Alloy 42 Plate: Controlled Expansion Material Guide

Introduction

Alloy 42 Plate is a nickel-iron controlled-expansion alloy plate containing approximately 42% nickel, with iron as the balance. It is used where metal components must maintain dimensional stability or expand at a rate compatible with selected glass, ceramic and semiconductor materials. Typical applications include glass-to-metal seals, electronic package frames, semiconductor lead-frame components, vacuum devices, optical supports, thermostat parts and precision instrument assemblies.

Alloy 42 is commonly identified as UNS K94100, FeNi42, 4J42 or material number 1.3917, depending on the applicable specification and regional designation system. ASTM F30 is a commonly referenced standard for iron-nickel sealing alloys in plate, sheet, strip, bar and other wrought forms. Buyers should verify chemistry, thermal-expansion requirements, delivery condition, dimensions and inspection documents rather than relying only on the commercial name “Alloy 42.”

What Makes Alloy 42 a Controlled-Expansion Material?

The dimensions of most metals increase as temperature rises and decrease as temperature falls. When two bonded materials expand at different rates, thermal stress develops at the interface. In a glass-to-metal seal, electronic package or precision optical assembly, excessive mismatch may crack the brittle material, distort the component or reduce hermetic integrity.

The nickel content of Alloy 42 is controlled so that its thermal-expansion curve remains comparatively low and stable over a defined temperature range. The alloy is commonly associated with a low and relatively constant coefficient of expansion from ambient temperature to approximately 300°C, although the exact values depend on chemistry, heat treatment, prior cold work and the specified test interval.

This expansion behavior makes Alloy 42 useful for sealing and supporting components made from selected glass compositions, ceramics, silicon and related electronic materials. Compatibility must still be confirmed with the exact adjoining material. Two products described as “glass” may have significantly different coefficients of expansion.

Alloy 42 Plate Product Data

Specification Item	Typical Supply Options	Buyer Check
Material	Alloy 42, FeNi42, 4J42, UNS K94100	Confirm the exact standard and chemistry limits.
Product Forms	Plate, sheet, strip, flat bar, cut plate and machined blank	Define whether the requirement is true plate, thin sheet or a precision-ground blank.
Typical Thickness	Approximately 0.5-100 mm, subject to mill capability	State tolerance and machining allowance.
Width and Length	Mill plate, cut-to-size plate or drawing-based blanks	Provide finished size, cutting allowance and edge requirements.
Condition	Annealed, cold rolled, stress relieved or customer specified	Match the condition to stamping, machining and final dimensional-stability requirements.
Surface	Hot rolled, pickled, cold rolled, polished, ground or machined	Specify roughness, flatness and cosmetic acceptance separately.
Documentation	MTC, EN 10204 3.1, chemistry, mechanical and dimensional reports	Request thermal-expansion results when they are an acceptance requirement.

Chemical Composition

Alloy 42 is essentially a binary nickel-iron alloy, but residual and minor elements must be controlled because they can influence workability, oxidation, magnetic properties and thermal expansion. The values below are typical reference ranges. Final acceptance should follow the ordered standard and batch-specific mill certificate.

Element	Typical Range or Limit, %	Material Significance
Nickel, Ni	Approximately 41.0-43.0	Primary element controlling the thermal-expansion curve.
Iron, Fe	Balance	Forms the main alloy matrix with nickel.
Carbon, C	Typically 0.05 maximum	Restricted to support ductility and controlled properties.
Manganese, Mn	Typically 0.80 maximum	Controlled for melting quality and consistency.
Silicon, Si	Typically 0.30 maximum	May influence oxidation and sealing-surface behavior.
Chromium, Copper and Cobalt	Controlled residual limits	Excessive residual content may alter expansion behavior or processing response.

Mechanical and Physical Properties

Mechanical properties vary with plate thickness, rolling reduction, annealing cycle and final condition. Controlled-expansion applications often place greater importance on chemistry, expansion behavior, flatness and dimensional stability than on maximum strength.

Property	Typical Direction	Engineering Relevance
Density	Approximately 8.1 g/cm³	Used for component and shipping-weight calculations.
Tensile Strength	Condition-dependent; commonly moderate in annealed plate	Affects handling, machining, stamping and structural integrity.
Elongation	Higher in annealed material and lower after cold work	Important for forming, stamping and deep-drawing operations.
Thermal Expansion	Low and relatively stable over a defined temperature interval	Controls compatibility with glass, ceramics, silicon and precision assemblies.
Magnetic Character	Ferromagnetic under normal conditions	Must be reviewed near magnetically sensitive electronics.
Thermal Conductivity	Lower than many ordinary structural metals	Affects temperature equalization, sealing cycles and machining heat.

