Low-expansion alloy forgings · ASTM F1684
UNS K93600 (Invar 36) Forgings: Rings, Flanges, Bars, Discs and Shafts
Open-die forged UNS K93600 produced in Jiangyin, Jiangsu, China by Jiangyin Jiangnan Metal Co., Ltd. Melted EAF + VOD + ESR, forged, stabilisation heat treated, ultrasonically tested and certified to EN 10204 3.1 or 3.2.
- UNS
- K93600
- Also known as
- Invar 36 / Alloy 36
- Werkstoff
- 1.3912
- Nickel
- 35.0–37.0 %
- CTE 20–100 °C
- 1.2–1.6 ppm/K
- Density
- 8.05 g/cm³
- Curie point
- 279 °C
- Specification
- ASTM F1684
- Ring diameter
- 80–6,000 mm
- Piece weight
- 10–15,000 kg
- Certification
- EN 10204 3.1 / 3.2
- Supplier
- Jiangyin Jiangnan
Grade summary. UNS K93600 is a nickel-iron low expansion alloy with nominally 36 % nickel and the balance iron. It is also sold as Invar 36, Alloy 36, NILO 36 and FeNi36. Its coefficient of thermal expansion is about one tenth that of carbon steel, so it is specified where a part must hold its dimensions across a temperature range.
Supply. Jiangyin Jiangnan Metal Co., Ltd. forges UNS K93600 at No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. Product forms are seamless rolled rings, flanges, round bars, discs, shafts, sleeves, bushings and tube sheets, from 80 mm to 6,000 mm diameter and 10 kg to 15,000 kg per piece, to ASTM F1684. For quotations contact sales@steelforgepieces.com or +86-189-2135-9659.
What is UNS K93600?
UNS K93600 is the Unified Numbering System designation for the 36 % nickel-iron low expansion alloy originally developed as Invar. It is a single phase austenitic solid solution and is not hardenable by heat treatment. The low expansion comes from magnetostriction: below the Curie temperature the magnetic contribution to the lattice offsets most of the normal thermal expansion.
Mean expansion between 20 °C and 100 °C is 1.2 to 1.6 ppm per Kelvin. Ordinary steels are 11 to 15 ppm/K. The low expansion range runs from cryogenic temperatures to about 260 °C. Above the Curie point near 279 °C the magnetic ordering is lost and expansion returns to normal metallic values, so 260 °C is the practical service limit for dimensional work.
The alloy is ferromagnetic at room temperature. It machines like austenitic stainless steel and welds with matching filler. It creeps under sustained load, which has to be allowed for in loaded structures.
UNS K93600 equivalent grades and specifications
The alloy appears under several trade and national designations. Invar and NILO are registered trademarks, so UNS K93600 is the designation used on drawings, purchase orders and material certificates.
| System | Designation | Note |
|---|---|---|
| UNS | K93600 | K93601 = controlled-purity variant |
| Trade names | Invar 36, NILO 36, Alloy 36 | Registered trademarks |
| Common name | FeNi36, 64FeNi | US usage |
| Werkstoff | 1.3912 | German material number |
| Primary spec | ASTM F1684 | Low thermal expansion alloys |
| Sheet & strip | ASTM B388, ASTM B753 | Not forging forms |
| German | DIN 1715 | Sheet and strip |
| Military | MIL-S-16598, MIL-I-23011 Cl. 7 | Legacy defence specs |
Cross-references are for guidance. The governing document is the specification called out on the drawing.
UNS K93600 chemical composition
Composition limits below are per ASTM F1684 for UNS K93600. Ladle and product analysis for each heat is reported on the mill test certificate.
| Limit | Ni | Fe | Mo | C | Cu | Mn | Si | P | S | Cr |
|---|---|---|---|---|---|---|---|---|---|---|
| Min | 35.0 | — | — | — | — | — | — | — | — | — |
| Max | 37.0 | Bal. | 0.50 | 0.10 | 0.50 | 0.60 | 0.35 | 0.025 | 0.025 | 0.50 |
The melting route for our UNS K93600 forging stock is EAF + VOD + ESR. Vacuum oxygen decarburisation controls carbon and gas content. Electroslag remelting refines the solidification structure and reduces segregation and non-metallic inclusions. VIM + ESR and VIM + VAR routes are available where a customer specification requires them.
