# Alloy 48 (UNS K94800 / ASTM F30) Forgings: Rings, Bars, Discs, Flanges Source page: https://www.steelforgepieces.com/Nickel-Alloy/Alloy-48.html Published: 12 May 2022. Last updated: 13 August 2026. Reviewed by the Metallurgical Engineering Team, Jiangyin Jiangnan Metal Co., Ltd. Designations: UNS K94800 | ASTM F30 | DIN 17745 | W.Nr. 1.3922, 1.3926, 1.3927 | AFNOR NF A54-301 | MIL-I-23011 Class 3 | AWS 092 --- ## Summary Alloy 48 is a binary nickel-iron controlled-expansion alloy containing nominally 48 % nickel, balance iron, specified under UNS K94800, ASTM F30, DIN 17745 and Werkstoff numbers 1.3922, 1.3926 and 1.3927. Its mean coefficient of thermal expansion, 8.5 x10-6/K over 20-100 C rising only to 9.1 x10-6/K over 20-500 C, is matched to soft lead and soda-lime glasses, so its dominant use is glass-to-metal sealing. It also serves industrial thermostats operating up to 450 C, below its inflection point of about 460 C. Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China that forges Alloy 48 / UNS K94800 into seamless rolled rings, round and flat bars, discs, flanges, sleeves, bushings, shafts and tube sheets to customer drawing, supplied annealed with EN 10204 3.1 or 3.2 certification. Contact: 0086-189-2135-9659, sales@steelforgepieces.com. Property values below are typical for the annealed alloy class and are given for design guidance. The values that govern a delivery are those on the material test certificate issued with it. ## Key figures | Property | Value | |---|---| | Nickel | 48 %, balance iron | | Mean CTE, 20-300 C | 8.7 x10-6/K | | Inflection point | 460 C (860 F) | | Density | 8.20 g/cm3 (0.296 lb/in3) | | Tensile strength, annealed, 20 C | 520 MPa (75 ksi) typical | | Melting point | 1450 C (2640 F) | | Maximum ring outside diameter | 2,500 mm, seamless rolled | --- ## What is Alloy 48? Alloy 48 is a binary nickel-iron controlled-expansion alloy with nominally 48 % nickel and the balance iron. It belongs to the same family as Invar 36 and Alloy 42; the three are separated only by nickel content, and that single variable sets the expansion behaviour of each. Below its inflection point the alloy is ferromagnetic, and magnetostriction partly cancels normal thermal expansion. That effect gives the whole Fe-Ni family its unusually flat expansion curves. Raising nickel from 36 % to 48 % weakens that cancellation, so expansion rises, but it also pushes the inflection point up from about 220 C to about 460 C. Alloy 48 therefore trades the very low room-temperature expansion of Invar 36 for a coefficient that stays almost constant over a much wider working range, which is what a glass-to-metal seal needs. The practical consequence: Alloy 48 expands at roughly 8.5 to 9.1 x10-6/K, which lands on top of soda-lime glass and soft lead (lead-alkali) glass. A seal made between them stays in near-zero stress through the whole cooling cycle from the sealing temperature down to ambient, and back up again in service. Secondary uses follow from the same flat curve: industrial thermostats to 450 C, bimetal elements, precision instrument parts, and shielding or structural parts in vacuum devices. Alloy 48 is not a corrosion-resistant or high-temperature structural alloy. It contains essentially no chromium (0.25 % maximum as a residual), so it oxidises like a plain steel and offers no useful resistance to acids or chlorides. Specify it for what it does, which is to hold a defined expansion coefficient, and choose Incoloy 800H or Inconel 600 where hot corrosion resistance is the requirement. Three points that decide the grade: - Flat to 450 C. Inflection point about 460 C, the highest of the three common binary Fe-Ni expansion grades, so the coefficient stays within about 0.3 x10-6/K from room temperature to 450 C. - Match. 8.5 to 9.1 x10-6/K coincides with soda-lime glass (about 9.0) and soft lead glass (about 9.2), the glasses used in lamps, valves and low-cost hermetic packages. - Condition. Residual cold work distorts the expansion coefficient. Forged Alloy 48 is supplied annealed at 850 to 1000 C in a protective atmosphere, which is also the condition all published data refers to. ## Equivalent designations and trade names | Body / region | Designation | Scope and notes | |---|---|---| | USA, UNS | K94800 | Generic Unified Numbering System designation | | USA, ASTM | ASTM F30 | Iron-nickel sealing alloys: sheet, strip, rod, bar, tubing and wire | | USA, military | MIL-I-23011 Class 3 | Legacy military designation for the 48 % Ni sealing alloy | | USA, welding | AWS 092 | Filler / wire designation | | Germany, DIN | DIN 17745 | Wrought nickel-iron alloys with defined physical properties (composition) | | Germany, Werkstoff | 1.3922, 1.3926, 1.3927 | Three material numbers cover the 48 % Ni sealing alloy variants; state which one your drawing calls for | | France, AFNOR | NF A54-301 | Composition standard | | Common names | Alloy 