A nickel-chromium alloy

Abstract

A nickel-chromium alloy, the alloy composition and its mass percentage are as follows: C ≤ 0.15%, Si 0.6 - 1.8%, Mn ≤ 0.6%, P ≤ 0.01%, S ≤ 0.01%, Cr 19 - 21%, Al ≤ 0.3%, Fe ≤ 1.2%, Ti 0.35 - 0.45%, Re 0.05 - 0.10%, B 0.005 - 0.010%, and the balance is Ni and unavoidable impurities. The mechanical and physical properties of the alloy of the present invention are superior to those of the existing Cr20Ni80 alloy. In terms of composition design, it does not add easily oxidized and volatile elements such as Zr, La, Ce, etc. that are difficult to accurately control during the existing process of "vacuum induction melting + electroslag remelting". The process has good reproducibility, strong operability, and is easy to promote.

Description

Technical Field

[0001] The present invention belongs to the field of metallic materials, and particularly relates to a nickel-chromium electrothermal alloy. Background Art

[0002] Electrothermal alloys are functional materials that can effectively convert electrical energy into heat energy and can be used as heating elements. According to chemical composition, they are divided into two major categories: Ni-Cr-(Fe) series alloys and Fe-Cr-Al series alloys.

[0003] Ni-Cr-(Fe) series alloys are alloy series with nickel as the matrix and different amounts of chromium (and iron) added. Compared with Fe-Cr-Al series alloys, Ni-Cr-(Fe) series alloys can form a stable and continuous γ solid solution, a single austenite structure, and a very narrow solidification temperature range, ensuring that the materials have highly uniform and stable mechanical and physical properties, which is the most ideal organizational structure for electrothermal alloys.

[0004] At present, there are mainly two grades of nickel-chromium alloys: Cr20Ni80 and Cr30Ni70. Among them, Cr20Ni80 is the most widely used. Its resistivity is 1.05 - 1.10 uΩ·m, melting point ≥ 1400 °C, service temperature up to 900 °C, and it has an extremely low coefficient of thermal expansion, good high-temperature oxidation resistance, and excellent hot and cold working properties. It has become an important electrothermal alloy material in major industrial countries.

[0005] However, there are significant differences in the performance and quality of Cr20Ni80 alloys in different countries. The service life of alloy wires in industrial developed countries such as Japan and the United States has reached 8000 h, and that in Russia also exceeds 6000 h. However, the service life of Cr20Ni80 alloy wires in some countries is only about 2000 h. The main reason is the differences in alloy composition design and processing technology.

[0006] To optimize the composition system and processing technology of Cr20Ni80 alloys, scientific research workers have done a lot of research work.

[0007] Publication No. CN112375930A discloses a high-resistance nickel-chromium electrothermal alloy and its production process. Its most important feature is the design of adding four trace elements, Ca, Y, La, and Ce, to improve the nucleation rate during solidification, refine grains, and improve alloy properties. However, its composition system is relatively complex, and the disclosed melting process is difficult to ensure the precise control of volatile and oxidizable elements such as Ca and Y, which is not advisable.

[0008] Publication No. CN110819850A discloses a nickel-chromium electrothermal alloy and its preparation method. The most important feature of this alloy is the design of adding elements such as zirconium, vanadium, molybdenum, and rare earths, and using powder metallurgy technology to obtain a resistivity greater than 1.3 Ωmm 2 / m, and an alloy with an operating temperature of 1350°C is a relatively novel technical solution, but its process is relatively complicated and its composition design is defective (such as containing harmful elements such as S and N), which is not desirable.

[0009] In addition, publication numbers CN101899593A, CN108901088A, etc. also disclose nickel-chromium alloys of different compositions, but either the composition system is complex or the material properties are poor, which are not desirable.

[0010] Therefore, designing Cr20Ni80 alloy with a more complete composition system and better material physical properties is one of the problems that need to be urgently solved in the development of electrothermal materials. Summary of the invention

[0011] The purpose of the present invention is to solve the problems of poor mechanical and electrical and thermal properties of the existing Cr20Ni80 alloy through reasonable composition design.