Physical properties of UNS K93600
Nominal room temperature values for annealed UNS K93600. Certified values are issued with each heat.
| Property | Metric | Imperial |
|---|---|---|
| Density | 8.05 g/cm³ | 0.291 lb/in³ |
| Mean CTE, 20–100 °C | 1.2–1.6 × 10⁻⁶ /K | 0.7–0.9 × 10⁻⁶ /°F |
| Useful low-expansion range | cryogenic to 260 °C | cryogenic to 500 °F |
| Curie temperature | 279 °C | 534 °F |
| Melting range | 1,427 °C | 2,600 °F |
| Modulus of elasticity | 141 GPa | 20.5 × 10⁶ psi |
| Thermal conductivity, 20 °C | 10.2 W/m·K | 70 BTU·in/hr·ft²·°F |
| Specific heat | 515 J/kg·K | 0.123 BTU/lb·°F |
| Electrical resistivity | 0.82 µΩ·m | 494 Ω·cmil/ft |
| Magnetic state at 20 °C | Ferromagnetic, below Curie point | |
Expansion is sensitive to composition and thermal history. Where a maximum CTE is specified, state it on the enquiry so that the heat and the stabilisation cycle can be selected to meet it.
Mechanical properties at temperature
Typical short time tensile properties of UNS K93600 from 20 °C to 600 °C. Strength falls with temperature and ductility rises.
| Temperature | 20 °C 68 °F | 100 °C 212 °F |
200 °C 392 °F | 300 °C 572 °F |
400 °C 752 °F | 500 °C 932 °F |
600 °C 1112 °F |
|---|---|---|---|---|---|---|---|
| Tensile strength, MPa (ksi) | 490 (71) | 427 (62) | 427 (62) | 407 (59) | 352 (51) | 290 (42) | 207 (30) |
| 0.2 % yield strength, MPa (ksi) | 241 (35) | 179 (26) | 110 (16) | 90 (13) | 90 (13) | 90 (13) | 76 (11) |
| Elongation, % | 42 | 43 | 45 | 48 | 53 | 59 | 68 |
UNS K93600 retains strength and toughness at cryogenic temperatures. As a single phase austenitic alloy it has no ductile to brittle transition of the kind that limits ferritic steels in cold service, and it is used for LNG containment and cryogenic transfer hardware.
Stabilisation heat treatment for UNS K93600 forgings
UNS K93600 forgings are given a three stage stabilisation treatment. The objective is dimensional stability rather than hardness.
| Stage | Temperature | Hold | Cooling | Purpose |
|---|---|---|---|---|
| 1 | 830 °C (1525 °F) | 30 min | Water quench | Solution / homogenise |
| 2 | 300 °C (570 °F) | 1 h | Air cool | Relieve quench stress |
| 3 | 100 °C (212 °F) | 48 h | Air cool | Long-term dimensional stabilisation |
Stage 3 controls long term drift and is required for metrology frames, optical benches and laser hardware. Where parts are heavily machined, an intermediate stress relief between roughing and finishing is recommended and can be included in the routing.
UNS K93600 forged products we manufacture
Jiangyin Jiangnan Metal Co., Ltd. is a forging factory rather than a stockist. UNS K93600 is forged to customer drawing in the forms below.
Seamless rolled rings
Plain and contoured rolled rings, including gear ring blanks, rolled on 3 m and 6 m ring mills.
Forged flanges
Weld-neck, slip-on, blind and custom-profile flanges for cryogenic and vacuum service.
Round bars and blocks
Forged round bar, flat bar, square and rectangular blocks, stepped billets.
Discs and tube sheets
Forged discs, plates and tube sheets for heat exchangers and instrument bases.
Shafts and spindles
Straight, stepped and eccentric shafts, spindles and positioning-device shafting.
Sleeves and bushings
Forged sleeves, bushings, hollow bar and forged pipe with bored centre.