48, Ni-Fe alloy 48, Nickel alloy 48, Glass Seal 48, Sealing alloy 48, Invar 48, Supra 50 | Descriptive names in trade use. "Invar 48" is a loose usage, because true Invar behaviour belongs to the 36 % Ni grade | | Trademarks | NILO 48, Pernifer 48 | NILO is a registered trademark of Special Metals Corporation; Pernifer of VDM Metals; Invar is associated with Aperam / Imphy Alloys. We do not sell under those brands | Trademark notice. NILO and NILOMAG are registered trademarks of Special Metals Corporation. Pernifer is a registered trademark of VDM Metals. Invar is a registered trademark associated with Aperam / Imphy Alloys. Inconel, Incoloy and Monel are registered trademarks of Special Metals Corporation; Kovar of CRS Holdings / Carpenter Technology. Material produced by those companies and sold under those brands is theirs. Material produced by Jiangyin Jiangnan Metal Co., Ltd. is correctly described as Alloy 48 / UNS K94800 / ASTM F30 / DIN 17745 / W.Nr. 1.3922, the same generic chemistry, manufactured independently. We are not affiliated with, sponsored by or endorsed by any of those trademark holders. ## Chemical composition Alloy 48 is a deliberately simple chemistry: nickel and iron, with every other element held down as a residual. The reason is physical rather than metallurgical fashion: the expansion coefficient is a strong function of nickel content, roughly 0.6 x10-6/K per 1 % Ni in this range, so tight nickel control is what actually buys a repeatable seal. | Element | Limit (wt %) | Function / remark | |---|---|---| | Nickel (Ni) | 48.0 nominal | Sets the expansion coefficient and the inflection point. Ordered to a narrow band around 48 % | | Chromium (Cr) | 0.25 max | Residual only; raises expansion and is not wanted here | | Manganese (Mn) | 0.80 max | Deoxidiser; sulphur control | | Silicon (Si) | 0.30 max | Deoxidiser; kept low to protect glass-sealing surface quality | | Carbon (C) | 0.05 max | Kept low because carbon causes gas evolution at the seal interface | | Aluminium (Al) | 0.10 max | Residual deoxidiser | | Phosphorus (P) | 0.025 max | Impurity | | Sulphur (S) | 0.025 max | Impurity; high S embrittles hot-worked Ni-Fe alloys | | Cobalt (Co) | incidental | Present as an incidental element; reported separately when required | | Iron (Fe) | balance | Matrix | Confirm the exact element limits against the revision of ASTM F30 or DIN 17745 in force at your contract date. Where a customer specification is tighter than the table above, we melt to the tighter limit and state both on the certificate. Melting route. Alloy 48 for forged product is melted by EAF plus VOD with electroslag remelting (ESR) where the order calls for improved cleanliness and a tighter nickel band. ESR is worth specifying for sealing-critical work: oxide stringers at a seal face are a leak path, not a cosmetic defect. ## Thermal expansion data Mean linear coefficient of thermal expansion from 20 C to each upper temperature, with the total expansion over that range, for annealed material. | Temperature range (C) | Range (F) | Total expansion (x10-3) | Mean coefficient (x10-6/C) | Mean coefficient (x10-6/F) | |---|---|---|---|---| | 20-100 | 68-212 | 0.68 | 8.5 | 4.7 | | 20-150 | 68-302 | 1.11 | 8.5 | 4.7 | | 20-200 | 68-392 | 1.55 | 8.6 | 4.8 | | 20-250 | 68-482 | 1.98 | 8.6 | 4.8 | | 20-300 | 68-572 | 2.44 | 8.7 | 4.8 | | 20-350 | 68-662 | 2.88 | 8.7 | 4.8 | | 20-400 | 68-752 | 3.34 | 8.8 | 4.9 | | 20-450 | 68-842 | 3.84 | 8.9 | 4.9 | | 20-500 | 68-932 | 4.37 | 9.1 | 5.1 | Read the curve, not one number. Between 20-100 C and 20-450 C the mean coefficient moves only from 8.5 to 8.9 x10-6/K, a 4.7 % change across 430 K. Above the inflection point near 460 C the ferromagnetic contribution disappears and the slope climbs steeply toward the roughly 13 x10-6/K typical of ordinary austenitic Fe-Ni. That is why 450 C is quoted as the practical service ceiling. Where the coefficient is contractual, specify dilatometry over your own temperature range and an acceptance band. See "How to specify an order", step 5. ## Glass-to-metal sealing A glass-to-metal seal fails for one of two reasons: the expansion curves diverge and the glass cracks, or the oxide layer at the interface is wrong and the glass never wets the metal. Alloy 48 addresses the first; surface preparation addresses the second. Matched seals. Alloy 48 forms a matched seal with soda-lime and soft lead glasses: both partners contract along nearly the same path from the sealing temperature to ambient, so residual stress stays low and the joint tolerates thermal cycling. In practice a small deliberate mismatch is often designed in so that the glass finishes in slight compression, because glass is far stronger in compression than in tension. Keep the metal's coefficient at or marginally above the glass through the cooling range and the seal ends compressed rather than pulled apart. Surface