RU2568541C2 - High-strength invar alloy - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to metallurgy, namely to high-strength invar alloys. The high-strength invar alloy is offered which contains wt %: nickel - from 25.0 up to less than 38.0, cobalt 0.5÷20.0, carbon 0.05÷1.2, titanium 0.05÷4.0, molybdenum 0.02÷6.0, vanadium 0.01÷4.0, niobium 0.02÷5.0, tungsten 0.02÷5.0, zirconium 0.01÷2.0, iron - the rest.

EFFECT: alloy is characterised by high strength, wide range of temperature coefficient of linear expansion, and also high Q factor of mechanical oscillations in the range of temperature coefficient of linear expansion (from 0,5 up to 7)·10^-6 K^-1.

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Description

The invention relates to metallurgy, specifically to high-strength invar alloys with a temporary tensile strength (σ _in ) up to 1900 MPa, with a low (from 3.5 to 7) · 10 ^-6 K ^-1 , and also minimal (from 0.5 to 3 , 5) · 10 ^-6 K ^{-1 the} value of the temperature coefficient of linear expansion (TEC) and with a high level of quality factor (Q≥10000) during mechanical vibrations.

Such alloys can be used in instrument engineering, aviation, rocket and space industry, in laser and cryogenic engineering, in metal optics, metrology, geodesy, as well as for creating high-strength structures that do not change their size when the temperature changes from 77 K to 600 K (from minus 196 to plus 327) ° C.

The quality factor (Q) during mechanical vibrations is characterized by energy dissipation during free mechanical vibrations of the system. The quality factor is inversely proportional to the attenuation rate of natural oscillations in the system. That is, the higher the quality factor of the oscillatory system, the lower the energy loss for each period and the slower the damping of the oscillations.

Known high-strength invar alloy (patent RU 2023739, IPC ⁵ C22C 38/12, published November 30, 1994) with low TLCR, containing, wt.%:

carbon - 0.001 ÷ 0.1;

nickel - 34 ÷ 50;

titanium - 0.5 ÷ 3.0;

molybdenum - 0.001 ÷ 2.2;

niobium - 0.001 ÷ 3;

aluminum - 0.3 ÷ 3;

iron is the rest.

The invar alloy has a TECL = (0.3 ÷ 3.0) · 10 ^-6 K ^-1 in the interval (20 ÷ 600) ° C with σ _in = 1220 MPa.

A disadvantage of the known alloy is that it cannot be used at low temperatures.

Another high-strength invar alloy is known (patent RU 2154692, IPC ⁷ C22C 30/00, C22C 38/14, C22C 19/03, published on 08/20/2000), containing, 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 - 0.01 ÷ 3.0;

iron - the rest,

when executing the following dependencies:

% nickel:% cobalt = 2.4 ÷ 24;

% titanium +% molybdenum:% carbon = 7-52;

% nickel +% cobalt:% titanium +% molybdenum +% vanadium = 9 ÷ 20.

The alloy has a low TEC value (less than 3 · 10 ^-6 K ^-1 ) in the temperature range from 77 K to 600 K (from minus 196 to plus 327) ° С and an increased level of σ _в - up to 1100 MPa.

The disadvantages of this alloy are a relatively low level of σ _in and a low value of quality factor during mechanical vibrations (Q≤3000).

The closest analogue of the claimed invention is a high-strength invar alloy (application KR 20020008240, IPC С22С 38/08, published on January 30, 2002 - prototype) with low TLCR containing one or more elements from the group consisting of carbon, molybdenum, titanium, tungsten, niobium , vanadium, which are added to an alloy consisting of iron, nickel and cobalt.

The alloy contains, wt.%:

nickel - 28.5 ÷ 30;

cobalt - 9 ÷ 14;

carbon - 0.1 ÷ 0.9;

molybdenum - 2.0 or less;

titanium 2.0 or less;

niobium - 2.0 or less;

vanadium - 2.0 or less and / or tungsten - 2.0 or less;

iron is the rest.

TECL ≤5.0 · 10 ^- K ^-1 , σ _in up to 1700 MPa.

From the materials presented in the description of the invention, it follows that molybdenum, titanium, tungsten, niobium, vanadium are introduced into the alloy simultaneously with carbon, but there is not a single example in which the joint introduction of these elements would be shown.

The disadvantages of the known alloy are:

- a relatively low level of mechanical strength (σ _in ≤1700 MPa);

- the minimum values of TECL are not realized - below 2.59 · 10 ^-6 K ^-1 .

The problem to which the invention is directed, is to obtain a high-strength invar alloy with a wide range of thermal expansion coefficient, including thermal expansion coefficient both with low values (from 3.5 to 7) · 10 ^-6 K ^-1 and with minimal (from 0.5 up to 3.5) · 10 ^-6 K ^-1 values and with a high level of quality factor during mechanical vibrations (Q≥10000).

