Precision Alloy 4J32 (Super-Invar / UNS K93500) Fe-Ni-Co Ultra-Low Thermal Expansion Precision Alloy Introduction

1. Material Overview

Alloy 4J32, internationally named Super-Invar, UNS K93500, Russian grade 32HKD, French Superieur Invar, is a classic iron-nickel-cobalt ultra-low expansion precision alloy standardized under national YB/T 5241 and international ASTM F1684 specifications. Different from conventional 4J36 Invar and glass-sealing 4J29 Kovar, 4J32 adopts optimized Ni-Co composite alloy design to realize ultra-minimal linear thermal expansion coefficient within -60°C ~ 80°C, delivering better dimensional stability than ordinary Invar alloys under room-temperature alternating temperature environments.

This alloy relies on the Invar magnetic volume compensation effect to restrain thermal expansion deformation, featuring extremely low CTE in near-ambient temperature zone, good ductility, fine cold working performance and stable austenitic matrix after standardized stabilization heat treatment. It can be matched with low-expansion quartz glass, optical glass and precision ceramic substrates for ultra-high precision instrument frames, optical lens holders, resonant cavity components and metering standard parts. Compared with 4J36, 4J32 achieves lower expansion rate at medium-low temperature, while its shortcoming lies in weaker low-temperature microstructure stability below -30°C with risk of martensite phase transformation, so it is mainly applied within the temperature range of -60°C ~ 100°C.

We supply full-series finished and semi-finished Alloy 4J32 products including cold rolled strips, thin foils, sheets, round bars, fine wires, thin-wall precision seamless tubes and custom miniature precision stampings, widely used in aerospace optoelectronics, precision metering instruments, semiconductor packaging, optical equipment and high-reliability electronic communication components worldwide.

2. Standard Chemical Composition (wt%)

All element limits fully comply with YB/T 5241 official industrial standard, all data sourced from authoritative alloy technical datasheets without arbitrary modification; strict impurity control guarantees consistent ultra-low expansion performance batch to batch:

Note: Nickel is the core element triggering the Invar ultra-low expansion effect; cobalt optimizes the CTE curve to reduce expansion coefficient within -60~80°C; trace copper improves machinability and homogenizes alloy microstructure. Ultra-low carbon prevents carbide precipitation which would break dimensional stability; strictly limited P and S avoid brittle intergranular inclusions that deteriorate expansion consistency.

3. Standard Heat Treatment & Core Physical / Mechanical Properties

3.1 Standard Stabilization Heat Treatment Procedure

To lock stable ultra-low thermal expansion performance, all finished Alloy 4J32 parts must undergo complete three-stage stabilization heat treatment under hydrogen or vacuum protective atmosphere:
1. Homogenization heating: 830~880°C, hold 60min, rapid water quenching to eliminate component segregation;
2. Intermediate tempering: 310~330°C, hold 60~240min to release quenching residual stress;
3. Low-temperature stabilization aging: 90~120°C long-time holding to stabilize austenitic matrix and suppress phase transformation tendency.
Cold-worked semi-finished products adopt stress relief annealing at 530~550°C to remove stamping/cutting residual stress without shifting expansion characteristics. Each production batch is attached with complete heat treatment logs, PMI spectral inspection reports and linear expansion coefficient test certification documents.

3.2 Room-Temperature Mechanical Properties (Stabilized Annealed State)

• Tensile Strength: ≥490 MPa
• 0.2% Offset Yield Strength: ≥240 MPa
• Elongation (50mm gauge length): ≥35%
• Brinell Hardness: ≤125 HB
• Elastic Modulus: 142 GPa

3.3 Key Physical & Thermal Expansion Characteristic Parameters

• Density: 8.12 g/cm³
• Thermal Conductivity: 13.9 W/(m·°C)
• Curie Temperature: ~230°C
• Melting Range: 1430 ~ 1450°C
• Typical Average Linear Expansion Coefficient (after standard stabilization treatment, unit: ×10⁻⁶/°C):
     
• 20 ~ 50°C: 0.7
• 20 ~ 100°C: ≤1.0
• 20 ~ 200°C: 1.4
• 20 ~ 300°C: 4.3

Alloy 4J32 maintains ultra-low expansion only within -60°C ~ 100°C; above 230°C, CTE rises sharply as Curie temperature is exceeded. Below -30°C, long-term service may trigger martensite transformation leading to dimensional drift, so low-temperature scenarios below -60°C prefer Alloy 4J36 instead.

4. Core Performance Advantages

4.1 Ultra-Low Thermal Expansion in Near-Ambient Temperature Zone

Within -60°C ~ 80°C, Alloy 4J32 delivers lower linear expansion coefficient than conventional 4J36 Invar, achieving minimal dimensional drift under daily temperature fluctuation. It eliminates measurement error, optical focal shift and frequency offset caused by ambient temperature change, the top choice for high-precision metering and optical structural parts.

4.2 Stable Dimensional Consistency After Standard Stabilization Treatment

Complete three-stage heat treatment homogenizes alloy grain structure, eliminates internal segregation and residual stress, locking repeatable ultra-low expansion performance. Mass-produced components show tiny batch-to-batch CTE deviation, fully satisfying large-volume manufacturing requirements for precision electronic and aerospace parts.