preparation, typical practice for Fe-Ni sealing alloys: - Decarburising anneal. Wet hydrogen at roughly 900 to 1050 C removes surface carbon that would otherwise evolve CO at the seal interface and produce bubbles. - Controlled oxidation. Heating in air at 600 to 1000 C grows the thin, adherent oxide film the glass dissolves into. Film thickness is set by time and temperature; too thick and the oxide itself becomes the weak layer. - Cleanliness. No residual cutting oil, no chloride from handling, no smeared metal from a dull tool. Design rules for forgings: - Keep welds out of the sealing zone. Weld metal made with nickel-based filler does not share the parent expansion coefficient, and the heat-affected zone will not either. - Supply and use the part annealed. Cold work from straightening, machining or forming shifts the coefficient and relaxes unpredictably at sealing temperature. - Design radii, not corners, where glass meets metal. A stress concentration in the glass at a sharp step is the usual crack origin. - For rings and flanges, ask for the seal face to be machined from a forged blank with circumferential grain flow. A ring rolled from a pierced blank gives more uniform behaviour around the circumference than one cut from plate. Approximate expansion coefficients for comparison, near room temperature, x10-6/K: Invar 36 1.5, borosilicate 7740 glass 3.3, sealing glass 7052 type 4.6, Fe-Ni-Co Kovar type 5.1, Alloy 42 5.3, alumina ceramic 96 % 7.0, Alloy 48 8.7, soda-lime glass 9.0, soft lead glass 9.2, carbon steel 12.0, 304 stainless steel 17.3. ## Mechanical properties Typical values, hot-rolled and annealed bar. | Temperature | Tensile strength | Yield strength (0.2 %) | Elongation on 50 mm | Reduction of area | |---|---|---|---|---| | 20 C (68 F) | 520 MPa (75 ksi) | 260 MPa (38 ksi) | 43 % | 72 % | | 100 C (212 F) | 480 MPa (70 ksi) | 210 MPa (30 ksi) | 43 % | 72 % | | 200 C (392 F) | 470 MPa (68 ksi) | 160 MPa (23 ksi) | 43 % | 72 % | | 300 C (572 F) | 460 MPa (67 ksi) | 150 MPa (22 ksi) | 43 % | 72 % | | 400 C (752 F) | 400 MPa (58 ksi) | 130 MPa (19 ksi) | 44 % | 70 % | | 500 C (932 F) | 320 MPa (46 ksi) | 120 MPa (17 ksi) | 47 % | 64 % | | 600 C (1112 F) | 240 MPa (35 ksi) | 110 MPa (16 ksi) | 51 % | 55 % | Hardness: | Condition | Vickers HV | Rockwell HRB | Use | |---|---|---|---| | Annealed | 150 max | 80 max | Standard supply condition for forgings and all sealing work | | Full hard (cold worked) | 240 min | 99 min | Strip and wire only; not a condition for expansion-critical parts | ASTM F30 sets minima, not typicals. The room-temperature figures most often quoted as the "spec" for Alloy 48 (520 MPa tensile, 260 MPa yield, 43 % elongation) are the values reported for annealed bar. On a purchase order, state whether you are calling for minimum guaranteed properties or accepting typical values, and state the test direction and specimen location for large forgings. ## Physical properties | Property | Value | Unit / condition | |---|---|---| | Density | 8.20 | g/cm3 (0.296 lb/in3) | | Melting point | 1450 | C (2640 F) | | Inflection point (magnetic transition) | 460 | C (860 F); the practical ceiling for controlled expansion | | Modulus of elasticity | 160 | GPa (23.2 x10^3 ksi), annealed | | Thermal conductivity at 20 C | 16.7 | W/m.K (116 Btu.in/ft2.h.F) | | Electrical resistivity at 20 C | 47 | microhm.cm | | Electrical resistivity at 100 / 200 / 300 C | 54 / 71 / 89 | microhm.cm | | Electrical resistivity at 400 / 500 / 600 C | 104 / 116 / 121 | microhm.cm | | Magnetic character | ferromagnetic | below the inflection point; paramagnetic above it | Resistivity rises steeply through the magnetic transition. That is useful if you are using the alloy in a heated element or need to model self-heating, and a reminder that controlled expansion is a magnetic effect, not a lattice curiosity. ## Alloy 48 vs Alloy 42 vs Invar 36 vs Fe-Ni-Co (Kovar type) | Property | Invar 36 | Alloy 42 | Alloy 48 | Fe-Ni-Co (Kovar type) | |---|---|---|---|---| | Nominal composition | 36 % Ni, bal Fe | 42 % Ni, bal Fe | 48 % Ni, bal Fe | 29 % Ni, 17 % Co, bal Fe | | UNS | K93600 / K93601 | K94100 | K94800 | K94610 | | Werkstoff no. | 1.3912 | 1.3917 | 1.3922 / 1.3926 / 1.3927 | 1.3981 | | Primary standard | ASTM B388 / B753 | ASTM F30 / F29 | ASTM F30 | ASTM F15 | | CTE 20-100 C (x10-6/K) | 1.5 | 5.3 | 8.5 | 6.0 | | CTE 20-300 C (x10-6/K) | 5.5 | 5.3 | 8.7 | 5.1 | | CTE 20-400 C (x10-6/K) | 8.4 | 6.2 | 8.8 | 4.9 | | Inflection point | 220 C | 370 C | 460 C | 450 C | | Density (g/cm3) | 8.11 | 8.11 | 8.20 | 8.16 | | Melting point | 1430 C | 1435 C | 1450 C | 1450 C | | Thermal conductivity (W/m.K) | 10.0 | 10.5 | 16.7 | 16.7 | | Resistivity at 20 C (microhm.cm) | 80 | 61 | 47 | 43 | | Modulus (GPa) | 140 | 150 | 160 | 130 | | Tensile / yield at 20 C | 490 / 240 MPa | 490 / 250 MPa | 520 / 260 MPa | 520 / 340 MPa | | Seals to | Not a sealing alloy | Hard