High strength invar alloy

 

(57) Abstract:

High strength Invar alloy contains the following components, wt.%: Nickel 25,0 - 48,0; cobalt 2,0 - 20,0; carbon of 0.01 - 0.4; titanium of 0.05 to 4.0; molybdenum of 0.02 to 5.0; vanadium from 0.01 to 3.0; iron rest, when the following dependencies: % Nickel / % cobalt = 2,4 - 24; % titanium + % molybdenum / % carbon = 7 - 52; % Nickel + % cobalt / % titanium + % molybdenum + % vanadium = 9 - 20. The technical result of the invention to provide a low temperature coefficient of linear expansion of less than 3 10-6TO-1in the temperature range from 77 to 600 K and increase strength properties. table 1.

The invention relates to metallurgy, specifically to the development of high-strength Invar alloys with a minimum value of temperature coefficient of linear expansion (TCLE) below 2,510-6K-1. Such alloys can be used in instrumentation, aviation and cryogenics, and for creating high-strength structures that do not change its size when you change the temperature from 77 to 600 K (-196 - +327oC).

Known Invar alloy H36 based on iron containing, by weight.%:

Nickel - 36

Iron - Rest

(Precision splost (strength inbelow 560 MPa).

Known Invar alloy based on iron and Nickel containing, wt.%:

Nickel - 28-31

Carbon - 0,4 -1,5

Iron - Rest

(A. S. N 4082856, MKI C 22 C 38/08, 1983).

For this alloy after quenching from high temperatures (above 1260oC) can be achieved by low-level alloy H36) values TCLE (0,5-1,5)10-6deg-1in the temperature range 100-335 K (-173 to +52oC). However, the above alloys have low strength properties (in600 MPa;of 0.2= 250 MPa). Perform thermal and deformation processing of such alloys by conventional metallurgical equipment very difficult. This is because the hardening and forging may be carried out at high temperatures (above 1260oC). To deform in a cold state, these materials are difficult because they have low ductility.

Known Invar alloy containing, by weight.%:

Nickel - 30-50

Cobalt - 20

Chrome 20

Niobium - 2,5-6

Carbon Up to 0.1

Manganese Up to 1

Silicon - 0.5

Molybdenum - 3.0

Titanium - 1-3

Aluminum is 0.1-20

Vanadium - 0.1

Zirconium - 0.1

Hafnium - Up 2

Bor - 0,03

iron - Rest

(paten the jig at 600 - 800oC (873 - 1073 K) can be achieved TCLE (3-6) 10-6K-1in the temperature interval 315-510oC (588-783 TO). However, the level values of the linear thermal expansion coefficient is quite high. These alloys do not fall into the class of materials with minimal thermal expansion (<3 10-6K-1).

Known Invar alloy containing, by weight.%:

Nickel - 41-41,5

Beryllium - 0,85 - 0,95

Iron - Rest

When this % Nickel/ % beryllium = 43-47.

(RF patent N 2000350, MKI C 22 C 38/08, 1993).

For this alloy can be achieved by high strength properties (of 0.2= 1200 MPa;in= 1300 MPa) while maintaining low values of coefficient of thermal expansion (TCLE = 2,4 10-6K-1) in the temperature range (-60 - +60oC). The main disadvantage of this alloy is the presence of highly toxic and environmentally hazardous beryllium. This alloy belongs to group 3 of toxicity. Smelting this alloy is difficult, as it requires special equipment and special methods of smelting and melting decontamination equipment.

The closest in technical essence and the achieved result is Invar alloy containing, by weight.%:

Carbon - 0,001-0,1

Nickel - 34-50

This alloy, according to the description of the patent, has high strength in= 1220 MPa while maintaining a low coefficient of thermal expansion (0,3 - 3,0) 10-6K-1in the temperature range 20 - 600oC (293 - 873 K). The disadvantage of this alloy is that it can be used at temperatures above room temperature (above 20oC).

The problem to which the invention is directed, is to obtain high-strength Invar alloy with low thermal expansion in the temperature range - 196 - +323oC (77-600 TO). With the popularity of Invar alloys, protected by patent N 2023739, the present invention solves the problem of extending the range of operating temperatures, as well as expanding Arsenal of technical tools for a specific purpose, i.e. the creation of Invar alloy new, previously unknown chemical composition with the given properties.

The invention consists in that the high strength Invar alloy contains the following components, wt%:

Nickel - 25,0 - 48,0

Cobalt - 2,0 - 20,0

Carbon - 0,01 - 0,4

Titanium - 0,05 - 4,0

Molybdenum - 0,02 - 5,0

Vanadium is 0.01 to 3.0

Iron - Rest

when running the following zavisimost the a / % carbon = 7-52.

Compared with the prototype of the proposed alloy is characterized by the additional introduction of cobalt and vanadium, the new number of components in the composition, as well as three dependencies between the amount of Nickel and cobalt; of Nickel, cobalt, titanium, molybdenum and vanadium, titanium, molybdenum and carbon.

The introduction of carbon in the Invar alloy increases the density of States at the Fermi level while increasing the stability of the FCC structure to a martensitic transformation. In addition, the carbon in solid solution is a source of local distortions. The emergence of local distortion contributes to the processes of redistribution of the atoms with the formation of submicrometers - areas, rich and poor Nickel. The proportion of areas that are rich in Nickel, increases with increasing concentration of Nickel and carbon in the alloy. As a result, creates a nuclear-magnetic structure, providing the formation of Invar and strength properties. The presence of carbon in the alloy containing carbidopa elements should contribute to the formation of spheroidal carbides with low thermal expansion. The formation of such carbides causes hardening alloys while maintaining low values of thermal expansion.