Standards and International Designations

Reference System	Common Designation	Procurement Note
UNS	K94100	Widely used designation for 42% nickel-iron controlled-expansion alloy.
ASTM	ASTM F30	Common specification reference for iron-nickel sealing alloys in wrought forms.
European Material Number	1.3917	Confirm the applicable EN, DIN or project specification.
Chinese Designation	4J42	Compare chemistry, expansion range and test requirements before substitution.
Composition Name	FeNi42 / 42Ni-Fe	Useful descriptive name but not a complete purchase specification.
Inspection Documentation	EN 10204 3.1 or agreed certificate	Specify whether actual thermal-expansion results are required.

Comparable designations should not be treated as automatically interchangeable. The chemistry limits, thermal-expansion test interval, product form, heat treatment and inspection requirements must be compared before approving a substitution.

Alloy 42 vs Invar 36, Kovar and Alloy 52

Material	Primary Character	Typical Selection Direction
Alloy 42	Approximately 42% Ni-Fe alloy with controlled expansion	Selected glass and ceramic seals, lead frames, semiconductor and precision electronic parts.
Invar 36	Very low expansion near ambient temperature	Metrology, optical structures, precision fixtures and dimensional standards.
Kovar	Fe-Ni-Co alloy designed for matched sealing with selected hard glasses and ceramics	Hermetic packages, vacuum devices and hard-glass sealing assemblies.
Alloy 52	Higher-nickel Fe-Ni controlled-expansion alloy	Selected glass, ceramic and electronic sealing systems requiring a different expansion curve.

Industrial Applications

Industry	Typical Alloy 42 Plate Component	Critical Requirement
Semiconductor Packaging	Lead-frame blanks, base plates, package frames and support components	Expansion compatibility, flatness, surface quality and precise dimensions.
Glass-to-Metal Sealing	Seal rings, frames, headers and feedthrough bases	Matching the expansion curve of the selected glass composition.
Vacuum Devices	Tube bases, windows, package supports and enclosure parts	Hermetic integrity, low contamination and stable sealing geometry.
Optical Equipment	Laser mounts, optical frames, detector supports and precision plates	Controlled movement during temperature changes.
Thermostatic Devices	Thermostat parts, thermoswitch components and laminated assemblies	Repeatable thermal response and controlled expansion.
Precision Instruments	Fixtures, measuring-system supports and machined structural plates	Dimensional stability, stress control and machining accuracy.

Machining, Forming and Heat Treatment

Machining

Alloy 42 can be machined using practices similar to those applied to nickel-iron alloys. It may work harden if the cutting tool rubs instead of cutting. Rigid setups, sharp tools, positive cutting geometry, steady feeds and effective coolant help control heat and surface finish.

Precision components should normally be rough machined before a suitable stress-relief or stabilization cycle, followed by finish machining. This sequence can reduce dimensional movement caused by releasing residual stresses from rolling, cutting or heavy stock removal.

Forming and Stamping

Annealed Alloy 42 plate and sheet have useful formability and can be stamped, bent and drawn into electronic and sealing components. Bend radius and forming direction should be selected according to thickness and condition. Cold working raises strength and hardness but may also alter residual stress and the thermal-expansion response.

Heat Treatment

Heat treatment may be used to restore ductility, control grain structure, relieve stress or prepare the material for a sealing operation. The correct cycle depends on product thickness, prior cold work and the final assembly process. Uncontrolled furnace exposure can create scale, distortion or property variation.

Where thermal expansion is critical, the purchaser should agree on the final material condition and whether expansion testing is performed before or after customer processing. Subsequent heavy cold work or an unsuitable heat cycle may change the delivered properties.

Limitations and Specification Risks

Not a stainless steel: Alloy 42 does not provide the general atmospheric and chemical corrosion resistance of stainless steel. Unprotected plate may oxidize or rust during humid storage or service.

Temperature-dependent expansion: A low expansion value over one temperature interval does not guarantee the same behavior over another interval.

Glass compatibility must be verified: Alloy 42 is suitable only when its expansion curve matches the selected glass or ceramic system.

Residual stress can cause movement: Heavy rolling, flattening, cutting or machining may introduce stress that is released during sealing or later heat exposure.

Magnetic behavior: Alloy 42 is ferromagnetic and may be unsuitable near components requiring low magnetic interference.