glass, lead frames | Soda-lime and soft lead glass | Borosilicate glass, alumina ceramic | | Typical use | Composite tooling, length standards, cryogenic and LNG work, low-expansion side of bimetal | Semiconductor lead frames, thermostat rods, bimetal strip | Glass-to-metal seals in lamps and valves, industrial thermostats to 450 C | Hermetic packages, feedthroughs, microwave and vacuum devices | The counter-intuitive row is CTE 20-400 C. Invar 36 has by far the lowest expansion at room temperature, but it has already passed its inflection point at 220 C, so by 400 C its mean coefficient (8.4) has almost caught Alloy 48 (8.8), and it is climbing while Alloy 48 is still flat. If your part cycles to 300 to 450 C, low room-temperature expansion is the wrong selection criterion. Compare mean coefficients over your range, not at ambient. ## Forging, annealing and dimensional stability Alloy 48 forges like an austenitic stainless: soft at temperature, ductile, with no phase transformation to manage on cooling. The difficulty is not force. It is keeping the finished part's expansion coefficient reproducible, which means controlling cold work and nickel segregation rather than chasing strength. Hot-working practice: - Forging range. Heat to approximately 1150 to 1200 C, finishing above 900 C. Working below that range work-hardens the alloy quickly and raises cracking risk at the surface. - Never in a sulphur-bearing atmosphere. Nickel-rich alloys suffer catastrophic sulphur embrittlement. Furnace fuel, refractory contamination and marking paint all have to be sulphur-free. This is the single most common cause of scrapped Ni-Fe forgings. - Forging ratio. A reduction of 4:1 or better breaks down the as-cast structure and evens out nickel segregation across the section. Uneven nickel means an uneven expansion coefficient across one part. - Cool slowly after the final blow, then anneal. Annealing. Anneal at 850 to 1000 C in a protective atmosphere, hold according to section thickness, then cool under control. Where maximum dimensional stability is required, the alloy must be used in the annealed condition; residual cold work distorts the coefficients of thermal expansion, so a part that is straightened, pressed or heavily machined after annealing will not reproduce the table values. Recommended route for expansion-critical forgings: forge, slow cool, rough machine with generous stock, anneal 850 to 1000 C in protective atmosphere, stress-relieve if further machining is heavy, finish machine with light cuts and sharp tools, final low-temperature stabilisation if the drawing demands it. Order the sequence on the drawing; do not leave it to the machine shop. Forging routes used for this grade: 1. Open-die forging. Shafts, blocks, discs and sleeves. Multi-step incremental reduction on 25 MN and 40 MN presses. 2. Seamless ring rolling. Rings from 200 mm to 2,500 mm OD with circumferential grain flow. Preferred route for seal rings and flanges. 3. Upset forging. Short, large-section discs, hubs and tube-sheet blanks. 4. Near-net-shape. Cuts machining stock by roughly 30 to 50 % on profiled parts. ## Welding and machining Welding. Alloy 48 is welded by manual metal arc, TIG, plasma, MIG and pulsed-arc processes using nickel-based filler metals: generically ERNi-1 (AWS A5.14) for plain nickel filler and ERNiCr-3 where a nickel-chromium deposit is wanted; the corresponding covered electrodes are of the ENi-1 / ENiCrFe type. MIG spray transfer and submerged-arc welding are not recommended for this alloy family. A weld is an expansion discontinuity. No commercial filler reproduces the 48 % Ni-Fe expansion curve, and the heat-affected zone is locally annealed or locally worked. Keep welds away from sealing surfaces and from any dimension that carries an expansion tolerance. If a joint is unavoidable in that zone, plan a full re-anneal afterwards and re-qualify the seal. Machining. Machine in the annealed condition with high-speed-steel or tungsten-carbide-tipped tooling. The alloy is gummy and work-hardens if the tool rubs: keep feed positive, keep the tool sharp, never dwell. | Operation | Cutting speed | Feed | Depth of cut | |---|---|---|---| | Rough turning | 30-45 m/min (98-148 ft/min) | 0.25-0.4 mm/rev | 1.25-2.5 mm | | Finish turning | 45-60 m/min (148-197 ft/min) | 0.10-0.25 mm/rev | 0.125-0.25 mm | | Drilling, dia 1.6 mm | 15-18 m/min peripheral | 0.03 mm/rev | peck cycle | | Drilling, dia 3.2 mm | 15-18 m/min peripheral | 0.05 mm/rev | peck cycle | | Drilling, dia 12.7 mm | 15-18 m/min peripheral | 0.13 mm/rev | peck cycle | | Drilling, dia 25.4 mm | 15-18 m/min peripheral | 0.30 mm/rev | peck cycle | Cutting fluid: straight cutting oil, EP medium duty, or soluble oil at 20:1 dilution for turning, drilling and milling; use a lower dilution ratio for other operations. Intermediate drill sizes pro rata. Remove all cutting fluid before any sealing or annealing