Ask the Expert:

Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS) is an invaluable tool in examining surface anomalies in vacuum heat-treated metal parts. Mike Johnson, 51���� of Western Pa’s Sales Director, explains how this tool can answer questions and solve complex problems.

1. What is a Scanning Electron Microscope (SEM)?

A Scanning Electron Microscope is a fine tool that uses a focused beam of electrons to examine a material’s surface. When the electrons interact with the sample, they produce signals that are detected and analyzed. These signals reveal detailed information about surface features and chemical composition, making SEM a highly effective tool for microscopic evaluation.

2. My medical component shows spotting after vacuum heat treatment—how can SEM help identify the root cause?

SEM analysis identifies the composition of contaminants within the spots, helping trace their origin. It can reveal whether the issue stems from manufacturing processes—such as machining fluids, cleaning fluids, grinding residue, or metal chips—or from handling contamination like glove fibers or environmental debris.

3. What is the most common source of contamination identified through SEM analysis?

A frequent source of surface contamination is the cleaning process (used) prior to heat treatment. While components may arrive at the heat treater visibly clean, SEM often detects residual cleaning or rinsing agents. These frequently include Chlorine, Calcium, and other residuals commonly found in city water. If aqueous cleaning methods are employed, the final rinse should always be performed with deionized water to avoid this potential contamination. The SEM may also uncover films or deposits caused by cross-contamination when multiple alloys are cleaned in the same system. For instance, analysis of spots on 304 stainless steel components once revealed copper contamination from foreign object debris (FOD). The cause was found to be cross-contamination in a cleaning system shared with copper components.

4. Can the vacuum furnace itself be a source of FOD surface contamination?

Yes. Furnaces may contribute to surface contamination of heat-treated parts. If your heat-treat supplier is equipped with an SEM, this is a sign they understand the science and intricacies of surface contamination, and they have the necessary tool to get to the root cause of the issue, whatever that cause may be.

Foreign object debris and residual contamination can impact the performance and reliability of vacuum heat-treated components. While initial detection may rely on visual inspection, SEM/EDS analysis produces precise compositional analysis for fast and efficient root cause analysis. Please contact me if you are interested in SEM analysis at 51����.

Learn more about Scanning Electron Microscopy

And featured in Today’s Medical Developments Magazine:

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Berlin, CT, July 15, 2026 – Construction and refurbishment are moving forward as the future home of 51���� Connecticut continues to take shape. Several vacuum furnaces have been set in place, the office areas are nearing completion, and work is actively progressing on the facility’s piping, electrical systems, and supporting infrastructure.

The 28,000-square-foot facility, located in Spruce Brook Industrial Park, remains on schedule for a fourth-quarter 2026 opening and will significantly expand 51����’ vacuum heat treating capabilities throughout the Northeast.

This newest location represents another important investment in our continued growth and commitment to serving customers with advanced vacuum heat treating technology, increased capacity, and the reliable service that has defined 51���� for decades.

For additional information about 51���� of Connecticut, contact Tim Steber at 1-855-934-3284 x1216 or email at tim@solaratm.com.

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1. What are some of the first steps I should take before sending parts out for vacuum heat treating?

Before vacuum thermal processing, ensuring the parts are free of foreign object debris (FOD) is essential. This includes removing contaminants like manufacturing oils, coolants, and machining residue. It’s also important to communicate whether the coolant used was water-based or oil-based—this helps your heat treater select the most effective cleaning method.

Many vacuum heat treaters use solvent degreasers for oil-based coolants and hot water/soap-based rinses for water-based coolants. Providing this information up front helps determine how to best prepare your parts for heat treatment.

Bottom line: Failing to address FOD can result in spotting, discoloration, or worse—surface contamination.

2. You made sure the parts are clean; now, how about the vacuum furnace?

Much like a home oven, vacuum furnaces require periodic cleaning—referred to in our world as a “bake-out.” This process removes residual FOD or contaminants left from previous runs.

Typical bake-out temperatures:

• Austenitic (300-series) steel grids, fixtures, and baskets: ~2150°F
• Furnace-only bake-out: ~2300–2400°F

Reaching these temperatures ensures even entrapped moisture in graphite components is eliminated—crucial for maintaining a clean process environment.

3. Okay, so the parts are clean and the furnace is clean. Are we ready to run?

Almost! One final but critical step: check the furnace leak rate.

• For most steels, aim for 20 microns/hour or less
• For reactive metals (like titanium), 5 microns/hour or less is ideal

Remember, all vacuum furnaces leak to some degree—perfection doesn’t exist in commercial heat treating. But keeping leak rates low is key to producing bright, shiny, contamination-free parts.

4. Now for the easy part: the thermal cycle. Right?

Well… not quite!

If you’re using partial pressure gas or backfill gas (nitrogen, argon or helium), you must also monitor the dew point and oxygen content of the process gas. When treating alloys that oxidize easily—even small traces of water vapor or oxygen can cause surface issues.

While dew point measures moisture, it does not measure oxygen. Using oxygen sensors alongside dew point monitoring provides a more complete picture of gas purity, ensuring optimal conditions for clean, bright results.

Also, consider the vacuum level:

• For 300/400 series stainless steels or PH alloys, a vacuum in the 10⁻⁴ Torr range (graphite hot zone) is typically sufficient.
• For titanium or reactive alloys, you’ll need a 10⁻⁶ Torr vacuum, which usually requires an all-metal (molybdenum) hot zone.

While graphite furnaces are capable, all-molybdenum systems offer superior part cleanliness for highly reactive materials.

Lastly, ensure proper thermocoupling of the load. Use contact thermocouples directly in a part or in a heat sink that represents the maximum cross-section. Poor thermocoupling can lead to a false sense of temperature stability—you may think the load is cool, but when the door opens, parts could still be hot enough to oxidize instantly (turning blue).

5. I followed all your recommendations, and the parts are still discolored! Why?

Even with every precaution, discoloration can still occur—and it’s understandably frustrating. But it’s important to distinguish between:

• Discoloration, which is superficial and doesn’t impact performance
• Surface contamination, which is detrimental, as it alters the surface microstructure

To confirm the difference, consider sending a representative part to a metallography lab. These labs can characterize the near-surface condition, helping you determine next steps—ranging from simple Scotch-Brite cleaning, to a chemical or mechanical etch that removes a few thousandths of material.

And featured in Today’s Medical Developments Magazine:

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Berlin, CT, May 19, 2025 – 51����, the largest family-owned heat treating company in the United States, is proud to announce the opening of its seventh U.S. heat treat operation — an existing industrial facility located in Berlin, Connecticut, slated for completion in 2026.

The 28,000-square-foot facility is located in the Spruce Brook Industrial Park and will further expand 51����’ footprint and capabilities in the Northeast region.

“We are excited to establish a new presence in Connecticut,” said Jamie Jones, President of 51���� of Eastern PA and Connecticut. “This strategic location allows us to better serve our growing customer base and continue supporting the aerospace, medical, and commercial manufacturing markets throughout New England.”

This expansion reinforces 51����’ commitment to providing innovative, high-quality vacuum heat treating solutions across the country while maintaining the personalized service and reliability that has made the company a trusted partner for decades.

Stay tuned for updates as we build our newest state-of-the-art facility!

For additional information about 51���� of Connecticut, contact Tim Steber at 1-855-934-3284 x1216 or email at tim@solaratm.com.

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