[0012] In order to solve the above technical problems, the technical solution of the present invention is: a nickel-chromium alloy, wherein the alloy components and their mass percentages are: C≤0.15%, Si 0.6-1.8%, Mn≤0.6%, P≤0.01%, S≤0.01%, Cr 19-21%, Al≤0.3%, Fe≤1.2%, Ti 0.35-0.45%, Re 0.05-0.10%, B 0.005-0.010%, and the balance is Ni and unavoidable impurities.

[0013] Preferably, the nickel-chromium alloy composition and its mass percentage are: C 0.05-0.10%, Si 0.8-1.2%, Mn0.2-0.4%, P≤0.008%, S≤0.006%, Cr 19.5-20.5%, Al 0.15-0.20%, Fe 0.5-1.0%, Ti 0.38-0.42%, Re 0.06-0.08%, B 0.007-0.009%, and the balance is Ni and unavoidable impurities.

[0014] Furthermore, the nickel-chromium alloy has a tensile strength of 140-158 MPa at 900°C and an impact toughness of 147-180 J / cm at 950°C. 2 , creep strength at 900℃, 1000h elongation 1% is 13~16MPa, elongation at 20℃ is ≥30%, linear expansion coefficient is a×10 -6 / ℃ (20~1000℃) is 16.48~16.71, and the resistivity at 20℃ is 1.18~1.20uΩ / m.

[0015] The components of the present invention play the following roles in the alloy:

[0016] (1) 0.05-0.1% Re is added to the alloy. Since Re is a 5d-block element and Ni is a 3d-block element, the Re atomic radius is 10% larger than that of Ni and has a large mismatch with Ni. After being added, it can effectively hinder dislocation movement, thereby increasing the strength of Ni, especially the creep strength. At the same time, since 20% of Re atoms are located at the grain boundary and form short-range ordered atomic clusters of about 1 nm, their larger ordered regions can inhibit the Cr 23 The precipitation of TCP phases such as C6 and Cr7C3 at grain boundaries improves the hot and cold processing properties of the alloy.

[0017] (2) 0.005-0.010% B is added to the alloy. The B in the alloy exists in the form of M3B2 and is enriched at the grain boundaries, increasing the grain boundary bonding strength. M3B2 is distributed in the form of particles or blocks, preventing grain boundary sliding and the formation of voids, and can significantly improve the mechanical properties of the alloy. In addition, an appropriate amount of B can also purify the grain boundaries and reduce the precipitation of harmful elements at the grain boundaries.

[0018] (3) 0.35-0.45% Ti is added to the alloy. Ti can form high-melting-point TiC with C, which is the first to precipitate during solidification and acts as an inhomogeneous nucleation particle to increase the nucleation rate and refine the grains. In addition, Ti, Al and Ni can form an ordered phase Ni3(Al, Ti), which is coherent with the matrix FCC phase. However, Ni3(Al, Ti) has reverse domain interface defects. Dislocations need to overcome APB energy when entering Ni3(Al, Ti) from the FCC phase. This requires paired dislocations to cross Ni3(Al, Ti), which completely restricts the movement of edge dislocations. At the same time, screw dislocations are locked by cross slip on the {111} plane, hindering dislocation movement. This hindrance is more obvious at high temperatures, which will improve the high-temperature strength of the material and reduce the linear expansion coefficient.

[0019] (4) Adding an appropriate amount of Al to the alloy can not only form Ni3 (Al, Ti), but also improve the oxidation resistance of the alloy. After adding Al, the main phase of the oxide film is Cr2O3 phase, and the secondary phase is α-Al2O3 phase. The α-Al2O3 phase can increase the adhesion between the Cr2O3 phase and the base metal. The free Al can also consume oxygen at high temperature, inhibit the oxygen penetration rate, and improve the oxidation resistance of the alloy.

[0020] The beneficial effects of adopting the above technical solution are:

[0021] The mechanical and physical properties of the alloy of the present invention are superior to those of the existing Cr20Ni80 alloy. In terms of composition design, no easily oxidized and volatile elements such as Zr, La, and Ce, which are difficult to accurately control in the existing process of "vacuum induction melting + electroslag remelting", are added. The process has good reproducibility, strong operability, and is easy to promote. DETAILED DESCRIPTION

[0022] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] Examples 1 - 14

[0024] The preparation process of nickel-chromium electrothermal alloy includes vacuum melting, electroslag remelting, homogenization treatment, forging, hot rolling, and solution treatment.