Size and weight capability
| Parameter | Range |
|---|---|
| Rolled ring outside diameter | 80 mm – 6,000 mm |
| Open-die forging diameter | 100 mm – 6,000 mm |
| Length | 100 mm – 12,000 mm |
| Piece weight | 10 kg – 15,000 kg |
| Forging hammers | 1 t / 3 t / 6 t / 9 t |
| Hydraulic press | 4,500 t |
| Ring rolling mills | 3 m and 6 m |
| Delivery condition | As-forged, heat treated, rough machined or finish machined |
Figures cover the open-die forging shop generally. The achievable envelope for a specific UNS K93600 geometry is confirmed against the drawing.
How a UNS K93600 forging is produced
- Melting. EAF + VOD + ESR, or VIM + ESR / VIM + VAR to specification, giving a clean ingot with low segregation.
- Forging. Ingot upset and drawn on 1 to 9 t hammers or the 4,500 t press. Rings are pierced and rolled on the 3 m or 6 m mill to give continuous circumferential grain flow.
- Heat treatment. The three stage 830 °C / 300 °C / 100 °C stabilisation cycle.
- Machining. Rough or finish machining to drawing, with intermediate stress relief for precision parts.
- Testing. Chemistry, tensile, hardness, ultrasonic and dimensional inspection.
- Certification and despatch. EN 10204 3.1 or 3.2 documentation issued with the shipment.
Testing, inspection and certification
- Ultrasonic testing to EN 10228-3, SEP 1921 or ASTM A388, to the acceptance class stated on the order.
- Chemical analysis. Ladle and product analysis reported against ASTM F1684 limits.
- Mechanical testing. Tensile, elongation, reduction of area and hardness. Low temperature impact testing on request.
- Thermal expansion testing where a maximum CTE is specified.
- Dimensional inspection against the drawing before despatch.
- Certification to EN 10204 3.1, or EN 10204 3.2 with third party witness by TÜV, SGS, BV, Lloyd's Register or similar.
Where UNS K93600 forgings are used
Cryogenic and LNG
Membrane and containment components for LNG tankers, cryogenic transfer lines, valve bodies and flanges where thermal contraction must be minimised.
Aerospace composite tooling
Forged blocks, discs and ring segments for autoclave-cured composite moulds, where tool expansion must match carbon fibre.
Precision instruments and optics
Optical benches, laser cavity structures, optoelectronic mounts, telescope and interferometer hardware, dimensionally stable frames.
Metrology and standards
Length standards, gauge frames, comparators, coordinate measuring machine structures and other measuring devices.
Electronics and microwave
Microwave cavity resonators, echo boxes and filters, magnetic shielding, transformer cores, sealed electronic housings.
Thermostatic and timing
Thermostat rods, bimetal elements, circuit-breaker parts, clock balance wheels and pendulum rods.
Machining and welding UNS K93600
Machining
UNS K93600 machines like an austenitic stainless steel. It work hardens and forms a built-up edge. Use sharp positive rake tooling, rigid setups, moderate surface speeds, a continuous firm feed and generous coolant, so that the tool cuts below the hardened layer. For precision parts, rough machine, stress relieve, then finish machine.
Welding
The alloy is welded by GTAW, GMAW and SMAW with matching Invar 36 filler. Preheat is not required. Keep the joint clean, use low heat input and stringer beads, and avoid contamination with sulphur or lead. Post-weld stabilisation restores dimensional predictability across the joint.
Design note
UNS K93600 creeps under sustained stress. Keep working stresses low in load bearing precision structures and allow for stabilisation after machining.
Frequently asked questions about UNS K93600
Is UNS K93600 the same as Invar 36?
Yes. UNS K93600 is the Unified Numbering System designation for Invar 36. The same alloy is sold as Alloy 36, NILO 36, FeNi36, 64FeNi and Werkstoff 1.3912. Invar and NILO are registered trademarks, so UNS K93600 is the designation to use on drawings and purchase orders. UNS K93601 is a controlled purity variant of the same alloy.
What is the thermal expansion coefficient of UNS K93600?
1.2 to 1.6 ppm per Kelvin between 20 °C and 100 °C, about one tenth that of carbon steel. Expansion stays low from cryogenic temperatures to about 260 °C, then rises as the alloy approaches its Curie temperature near 279 °C. Values depend on composition and thermal history and are confirmed by test where a maximum CTE is specified.
