Invar 36 is a nickel-steel alloy containing 36% nickel and 64% steel, coupled with 0.5% each of carbon and manganese, with metallurgically negligible quantities of sulfur, phosphorus, and other elements. It has a low thermal expansion, which makes it highly sought-after for applications requiring dimensional stability for a wide range of temperatures.
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Below, we detail some of the most notable properties and applications for Invar 36 components and explain why purchasing Invar from a reputable metal supplier can save you time and money when it comes to machining.
Before discussing various Invar 36 components, let’s have a look at some of its unique properties.
The rate at which metals expand or contract with a subsequent rise or decrease in temperature is known as their coefficient of thermal expansion (CTE). Invar 36 has a very low CTE of about 1ppm/K over a limited temperature range of 39.2-96.8°F, and the rate of thermal expansion is roughly one-tenth that of carbon steel at temperatures up to 400°F. It has the lowest thermal expansion rate of any metal. The following table shows the average CTE of Invar 36 for different temperatures.
Temperature (°F) Average CTE [in/in/°F x 10(-6)] 200 0.72 300 1.17 500 2.32 700 4.22Invar 36 offers high resistance to corrosion, as it can be left for months in an oxidative environment without showing any rust spots. Though its affinity to oxidation is much less than that of ordinary steel, it is imperative to grease the Invar 36 component for the highest corrosion resistance.
The remarkably low CTE of Invar 36 at room temperature, coupled with low temporal change, offers superior dimensional stability to Invar components. Therefore, Invar 36 is extensively used for designing precision mechanical systems in different industries.
Invar 36 is prized by engineers for its phenomenal CTE and dimensional stability. Thus, the alloy finds a wide range of applications ranging from watch parts to satellites. However, we will discuss some of the more notable applications of the Invar 36 alloy below.
Invar 36 is extensively used for building tapes, as Invar tapes can quickly measure a baseline with higher accuracy rather than steel tapes. Because of Invar’s low thermal expansion and high corrosion resistance, it can withstand the outdoors with no oxidation. Thus, Invar 36 tapes are good for parts of devices required to produce a constant dimension under varying climatic conditions.
Invar 36 tubes are useful as boiler tubes requiring high dimensional stability and low thermal expansions. Invar 36 tubes display low thermal expansion up to 200°C and retain strength even at cryogenic temperatures. The tubes are available in various sizes and forms for various industries such as food, oil, gas, and pharmaceuticals.
The period of a clock pendulum depends on the length of the pendulum rod, which can vary with temperature. Any temperature change can manipulate the actual readings of the clock—for example, an increase in temperature will cause the rod to expand and will make the pendulum longer. This causes the clock to lose time, thus making it inaccurate. Because of its low thermal expansion, Invar 36 is often used to manufacture pendulum clocks to maintain time accuracy.
Bimetallic strips are used in thermometers to convert a change in temperature into mechanical displacement. They’re also used to build precision instruments. The bimetallic strip is made up of yellow brass and Invar. As brass tends to curve more than Invar when heated beyond room temperature, incorporating a combination of both works perfectly to measure high and low temperatures.
Machining Invar 36 components can be a challenging process for even expert machinists. Invar 36 may seem very similar to steel, but it is very soft and ductile under an annealed condition, making it hard to machine. Machining produces gummy chips that stick around the tool. Also, Invar 36 is prone to work hardening. That said, the surface goes through plastic deformation ahead of the tool and gets harder to cut through with each pass, leading to a poor surface finish and broken tools.
Machining Invar 36 requires the relevant expertise and the right tools, such as chip breakers, to overcome challenges with ease. Using a chip breaker can help avoid too much accumulation of gummy chips around the tool. Using other sharp tools with more teeth also helps.
The machining setup may change with the type of tools selected for the job. For instance, a rigid setup is imperative to minimize chatter and avoid work hardening while using carbide tools. However, no such arrangements are necessary while working with helical tools. Post-machining, Invar products must be annealed to release any internal stress present to ensure dimensional stability.
Considering the number of unique requirements for machining Invar 36 components, transforming Invar into usable parts can be a costly process for smaller machine shops and fabricators on tight budgets.
For more than two decades, Industrial Metal Service has worked with fabricators, welders, and machinists from the San Francisco Bay Area and beyond supplying precision-cut Invar stock at a reasonable price to meet unique project requirements.
We supply new metals sourced straight from U.S. mills—however, for smaller machine shops on a tight budget, we can also provide verified metal remnants obtained from larger manufacturers that no longer require the scrap. Aside from Invar 36, we also supply other popular metals such as steel, aluminum, titanium, and copper.