The technical result of the invention is to increase the strength of the invar alloy (temporary tensile strength) and its quality factor during mechanical vibrations while expanding the range of thermal expansion coefficient, including thermal expansion coefficient both with low values (from 3.5 to 7) · 10 ^-6 K ^-1 and with minimal (from 0.5 to 3.5) · 10 ^-6 K ^-1 values.

The specified technical result is achieved in that a high-strength invar alloy with a high level of quality, containing nickel, cobalt, carbon, titanium, molybdenum, vanadium, niobium, tungsten and iron, according to the invention additionally contains zirconium, in the following ratio, wt. %:

nickel - from 25.0 to less than 38.0;

cobalt - 0.5 ÷ 20.0;

carbon - 0.05 ÷ 1.2;

titanium - 0.05 ÷ 4.0;

molybdenum - 0.02 ÷ 6.0;

vanadium - 0.01 ÷ 4.0;

niobium - 0.02 ÷ 5.0;

tungsten - 0.02 ÷ 5.0;

zirconium 0.01 ÷ 2.0;

iron - the rest,

when executing the following dependencies:

(% molybdenum +% zirconium):% vanadium = 1-80;

(% molybdenum +% vanadium +% zirconium):% carbon = 2-80.

Compared with the prototype, the proposed alloy is different:

- the presence of a new additional element - zirconium;

- the content of nickel, cobalt, carbon, titanium, molybdenum, vanadium, niobium, tungsten;

- two dependencies: between the amounts of molybdenum, zirconium and vanadium, as well as molybdenum, vanadium, zirconium and carbon.

Compared with the prototype, the alloy has:

- higher strength - σ _in up to 1900 MPa (prototype up to 1700 MPa);

- an extended range of TEC values (from 0.5 to 7.0) · 10 ^-6 K ^-1 [prototype (2.59 ÷ 5.0) · 10 ^-6 K ^-1 ];

- high quality factor with mechanical vibrations Q = 10000 ÷ 30000.

The significance of the new features for obtaining the claimed technical result is as follows.

An increase in nickel content up to 38.0% compared with the prototype, where the upper limit of the nickel content is 30.0%, is necessary for the implementation of the declared low TEC value (up to 7.0 · 10 ^-6 K ^-1 ).

When the nickel content in the alloy is more than 38.0%, an electronic and atomic structure is formed that no longer provides a low level of thermal expansion coefficient.

The decrease in nickel content to 25.0% compared with the prototype, where the lower limit of the nickel content is 28.5%, it is necessary to implement the claimed low value of TECL (up to 7.0 · 10 ^-6 K ^-1 ) and achieve high strength properties.

The minimum nickel content in the alloy is 25%. With a lower nickel content, the formation of concentration inhomogeneities and short-range order regions is difficult, and therefore, the incentive to increase strength properties decreases, in addition, when the nickel content is less than 25%, the alloy's resistance to γ → α martensitic transformation decreases. The formation of the α phase due to the occurrence of martensitic transformation affects the mechanical properties and leads to a significant increase in thermal expansion.

Cobalt is introduced mainly with the aim of decreasing the thermal expansion coefficient and expanding the temperature range with low thermal expansion coefficient.

The increase in cobalt content to 20.0% compared with the prototype, where the upper limit of the cobalt content is 14.0%, it is necessary to reduce the value of thermal expansion (TEC).

It is impractical to increase the cobalt content above 20%, since the temperature of the onset of martensitic transformation rises, the α phase forms, and the alloy loses invariable properties.

The reduction of cobalt content to 0.5% compared with the prototype, where the lower limit of the cobalt content is 9.0%, it is necessary to increase the level of mechanical properties due to the formation of nickel-containing intermetallic phases, as well as to reduce the thermal expansion.

When the cobalt content is less than 0.5%, the TEC value is practically not reduced, which does not allow one of the objectives of the invention to be realized - achieving the minimum TEC value.

An increase in carbon content to 1.2% compared with the prototype, where the upper limit of carbon content is 0.9%, is necessary to increase the strength σ _in and Q factor due to the formation of finely dispersed carbides on lattice defects, as well as to reduce thermal expansion and expansion temperature range with low LTEC.

When the carbon content in the alloy is more than 1.2%, a significant embrittlement of the alloy and a decrease in the strength σ _in and the quality factor Q occur, since not all carbon will be in the form of carbides, as well as in solid solution. A significant part of it is released in the form of graphite, which leads to embrittlement of the alloy and a decrease in the quality factor Q.