Minimalise on the nature of the atomic distribution, the formation of carbides and concentration inhomogeneities in submicrometer that should not lead to hardening of the alloy. When the carbon content in the alloy more of 0.4% is the embrittlement of the alloy and decrease in strength, because not all of the carbon will be in solid solution and a large part of it is allocated in the form of graphite.

The minimum Nickel content in the alloy is 25%. At a lower content of Nickel education concentration discontinuities and regions of the middle order is difficult, and therefore, decreases the incentive to improve strength properties, except that when the Nickel content is less than 25% reduced the resistance of the alloy to the martensitic transformation. Education phase due to leakage of martensitic transformation deteriorates the mechanical properties and leads to a significant increase in thermal expansion. When the Nickel content in the alloy more than 48% is formed such electronic and atomic structure, which no longer provides a low coefficient of thermal expansion. This is because at higher Nickel content (more than 48%) are formed of concentration inhomogeneity of large size (more than 50 - 100 ).

Titanium is introduced into cu grains during heating alloys for quenching and thereby prevents embrittlement. Titanium inhibits the grain growth when its content is not less than 0.05%. When the content of titanium in the alloy is less than 0.05% of its influence on the grain growth, and hence on the mechanical properties is insignificant. Introduction titanium carbon-containing alloys also contributes to the formation of high-strength titanium carbide. The formation of carbides of titanium promotes hardening alloys. When the titanium content is more of 4.0% is a significant increase in the coefficient of thermal expansion. Therefore, to increase the titanium content in the alloy more than 4,0% inappropriate.

Cobalt is introduced mainly in order to reduce the magnitude of thermal expansion. To increase the content of cobalt is higher than 20% is impractical, since it increases the temperature at which the martensite transformation and the alloy loses Invar properties. When the content of cobalt is less than 2% of the value of the linear thermal expansion coefficient does not drop, which does not allow to implement one of the goals of the invention: the minimum value of the linear thermal expansion coefficient.

Vanadium is introduced into the alloys with the aim of improving mechanical properties, mainly to increase the yield strength and durability. Introduction in the alloys of vanadium promotes the formation of spheroidal carbides VA is there hardening of the alloys while maintaining a sufficiently high level of plasticity. In addition, the introduction of vanadium, and titanium inhibits the grain growth during heating alloys for quenching and thereby prevents embrittlement of the alloys. Vanadium inhibits the grain growth when its content exceeding 0.01%. When the content of vanadium in the alloy is less than 0.01% of its influence on the grain growth, and hence on the mechanical properties is insignificant. When the vanadium content greater than 3% is a significant increase in linear thermal expansion coefficient, and the alloy loses Invar properties. In this regard, to increase the content of vanadium in the alloy is greater than 3% is impractical.

Molybdenum is introduced to reduce the preferential allocation of particles of hardening phases at the grain boundaries, leading to increased toughness, as well as for the formation of complex carbides (Mo, V) S. the Maximum amount of molybdenum required for this purpose, no more than 5%. When the content of molybdenum in the alloy is less than 0.02% of its influence on the properties of practically absent.

The ratio of Nickel to cobalt should be a 2.4 - 24. It is determined by the concentration of electrons per atom required to form Invar properties.

The ratio of the total content of Nickel and cobalt to the total content of titanium, molybdenum and van is about to be 7 - 52; it is determined by the amount of vanadium, molybdenum, titanium and carbon, which is necessary for the formation of hardening carbide phases. When the mixing ratio is less than specified, the impetus for the formation of hardening phases to be insignificant, which will not allow to achieve significant hardening. With a larger ratio of the components will increase thermal expansion, which will not allow to obtain alloys with a minimum value of thermal expansion (less than 3 10-6TO-1).

Only the combination of all of these features provides a solution to the problem. As a result, the alloy has a low value of linear thermal expansion coefficient of less than 3 10-6TO-1in the temperature range from 77 to 600 K (- 196 - +327oC) and a high level of durability properties.

The above distinctive features of the prototype features determine the compliance of the claimed invention, the criterion of "novelty."

For each distinctive feature conducted a search of the known solutions with similar features that perform the same function on the scientific and technical literature and patent documents. The absence of such solutions demonstrates compliance with the proposed invention, the criterion of "inventive step".

oC. Then was quenched in water from 1000oC. Hardening treatment was performed at temperatures of 500 - 800oC. the values of the linear thermal expansion coefficient was determined using a quartz dilatometer sensitivity 1 m/mm, the alloy Compositions and the results of measurements are shown in Table 1.

Offer Invar alloys can be used in cryogenic engineering, precision instruments, laser technology, Metrology. The use of the proposed Invar alloys in the above areas allow to increase twice the accuracy and stability of the devices under cyclic temperature changes. The presence of such alloys allows you to create new designs that require high-strength materials with a minimum value of temperature coefficient of linear expansion in a wide range of temperatures.

High strength Invar alloy containing Nickel, carbon, titanium, molybdenum, and iron, characterized in that it further contains cobalt and vanadium in the following ratio, wt.%:

Nickel - 25,0 - 48,0

Cobalt - 2,0 - 20,0

Carbon - 0,01 - 0,4

Titanium - 0,05 - 4,0

Molybdenum - 0,02 - 5,0

Vanadium is 0.01 to 3.0

Iron - Rest

if you follow the Ethan + % molybdenum + % vanadium = 9 - 20.

 

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