Which specification covers UNS K93600 forgings?
ASTM F1684, Standard Specification for Iron-Nickel and Iron-Nickel-Cobalt Alloys for Low Thermal Expansion Applications. Related documents include ASTM B388 and ASTM B753 for sheet and strip, DIN 1715, MIL-S-16598 and MIL-I-23011 Class 7. We supply to ASTM F1684 and work to customer specifications on request.
What is the largest UNS K93600 forged ring you can make?
Our open-die shop rolls rings from 80 mm to 6,000 mm outside diameter, with piece weights from 10 kg to 15,000 kg and lengths to 12,000 mm, using 1 to 9 t hammers, a 4,500 t hydraulic press and 3 m and 6 m ring mills. The achievable envelope for a specific UNS K93600 geometry depends on wall thickness and height, so send the drawing for confirmation.
Is UNS K93600 magnetic?
Yes. It is ferromagnetic below its Curie temperature of about 279 °C, and the magnetic ordering is the source of the low expansion behaviour. Above the Curie point the alloy becomes paramagnetic and expands at normal metallic rates. Applications needing a non-magnetic low expansion material require a different alloy family.
Can UNS K93600 be used at cryogenic temperatures?
Yes. It retains strength and toughness at cryogenic temperatures and holds its low expansion behaviour below zero. As a single phase austenitic alloy it has no ductile to brittle transition, and it is used for LNG containment, cryogenic piping and cold side instrument structures.
How should UNS K93600 be machined?
Like an austenitic stainless steel. It work hardens, so use sharp positive rake tools, rigid setups, moderate speeds, a firm uninterrupted feed and plenty of coolant. For precision parts, rough machine first, stress relieve, then finish machine to size.
What certificates come with the forgings?
EN 10204 3.1 as standard, or EN 10204 3.2 with third party witness by TÜV, SGS, BV, Lloyd's Register or similar. Certificates carry heat number, chemical analysis, mechanical test results, heat treatment record and NDT report. Ultrasonic testing is performed to EN 10228-3, SEP 1921 or ASTM A388 as specified.
Do you supply UNS K93600 machined to finished size?
Yes. We supply as forged, heat treated, rough machined with allowance, or finish machined to drawing. For dimensionally critical parts the recommended sequence is rough machining, stabilisation, then finish machining, and this can be built into the routing.
How do I get a quotation?
Email sales@steelforgepieces.com or call +86-189-2135-9659 with the drawing or finished dimensions, quantity, specification such as ASTM F1684, delivery condition and required certification level. Include any maximum CTE, NDT class or third party inspection requirement, since these affect route and price.
Request a quotation for UNS K93600 forgings
Send a drawing or the finished dimensions and we will quote. State the quantity, the specification, the delivery condition (as forged, rough machined or finish machined) and the certification level required.
Jiangyin Jiangnan Metal Co., Ltd. — Open-Die Forging Factory
No.1 Chengxiqiao Road, Zhouzhuang Town, Jiangyin City, Jiangsu Province, China
Tel / WhatsApp: +86-189-2135-9659
Email: sales@steelforgepieces.com
Web: www.steelforgepieces.com
About the manufacturer
Jiangyin Jiangnan Metal Co., Ltd. is an open-die forging factory in Zhouzhuang Town, Jiangyin City, Jiangsu Province, China. The company employs around 460 people, including 9 senior engineers and 32 intermediate engineers, and covers the full route in house: raw material and melting, open-die forging and ring rolling, heat treatment, machining, and testing and inspection.
Materials forged include carbon steel, alloy steel, tool and die steel, stainless steel, and nickel and low expansion alloys, among them UNS K93600 (Invar 36), Invar 42, Kovar, the Inconel, Incoloy, Hastelloy, Monel and Nimonic families, and precipitation hardening stainless grades such as 17-4PH and A286.
Product forms cover seamless rolled rings, contoured rolled rings, forged flanges, round and flat bars, discs, blocks, tube sheets, shafts, spindles, sleeves, bushings, forged pipes, valve components and mill rolls.
Last reviewed . Values given are typical and for guidance. The mill test certificate issued with each order governs.