Titanium is introduced into alloys in order to increase the level of mechanical properties, increase the strength σ _in , Q factor Q and ductility.

The introduction of titanium into carbon-containing alloys contributes to the formation of high-strength titanium carbide. The formation of titanium carbides contributes to the hardening of alloys and an increase in the quality factor of Q.

The increase in titanium content to 4.0% compared with the prototype, where the upper limit of the titanium content is 2.0%, it is necessary to increase the level of mechanical properties due to the formation of titanium carbides.

When the titanium content is more than 4.0%, a significant increase in the coefficient of thermal expansion occurs. Therefore, increasing the titanium content in the alloy more than 4.0% is impractical.

The introduction of titanium prevents grain growth during heating of alloys for quenching and thereby prevents embrittlement. Titanium inhibits grain growth when its content is not less than 0.05%. When the titanium content in the alloy is less than 0.05%, its effect on grain growth and, consequently, on mechanical properties (ductility) is negligible.

Zirconium is introduced mainly to increase the ductility, as well as the strength properties and quality factor of Q. Zirconium, due to its high affinity with oxygen and nitrogen, binds these embedded atoms, which leads to an increase in ductility. Along with this, the formation of zirconium carbides, including on structural defects, leads to hardening and an increase in the quality factor Q. The effect of binding of oxygen and nitrogen by zirconium atoms and, accordingly, an increase in ductility, is manifested when the zirconium content is more than 0.01%. With a lower zirconium content, this effect is not significant. Strengthening and improving the quality factor of Q due to the formation of the carbide phase of zirconium is most effectively realized when the zirconium content is up to 2.0%. At a higher content of zirconium, embrittlement of the alloy occurs due to an increase in the size of zirconium carbides, as well as a significant increase in LTEC.

Niobium is introduced mainly to increase the quality factor during mechanical vibrations Q, as well as to increase the strength of the alloy while maintaining a high level of ductility.

The increase in Q is due to the formation of finely dispersed niobium carbides, mainly at lattice defects — dislocations, twins, and grain boundaries. The defects are fixed, and they cease to be centers of scattering of elastic energy, which leads to an increase in the quality factor under mechanical vibrations. The precipitation of niobium carbides at the grain boundaries prevents grain growth at elevated temperatures (above 1100 ° C), which leads to the preservation of a high level of plasticity as a result of subsequent hardening thermodeformational treatments.

The most effective fixing of defects and, accordingly, an increase in the quality factor Q occurs when the niobium content in the alloy is above 0.02%. With a lower niobium content, the fixation of the dislocation to niobium carbides is insignificant and, accordingly, the effect of an increase in the Q factor is practically not detected.

An increase in the niobium content to 5.0% compared with the prototype, where the upper limit of the niobium content is 2.0%, is necessary to increase the quality factor during mechanical vibrations (Q), as well as the level of mechanical properties (σ _in ; σ _0.2 ).

When the niobium content is more than 5.0%, a significant increase in the thermal expansion coefficient occurs, and the alloy loses invariable properties. In this regard, an increase in the niobium content in the alloy above 5.0% is impractical.

Vanadium is introduced into alloys in order to increase the level of mechanical properties, mainly to increase the strength and quality factor Q. Introduction of vanadium into alloys promotes the formation of high-strength vanadium carbides. Due to the fact that the formation of vanadium carbides occurs homogeneously throughout the grain volume, this contributes to the hardening of the alloys while maintaining a sufficiently high level of ductility. In addition, the introduction of vanadium, as well as titanium, prevents grain growth during heating of alloys for quenching and thereby prevents the embrittlement of alloys. The most effective increase in the level of mechanical properties occurs when the vanadium content in the alloy is more than 0.01%. With a lower content of vanadium, the effect of increasing the mechanical properties is not detected.

An increase in the content of vanadium to 4.0% compared with the prototype, where the upper limit of the content of vanadium is 2.0%, it is necessary to increase the level of mechanical properties due to the formation of vanadium carbides.

With a vanadium content of more than 4.0%, a significant increase in the thermal expansion coefficient occurs, and the alloy loses its invariable properties. In this regard, to increase the vanadium content of more than 4.0% is impractical.

Molybdenum and tungsten, along with zirconium, are introduced to increase the strength of the alloy while maintaining ductility. To effectively increase the level of mechanical properties due to the precipitation of the hardening carbide phases of molybdenum and (or) tungsten (zirconium), vanadium is necessary in the alloy. Vanadium carbides are formed homogeneously in the alloy and are the centers of the subsequent formation of hardening complex carbides of molybdenum and (or) tungsten (W, V) C; (Mo, V) C, (Zr, V) C; (Mo, Zr, V) C. The formation of carbides of molybdenum and / or tungsten in the absence of vanadium (Mo ₂ C); (W, C) leads to a slight increase in strength and at the same time to a significant increase in fragility. This is due to the fact that in the absence of vanadium, the hardening carbide phase of molybdenum, and / or tungsten, and / or zirconium is formed mainly at grain boundaries, which leads to an increase in brittleness.

