iron-based alloy powder are similar to those of Example 3. The difference between this comparative example and Example 3 is that in this comparative example, an equal amount of arsenic is used to replace antimony in the impurities.

[0065] Test Example 1. Mechanical Property Test

[0066] Test samples: The iron-based alloy powders prepared in Examples 1 - 5, Comparative Example 4, and Comparative Example 5 were subjected to static pressure molding and then sintered in an ultra-high temperature graphitization furnace, followed by cooling to obtain sintered blocks.

[0067] The pressure for the static pressure molding was 500 MPa, and the pressure holding time was 100 s. The specific sintering process was as follows: After placing the green compact in the ultra-high temperature graphitization furnace, it was heated to 200°C, held for sintering for 1 h, then continuously heated to 600°C, held for sintering for 2 h, then continuously heated to 1500°C, held for sintering for 4 h, then continuously heated to 2500°C, held for sintering for 5 h, and then continuously heated to 2900°C, held for sintering for 5 h.

[0068] Test method: Refer to "GB / T 222 - 2002 Metallic Materials - Tensile Testing at Room Temperature" to test the yield strength and tensile strength of the test samples.

[0069] Test results: See Table 1.

[0070] Table 1. Test Results of Mechanical Properties

[0071]

[0072] As can be seen from Table 1, the sintered blocks of the corrosion-resistant iron-based alloy provided by the present invention have excellent mechanical properties, with a tensile strength reaching 421.7 - 480.1 MPa and a yield strength reaching 320.4 - 364.6 MPa. Comparative Example 4 and Comparative Example 5 are similar to Example 4. In Comparative Example 4, the addition amount of carbon in the formulation was reduced, but the mechanical properties of the sintered blocks of the corrosion-resistant iron-based alloy obtained were greatly reduced. This shows that in the formulation of the present invention, carbon can act as a reducing agent to reduce the oxidized metal and ensure the mechanical properties of the material.

[0073] Test Example 2. Corrosion Resistance Test

[0074] Test samples: The iron-based alloy powders prepared in Examples 1 - 5, Comparative Examples 1 - 12

[0075] Test method: Refer to JB / T 7901-2001 "Full immersion test method for laboratory uniform corrosion of metallic materials" to conduct corrosion resistance tests on test samples and calculate the corrosion rate. The test solutions used are NaCl solution with a mass percentage of 0.15%, HCl solution with a pH value of 4.5, and NaOH solution with a pH value of 8.5. The test time is 72 h, and the test temperatures are 25 °C and 50 °C respectively.

[0076] Test results: The test results are shown in Table 2.

[0077] Table 2 Test results of corrosion resistance performance

[0078]

[0079]

[0080] As can be seen from Table 2, the corrosion rate of the iron-based alloy powder provided by the present invention in the NaCl solution with a mass percentage of 0.15% at 25 °C is 0.12 - 0.20 mm / a, the corrosion rate in the HCl solution with a pH value of 4.5 is 0.32 - 0.41 mm / a, and the corrosion rate in the NaOH solution with a pH value of 8.5 is 0.20 - 0.26 mm / a; at 50 °C, the corrosion rate in the NaCl solution with a mass percentage of 0.15% is 0.22 - 0.31 mm / a, the corrosion rate in the HCl solution with a pH value of 4.5 is 0.50 - 0.58 mm / a, and the corrosion rate in the NaOH solution with a pH value of 8.5 is 0.35 - 0.43 mm / a. Therefore, the iron-based alloy powder provided by the present invention has good corrosion resistance.

[0081] Compared with Example 3, the addition amount of chromium element in Comparative Example 1 increases, but the corrosion rates of the prepared iron-based alloy powder in acids, alkalis and salts all increase. This shows that when the addition amount of chromium element is too large, the internal stress in the formed oxide film increases, resulting in cracking of the oxide film and a decrease in corrosion resistance. In Comparative Examples 2 and 3, other alloy elements are used to replace titanium element, but the high-temperature corrosion rate of the prepared iron-based alloy powder increases significantly. This shows that in the formula of the present invention, the addition of titanium element can improve the high-temperature corrosion resistance of the iron-based alloy powder. In Comparative Examples 6-8, the components and dosage ratios of rare earth elements are changed, but the corrosion rates of the prepared iron-based alloy powder in acids, alkalis and salts all increase to varying degrees. This shows that the rare earth elements used in the present invention can refine the grains and give full play to the role of grain boundary corrosion resistance. Changing the components of rare earth elements or the dosage ratios of rare earth elements cannot achieve the technical effects of the present invention. In Comparative Examples 9 and 10, the components and dosage of impurities in the iron-based alloy powder are changed, but the corrosion rate of the prepared iron-based alloy powder in acid increases significantly. This shows that the components of impurities in the formula of the present invention interact with each other, playing a role of 1 + 1 > 2, and can significantly improve the corrosion resistance of the iron-based alloy powder under acidic conditions.

[0082] Compared with Example 4, in Comparative Example 4, the addition amount of carbon is reduced, and the corrosion rates of the prepared iron-based alloy powder in acids, alkalis and salts decrease to varying degrees. In Comparative Example 5, the addition amount of carbon is increased, and the corrosion rates of the prepared iron-based alloy powder in acids, alkalis and salts decrease significantly. This shows that the addition amount of carbon element in the formula of the present invention has been optimized.

[0083] The above embodiments only illustratively explain the preparation method of the present invention, rather than limiting the present invention. Any person familiar with this technology in the art shall not modify the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the technical idea provided by the present invention are still covered by the claims of the present invention.

Claims

1. A corrosion-resistant iron-based alloy powder, characterized in that: It includes the following components and their weight percentages: chromium 5.3-7.5%, nickel 1.0-2.0%, molybdenum 4.5-7.0%, titanium 2.0-4.5%, carbon 1.4-1.8%, rare earth elements 0.5-1.5%, impurities 0.05-0.13%, and the balance iron; The rare earth elements are composed of cerium, samarium and erbium in a mass ratio of 3-7:5-9:11-13; The impurities are composed of antimony, arsenic and tin in a mass ratio of 2-5:1-3:5-9.

2. The corrosion-resistant iron-based alloy powder according to claim 1, characterized in that: It includes the following components and their weight percentages: 6.6% chromium, 1.5% nickel, 6.3% molybdenum, 3.2% titanium, 1.6% carbon, 0.9% rare earth elements, 0.09% impurities, and the balance iron.

3. The corrosion-resistant iron-based alloy powder according to claim 1, characterized in that: The rare earth elements are composed of cerium, samarium and erbium in a mass ratio of 5:7:

12.

4. The corrosion-resistant iron-based alloy powder according to claim 1, characterized in that: The rare earth elements are composed of cerium, samarium and erbium in a mass ratio of 3:5:

11.

5. The corrosion-resistant iron-based alloy powder according to claim 1, characterized in that: The impurities are composed of antimony, arsenic and tin in a mass ratio of 4:2:

7.

6. The method for preparing the corrosion-resistant iron-based alloy powder according to any one of claims 1 to 5, characterized in that: Specifically, a formulated amount of chromium, nickel, molybdenum, titanium, carbon, rare earth elements, impurities and iron are placed in a vacuum induction furnace and heated until they are all melted into liquid. Then, they are atomized and dried through an atomizing nozzle under the conditions of nitrogen as an atomizing medium and water as a cooling medium for the outer periphery of the furnace body to obtain corrosion-resistant iron-based alloy powder.

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