[0025] (1) Vacuum smelting: Charge materials according to the composition and load into the furnace. Among them, electrolytic nickel, metallic chromium, and pure iron are loaded into the crucible, and metallic silicon, electrolytic manganese, aluminum pellets, sponge titanium, metallic rhenium, and ferrosilicon boron are loaded into the secondary bin; evacuate to ≤5 Pa and apply electricity to melt. After melting, adjust the vacuum degree to ≤0.1 Pa and the temperature to 1580 - 1620 °C, and refine for 40 - 60 min; then stop the vacuum and fill with 30000 Pa argon gas, add alloys such as Si, Mn, Al, Ti, Re, and B-Fe. After the composition is qualified, adjust the molten steel temperature to 1430 - 1460 °C and cast into ingots.

[0026] (2) Electroslag remelting: Stress relieve anneal and polish the vacuum ingots, and then perform electroslag remelting, controlling the melting rate at 3.5 - 5 kg / min. Argon gas is introduced as a protective gas during smelting.

[0027] (3) Homogenization treatment: Put the electroslag ingots into a heating furnace with an argon protective atmosphere. First, heat up to 650 - 700 °C in 2 - 3 h, hold for 1 - 2 h, then heat up to 1100 - 1150 °C in 2 - 3 h, and the holding time is ≥10 h.

[0028] (4) Forging: After homogenization treatment, the ingots are taken out of the furnace for forging. The initial forging temperature is 1050 - 1100 °C, the final forging temperature is 900 - 1000 °C, and the forging ratio is ≥20.

[0029] (5) Hot rolling: Hot roll the forgings. The starting rolling temperature is 1150 - 1200 °C, the wire spitting temperature is 950 - 1050 °C, and the rolled wire rod is placed on the cooling bed for air cooling.

[0030] (6) Solution treatment: Perform solution treatment on the wire rod at a temperature of 1000 - 1100 °C for 2 - 4 h.

[0031] Examples 1 - 14 are produced according to the above production process. The specific alloy compositions and alloy properties of each example are shown in Tables 1 and 2 respectively. At the same time, Table 2 also lists the properties of the common Cr20Ni80 steel sold on the market.

[0032] Table 1

[0033]

[0034]

[0035] Table 2

[0036]

[0037]

[0038] The above embodiments are only used to illustrate rather than limit the technical solutions of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that: the present invention can still be modified or equivalently replaced, and any modification or partial replacement without departing from the spirit and scope of the present invention shall be covered by the scope of the claims of the present invention.

Claims

1. A nickel-chromium alloy, characterized in that, The composition of the alloy and its mass percentage are as follows: C ≤0.15%, Si 0.6 - 1.8%, Mn ≤0.6%, P ≤0.01%, S ≤0.01%, Cr 19 - 21%, Al ≤0.3%, Fe ≤1.2%, Ti 0.35 - 0.45%, Re 0.05 - 0.10%, B 0.005 - 0.010%, and the balance is Ni and unavoidable impurities; The nickel-chromium alloy has a tensile strength of 140 - 158 MPa at 900 °C, an impact toughness of 147 - 180 J / cm at 950 °C 2 , a creep strength of 13 - 16 MPa with a 1% elongation at 900 °C for 1000 h, an elongation rate of ≥ 30% at 20 °C, and a linear expansion coefficient of 16.48 - 16.71×10 -6 / °C from 20 °C to 1000 °C, and a resistivity of 1.18 - 1.20 μΩ / m at 20 °C.

2. A nickel-chromium alloy according to claim 1, characterized in that, The composition of the alloy and its mass percentage are as follows: C 0.05 - 0.10%, Si 0.8 - 1.2%, Mn 0.2 - 0.4%, P ≤0.008%, S ≤0.006%, Cr 19.5 - 20.5%, Al 0.15 - 0.20%, Fe 0.5 - 1.0%, Ti 0.38 - 0.42%, Re 0.06 - 0.08%, B 0.007 - 0.009%, and the balance is Ni and unavoidable impurities.

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