Controlled-expansion nickel-iron alloy · open-die forgings

Alloy 48 (UNS K94800 / ASTM F30) Forgings: Rings, Bars, Discs, Flanges

🇺🇸 UNS K94800
🇺🇸 ASTM F30
🇩🇪 DIN 17745
🇩🇪 W.Nr. 1.3922 · 1.3926 · 1.3927
🇫🇷 AFNOR NF A54-301
🇺🇸 MIL I-23011 Cl. 3
AWS 092

Published: 12 May 2022 · Last updated: 13 August 2026 · Technically reviewed by the Metallurgical Engineering Team, Jiangyin Jiangnan Metal Co., Ltd.

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 ×10⁻⁶/K over 20–100 °C rising only to 9.1 ×10⁻⁶/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.

Sources for the property data on this page are listed under References. Values are typical for the annealed alloy class; melt-specific results are reported on the material test certificate issued with each order.

Nickel: 48 %balance iron
CTE 20–300 °C: 8.7×10⁻⁶/K
Inflection point: 460 °C860 °F
Density: 8.20g/cm³ (0.296 lb/in³)
Tensile, annealed: 520MPa (75 ksi) typical
Melting point: 1450 °C2640 °F
Max ring OD: 2500mm, seamless rolled

What is Alloy 48?

Alloy 48 is a binary nickel-iron controlled-expansion alloy containing nominally 48 % nickel with 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 8.5–9.1 ×10⁻⁶/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.

Why 48 % Ni

Flat to 450 °C

Inflection point ≈ 460 °C, the highest of the three common binary Fe-Ni expansion grades, so the coefficient stays within ±0.3 ×10⁻⁶/K from room temperature to 450 °C.

Match

Soft glass

8.5–9.1 ×10⁻⁶/K coincides with soda-lime (≈9.0) and soft lead glass (≈9.2), the glasses used in lamps, valves and low-cost hermetic packages.

Condition

Always annealed

Residual cold work distorts the expansion coefficient. Forged Alloy 48 is supplied annealed at 850–1000 °C in a protective atmosphere, which is also the condition all published data refers to.

Equivalent designations and trade names for Alloy 48

Engineers meet this alloy under a dozen names. The generic designations below all describe the same 48 % Ni-Fe chemistry and Jiangyin Jiangnan Metal Co., Ltd. accepts purchase orders written against any of them.

Table 1. Alloy 48 / UNS K94800 designations, standards 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® is a registered trademark of VDM Metals; Invar® is associated with Aperam / Imphy Alloys. We do not sell under those brands. See the trademark notice below.

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® is a registered trademark 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.

What is the chemical composition of Alloy 48?

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 ×10⁻⁶/K per 1 % Ni in this range), so tight nickel control is what actually buys a repeatable seal.

Table 2. Alloy 48 (UNS K94800) chemical composition, weight %, as supplied by Jiangyin Jiangnan Metal Co., Ltd.
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 on the certificate 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 + 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.

Alloy 48 thermal expansion: the number you actually buy

This is the defining property of the grade. The table gives the mean linear coefficient of thermal expansion from 20 °C to each upper temperature, together with the total expansion over that range, for annealed material.

Table 3. Typical thermal expansion of Alloy 48 (UNS K94800), annealed
Temperature range (°C)	Range (°F)	Total expansion (×10⁻³)	Mean coefficient (×10⁻⁶/°C)	Mean coefficient (×10⁻⁶/°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 ×10⁻⁶/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 ~13 ×10⁻⁶/K typical of ordinary austenitic Fe-Ni. That is why 450 °C is quoted as the practical service ceiling.

Values are typical for annealed material of this alloy class and are given for design guidance. Where the coefficient is contractual, specify dilatometry over your own temperature range and an acceptance band. See how to specify an order, step 5.

Expansion & glass-match calculator

Enter a length and a temperature range to get the real dimensional change of an Alloy 48 part, then check how closely your sealing partner tracks it.

Part length or diameter (mm) Start temperature (°C) End temperature (°C)

Compare against

Where Alloy 48 sits on the expansion scale

Invar 36 (36 % Ni)1.5

Borosilicate 77403.3

Sealing glass 70524.6

Fe-Ni-Co (Kovar type)5.1

Alloy 42 (42 % Ni)5.3

Alumina ceramic 96 %7.0

Alloy 48 (48 % Ni)8.7

Soda-lime glass9.0

Soft lead glass9.2

Carbon steel12.0

304 stainless steel17.3

0×10⁻⁶/K, approximate mean values near room temperature18

Glass and ceramic coefficients are nominal figures for the material class and vary by formulation. Always use the expansion curve supplied by your glass maker for a production seal design.

Glass-to-metal sealing with Alloy 48

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 and the useful mismatch

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, which Jiangyin Jiangnan Metal Co., Ltd. can carry out or leave to your sealing house:

Decarburising anneal. Wet hydrogen at roughly 900–1050 °C removes surface carbon that would otherwise evolve CO at the seal interface and produce bubbles.
Controlled oxidation. Heating in air at 600–1000 °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 that matter 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.