Invar powder is a nickel-iron alloy powder composed of iron and nickel in proportions that result in an extremely low coefficient of thermal expansion. The name “invar” comes from the word “invariable”, referring to its stable dimensions and resistance to thermal expansion and contraction.
Invar powder has become an important material in applications requiring precision and accuracy over a range of temperatures. Its unique properties allow invar powder to be used in optical, electronic, structural, and other applications where maintaining part dimensions and clearance tolerances is critical.
This guide provides a detailed overview of invar powder covering its composition, key properties, production methods, applications, specifications, and other technical data. Comparisons are made between invar and other low expansion alloys. Supplier information, safety handling procedures, testing standards, and a FAQ section are also included.
Invar powder contains a range of 36-38% nickel by weight, with the balance being iron. Small amounts of other alloying elements such as manganese, silicon, and carbon may also be present.
The precise nickel content within this range is adjusted based on the desired coefficient of thermal expansion for the application. Higher nickel percentages result in lower thermal expansion coefficients.
Table 1: Typical Composition of Invar Powder
ComponentWeight %Nickel (Ni)36 – 38%Iron (Fe)BalanceManganese (Mn)0 – 0.5%Silicon (Si)0 – 0.5%Carbon (C)0 – 0.1%The iron-nickel proportions generate an austenitic face-centered cubic crystal structure that minimizes volume changes over temperature variations.
This unique behavior results from the opposing effects of nickel and iron on the alloy’s physical properties. Iron has a positive coefficient of thermal expansion whereas nickel has a negative coefficient. At around 36% nickel content, these effects counterbalance each other leading to very low net thermal expansion.
PREPed Metal PowdersThe defining property of invar powder is its low coefficient of thermal expansion (CTE). The CTE measures the degree of expansion or contraction per degree temperature change.
Typical values for the CTE of invar powder range from ~1.2 x 10-6/°C at 20°C to ~1.8 x 10-6/°C between 100-300°C. This is significantly lower than most other metals.
For comparison, aluminum has a CTE of ~24 x 10-6/°C and stainless steel is ~17 x 10-6/°C. This makes invar highly dimensionally stable over a wide temperature band.
Table 2: Key Properties of Invar Powder
PropertyValuesCoefficient of Thermal Expansion1.2 – 1.8 x 10-6/°CDensity8.0 – 8.2 g/ccSpecific Heat450 J/kg·KThermal Conductivity10 – 30 W/m·KElectrical Resistivity70 – 80 μΩ·cmYoung’s Modulus140 – 145 GPaPoisson’s Ratio0.294 – 0.305Tensile Strength200 – 240 MPaMelting Point1420 – 1450°CIn addition to thermal stability, invar powder offers:
The combination of properties allows invar powder to perform well in demanding operating environments. Parts maintain accuracy through temperature fluctuations and resist deformation under load.
Invar powder is produced via gas atomization, a process that involves melting the alloy and disintegrating the molten stream into fine droplets. High-pressure gas jets strike the metal stream, causing it to break up into spherical powder particles.
The particle size distribution is controlled through the gas flow rate, nozzle design, and other parameters. Gas atomized invar powder commonly has particle sizes ranging from 10 to 150 microns. Finer atomization can produce sub-micron powder.
Water atomization is another method used to make invar powder, typically with larger particle sizes. The molten alloy stream is shattered by high-pressure water jets.
Gas atomized powder has a smooth surface morphology compared to water atomized and exhibits better flow characteristics.
After solidification, the invar powder undergoes sieving to obtain the desired particle size fractions. It may also be annealed to relieve stresses from processing and optimize properties.
The applications of invar powder leverage its extremely low and predictable coefficient of thermal expansion. It is used where maintaining part dimensions, clearance tolerances, alignment, and precision over temperature variations is critical.
Table 3: Applications of Invar Powder
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IndustryApplicationOpticsMirror blanks, reflectors, mounts, optical benchesElectronicsPrecision resistors, substrates, seals, connectorsDefenseFire control instruments, inertial guidance systemsAerospaceAntennas, composite matrices, satellite and telescope componentsEnergySeals for fuel cells, batteries, high-temperature gasketsAutomotiveOxygen sensors, fuel injection systemsSome specific applications include:
In these and other challenging applications, invar’s exceptional thermal dimensional stability provides design robustness and ensures critical performance parameters are not impacted by temperature changes.
Invar Powder: Composition, Properties, and Applications 4Invar powder is available in various size ranges, purities, and alloy grades tailored to different fabrication processes and end-use requirements.