Designation confusion: Invar 42, Alloy 42, FeNi42 and 4J42 are commonly used as comparable names, but the ordered specification must control acceptance.

Certificates, Testing and Traceability

Heat-number traceability should connect each plate, sheet or cut blank to its production heat and processing lot. Product markings, package labels, the packing list and the MTC should show consistent grade, heat number, dimensions and purchase-order information.

EN 10204 3.1 MTC

An EN 10204 3.1 certificate can report the heat number, specification, chemical composition, mechanical properties, product dimensions and delivered condition. It should not be assumed that a standard 3.1 certificate automatically includes measured thermal-expansion data. That test must be stated separately when required.

Thermal-Expansion Testing

A dilatometer can measure dimensional change over a defined temperature interval. The test request should state the starting and ending temperatures, heating rate, specimen orientation, number of specimens and reporting method. Results from different temperature intervals should not be compared as though they were identical.

PMI and Dimensional Inspection

PMI can support alloy identification and anti-mix control by verifying the high nickel content. It does not independently prove compliance with the complete thermal-expansion requirement. Dimensional inspection should cover thickness, width, length, flatness, squareness and any drawing-specific tolerances.

UT may be specified for thick plate or critical machined blanks when internal soundness is important. It is not automatically necessary for every thin sheet or stamped electronic component. Surface inspection, chemistry, dimensional control and thermal testing are often more relevant for typical Alloy 42 applications.

Alloy 42 Plate RFQ Checklist

✅ State Alloy 42, UNS K94100, FeNi42, 4J42 or the approved designation.

✅ Identify ASTM F30 or the applicable customer specification.

✅ Provide thickness, width, length, flatness and dimensional tolerances.

✅ Specify annealed, cold-rolled, stress-relieved or another delivery condition.

✅ Define hot-rolled, pickled, polished, ground or machined surface.

✅ State the adjoining glass, ceramic, silicon or other material where applicable.

✅ Define the operating and test temperature range.

✅ Request EN 10204 3.1, chemistry, mechanical, expansion, PMI or UT reports as needed.

✅ Specify anti-rust protection, marking, export packing, quantity and destination port.

FAQ

What is Alloy 42 plate?

Alloy 42 plate is a controlled-expansion nickel-iron alloy plate containing approximately 42% nickel. It is used for glass-to-metal sealing, semiconductor packaging, precision electronics, optical components and other applications requiring predictable thermal expansion.

Is Alloy 42 the same as FeNi42 or 4J42?

Alloy 42, FeNi42 and 4J42 are commonly used for comparable 42% nickel-iron controlled-expansion materials. Buyers should still compare chemistry, thermal-expansion limits, heat treatment and product-standard requirements before approving them as equivalent.

What is the difference between Alloy 42 and Invar 36?

Invar 36 is selected for extremely low dimensional change near ambient temperatures. Alloy 42 has a higher expansion rate that is more compatible with selected glass, ceramic and silicon materials. The correct choice depends on the adjoining material and operating temperature range.

What certificate should buyers request for Alloy 42 plate?

Buyers commonly request an EN 10204 3.1 MTC containing heat number, chemistry, mechanical properties, dimensions and delivery condition. A separate thermal-expansion report should be specified when coefficient-of-expansion data is required for acceptance.

Related Controlled-Expansion Alloy Products

Product	Typical Procurement Use
UNS K94100 ASTM F30 Alloy 42 Plate	Controlled-expansion plate, sheet and machined blanks for sealing, electronics and precision equipment.
4J42 Controlled Expansion Alloy Bar	Round or shaped stock for machined sealing parts, pins, rods and precision components.
Invar 36 Alloy Plate	Ultra-low-expansion plate for metrology, optical structures, precision tooling and instruments.
Alloy 52 Controlled Expansion Plate	Higher-nickel Fe-Ni plate for selected glass, ceramic, vacuum and electronic applications.
Controlled Expansion Alloy Range	Alloy 42, Invar, Kovar and related Fe-Ni or Fe-Ni-Co materials for precision industrial applications.

Conclusion

Alloy 42 plate is a 42% nickel-iron controlled-expansion material used where predictable dimensional change and compatibility with selected glass, ceramics or silicon are required. It is commonly specified as UNS K94100, FeNi42, 4J42 or ASTM F30 material. Successful procurement depends on controlling chemistry, temperature-dependent expansion, heat-treatment condition, flatness, surface finish and traceability rather than purchasing by trade name alone.