What are the mechanical properties of Alloy 48?

Alloy 48 is a soft, extremely ductile alloy, closer to an annealed austenitic stainless in feel than to a structural steel. Elongation around 43 % and reduction of area around 72 % are what make it forgeable into rings and deep-drawn or spun components. Strength is not the reason anyone chooses it.

Table 4. Typical mechanical properties of Alloy 48, 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 %

Table 5. Hardness of Alloy 48
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 of Alloy 48

Table 6. Physical properties of Alloy 48 (UNS K94800), annealed
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 × 10³ ksi), annealed
Thermal conductivity at 20 °C	16.7	W/m·K (116 Btu·in/ft²·h·°F)
Electrical resistivity at 20 °C	47	µΩ·cm
Electrical resistivity at 100 / 200 / 300 °C	54 / 71 / 89	µΩ·cm
Electrical resistivity at 400 / 500 / 600 °C	104 / 116 / 121	µΩ·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)

These four grades cover almost all controlled-expansion work. Choosing between them is a single question: what does the metal have to track, and how hot does it get?

Table 7. Controlled-expansion alloy comparison, annealed material
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 (×10⁻⁶/K)	1.5	5.3	8.5	6.0
CTE 20–300 °C (×10⁻⁶/K)	5.5	5.3	8.7	5.1
CTE 20–400 °C (×10⁻⁶/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 (µΩ·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 300–450 °C, low room-temperature expansion is the wrong selection criterion. Compare mean coefficients over your range, not at ambient.

Related grade pages: Invar 36 forgings · Invar 42 / Alloy 42 forgings · NI-SPAN-C Alloy 902 (constant-modulus Ni-Fe alloy for springs and transducers).

Controlled-expansion grade selector

Tell it what the part must match and how hot it runs; it returns the grade the physics supports, including when the answer is not Alloy 48.

What must the part match? Maximum service temperature (°C)

Screening guidance only. Final material selection for a hermetic or safety-critical seal should be confirmed by your own qualification testing.

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 1150–1200 °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: the step that sets the property you are buying

Anneal at 850–1000 °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 850–1000 °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 we use for this grade

Open-die forgingShafts, blocks, discs and sleeves. Multi-step incremental reduction on 25 MN and 40 MN presses.
Seamless ring rollingRings from 200 mm to 2,500 mm OD with circumferential grain flow. Preferred route for seal rings and flanges.
Upset forgingShort, large-section discs, hubs and tube-sheet blanks.
Near-net-shapeCuts machining stock by roughly 30–50 % on profiled parts. Worth doing when the alloy is this expensive per kilogram.

Welding and machining Alloy 48

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.

Table 8. Starting machining parameters for annealed Alloy 48
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, Ø 1.6 mm	15–18 m/min peripheral	0.03 mm/rev	peck cycle
Drilling, Ø 3.2 mm	15–18 m/min peripheral	0.05 mm/rev	peck cycle
Drilling, Ø 12.7 mm	15–18 m/min peripheral	0.13 mm/rev	peck cycle
Drilling, Ø 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.

Alloy 48 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.

Forged forms available in Alloy 48 / UNS K94800

Seamless rolled rings

Rectangular, contoured and T-section rings with circumferential grain flow: seal rings, retaining rings, flange blanks.

Forged discs & hubs

Solid or trepanned discs for end plates, closures and instrument bodies.

Round & flat bars

Cut-to-length forged bar stock for machining shops, thermostat rods and sealing pins.

Flanges

Weld-neck, blind and custom-profile flanges forged to drawing.

Sleeves, bushings & spacers

Hollow forgings for feedthroughs, positioning devices and instrument mountings.

Tube sheets & plates

Forged and rolled plate blanks, drilled to drawing on request. See forged tube sheets.

Shafts & spindles

Long open-die forgings, rough or finish machined.

Blocks & blanks

Forged blocks for onward machining, supplied annealed with generous stock.

Near-net-shape forgings

Profiled to your drawing to cut machining loss on an expensive alloy.

Table 9. Plant forging envelope (all grades) and equipment
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 × 4 × 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 1,000× · 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 200–2,000 mm OD range.

Alloy 48 forging weight calculator

Density 8.20 g/cm³. Use the result to populate an RFQ, and remember the forged weight is higher than the finished weight.

Shape

Outside diameter (mm) Inside diameter (mm) Length / height (mm)

Machining allowance

Standards, testing and certification

Testing performed

Table 10. Inspection and test scope for Alloy 48 forgings
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 TÜV) 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

Primary application

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. Forged rings, sleeves and machined pins carry the seal.

Thermal control

Industrial thermostats to 450 °C

Thermostat bodies, rods and bimetal elements where the expansion coefficient must stay predictable across the whole regulating range. The 460 °C inflection point is the reason this grade rather than Alloy 42.

Electrical

Circuit breakers & temperature regulators

Trip elements and regulator components that convert a temperature change into a repeatable displacement.

Instruments

Precision and scientific instruments

Frames, spacers and mountings where a defined, stable expansion is more valuable than strength, including clock balance wheels and regulator components.