operation. ## Forged forms and production capability Jiangyin Jiangnan Metal Co., Ltd. has forged open-die parts and seamless rolled rings since 2008 at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, and exports to more than 40 countries under an ISO 9001:2015 quality system. Alloy 48 is produced to order rather than held in stock, because the grade is bought against a specific nickel band and a specific annealed condition. Forms available in Alloy 48 / UNS K94800: seamless rolled rings (rectangular, contoured, T-section); forged discs and hubs; round and flat bars; flanges (weld-neck, blind, custom profile); sleeves, bushings and spacers; tube sheets and plates; shafts and spindles; blocks and blanks; near-net-shape forgings to drawing. | Equipment | Capability | |---|---| | 40 MN free-die hydraulic press | Max ingot 12 t, max diameter 1,800 mm, max length 8,000 mm | | 25 MN free-die hydraulic press | Max ingot 6 t, faster cycle, preferred for bars and shafts | | Forging hammers, 1 / 3 / 5 / 9 t | Small and medium open-die work | | Radial-axial ring mill | Max OD 2,500 mm, max height 600 mm, min wall 30 mm | | Bogie-hearth annealing furnace | 8 x 4 x 2 m chamber, to 1,100 C, +/-5 C uniformity, protective atmosphere available | | Laboratory | Optical emission spectrometer, 300 kN universal test machine, impact testing, metallography to 1,000x, hardness HV / HB / HRB | | Non-destructive testing | Phased-array ultrasonic, fluorescent penetrant, magnetic particle | Grade-specific limits. The envelope above is the plant maximum. For Alloy 48 the practical maximum on any given order is also set by the melt lot size available for a 48 % Ni heat, so confirm the achievable size and weight at quotation rather than assuming the plant maximum. Typical Alloy 48 orders run from a few kilograms of bar to rings in the 200 to 2,000 mm OD range. ## Standards, testing and certification Material standards: ASTM F30, DIN 17745, W.Nr. 1.3922 / 1.3926 / 1.3927, AFNOR NF A54-301, UNS K94800, MIL-I-23011 Class 3. | Test | Method / standard | When | |---|---|---| | Chemical analysis | Optical emission spectrometry, heat and product analysis | Every heat; product analysis on request | | Tensile test | ASTM E8 / ISO 6892-1, annealed condition | Every heat-treatment batch | | Hardness | HV or HRB, annealed 150 HV max | Every batch | | Ultrasonic testing | EN 10228-3, SEP 1921 or ASTM A388; state class on the order | As specified; standard for rings and discs above 50 mm section | | Penetrant testing | ASTM E165 / EN ISO 3452 | On request, machined surfaces | | Thermal expansion | Dilatometry over the customer's temperature range | On request; specify range and acceptance band | | Grain size / microstructure | ASTM E112 metallography | On request | | Dimensional | Per drawing, before and after final machining | Every part | Certification. EN 10204 3.1 mill certificate is issued as standard with every Alloy 48 order. EN 10204 3.2 with third-party witness (Lloyd's Register, DNV, Bureau Veritas, ABS or TUV) is available on request and is arranged per order. Certificates state the heat number, chemistry, heat-treatment record, mechanical results and all equivalent designations the material satisfies, so a single certificate can be presented against a UNS, ASTM, DIN or AFNOR purchase order. ## Where Alloy 48 forgings are used - Glass-to-metal seals in soft glass. Incandescent and specialty lamp bulbs, radio and vacuum valves, and hermetic packages sealed with soda-lime or soft lead glass. - Industrial thermostats to 450 C. Thermostat bodies, rods and bimetal elements where the expansion coefficient must stay predictable across the whole regulating range. - Circuit breakers and temperature regulators. Trip elements and regulator components that convert a temperature change into a repeatable displacement. - Precision and scientific instruments. Frames, spacers and mountings, including clock balance wheels and regulator components. - Vacuum devices and feedthroughs. Housings, flanges and bushings for microelectronic and vacuum hardware using soft-glass insulation. - Sealed joints in process hardware. Valve parts, seat rings, sleeves and tube sheets in assemblies that carry a glass or ceramic joint. Two applications frequently mis-attributed to Alloy 48. Membrane containment for LNG tankers and transfer lines uses Invar 36, not Alloy 48; the requirement there is minimum movement at cryogenic temperature, which is the 36 % Ni grade. Semiconductor lead frames are normally Alloy 42. If a datasheet lists all three applications under Alloy 48, it has copied a family description rather than a grade description. ## How to specify an Alloy 48 forging order 1. State the generic designation. Alloy 48 / UNS K94800 / ASTM F30, plus W.Nr. 1.3922 or DIN 17745 for European projects. Ordering under a trademark restricts the order to that producer. 