4.3 Excellent Cold Fabricability for Miniature Precision Parts

Annealed 4J32 features outstanding ductility, supporting ultra-thin foil rolling, deep drawing, fine wire drawing, precision CNC turning and laser cutting. It can be processed into micro frames, tiny lens holders, thin resonant cavity shells and ultra-thin instrument standard strips without cracking during cold forming.

4.4 Matching Expansion with Low-Expansion Optical & Quartz Glass

Its CTE curve closely matches quartz glass and low-expansion borosilicate optical glass in room temperature range, greatly reducing thermal stress at metal-glass assembly interfaces. It avoids lens frame deformation, optical element displacement and seal microcracks during temperature cycling, widely adopted for aerospace optical remote sensing components.

4.5 Moderate Atmospheric Corrosion Resistance & Vacuum Compatibility

The alloy resists mild atmospheric oxidation, fresh water and weak salt spray corrosion without surface rust under normal storage conditions. After high-temperature hydrogen stabilization treatment, internal gas content is extremely low, suitable for high-vacuum optical instruments and hermetic precision packaging devices.

5. Full Product Range & Specifications

We supply complete YB/T 5241 & ASTM F1684 standard Alloy 4J32 precision alloy semi-finished and finished products tailored for ultra-precision dimensional stability systems:

• Cold Rolled Strips, Sheets & Ultra-Thin Foils: Foils 0.03~0.5mm, medium strips 0.5~6.0mm, thick plates 6~120mm; customized slitting, flatness correction and precision surface polishing for optical frame blanks
• Round Bars & Fine Wires: Hot rolled & cold drawn bars Φ3~130mm, fine wires Φ0.08~6.0mm for instrument standard parts, clock balance wheels and electronic resonant components
• Thin-Wall Precision Seamless Tubes: OD 2~75mm, wall thickness 0.1~7mm for vacuum resonant cavities, optical instrument sleeve housings and micro sensor shells
• Custom Precision Stampings & Miniature Machined Parts: Aerospace optical lens frames, metering standard gauge bases, semiconductor low-expansion packaging frames and radio frequency resonant cavity structural components

Factory Quality Assurance: Batch PMI spectral chemical inspection, full linear expansion coefficient testing, tensile & hardness mechanical testing, 100% surface defect visual inspection, vacuum degassing performance verification. All shipments are delivered with EN 10204 3.1 official mill test certificates.

6. Main Industrial Application Fields

• Aerospace Optoelectronic Equipment: Satellite remote sensing optical lens support frames, aerospace precision optical system structural parts, airborne high-precision navigation instrument housings, star sensor base components
• Precision Metering & Measuring Instruments: Standard length gauges, optical interferometer base frames, high-precision dial instrument core parts, thermal compensation structural components for analytical instruments
• Semiconductor & Microelectronics Packaging: Low-expansion chip carrier frames, precision hermetic packaging bases, microwave radio frequency resonant cavity shells, high-stability oscillator component blanks
• Optical & Laser Equipment: Laser tube fixing frames, optical fiber collimator support parts, quartz glass metal matching assembly components, precision optical bench structural parts
• Timing & Radio Frequency Components: High-precision clock balance wheels, crystal oscillator fixing bases, microwave filter low-drift structural parts, precision thermal bimetal passive layers

7. Full-Process Quality Control & Permanent Laser Marking

All Alloy 4J32 precision alloy products adopt unified full-process inspection workflow consistent with our complete alloy portfolio: Raw material smelting composition verification → Hot rolling / cold drawing forming → Three-stage vacuum/hydrogen stabilization heat treatment → Precision slitting / CNC machining → Linear expansion coefficient performance testing → Mechanical property inspection → High-purity surface cleaning & passivation → Laser permanent marking → Anti-oxidation vacuum moisture-proof packaging.

Finished products are free from surface scratches, oxide inclusions, delamination and dimensional out-of-tolerance defects. Standard laser marking includes brand information, Alloy 4J32 / Super-Invar / UNS K93500 grade, executed YB/T 5241 & ASTM F1684 standards, heat batch number, product dimension specification and production serial number, achieving full traceability for international precision instrument manufacturers’ third-party inspection and bulk procurement acceptance.

8. Future Industry Development Trends

Digital CTE Simulation Design Standardization: FEA thermal expansion stress simulation becomes mandatory pre-production design procedure, optimizing component wall thickness and assembly clearance to minimize temperature-induced measurement drift for high-precision equipment.

High-Purity Ultra-Thin Foil Demand Surge: Miniaturization of aerospace optical sensors and high-end semiconductor chips drives rising demand for 0.03~0.2mm ultra-thin stabilized 4J32 foils for lightweight ultra-precision structural assemblies.

Custom Low-Temperature Stabilized Grade Upgrading: Custom modified 4J32 with optimized Ni-Co ratio will be developed to improve low-temperature austenite stability, expanding applicable temperature range to -100°C cryogenic precision equipment.

Integrated Matching Precision Component Serialization: Standardized 4J32 finished machined lens frames, resonant cavity shells and packaging bases realize one-stop component supply for optoelectronic EPC manufacturers, cutting customer secondary processing costs.

Low-Carbon Near-Net-Shape Precision Forming Technology Popularization: Precision stamping and additive manufacturing replace traditional full-cutting processing to reduce raw material waste; continuous low-energy hydrogen heat treatment complies with global carbon neutrality infrastructure standards.

Contact us for more product information today.