Table 4: Invar Powder Size Specifications
Mesh SizeMicron Size-140Less than 106 μm-100150 μm-325Less than 45 μm-40038 μm-63520 μm-10 μm10 μm-2.5 μm2.5 μmFiner invar powder is suited for additive manufacturing methods requiring flowability and packing density. Coarser powder works for conventional press-and-sinter fabrication.
Chemical purity levels range from 99% for industrial grades to 99.9% or higher for high-performance applications. Oxygen content must be kept below 50 ppm.
Custom alloys with nickel varied from 36-38% produce CTEs from ~0.9 x 10-6/°C to ~2 x 10-6/°C. Mn, Si, and C may also be adjusted.
Table 5: Invar Powder Alloy Grades
Alloy GradeNickel %CTE x 10-6/°CInvar 36®36%~1.2Nilo 36®36%~1.2Pernifer 36®36%~1.2Invar 38®38%~0.9International standards for chemical composition include:
Invar powder is available from leading global suppliers of specialty metal powders. Typical pricing is between $50/kg to $120/kg based on alloy grade, powder size, and order quantity.
Table 6: Invar Powder Suppliers
SupplierProduct GradesSandvikOsprey® Invar powdersHoganasAstaloy® InvarKymeraInvar 36, Invar 38CNPCInvar alloy powdersEpson AtmixInvar fine powdersHandling and Safety
Invar powder poses no significant health hazards. However, standard safety precautions for handling and working with metallic powders should be followed.
Invar powder should be stored in closed containers in a clean, dry environment. Avoid conditions allowing oxidation or contamination from moisture.
To ensure invar powder meets specifications, a variety of testing and inspection procedures are used:
Certificates of analysis from reputable suppliers confirm invar powder meets the required grade criteria.
Invar vs. Other Low Expansion Alloys
While invar has the lowest CTE of common alloys, there are other nickel and iron-nickel alloys engineered to provide very low thermal expansion.
Table 7: Comparison of Low CTE Alloy Powders
AlloyCTE x 10-6/°CCompositionNotesInvar 36~1.236% Ni, balance FeLowest CTE, high strengthInvar 38~0.938% Ni, balance FeLower CTE than Invar 36Kovar~5.929% Ni, 17% Co, bal. FeCTE between Invar and steelAlloy 45~545% Ni, bal. FeLess expensive than invarAlloy 46~246% Ni, bal. FeCTE closer to invarSuper Invar~0.432% Ni, bal. Fe + Co additionsExtremely low CTETable 8: Comparison of Pros and Cons
AlloyProsConsInvarVery low, stable CTEMore expensive than other alloysExcellent strengthHigher density than Al or polymersGood corrosion resistanceKovarLower cost than invarHigher CTE than invarEasy to machine and formLess thermally stableSeals to borosilicate glassAlloy 45Less expensive than invarLower performance than invarWorkable CTE for many usesAlloy 46Lower CTE than Alloy 45Still higher CTE than invarGood combination of propertiesSuper InvarExtremely low CTEMore difficult to sourceSuperior thermal stabilityHigher costFor the most demanding applications requiring maximum dimensional stability over temperature variations, invar’s very low and highly predictable CTE makes it unmatched.
Where cost is a larger factor but thermal performance must still be good, lower nickel alloys like Kovar and Alloy 45 present affordable alternatives with a compromise on expansion characteristics.
Invar Powder: Composition, Properties, and Applications 5What is invar powder made of?
Invar powder consists primarily of 36-38% nickel with the balance being iron. Small amounts of manganese, silicon, and carbon may be present as well. This composition results in an extremely low coefficient of thermal expansion.
How is invar powder produced?
It is manufactured via gas atomization where the alloy is melted and disintegrated into fine spherical particles using high-pressure gas jets. This allows tight control over powder size distribution and morphology.
What is invar powder used for?
It is used in applications where dimensional stability and precision tolerances must be maintained as temperature varies. Common uses include optics, electronics, aerospace components, precision instruments, seals, and substrates.
What are the key properties of invar powder?
What standards apply to invar powder?
ASTM F3061 and DIN 1.3912 cover the chemical composition for the 36% nickel low expansion invar alloys used in seals and precision applications.
How does invar powder compare to other low expansion alloys?
Invar has the lowest CTE of any common alloy. Kovar and Alloy 46 provide lower cost alternatives but with some sacrifice in thermal stability. Super invar has an extremely low CTE but is more expensive and less available.
What particle sizes and grades are available?
Invar powder can be supplied in size ranges from 10 to 150 microns. Common nickels content are 36% (Invar 36) and 38% (Invar 38). Higher nickel gives lower expansion. Custom alloys are also produced.
How should invar powder be handled and stored?
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