2. Declare the sealing partner. Name the glass or ceramic, or give the target mean coefficient and the temperature range. This is what decides Alloy 48 versus Alloy 42 versus a Fe-Ni-Co grade. 3. Specify the delivery condition. Annealed, 850 to 1000 C, protective atmosphere. Cold-worked material will not reproduce the published expansion values. 4. Define shape and machining stock. Forged shape, finished dimensions and the allowance you expect, or send the drawing and let us propose the forging envelope. 5. Call out expansion testing if contractual. Dilatometry range, acceptance band and sample position. Chemistry alone does not guarantee a coefficient. 6. Specify NDT. Ultrasonic standard and class (EN 10228-3, SEP 1921 or ASTM A388), plus any penetrant requirement and the surfaces concerned. 7. Fix certification and commercial terms. EN 10204 3.1 or 3.2, quantity, required date, incoterm (EXW Jiangyin, FOB Shanghai, CIF or DDP). Drawing callout template: ``` MATERIAL: Alloy 48 / UNS K94800 / ASTM F30 (also satisfies DIN 17745, W.Nr. 1.3922, AFNOR NF A54-301) CONDITION: Annealed 850-1000 C, protective atmosphere, controlled cool EXPANSION: Mean CTE 8.5-9.0 x10-6/K over 20-400 C, verified by dilatometry on a sample taken from the forging, not from the billet HARDNESS: 150 HV max NDT: UT per EN 10228-3 quality class 3 (or ASTM A388 Class B) SURFACE: Ra <= 1.6 micrometre on sealing faces; no cutting-fluid residue CERTIFICATION: EN 10204 3.1 (3.2 with third-party witness if required) MARKING: Heat number and drawing number, low-stress vibro-etch, sulphur-free ink ``` ## Common mistakes when ordering Alloy 48 1. Ordering by trademark. Write Alloy 48 / UNS K94800 / ASTM F30 when you want the generic chemistry. 2. Specifying chemistry but not condition. Chemistry does not deliver an expansion coefficient. The annealed condition does. 3. Comparing coefficients at room temperature only. Invar 36 looks better at 20 C and is worse at 400 C. Compare mean coefficients over your own service range. 4. Using Alloy 48 above 460 C. Past the inflection point the controlled-expansion behaviour disappears. 5. Expecting corrosion resistance. With 0.25 % Cr maximum this alloy rusts like plain steel. 6. Welding through the sealing zone. Filler metal and heat-affected zone do not share the parent expansion curve. 7. Machining after the final anneal. Heavy final cuts reintroduce cold work at the surface that has to hold the seal. 8. Leaving sulphur on the part. Cutting oil, marking paint or a sulphur-bearing furnace atmosphere will embrittle a nickel-rich alloy on the next heat cycle. ## Glossary **Alloy 48.** Binary nickel-iron controlled-expansion alloy with nominally 48 % nickel, balance iron. UNS K94800; ASTM F30; DIN 17745; W.Nr. 1.3922, 1.3926, 1.3927. **Controlled-expansion alloy.** An alloy whose coefficient of thermal expansion is engineered to a target value rather than left as a by-product of composition, the Fe-Ni family being the classic example. **Coefficient of thermal expansion (CTE).** Fractional change in length per kelvin. Quoted here as a mean coefficient over a stated range from 20 C, which is the form used in sealing design. **Inflection point.** The temperature at which the ferromagnetic contribution to expansion disappears and the expansion curve steepens, about 460 C for Alloy 48. Also referred to as the Curie or magnetic transition temperature. **Matched seal.** A glass-to-metal seal in which both partners have closely similar expansion curves, so the joint cools with minimal residual stress. **Compression seal.** A seal designed so that the metal contracts more than the glass, leaving the glass in compression. The deliberate small mismatch exploits the strength of glass in compression. **Decarburising anneal.** Wet-hydrogen treatment that strips surface carbon before glass sealing, preventing gas evolution at the interface. **ASTM F30.** Standard specification covering iron-nickel sealing alloys in sheet, strip, rod, bar, tubing and wire form. **UNS K94800.** Unified Numbering System designation for the 48 % nickel-iron sealing alloy. **EN 10204 3.1 / 3.2.** Inspection-document types. 3.1 is issued by the manufacturer's independent inspection department; 3.2 is countersigned by a third-party inspector nominated by the buyer. **EN 10228-3.** European standard for ultrasonic testing of ferritic or martensitic steel forgings, commonly invoked for forged rings and discs. **Open-die forging.** Hot forging between flat or simple dies with incremental reduction. The route for large rings, shafts, discs and blocks in small quantities. **Seamless rolled ring.** A ring produced by piercing a forged billet and rolling it out on a ring mill, giving continuous circumferential grain flow. ## Frequently asked questions **What is Alloy 48?