Vacuum & electronics

Vacuum devices and feedthroughs

Housings, flanges and bushings for microelectronic and vacuum hardware using soft-glass insulation.

Process equipment

Sealed joints in process hardware

Valve parts, seat rings, sleeves and tube sheets in assemblies that carry a glass or ceramic joint. See forged valve seat rings.

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

Seven lines on a purchase order remove almost every ambiguity that delays an Alloy 48 quotation.

State the generic designationAlloy 48 / UNS K94800 / ASTM F30, plus W.Nr. 1.3922 or DIN 17745 for European projects. Ordering under a trademark such as NILO 48 or Pernifer 48 restricts the order to that producer.
Declare the sealing partnerName 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.
Specify the delivery conditionAnnealed, 850–1000 °C, protective atmosphere. Cold-worked material will not reproduce the published expansion values.
Define shape and machining stockForged shape, finished dimensions and the allowance you expect, or send the drawing and let us propose the forging envelope.
Call out expansion testing if contractualDilatometry range, acceptance band and sample position. Chemistry alone does not guarantee a coefficient.
Specify NDTUltrasonic standard and class (EN 10228-3, SEP 1921 or ASTM A388), plus any penetrant requirement and the surfaces concerned.
Fix certification and commercial termsEN 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 ×10⁻⁶/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 µm 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

A purchase order that says "NILO 48" can technically only be filled by Special Metals. 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. Always write the annealing requirement on the order.

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. If your part sees 500 °C, the grade is wrong regardless of strength.

5. Expecting corrosion resistance

With ≤0.25 % Cr this alloy rusts like plain steel. Protect it, or choose a chromium-bearing grade for the corrosive part of the assembly.

6. Welding through the sealing zone

Filler metal and HAZ do not share the parent expansion curve. Move the joint, or re-anneal and re-qualify.

7. Machining after the final anneal

Heavy final cuts reintroduce cold work at exactly the surface that has to hold the seal. Sequence the operations on the drawing.

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. Clean before heating, every time.

Alloy 48 RFQ text generator

Fill in what you know; copy the generated text into an email to sales@steelforgepieces.com or send it over WhatsApp.

Forged shape Quantity (pieces)

Dimensions (free text)

Sealing partner / application Certification

Ultrasonic testing Expansion test

Delivery term Destination

Anything else we should know Your RFQ

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 is 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. This 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 about Alloy 48

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 ×10⁻⁶ per kelvin between 20 and 500 °C, is deliberately 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® is a registered trademark of VDM Metals, and Invar® is a registered trademark 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 ×10⁻⁶/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. Full table: thermal expansion data.

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 ×10⁻⁶/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 ×10⁻⁶/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 ×10⁻⁶/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 ×10⁻⁶/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, which is why Alloy 48 holds a flat expansion curve to the highest temperature of the three. Side-by-side data: comparison table.

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. Use this figure when converting a machined drawing volume into forging weight for an RFQ, or use the weight calculator above.

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 TÜV 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. Alloy 48 is a controlled-expansion alloy, not a corrosion-resistant or high-temperature structural alloy; 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

ASTM F30, Standard Specification for Iron-Nickel Sealing Alloys, ASTM International, West Conshohocken, PA.
ASTM F29, Standard Specification for Dilatometric Linear Thermal Expansion of Electronic Materials (wire product requirements for related grades), ASTM International.
DIN 17745, Wrought nickel-iron alloys with defined physical properties, Deutsches Institut für Normung.
AFNOR NF A54-301 (composition of controlled-expansion nickel-iron alloys), Association Française de Normalisation.
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 on this page.
ASM Handbook, Volume 2: Properties and Selection: Nonferrous Alloys and Special-Purpose Materials, ASM International; chapter on controlled-expansion alloys.
ASM Handbook, Volume 14A: Metalworking: Bulk Forming, ASM International; open-die forging and ring rolling practice.
EN 10204, Metallic products, types of inspection documents, CEN, Brussels.
EN 10228-3, Non-destructive testing of steel forgings, Part 3: Ultrasonic testing of ferritic or martensitic steel forgings, CEN.
SEP 1921, Ultrasonic testing of forgings, Stahl-Eisen-Prüfblatt, Verein Deutscher Eisenhüttenleute.
ASTM A388, Standard Practice for Ultrasonic Examination of Steel Forgings, ASTM International.
ASTM E8 / ISO 6892-1, tensile testing of metallic materials.
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. Property values on this page are typical for the annealed alloy class and are provided for design guidance. The values that govern a delivery are those on the material test certificate issued with it.

Request an Alloy 48 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
📍 No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
📞 0086-189-2135-9659 · 📧 sales@steelforgepieces.com

Email us WhatsApp Call 0086-189-2135-9659 Contact page

Related grades and forged products

Disclaimer and trademark notice. 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; Hastelloy® of Haynes International; Nitronic® and 17-4 PH® of Cleveland-Cliffs Inc. 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. All other trademarks are the property of their respective owners.