The increase in the content of molybdenum to 6.0% and tungsten to 5.0% compared with the prototype, where the upper limit of the content of molybdenum and tungsten is 2.0%, it is necessary to increase the level of mechanical properties.

The maximum amount of molybdenum required for this purpose is not more than 6.0%, tungsten not more than 5.0%. When the content of molybdenum and tungsten in the alloy is less than 0.02%, their effect on the properties of the alloy is practically absent.

The ratio of the content of molybdenum and zirconium to vanadium should be 1 ÷ 80. It is determined by the conditions of homogeneous nucleation and growth of the strengthening carbide phase (Mo, Zr, V) С. Only in the case of homogeneous nucleation and growth can a substantial increase in strength and quality factor Q be realized while maintaining high ductility. When the component ratio is less than the specified value, the incentive for the formation of the strengthening phase (Mo, Zr, V) C will be insignificant, which will not allow to achieve significant hardening and increase the quality factor Q. At more than 80, the ratio of components will mainly form the phases Mo ₂ C, Zr ₂ C at the grain boundaries, which leads to a significant embrittlement of the alloys.

The ratio of the sum of the content of molybdenum, vanadium and zirconium to the carbon content should be 2 ÷ 80. This ratio is determined by the amount of molybdenum, vanadium, zirconium and carbon, which is necessary for the formation of hardening carbide phases. If the ratio of the components is less than those indicated, the incentive for the formation of hardening phases will be insignificant, which will not allow to achieve appreciable hardening and increase the quality factor Q. With a larger ratio of components, thermal expansion will increase, which will not allow to obtain alloys with a minimum (≤3.5 · 10 ^-6 K ^-1 ) the value of TECL and low (<7.0 · 10 ^-6 K ^-1 ) the value of TECL.

Examples

The alloys were smelted in an induction furnace. Forging was carried out at temperatures (1000 ÷ 1100) ° C. Then, quenching in water was performed from 1000 ° C and hardening treatment at temperatures (500 ÷ 800) ° C. The TEC values were determined using a quartz dilatometer with a sensitivity of 1 μm / mm. The compositions of the alloys and the measurement results are shown in table 1.

As follows from table 1, alloys 1 ÷ 6, the composition of which corresponds to the declared invar alloy, have high values of tensile strength and Q factor Q. At the same time, the minimum TEC values correspond to alloys 1, 5, 6, while the low TEC values correspond to alloys 2, 3, 4.

All alloys, the composition of which does not correspond to the declared composition (alloys 7 ÷ 12), have lower values of strength and quality factor Q. In addition, none of the alloys (7 ÷ 12) is an alloy with a minimum and low TEC value.

Thus, the technical result is an increase in the strength of the invar alloy and its quality factor during mechanical vibrations with an expanded range of thermal expansion coefficient, including thermal expansion coefficient both with low values (from 3.5 to 7) · 10 ^-6 K ^-1 and with minimal (from 0 , 5 to 3.5) · 10 ^-6 K ^-1 values, achieved by the claimed invention.

The proposed high-strength invar alloys with high quality factor during mechanical vibrations can be used, in particular, in the following areas of industry and technology:

- navigation equipment: mechanical and laser gyroscopes, accelerometers, elastic vibro-suspensions;

- deformation pressure sensors;

- Electromechanical filters, delay lines, microwave resonators;

- high strength antennas;

- instrumentation: displacement sensors, elastic elements of chronometers and loaded mechanisms, non-expanding suspensions;

- laser technology - frames and quotation units of laser resonators;

- cryogenic equipment: cold pipes, compressors, valves, dewar, pipe fittings.

Claims (1)

High-strength invar alloy containing nickel, cobalt, carbon, titanium, molybdenum, vanadium, niobium, tungsten and iron, characterized in that it additionally contains zirconium, in the following ratio, wt.%:
nickel 25.0 to less than 38.0 cobalt 0.5 ÷ 20.0 carbon 0.05 ÷ 1.2 titanium 0.05 ÷ 4.0 molybdenum 0.02 ÷ 6.0 vanadium 0.01 ÷ 4.0 niobium 0.02 ÷ 5.0 tungsten 0.02 ÷ 5.0 zirconium 0.01 ÷ 2.0 iron rest
when performing the following ratios:
(% molybdenum +% zirconium):% vanadium = 1 ÷ 80;
(% molybdenum +% vanadium +% zirconium):% carbon = 2 ÷ 80.