** Alloy 48 is a binary nickel-iron controlled-expansion alloy containing nominally 48 % nickel with the balance iron. It is covered by ASTM F30 and DIN 17745 and carries UNS number K94800 and Werkstoff numbers 1.3922, 1.3926 and 1.3927. Its mean coefficient of thermal expansion, 8.5 to 9.1 x10-6 per kelvin between 20 and 500 C, is matched to soft lead and soda-lime glasses, which makes glass-to-metal sealing its main application. It is also used for industrial thermostats operating up to 450 C. Jiangyin Jiangnan Metal Co., Ltd., an open-die forging factory at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China, forges Alloy 48 into rings, bars, discs, flanges, sleeves and tube sheets. **Are Alloy 48, NILO 48, Pernifer 48, Invar 48 and UNS K94800 the same material?** They describe the same 48 % nickel-iron chemistry, but not all of the names are generic. UNS K94800, ASTM F30, DIN 17745, W.Nr. 1.3922 / 1.3926 / 1.3927, AFNOR NF A54-301 and AWS 092 are generic designations that any producer may use. NILO is a registered trademark of Special Metals Corporation, Pernifer of VDM Metals, and Invar is associated with Aperam / Imphy Alloys. Jiangyin Jiangnan Metal Co., Ltd. supplies the generic equivalent and certifies it as Alloy 48 / UNS K94800 / ASTM F30 / W.Nr. 1.3922; it is not affiliated with, sponsored by or endorsed by those trademark owners. **What is the coefficient of thermal expansion of Alloy 48?** For annealed Alloy 48 the mean linear coefficient of thermal expansion is approximately 8.5 x10-6/K over 20-100 C, 8.6 over 20-200 C, 8.7 over 20-300 C, 8.8 over 20-400 C, 8.9 over 20-450 C and 9.1 over 20-500 C. The curve stays nearly flat because the alloy is used below its inflection point of about 460 C. Residual cold work distorts these values, which is why Alloy 48 is supplied and used in the annealed condition. **Which glasses can be sealed to Alloy 48?** Alloy 48 is matched to the soft glasses: soda-lime glass and soft lead (lead-alkali) glass, both of which expand at roughly 8.5 to 9.5 x10-6/K. Typical seals include incandescent lamp bulbs, radio and vacuum valves, and microelectronic packages using soft glass. Borosilicate glasses such as the 7052 and 7056 types and alumina ceramics expand far less and require a Fe-Ni-Co alloy of the Kovar type instead, while Alloy 42 suits semiconductor lead frames and some hard-glass work. **What is the difference between Alloy 48, Invar 36 and Alloy 42?** All three are binary nickel-iron alloys separated by nickel content. Invar 36, with 36 % Ni, has the lowest expansion, about 1.5 x10-6/K near room temperature, and is used for dimensional stability, composite tooling and cryogenic work. Alloy 42, with 42 % Ni, expands at about 5.3 x10-6/K and is used for semiconductor lead frames, thermostat rods and hard-glass sealing. Alloy 48, with 48 % Ni, expands at about 8.5 to 9.1 x10-6/K and is used where the metal must track soft soda-lime or lead glass. Inflection points rise with nickel: about 220 C for Invar 36, 370 C for Alloy 42 and 460 C for Alloy 48. **What are the mechanical properties of Alloy 48?** Hot-forged and annealed Alloy 48 bar shows a typical room-temperature tensile strength of 520 MPa (75 ksi), a 0.2 % yield strength of 260 MPa (38 ksi), elongation of about 43 % on 50 mm and reduction of area of about 72 %. Annealed hardness is 150 HV maximum, roughly 80 HRB. Strength falls with temperature to about 400 MPa at 400 C and 320 MPa at 500 C, while ductility rises. **What is the density of Alloy 48?** The density of Alloy 48 / UNS K94800 is 8.20 g/cm3, equal to 0.296 lb/in3. **How is Alloy 48 forged and heat treated?** Alloy 48 is hot worked in the approximate range 1150 to 1200 C with finishing above 900 C, then cooled and annealed. Annealing is carried out between 850 and 1000 C in a protective atmosphere, followed by controlled cooling, because dimensional stability and a repeatable expansion coefficient depend on a fully annealed, cold-work-free structure. Jiangyin Jiangnan Metal Co., Ltd. forges the grade on 25 MN and 40 MN open-die hydraulic presses and rolls seamless rings up to 2,500 mm outside diameter. **Can Alloy 48 be welded and machined?** Yes. Alloy 48 is welded by manual metal arc, TIG, MIG, plasma and pulsed-arc processes using nickel-based consumables; MIG spray transfer and submerged-arc welding are not recommended for this alloy family. Weld metal expansion rarely matches the parent alloy, so welds should be kept out of the sealing zone. Machining is carried out in the annealed condition with high-speed-steel or carbide tooling: rough turning at 30 to 45 m/min with 0.25 to 0.4 mm/rev feed, finish turning at 45 to 60 m/min with 0.1 to 0.25 mm/rev, using sulphurised cutting oil or a 20:1 soluble oil. **What forms and sizes of Alloy 48 forgings are available?