When Should You Use Kovar Instead of Stainless Steel?

When Should You Use Kovar Instead of Stainless Steel?

When selecting specialist metals, consistency and traceability are just as important as price.

The short answer is that Kovar should be used instead of stainless steel when your application requires controlled thermal expansion, particularly where metal must bond reliably with glass or ceramics. Stainless steel remains the better choice for corrosion resistance, general strength, and cost-sensitive structural use.

This distinction matters in industries where even minor dimensional movement can lead to failure. Electronics, aerospace components, and vacuum systems are typical examples where Kovar offers clear advantages.

What makes Kovar different from stainless steel?

Kovar is a nickel cobalt ferrous alloy designed to match the thermal expansion of borosilicate glass and certain ceramics over a defined temperature range. Stainless steel, by contrast, is engineered primarily for corrosion resistance and mechanical strength.

Thermal expansion properties

The defining feature of Kovar is its low and controlled coefficient of thermal expansion. This allows it to expand and contract at a similar rate to glass, reducing stress at bonded interfaces.

According to ASM International, matching thermal expansion is essential in hermetic sealing applications to prevent cracking and long-term failure.

Stainless steel expands more under heat, which can create stress fractures when paired with brittle materials.

Composition and structure

Kovar typically contains iron, nickel, and cobalt. This composition gives it stable thermal behaviour across a defined temperature range.

Stainless steel includes chromium, which provides corrosion resistance but does not offer the same expansion control.

Key advantages of Kovar in specialist applications

Glass to metal sealing

Kovar is widely used in hermetic seals. These are critical in electronic packages, sensors, and vacuum tubes. The matched expansion prevents leaks and maintains long-term integrity.

If your component must remain airtight under temperature cycling, Kovar is often the safer option.

Dimensional stability under temperature change

In precision assemblies, even small changes in size can affect performance. Kovar expands in a more controlled and predictable way than stainless steel when temperatures fluctuate.

This is particularly relevant in aerospace and instrumentation, where tolerances are tight and failure is not acceptable.

Electrical and electronic uses

Kovar is commonly used in semiconductor packaging and feedthroughs. Its stability supports long term reliability in sealed electronic components over time.

For more detail on material behaviour and processing, see our guide to City Special Metals.

When stainless steel is the better option

Kovar is not a universal replacement. In many cases, stainless steel remains the more practical choice.

Corrosion resistance

Stainless steel performs well in harsh environments, including marine and chemical exposure. Kovar offers moderate corrosion resistance but typically requires surface treatment in demanding environments.

Strength and structural use

For load-bearing components, stainless steel provides higher strength and durability. It is better suited to frameworks, fixings, and general fabrication.

Cost considerations

Kovar is a specialist alloy and typically more expensive. If thermal expansion is not a concern, stainless steel is often more cost-effective.

Kovar vs stainless steel, practical comparison

In day-to-day engineering decisions, the choice comes down to application requirements:

• Use Kovar where thermal compatibility with glass or ceramics is critical
• Use stainless steel where strength, corrosion resistance, or cost efficiency are the priority

Choosing the wrong material can lead to premature failure, especially in sealed or high-precision environments.

Machining considerations for Kovar

Kovar can be machined using conventional methods, but it behaves differently from stainless steel. Tool wear, cutting speeds, and finishing processes all need careful control.

Kovar machining ensures the material retains its properties and avoids introducing stress that could affect performance.

If you are specifying this material, it is worth reviewing machining guidance alongside your design requirements. 

How to choose the right material for your project

Material selection should be based on function, environment, and long-term performance.

Ask a few practical questions:

• Will the component be exposed to temperature cycling?
• Does it need to bond with glass or ceramics?
• Are corrosion resistance or structural strength more important?

If thermal expansion compatibility is critical, Kovar is usually the correct choice. If not, stainless steel often delivers better overall value.

Working with an experienced supplier helps ensure materials meet both performance and compliance standards. It also reduces the risk of costly redesigns later in the project.

FAQs

What is Kovar mainly used for?

Kovar is used in applications that require stable thermal expansion, such as glass to metal seals, electronic components, and vacuum systems.

Is Kovar stronger than stainless steel?

No. Stainless steel generally offers higher mechanical strength, making it more suitable for structural applications.

Why is Kovar used in electronics?

Its thermal expansion matches glass and ceramics, which helps maintain airtight seals and stable performance in electronic packages.

Can Kovar replace stainless steel?

Only in specific cases. Kovar is ideal for thermal stability, while stainless steel is better for general engineering and corrosion resistance.

Contact Us

If you are unsure which material is right for your application, speaking to a specialist can help. For tailored advice or a quick quotation, visit the City Special Metals contact page and discuss your requirements with the team.