** Jiangyin Jiangnan Metal Co., Ltd. supplies Alloy 48 as seamless rolled rings, forged discs and hubs, round and flat bars, flanges, sleeves, bushings, tube sheets, shafts and near-net-shape open-die forgings to drawing. The plant envelope is rings to 2,500 mm outside diameter, discs to 1,800 mm diameter, shafts to 8 m in length, bar from 25 to 500 mm diameter and single-piece weights to 8,000 kg; the practical limit for any given Alloy 48 order also depends on melt lot size and is confirmed at quotation. **Which standards and certificates apply to Alloy 48 forgings?** Chemistry and product requirements follow ASTM F30 for sheet, strip, rod, bar, tubing and wire, with DIN 17745 and AFNOR NF A54-301 as the European composition standards and MIL-I-23011 Class 3 where a military designation is required. Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 as specified. Certificates are issued to EN 10204 3.1 as standard, or EN 10204 3.2 with third-party witness such as Lloyd's, DNV, BV, ABS or TUV on request. **What is the maximum service temperature of Alloy 48?** Alloy 48 is used for industrial thermostats up to 450 C (840 F). Above the inflection point of about 460 C the expansion coefficient rises sharply and the alloy loses its controlled-expansion behaviour, so it should not be specified as an expansion-matched material above that temperature. For oxidising service above 500 C consider Incoloy 800H or Inconel 600 instead. **What is the lead time for Alloy 48 forgings?** Typical lead time for Alloy 48 forged rings, bars and discs is 8 to 12 weeks from order confirmation, driven mainly by melt scheduling because the grade is produced in dedicated lots rather than held in stock. Orders requiring EN 10204 3.2 third-party witness add roughly 2 weeks. Send a drawing or size list to sales@steelforgepieces.com or call 0086-189-2135-9659 for a quotation within 24 hours. ## References 1. ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys, ASTM International. 2. ASTM F29, Standard Specification for Dilatometric Linear Thermal Expansion of Electronic Materials, ASTM International. 3. DIN 17745, Wrought nickel-iron alloys with defined physical properties, Deutsches Institut fuer Normung. 4. AFNOR NF A54-301, composition of controlled-expansion nickel-iron alloys. 5. Special Metals Corporation, The NILO and NILOMAG Nickel-Iron Alloys, publication SMC-031. Source of the expansion, resistivity, mechanical and physical data tabulated for the 48 % Ni alloy class. 6. ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International; chapter on controlled-expansion alloys. 7. ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International; open-die forging and ring rolling practice. 8. EN 10204, Metallic products, types of inspection documents, CEN. 9. EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN. 10. SEP 1921, Ultrasonic testing of forgings, Stahl-Eisen-Pruefblatt. 11. ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International. 12. ASTM E8 / ISO 6892-1, tensile testing of metallic materials. 13. MIL-I-23011, Iron-Nickel Alloys for Glass-to-Metal Sealing, Class 3 (48 % nickel). Standards are cited by number without revision; procure against the revision in force at your contract date. ## Request a quotation Send a drawing, a sketch or a size list. We reply within 24 hours with price, achievable size, lead time and the certification package. If the application is a glass seal, tell us the glass, because it changes the answer. Jiangyin Jiangnan Metal Co., Ltd. | Open-Die Forging Factory Address: No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China Phone: 0086-189-2135-9659 Email: sales@steelforgepieces.com WhatsApp: https://wa.me/8618921359659 Web: https://www.steelforgepieces.com/ ## Related grades - Invar 36: https://www.steelforgepieces.com/Nickel-Alloy/Invar-36.html - Invar 42 / Alloy 42: https://www.steelforgepieces.com/Nickel-Alloy/Invar-42.html - NI-SPAN-C Alloy 902: https://www.steelforgepieces.com/Nickel-Alloy/NI-SPAN-C-Alloy-902.html - Incoloy A-286: https://www.steelforgepieces.com/Nickel-Alloy/Incoloy-A-286.html - Incoloy 800H: https://www.steelforgepieces.com/Nickel-Alloy/Incoloy-800H.html - Inconel 600: https://www.steelforgepieces.com/Nickel-Alloy/Inconel-600.html - Inconel 718: https://www.steelforgepieces.com/Nickel-Alloy/Inconel-718.html - Monel 400: https://www.steelforgepieces.com/Nickel-Alloy/Monel-400.html - All nickel alloys: https://www.steelforgepieces.com/Nickel-Alloy/ - All forged products: https://www.steelforgepieces.com/Products/ Trademark and disclaimer. The technical data on this page is published for informational and design guidance purposes and does not constitute a warranty of properties for any particular application. NILO and NILOMAG are registered trademarks of Special Metals Corporation; Pernifer of VDM Metals; Invar is associated with Aperam / Imphy Alloys; Kovar of CRS Holdings / Carpenter Technology; Inconel, Incoloy and Monel of Special Metals Corporation. Jiangyin Jiangnan Metal Co., Ltd. is not affiliated with, sponsored by or endorsed by any of these trademark holders and supplies material under the generic designations shown.